Duncan Schwaller

Quentin Weinbach

Keywords: Diketopyrrolopyrrole, organic semiconductors, hydrogen bonds

Many thanks to my peers, colleagues, and friends in the team:

First, I would like to thank God for all his blessings and for having accompanied me throughout my career, for being my strength in my weakest moments and providing me a life full of learning.

I thank both of my parents, Nelson Ávila and Lourdes Rovelo, for supporting me every moment of my life, for the instilled values and principles, for the opportunity of having an excellent education throughout my life and foremost, for all of the love I have received from them.

In the same way I want to thank both of my sisters, first to the elder one, Nielsen, who has been a professional development example, and to my youngest sister, Nelbeth, for always believing in me and motivating me to do my best. To both, for being an important part of my life, filling it with happiness, good moments and laughs. I want to thank my thesis directors, Dr. Dominique Collin and Dr. Amparo Ruiz Carretero, for their help and support throughout this thesis. I want to express my deepest gratitude to Amparo, for her patience, advices, guidance and responsiveness. Thank you not only for believing in me, but for all your support, the opportunity of growing as a professional, for teaching me something new everyday, and for all the time you dedicated while working together during the past four years! Thank you for sharing all your knowledge and experience with me and for always pushing me to reach my highest potential. I wish nothing but the best for your future projects, both professionally and personally. I would also like to thank Dr. Martin Brinkmann and Dr. Philippe Mésini for fruitful discussions and their guidance in the interpretation of the obtained results, your contributions helped me a lot.

A huge thanks to Dr. Jean-Philippe Lamps for providing help daily during the entirety of the PhD. Thank you for always being helpful, for sharing tips and advice so that when setting up a reaction everything went smoothly. Thank you for making sure that we are always wellequipped and that we have enough reagents and solvents to perform reactions in the best way possible. Thank you for your support, contributions, and goodwill. You're an essential part of the SYCOMMOR team. I would like to thank my friends and colleagues in the lab, Dr. Ana García and MSc. Gabriel Martínez for sharing their insight, knowledge, and time. Thank you for allowing me to speak in Spanish daily and providing the Hispanic vibe in the lab. Ana, I wish you success in your professional career and that you manage to achieve your goal of becoming a researcher for CNRS. Gabriel, good luck in the rest of the PhD, keep up the good work and motivation.

Chapter V

In the previous chapters the beginning of the comparative and systematic studies done on Hbonded -conjugated materials based on DPP was shown. So far, we have found that even subtle differences in the molecular structure among DPP families and the different selfassembly properties can impact optoelectronic properties.

Furthermore, other parameters such as sample preparation, solvent chosen, concentration and temperature can influence the H-bonding ability, making the optimization process very complex. In this sense, we are starting to work on the in-situ control over the morphology and electric properties to gather as much information as possible and build up a screening protocol.

In this regard, our intention is to upgrade an existing setup by adding a properties analyser and choose an electronic parameter of interest. Nevertheless, before moving to our studies using said setup, we have studied several H-bonded DPP systems individually before and after exposure to solvent vapour and temperature. The work shown in this chapter explores the alignment techniques that can be used for these systems. Particularly, this has been done with the DPP derivatives presented in chapter III. vi Résumé en français

RÉSUMÉ EN FRANÇAIS

vii Cette thèse a été divisée en cinq chapitres et chacun d'eux est résumé dans ce document.

Chapitre I : Introduction

L'énergie est l'approvisionnement le plus important de l'humanité pour le bon fonctionnement de la société telle qu'on la connaît. Les activités comme la production, la distribution, le stockage et la consommation ne seraient pas possibles sans énergie. Son utilisation et ses applications sont si profondément enracinées dans la vie quotidienne, que la plupart des personnes l'ont considéré comme acquis.

Comme nous le constatons, notre consommation énergétique n'a fait que croitre de façon drastique au cours du temps. Depuis les temps préhistoriques avec la découverte du feu, elle n'a cessé d'augmenter progressivement au cours des siècles pour s'intensifier avec la révolution industrielle et s'accroitre de façon exponentielle depuis, le tout considéré comme une conséquence logique de la modernisation des activités économiques.

Pendant les trois dernières décennies, l'utilisation de l'énergie a dramatiquement augmenté partout dans le monde, en passant de 8,6 milliards de tonnes d'équivalent de pétrole (Gtep) en 1995 à 13,2 Gtep en 2015, [1] et ne va pas cesser d'augmenter tant dans les pays dits « développés » que dans les pays considérés comme émergents. Si l'on considère le besoin énergétique actuel de la Chine, son développement économique l'a amené à consommer la plus importante part de matières premières énergivores produites dans le monde. [1] La Chine est actuellement le pays avec la plus grande consommation énergétique, doublant presque celle des États-Unis, qui se place en deuxième place comme le montre la Figure 1.

Figure 1 La Chine en tête de la consommation énergétique mondiale avec 145,46 exajoules (EJ).*Adaptée. [2] La consommation énergétique mondiale repose sur les sources primaires d'énergie, qui peuvent prendre plusieurs formes et avoir différentes origines. En revanche, ces sources primaires d'énergie sont transformées en une source secondaire, l'électricité, qui peut être distribuée par des lignes électriques ou autres infrastructures de transport afin d'assurer la demande énergétique d'un complexe industriel voire d'un pays en entier. Trois sources viii principales d'énergie pour la production d'électricité existent : fossile, nucléaire et renouvelable.

Les énergies non renouvelables ont longtemps été privilégiées, en raison d'un cout moins élevé que celles issues de sources renouvelables. L'importance croissante des problèmes environnementaux et le changement climatique provoqué par la production d'énergie à partir de combustibles fossiles sont devenus un problème mondial majeur, ce qui a fait que les technologies liées à la production d'énergie renouvelable sont considérées comme une solution pour réduire et atténuer les émissions de gaz à effet de serre dans l'atmosphère grâce à la production d'énergie propre.

L'énergie solaire fournit une source d'électricité ayant le taux de croissance le plus élevé et le plus abordable. Le soleil produit constamment de l'énergie et est donc considéré comme la source d'énergie renouvelable disponible la plus abondante. À travers l'histoire, elle a été utilisée comme énergie thermique pour cuisiner ou pour chauffer des fluides de travail comme l'eau pour des applications domestiques ou industrielles, mais plus récemment, elle a commencé à être utilisée pour transformer les rayons solaires en électricité à travers l'utilisation de dispositifs photovoltaïques (PV).

Les dispositifs PV sont des appareils électriques qui transforment la lumière du soleil directement en électricité en utilisant l'effet photovoltaïque. Elles sont traditionnellement faites à base de silicium et fonctionnent comme montré sur la Figure 2.

Figure 2 Structure et principe de fonctionnement d'un dispositif photovoltaïque à silicium.*Adaptée. [3] L'évolution de l'industrie PV est remarquable à la vue des succès technologiques obtenus au niveau de la mise en forme, de l'installation, et des réductions des coûts. Par suite, les dispositifs solaires PV ont réussi à dominer l'industrie des énergies renouvelables. En outre, la dynamique de cette industrie permet régulièrement d'apporter des innovations intégrées rapidement dans la chaîne de production.

Le principal moteur de ces innovations a été la recherche d'une plus grande efficacité, ce qui est essentiel pour une fabrication compétitive de modules, car elle diminue directement les oton is re lected and lost oton releases an electron e released electrons ove to t e outer circuit

Silicon doped with Phosphorous

Silicon doped with oron p n unction ix coûts de traitement des cellules solaires en réduisant les quantités requises pour une puissance électrique donnée. La croissance future de l'industrie solaire PV dépend en grande partie de la réduction des coûts en utilisant des matériaux adéquats et c'est là que tous les développements de l'électronique organique deviennent pertinents.

Les semi-conducteurs organiques sont principalement faits à partir de carbone et hydrogène, avec quelques hétéroatomes comme le soufre, l'oxygène et l'azote. Ils sont souvent dotés d'un système d'électrons libres, cela est dû à l'exceptionnelle nature de l'atome de carbone, qui peut former différents types de structures à travers des liaisons covalentes  et .

Les liaisons  sont formées par l'hybridation des orbitaux moléculaires entre atomes de carbone adjacents, tandis que les liaisons  sont formées par le chevauchement d'orbitaux d'atomes de carbone qui ne participent pas à la formation de liaison  (Figure 3). Les liaisons  sont relativement fortes et les électrons sont plus facilement localisables. En revanche, les électrons  sont largement délocalisés, ce qui rend les liaisons  plus faibles que les liaisons . Des molécules qui contiennent plusieurs électrons délocalisés sont connues comme systèmes conjuguées, cette délocalisation des électrons dote les semi-conducteurs organiques de propriétés remarquables. Les semi-conducteurs organiques combinent les bénéfices chimiques et mécaniques des composés organiques avec les avantages des matériaux semi-conducteurs ; ce qui rend possible l'obtention de structures versatiles qui peuvent être modifiés par synthèse chimique pour améliorer leur capacité d'absorption de lumière ou leur conductivité électrique. L'utilisation de composés organiques comme matériaux actifs dans des dispositifs électroniques et optoélectroniques a mené au développement de méthodes à bas prix pour fabriquer des structures qui soient utiles mais inaccessibles lorsqu'on utilise des semiconducteurs traditionnels. Ils sont souvent utilisés en couche mince dans diverses applications comme l'affichage des écrans ou les cellules solaires.

Les qualités prometteuses des dispositifs organiques photovoltaïques (OPV) leur ont valu beaucoup d'attention, car ils ont la facilité de traitement en solution, des propriétés x électroniques modifiables, une basse température de fabrication et ils sont aussi relativement peu chers à produire et moins nocifs sur l'environnement.

Il existe plusieurs paramètres qui peuvent influencer la morphologie et la distribution spatiale moléculaire des semi-conducteurs organiques en couche mince, ce qui crée des opportunités pour ajuster les propriétés de transport. En plus, des changements de paramètres de traitement comme la vitesse de dépôt, le type de solvant utilisé ou la procédure de recuit peuvent entraîner des changements des propriétés du système.

La combinaison de tous ces paramètres gouverne donc la morphologie et la distribution spatiale moléculaire des semi-conducteurs organiques en couche mince, ce qui est essentiel pour obtenir une bonne performance électronique d'un système moléculaire. [4] De plus, la morphologie des matériaux semi-conducteurs organiques peut aussi être modifiée par d'assemblages supramoléculaires. C'est le cas des systèmes  conjugués, qui ont tendance à former des agrégats et parfois même des grandes cristallites en fonction des conditions de traitement. [5] En général, l'agrégation peut être contrôlée dès la conception moléculaire, le choix du solvant et les étapes du traitement thermique. Dans le cas de systèmes  conjugués comme les polymères, l'alignement des chaînes mène à une organisation au niveau microscopique ou mésoscopique, permettant la réalisation de structures supramoléculaires.

Les composés supramoléculaires sont considérés comme un groupe de molécules où chaque élément individuel confère à la globalité de l'assemblage de propriétés par des interactions non covalentes. Pendant les trente dernières années, l'auto-organisation des molécules utilisant des nombreuses interactions supramoléculaires a suscité beaucoup d'intérêt en raison du nombre important d'assemblages pouvant être réalisés, ayant des propriétés ajustables [6] parfois exceptionnelles.

Parmi les différentes interactions non covalentes utilisées en chimie supramoléculaire, les liaisons hydrogène (liaisons-H) présentent l'avantage de guider de manière efficace l'autoassemblage des matériaux organiques rendant possible la modification des propriétés dans les procédés d'agrégation.

Une liaison-H est une interaction où un atome d'hydrogène est attiré par deux autres atomes, et pas par un seul atome comme habituellement, il agît donc comme un pont qui connecte les deux atomes comme montré sur la Figure 4, où l'espèce X-H est souvent connue comme le donneur, tandis que Y-Z est connue comme l'accepteur. La liaison-H est souvent décrite comme une interaction d'attraction dans laquelle un atome d'hydrogène électropositif intervient entre deux espèces électronégatives X et Y pour les rapprocher.

La liaison-H est assez forte pour maintenir ensemble les molécules XH et YZ à des températures normales et agît aussi dans une direction donnée pour que leurs associations soient spécifique à l'orientation. Malgré tout, selon la nature des espèces X et Y, elle peut s'affaiblir suffisamment pour permettre aux molécules de se séparer, ce qui entraîne une perte de la spécificité de l'orientation dans l'association de XH et YZ, comme c'est le cas des interactions hydrophobiques. [7] xi Figure 4 Représentation schématique des 4 espèces atomiques engagées dans une liaison-H.

Les liaisons-H peuvent déterminer la conformation moléculaire, l'agrégation et la fonctionnalité d'un grand nombre de systèmes chimiques, sans elles, les structures en bois collapseraient, le ciment s'émietterait, les océans s'évaporeraient et les êtres humains se désintègreraient en matière inerte.

Les éléments constitutifs des acides nucléiques naturels sont un des exemples les plus connus illustrant l'importance de la liaison hydrogène. Ces liaisons ont tou ours été considérées très pertinentes dans les procédés biologiques, comme dans la reconnaissance entre la purine et la pyrimidine dans l'acide désoxyribonucléique (ADN) (Figure 5), ou dans la catalyse enzymatique et la formation des hélices  et  [8] Figure 5 Reconnaissance moléculaire entre la purine et la pyrimidine qui créent les bases de l'ADN à travers la formation sélective des liaisons-H.

Étant donné que les interactions des liaisons-H sont si répandues dans la nature, il n'est pas surprenant qu'elles puissent également être exploitées comme outil de conception moléculaire pour obtenir des matériaux organiques semi-conducteurs et conducteurs. Par exemple, la liaison-H est cruciale pour les interactions supramoléculaires qui permettent la création de nombreux ensembles donneurs/accepteurs photo actifs. [9] Il est possible de trouver dans la littérature plusieurs exemples où les liaisons-H sont utilisées pour des applications photovoltaïques, la Figure 6 résume les cas les plus courants utilisés pour la fabrication de cellules solaires organiques, même si des exemples de transistors existent. [10]

des matériaux utilisés pour la fabrication des cellules solaires organiques portant de liaisons-H sont nuisibles (A et B) ou bénéfiques (C et D).

Néanmoins, des résultats contradictoires sont souvent décrits pour les cas où des matériaux donneurs et accepteurs portent des groupes capables de former des liaisons-H et aussi pour des cas où seulement un des éléments a la capacité de les former. Les Figure 6A et Figure 6B montrent deux cas où des oligo-thiophènes ont été modifiés pour porter des groupes amides ou ester à la périphérie. [11,12] Dans les deux cas, du chloroforme a été utilisé pour préparer le mélange de matériaux d'accepteur et donneur, ce qui d'un point de vue supramoléculaire n'est pas le meilleur choix car il est souvent utilisé comme « un bon solvant » pour éviter l'agrégation. Par ailleurs, dans ces deux travaux de recherche, l'efficacité de la cellule solaire est inférieure lorsque les mélanges sont faits avec des dérivés capables de former des liaisons-H. Par ailleurs, même si les structures moléculaires des exemples montrés sur la Figure 6C et la Figure 6D sont différentes, en comparaison à la similarité qui existe entre les deux exemples présentés précédemment, des résultats contradictoires sont obtenus. En l'occurrence, dans le cas de la Figure 6C, les auteurs démontrent que la molécule sans capacité de former des liaisons-H a besoin du double de concentration pour obtenir une efficacité semblable à celle de sa contrepartie qui peut former des liaisons-H, mais qui a majoritairement pour désavantage un faible courant de court-circuit. [13] En outre, dans l'exemple de la Figure 6D, une efficacité plus grande est obtenue pour le dérivé du dicétopyrrolopyrrole (DPP) portant des groupes amides. [14] Il est évident qu'il n'existe pas de consensus sur l'impact positif ou négatif des matériaux portant des liaisons-H sur les dispositifs solaires. Cependant, il est important de remarquer qu'il n'est pas possible de comparer tous les différents paramètres entre ces études. La différence entre les divers paramètres présentés comme : le type de système  conjugué, le type d'unité qui peut former des liaisons-H, le solvant choisi et la proportion de xiii donneur/accepteur utilisé, parmi d'autres, est trop vaste. Ce qui rend difficile la tâche de faire une comparaison significative. De plus, le manque d'études de l'auto-assemblage dans la plupart des cas, néglige l'information concernant le type de structures formées par les systèmes à liaisons-H, ce qui est essentiel pour comprendre la performance des dispositifs.

Pour cette raison, le but de cette thèse est de déterminer l'impact des liaisons-H sur les propriétés optoélectroniques des semi-conducteurs organiques en faisant des études systématiques et comparatives en utilisant le DPP comme système modèle. En plus, cette étude systématique vise à identifier les conditions nécessaires pour pouvoir fabriquer des dispositifs électroniques efficaces.

Les DPPs sont des molécules qui ont été largement étudiées et sont parmi les meilleurs éléments électro-actifs utilisés pour des applications dans le domaine des semiconducteurs [15,16] depuis leur découverte par Farnum dans les années 70, lorsqu'il essayait d'obtenir une azetinone. [17] Le DPP est un des pigments le plus utilisé pour des applications industrielles et dans la recherche de nouveaux matériaux. Plusieurs exemples de polymères et d'oligomères peuvent être trouvés pour la fabrication de cellules organique solaires [18] , de transistors organiques [19,20] , et de capteurs. [21,22] Figure 7 Structure chimique détaillée d'un DPP avec la numération correspondante de ses atomes, des groupes capables de former des liaisons-H et de ses principales positions de fonctionnalisation.

La structure chimique d'une molécule de 2,5-Dihydropyrrolo[4,3-c] pyrrolo-1,4-dione est présentée sur la Figure 7, et usqu'à présent il n'existe pas des rapports de la synthèse de cette structure. Les dérivés de DPP les plus connus portent souvent des substituants aromatiques sur les positions -3 et -6, bien qu'il existe aussi des composés avec des groupes aliphatiques. [23,24] Le DPP étant déjà une molécule possédant déjà des liaisons-H, à cause de son insolubilité, on peut l'employer dans les techniques de dépôt sous vide ou l'utiliser comme un pigment latent après un traitement thermique ou acide. Mais grâce à la possibilité de fonctionnalisation du noyau DPP, il est possible d'introduire plusieurs types de groupes capables de former des liaisons-H, ce qui rend possible l'étude de son agrégation en solution et son utilisation pour la fabrication de dispositifs.

xiv Une stratégie très utilisée pour rajouter des liaisons-H dans la structure moléculaire du DPP consiste à rattacher des groupes amides à la périphérie des groupes aromatiques qui sont liés au noyau central du DPP.

Cette thèse porte sur une étude systématique utilisant comme système modèle un élément électro actif de DPP portant des thiophènes rattachés au noyau. Plusieurs paramètres en rapport aux liaisons-H seront testés, puis cette étude sera étendue aux semi-conducteurs de pointe comme les rhodanines [25,26] ou l'isoindigo [27,28] . Finalement, l'étude sera étendue à des molécules d'accepteurs et des mélanges donneur-accepteur y compris les fullerènes et accepteur non basés sur les fullerènes. [29,30] Dans cette thèse, l'influence de différents paramètres sera évaluée, en l'occurrence :

✓ Le type de groupe capable de former la liaison-H : Amides, urées, systèmes auto-complémentaires et autres.

✓

La position des liaisons-H dans la structure moléculaire : en périphérie ou intégrée dans les chaînes. ✓ La solubilité : différentes longueurs et ramifications des chaînes alkylées. ✓ La topologie des liaisons-H dans les bras amide. ✓ La chiralité dans les bras attachés au noyau DPP.

Le DPP a été choisi comme système modèle en raison de ses grandes propriétés optoélectroniques et sa versatilité de fonctionnalisation, ainsi que de la possibilité qu'il fournisse une vision globale de l'influence des liaisons-H dans l'organique électronique et pour explorer la généralité des résultats, lorsqu'ils sont transposés à tout autre semi-conducteur.

Jusqu'à présent, plusieurs familles de DPP portant des liaisons-H ont été étudiées et sont présentées sur la Figure 8. Cette thèse abordera l'étude de trois de ces familles, en particulier le chapitre II couvrira la famille des bisamides [31] (Figure 8b). Le chapitre III abordera l'étude de l'expansion de la famille des bisamides avec une solubilité améliorée et des changements en topologie (Figure 8d). Ensuite, dans le chapitre IV l'impact de garder le même type de chaîne alkyle, alors que la position et la topologie des groupes amides change sera discuté (Figure 8e). Enfin, dans le chapitre V des résultats préliminaires sur l'impact des changements du solvant sur la morphologie et l'orientation des agrégats formés par les dérivés décrits dans le chapitre III seront présentés.

Chapitre II : Exploration de la fonction amide

Pour ce chapitre, une attention particulière est accordée aux dérivés de DPP capables de former des liaisons-H, en utilisant des groupes amides couplés et rattachés au noyau  conjugué par une chaîne flexible à six carbones. Cette conception a été choisie parce que notre groupe a commencé des études systématiques avec des dérivés contenant des semicarbazones directement rattachées au noyau DPP. [32] Les dérivés de semicarbazone donnent des molécules très rigides avec une solubilité limitée et avec une dynamique de recombinaison rapide lorsque leurs propriétés de photoconductivité ont été criblées. Néanmoins, leurs propriétés d'auto-assemblage et morphologiques fournissent des informations très utiles pour poursuivre la conception de nouvelles familles de DPP portant des liaisons-H.

Dans cette partie de la thèse, des molécules complètement différentes ont été conçues, leur fonctionnalisation a été faite sur le lactame et non pas sur le thiophène, comme pour les dérivés de semicarbazone (Figure 9). La liaison-H a aussi été espacée à travers une chaîne flexible, pour comparer les processus d'auto-assemblage. Enfin, la chiralité a été introduite comme paramètre d'étude et un centre chiral à côté de la fonction amide a été rajouté. Le groupe amide a été choisi, car il s'agit de l'un des groupes de liaisons-H le plus exploré historiquement et qui peut être retrouvé dans tous les domaines de la chimie. [33] Il est un candidat parfait pour étudier les processus d'auto-assemblage dans lequel l'agrégation H et J sont impliquées grâce à leurs procédures de synthèse, bien connues pour leur capacité d'être rajoutés dans tout type de molécules et aussi à leur facilité de caractérisation par des techniques de spectroscopie, telles que la spectroscopie infrarouge.

L'autre paramètre qui a été évalué pour cette famille de DPPs est la chiralité, qui peut aussi avoir un impact sur les propriétés d'autoassemblage et dans le cas des semiconducteurs, sur les propriétés optoélectroniques. [34,35] La chiralité a déjà été évaluée dans des dérivés du DPP, principalement en rajoutant des chaînes alkyle chirales comme le 2-ethylhexyl [36][37][38][39] , des molécules d'hélicène, [40] ou en rajoutant des dérivés du myrtenal. [41] Ici, la synthèse des dérivés fonctionnalisés sur le lactame (comme montré sur la Figure 9) est décrite, ainsi que la caractérisation de leurs propriétés optiques et d'autoassemblage, ce qui aidera dans la compréhension des propriétés de transport de charge qui ont été mesurées à l'aide d'une technique sans électrodes basée sur la conductivité de micro-onde.

Le noyau de DPP a été synthétisé par la réaction de cyclisation entre le 2thiophènecarbonitrile et le diéthyl succinate, en suivant un protocole déjà décrit. [42] Trois molécules finales, DPPBA, (S)-DPPBA et (R)-DPPBA, ont été obtenues via des réactions d'alkylation avec des bras amides contenant un mésilate (Schéma 1). Ces bras amides ont été obtenus en faisant réagir la ε-caprolactone avec des dérivés d'amine (achiraux et chiraux) et en rajoutant le groupe mésilate par la suite. La DPP a été N-alkylé en utilisant le carbonate de césium comme base pour déprotoner et la DMF a été utilisée comme solvant, comme mentionné dans d'autres alkylations de DPP. [43,44] Les rendements sont faibles (10%) en raison de réactions additionnelles qui conduisent à des sous-produits isolés et identifiés, comme les isomères O-alkylés. Au début les trois composés dissouts dans le chloroforme (2,5 mg/ml) ont été étudiés. Il a été observé que les spectres des trois dérivés présentent des larges bandes d'absorption entre 415 et 600 nm à 20 °C (Figure 10a). Les dérivés chiraux présentent eux une bande Cette bande n'est pas observée pour DPPBA, même dans des solutions très concentrées. Cette bande peut être attribuée à la formation d'agrégats de type J, comme pour des dérivés de DPP portant des liaisons-H, y compris les dérivés de DPP semicarbazone reportés par notre équipe. [32,45,46] Ce signal est lié à la formation des liaisons-H, puisqu'il disparaît lorsqu'on rajoute du méthanol (un solvant qui rentre en compétition avec les liaisons-H) à des solutions de (S)-DPPBA et (R)-DPPBA.

Les propriétés optiques ont aussi été mesurées dans différents solvants : toluène, chlorobenzène, cyclohexane et acétate d'éthyle. Dans ces solvants, pour les trois dérivés, les bandes d'agrégats J deviennent encore plus intenses que pour le cas du chloroforme (Figure 10b à d). Un épaulement se produit vers 480 nm dans plusieurs solvants, ce qui est attribué à la formation d'agrégats de type H. Des spectres IRTF en solution utilisant du chloroforme deutéré comme solvant prouvent l'existence de liaisons-H dans ces dérivés bisamides (Figure 11). DPPBA présente une bande à 3450 cm -1 pour l'élongation de la liaison NH, ce qui est caractéristique des groupements amides libres. Cela prouve que DPPBA ne forme pas des liaisons-H dans le chloroforme. Un autre signal est vu vers 1659 cm -1 , ce qui correspond aussi à des amides libres.

D'un autre côté, à température ambiante, (S)-DPPBA et (R)-DPPBA présentent de bandes vers 3439 cm -1 et 3297 cm -1 dans la région de l'élongation de la liaison NH. La première bande est attribuée à un groupe amide libre comme pour le cas précèdent, la deuxième bande correspond à des groupes amides engagés dans des liaisons-H. Par conséquent, (S)-DPPBA et (R)-DPPBA forment partiellement des liaisons-H en solution.

Dans le domaine situé entre 1600 cm -1 et 1700 cm -1 , (S)-DPPBA et (R)-DPPBA présentent trois pics vers 1632 cm -1 , 1648 cm -1 et 1663 cm -1 . Les deux premiers pics correspondent à des groupes amide engagés dans des liaisons-H fortes et faibles respectivement [47] , tandis que le troisième pic correspond à un groupe amide libre, comme observé pour DPPBA.

Des mesures en diluant la concentration et en faisant varier la température ont aussi été faites pour continuer à explorer le processus d'agrégation. Les bandes d'agrégats J sont observées après dilution, même à des concentrations faibles dans les solvants qui favorisent la formation des liaisons-H. Lorsque la température augmente, les bandes d'agrégats J sont tou ours Cette tendance a été observée pour les trois dérivés, mais pour les dérivés chiraux, la bande d'agrégats J disparaît à très hautes températures et à des faibles concentrations lorsqu'on les compare avec le dérivé achiral. Ce qui prouve que les dérivés chiraux forment des agrégats plus stables que le dérivé achiral correspondant.

Pour étudier les dérivés chiraux, des mesures de dichroïsme circulaire en solution ont été faites, et des signaux avec un fort effet Cotton sont retrouvés pour les dérivés chiraux, mais pas de signal pour DPPBA, même dans des conditions d'agrégation. Des études morphologiques ont été faites par MET en déposant des solutions de ces dérivés dans les différents solvants utilisés précédemment. Dans chaque solvant, des clichés avec des structures ayant des rapports d'aspect différent ont été obtenus pour les trois dérivés. Les dérivés chiraux présentent des structures hélicoïdales dans presque tous les solvants, tandis que DPPBA présente différentes structures unidimensionnelles (Figure 14). L'importance des liaisons-H a été mise en évidence lorsque des échantillons ont été mis en présence de vapeurs des solvants. Cette exposition favorise l'auto-assemblage, ce qui a été confirmé par l'augmentation de la photoconductivité.

xxi En revanche, les valeurs de photoconductivités ont beaucoup diminué lorsque les échantillons ont été immergés dans des solvants en compétition avec les liaisons-H. Cet effet n'a pas été observé pour les dérivés chiraux, ce qui indique que le centre chiral à côté de la liaison-H encombre le transport de charges. Ces résultats ont aidé à la conception des prochains composés DPPs qui seront étudiés par la suite. 17). Des bandes supplémentaires apparaissent pour des énergies plus basses lorsque les mesures de HDPPBA-C et HDPPBA-N sont réalisées dans des solvants différents comme le chlorobenzène, le toluène et l'acétate d'éthyle (Figure 18 a et b). On remarque que la bande située vers 620 nm n'est pas présente pour la molécule HDPPH, qui présente un spectre similaire dans tous les autres solvants (Figure 18c). Cette bande peut être attribuée à la formation d'agrégats J, comme cela est observé pour la famille de DPP décrite au chapitre II et dans la littérature. [31,[48][49][50] En outre, les différences entre les dérivés amide et la molécule de contrôle, suggèrent que les liaisons-H sont impliquées dans la formation de ce type d'agrégat. Cette interprétation est confirmée par les spectres UVvis lors de l'a out de méthanol, où on observe que la bande d'agrégats J disparaît comme pour la famille précédente. Les valeurs de photoconductivité pour HDPPBA-C et HDPPBA-N sont très similaires, étant respectivement de 2.0 x 10 -5 cm -2 V -1 s -1 et 1.6 x 10 -5 cm -2 V -1 s -1 . Ces valeurs sont nettement plus grandes que la valeur trouvée pour HDPPH, 5.8 x 10 -6 cm -2 V -1 s -1 , un ordre de grandeur plus petit que pour les dérivés capables de former des liaisons-H.

Ces résultats mettent en évidence le rôle bénéfique des liaisons

Chapitre IV : Expansion de la famille bisamide : influence de la position et de la topologie

Dans ce chapitre, l'ob ectif principal est de tester l'influence de la position de la liaison-H par rapport au noyau principal, ainsi que l'effet de topologie de l'amide. Dans cette nouvelle famille, la position de la liaison-H dans les molécules thiophènes a été changée (Figure 22). Les thiophènes sur le noyau DPP ont été fonctionnalisés avec des bras amide, tandis que des chaînes alkyles sont placées sur les lactames. En général, les dérivés de DPP portant des thiophènes sont souvent fonctionnalisés pour servir comme produit de départ pour les réactions de couplage croisé, réalisées en présence de Palladium. [51] xxviii xxxi La possibilité d'un couplage de Sonogashira avec un DPP [52,53] Au départ, ces études ont porté sur la caractérisation thermique de ces dérivés pour connaître leur température de dégradation et leur stabilité thermique. Il a été est possible ainsi d'évaluer le domaine de température compatible avec un processus de recuit. L'analyse thermogravimétrique (ATG), a été réalisée en chauffant des échantillons à partir de 25 °C usqu'à 300 °C à une vitesse de 5 °C/min sous atmosphère d'azote.

Les résultats obtenus montrent que HDPPBA-C (Figure 30a) et HDPPBA-N (Figure 30b) sont thermiquement stables dans ce domaine de température, car ils n'ont pas perdu plus de 1% en masse. D'autre part, HDPPH (Figure 30c) subit une perte de 2% en masse aux alentours de 230 °C et une perte massique de presque 10% vers 300 °C. Cette différence a été attribuée au fait que HDPPH ne possède pas la capacité de former des liaisons-H, ainsi qu'au caractère de donneur d'électrons des chaînes alkyles. En fait, l'introduction des groupes hexyles sur les atomes d'azote modifie la structure plate de la molécule, ce qui provoque une défragmentation plus facile de celle-ci lorsqu'on la chauffe. [54,55] Figure À partir de ces données expérimentales, il a été possible de déterminer les conditions nécessaires pour réaliser une calorimétrie différentielle à balayage (DSC). Ces mesures visaient à comprendre le comportement de fusion de ces composés. Les résultats de DSCs de HDPPBA-C, HDPPBA-N et HDPPH sont présentés sur la Figure 31, les deux premiers composés ont des points de fusion de 218 °C (Figure 31a) et 204 °C (Figure 31b), respectivement, tandis que HDPPH a un point de fusion substantiellement plus bas, 159 °C (Figure 31c). Pour avoir une meilleure compréhension des assemblages formés par ces composés, des films à couche mince ont été étudiés. En particulier, l'orientation structurelle de molécules auto-assemblées a été suivie par diffraction d'électrons (DE) en préparant des films sur différents substrats. Le premier groupe d'expériences sur substrat a consisté à réaliser un dépôt d'une goutte de chacun des composés en solution dans du chlorobenzène (concentration de 2,5 mg/ml). Ce dépôt a été fait sur des grilles en carbone pour MET, l'excès de solvant étant retiré à l'aide d'un buvard.

Le premier composé analysé est HDPPBA-C, pour lequel la direction de l'empilement des molécules de DPP est trouvée parallèle à l'axe des fibres (Figure V. 6). En plus, les molécules forment des colonnes qui sont penchées par rapport à l'axe de la fibre. Le diffractogramme montre la périodicité des amides portant des liaisons-H avec la distance charactéristique de 4.9 Angstroms (Å). xxxvii substrat de polytetrafluoroethylène (PTFE) en faisant un dépôt par goutte comme précédemment, mais en chauffant ensuite le film à 240 °C, température bien au-delà de celle de fusion de HDPPBA-C. La température de l'échantillon a ensuite été amenée à température ambiante pour qu'il cristallise.

Les résultats précédents ont montré qu'il est possible de contrôler l'orientation d'agrégats en faisant fondre le film. L'impact de la vapeur de solvant a aussi été évalué. Des films préparés par dépôt de goutte ont également été soumis à un recuit d'une heure en présence de vapeur de chloroforme. La température de recuit était située au-delà de la température de fusion de l'échantillon. Les résultats obtenus montrent que HDPPBA-C présente la même structure que les échantillons qui ont été préparés par dépôt de goutte sans recuit thermique, mais avec des réflexions plus fortes indiquant une meilleure cristallisation et orientation, sans stries des réflexions (Figure 33). En utilisant les clichés de DE, il a été possible de construire un modèle simple des structures formées par ces agrégats (Figure 34). Les réflexions peuvent être indexées sur une cellule unitaire orthorhombique simple. Ces études préliminaires ont fourni un aperçu des moyens pour contrôler la morphologie des assemblages formés par les dérivés de DPP, ce qui devrait maintenant ouvrir la voie à la conception d'un processus de criblage en temps réel des dispositifs électroniques organiques. Energy is humanity's most essential supply for the correct functioning of society as we know it; activities such as production, distribution, stockage and consumption are not possible without energy. Its uses and applications are so deeply ingrained in our daily lives, that most people have taken it for granted. In fact, our energy consumption has been increasing since prehistoric times with the discovery of fire, considerably enlarged during industrial revolution and has nowadays exponentially augmented since then; all being a consequence of the modernization of economic activities.

In the past three decades, energy use has dramatically risen all around the world, fluctuating from 8 588.9 million tonnes of oil equivalent (Mtoe) in 1995 to 13 147.3 Mtoe in 2015. [1] As more countries start to develop, energy demand will also increase, for instance China's growth has raised the proportion of energy-intensive commodities produced globally. [1] China is currently the country leading energy consumption, almost doubling the consumption of the United States of America (USA), which is the second most energy consuming country as presented in Figure I. 1.

Figure I. 1 China leads the energy consumption with 145.46 exajoules (EJ)

.*Adapted. [2] It has been projected by the Energy Information Administration (EIA) that the world energy consumption will augment by approximately 50% in the next 30 years. [3] Most of this growth is expected to come from the industrial sector, accounting for the largest share of energy consumption compared to other sectors, such as transportation and building.

On the other hand, energy consumption does not only depend on industrial activity, the corona virus disease (Covid-19) pandemic has affected the global energy demand, which is set to rise by 4.6% in 2021. [4] The pandemic has produced more disturbance to the energy sector than any other recent historical event, and its impact and consequences will be felt for years. It is still difficult to assess if the Covid-19 pandemic portrays a setback to all the efforts towards ensuring a more sustainable energy system or if it could be considered as a catalyst that will hasten the pace towards a change. What is certain is that this crisis has brought back the fact that crucial changes in energy policy must be taken worldwide.

Trends in the global emissions of carbon dioxide (CO2) and other air pollutants continue to warn about the rapid climate change and underline that strong coordinated action is needed urgently to reduce these gas emissions; that result in the rise of temperatures of the planet. For this reason, different scenarios have been projected such as the Stated Policies Scenario (STEPS), in which Covid-19 is gradually brought under control and the global economy returns to pre-crisis levels within one year. [5] Another envisioned scenario is the Sustainable Development Scenario (SDS), where clean energy policies and investments emerge setting the energy system on track to achieve sustainable energy objectives in full, including the Paris Agreement, energy access and air quality goals. [6] Addressing all this thematic would go beyond the purpose of this work, although it is important to briefly discuss it, as it gives context on the role of energy in our society and thus, highlights the importance to know how we are currently satisfying this crucial need.

II.2) Sources of energy

The world's energy consumption relies on primary energy sources, which can take many forms and origins. In turn, these primary sources are converted into a secondary energy source, electricity, which is distributed through power lines and other transmission infrastructures; to satiate the energy demand of an industrial complex or even an entire country. There are three main sources of energy for electricity generation and they will be briefly discussed in this section.

a) Fossil fuels

Before the Industrial Revolution, mankind depended on very rudimentary forms of energy: human and animal muscle, as well as burning materials such as wood. Since then, fossil fuels have been an essential driver of economic, social and technological development. Currently, at the global scale electricity is mostly produced from fossil fuels and its share was estimated to be around 64% in 2019. [7] Fossil fuels include coal, oil and gas, all of which have an important role in global energy systems; although they possess several negative impacts as once they are burned, they produce CO2 and become the largest driver of global climate change. Additionally, they contribute to local air pollution, which has been linked to millions of premature deaths every year. [8] Almost one third of global electricity generation is supplied by coal [9] , which has been classified into four main ranks: anthracite, bituminous, subbituminous, and lignite. The ranking depends on the types and amounts of carbon contained in the coal and on the amount of heat energy it releases when burned. [10] On the other hand, we have crude oil, which has remained dominant in the world energy supply over the past half century, and finds most of its applications in heating and transportation. It is particularly useful as source of energy because of its high energy density when it is burned in the presence of oxygen. Crude oil is composed of mixtures of hydrocarbons that formed from the remains of animals and plants that lived millions of years ago in a marine environment. Over thousands of millennia, these remains were covered by layers of sand, silt, and rock; which in unison with the heat from the Earth's core and the pressure from these layers, turned into what we now call petroleum. [11] It is found in underground reservoirs and once it is extracted, it is sent to a refinery, where it is separated into a wide variety of derivatives. These petroleum derivatives include gasoline, jet fuel, waxes, lubricating oils, and even asphalt.

Although the use of oil is still increasing and focused in industries such as petrochemicals and transportation, where its substitution is difficult, it is still used to produce electricity to a small extent. There are three major ways to convert oil into electricity: [12] -Conventional steam, where oil is burned to heat water, creating steam which is used to propel a turbine and generate electricity. -Combustion turbine, where oil is burned under pressure, producing hot exhaust gases that spin a turbine which then generates electricity. -Combined-cycle technology, where oil is first combusted in a combustion turbine, using the heated exhaust gases to generate electricity. After these exhaust gases are recovered, they heat water in a boiler, creating steam to drive a second turbine.

It is estimated that oil will at least continue to play the leading role in satisfying global energy needs for the following 20 years, even though the future supply of crude oil may be severely limited. [13] Finally, natural gas is considered the cleanest burning and fastest growing fossil fuel, accounting for roughly one third of total energy demand growth through the last decade. [14] Natural gas is a combustible mixture of hydrocarbon gases, formed primarily of methane and its composition can differ extensively as it is produced in a similar process as crude oil. It is formed from organic particles that were covered in mud and other sediment, which accumulated over time, exerting high pressure on the organic matter, which ended up compressing it. This compression, combined with high temperatures found deep underneath the Earth, breaks down the carbon bonds in the organic matter. As one gets deeper in these layers, temperature increases. At lower temperatures, more oil is produced whereas at higher temperatures, more natural gas is created. Since natural gas has a low density, once it has formed, it will rise toward the surface of the Earth through loose, shale type rock and other materials, where it will rise up until it gets in a geological formation that is able to trap the gas under the ground and form a reservoir and is later extracted.

Natural gas is deployed as a major source of electricity generation in gas turbines and steam turbines. It does not have as many environmental disadvantages compared to the previously mentioned fossil fuels, particularly in terms of air quality and greenhouse gas emissions as it has been estimated that it emits 50% less environmental pollution than other fossil fuels. [15] Additionally, its ease of storability and the operational flexibility of gas-fired power plants allows it to respond to both seasonal and short-term demand fluctuations, as well as enhancing electricity supply security in power systems with a growing share of variable renewables. It also finds several applications in areas such as the industrial, residential, commercial and transportation sectors. [16] b) Nuclear energy

In the 1930s, the idea of nuclear power began to flourish when the physicist Enrico Fermi demonstrated that neutrons were able to split atoms. Fermi led a team that achieved the first nuclear chain reaction in 1942 at the University of Chicago. [17] Nuclear energy originates from a process called fission where uranium atoms are split, generating heat that is used to produce steam, which is further used by a turbine generator to produce electricity.

It is often produced using a Pressurized Water Reactor (PWR) as shown in Figure I. 2, its function is to store and control the nuclear fission using uranium as nuclear fuel. The uranium is processed into small ceramic pellets and stacked together into sealed metal tubes known as fuel rods. Inside the reactor vessel, the fuel rods are submerged in water that has a dual purpose, functioning as a coolant and as moderator. The moderator aids in slowing down the neutrons produced by fission, which in turn helps to sustain the chain reaction. Reproduced. [18] As a mean to reduce or increase the rate of the chain reaction, control rods can be inserted or withdrawn into the reactor core. The reaction heats water in a primary coolant loop by thermal conduction, which is then pumped into a heat exchanger called the steam generator, where it flows through small tubes. Energy is transferred through the walls of these tubes, exchanging heat with a secondary coolant stream at lower pressure located on the sheet side of the heat exchanger, where the secondary coolant evaporates to pressurized steam. This energy transfer is performed without mixing the two fluids to prevent the secondary coolant from becoming radioactive. The generated steam is then fed to a turbine, which finally converts it into electricity and is eventually distributed to cities.

Nowadays, nuclear energy is the second-largest source of low-carbon electricity, with 452 operating reactors worldwide, and in 2018 it was estimated they provide 10% of global electricity supply. [19] The countries that lead nuclear power generation are the USA, France, China, Russia, and South Korea. [20] Despite its lower carbon emission footprint, electricity generation from nuclear reactors possesses several disadvantages and is not considered as renewable energy, given its dependence on a finite resource that requires mining of uraninite. But the most prominent problem is the potential risk of a reactor meltdown, as its devastating consequences have been shown by the nuclear accident at Chernobyl in 1986. [21] More recently, the accident at Fukushima Daiichi in 2011 caused by a huge earthquake and tsunami essentially highlighted the flaws in the design of this type of reactors. [22] Other issues related to nuclear power include the produced nuclear waste, which remains dangerously radioactive for thousands of years making it difficult to store. Many nuclear plants are located near coasts because of the proximity to water for cooling, where due to climate change they face risk of more extreme storms and rising sea levels.

c) Renewable energy sources

It is unequivocal that the growing significance of environmental problems and climate change is a direct consequence of the world energy reliance on fossil fuels. Non-renewable energy sources took over because they seemed much cheaper than the renewable sources.

Nevertheless, environmental problems have risen awareness, making renewable energy technologies considered as a solution to reduce and mitigate greenhouse gas emissions in the atmosphere through clean energy generation.

Although, their most prominent feature is that they are often considered as virtually infinite and that once facilities are operational, energy investments are spent on materials and personnel to expand and maintain the facilities. The share of renewable energy in global electricity generation jumped to 29% in 2020 as demand for all other fuels declined. [23] Similarly to fossil fuels, there are multiple types of renewable energy, but they can be divided into 5 major categories: hydropower, wind, bioenergy, geothermal and solar.

Currently, hydropower is the leading renewable energy in the world, supplying roughly 17% of total global electricity in over 160 countries. [24] Hydropower consists on using the kinetic energy of flowing water to move a turbine and generate electricity, which is then fed into the electrical grid. The endless nature of the cycle of water makes this process a reliable and clean way of producing electricity. Based on the way they function they can be classified into three types:

-Impoundment: Using a dam to store river water in a reservoir, the water is then released from the reservoir flowing through a turbine, activating a generator to produce electricity. The amount of released water depends on electricity needs or the level of water in the reservoir. -Diversion: Also known as run-of-river, this facility channels a portion of a river through a canal to then power a turbine. Sometimes it might not require the use of a dam. -Pumped storage: It functions as a battery by storing the electricity for later use. Water is pumped from a reservoir at a lower elevation to a reservoir at higher elevation and in periods of high electrical demand, the water is released back to the lower reservoir, turning a turbine and generating electricity.

The size of the installed capacity determines if hydropower stations are expressed as small, medium or large as depicted in Table I. 1, and the size of the installed plant has to be done according to the environment in which they will be implemented. For instance, major disadvantages of large hydropower plants are energy loss due to long transmission lines, which end up harming the surrounding ecology and the subsequent deforestation and waste of underground resources to build the facilities.

Table I. 1 Typical classification of hydropower stations.*Adapted. [24] Type Capacity in Megawatts (MW) Small <10 MW Medium 10 to 300 MW Large >300 MW Some advantages of the small-scale hydropower plants are the reliable and flexible operation, as well as the ease of maintenance. In addition, small power plants have gained attention because they have the highest potential for electrification in rural and remote areas in which grid connection is not available. [25] Despite being a renewable source of energy, hydropower can still be responsible for environmental problems disrupting aquatic ecosystems, which is why new projects are required to go through an Environmental and Social Impact Assessment. [26] Taking the second spot in renewable energy supply, wind power has grown at a fast pace over the last two decades. Global wind power capacity was estimated to be above 740 Gigawatts (GW) in 2020, which has grown more than double since 2014. [27] China and the USA, currently lead and continue to grow in wind power output, together representing more than half of global wind output. [23] In the same spirit as hydropower, wind power transforms kinetic energy from the wind by using a turbine that converts it into electricity by using the aerodynamic force from rotor blades. As wind flows across the blade, the air pressure on one of its side decreases, and this difference in air pressure across the two sides of the blade creates lift and drag. Since the force of the lift is stronger than the drag, the rotor spins powering a generator, thus transforming the aerodynamic force into electricity. A simplified chart of this process is shown on Figure I. 3.

Figure I. 3

The different stages of transformation of wind force into electricity in a typical wind turbine system.*Reproduced. [28] The design and installation of the turbines depends on the wind flow speed and its patterns, which can fluctuate and be modified by bodies of water, vegetation, and differences in terrain.

The size of the rotor has also an influence in the power output, the larger the blade, the more electricity it can generate.

Two major types of wind turbines exist:

-Horizontal axis turbines: Endowed with three blades that face into the wind's direction, with the turbine pivoting at the top of the tower, usually known as "upwind" operation. -Vertical axis turbines: These turbines are omnidirectional, and hence do not required to be adjusted to point into the wind to operate.

Wind power is often classified into two major categories, land based and offshore based. Land based wind power groups together several turbines what is known as a wind farm. Offshore wind turbines are installed in the ocean, they tend to be bigger than their land counterparts, generating vast amounts of energy. For a comparison, in 2015 the average rating of wind turbines installed in Europe was 2.7 MW for onshore and 4.2 MW for offshore, nowadays 8 MW wind turbines with a diameter of 164 meters (m) are installed offshore. [28] Wind power has yet many challenges to overcome, such as being able to compete economically with conventional electricity generation sources and some locations may not be windy enough to be cost competitive. On the other hand, good land-based wind sites are often located in remote locations, thus increasing the cost of transmission lines as they must be built to bring the electricity from the wind farm to the city. It also faces a competition between land that is suitable for wind-turbine installation vs alternative uses such as agriculture or livestock, which might be more highly valued than electricity generation. Last but not least, turbines might cause noise and aesthetic pollution, as well as impact local wildlife since birds have been killed by flying into spinning turbine blades. [29] Similarly, another renewable source that is currently helping us to meet our energy demand is bioenergy, which is derived from recently living organic materials usually referred to as biomass. It can be used to produce transportation fuels, heat, electricity, and even other type of products such as plastics. Biomass is often derived from organic materials that include:

-Crop wastes -Forest residues -Purpose-grown grasses -Woody energy crops -Microalgae -Urban waste -Food waste

The USA and Brazil, are currently leading the production of biofuels and account for around 80% of global production. [27] In 2018, bioenergy was the third largest renewable electricity generating source with a share of 9% of global production. [30] Energy from biomass plays an important role in the global energy system, as it can significantly reduce carbon emissions, especially in sectors like manufacturing and transportation, where it is difficult to decarbonize.

In the same way as for fossil fuel, bioenergy technologies convert renewable biomass fuels into heat and electricity, for instance dry combustible feedstocks such as wood pellets are burnt in boilers or furnaces. This heat is used to boil water, producing steam which then powers a turbine to generate electricity. Biomass can also substitute a portion of coal in an existing power plant furnace, combusting both materials at the same time in a process called cofiring. [31] For wet feedstocks, like food waste for example, biogas can be produced by putting the waste into sealed tanks where they rot and produce methane gas. Inside these oxygen-free tanks, often called digesters, matter gets decomposed by anaerobic bacteria that produce methane and other byproducts to form biogas. The gas is captured and purified to be further burnt to generate electricity or distributed to be used for cooking and heating purposes.

Biomass can also be converted to a gaseous or liquid fuel through gasification and pyrolysis. [32] In the gasification process, solid biomass materials are exposed to high temperatures with very little oxygen present, producing synthesis gas. This gas mixture consists mostly of carbon monoxide and hydrogen, which can then be burned in a conventional boiler to produce electricity or used to replace natural gas in a combined-cycle gas turbine. On the other hand, pyrolysis uses a similar process to gasification but under different operating conditions, lower temperatures and in the absence of oxygen, producing a crude bio-oil. This bio-oil is then substituted for fuel used in engines used for electricity production.

While biopower possesses advantages such as being a widely available renewable source of energy, being less expensive than traditional fuels and considered as a carbon neutral emitting source, reducing the overreliance of fossil fuels, there are also some intrinsic disadvantages.

Biomass energy is not as efficient as fossil fuels and is sometimes fortified with fossil fuels to increase its efficiency. [33] Furthermore, it is not entirely clean, as the use of animal and human waste increases the amount of methane gases, which damages the environment. Additionally, the pollution created from burning natural materials can be considered as bad as burning coal and other types of energy resources.

An additional disadvantage is that wood is often considered as the principal source of biomass energy, and vast amounts must be burned to produce the desired amount of power, potentially leading to deforestation as energetic demand will continue to grow. Lastly, bioenergy requires the utilization of vast amounts of land, a resource that is limited in supply. Even though there are some downsides to biopower, it is considered as a necessary transitional element of global energy generation, that will play an important role over the next few decades. [34] Another renewable energy that uses heating principles to produce electricity is geothermal power. Thermal energy produces underground reservoirs of hot water that exist in a wide range of temperatures, depending on the depth. This thermal energy originates from the formation of the planet and the slow decay of radioactive particles in the Earth's core. As presented on Figure I. 4, the earth's interior can be divided into four main layers: the inner core made of solid iron, an outer core of hot molten rock called magma, a mantle of magma and rock surrounding the outer core and finally a crust of solid rock that forms the continents and ocean floors. [35] The heat that stems from the core travels through the layers, all the way to the crust where rocks and water absorb the heat from deep underground. This thermal energy is accessed by drilling water or steam wells in a process like drilling for oil and geothermal power plants use turbines and generators to convert this heat into electricity. There are three main types of geothermal power plants [36] :

-Dry Steam: They draw power from underground resources of steam, which is piped directly from underground wells to the power plant where it is directed into a turbine. -Flash Steam: These are the most common and use geothermal reservoirs of water with temperatures greater than 182°C. This very hot water flows up through wells in the ground under its own pressure, which decreases as it flows upward inducing the hot water to boil into steam. The steam is then separated from the water and used to power a turbine. The leftover water and condensed steam are injected back into the reservoir, making this a sustainable resource. -Binary Steam: They operate with water at temperatures ranging between 107-182°C, using the heat from the hot water to boil a secondary fluid that has a low boiling point. Both fluids are kept separated during the whole process, since the secondary fluid is vaporized in a heat exchanger and used to turn a turbine. The water is then injected back into the ground to be reheated.

The USA is the world's largest electric geothermal producer, although geothermal energy finds applications in other fields, mostly for thermal applications in bathing, house heating and industry. The direct use of geothermal energy for thermal applications continues to grow worldwide, roughly 8% every year, but the market remains geographically concentrated, with only four countries (China, Turkey, Iceland and Japan), representing three-quarters of all direct geothermal use. [27] One of the biggest advantages of geothermal energy is that it is a very predictable and reliable source of energy, having no restrictions in terms of weather conditions especially in comparison to other renewable energy resources like wind energy. Moreover, geothermal power plants have a small land footprint since the energy comes from within the earth, and large land surface to harness it is not required. [37] On the other hand, the greatest disadvantage of geothermal energy is that geothermal power plants can only be built at specific sites, since reservoirs above 100°C are necessary for most geothermal plants, and these reservoirs are only found near tectonic plate boundaries or volcanoes. Additionally, the geothermal facilities have a high upfront construction cost, most of it is associated with the difficulty and cost of drilling deep into the Earth to access the geothermal reservoirs. Finally, geothermal plants can cause earthquakes as drilling deep underground is known to cause instability, which can lead to earthquakes at the surface of the Earth; for instance, a promising geothermal project in the Alsace region of France was suspended in late 2020, after a series of earthquakes that were attributed to geothermal drilling and well stimulation on the northern outskirts of Strasbourg. [38,39] Finally, being the fastest growing and most affordable source of electricity, solar power is the last renewable source of energy that will be discussed. The sun has produced energy for billions of years and is so considered as the most abundant renewable energy source available. Throughout history, solar energy has been used as thermal energy to cook or to heat working fluids like water for domestic or industrial use, but more recently it started to be used to convert sunlight into electricity through photovoltaic (PV) devices.

A solar PV cell is an electrical device that converts the energy of sunlight directly into electricity by using the photovoltaic effect. Edmond Becquerel discovered the photovoltaic effect in 1839, while performing experiments with an electrolytic cell composed of two metal electrodes, concluding that some of them produced small amounts of electric current when exposed to sunlight. [40] In 1873, the British engineer Willoughby Smith discovered the photoconductivity of selenium, which varies its electrical conductivity upon illumination of its surface. Ten years later, Charles Fritts invented the first solar cell by using selenium, although too low for practical applications, this cell showed a power conversion efficiency (PCE) of roughly 1%. [41] It was not until 1941, that Russel Ohl produced and patented the first silicon cell, more efficient than the selenium one, and within few years silicon-based photovoltaic cells reached PCE of 15%; this made them suitable for practical applications and even to start being deployed to power space satellites. [42,43] Many solar cells and PV modules have been developed since the 1950s and are still intensively studied and improved to this day. The basic functioning of a traditional silicon PV cell is described in Figure I. 5. Nowadays a PV cell is made of semiconducting materials that absorb the photons emitted by the sun and as the photons are absorbed by the semiconducting material, they release the electrons from its atoms; leaving an unoccupied space that can be filled by other randomly moving electrons looking for another "hole" to be occupied.

Although, to produce an electric current, the electrons must flow in the same direction and this is achieved by using two different layers. In the case of silicon-based PV, the first layer is doped with atoms of phosphorus, which has one more electron than silicon, while the second layer is doped with atoms of boron, which has one less electron. When exposed to the sun, the resulting "sandwich" functions like a battery: the layer with an excess of electrons becomes the negative terminal (n-side) and the side that has a deficit of electrons becomes the positive terminal (p-side), generating an electric field at the junction between the two layers. This electric field sweeps electrons to the n-side, while the holes drift to the p-side, in turn the electrons and holes are directed to the electrical contacts applied to both sides, flowing to the external circuit as electricity. To minimize photon loss due to surface reflection an antireflective coating is added to the top of the cell. [44] The operation of PV cells is based on 3 basic principles: the first one being the absorption of light, to generate the electron-hole pairs; the second is the separation of charge carriers of opposite types and finally the extraction of those carriers to an external circuit. In this sense, three main types of PV cells can be found:

-Crystalline Silicon Cells: Accounting for more than 95% of the solar cell market. In commercial applications, with efficiencies up to 27%. [45] -Perovskites: These solar cells are made from hybrid materials, containing both organic and inorganic parts. Their PCEs at the laboratory scale has reached values of 25.2%. [46] Although a lot of research still needs to be done before the cells can be mass produced, due to instability problems, perovskites have many advantages such as being lightweight and flexible. Moreover, they are cheap to produce. [47,48] -Organic Cells: They use organic molecules or polymers instead of semiconducting minerals. The cells continue to have a low conversion efficiency (compared to the previous ones) and a short lifetime, but they are potentially a low-cost alternative in terms of production. [49] Demand for solar PV is thriving as it becomes the most competitive option for electricity generation, both for residential and commercial applications; this growth is shown on Figure I.

6, where global capacity reached roughly 760 GW in 2020. [27] Additionally, the price of silicon cells has dropped in recent years, making PVs very competitive compared to other sources of electricity. [50] Figure I. 6 Solar PV Global Capacity and Annual Additions in the last decade.*Reproduced. [27] Solar PV has an important role in electricity generation in a growing number of countries, and by the end of 2020, at least 15 countries had enough capacity in operation to meet at least 5% of their electricity demand with solar PV. For instance, solar PV accounted for around 11.2% of annual generation in Honduras and for notable shares in Germany (10.5%) and Greece (10.4%) just to mention a few. [27] The use of solar energy has two main benefits: these systems do not produce air pollutants and they can be installed on buildings, having minimal effects on the environment. Nevertheless, despite its rapid growth, it still possesses some limitations, the main one being that the amount of sunlight that arrives at the earth's surface is not constant. It can vary depending on location, time of the day, season of the year, and weather conditions. Additionally, the amount of sunlight reaching a square meter of the earth's surface is relatively small, hence a large surface area is necessary to collect a good amount of energy; requiring a lot of space and increasing the amount of solar panels necessary to meet the energy demand.

Although pollution related to solar energy systems is far less compared to other sources of energy, there are also some toxic materials and hazardous products used during the manufacturing process of PV systems, which can indirectly affect the environment, particularly in the case of perovskites.

Additionally, contrary to fossil fuels, it is not easy to store energy from renewable sources. The electricity produced from PV is direct current, which is used to charge the batteries; thus, requiring battery replacement on a regular basis.

Finally, even though there has been a rapid decline in solar technology costs in the last decade, the overall costs to generate solar power remain high. Hence researchers are focusing on improving the competitiveness of solar power and towards PV technologies to enhance their efficiency, stability, manufacturability, and availability.

To summarize, renewable energy is helping us to meet our current energy demand, although they also present a variety of obstacles such as the irregularity of weather, wind, and solar cycles, which hinder that the electric generation of a country can solely rely on them. Lastly, the high cost of the initial investment to install these technologies is not always affordable.

II.3) Sustainability

Worldwide, environmental pollution is a considerable concern and furthermore, the demand and prices of fossil fuels and its derived products continue to rise; and so renewable forms of energy are becoming more attractive. The current energy system has environmental impacts that extend beyond the by-products of combustion, such as climate change, biodiversity loss, the release of hazardous chemicals into the environment, and water scarcity.

These aspects have increased the focus on sustainable energy resources derived from wind power, hydro power, solar power, biomass, and geothermal power. This sustainability aims to meet the energy needs of the present without compromising the ability of future generations to meet their own needs, meaning that sustainable energy must become a power which can be replenished within a human lifetime and causes no long-term damage to the environment.

Actions have already been taken to mitigate these environmental impacts, for instance, the Paris Agreement has the objective of holding the increase in the global average temperature to well below 2 °C. [51] The physical impacts of climate change are among the challenges that renewable energies will have to face, as they have implications for the reliability and performance of energy generation. Furthermore, in order to meet the 2 °C climate goal, the share of renewable energy in the final energy consumption must increase above 65% by 2050. [52] Meeting the current and future energy demand in a sustainable way is a critical challenge in the global ambition to reduce the impact of climate change, while maintaining economic growth. Additionally, electricity is essential for health care, education, and economic development and improving energy access in the least-developed countries and making energy cleaner are essential to achieve most of the United Nations 2030 Sustainable Development Goals. [53] While renewable energy is plentiful, most of the environmental impact is related to the manufacturing of the equipment required to harness energy. In this regard, due to its less harmful impacts on the environment, solar energy is often considered as the best and most attractive candidate to ensure a sustainable way to produce energy in future. Being practically inexhaustible, almost pollution-free, silent, and having no mechanical involved parts, solar power will clearly continue to be essential in the upcoming decades.

The evolution of the solar PV industry so far has been remarkable, with several milestones achieved in recent years in terms of installations, cost reductions and technological advancements; as a result, solar PV power installations have been dominating the renewables industry in the past years.

Moreover, the solar PV industry is changing rapidly, with innovations occurring along the entire chain of production. The major driver for innovation has been the push for higher efficiency, which is essential for competitive module manufacturing, since it directly decreases cell processing costs by reducing quantities required for a given output. The further growth of the solar PV industry largely depends on reducing the costs by using adequate materials and this is where all the developments in organic electronics become important.

II. Organic Electronics

Organic semiconductors combine the chemical and mechanical benefits of organic compounds with the electronic advantages of semiconducting materials; obtaining versatile structures that can be altered through chemical synthesis to improve their ability to absorb light or conduct electricity. The use of organic compounds as active materials in electronic and optoelectronic devices has led to low-cost methods for fabricating useful structures that are inaccessible when using conventional semiconductors.

Hence, organic electronics has been studied in the fields of physics and chemistry for more than 70 years, with its main attraction being the ability to modify chemical structure in ways that could directly impact the properties of the materials when deposited in thin films. Being the first person to observe electroluminescence in organic materials, André Bernanose is often considered the father of organic light emitting diodes (OLEDs), although it was not until 1987 that Ching W. Tang reported the fabrication of a practical OLED device. [54] This OLED incorporated a double-layer structure motif composed of copper phthalocyanine and a derivative of perylenetetracarboxylic dianhydride.

Since that first demonstration, organic thin films have proven useful for several applications, and are nowadays used to create digital displays in devices such as televisions, computer monitors, smartphones, and even handheld game consoles. Furthermore, the charge carrier transport properties of molecular organic materials have been investigated extensively, which has led to the development of semiconducting materials that are used for electricity applications.

II.1) Organic semiconducting materials

Organic semiconductors are mostly made up by carbon and hydrogen atoms, with a few heteroatoms such as sulfur, oxygen, and nitrogen. These materials combine the electronic advantages of semiconducting materials with the chemical and mechanical benefits of organic compounds, like polymers.

In this sense, these materials are capable of absorbing light, conduct electricity, and emit light; these properties are all linked to the material's structure, which can easily be modified on the chemical synthesis. Chemical modification not only permits tuning of electronic properties but can also help to improve solubility or modify the material to make it mechanically robust, lightweight, and/or flexible.

Furthermore, a semiconductor is a material whose resistivity lies between the values of a conductor and an insulator (10 -4 -0.5 Ω•m). [55] However, the resistance of a semiconductor material decreases with an increase in temperature, as the energy gap between conduction and valence band is narrow for semiconductors when compared to insulators. The energy gap is the energy required to promote a valence electron bound to an atom to become a conduction electron, which serves as a charge carrier to conduct an electric current as it is free to move within the crystal lattice of a solid material. The valence band of a semiconductor is almost filled by electrons, whereas the conduction band is nearly empty. The forbidden energy gap is small, close to 1 electronvolt (eV), therefore, a small amount of energy is required for valence electrons to move into the conduction band. And so, a rise in temperature allows electrons in the valence band to gain energy and jump to the conduction band. As a result, semiconductors can change from insulators to conductors due to variations in temperature.

While they show semiconducting properties, inorganic and organic materials have strongly different "semiconducting" nature and so, semiconductors can be classified in two categories:

-Intrinsic: Commonly known as a pure semiconductor, having the ability to create electron-hole pairs at room temperature. When a potential is applied across it, conduction is induced through free electrons and holes that are generated by the breaking of covalent bonds through thermal energy. Consequently, the current flow in the intrinsic semiconductor is a combination of electron and hole. They are often attributed to inorganic materials. -Extrinsic: Also called impure semiconductor and often associated to organic materials.

It consists of a mixture of an intrinsic semiconductor with impurities. At room temperature, the intrinsic semiconductor has small conduction, so in order to improve its conductivity, a small amount of impurity is added. This process is called doping and when performed, either the number of electrons increases, or the number of holes increases depending on the dopant. Addition of pentavalent impurities produces free electrons (n-type semiconductor), while in the case of trivalent impurities, additional holes are generated (p-type semiconductor).

The differences between intrinsic and extrinsic semiconductors are compiled in Table I. 2. These differences between organic and inorganic semiconductors show that deep understanding on their electronic structure is needed in order to understand their photophysical properties, as well as useful when designing and improving semiconductor devices.

Table I. 2 Differences between intrinsic and extrinsic semiconductors.*Adapted. [55] In addition, organic semiconductors can be used in three ways: amorphous molecular films, molecular crystals and polymer films. As the name implies it, in the first application, organic molecules are deposited as an amorphous film through evaporation or spin-coating, forming thin films; which can then be used for device applications such as OLEDs.

Factors

In the second method, molecular crystals are formed using organic molecules such as naphthalene. A crystal consists of a lattice and a basis, for instance atoms like silicon can form a crystal through covalent bonding. In the same way, organic molecules are also able to form the basis of a crystal that is held together via van der Waals interactions. The charge mobilities that can be obtained in molecular crystals are high compared to those in non-crystalline organic materials, which makes them very suitable for transistor applications. [START_REF] Wang | [END_REF] Lastly, polymer films are applied through several deposition techniques including simple spincoating or ink-jet deposition. Polymers are molecules that have been covalently coupled together, bearing repeating units that form a chain like structure. They are more suitable to blending than small molecules since polymer blends are thermodynamically more stable and less susceptible to crystallization.

Furthermore, organic semiconductors are quite unique since their solid-state properties are attributed to a hierarchical structure of atom-molecule-solid. Atoms link together by covalent bonds, composing molecules, which in turn are held together by van der Waals interactions and create the solid material. This hierarchy is possible due to π-electrons, which are the source for all the functional electronic properties of organic semiconductors.

II.2) Properties of organic semiconductors

Organic molecular materials used as semiconductors are endowed of a free electron system, this is due to the exceptional nature of the carbon atom, which can form several types of structures through stable covalent -and -bonds. The -bonds are formed by hybrid orbitals between the adjacent carbon atoms, whereas the π-bonds are formed by the overlap between orbitals of adjacent carbon atoms that do not participate in the formation of -bonds, a simplified scheme is shown in Figure I. 7. The -bonds are relatively strong and the electrons in the -bonds are likely to be localized. In contrast, the π-electrons are widely delocalized making -bonds weaker than -bonds. Molecules containing several delocalized electrons are known as conjugated systems, this delocalization of electrons bestows organic semiconductors with special properties.

One of said properties is that these materials can show strong colors, in contrast to usual organic or plastic materials that are formed only by the σ-bonds and do not possess colors. Since σ-bonds are so strong in non-conjugated molecules, the electronic excitation energy becomes high and the optical gap energy is much larger than the visible photon energy range, which is between 1.6-3.3 eV. On the other hand, when the π-electrons are delocalized across a molecule, the electronic excitation energy considerably decreases, making the materials to become colored due to the absorption of visible light.

Another property these materials possess is that they tend to have large dipolar moments, and hence are able to strongly couple with electromagnetic waves. This is once again due to the electronic π-system, which typically delocalizes electrons within the molecule; furthermore, the gap between binding and anti-binding can be manipulated by controlling the size of the πsystem (degree of conjugation). [START_REF] Riede | Reference Module in Materials Science and Materials Engineering[END_REF] Figure I. 7 Simplified schematic for a linear carbon chain connected with and bonds.

Finally, molecules containing aromatic groups can self-organize to form crystals when they gather; furthermore, if the molecular shapes have relatively high symmetry, molecules can be packed densely. This phenomenon is known as π-stacking and will be further discussed in detail throughout this chapter. In the crystals composed of densely packed molecules, molecular orbitals of -electrons, can overlap and interact with those of the adjacent molecules. Consequently, the electronic states of the π-electrons are extended widely over the crystals. These intermolecular interactions between the combination of adjacent molecules play an important role in the charge carrier transportation of organic semiconductors.

An essential tool to determine the -electronic states of organic semiconductors is molecular orbital (MO) theory, which is based on the concept that the electrons are not assigned to the individual bonds between atoms, but to the molecular orbital that is extended to the whole molecule. [START_REF] Wagnière | Introduction to Elementary Molecular Orbital Theory and to Semiempirical Methods[END_REF] In the simplest MO calculations, empirical values are used to describe electronic states in the molecules. In the same regard, calculations using density functional theory (DFT) are more frequently used to calculate ground states of many -electron systems; the method is based on the calculation of distribution function of electron density and the effective potential. [START_REF] Hasegawa | Organic Electronics Materials and Devices[END_REF] Moreover, predicting what kind of crystal structure can be formed by a molecule before it is synthesized and crystallized is a difficult task. However, the stability of molecular packing in the crystals can be studied using molecular dynamics (MD) simulations, which simulate the motion of atoms and molecules while assuming an interatomic potential. Although, it is still compulsory to synthesize the materials and to conduct the crystal structure analyses for the proper development and design of organic semiconducting devices.

II.3) Design of molecules for organic semiconductors

As previously mentioned, the rate of charge transport in organic semiconductors is ruled by electron-electron, as well as by electron-vibration interactions. However, factors such as defects, impurities, charge carrier densities, electrical fields, temperature and pressure can also have an influence. The inability to predict the extent of the previously mentioned factors makes virtually impossible to accurately predict the charge transport properties of small molecules or polymers from their individual molecular structures. Nevertheless, molecular design has proven to be a useful tool in development of promising organic semiconductors.

The molecular design of these materials can be divided into four main constituting components, as depicted in Figure I. 8. Such a structure can be a single molecule or a repeating unit in a conjugated polymer. The conjugated core (backbone) and alkyl chains govern a big part of the electronic properties, like energy bandgap and solubility, as well as they influence the molecular packing.

Figure I. 8 Representation of a typical π-conjugated system.*Adapted. [START_REF] Mei | [END_REF] Another effective way to tune electronic properties, solubility and molecular packing is by the addition of heteroatoms, for instance thiophene rings are known to be an extremely important unit to obtain high-performance organic semiconductors. In the same spirit, core substitution affects electronic properties, solubility and molecular arrangements, this is done by changing the carbon/hydrogen ratio or by introducing halogen atoms, which modifies the dipolar moment of the structure.

The incorporation of side chains is commonly done to improve the solubility, while they may also impact electronic properties in the solid state by changing molecular packing structures or altering the torsion conformation of the conjugated backbone. Side chains are typically insulating, as a result, if an excessive amount of side chains is present, the mass percentage of conjugated segments decreases. The importance of each constituting component in the design of semiconductors is briefly highlighted below.

a) Effect of conjugation extension and aromaticity

There are many studies confirming that conjugation extension in small molecules is a viable approach to improve charge mobility, particularly for the linear acene family. [61][62][63] As can be seen in Figure I. 9, linear acenes are aromatic hydrocarbons composed of fused benzene rings. From a theoretical point of view, as well as performance wise, they have been of great interest; for instance, anthracene is one member of the acene family with reported transistor characteristics, showing a mobility of 0.02 cm 2 /(V•s) when measured at low temperature. [61] In practical applications, the selection of the acene core length is a combination of the theoretical performance limit, chemical stability and ease of processing. The thin film morphology is also strongly dependent on the molecular size: smaller acenes have a tendency to give more three-dimensional growth, while larger acenes lead to small grains due to lower diffusivity at a given temperature. [64] Moreover, with increasing number of rings, solubility is tough to achieve and hence, requires the addition of solubilizing groups, which may ultimately reduce the mobility of the soluble derivatives due to the insulating nature of alkyl chains. To circumvent these issues, several approaches have been reported, including replacement of some benzene rings with other heteroaromatic rings to lower the aromaticity, attaching bulky substituents, and substitution with electron-withdrawing groups. [START_REF] Mei | [END_REF] Figure I. 9 A few members of the linear acene family.

Ultimately, it is possible to say that the combination of conjugation extension and proper lowering of aromaticity is an effective way to achieve high charge mobilities for fused ring systems with good stability. In fact, there are additional examples which have used the above design principles and resulted in stable high-performance organic semiconductors. [65,66] b) Heteroatom replacement

The addition of a heteroatom can have a big impact on the electronic structure and crystal packing of a conjugated system, and most commonly, heteroatom replacement ranges from chalcogen atoms to nitrogen. For instance, in the quaterchalcogenophene family presented in Figure I. 10, switching from sulfur to selenium has a slight effect in the mobility. [67,68] However, in 2,6-diphenylbenzodichalcogenophenes, replacing sulfur by selenium had a great effect on the charge mobility, almost doubling in value. [69] Surprisingly, the trend did not continue when selenium was replaced by tellurium, and the mobility dropped about 2 orders of magnitude compared to the sulfur derivative. On the other hand, the chemistry of sulfur is more versatile when compared to that of selenium and tellurium, coupled with the higher toxicity and environmental impact of selenium and tellurium, their use in practical applications has been discouraged.

Figure I. 10 Influence of heteroatom replacement in mobility values for two different

molecules used for organic semiconductors. Mobilities were measured for vacuum deposited films of the materials.*Adapted. [START_REF] Mei | [END_REF] The heteroatom effect between sulfur and nitrogen has been explored in other families, such as the ones depicted on although this was measured in single crystal OFETs. [70,71] Conversely, the syn-dibenzothieno[b,d]pyrrole (syn-DBTP) exhibit no field effect properties, while its sulfur counterpart (BBTT) exhibited a mobility of 0.5 cm 2 /(V•s). [72] However, the introduction of N-H•••π interactions is not always detrimental, for instance in indo[3,2b]carbozole (ICZ), extremely favorable bidirectional electronic coupling in crystals has been observed. OFETs of ICZ gave satisfying mobility values, whereas its sulfur counterpart, benzo[1,2-b:4,5-b′]bis[b]benzothiophene ( T), had 10 times smaller mobility values. [73] Furthermore, an increase in charge mobility in OFET devices was often reported in linear acenes, when some of the carbons are replaced with nitrogen atoms. [74] Nevertheless, more experiments are needed to further extend and study this phenomenon to other systems.

Figure I. 11 Effect of N-H•••π interactions on the mobilities of different families.

± All mobilities were measured for vacuum deposited films except for DBTDT.*Adapted. [START_REF] Mei | [END_REF] c) Core Substitution with Electron Withdrawing Groups

The substitution on a conjugated core with electron withdrawing groups, such as halogens or nitriles (CN), usually enhances stability against oxidation, leads to changes in molecular packing and can potentially induce a transition from p-type materials to ambipolar or n-type materials. Electron withdrawing groups are capable of pulling electron density away from a πconjugated system, either through an inductive effect or by resonance. On the contrary, electron donating groups, such as alkoxy or alkyl thioether, typically increase oxidation potential and reduce stability.

The development and stability of n-type organic semiconductors that can operate under ambient conditions, to complement high performance p-type materials for making organic integrated circuits, has been one of the obstacles that the organic electronic community has had the most issues with.

In this regard, MO theory plays an important role, as most often in π-conjugated systems, the highest occupied molecular orbital (HOMO) and the lowest unoccupied molecular orbital (LUMO) are respectively the binding π-state and the anti-binding π*-state. This means that the HOMO can be related with the valence band and the LUMO with the conduction band of a semiconductor. It has been reported that to achieve operational stability in air, organic semiconductors must be designed with low lying LUMO levels, since electron affinity needs to be at least 3.0 eV but should not be much greater than 4.0 eV. [75] The most common way to achieve air-stable n-type organic semiconductors is through perfluorination. For instance, replacing all hydrogen by fluorine (F) atoms in pentacene leads to perfluoropentacene; for which ionization energy increased roughly by 0.6 eV with respect to pentacene. Furthermore, electron affinity increased by 0.7 eV, translating into better air stability and ease of electron injection. [76] Finally, perfluoropentacene has different crystal packing from pentacene, suggesting the intrinsic hole and electron mobilities might be lower in perfluoropentacene. [77] Furthermore, the importance of fluorination in the backbone of conjugated polymers has recently been reviewed [78] , where a general understanding of the impact of fluorination on the device performances has been discussed. Additionally, atomic substitution of the polymer backbone with fluorine atoms has attracted a lot of attention, since, fluorine atoms impact positively some of the key features of such polymers including the lowering of the energy levels. [79] It is worth mentioning that in the case of partial fluorination, ambipolar materials are obtained. [80] Besides fluorination, chlorination has proven to be more effective at dropping the LUMO level of the resulting molecules, this has been attributed to the fact that a chlorine (Cl) atom contains empty 3d orbitals able to accept π-electrons from the conjugated core, whereas F does not possess empty orbitals for such delocalization.

On the other hand, the position of the substitution plays an important role on charge transport properties and crystal packing. For instance, chlorinated derivatives such as 5-chlorotetracene (ClT), 5,11-dichlorotetracene (DClT) and 5,6,11,12-tetrachlorotetracene (TClT) were obtained and tested in OFETs, as shown in Figure I. 12. [81,82] Figure I. 12 Representative acene chlorinated derivatives along with their respective hole mobility values. All mobilities were measured for single crystals. [START_REF] Mei | [END_REF] Yet, none of these molecules presented n-type charge transport properties; but both DClT and TClT displayed rather good hole mobilities. In contrast, halogenation altered the crystal packings from a herringbone-type structure for ClT to a face-to-face slipped π-stacking motif for DClT and TClT, which is what might explain the difference in their charge transport properties. Further studies of the effects of halogenation on the properties of organic semiconductors have been broadly done and summarized. [83] Possibly, perylene diimide and naphthalene diimide derivatives are the most studied air-stable n-channel (hole-transporting) organic semiconductors, and upon addition of electron withdrawing groups, numerous high mobility air-stable materials have been reported. [84] d) Incorporation of side chains

As it was briefly mentioned before, the inclusion of side chains on conjugated cores is principally done to add solubilizing groups that ease solution-processability of organic semiconductors. Alkyl chains are considered insulating materials; hence, they do not contribute to charge transport directly. However, these side chains can considerably impact the charge transport properties by affecting molecular packing and the thin film morphology. [85,86] For instance, to prevent dimerization and improve their stability against oxidation, alkylation or arylation of peri-positions have been performed in acene derivatives. Furthermore, this also changed their packing motifs from a herringbone pattern to a face-to-face π-stacking, by diminishing the C-H•••π interactions. [87,88] In the same way as for halogen substitution, the packing of the crystals is susceptible to the position of alkylation. [89] Additionally, other reports have found that the size of the alkyl chain plays a significant role in two dimension (2D) and three dimension (3D) polycrystallite formation, which ultimately impacts the charge mobility. [90] In addition, the attachment of alkyl chains is not only limited to carbon atoms, N-alkylation introduces solubilizing groups when the conjugated core has nitrogen atoms. Nevertheless, this can block N-H•••π interactions, which in turn can possibly change the molecular packing. Such an example was mentioned before, where the synergy of N-H•••π interactions in ICZ crystals resulted in strong bidirectional electronic coupling, enhancing the charge transport. [73] Moreover, hydrophilic triglyme chains and other oligo ethers have also been used as side chains in conjugated molecules. [91] Unique features can be obtained when both hydrophilic triglyme and hydrophobic alkyl chains are substituted on the same conjugated core, resulting in amphiphilic molecular design, which can sometimes be advantageous on charge transport. [START_REF] Mei | [END_REF] Another type of substituents are branched side chains, since linear side chains usually do not impart enough solubility for various printing techniques; unfortunately, they have a tendency to disrupt crystal packing, which results in poor mobilities. In an attempt to solve these issues, thermally cleavable aliphatic carbonyloxy substituents have been introduced onto conjugated cores such as sexithiophene. The carbonyloxy group is volatilized upon thermal treatment, and two short hydrocarbon chains remain at the terminal thiophene rings. [92] Finally, another unique side chain that can be used is the cyclohexyl group, which has been frequently known to add steric bulkiness at the periphery of the core, providing improved solubility without having a detrimental consequence on the molecular packing in the thin film phase. [93] II.4) Importance of Morphology

The promising qualities of organic photovoltaic devices (OPVs) have made them receive a lot of attention, as they have the ease of solution processability, tunable electronic properties, low manufacturing temperature, as well as being relatively cheap and less environmental impactful. They have exceeded certified efficiencies of 17% to date, close to efficiency values obtained by low-cost commercial silicon solar cells. [94,95] The operation of OPVs can be summarized in five steps (Figure I. 13). First, the absorption of incident light excites electrons and when light with high enough energy levels is absorbed, electrons excited from the HOMO to the LUMO generate an exciton. If the energy of the absorbed light is greater than the band gap, the electron will move to a higher energy level than the LUMO and decay down in a process known as thermalization, which results in an energy loss in the form of heat.

Secondly, the diffusion of the exciton occurs between the donor-acceptor interface and the organic semiconductor component, where the offset between LUMO levels will drive exciton dissociation. Although, this must occur within a certain amount of time otherwise the excited electron will return to the empty energy state (leaving a hole), this process is often referred as recombination. The time taken is known as the exciton lifetime, which is often represented as the distance that the exciton can diffuse in this time (usually about 10nm).

Thirdly, a dissociation of the exciton across this interface ensues, the electron moves to the acceptor material and the hole will remain on the donor. The charge carriers will still be attracted, and charge-transfer state happens. When the distance between the pair increases, the attraction decreases. Ultimately, a charge-separated state is formed as the binding energy between them is surpassed by thermal energy. While the electron-hole pair is still attracted in the charge-transfer state, recombination can take place across the interface between both materials.

Figure I. 13 An approximation of the basic steps that govern OPV function under light

illumination.*Reproduced. [START_REF]Organic Photovoltaic (OPV) Cells | How Organic Solar Cells Work | Ossila[END_REF] Next, the charge-carriers will diffuse to the appropriate electrodes through the relevant interfacial layers; for instance, the holes will travel to the anode and the electrons to the cathode. Finally, a charge-carrier collection process arises at the electrodes and the charge carriers are used to do work in the external circuit of the cell to generate an electric current.

It is important to consider that at several stages, the electron and hole can recombine, wasting the absorbed energy used for initial excitation. Furthermore, recombination can be categorized as either geminate, were the initially produced electron-hole pair recombines before exciton dissociation; or as non-geminate, where the free electrons and holes can recombine, regardless of their source. Both processes can be radiative, which is when a photon is released or non-radiative, meaning that no photon is released. [START_REF] Menke | [END_REF] The first two-component OPV was proposed by Tang et al in 1986 [98] , but efficiencies remained low for several years as they relied on bilayer cells. The main issue being that excitons are only able to dissociate at the interface between donor and acceptor, generally diffusing around 10 nm before decaying back to the ground state. [99] Although, the total active layer required to efficiently absorb light usually has a thickness of more than 100 nm, this means that bilayer cells are either too thin to properly absorb, or too thick for efficient exciton dissociation.

The solution to this is known as the bulk heterojunction (BHJ) cell and it was conceived in 1995. [100,100] In this type of device, instead of a strict two-layer system, the donor and acceptor materials are intimately mixed at the nanoscale level, which allows the interfaces to be dispersed across the active layer, while preserving the required thickness for absorption.

There have been countless refinements in morphology control [101,102] , development of new donors and acceptors [103] , and technical expertise, which all together has led to modern BHJ OPVs reach efficiencies over 17%. [94] Most OPVs used in modern research are solution-processed BHJ cells, where depending on the orientation of the electrodes, the architecture can be considered as conventional or inverted (Figure I. 14). The hole-and electron-transporting at the interfacial layers facilitates the charge-carrier transport on either side of the active layer. Typically, the hole-transporting layer (HTL) in a conventional stack is made from Poly(3,4-ethylenedioxythiophene) polystyrene sulfonate (PEDOT:PSS) and is often paired with an Indium Tin Oxide (ITO) anode. Whilst a typical electron-transporting layer (ETL) is calcium, often paired with an aluminum cathode. These layers promote the transport of one type of charge carrier through favorable energy level positioning, while hindering the transport of the other carrier. As result, the HTL is frequently known as the electron-blocking layer, and vice versa. 14 The stacks used in a conventional and inverted OPV cell, where the layers are not given to scale.*Adapted. [START_REF]Organic Photovoltaic (OPV) Cells | How Organic Solar Cells Work | Ossila[END_REF] Noteworthy advances in high-performance and air-stable organic semiconductors have been achieved through molecular design. However, charge carrier mobility is usually determined by the strength of electronic coupling between the hopping sites, their disorder, and their geometric reorganization energy. Therefore, by increasing structural order, charge transport can be improved. For instance, for small molecules this can be achieved through selfassembly, whereas in the case of conjugated polymers, chain alignment is used.

Figure I.
Although, these procedures have a major disadvantage, as for polymer films, structural ordering can only be established at a microscopic or mesoscopic level and achieving macroscopic ordering with films made from small molecules can also be challenging. Consequently, local ordering can give rise to defect-containing regions, such as grain boundaries and domain walls between ordered domains, which can then act as traps for charge carriers and compensate the local mobility enhancement due to microscopic ordering.

Furthermore, there are several parameters that can influence the morphology and molecular packing of organic semiconductor thin films, leading to opportunities for tuning charge transport properties. Moreover, changes of processing parameters like the rate of deposition, the type of solvent used and even annealing treatment, can lead to a range of field-effect mobilities with different orders of magnitude within the same material system. [104] The principal causes of this phenomenon are the complexity of the crystal growth and the nucleation processes involved in the thin film formation.

Additionally, in solution processing methods such as spin coating or drop casting, crystal formation happens in a multiphase environment, where solvent vapor, the solution's layer and the substrate have interactions. The nucleation and crystal growth are heavily affected by the exchanges between solute, solvent, and substrate, as well as by the presence of phase boundaries, and by mass and heat transport processes. [85] The combination of all these parameters governs the morphology and molecular packing of organic semiconductor thin films, which are critical to achieve high electronic performance in a given molecular system. [105] For instance molecular packing can be tuned by non-synthetic approaches, some studies have even shown that a small displacement between adjacent molecules leads to a significant change in charge carrier mobility. [106] On the other hand, varying the processing conditions can modify the molecular packing due to the multiple crystal structures (polymorphs) that can be formed. Since organic crystals are characterized by weak intermolecular interactions, like π-π stacking, they can adopt several polymorphic forms. [107] In spite of the importance of molecular packing on charge transport properties, controlling polymorphism has not been deeply explored, and most studies have been performed on pentacene polymorphs deposited from the vapor phase. These approaches contain the tuning of film thickness [108] ,the chemistry of the used substrate [109] , and temperature among a plethora of different parameters. [110,111] Another equally important way to achieve high electrical performance is through single crystal devices, where controlling crystal morphology is essential. High performance organic thin film transistors (OTFTs) can be produced from vapor phase or solution, to then form polycrystalline thin films, aligned micro crystals or single crystals. Single-crystalline thin films are preferred for multiple reasons, the first one being the scarcity of grain boundaries, leading to an absence of molecular disorder in single-crystalline domains, which is essential for achieving high electrical performance. [112] The second reason is the reduction of structural defects and chemical impurities, making single crystals suitable for fundamental studies of intrinsic charge carrier mobility. Lastly, the ability to directly pattern OTFTs during film formation ensures a high quality dielectric-semiconductor interface, leading to outstanding device performance. [113] Furthermore, direct patterning also permits high device density over a large area, which is valuable for industrial scale production.

In the same spirit, different techniques to produce aligned single-crystalline ribbons over a large area have been developed, one such example is the droplet-pinned crystallization method (DPC). [114] This approach has allowed well-aligned C60 single-crystal needles and ribbons, along with electron mobility values of 11 cm 2 /(V•s). In this process, the nucleation density is adjusted by changing the concentration in solution as shown in Figure I. 15, with the help of a small piece of silicon wafer, the droplet is pinned, yielding to a steady receding contact line. It has been inferred that the reason why such high device performance is obtained through this method is in part due to the intimate crystal interface with the dielectric during in situ growth of single crystals on the device substrates. However, the main drawback of DPC is its applicability to high-throughput industrial manufacturing, because of the somewhat long processing time. [114] These examples demonstrate the challenges and opportunities in fabricating aligned, patterned, single-crystal arrays; moreover, they have shown that to successfully develop organic semiconductors, controlling the processing techniques is also important, as they have an impact in device morphology. However, as it was previously mentioned another way in which the morphology of organic semiconductor materials can be tuned is through supramolecular assemblies; as π-conjugated materials tend to form aggregates, and sometimes even larger crystallites depending on processing conditions. [START_REF] Köhler | Electronic Processes in Organic Semiconductors: An Introduction[END_REF] In general, the aggregation can be controlled by molecular design, the choice of solvent and thermal treatment steps. In the case of π-conjugated polymers, alignment of the chains leads to ordering on a microscopic or mesoscopic level, creating supramolecular structures. Therefore, it is essential to address the role of supramolecular chemistry in organic electronics.

III.

Supramolecular Chemistry in Organic Electronics III.1) What are supramolecular systems? First, it is important to define what supramolecular chemistry is. In words of one of its founding fathers, Jean-Marie Lehn, it has been described as "the chemistry beyond the molecule", since it comprises the study of molecular assemblies and of intermolecular bonds. [START_REF] Lehn | [END_REF] A supramolecular compound is considered as a group of molecular components endowed with properties from each individual element to the entirety of the assembly, by non-covalent interactions.

For the past three decades, self-organization of molecules using various supramolecular interactions has gained a lot of attention, due to the large number of versatile assemblies that can be obtained with tunable and exceptional properties. [117] Hence, it has become vital to study the various aspects of supramolecular chemistry, since crucial and deciding factors of assembling molecules depend on the incorporation of suitable functional moieties. In this sense, molecules can self-organize in a programmed manner gathering amended properties and the reversibility of functional properties, through monomer-aggregate transitions, has served as inspiration to design new functional assemblies.

Undoubtedly, the control over the self-organization remains a challenging task, although morphologies with defined size and shape can also be tuned. This has led the majority of recent work to focus on the expansion of self-assembling synthetic pathways towards supramolecular materials that often self-assemble using a plethora of cooperatively working interactions, ranging from Van der Waals forces, to electrostatic interaction, to metal coordination, hydrophobicity and even hydrogen bonding (H-bonding). [118] In general, research in modern supramolecular chemistry covers host-guest systems, but also molecular devices and machines, molecular recognition, as well as self-assembly and selforganization. This rapid expansion in supramolecular chemistry has resulted in an enormous diversity of chemical systems, with applications in many fields. Although, in the next sections special emphasis will be given to organic electronics applications.

For instance, supramolecular electronics has been proposed as a promising intermediaryscale approach that rests on the design of electronic components, with sizes between micrometers for plastic electronics and nanometers for molecular electronics. Supramolecular engineering controls the self-assembly processes through thermodynamic processes and non-covalent forces. [117,119] This represents a crucial bottom-up strategy to build and process relatively soft functional ob ects while introducing "pseudo-crystalline" electroactive domains corresponding to this typical intermediate length, therefore a deeper discussion in this field follows.

III.2) Semiconducting polymers and small semiconducting molecules

Semiconducting polymers are a special class of materials that have been designed for an extensive range of electronic applications due to their semiconducting, conducting, electrochemical, and/or optical properties. For instance, polymer solar cells (PSCs) are very attractive as they possess some advantageous features [120] including:

-Thin-film architecture -Low material consumption -Utilization of efficient solution processes -Low manufacturing energy requirements -Low specific weight and mechanical flexibility -Tunable material properties -High transparency All of the above allow the electronic and physical properties of conjugated polymers to be extensively optimized, which in turn has permitted them to find effective application in devices, such as OPVs, OFETs, and OLEDs. [START_REF] Mei | [END_REF][121][122][123] . Moreover, their synthetic flexibility and tunability have allowed them to be applied in other fields, such as electrochromic devices, chemical sensors, organic lasers, and biological applications. [124][125][126][127] Despite that initially the main goal of studying conjugated polymers was the comprehension of fundamental properties such as conductivity, electrochemistry, and photophysical properties, it subsequently evolved through the years into understanding how small changes in the structure can influence the performance for a given application. Therefore, throughout the decades the progression and development of conjugated polymers has gone from simple repeating units, such as polyacetylene, to poly (3-hexylthiophene) (P3HT), and to PM6 (Figure I. 16). [START_REF] Reynolds | Conjugated Polymers: Perspective, Theory, and New Materials[END_REF] Figure I. 16 Evolution of semiconducting polymers throughout the recent decades.*Adapted. [START_REF] Pankow | [END_REF] One of the most important structural developments in the field of conjugated polymers has been the improvement of polymerization conditions to prepare polymers with high structural fidelity, such as regio-regular P3HT and donor-acceptor copolymers (PM6). Furthermore, the ability to tune the electronic and physical properties through the addition heteroatoms along the π-conjugated backbone, the introduction of sidechains for improving solubility or tailoring physical properties have also impacted their development. [START_REF] Pankow | [END_REF] Moreover, their evolution can be tracked since the early 2000's, when an enormous amount of research was performed using P3HT to improve solar cells, with the first P3HT:PC M cells possessing a PCE of 2.8% [130] ,for which by 2010 the average PCE had only slightly increased up to 3% [131] ; all the way to non-fullerene acceptors blended with PM6 which have recently reported PCEs over 18%. [132] Even though OPVs are still not comparable to silicon cells in peak efficiency, since the latter tend to perform better under the low light intensities and elevated temperatures usually experienced in real world conditions, they have the potential for use in utility-scale applications. [START_REF] Krebs | Stability and Degradation of Organic and Polymer Solar Cells: Krebs/Stability and Degradation of Organic and Polymer Solar Cells[END_REF] Additionally, OPVs can be prepared using high-throughput manufacturing processes on flexible substrates, due to the compatibility of organic semiconductors with solution processing, diversifying their applicability, which is something most inorganic solar cells cannot do.

Whereas polymer OPVs receive more attention, solar cells created from solution-processed small molecule donor materials have rapidly grown in the last decade, with systems that have reached PCEs over 10%. [START_REF] Kan | [END_REF]135] Their continued improvement is essential because they offer multiple advantages over polymer donors.

The individuality of small molecules is an advantage that is not present in the case of conjugated polymers, which always consist of mixtures of components with different molecular weights. The preparation of polymers itself is a complicated task, and their purification is even harder, as traditional methods such as chromatography on silica, or distillation are not useful. Hence, controlling the quality of conjugated polymers is difficult and frequently leads to a strong variation between each batch, utterly impacting their physical and electronic properties. In contrast, small molecules can be widely purified and have fully reproducible physical and electronic properties, making the latest research to strongly focus on small molecules.

Small molecules can also evade defects like chain kinks and chain-end defects, which are usually present in polymers and can lead to structural disorder and to low-lying trap states. [136,137] Furthermore, even when compared to polymers that require fewer synthetic steps or that obtain higher PCEs, small molecules can compete with them when a simpler work-up and purification protocol helps them keeping the estimated module cost at similar values. [138] It is important that small molecules at the active layer of organic solar cells are well ordered, allowing for efficient generation of charges and their transport to the electrodes. Controlling the morphology of small molecular solar cells is considered a major holdup, since well-ordered self-assembling small molecular donor/acceptor composites must be designed to obtain high performance in organic solar cells.

Throughout the years, most of the used acceptors were derived from fullerene, normally in the form of [6,6]-phenyl-C61-butyric acid methyl ester (PCBM); however, there has recently been a significant movement towards non-fullerene acceptors (NFAs), particularly those that are built from small molecules. In contrast to typical fullerene acceptors, which have poor absorption of light in the visible spectrum, NFAs are often designed to have high absorbance, which allows generation of excitons at both, the donor and acceptor components of the active layer. In this sense, bilayer and diffusion bilayer devices have been designed and these dyesensitized organic solar cells rely on the supramolecular interactions between the layers of the photon absorbing organic dye, the donors/acceptors, and the substrate.

In the same way as for polymers, small molecule organic semiconductors have constantly been evolving from simple to very complex structures (Figure I. 17). Since the 1960s, anthracene derivatives have been intensively studied as an interesting building block and starting material in OLEDs, [139] due to their unusual photoluminescence and electroluminescence properties, as well as their excellent electrochemical properties and ease of modification. [140] They can be classified into several categories according to the different substituent groups: non-heteroaryl substituted anthracene derivatives; silyl-substituted anthracene derivatives; electron-rich groups substituted anthracene derivatives; electrondeficient groups substituted anthracene derivatives; bipolar anthracene derivatives and large π-conjugation substituted anthracene derivatives. [141] Furthermore, as it was previously discussed in section II, their conjugation can be extended to obtain acene derivatives, which highlights how they have played a key role in the development and applications of OLEDs materials.

Figure I. 17 Evolution of small semiconducting molecules throughout the recent decades.

For instance, tetracene and pentacene are the most widely investigated p-type conjugated materials in OFETs with high carrier mobilities of up to 0.1 and 3 cm 2 /(V•s), respectively. [START_REF] Pope | Electronic Processes in Organic Crystals and Polymers[END_REF][START_REF] Horowitz | [END_REF] Due to their planar -conjugated structure, they have a relatively low band gap of 1.7 eV and these materials were as well investigated as p-type semiconductors in photovoltaics. Additionally, OSCs fabricated using tetracene/C60-heterojunctions as photoactive layer resulted have reported PCEs of 2.3 %. [144] Development of organic semiconductor materials has thrived in the past decades and in 1989, an oligothiophene called α-sexithiophene was implemented as an active semiconductor material in OFETs. [145] Later on, Sakai et al. prepared an OSC device using α-sexithiophene as donor and C60 as an acceptor, which exhibited a PCE close to 0.8 %. [146] The structure eventually evolved to 𝛼,𝜔-bis-(dicyanovinylene)-sexithiophene (DCV6T), shown in (Figure I. 17), and BHJ solar cells were prepared along with C60. [147] The device was prepared on a heated substrate at 90 °C and gave an excellent PCE of 4.9 %. In comparison, devices prepared without substrate heating showed a PCE of only 2.1 %. The increased performance of devices prepared on heated substrates was due to a large increase in short circuit current and fill factor (FF), which was attributed to a change in mixed-layer morphology induced when heating the substrate. Hence, a strong phase separation is facilitated and leads to a better charge transport within the percolation pathways of the mixed layer.

Finally, a liquid crystalline molecule based on benzodithiophene terthiophene rhodanine with two small electronegative chlorine atoms (BTR-Cl) was recently developed (Figure I. 17), [148] and a 14.7% PCE was obtained when using a BTR-Cl:Y6 system. [149] These performance enhancements are mainly attributed to the precise morphology control, which yields to enhanced absorption, improved crystallinity, reduced trap-assistant recombination and suppressed energetic disorder. Despite all this progress in small molecule organic semiconductors, one of the disadvantages they still have is their poor device stability under various operation conditions, such as light soaking and damp heat. This is one of the issues that should be addressed before starting their mass production and industrial applications, while several studies on the stability of small molecule OPVs have recently been conducted, deeper research is required to settle this matter. [150][151][152][153] Another significant problem is the fast drop in solar cell parameters at the beginning of device operation, principally the rapid drop in the open circuit voltage (VOC). [154] It is believed that one of the possible causes of this phenomenon is the trap formation in the photoactive layer during light soaking. [151,155,156] Compared to polymers, small molecules are reorganized more readily, and their local morphology is altered in the presence of external stress, such as heat or light, which can lead to divergence from the optimized BHJ and result in FF and VOC losses. One example of a bulk morphology change is the phase separation of small molecules and fullerenes in small molecule BHJ blends, which would result in the formation of large pure donor and acceptor phase crystallites. [157,158] It has been shown that both types of semiconducting materials have different virtues and limitations, but supramolecular chemistry has the potential to combine the best characteristics of polymers and small molecules. In this sense, the performance of OPVs can be influenced by using supramolecular interactions such as H-bonding and/or π-π stacking and it will now be presented.

III.3) Supramolecular approaches in organic electronics

In general, supramolecular structures are formed by rational design, [159,160] allowing the molecules to interact without any additional treatment. Thanks to such control, it is possible to build semiconducting systems where the electroactive motifs are precisely organized by noncovalent interactions, into functional supramolecular polymers [119] . In this sense, by functionalizing very simple electroactive segments, the optical and self-assembly properties can be tuned while controlling the interplay between non-covalent interactions.

As it has been discussed before, a lot of effort has been made toward the development of conducting organic materials during the past decades. In addition to films of conducting polymers and single molecules, the emergence of supramolecular electronics is a promising field of investigation. [162,163] For instance, Giuseppone and co-workers have reported the synthesis of nanostructures based on triarylamine stacks, along with their addressable selfconstruction between two electrodes, representing a major progress in the control of supramolecular electroactive materials at the 100 nm length scale (Figure I. 18). [164][165][166] Triarylamine-type molecules are very effective functional units that are extensively used as photoconductors and charge carriers, since they display high hole-transport mobility, being possible to incorporate them in OLEDs. [164] Figure I. 18 Light-triggered self-construction of supramolecular organic nanowires as metallic interconnects.*Adapted. [164] In their work, supramolecular triarylamine nanowires were created by simple light irradiation of solution prepared in chloroform, this allowed the production of a catalytic amount of triarylammonium radicals that piled with their neutral counterparts along nucleation-growth and self-replication processes. Additionally, the stimuli-responsive supramolecular scaffolds were reversibly broken up by heating. By using these principles and by applying an electric field directly between the electrodes, the localization and directionality of the elongation of fibers were addressed and exceptional channel conductivity were measured for these selfconstructing devices, exceeding 5 × 10 3 S/m. [167] Another exciting example of supramolecular structures applied to organic electronics are thiophene derivatives, in particular in their oligomer form, finding applications in OFETs. [START_REF] Perepichka | Handbook of Thiophene-Based Materials: Applications in Organic Electronics and Photonics[END_REF] For instance, the group of Barbarella combined a wet lithographic technique with the nonsolvent vapor-induced crystallization of octathiophene derivatives to form aligned fibers with precise control over density and size in OFETs (Figure I. 19). [START_REF] Gentili | [END_REF] These compounds are able to self-assemble into thermodynamically stable supramolecular crystalline fibers when exposed to vapor of a non-solvent.

The procedure consisted of taking an airtight container saturated with non-solvent vapor, an elastomeric stamp, consisting of parallel lines, which was then placed in contact with a solution containing one of the compounds. The film was spread on a SiO2/Si substrate with or without gold electrode. A confinement effect is produced due to the capillary forces that pin the solution under stamp protrusions, while the self-assembly process induced by non-solvent vapor takes place and leads to the formation of a well-oriented array of fibers imposed by the motif of the stamp protrusions. [START_REF] Gentili | [END_REF] The combination of thioalkyl substituents and head-to-head substitution, induced aggregation mainly via S-S non-covalent interactions and a high degree of control of the supramolecular self-assembly was also achieved through the non-covalent interaction of the π-conjugated structure. This is critical for applications in flexible electronic devices of organic chargetransport materials, because their electronic properties depend on both, the chemical structure and the molecular packing/orientation. [170] In particular, fibers can facilitate charge carrier mobility through long-range molecular orientation with respect to device electrodes. [171] Furthermore, this strategy allowed precise control over density, orientation, and size of supramolecular semiconducting fibers in OFETs and proved that well-aligned fibers exhibit a substantial enhancement of electrical performances. Devices made of all aligned fibers showed saturated charge mobilities increased by about three orders of magnitude when compared to randomly distributed fibers and a strong decrease of the threshold voltages. These results show that supramolecular alignment of fibers through confinement effect is an attractive technique in fabrication of OFETs and could be applied for many other known supramolecular fibers.

Examples of supramolecular polymer strategies in organic electronics can also be found, for instance in perylene bisimide incorporating H-bonding motifs that co-polymerize with ditopic building blocks into millimeter-long fibers (Figure I. 20). [172] Remarkably, the stacking of perylene units was not the driving force of the polymerization along the long axis of the fibers, but contributed to the height of the nanostructure.

Figure I. 20 Formation of discrete 1D elongated nanoobjects from a flexible hydrogen bonded supramolecular polymer containing perylene bis-imide chromophores in the main chain.

Adapted. [172] The extremely long perylene bis-imide nanofibers were formed through complexation between complementary triple H-bonding modules. Moreover, the intrinsic 1D electron mobility observed for these nanofibers competed at the time with the highest mobilities of columnar stacks of other fluorescent dyes with high thermal and photo-stability, which were usually employed to explore 1D self-assemblies as photon-and electron-carriers in optoelectronic nanodevices. [173] This structural transition which arises from a molecular rearrangement from rosette to linear type, is associated with a remarkable increase in transient photoconductivity.

They also showed that hydrogen bonded (H-bonded) networks incorporating perylene units can be structurally rearranged from fibrillar assemblies to lamellar structures in the bulk upon heating. [174] This last example showed that hydrogen bonds (H-bonds) can efficiently guide the self-assembly of organic materials, which also enables the tuning of the properties in aggregation processes, hence the next section will review them in more detail.

III.4) H-bonded supramolecular electronic materials

The first question one might ask is: why are H-bonds so special? It turns out that a hydrogen bond is an interaction where a hydrogen atom is attracted to two atoms, rather than just one, acting like a bridge between them and can usually be represented as shown in Figure I. 21, where species X-H is often referred as donor, whereas Y-Z is known as the acceptor. It is often described as an attractive interaction in which an electropositive hydrogen atom mediates between two electronegative species X and Y, bringing them closer together.

The hydrogen bond is strong enough to hold molecules such as XH and YZ together at normal temperatures, and it is also directional enough so that this association is orientationally specific. Nevertheless, and depending on the nature of X and Y, it can also weaken enough to allow these molecules to come apart, permitting loss of orientational specificity in the association of XH and YZ, like a hydrophobic interaction. [175] Figure I. 21 Typical representation of the 4 atomic species involved in H-bonds.

Usually, H-bonds are formed when a hydrogen atom is covalently bonded to a highly electronegative atom such as N, O, Cl or F, hence it presents a partial positive charge and can be strongly attracted by another electronegative atom in another or in the same molecule, respectively forming an intermolecular or an intramolecular hydrogen bond.

In this sense, the hydrogen bond can play a crucial role both in stabilizing static structures and in mediating dynamic processes, giving it its importance as a structure-defining element in supramolecular chemistry and as a major facilitator of biological reactions. [176] Depending on the nature of X, Y, and Z, the energy of a hydrogen bond is between 0.5 to 40 kcal•mol -1 . [175] The strongest H-bonds are as strong as the weakest of covalent bonds, while the weakest Hbonds are practically indistinguishable, and it is this intermediate energy range what makes them able to quickly associate and dissociate at ambient temperatures.

Over the years, the concept of the hydrogen bond has become more relaxed to include weaker and more dispersive interactions, provided that some electrostatic character remains. The hydrogen bond is a complex interaction that has at least four chemical characteristics [177] :

-Electrostatic (acid/base) -Polarization (hard/soft) -Van der Waals (dispersion/repulsion); -Covalency (charge transfer).

H-bonds can determine the molecular conformation, molecular aggregation, and the function of an immense number of chemical systems, having a huge impact on our daily life. Without them, wooden structures would collapse, concrete would crumble, oceans would evaporate, and human beings would disintegrate into random pieces or into inert matter. Furthermore, the surprising properties of water, such as its high boiling point (100 ºC vs -60,7 ºC for H2S), the contraction of solid water upon melting and its maximum density in the solid state at 3.98 ºC, are based on the network formation of H-bonds. [START_REF] Hadzi | Theoretical Treatments of Hydrogen Bonding[END_REF] There are some strongly donating and accepting groups, such as -COOH, -OH, -CONH2 and -CONHR that form the same type of H-bonds when they are included in an organic aggregate or when they behave as ligands in metallic complexes. The energy of the H-bonds with these groups are usually at least one order of magnitude higher than for the rest of non-covalent interactions and in solution, the thermodynamic stability of hydrogen-bonded species strongly depends on the solvent. They are usually more stable and unable to form H-bonds in apolar solvents like alkanes. On the other hand, the stability is lower in solvents with donor or acceptor hydrogen-bonding ability. , enzymatic catalysis and the formation of α and β helixes. [START_REF] Jeffrey | Hydrogen Bonding in Biological Structures[END_REF]

Figure I. 22 Molecular recognition between purine and pyrimidine creating the bases of DNA through the selective formation of H-bonds

Since H-bonding interactions are so prevalent in nature, it is not surprising that H-bonds can also be exploited as a molecular design tool for obtaining organic semiconducting and conducing materials. For instance, H-bonding is crucial for supramolecular interactions that permit the creation of numerous photoactive donor/acceptor assemblies. [START_REF] Chu | [END_REF] An example of these type of materials can be found in a fullerene derivative attached to a barbituric acid framework (FBA in Figure I. 23), which has been applied as a building block for the development of a variety of H-bonded supramolecular ensembles. [181,182] Additionally, a similar photophysical study was performed in another H-bonded fullereneoligophenylenevinylene system, providing comparable results. [183] The self-assembling of FBA with the complementary oligothiophene donor (Figure I. 23) permitted the fabrication of photoelectrochemical devices that provided clear photocurrent response under white light irradiation.

An interesting approach to design light-harvesting electron donor materials for organic solar cells was presented by Cheng et al. [184] , it consisted on a conjugated thiophene-fluorene copolymer that was tweaked with chelating terpyridyl units (PTPy), which are known for their strong affinity for complex formation. This work resulted in organic solar cells which exhibited PCE of 0.12% and EQE of 12%. Hence, a similar approach was explored by Liang et al. who applied H-bonding to construct supramolecular donor supramolecular polymers as it can be seen in Figure I. 23. [185] DNA Figure I. 23 The formation of a hydrogen-bonded supramolecular system based on the fullerene derivative FBA and oligothiophene derivative. [186] Figure I. 24 a) The formation of supramolecular electron donor polymer via hydrogenbonding complexation of nonconjugated polymer with small molecular organic dye and b) molecular structures of the best performing polymer (P-HA) and dye (D-HD) combination.*Reproduced. [186] For instance, a PMMA-based polymer was modified with an electron donor block bearing pyridyl end groups, producing a hydrogen-bonding acceptor polymer (P-HA). The pyridyl unit of P-HA can form H-bonds with the carboxyl group of a small molecular hydrogen-donor dye (D-HD). Consequentially, the supramolecular polymer yielded PCE of 0.5% in BHJSCs with PCBM, an impressive considering the relatively simple molecular structures of the applied materials.

Other examples of H-bonded systems with photovoltaic applications have been reported in literature and small molecules symmetrically modified with amides or ester groups in the periphery. [188,189] In both cases, chloroform was used as the solvent to blend donor and acceptor materials, which from a supramolecular point of view is not the best choice since it is commonly used as a "good solvent" to avoid aggregation. Furthermore, in these two works the solar cell efficiency was lower for all the blends where the H-bonding derivatives were involved.

On Detrimental Beneficial contradictory results were found. For instance, in the case depicted in Figure I. 25C, the authors found out that the molecule without the ability to form H-bonds needed double the concentration to achieve similar efficiency as the hydrogen-bonded donor, the main drawback being its low short circuit current. [190] When the donor molecules were well interconnected thanks to H-bonding, the current was much higher, which also increased the FF. Furthermore, in the example shown in Figure I. 25D, higher efficiency was found for the amidecontaining a diketopyrrolopyrrole (DPP) donor molecule, even in the most optimized conditions for both donor molecules. [191] In this case, several solvents were tested and it was found out that the best solvent was chlorobenzene for solubility issues.

As it has just been discussed, the results with H-bonded materials do not seem to agree on its positive or negative role on solar cell devices. Nevertheless, it is important to remark that it is not possible to compare all the parameters previously shown. The type of π-conjugated segment, type of hydrogen-bonding unit, solvent utilized and the donor/acceptor ratio among other parameters are different in all the cases, making very difficult to make a fair comparison. Furthermore, the lack of self-assembly studies in most of the cases, neglects the information regarding the type of structures formed by the H-bonded systems, which is something crucial to understand the device performance.

Since the aim of this PhD is to elucidate the impact of H-bonds in the optoelectronic properties of organic semiconductors, systematic and comparative studies have been done using DPP as a model system. In addition, this systematic study aims to help screening the required conditions needed to fabricate efficient electronic devices.

DPPs are extensively studied molecules and are among the best electroactive segments used in semiconductors, [192,193] since their discovery by Farnum [194] in the 70's while trying to synthesize azetinone, DPP has been one of the most used pigments in industrial applications and in the search of new materials. Multiple examples of polymers and small molecules can be found for the fabrication of organic solar cells, [195] OFETs, [196,197] and sensors. [198,199] While H-bonding is the principal and strongest stabilizing interaction within these assemblies, their structures vary dramatically depending on the nature of the pendant heteroaromatic substituents. [200] It was proven that co-assembly can be achieved through H-bonding of the DPP lactam group with a carboxylic acid, which persists in both single crystals and interfacial layers. This work suggests that there is an unexpected tendency of DPP derivatives to assemble on graphite in a twisted conformation, providing stronger intermolecular interactions and higher molecular density. Therefore, these materials have proven to be interesting and will be discussed in more detail.

IV.

The Diketopyrrolopyrrole pigment IV.1) History and synthesis DPP derivatives were first reported in 1974 as one of the products of a modified Reformatsky reaction that aimed and failed to produce azetinone derivatives as shown in Scheme I. 1. [194] Farnum et al. attempted to optimize the reaction conditions to increase the yield of phenylfunctionalized DPP (DPP-Ph, Scheme I. 1), while additionally looking for an elucidation of its formation. Nonetheless, the yield never exceeded 20%, stopping their work on the subject and publishing the results as "the discovery of a pigment chromophore." [194] Scheme I. 1 First and accidental synthesis of DPP-Ph.

The chemical structure of a 2,5-Dihydropyrrolo[4,3-c] pyrrolo-1,4-dione molecule is shown in Figure I. 26 and up to now, this structure has not been reported to be synthesized. The most commonly known DPP derivatives generally have aromatic substituents at the -3 and -6 positions, although compounds with aliphatic groups are also known. [201,202] Their physical properties such as their high melting point (>350 °C), high insolubility and prominent red color would have been most probably forgotten, if it had not appealed the attention of researchers from Ciba-Geigy AG (currently part of BASF), who came across a compilation of interesting reactions published by Ranganathan in 1980.

Afterwards, the chemistry along with the applications were developed, and in 1986 the first DPP pigment was introduced to the market. [START_REF] Rochat | Preparation of Pyrrolo[END_REF][START_REF] Cassar | Diketopyrrolo[END_REF] Since then, several other DPP pigments have been presented to the market for conventional pigment applications such as fibers, inks, paints and plastics. [START_REF]High Performance Pigments[END_REF] The interest in their high tech applications has grown increasingly in recent years, as DPP derivatives exhibit remarkable resistance against chemical, heat, light and climate stimuli, resulting in more than 9000 patents in different areas. [206] Figure I. 26 Chemical structure of the DPP core with its corresponding atom numeration, hydrogen-bonding groups, and main functionalization positions.

While used in many fields, the majority of DPP articles comprehend the use of DPP derivatives in semiconductor electronic devices, such as solar cells, [195,[START_REF] Tang | [END_REF] OFETs [197,208] and OLEDs. [123,[209][210][211] IV.2) Reactivity of DPPs DPP derivatives contain several reactive groups within their structure susceptible to electrophilic attack, such as oxygen and nitrogen atoms in the amide group, in addition to the double bonds in the DPP core and the aryl groups at the -3 and -6 positions. Conversely, the carbonyl carbon atom or the α, β -unsaturated system within the bicyclic DPP unit are prone to nucleophilic attack through Michael addition. Furthermore, reactions with nucleophiles can also be performed in the aromatic substituents. In this section, the main chemical reactions that DPP derivatives can undergo will be summarized. For a deeper and extended comprehension, the reader is once again referred to the work of Grzybowski et al. [212] a The O-alkylation is favored in neutral conditions and at low temperature, since the product is kinetically more stable, whereas the N-alkylation is predominantly observed at high temperatures. Thermal rearrangement is also possible when the reaction is performed over long reaction times with excess of alkylation reagents at high temperatures, yielding both alkylated derivatives. [START_REF] Pop | [END_REF] On the other hand, DPPs are deprotonated to give anions under basic conditions, distributing the charges amid the two heteroatoms and promoting the alkylation at either or both N-and O-atoms. [215,216] The most common solvents for alkylation are N,N-dimethylformamide (DMF) [217,218] and N-methylpyrrolidone (NMP), [219] even though the use of acetonitrile, a greener solvent, has been recently reported, [START_REF] Pop | [END_REF] being possible to run the reaction at room temperature and with shorter reaction times.

b) Reactions of the aromatic substituents at the -3 and -6 positions of DPP Most DPP derivatives possess aromatic substituents at the -3 and -6 position. Therefore, they may experience the typical reactions of aromatic compounds, especially electrophilic aromatic substitution. [START_REF] Rochat | Preparation of Pyrrolo[END_REF][START_REF] Cassar | Diketopyrrolo[END_REF][START_REF]High Performance Pigments[END_REF] The sulfonation of DPPs is widely used to produce salts used as thermal stabilizer surfactants, improving the rheological properties of DPP paint formulations. [START_REF] Rochat | Preparation of Pyrrolo[END_REF][START_REF] Cassar | Diketopyrrolo[END_REF][START_REF]High Performance Pigments[END_REF][START_REF] Jost | Pigment Compositions[END_REF] One of the main reactions performed is the halogenation of heteroaromatic substituents in DPPs, such as thiophene, furan, and selenophene. [START_REF] Woo | [END_REF][222][223] Bromination can be performed by exposing DPPs derivatives to gaseous bromine, but is most frequently done by using Nbromosuccinimide (NBS), as illustrated on Scheme I. 2.

Scheme I. 2 Bromination of heteroaromatic substituents in DPPs.

DPPs can also be copolymerized to generate biaryl compounds with electron-rich aromatic compounds, due to the electron-accepting character of the DPP unit. Suzuki and Stille couplings are effective procedures for the synthesis of biaryl derivatives [224,225] The produced copolymers are of the donor-acceptor (D/A) type, having high charge mobility and low-energy bandgap; allowing the material to be applied in semiconducting devices. [209,211,226,227] Finally, thiophene DPP derivatives can experience reactions with lithium diisopropylAmide (LDA) at the -5 positions of thienyl groups, which can be used to introduce new substituents that can lead to further reactions. [228,229] A common example of such substitution is shown in Scheme I. 3, where the formylation leads to dialdehyde DPP derivatives when the reaction is performed with DMF.

Scheme I. 3 Formylation of thiophene-DPP derivatives.

IV. Besides, the NH•••O H-bonds connect the DPP molecules to achieve stability similar to those of polymers. The linear chains are parallel to each other and to the plane, while brick wallpattern π-π stacking is found perpendicular to the plane (Figure I. 28). [230][231][232] This same structural behavior is seen in other H-bonded pigments, such as indigo, [233,234] perylene bisimides, [235] quinacridone [236,237] or epindolidione, [236] yet the H-bonding distances were found to be shorter in DPP. [238] Even though many authors have claimed that amine and carbonyl groups should be avoided in the molecular structures of semiconductors due to a possible disruption of the conjugation, [239] it has been demonstrated that maximizing the charge transfer integrals through neighboring molecules can enhance the mobility. [238] In this sense, crystal engineering through H-bonding has been one of the main strategies applied in device fabrication.

Early investigations by Mizuguchi [240][241][242][243][244][245][246][247] at the end of the 80's and early 90's show the crystal and electronic structures of several small H-bonded DPP molecules, starting from 1,4-diketo-3,6-diphenyl-pyrrolo-[4,4-c]-pyrrole [240][241][242] and extending it to the dithioketo, [248] pyridinecontaining [249,250] and halogenated analogues. [243] The conclusions of these studies showed that the intermolecular NH···O H-bonds result in a bathochromic shift in the absorption maxima upon crystallization with respect to solutions (Figure I. 29), and that the spectral shape in solid state differs substantially from the one in solution mainly depending on the extent of the molecular overlap along the stacking axis. When the molecular overlap is insignificant, the solid state and solution absorption spectra are quite similar and when the molecular overlap increases along the stacking axis, the absorption maximum shows a hypsochromic shift, making the color more yellow. [230] The authors concluded that the "head-to-tail" arrangement caused by H-bonding is found to displace the absorption maximum towards longer wavelengths, while the stack pair or parallel arrangement significantly contributes to the hypsochromic shift. [230] In this work, the exciton coupling model based on the interaction between transition dipoles was used to qualitatively interpret the correlation between the crystal and electronic structures in DPP derivatives. This way, it could be understood why the famous "Ferrari red" pigment (p-ClDPP) shows bright red color mainly due to the formation of the "head-to-tail" arrangement thanks to H-bonding vs the yellowish color in m-substituted derivatives, where the stack pair contribution (hypsochromic shift) overpowers the H-bonding. These initial findings led to the study of different applications, such as H2 gas sensors, [250] information storage [244] and the study of photoconductivity. [246] Still until very recently the supramolecular ordering of H-bonded DPP pigments have continued to be studied. Perepichka et al, [200] used scanning tunneling microscopy (STM) combined with X-ray crystallographic analysis to demonstrate how the interactions of heteroatoms in the aromatic substituents of the DPP core interplay with hydrogen-bonding and the final influence on charge transport properties. The authors studied the supramolecular order of H-bonded difuran, dithiophene and diphenyl DPP derivatives in monolayers at the solid-liquid interface and in bulk crystalline solids. This study demonstrated that even though H-bonding is the main and strongest interaction in the supramolecular assemblies of the DPP derivatives described, their structures change radically depending on the nature of the aromatic substituents (furan, phenyl or thiophene). The diphenyl derivative was found to form exclusively H-bonded homoassemblies; the difuran DPP preferentially co-assembles with alkanoic acids (used to create the solid-liquid interface), and the dithiophene substituted DPP either co-assembles with alkanoic acids or self-assembles in one of two H-bonded polymorphs depending on the conditions.

Remarkably, one of these two polymorphs shows an out-of-place (in graphite) twist of the thiophene rings that provides for stronger intermolecular interactions and higher molecular density. This was the first case reported of a planar molecule reorganizing into a less favorable twisted geometry and it could help for example in OFET applications, where the interfacial layer plays a crucial role in the device properties. b) Vacuum deposited thin films and the use of the latent pigment strategy

In 1997, Iqbal et al [251] showed a method to achieve soluble DPP derivatives by introducing tert-butoxycarbonyl (t-Boc) protecting groups, synthesizing the so-called "latent pigments" that render the final dye after thermal cleavage of the t-Boc groups, which decomposes into isobutene and CO2 at approximately 180 ºC (Figure I. 30).

Later on, this technique has been widely used for the fabrication of thin films cast from solution, which is an easier and cheaper method than vacuum deposition techniques, even though several parameters such as removal rate, the nucleation and growth mechanism of the thermally converted derivatives and the role of the volatilized molecules needed to be explored. Several studies have been reported on the influence of the solubilizing group removal on the morphology and properties of H-bonded DPPs.

Figure I. 30 a) Schematic illustration of the H-bonding network of DPP. b) Insoluble

parent DPP pigment and soluble latent pigment.*Adapted. [251] For instance, Salammal et al [252] studied the role of the solubilizing group removal rate on the grain size and crystallinity of DPP-4T (Figure I. 31). The authors studied the use of different heating rates ranging from 0.1 to 50 ºC/min until reaching 225 ºC, and the isothermal decarboxylation of the DPP-4T precursor at different temperatures. In this case, it was found that the crystallite size increased from 344 to 976 nm when the precursor film was heated up to 225 ºC increasing the heating rate from 0.1 to 50 ºC/min, while improving the crystallinity as well. This result could be explained due the formation of H-bonding between decarboxylated molecules during the removal process. If the heating rate is too low, the t-Boc groups not cleaved can hinder the formation of H-bonds (N-H···O) with neighboring molecules, decreasing the crystallite size and crystallinity due to the disruption in growth in one dimension and trapping of t-Boc in the network. On the other hand, when the heating rate or the isothermal deprotection temperature increase, the volatilized isobutene and CO2 can scape easily from the network, and the growth of crystallites is facilitated by the simultaneous decarboxylation of both t-Boc groups that results in the formation of H-bonds.

Figure I. 31 Schematic representation of the impact of the heating rate on morphology

and final grain size.*Reproduced. [252] One of the first examples of electronic devices using thermal removal of solubilizing groups was reported by Sakai et al in 2008. [237] This work reports the use of phenyl substituted DPP using the t-Boc-protected latent pigment that is soluble in common organic solvents. OFETs were fabricated by spin coating the latent pigment and by thermally annealing at 180 ºC-200 ºC for 15 minutes, to yield the deprotected DPP able to form H-bonds. Mobility values in the order of 10 -6 . cm 2 /(V•s) were obtained, which were similar (10 -5 cm 2 /(V•s)) to the ones obtained by vacuum depositing the same type of material. The authors reported a difference in morphology when films were spin coated from solution and then the H-bonds were thermally regenerated, and when the H-bonded pigments were vacuum deposited. In the first case, the films studied by scanning electron microscopy (SEM) showed a rough and uneven surface with needle-like structures vs a very smooth surface when the DPP derivatives were vacuum deposited.

The authors demonstrated the simplicity of the preparation method but later, Yamashita et al [253] reported that the mobility values in the work of Sakai could be due to the production of CO2 and isobutene released during the thermal annealing process, which negatively impacted the morphology of the spin coated film. The work of Yamashita shows larger DPP derivatives (Figure I. 32a) for the fabrication of OFETs using the same strategy. In this case, OFETs that showed ambipolar charge-carrier transfer with field effect mobility values of μh of 6.7 x 10 -3 cm 2 /(V•s) and μe of 5. In both cases, a shoulder band at lower energy appears, that dramatically increases after thermal treatment and that is related to the formation of H-bonds. The authors use infrared (IR) measurements to confirm the appearance of H-bonds on the thermally treated films, being this technique fundamental in these types of studies. OFET devices were fabricated and field-effect mobility values were measured in devices made with the latent pigments and with Hbonded films. In the first case, hole mobility values in the order of 10 -6 and 10 -5 cm 2 /(V•s) were found (similar to the studies of Sakai years before) and that were enhanced by two orders of magnitude after thermal cleavage of the t-Boc groups. Interestingly, derivative NH BTTDPP2 containing two DPP moieties in the structure, exhibited well-balanced hole and electron mobilities in the order of 10 -3 cm 2 /(V•s). .*Reproduced. [253] Previously, a H-bonded DPP system containing electron withdrawing -CF3 groups in paraposition used as n-channel semiconductors with electron mobility values of 2.9 x 10 -2 cm 2 /(V•s) were reported by this group. [254] In this case, the devices were fabricated by vacuum deposition directly from the H-bonded pigment, while the latter study was the first one finding ambipolar behavior using hydrogen-bonded DPP molecules and processing the devices from solution.

Other reports using vacuum deposition techniques of H-bonded DPPs present archetypical derivatives (Figure I. 33a) containing in this case halogen (-Cl and -Br) substituents in thepara position of the phenyl rings that decorate the DPP core. [238] In this work, the results are complemented with DFT calculations to better understand the charge transport studies. The authors used anodically-grown AlOx passivated with tetratetracontane (C44H90) as a composite low surface-energy dielectric to fabricate OFET devices because they found out in previous works on indigo dyes that low surface-energy dielectrics were crucial to enhance high mobility in H-bonded small molecule devices. [255] The final mobility values were enhanced several a)

c) b)

orders of magnitude with respect to the initial report by Sakai et al, [237] who used phenylsubstituted DPP as well. [238] To demonstrate the strength of this strategy, more sophisticated oligomers have been reported recently, as for example the work of Zhu et al., [256] where two DPP oligomers with different number of phenyl and thiophene rings were attached to the central DPP core, which was functionalized with thermo labile groups were based on 2-methylhexyl-2-oxylcarbonyl. In this case, field effect behavior was only found for the derivative containing thiophene rings (HTBT), including its latent pigment. Other examples as the work of Mula et al. [257] showing thiophenecapped DPP coupled to triazatruxene (TAT) derivatives (Figure I. 34) with μh of 4.2 x 10 -4 cm 2 /(V•s). Interestingly, the charge transport properties were unaffected when blends of NH-TATDPP and phenyl [6,6]-Phenyl C71 butyric acid methyl ester (PC71BM) were studied, emphasizing the robustness of the morphology when NH-TATDPP was used as donor material.

The use of thermo-cleavable side chains has been applied in semiconductors containing longer solubilizing chains, especially when using polymers. Sun et al [258] reported a DPPbased polymer containing 2-octyldodecanoyl side chains that can be thermally removed at 200 °C to generate a side chain-free conjugated polymer. X-ray diffraction (XRD) measurements and atomic force microscopy (AFM) images show the thin film progress upon thermal decomposition of the side chains. The as-spun films showed a diffraction peak at 2θ a) b) c) of 4.40°, which corresponds to a d-spacing of 20.1 Å and that was attributed to the interlamellar distance. Upon raising the temperature, the primary peak of the thin film became more intense as a result of the improved molecular ordering by thermal annealing. When reaching 200 °C for 3 hours, the main diffraction peak disappeared as a result of the total elimination of the side chains, which resulted in the shortening of the interlayer distance.

AFM images showed that at 150 °C the films were quite smooth, while at 200 °C for 3 hours, the nanograins initially formed evolved into connected nanofibers with higher roughness and large gaps between domains. When the charge transport properties were studied, the hole mobility values when annealing at 150 °C (μh = 0.096 cm 2 /(V•s)) were one order of magnitude lower than the mobility of the polymer with solubilizing alkyl chains previously reported. [259] Still at 200 °C, the mobility values (μh = 0.078 cm 2 /(V•s)) were lower than at 150 °C. The authors concluded that the amorphous nature of the decarboxylated polymer needs to be taken into account, being in this case an efficient material for charge transport.

Figure I. 34 Synthesis of compound NH-TATDPP.*Reproduced. [257] Other DPP polymers with thermo-cleavable groups can be found in literature. Lee et al [260] for example, reported inversion of the dominant polarity in H-bonded DPP derivatives upon thermal treatment using low bandgap polymers (Boc-PTDPP, Figure I. 35a) in this case. In this work, OFET devices were fabricated applying a solution-sheared deposition technique, where a volume of the H-bonded DPP was placed between two preheated silicon wafers that move relative to each other at a specific rate (Figure I. 35b). This way, the semiconductor molecules can form highly crystalline and elongated grains along the shearing direction. The authors compared drop cast and solution-sheared films using IR spectroscopy before and after thermal annealing. The C=O stretching signal disappears after thermal treatment with a concomitant appearance of the N-H band as a consequence of the carbamate deprotection.

As an indication of the formation of H-bonds, the ᶹC=O (amide) shifted to lower energies. Remarkably, the solution-sheared films showed further shift of the ᶹC=O (amide) compared to the drop cast films, probably due to stronger H-bonding in the solid state in these types of films.

The ambipolar Boc-PTDPP was integrated into transistors and showed p-channel dominant characteristics, resulting in μh and μe of 1.32 x 10 -2 cm 2 /(V•s) and 2.3 x 10 -3 cm 2 /(V•s), respectively. These values are one order of magnitude higher than the values found in devices made by drop-casting the polymer. After decarboxylation at 200 ºC the dominant polarity of charge carriers changed from positive to negative in devices fabricated by solution-shearing, reaching μe of 4.6 x 10 -2 cm 2 /(V•s) and decreasing μh in one order of magnitude. DFT studies suggest that the LUMO orbitals of the deprotected polymer become much more delocalized than the protected polymer, which is favorable for n-channel conduction. Furthermore, the downshift of the HOMO-LUMO levels after thermal treatment could decrease the injection barrier for holes. The authors also suggest that the removal of t-Boc groups could act as electron traps and facilitate electron transport. [260] Even though most of the examples report the fabrication of OFET devices, some reports can be found on the fabrication of BHJSCs. Brovelli et al. [261] used this strategy to optimize the charge separation efficiency at the donor/acceptor interface in an attempt to form interpenetrated phase separated percolation pathways. Proof-of-principle devices consisting of 100 nm blends of t-Boc protected DPP-Ph and PCBM were fabricated and the performance was followed at different thermal treatment times. While the VOC showed no dependence on increasing the thermal treatment time from 0 to 300 s, the short circuit current showed a 30fold increase (reaching its maximum at 270 s of treatment time), resulting in a 20-fold enhancement of efficiency with respect to the pristine device.

The morphology of the devices was followed by AFM and XRD during the thermal treatment and it was observed that the films changed from being uniform with roughness below 1 nm at the initial state, to an increase in crystallinity and formation of 10-20 nm three-dimensional crystalline domains at 270 s of thermal treatment. The blends were stored in air under ambient illumination for up to 6 months, finding the same morphological features and emphasizing the strength of this strategy to stabilize the nanoarchitecture of the blend. Control experiments were carried out using a DPP containing alkyl tails (ethylhexyl) and interestingly, the efficiency values were lower emphasizing the effect of the hydrogen-bonding strategy.

c) Mono-alkylated DPPs

Even though the DPP with unsubstituted amides lack solubility and should be processed via vacuum deposition or by the latent pigment technology, the mono-alkylated DPP derivatives show very interesting properties while combining solubility and ability to form H-bonds. Patil et al, [262] reported mono-hexyl phenyl and mono-hexyl thiophene DPP derivatives (PDPP-MH and TDPP-MH, Figure I. 36a) and studied their properties by single crystal X-ray analysis and correlated the results to the charge transport properties in both, mono and di-alkylated analogues. The authors found that while the di-alkylated analogues show herringbone packing arrangements, the mono-alkylated derivatives crystallize in a co-facial layered structure thanks to the formation of intermolecular H-bonding between the free amide groups. Charge carrier mobility values (p-type) two orders of magnitude higher were found for the monoalkylated derivatives compared to the di-alkylated analogues. The authors explain that according to the crystal structures and theoretical calculations, charge transport occurs in two or three directions while it happens in only one direction for the di-alkylated derivatives.

Figure I. 36 a) Co-facial packing via H-bonding in PDPP-MH and TDPP-MH. b) Molecular packing of two of the studied mono-alkylated DPP derivatives, one showing anisotropy of the p-stacking along the a axis (top) and another one showing co-facial herringbone arrangement (bottom).

Pop and Amabilino showed similar results extending their study to a larger variety of di-and mono-alkylated thiophene-capped DPPs. [263] In this case, the authors found out herringbone structures in some of the mono-alkylated DPP derivatives. Particularly, the authors observed that the mono-substituted DPPs with hexyl and ethyl acetate substituents were less distorted

PDPP-MH TDPP-MH a) b)

than the other derivatives of the series, causing stronger intermolecular H-bonding that increases the molecular overlap and planarity of the DPP cores (Figure I. 36b). More specifically, the mono-substituted DPP with ethyl acetate showed high potential for optimizing the charge transport properties in be applied in organic electronic devices.

Other examples of mono-alkylated DPP derivatives have been reported in literature but most of them have been applied as anion sensors thanks to the binding of anions by H-bonding with the free amide in one of the lactam rings. [264][265][266] IV.3.2) DPPs with H-bonding groups in different positions: polymers and small molecules Even though the DPP molecule is considered an H-bonded pigment as shown in the previous section, it can only be processed by vacuum deposition or using the latent pigment technology after applying thermal or acid treatment. Due to the possibility of functionalization of the DPP core, it is possible to introduce different types of H-bonding motifs in soluble derivatives, making possible to study the aggregation in solution as well as device fabrication.

a) Amide-functionalized DPP systems One common strategy for introducing H-bonds into the molecular structure of DPP derivatives is attaching amide groups at the periphery of the aromatic rings attached to the central DPP core. This strategy is usually based on introducing an aldehyde group that can react subsequently with electron-deficient acetamides via Knoevenagel condensation. In this sense, most of the examples found in literature are based on linear molecules, even though some cases of hairpin-shaped DPP derivatives are also reported. An example of the latter approach was reported by Stupp et al, [267] where a hydrogen-bonded small molecule containing trans-1,2-diamidocyclohexane and two DPP conjugated arms (Figure I. 37), were fabricated with the hairpin derivative DPPHP as the donor material, and PC71BM as the acceptor, finding that a stepwise self-assembly process was needed to achieve functional devices (Figure I. 37). When both components were mixed in solution in an attempt to simultaneously assemble them into organized structures, non-working devices were found (Figure I. 37, top).

On the other hand, a slow cooling process starting from the molecularly dissolved state of the hairpin-shaped derivative (Figure I. 37, bottom), yielded robust supramolecular wires that were not disrupted when PC71BM was added, resulting in well-defined heterostructures with improved efficiency. The self-assembly processes were followed by cryogenic transmission electron microscopy (cryo-TEM) and AFM, observing the presence of nanofibers in solution that were still present after the addition of PC71BM and visible on the solar cell active layer (

b). AFM image of the active layer of a device fabricated by the stepwise self-assembly pathway c

).*Reproduced. [188] Despite the proof-of-concept strategy used by Stupp et al., [191] the solar cell efficiency obtained was too low. Therefore, the same group proposed the use of linear H-bonded DPPs (A-Amide) containing terminal amide groups (Figure I. 38) for the fabrication of BHJSCs. In this case, symmetric and asymmetric H-bonded DPP derivatives were studied, finding that the asymmetric derivatives showed improved solubility and more efficient devices.

The authors synthesized control molecules containing ester functional groups instead of amides (A-Ester). Both, A-Amide and A-Ester, showed very similar optoelectronic properties but different morphologies on thin film. While A-Ester active layers revealed greater crystallinity and π-π stacking analyzed by grazing incidence X-ray diffraction (GIXD), the active layers of devices made with A-Amide presented short fiber-like supramolecular aggregates with much smaller domain sizes and less ordered than the A-Ester active layers.

Interestingly, the devices fabricated in blends with PC71BM show PCE 50% higher for A-Amide than for A-Ester. All the results point out that the H-bonds compete with long-range π-π stacking interactions, resulting in interconnected and nanoscale smaller donor domains vs highly crystalline larger domains obtained with A-Ester. Such morphology seems to nearly double the device efficiency when the H-bonded donors are present. The authors showed that with a good compromise between solubility and the formation of the appropriate nanostructures, this general strategy could be used to optimize function. Remarkably, there were simultaneous studies reported by other groups where H-bonded semiconductors different to DPP were functionalized with terminal amides. In this case, the presence of Hbonding resulted to be detrimental for device performance. [268] However, only one solvent was used to prepare the devices and it is possible that poor solubility played an important role in that case.

The terminal amide strategy has been reported by other groups, finding very interesting results and applications. For example, Ghosh et al. [269] reported a DPP-based small molecule (DPP-Amide) with terminal amide groups that formed a black colored gel in toluene (Figure I. 39a and b). In this case, the derivative reported was symmetric, containing dodecyl branches as solubilizing alkyl tails, vs butyloctyl alkyl tails in the previous example. Figure I. 39c shows the absorption spectra of DPP-Amide in monomeric state using chloroform as a good solvent and in aggregated state in toluene. It can be observed that the spectrum in aggregated state is very different from the spectrum in the molecularly dissolved state, appearing typical bands corresponding to the formation of H-and J-aggregates, a behavior previously observed in other DPP [270,271] and H-bonded systems. [272]

Figure I. 38 Structures of A-Amide and A-Ester and schematic illustration of active layer morphology for A-Amide (a) and A-Ester devices (b)

.*Adapted. [191] Figure I. 39 a) Molecular structure of DPP-Amide. b) Photograph of a dilute solution of DPP-Amide in chloroform and the gel formed in toluene (inverted vial). c) UV-Vis spectra of DPP-Amide in monomeric state and aggregated state.*Adapted. [269] DPP-Amide was successfully employed to fabricate a composite material together with polydimethylsiloxane (PDMS). A small amount of the self-assembled fibers formed by DPP-Amide were incorporated into the PDMS matrix, obtaining a self-standing filter. Thanks to its absorption properties, covering the visible region and being transparent in the near IR region could be employed in anti-counterfeiting, infrared photography and forensic applications.

Furthermore, DPP-Amide was employed to fabricate a hybrid system with PC71BM, resulting in the formation of a hybrid gel under certain conditions (Figure I. 40). [273] In this case, a selfsorted p-n heterojunctions with broad absorption and low band, which was not possible with other hybrid systems especially the ones based on perylene bisimides. [274] The importance of the self-assembled state by H-bonding was observed by measuring emission quenching upon the addition of PC71BM. While the addition of PC71BM to solutions of DPP-Amide or DPP-Ester in their molecularly dissolved state (chloroform) no emission quenching was observed, indicating the absence of electron transfer processes, finding the same effect in toluene solutions of DPP-Ester. In contrast, when different ratios of PC71BM were added to toluene solutions of DPP-Amide (aggregated conditions), attenuation in the emission signal of DPP-Amide was observed with increasing weight ratio of PC71BM (

ratio) hybrid assembly (red, dashdot). b) Emission spectra of DPP-Amide in toluene (λex=680 nm) with different blend ratio of PC71BM. c) The plot showing increase in photoconductivity of DPP-Amide and DPP-Ester upon addition of PC71BM (1 : 1 wt. ratio)

.*Adapted. [273] c) b) a)

Figure I. 41 Structures of the three diphenyl-DPP derivatives used to modulate charger carrier polarity.*Adapted. [275] More recently, the terminal functionalization of DPP semiconductors has been used to modulate charge carrier polarity. Ghosh et al., [275] reported three DPP derivatives with the same π-conjugated backbone symmetrically functionalized with amide, ester and cyano groups (Figure I. 41). The authors used FP-TRMC as well to confirm that the n-type charge carrier mobility increased with higher acceptor strength and OFET devices were fabricated to confirm the change of polarity from p-to n-type. [275] The photoconductivity of the three derivatives on thin film was measured either in their pristine state or by mixing them with PC71BM to analyze the p-type charge mobility. When the amidefunctionalized derivative was spin-coated from toluene solutions, an enhancement in photoconductivity was observed in comparison to the chloroform films. This was a clear indication of the importance of the H-bonding formation. Interestingly, in blends with PC71BM (Figure I. 42b) the amide-functionalized derivative showed enhanced photoconductivity related to the pristine film. On the other hand, the blends made with the ester-functionalized DPP exhibited much lower photoconductivity enhancement with respect to the pristine film and a decrease in photoconductivity in blends made with the dicyano derivative.

These results indicate a transition from p-type character of the amide derivative to n-type character in the cyano derivative. Inversely, the three derivatives were blended with P3HT (Figure I. 42a to c) to evaluate the n-type character, finding in this case the opposite trend. However, the solvent used in this case was chlorobenzene instead of chloroform, which could yield different supramolecular structures with different electronic properties, especially in the case of the H-bonded derivative. The mobility values were calculated by fabricating FET devices, finding μh of 1.3 x 10 -2 cm 2 /(V•s) for the amide derivative, while μe of 1.5 x 10 -2 cm 2 /(V•s) for the ester derivative and of 1 x 10 -2 cm 2 /(V•s) for the dicyano DPP. With these results the authors offered an alternative strategy to modulate charge transport properties.

b) Complementary H-bonding groups incorporated in DPPs

Complementary H-bonding between two conjugated species to form hetero-aggregates is a great strategy to achieve hierarchical structures, being p-n heterojunctions in the case of semiconductors. In this sense, H-bonding motifs able to form multiple and complementary bonds with other conjugated systems have been incorporated into DPP derivatives. Braunschweig et al., [276,277] studied systems composed of DPP donors with chiral and achiral side chains. These systems can form triple H-bonds with PDI acceptors and assemble into superstructures (Figure I. 43a to c). They discovered that by heating solutions containing both type of molecules, achiral PDIs bind to disordered DPP stacks upon cooling, this then leads to the development of chiral superstructures.

Additionally, a model was developed to elucidate the structural cues that induce the transition from a disordered aggregate into a chiral helix. The major breakthrough of this model is that it allowed the quantitative determination of all the thermodynamic parameters, while also establishing that the H-bonding and the subsequent helix formation process are enthalpically favored but entropically disfavored. [276] Recently, this same group has explored six superstructures featuring different geometries, resulting in subtle changes in the solid-state packing of the DPPs. [278] They achieved this by performing combinations of two DPPs and three rylenes to form six hierarchical superstructures that assemble as a result of orthogonal H-bonding and π•••π stacking (Figure I. 43d to f). The changes in inter-DPP stacking that are templated by the neighboring rylenes have a subtle effect on the excited-state dynamics and on the activation of new pathways such as singlet fission (SF).

The exclusive benefits of combinatorial supramolecular assembly demonstrated the impact of the structure on advanced light management in the form of SF, affording triplet quantum yields as high as 65% for a correlated pair of triplets and 15% for an uncorrelated pair of triplets. [278] The changes in the molecular structures of the components resulted in various 1D and 2D morphologies, whose long-range order and geometric differences have an influence on the management of light. Further studies of these supramolecular scaffoldings will be important to understand the morphology dependence on the photophysics of the supramolecular heterojunctions in order to maximize the junction area to achieve efficient charge separation and transport. [278]

Figure I. 43 a) DPP donor (red) and PDI acceptor (blue) molecules 1-3 are capable of b) heteroaggregation through a combination of H-bonding and π-π stacking, resulting in c

) well-ordered superstructures.*Adapted. [276] d) Library composed of three rylenes and two diketopyrrolopyrroles, e) supramolecular assembly via triple H-bonding and π-π stacking results in DPP-rylene superstructures, and f) superstructures vary in the DPP and rylene components and DPP/rylene stoichiometry.*Adapted. [278] Braunschweig et al., have also performed studies to determine how solubilizing side chains, the conjugation length and the type of H-bonding groups affect the homo-assembly of DPPs into J-aggregates. [279] These studies were performed by variable temperature (VT) UV-Vis titrations in toluene on multiple thiophene DPP derivatives (Figure I. 44). They reported that the presence of diamidopyridine (DAP) groups and their ability to form H-bonds improved considerably the driving force for assembly into larger clusters compared to those without the DAP group. According to their findings, the interplay of π-π stacking, H-bonding, van der Waals forces, solvent, concentration and temperature is responsible for the size, structure, stability and spectroscopic attributes of the resulting superstructures.

Moreover, the main discovery in this work was that these molecules assemble into slip-stacked geometries, described as J-aggregates. They also managed to derive two equations for the calculation of the size of aggregated stacks and its average mole fraction. [279] These findings are very important since the structure and properties of supramolecular assemblies are intimately linked, and small changes in the relative orientations of stacks can have great impact on their optoelectronic properties and device performance. [280,281] [282] c) Other H-bonding motifs present in DPP derivatives Our group has shown for example the introduction of semicarbazone functionalities into the simple thiophene-capped DPP core. [283] Two DPP derivatives were synthesized (Figure I. 45a and b) and the appearance of J-aggregates due to H-bonding formation was observed. We observed the increase of the J-aggregate band in solvents that promote the formation of Hbonds vs chloroform, which was used as a good solvent. The addition of methanol, a solvent that competes with the formation of H-bonds, resulted in the disappearance of the J-aggregate bands, putting in evidence the participation of H-bonds in the formation of such kinds of aggregates (Figure I. 45c and d). Furthermore, by tuning the aggregation state of these simple derivatives using different solvents, concentrations and temperature, it was possible to tune the energy bandgaps and cover large regions of the solar spectrum even reaching the near IR region. Different 1D structures were found, which presented different optical properties, making these small molecules very interesting to compare the different aggregation conditions on device efficiency.

Figure I. 45 Structures of DPPSC (a) and Br DPPSC (b). Normalized absorption spectra in solution of DPPSC (c) and (d)

BrDPPC upon the addition of methanol.*Adadpted. [283] The presence of semicarbazone groups has also been found in other DPP derivatives that were used as colorimetric chemosensors for fluoride ions. [198] This same group reported another chemosensor for fluoride ions using phenylhydrazone [199] as the H-bonding unit. In these cases, the H-bonding groups were employed to bind the fluoride ions and the supramolecular structures formed by them were not studied.

An example of a bola-amphiphilic DPP derivative has also been reported [284] to obtain supramolecular nanofibers by combination of H-bonding and π-π stacking (Figure I. 46b). Two carboxylic acids were attached to the DPP core through a C10 alkyl linker to obtain the bolaamphiphile compound that resulted to form nanofibers in aqueous solution. The self-assembly properties of DPP-11a were studied by UV-Vis spectroscopy in different solvents, using tetrahydrofuran (THF) as a good solvent and water as a bad solvent and probing the absorption spectra at different times (Figure I. 46d). In this case, the evolution of the bands and the appearance of aggregate bands (J-aggregate) manifest the important role of H-bonds to tune the formation of different morphologies. In this case, THF solutions drop cast on mica showed the formation of nanoparticles, while the aqueous solutions presented the formation of nanofibers. [284] d) H-bonds incorporated into DPP-based polymers H-bonding groups have also been integrated into the structure of semiconducting polymers to achieve enhanced charge transport and expand the applications into sensing devices. Zhang et al [285] incorporated thymine groups in the side chains of a thiophene-functionalized DPP polymer (PDPP4T-6) (Figure I. 47a). Thymine is one of the four nucleobases in DNA and has been demonstrated to bind with certain metal ions, such as Pd(II) and Hg(II). [286] FET devices were fabricated by spin-coating solutions of DPP4T-T and controls molecule PDPP4T-A (with branched alkyl tails) and PDPP4T-B (with branched and linear alkyl tails), finding μh values higher for the polymer containing thymine. This result was rationalized considering the enhancement of the film crystallinity due to H-bonding in comparison with the conjugated polymers containing only alkyl chains. This was demonstrated with grazing incidence wideangle X-ray scattering (GIWAXS) measurements, which showed improved lamellar stacking than the films made with the control molecules. Furthermore, the FET devices made with the thymine-containing polymer were used as sensors for CO and H2S. The incorporation of Pd(II) and Hg(II) was achieved through the airwater interface coordination. After the metallic ion coordination, FETs were fabricated and exposed to different gaseous analytes and solvent vapors. The polymer containing Pd(II) could detect CO in concentrations as low as 10 ppb, while devices made with Hg(II) coordinated ions could sense S2Hg down to 1 ppb. In this case, the introduction of H-bonding functionalities in semiconducting polymers resulted not only in a mobility enhancement, but also in additional applications and properties.

to the conjugated backbone and the illustration of T-T Intermolecular Hbonding and the coordination with Pd(II) and Hg(II)

.*Reproduced. [285] b) Chemical Structures of pDPP4T-1, pDPP4T-2, pDPP4T-3, and pDPP4T, and illustration of the design rationale for the incorporation of urea groups in the side chains of conjugated D-A polymers.*Reproduced. [287] c) Chemical structures of DPP polymers containing lysine residues.*Reproduced. [288] Urea groups have also been introduced in the pending chains of DPP polymers. Zhang et al, [287] reported three DPP-based polymers containing different ratios of urea groups and branched alkyl chains (Figure I. 47b). OFETS and BHJSCs were fabricated with these polymers and the control DPP polymer without urea units. The authors found out that the polymer containing the lowest ratio (1:30) of urea groups, showed the highest hole mobility (μh = 13.1 cm 2 /(V•s)). The influence of the presence of urea groups in DPP polymers was also studied in BHJSCs, finding in this case that the polymer with the highest ratio of urea groups (1:30) presented the best efficiency of all (6.8%), including the control devices made with polymers without urea groups.

The high mobility values found were attributed to the enhancement of lamellar packing order of the alkyl said chains on the thin films prepared thanks to the H-bonding interactions led by the urea groups and the appearance of inter-chain π-π stacking after thermal annealing at 100 ºC. Regarding the solar cell devices, the presence of urea groups was found to guide the assembly of the polymers into nanofibers and direct the ordered aggregation of the acceptor material, resulting in micro-phase separation in the blends were charge separation can be enhanced, compared to the control polymers without urea groups.

The use of H-bonds in DPP polymers has also interesting applications in bioelectronics. Du et al, [288] reported a DPP polymer containing lysine side chains (Figure I. 47c) that was applied in neural cell adhesion and growth. This way, it was not necessary to use other biological coating steps on electrical devices, making them promising materials for applications in However, the strong H-bonding ability of lysine resulted in very strong intermolecular aggregation and lack of solubility. The lysine groups were protected with t-Boc groups to provide solubility and deprotected subsequently with trifluroacetic acid (TFA) to render protonated lysine units, which increased the surface charge and improved cell adhesion.

Of course everything that has been presented is just the tip of the iceberg, more information on DPPs can be found in literature [289] . Nevertheless, now that the current state of the art regarding H-bonded DPP systems has been discussed, it is finally time to discuss about their role in this thesis.

IV.4) Role of DPP in this thesis

As it was previously mentioned, this PhD work consists of a systematic study based on a simple thiophene-capped DPP electroactive segment as a model system, several H-bonding parameters will be explored and subsequently, the results will be extended to state of the art semiconductors, such as rhodanine-containing systems [START_REF] Kan | [END_REF]290] or isoindigo-based [291,292] semiconductors (Figure I. 48). Finally, the study will be extended to acceptor molecules and donor-acceptor blends, including fullerene and NFAs (Figure I. 48). [293,294] In this thesis, the effect of varying several parameters has been evaluated, for instance:

✓ Type of H-bonding functionality: Amide, urea, self-complementary systems, and others.

✓

Position of the H-bonds in the molecular structure: peripheral or embedded in the solubilizing alkyl tails. ✓ Solubility: different lengths and branching of alkyl tails.

✓

Topology of the H-bonds in amides arms. ✓ Chirality within the pending arms attached to the DPP core.

Regarding supramolecular electronic systems, the optoelectronic properties and the structural aspects of these systems must be optimized to reach good performance in the final applications. DPP has been chosen as the model system due to its great electronic properties and functionalization versatility, as well as the possibility that it will provide an overview of the influence of H-bonding and explore how general the results are when translated to any other semiconductor.

The simple DPP derivative having two thiophene rings is one of the most used starting materials to synthesize semiconducting polymers and oligomers. [295] The optoelectronic and self-assembly properties of DPP derivatives mainly depend on the aromatic groups attached to the DPP core, and in many studies they are modified with electron-donating(withdrawing) groups. [195,[296][297][298] Interestingly, H-bonding is a great tool to tune the optoelectronic and selfassembly properties of small DPP derivatives without enlarging the thiophene DPP core. The examples of hydrogen-bonded DPP found in literature usually utilize the non-alkylated version of the pyrrole rings, [237,238] which normally are vacuum deposited due to insolubility as shown in the previous paragraphs or DPP oligomers modified in the peripheral positions with amide bonds. [191,269,299] So far, several H-bonded DPP families have been studied and can be seen in Figure I. 49. This thesis will address the study of three of these families, in particular chapter II will cover the bisamide familiy [START_REF] Militzer | Exploring the amide function: Impact of chirality and solubility References[END_REF] (Figure I. 49b). Chapter III will cover the study of the expansion of the bisamide family with enhanced solubility and amide topology changes (Figure I. 49d). Next, in chapter IV the impact of keeping the same solubilizing alkyl chains, while changing the position and topology of the amide bonds (Figure I. 49e) is discussed. Finally, in chapter V preliminary results on the impact of solvent in changes in morphology of some of the derivatives described in chapter III will be presented. In this thesis, I have worked on families with very different designs from the previously studied families in our group. [283] This way, very different parameters can be compared at the same time along with their optimization. As it has been shown in chapter I, supramolecular strategies have been applied in the field of organic electronics. [1][2][3][4][5][6][7][8][9] It was also discussed that the use of H-bonds is a topic still unexplored and without consensus on the results. In this chapter, special focus is put on H-bonded DPP derivatives containing amide bonds coupled to the -conjugated core through a flexible six carbon linker. This design was chosen because our group started the systematic studies with derivatives containing semicarbazone units directly attached to the DPP core. [10] The semicarbazone derivatives resulted in very rigid molecules with limited solubility and with fast recombination dynamics when their photoconductivity properties were screened. Nevertheless, their self-assembly and morphological properties provided very useful information on how to continue designing other components of the H-bonded DPP family.

In this part of the thesis, totally different molecules were designed, where the functionalization was done on the lactam rings vs the thiophene rings as in the semicarbazone derivatives (Figure II. 1) and the H-bonding group was separated through a flexible linker to compare the self-assembly process. In addition, chirality was added as a parameter, so a chiral center next to the amide group (Figure II. 1) was introduced. Particularly, my task was synthesizing the (R)-enantiomer and perform the full characterization, while the (S)-enantiomer was made by a former PhD student of our group. Nevertheless, I synthesized all three derivatives to obtain enough amount of every compound to do a fair comparison for the results.

Figure II. 1 Structural comparison between the semicarbazone family and the bisamide family.

The amide group was chosen since it is one of the most explored H-bonding groups in history and found almost in all the fields of chemistry. [11] The well-known synthetic procedures to introduce them into any type of molecule, and their easy characterization by spectroscopy techniques, such as infrared spectroscopy, make them the perfect candidates to study selfassembly processes where H-and J-aggregation are involved and some of these examples are illustrated in Figure II. 2.

vs

Rigid molecule

Functionalized in Thiophene

Flexible chiral molecule

Functionalized in Lactam Ring

For instance, Stupp et al. [12] have shown a hairpin-shaped molecule containing a sexithiophene unit as the electroactive segment attached to a trans-1,2-diamidocyclohexane (DACH), as the self-assembly motif (Figure II. 2a). In this case, the coexistence of H-and Jaggregates results in the broadening of the wavelength spectral range of optical absorption, and in the formation of semiconducting nanowires.

Similar results were observed by Ghosh et al. [13] They found Davydov splitting [14] in a DPP system symmetrically functionalized with amide bonds (Figure II. 2b). The authors observed the presence of H-and J-type aggregates upon self-assembly conditions. [13] Dilute solutions in chloroform and toluene showed absorption spectra of the monomeric species. In contrast, under aggregation conditions, the absorption spectrum differs from the one at low concentration. In this case, new bands appear at higher and lower energies, being H-and Jtype aggregates, respectively, and achieving spectral coverage in the visible region and transparency in the near infrared region.

Figure II. 2 A few examples of previously explored -conjugated systems containing amide functionalities and explored in the supramolecular field.

The field of perovskite photovoltaic devices has also benefitted from the presence of amides in materials showing J-aggregates. Kaneko et al. [15] have shown H-bonded tetrathiofulvalene (TTF) derivatives containing amide groups (Figure II. 2c) that have been used as dopant-free hole transport materials in perovskite solar cells. In this case, the H-bonded TTF derivatives had electrical conductivity values higher than spiro-OMeTAD (2,2',7,7'-Tetrakis[N,N-di(4methoxyphenyl)amino]-9,9'-spirobifluorene, which is the most usual hole transport material. [16] J-type aggregates were found in H-bonded TTF thin films leading to the formation of nanofibers with enhanced mobility.

a) b) c) d)

Finally, many examples with perylene bisimide (PBI) derivatives with pending amide groups exhibiting J-aggregates have been reported. The Würthner group has shown multiple examples of self-assembled PBIs [17] containing amide bonds as well as other self-assembly motifs. Back in 2008 they showed a study on how to control H-and J-type homo-and heteroaggregates in amide-containing PBIs. For this purpose, they synthesized several PBI derivatives (Figure II. 2d) with the same core and amide groups as H-bonding motifs and changed the alkyl chains. [18] The authors found that the steric effects in the peripheral side chains dictated the selfassembly mode, going from the usually found H-type to the J-type aggregates. PBIs containing linear alkyl side chains, which are sterically less demanding, formed face-to-face H-type aggregates, while the PBIs having branched alkyl tails, formed slipped J-aggregates or did not aggregate.

As part of this study, the other parameter that was evaluated in this DPP family was chirality, which can impact the self-assembly properties as well, and in the case of semiconductors their optoelectronic properties. [19,20] For instance, molecular chirality plays an important role in chemistry in pharmaceutical applications [21] , whereas in biology numerous chiral molecules with asymmetric arrangements of atoms exist widely in nature, such as in amino acids and sugars. [22] As it has been discussed before, one of the most powerful methods for preparing different scales of functional materials is through self-assembly; in the same way, chiral information can also pass from single molecules to supramolecular assemblies and then to macroscopic superstructures. [23] Additionally, - stacking interactions are frequently used as a preliminary driving force for the self-assembly of structures based on conjugated molecules.

Furthermore, a number of similarities have been observed between H-bonding and - stacking interactions. Hence, supramolecular chirality has mainly been explored in organic semiconductors using - stacking and H-bonding. [19,[24][25][26][27] . In this sense, chirality is amplified when the molecular chirality is transferred to the supramolecular structures, making new properties emerge. Therefore, using conjugated molecules with one-handed chirality as building blocks to prepare hierarchical superstructures by mimicking the self-assembly behavior of biomolecules is a state-of-the-art strategy for designing novel functional nanomaterials. [28,29] Palmans and Meijer reviewed chirality in supramolecular aggregates, making especial emphasis in non-covalent systems and on the factors that affect the amplification of chirality in dynamic supramolecular aggregates. [30] One very interesting example that utilizes Hbonding, - stacking and chirality is the study of benzene-1,3,5-tricarboxamide derivatives (Figure II. 3a). [31] The aggregates formed by these derivatives demonstrated pronounced amplification of chirality and the energy for helical reversal and mismatch were on the order of magnitude of 1.2 kJ•mol -1 . [32]

Figure II. 3 Structures of a) benzene-1,3,5-tricarboxamide derivatives and b) their urea derivatives counterparts.

Furthermore, the introduction of additional H-bonds by replacing the amide group by a urea group (Figure II. 3b) afforded compounds that showed slight circular dichroism (CD) effect in alkane solutions, which is indicative of the presence of ordered stacks. Mixing solutions of achiral urea with chiral amide illustrated the effect of a mismatch of the secondary H-bonding interactions in these systems; in particular, mixtures containing between 5-20% of chiral amide with achiral urea resulted in amplification of chirality. [33] However, when a mixture of 85% of achiral urea derivative and 15% of chiral amide was prepared, the CD effect present in the mixture disappeared over time.

Another example of supramolecular chirality is the one reported by Aida et al [34] , where they reported an unprecedentedly high degree of chiral amplification of supramolecular helices in a system using triphenylamine (TPA), a propeller-shaped molecule (Figure II. 4a). This was achieved by using a strategy known as "the sergeants and soldiers experiment" [35] , where few sergeants (chiral units) can control the movements of large numbers of cooperative soldiers (achiral units). In their work one sergeant controlled the handedness of 500 soldiers in supramolecular helices and they manage to demonstrate that a TPA derivative could switch its role from sergeant to soldier and vice versa depending on its partners.

They investigated their self-assembly behavior in cyclohexane finding that they formed supramolecular aggregates at room temperature. AFM measurements revealed that derivative Finally they also found that one-handed helices of A could be obtained by mixing an unusually small fraction of C3(S) with A, in other words, the chiral information of the side chains of C3(S) was efficiently amplified into the handedness of the supramolecular helices of A. The study the proved that the handedness of the helices was fully controlled using a 0.2 mol% fraction of sergeants and provided valuable insights into the construction of helical structures and a novel design strategy for supramolecular chiral amplification. Chirality has been introduced in DPP derivatives mainly by linking them to chiral alkyl tails, usually 2-ethylhexyl [36][37][38][39] , to helicene molecules, [40] or adding myrtenal derivatives. [41] For instance, when the effects of stereoisomerism of DPP(TBFu)2 derivatives (Figure II. 4) in their crystal structures and the optoelectrical properties were studied, they found that the crystal structures and FET mobilities were sensitive to stereoisomerism, whereas optical properties were not. [36] Additionally, isolated stereoisomers exhibit different FET mobilities correlated to their different crystal structures.

The crystallization of DPP(TBFu)2 derivatives was found to be dominated by the mesomere, which possessed the greatest crystallization tendency among the three. The RR-isomer and SS-isomer which are enantiomers showed very similar crystal structures, thin-film morphologies and FET properties, while the mesomer exhibited different characteristics.

According to their single-crystal structures, the mesomer has a coplanar conjugated backbone favoring intermolecular - stacking and a shorter plan-to-plan distance; while the other two chiral compounds exhibited twisted conjugated backbone and therefore inferior intermolecular stacking.

Figure II. 5 Chemical structure of DPP(TBFu)2 with two chiral carbons highlighted, 1

and 2, and the resulting stereoisomers relating to the configurations of the two chiral carbons.*Adapted. [36] When DPP linked to helicene derivatives (Figure II. 6) were studied they found they showed intense electronic CD in the visible and near-IR region. [40] The UV-vis absorption spectra of mono, disubstututed and oligomers of these derivatives were recorded in dichloromethane solutions. The comparison with their corresponding precursors showed that the mono substituted derivative had red shifted bands with respect to both precursors (by about 20 nm relative to DPPBr), which clearly reflects an extension of the π-conjugation between the DPP dye and the helicene via the alkynyl bridge. Interestingly, going from one DPP substituent into two in H6(DPP)2 (Figure II. 5), did not further red-shifted the absorption, which indicated lack of electronic conjugation through the whole helix. Accordingly, the high molar extinction coefficients in the visible part of the spectrum were approximately proportional to the number of DPP units within the molecule.

Furthermore, the association between enantiopure hexahelicene and DPP provided molecular and macromolecular helical π-conjugated molecules while also showing that chiral helicenes symmetrically functionalized by DPP units display an exciton coupling effect, which resulted in a strong synergy between the chiral helical π-conjugated core and the photophysical properties of the DPP. Lastly, for the DPP myrtenal derivatives (Figure II. 7) the attachment of one or two chiral units was done at the end positions (extremities) of the DPP core and its influence on self-assembly for was studied. [41] These derivatives showed how the chiral at-end strategy is a way to influence the organization of optically active aggregates of chromophores. In this case, chiral substitution at both extremities was necessary to create significant optical activity in solution.

Stereoisomer

Additionally, the results demonstrated that CD is an extremely sensitive probe for the organization of these compounds, as very modest changes in the absorption spectra were observed, making the chiral structures useful for the understanding of related self-assembled structures in general. Although, OPV devices prepared using these myrtenal DPP derivatives as donors and PCBM as an acceptor gave very low PCE and short circuit current values, around an order of magnitude lower than devices made with P3HT:PCBM under similar conditions. They attributed the poor performance to be related to the low charge carrier mobility of the materials, as mobility in chiral materials is known to be extremely sensitive to supramolecular organization. [42] Finally, the morphological analysis revealed that the monosubstituted derivative is more inclined to form ordered crystalline domains when spun-cast as a blend with PC61BM.

Having briefly reviewed some examples containing amides, DPP derivatives and chiral groups, it is now appropriate to present what was performed for the new DPP family. In this chapter, the synthesis of the lactam functionalized derivatives shown in Figure II. 1 will be described, as well as their optical and self-assembly properties characterization, which will help in the understanding of the charge transport properties measured by electrodeless techniques based on microwave conductivity.

II. Results and Discussion

II.1) Synthesis

The main DPP core was synthesized by the cyclization reaction between 2thiophenecarbonitrile and diethylsuccinate, following a reported protocol. [43] The final DPPBA, (S)-DPPBA and (R)-DPPBA were obtained via alkylation reactions with the mesylated amidecontaining branches (Scheme II. 1). These branches were synthesized by reacting εcaprolactone with the corresponding amine derivatives (chiral and achiral) and subsequently adding the mesylate activating group (Scheme II. 1). The DPP was N-alkylated with cesium carbonate as the base to deprotonate and DMF as the solvent like in similar DPP alkylation reactions reported. [44,45] The yields are low (10%) because of the produced sub-products isolated and identified, such as the O-alkylated isomers.

Different reaction conditions were tested to increase the N-alkylation yield. For instance, the reactions were performed under microwave irradiation as the heating source. In a first attempt, the reaction was carried out at room temperature to slow the formation of sub-products, since at high temperature and basic conditions, both N-and O-alkylation are favoured. [46] After one hour, only the mono N-alkylated product was obtained together with unreacted DPP and mesylate. When the reaction time increased, the O-alkylated isomer was already formed and the desired product was found at low yield (5-8%).

Scheme II. 1 Synthetic pathway towards DPPBA, (S)-DPPBA and (R)-DPPBA. iii) Microwave irradiation (P = 150 W, DMF, 2 h, 120 ºC for (S)-DPPBA and P = 150 W, DMF, 2h, 70 ºC for (R)-DPPBA).

In a second attempt, the reaction was performed at 120 ºC for one hour, adding a few drops of DMF to make a heterogeneous reaction mixture, demonstrated to work better for microwave reactions. [53,54] In this case, the major products were the N-alkylated derivative accompanied by the O-alkylated isomer. Both products were isolated by column chromatography, finding yields of 15% for the (S)-enantiomer, but not higher than 10% for the (R). The reactions were performed at lower temperatures (70-80 ºC) to achieve the bis-alkylated derivatives and try to avoid O-alkylated isomers. However, the (S)-enantiomer was obtained in 8% yield, and the (R) in yields of 15-22%. In acetonitrile, a greener solvent, the yields were even lower either with microwave irradiation or conventional heating.

II.2) Optical and self-assembly properties

After synthesizing the target compounds, we proceded to study the optical and self-assembly properties. Particularly, we used UV/Vis absorption, FTIR and CD spectroscopies in solution and in the solid state to shed light into the assembly processes of the three derivatives, and transmission electron microscopy (TEM) was used to study the formation of supramolecular structures. ). This band could be attributed to the formation of J-type aggregates, as for other H-bonded DPP derivatives, including semicarbazone-containing DPPs reported earlier by our group. [10,47,48] This signal is related to the formation of H-bonds since it disappears when methanol, an H-bonding competing solvent, is added to (S)-DPPBA and (R)-DPPBA (Figure II. 9). So far, it was the first time that we observed aggregation bands in chloroform, which is normally a good solvent for the H-bonded DPP derivatives we have reported until the moment.

The presence of such a band, already indicates the stronger aggregation tendency of the chiral derivatives in comparison to the achiral. FTIR spectra of chloroform solutions at room temperature proved the existence of H-bonds in the bisamide derivatives (Figure II. 10a). DPPBA showed only one band at 3450 cm -1 in the NH stretching area, which is characteristic of the NH stretching mode (amide A) of free amide groups. This result points out that DPPBA is not H-bonded in chloroform.

The amide I mode is found at 1659 cm -1 , which also corresponds to free amide groups. On the other hand, (S)-DPPBA and (R)-DPPBA showed two bands at 3439 cm -1 and 3297 cm -1 in the NH stretching area at room temperature (Figure II. 10a). The first band can be attributed to the free amide, analogously to the band at 3450 cm -1 for DPPBA; the second band corresponds to H-bonded amide groups. Hence, (S)-DPPBA and (R)-DPPBA are partially Hbonded. In the region between 1600 cm -1 and 1700 cm -1 , (S)-DPPBA and (R)-DPPBA show three peaks at 1632 cm -1 , 1648 cm -1 and 1663 cm -1 . The peak at 1632 cm -1 corresponds to amide groups engaged in strong H-bonds [49] , while the peak at 1648 cm -1 corresponds to weaker bonds. The peak at 1663 cm -1 matches with the peak for free amide observed with DPPBA.

When increasing gradually the temperature from 27 to 59 °C the spectra of DPPBA did not show significant evolution. In contrast, for the chiral derivatives, the peaks corresponding to H-bonded amides gradually decreased and fully disappear at 45 °C. At this temperature, the spectrum of (S)-DPPBA matches the one of DPPBA at room temperature (Figure II. 11).

The optical properties were measured in different solvents: toluene, chlorobenzene, cyclohexane and ethyl acetate. In these solvents, the J-aggregate band becomes more intense than in chloroform for the three derivatives ( Thanks to the formation of J-aggregates it is possible to cover a larger zone of the spectrum and to tune the energy band gap. This is very interesting since the optoelectronic properties can be modified by varying the aggregation state without modifying the molecule. Furthermore,

 (nm)

0.08 mg/ml 0.17 mg/ml 0.6 mg/ml 1.6 mg/l 300 400 500 600 700 800 0 This trend was also observed for the three derivatives, but the J-aggregate bands disappeared at higher temperatures and lower concentrations for the chiral derivatives compared to the achiral one. This proves that the chiral derivatives form more stable aggregates than the achiral one.

The absorption properties were also measured on cast thin films, showing a bathochromic shift with the appearance of a predominant J-aggregate band, as an effect of planarization with respect to the solutions. This result is independent from the casting solvent (Figure II

II.3) Electrical properties

After exploring the aggregation ability of the amide-containing molecules, knowing their electrical properties was the next topic of interest. The photoconductivity properties were explored using electrodeless techniques based on microwave conductivity. This part of the work was done in collaboration with the group of Prof. Shu Seki from the University of Kyoto (Japan). This group has pioneered contactless techniques to measure a wide variety of electronic properties. This means that the molecules can be explored simply by drop casting without the need of making an entire device. Particularly, they measured the photoconductivity of the two chiral molecules and the achiral one using Flash-Photolysis Time Resolved Microwave Conductivity (FP-TRMC). It is a technique that provides a measure of photoconductivity as ΦΣμ were Φ is the charge carrier generation quantum yield and Σμ is the sum of charge carrier mobilities of electrons and holes. [50][51][52] The samples are drop cast onto quartz substrates and exposed to a 355 nm pulsed laser. Once the irradiation stops, the charge recombination lifetime is recorded.

For these compounds, films were prepared by drop casting them from chloroform solutions (Figure II. 21), and their photoconductivity was analysed before and after solvent vapor annealing and the solvent annealing protocol was:

1) To expose to ethyl acetate for 24 h 2) To methanol vapor for 24 h: ethyl acetate promotes efficiently aggregation of the molecules, and methanol disrupts H-bonds. t1/2 amounts 2 x 10 -5 s for DPPBA, 5 x 10 -6 s for (S)-DPPBA, and 7 x 10 -6 s for (R)-DPPBA (Table II. 2). It seems that the lower solubility of the chiral DPPs and the presence of the methyl group next to the amide group are detrimental for the charge carrier pathways.

Table II. 1 Photoconductivity values for the three derivatives before and after solvent annealing.

Compound

ΦΣµ (cm 2 V -1 s -1 ) Before solvent annealing

Solvent vapor exposure

ΦΣµ (cm 2 V -1 s -1 ) After solvent annealing DPPBA 5 × 10 To assess the impact of the self-assembled structure quantitatively on the charge carrier pathways, the photoconductivity signal was traced at each step of the solvent annealing protocol in an identical film of each compound. Interestingly, the highest photoconductivity (7.5 x 10 -5 cm 2 V -1 s -1 , Table II The photoconductivity value increased up to 1.5 fold from the initial 5.0 x 10 -5 cm 2 V -1 s -1 , emphasizing the importance of promoting the H-bonding strength. On the other hand, methanol vapor annealing did not show any significant effect on photoconductivity (Figure II. 22e) in DPPBA. It seems that only methanol vapor is not enough to disrupt H-bonds in the condensed phase. However, when the film previously exposed to ethyl acetate was soaked in methanol, the photoconductivity decreased dramatically as well as the lifetime (Figure II. 22f, Table II.

3).

This result highlights the important role of H-bonding to facilitate the charge carrier pathways in the self-assembled structures. Regarding the chiral derivatives (S)-and (R)-DPPBA, no differences in photoconductivity were found during the solvent annealing protocols (Figure II. 23, Table II. 1). This would suggest that tightly-bound self-assembled structures were already formed in the solution phases, and the annealing is no longer efficient to cause significant rearrangements in the molecular packing structures of chiral substances. The presence of a methyl group next to the H-bonding (amide) motif and the lower solubility of both chiral isomers compared to DPPBA, might be supportive for the stability of the self-assembled structures.

Table II. 2 Rate constant (calculated after 3 µs after pulse excitation) and half lifetime values for the three derivatives.

DPPBA (S)-DPPBA (R)-DPPBA k (s -1 )

3 × 10

II.4) Conclusions

In conclusion, three amide-containing DPP derivatives were synthesized and characterized, two of them bearing chiral centers. The three derivatives aggregate and form J-type aggregates, where H-bonds are involved. The aggregation is particularly strong in the chiral derivatives, which show aggregate signals in solvents where the achiral DPP is fully dissociated.

The photoconductivity measurements performed using FP-TRMC indicate that the achiral derivative has superior values of photoconductivity as well as slower recombination of the charge carriers. The importance of H-bonding is highlighted by annealing samples in solvents that promote self-assembly, where the photoconductivity values increased. In contrast, the photoconductivity values decreased dramatically when the samples were soaked in H-bonding competing solvents. This effect was not observed for the chiral derivatives, indicating that the chiral center next to the H-bonding functionality might hinder charge transport.

These results have helped in the design of the next H-bonded DPP families that will continue to be used in the systematic and comparative studies. In this regard, chapter III shows how the solubility of the derivatives described in this chapter can be increased by adding solubilizing alkyl tails in the thiophene rings. However, the incorporation of chirality while increasing solubility is being explored by another colleague in my group, while I have focused on drastically changing other H-bonding parameters that can influence the self-assembly properties, as for example the amide topology also described in chapter III. time / s

 / m 2 V -1 s -1 c) d)
The work of this chapter resulted in a publication and all the details can be found here:

Chemistry -A European Journal. 2020, 26, 9998-10004, 10.1002/chem.202001540.

III. Experimental III.1) Materials and methods

All reagents and solvents were obtained from commercial suppliers and purified or dried according to standard procedures. Column chromatography was performed on silica gel (VWR Silica 60, particle size 0.040-0.063 mm). Solvents for spectroscopic studies were of spectroscopic grade and used as received. Elemental analysis was performed on a Thermofischer Scientific Flash 2000. Matrix-assisted laser desorption/ionisation-time of filght (MALDI) was performed in a Bruker Daltonics. 1 H and 13 C spectra were recorded in CDCl3 on a Bruker Avance 400 MHz spectrometer and/or Bruker Avance III HD 500 MHz spectrometer. UV-vis measurements were performed in a conventional quartz cell (light pass 1 mm) on a Cary 5000 UV-Vis-NIR spectrophotometer. TEM measurements were done with a Technai G2 (FEI) microscope with an accelerating voltage of 200 kV. 5 µL of the sample solution were deposited onto a freshly glow discharged carbon-covered grid (400 mesh). The suspension was left for 2 min, and then, the grid was negatively stained with 5 µL of uranyl acetate (2% in water) for another 1 min and finally blotted using a filter paper.

FTIR spectra were recorded with a Vertex 70 from Bruker Optics, equipped with MCT detector and a black-body source. The spectra of the solids were measured by ATR on diamond. The solutions were studied in cells from Specac Pike with KBr NaCl windows. For the VT experiments the solutions were inserted in a home-made cell between two NaCl windows. The cell was inserted in a Linkam heating stage, hold in a horizontal measurement chamber. The spectra were measured with the built-in MCT detector of the Vertex 70. The spectra were compensated from CO2 and moisture with OPUS from Bruker. The solvent intensities were measured separately and subtracted. The spin coated samples were prepared using a Spin 150 spin coater at 2000 rpm using 80 µl of solution on glass slides or silicon wafers.

Charge carrier mobilities were evaluated by FP-TRMC at room temperature. [48,53] The thin films of samples were fabricated by drop-cast method onto quartz substrates (9 × 40 mm 2 , 1 mm thick). Charge carriers were injected into the materials via photo-ionization with a third harmonic generation (λ = 355 nm) of a Spectra Physics model INDI-HG Nd:YAG laser pulses at 10 Hz with a pulse duration of ca. 5 ns. The photon density of a 355 nm pulse was modulated from 4.5 × 10 15 photons cm -2 pulse -1 . The microwave frequency and power were set at ~9.1 GHz and 3 mW, respectively, and guided into a microwave cavity. The Q-factor of the microwave cavity loaded with the sample was 2200, and the substrates with the compound films were set at the point of electric field maximum. The reflected power of the probing microwave, picked up by a diode (rise time < 1 ns), was monitored by a Tektronics model TDS3032B digital oscilloscope after an amplification by Ciao Electronics CA812-304 FET amplifier system. The observed change in the reflected microwave power (ΔPr) was normalised with the steady reflection of the microwave from the cavity (Pr), and converted directly into the product of a photocarrier generation yield (Φ) and the sum of photo-generated electron/hole mobilities (Σµ),

 = 1/(εI0Flight) × (/A) × (Pr/Pr) (1)
where ε, A, I0, and Flight are elementary charge, sensitivity factor (S -1 cm), incident photon density of the excitation laser (photon cm -2 ), and filling factor (cm -1 ), respectively. The value of Flight was calculated based on the overlap of the area of photo-carrier injection (presumed to be proportional to the absorbance of excitation light by the sample film) with electric field strength distribution in the cavity derived from a calculation code of CST Microwave Studio from AET Inc.

III.2) Synthetic procedure

N-hexyl-6-hydroxyhexanamide:

A solution of hexylamine (3.8 g, 37.3 mmol) in toluene was stirred at room temperature and caprolactone (2.85 g, 24.7 mmol) was added dropwise. The mixture was then stirred for 90 min at 130 °C and cooled down to room temperature. The crude was extracted with DCM (50 ml) and washed with a 1 M solution of HCl, then with a solution of NaHCO3 (aq). The organic phase was dried with MgSO4, filtered, and concentrated under reduced pressure. The final product was purified by recrystallization (75% ethyl acetate/cyclohexane) and obtained as white crystals (2.82 g, 53%).

6-(hexylamino)-6-oxohexyl methanesulfonate:

A solution of N-hexyl-6-hydroxyhexanamide (2.8 g, 13 mmol) and triethylamine (2.8 g, 28 mmol) in anhydrous THF (45 ml) was stirred under argon atmosphere at 0°C. Methanesulfonyl chloride (3.5 g, 28 mmol) was added dropwise. The mixture was stirred at room temperature for 30 min, poured in iced water (100 ml) and extracted with DCM. The organic phase was dried with MgSO4, filtered and concentrated under reduced pressure. The desired compound was purified by column chromatography (ethyl acetate) and dried under reduced pressure as a white solid (3.1 g, 82%). A solution of (S)-heptan-2-amine (11.34 g, 98.4 mmol) in toluene was stirred at room temperature and -caprolactone (7.49 g, 65.6 mmol) was added dropwise. The mixture was then stirred for 4 h at 130 °C and cooled down to room temperature. The crude was extracted with DCM (300 ml), washed with a 1 M solution of HCl, and with a solution of NaHCO3 (aq). The organic phase was dried with MgSO4, filtered, and concentrated under reduced pressure. The final product was obtained after washing (75% ethyl acetate/cyclohexane) as a pink oil (10.77 g, 61%). H-NMR (400 MHz, CDCl3): δ [ppm] 5.2 (d, 1Hk), 3.99 (ddm, J = 13.4 Hz, 8.6 Hz, 6.7 Hz, 1Hj), 3.66 (t, J= 6.5 Hz, 2Hi), , 2.16 (t, J= 7.3 Hz, 2Hh),1.67 (m, J= 7.2 Hz, 2Hg), 1.60 (m, J= 6.9 Hz, 2Hf), 1.41 (m, J= 6.7 Hz, 4He), 1.34-1.26 (m, 6Hd), 1.22 (d, J= 6.1 Hz, 1Hc), 1.12 (d, J= 6.5 Hz, 3Hb), 0.88 (t, J= 6.6 Hz, 3Ha). A solution of (S)-N-(heptan-2-yl)-6-hydroxyhexanamide (4 g, 17.4 mmol) and triethylamine (5.29 g, 52.3 mmol) in anhydrous THF (65 ml) was stirred under argon atmosphere at 0°C. Methanesulfonyl chloride (6 g, 52.3 mmol) was added dropwise. The mixture was stirred at room temperature overnight, poured in iced water (150 ml) and extracted in DCM. The organic phase was dried with MgSO4, filtered and concentrated under reduced pressure. The desired compound was purified by column chromatography (ethyl acetate) and dried under reduced pressure and obtained as a white solid (5.18 g, 77%). A solution of (R)-heptan-2-amine (11.34 g, 98.4 mmol) was stirred at room temperature. εcaprolactone (7.49 g, 65.6 mmol) was added dropwise. The mixture was then stirred for 4 hours at 130°C and cooled down to room temperature. The crude was extracted with DCM (300 ml) and washed with a 1 M solution of HCl, then with a saturated solution of NaHCO3 (aq). The organic phase was dried with MgSO4, filtered and concentrated under reduced pressure. The final product was obtained after washing (75% ethyl acetate/cyclohexane) as a pink oil (8.88 g, 59%). A solution of (R)-N-(heptan-2-yl)-6-hydroxyhexanamide (4 g, 17.4 mmol) and triethylamine (5.29 g, 52.3 mmol) in anhydrous THF (65 ml) was stirred under argon atmosphere at 0°C. Methanesulfonyl chloride (6 g, 52.3 mmol) was added dropwise. The mixture was stirred at room temperature overnight, poured in iced water (150 ml) and extracted in DCM. The organic phase was dried with MgSO4, filtered and concentrated under reduced pressure. The desired compound was purified by column chromatography (ethyl acetate) and dried under reduced pressure and obtained as a white solid (4.12 g, 77%). A solution of 2-thiophenecarbonitrile (10.4 g, 95 mmol) and potassium tert-butoxyde (12.3 g, 109 mmol) was stirred under argon in tert-amyl alcohol (200ml) at 120°C. Diethyl succinate (8.25g, 47mmol) was then added dropwise. The solution was stirred at 120 °C overnight and then cooled down to room temperature. The mixture was neutralized with 5 ml of concentrated acetic acid while being vigorously stirred for two hours at room temperature. The crude was filtered and washed several times with MeOH and dried to afford TDPP as a dark red solid (11.6 g, 82 %). A suspension of TDPP (2 g, 6.8 mmol) in anhydrous DMF (150 ml) was stirred under argon atmosphere at 120°C. Cesium carbonate (5.4 g, 16.5 mmol) was added progressively. The mixture was stirred for 1h at 120°C then a solution of 6-(hexylamino)-6-oxohexyl methanesulfonate (12.24 g, 42 mmol) in anhydrous DMF was added dropwise. The solution was stirred overnight at 120°C and was cooled down to room temperature. The crude was a b c d added to distilled water (600ml) and extracted with DCM. After collecting the organic phase, the solvent was removed under vacuum and the product was purified by column chromatography (DCM:Cyclohexane 50:50) to afford DPPBA as a purple solid (438 mg, 10%). 1 H-NMR (400 MHz, CDCl3) δ [ppm]: 8.91 (dd, J = 4.0 Hz, 1.1Hz, 2Hk), 7.66 (dd, J = 5.0 Hz, 1.1 Hz, 2Hj), 7.29 (dd, J = 5.0 Hz, 4.0 Hz, 2Hi), 5.48 (m, 2Hh), 4.09 (t, J = 7.7 Hz, 4Hg), 3.23 (q, J = 6.7 Hz, 4Hf), 2.18 (t, J = 7.6 Hz, 4He), 1.79-1.69 (m, 8Hd), 1.48-1.45 (m, 4Hc), 1.32-1.27 (m, 16Hb), 0.89 (t, J = 6.9 Hz, 6Ha).

6,6'-(1,4-dioxo-3,6-di(thiophen-2-yl)pyrrolo[3,4-c]pyrrole-2,5(1H,4H)-diyl)bis(N-((S)heptan-2-yl)hexanamide) (S)-DPPBA:

A suspension of TDPP (650 mg, 2 mmol) in anhydrous DMF (15 ml) was stirred under argon atmosphere at 120°C. Cesium carbonate (2.17 g, 6.62 mmol) was added progressively. The mixture was stirred for 1h at 120°C and then a solution of (S)-6-(heptan-2-ylamino)-6-oxohexyl methanesulfonate (2 g, 6.5 mmol) in anhydrous DMF was added dropwise. The solution was stirred overnight at 120°C and cooled down to room temperature to be then dropped in distilled water (600ml). The crude was extracted with DCM. After collecting the organic phase, the solvent was removed under vacuum and the product was purified by column chromatography (DCM:Cyclohexane 50:50) to afford (S)-DPPBA as a purple solid (150 mg, 9%). 1 H-NMR (400 MHz, CDCl3) δ [ppm]: 8.91 (dd, J= 3.9 Hz, 1.0 Hz, 2 Hn), 7.65 (dd, J= 5.0 Hz, 1.0 Hz, 2Hm), 7.3 (t, J= 4.5 Hz, 2Hl), 5.23 (d, J= 8.6 Hz, 2Hk), 4.09 (t, J= 7.7 Hz, 4Hj), 3.97 (m, J=5.5 Hz, 2Hi), 2.16 (t, J= 7.6 Hz, 4Hh), 1.79 (m, J= 7.5 Hz, 4Hg), 1.71 (m, J= 7.5 Hz, 4Hf), 1.48 (m, J= 3.9 Hz, 4He), 1.42-1.38 (m, 4Hd), 1.33-1.27 (m, 12 Hc), 1.11 (d, J= 6.6 Hz, 6Hb), 0.88 (t, J= 6.7 Hz, 6Ha).

(1H,4H)-diyl)bis(N-((R)heptan-2-yl)hexanamide) (R)-DPPBA:

A suspension of TDPP (500 mg, 1.66 mmol), cesium carbonate (1.35 g, 4.15 mmol) and (R)-6-(heptan-2-ylamino)-6-oxohexyl methanesulfonate (0.95 g, 4.15 mmol) in anhydrous DMF (1 ml) under stirring was reacted in the microwave. The reaction was performed in two steps in the microwave at 150 W, first for 2h at 20°C and then for 0.5 h at 70°C. Once it was cooled down to room temperature, the mixture was dropped in distilled water (300ml) and the crude was extracted with DCM. After collecting the organic phase, the solvent was removed under vacuum and the product was purified by column chromatography (DCM:Cyclohexane 50:50) to afford (R)-DPPBA as a purple solid (265 mg, 22%). 1 H-NMR (400 MHz, CDCl3) δ [ppm]: 8.91 (dd, J= 3.9 Hz, 1.1 Hz, 2 Hn), 7.65 (dd, J= 5.0 Hz, 1.0 Hz, 2Hm), 7.3 (dd, J= 5.0 Hz, 4.0 Hz, 2Hl), 5.22 (d, J= 8.7 Hz, 2Hk), 4.09 (t, J= 7.7 Hz, 4Hj), 3.97 (m, J=7.1 Hz, 2Hi), 2.16 (t, J= 7.6 Hz, 4Hh), 1.79 (m, J= 6.2 Hz, 4Hg), 1.71 (m, J= 5.8 Hz, 4Hf), 1.48 (md, J= 7.8 Hz, 2.5 Hz, 4He), 1.43-1.37 (m, 4Hd), 1.33-1.23 (m, 12 Hc), 1.11 (d, J= 6.6 Hz, 6Hb), 0.88 (t, J= 6.6 Hz, 6Ha). Following the design of H-bonded derivatives to complete our library, we continued studying other parameters that impact the formation of H-bonds. In this case, we decided to increase solubility of the bisamide derivatives shown in Chapter II and additionally, we explored the amide topology impact on the self-assembly and electrical properties.

The bisamide DPP derivatives were designed containing additional alkyl chains to improve their solubility. In this chapter, the thiophene rings on the DPP were functionalized with hexyl chains, while keeping the same amide branch in the lactam rings (Figure III. 1).

Figure III. 1 Chemical structure of a bisamide DPP alkylated on the thiophenes.

Additionally, a comparison of two DPP derivatives containing amide groups attached to the lactam rings through a six carbons alkyl linker with N-or C-centered topology, and hexyl alkyl tails in the thiophene rings (to provide solubility), with respect to the previously reported amidecontaining DPP derivatives with unsubstituted thiophenes was performed.

Together with the two H-bonded derivatives, a DPP molecule having only hexyl alkyl tails as a control was also synthesized. The self-assembly processes of the N-and C-centered amidecontaining DPP derivatives were once again followed with different spectroscopy and microscopy techniques, and the charge transport properties were studied with FP-TRMC. The results are compared to the control molecule and the positive role of H-bonds in the electronic properties was highlighted.

An important factor to consider when designing organic semiconductor devices is solubility, as they are often prepared through solution processing. Moreover, the solubility of the DPP derivatives previously synthesized by our group has frequently made difficult to perform experiments where high concentration in solution was required. Additionally, as discussed in chapter II, a lower solubility can be detrimental for the charge carrier pathways. Hence, improving their solubility became a necessity.

It was envisioned that one possible way to increase the solubility of the DPP core could be by adding alkyl chains to the thiophene rings. As one of the main objectives of using DPP as model system is to explore several derivatives and evaluate the effect of solubility in these compounds. Additionally, this step provided insight on how to synthesize DPP derivatives that bear flexible H-bonding groups that are not directly attached to the lactam ring (Figure III. 2).

Figure III. 2 Structural comparison between previous and new envisioned DPP derivatives.

Apart from studying the influence of solubility, the topology of the amide (N-or C-centered) was evaluated; a subtle, but very important parameter able to change the self-assembly of a given system and hence, the properties. [1,2] For instance, Philipps et al have compared the self-assembly behavior of a series of C2-and C3-symmetrical oligo(p-phenyleneethynylene)s (OPEs) [5] , (Figure III. 3), differing only in the amide topology, N-or C-centered. They reported how the delicate interplay between Hbonding and preorganization determines the evolution and final outcome of supramolecular nanostructures. The investigations were first carried out on linear OPEs (1 and 2), and these results were then compared with those obtained for the C3-symmetrical derivatives (3 and 4) to confirm the generalization of the trends found.

Figure III. 3 Chemical structures of OPEs 1-4.

The highlighted portions show the nature of amide connectivity, N-centered in blue and C-centered in pink.*Adapted. [5] The theory they presented along with the various experiments they performed, revealed how this subtle structural change brings about differences in their photophysical and supramolecular properties, such as molecular packing and aggregate morphology. One of their main findings was that a strong charge-transfer character for HOMO-LUMO excitations can significantly affect the emission characteristics in C-centered systems. Additionally, the N-centered molecules showed a much stronger HOMO-LUMO overlap than their C-centered counterparts, which is an indication of more allowed electronic transitions for the N-centered derivatives.

Furthermore, when variable-temperature UV/Vis studies were performed, significant differences in the optical properties caused by aggregation were observed for all molecules, especially when performed in a poor solvent such as methylcyclohexane. For instance, the emission studies of OPE 1 showed a slight fluorescence enhancement when the temperature was decreased. Moreover, for both N-centered OPEs 1 and 3, a blue shift of the absorption maximum along with the appearance of a red-shifted shoulder was observed, which are in accordance with a face-to-face stacking of the OPE units with a slightly twisted arrangement to favor H-bonding interactions.

On the other hand, the measurements of the C-centered OPEs in MCH gave rather different observations, for instance, unlike OPE 1, OPE 2 displays no increase in absorption. Additionally, AFM revealed a dissimilar interplay of non-covalent interactions, which resulted in distinct nanostructure morphologies for OPE 1 and OPE 2. While OPE 1 self-assembled into highly entangled fibers of several microns in length, OPE 2 formed considerably smaller round-shaped discrete aggregates.

Another system where the effect of the amide topology was evaluated was in the local molecular packing of different benzene-1,3,5-tricarboxamides with either C-centered or Ncentered amide groups (Figure III. 4). [2] It was shown that the 1 H-NMR spectra vary between the solution and the solid state due to the shielding impact of neighboring molecules and intramolecular polarization effects. This study also demonstrated that solid-state NMR in combination with Car-Parrinello Molecular Dynamics simulations and DFT calculations of NMR chemical shift is highly suited to elucidate the geometry of supramolecular assemblies. Furthermore, solid-state NMR provided unique insight into the dynamics of the N-centered derivative.

Figure III. 4 Chemical structure of the benzene-1,3,5-tricarboxamides derivatives with different amide topology.

These examples provided evidence on how changes in amide topology can influence the different properties of supramolecular assemblies. In the family described in this chapter, the position of the H-bonding units is maintained in the lactam rings while in the next chapter the impact of exchanging the H-bonding position within the conjugated structure will be explored.

In this sense, a succinic cyclization approach was envisioned, it consists of alkylating a thiophene ring and further functionalize it to finally perform the cyclization reaction that is normally used to obtain the DPP core. Particularly, I took care of the synthesis of the Ccentered amide, while another PhD student involved in the project, synthesized the N-center analogue. Together we characterized the self-assembly and optical properties. This synthesis is discussed in the next section.

II.

Results and Discussion

II.1) Synthesis

Molecules HDPPBA-C and HDPPBA-N were synthesized via a succinic cyclization approach (Scheme III. 1) starting with the functionalization of the thiophene ring and finalizing with a cyclization reaction to form the DPP core. Initially, the thiophene ring was alkylated with hexyl bromide (1) in high yield, and subsequently, a nitrile group was introduced in position 5 after replacement of a bromine atom obtaining (2) (Scheme III. 1). Then 5-hexylthiophene-2carbonitrile (3) reacted with diethylsuccinate in the presence of potassium t-butoxide to form the hexyl-functionalized thiophene-capped DPP main core (4) in 72% yield. In a last step, the lactam rings of the DPP were alkylated with the amide-containing branches that were synthesized in parallel.

The mesylated carbon-centered amide (-CONH) branch was synthesized as described in chapter II. On the other hand, Schotten-Baumann conditions were followed to obtain the Ncentered amide (-NHCO) branch (Scheme III. 2). In this case the acylation of 5-amino-1pentanol with heptanoyl chloride was carried out in a biphasic system of dichloromethane and a basic aqueous solution. The use of base drives the equilibrium of the reaction towards the formation of the amide, obtained in high yield (91%). Next, the N-centered amide was treated with methanesulfonyl chloride to achieve the mesylated amide-containing branch (Scheme III.

2).

Scheme III. 1 Synthetic route towards HDPPBA-C and HDPPBA-N.

The last step was the alkylation of the DPP core functionalized with hexyl tails in the thiophenes with the amide-containing branches. In this case, neither the N,O-and/or O,O'alkylated isomers were obtained, which are common side products of this reaction. In this sense, the starting material (4) seems to provide higher regioselectivity towards the N,N'alkylated products. It might be explained by the improved solubility of the starting material (introduction of hexyl groups in the thiophene vs previously reported DPP without functionalization in the thiophenes [6] ), the steric hindrance provided by the hexyl chains with respect to the DPP carbonyl groups, the lower reaction temperature (80 ºC in CH3CN vs 120 ºC in DMF) and the choice of base (cesium carbonate vs potassium carbonate).

The improved regioselectivity resulted in higher yields for the alkylation reactions in the lactams, reaching 30% in comparison to the same reaction using non-alkylated on the thiophene DPP derivatives reported in chapter II. The control molecule HDPPH was synthesized following the same strategy (Scheme III. 3) but the lactam rings were alkylated with hexyl bromide.

Scheme III. 2 Synthesis of the N-centered amide branch.

Scheme III. 3 Alkylation of ( 4) to obtain HDPPH.

II.2) Optical and self-assembly properties

The optical and self-assembly properties of HDPPBA-C, HDPPBA-N and HDPPH were followed with UV-Vis absorption in solution and on thin film at variable temperature in different solvents and concentrations, as well as by FTIR. The amide-containing derivatives and the control molecule display broad absorption bands ranging from 400 to 600 nm at 20 °C in chloroform with absorption maxima at  = 521 nm and  = 560 nm ( This band could be attributed to the formation of J-type aggregates, as observed for the other families of H-bonded DPPs previously described in chapter II and in literature. [6][7][8][9] Furthermore, the differences found between the amide derivatives and the control suggest that H-bonds are involved in the formation of such type of aggregate. This hypothesis was confirmed by measuring spectra upon the addition of methanol, finding the disappearance of the J-aggregate band (Figure III. 8) in the same way as it occurred for the previous bisamide DPP family.

When comparing to the previously described amide-containing DPPs in chapter II, where the α-position of the thiophene was not functionalized with hexyl tails, a bathochromic shift of 10 nm of the J-aggregate band was observed. To explore this difference, preliminary results u.)

 (nm)

1 mg/ml 0.5 mg/ml 0.25 mg/ml 0.125 mg/ml 0.06 mg/ml 0.03 mg/ml HDPPBA-N, RT, CHCl 3 300 400 500 600 700 800 0.0 0.5

u.)

 (nm) 20C 40C 60C
HDPPBA-N, 0.5 mg/ml, CHCl Even though HDPPBA-C and HDPPBA-N display aggregate bands, that are not present in the control molecule, differences between them could also be observed. HDPPBA-C presents a bathochromic shift in all the solvents compared to HDPPBA-N, and the J-aggregate is more pronounced in all the solvents tested, presumably as a sign of stronger aggregation in the Ccentered amide than in the N-centered derivative. This effect could be observed by the naked eye since solutions of both amide derivatives in the same solvent and concentration, have different colors (Figure III. 9).

Furthermore, the disappearance of the J-aggregate band was observed as well upon diluting ( FTIR spectra of powders at room temperature proved the existence of H-bonds in the bisamide derivatives. HDPPBA-C and HDPPBA-N showed a band a 3303 cm -1 assigned to the NH stretching bands of the amides. This frequency shows the amides are H-bonded (Figure III. 11 left). In the region between 1600 cm -1 and 1700 cm -1 , the amide derivatives and the control show peaks at 1655 cm -1 , corresponding to the amide I bands of the lactam rings of the DPP core. In the same area, the other peaks at 1641 cm -1 and 1637 cm -1 for HDPPBA-C and HDPPBA-N respectively, correspond to amide groups engaged in H-bonding (Figure III. 11 In the case of HDPPBA-C, a great disparity of fibers with different width and length were observed in toluene, ethyl acetate and cyclohexane (Figure III. 12a-e). The fibers are wavy, intertwined in bundles of rectangular size, and their length can exceed 15 mm. The structures in chlorobenzene are slightly different, finding elongated fibers as well, but narrower, less twisted than in the other solvents and with sharper edges. In chloroform, there are much smaller fibers that are straight and flat. These are the usual structures previously observed for the other DPP families studied in chloroform and it seems to be in part due to drying effects.

Regarding HDPPBA-N the structures observed are different from those of HDPPBA-C, finding very similar fibers in all the solvents except for chloroform (Figure III. 12f-j). Elongated fibers of up to 5 mm are found, but generally smaller than those of HDPPBA-C. They are wavy and twisted fibers, are very variable in size and they appear to be folded into several thin layers, well individualized. In the case of chloroform, the fibers are very different and in some areas of the sample, they resemble the fibers found in HDPPBA-C.

Taking into account the H-bonded DPP families previously described in chapter II, it can be seen that for this particular family there is less variety of morphologies than for the bisamides without functionalization in the thiophene rings or compared to the semicarbazone-based family [10] , especially for HDPPBA-N that self-assembles in almost identical morphologies in all of the tested solvents.

A similar effect is observed regarding the UV-Vis absorption data, while J-aggregates are present in all the families studied so far, in solvents that promote self-assembly, this band is the predominant one in certain solvents for HDPPBA, (S)-HDPPBA and (R)-DPPBA, where the thiophene rings are not substituted. It has been hypothesized that the increase of solubility could be the responsible for the different behavior of HDPPBA-C and HDPPBA-N, as well as the change in amide topology in the case of the N-center derivative, which seems to guide the assembly towards smaller aggregates. The photoconductivity values of HDPPBA-C and HDPPBA-N are very similar, being of 2.0 x 10 -5 cm -2 V -1 s -1 and 1.6 x 10 -5 cm -2 V -1 s -1 (Table III. 1, entries 4 and 5), respectively. These values are clearly larger than the value found for HDPPH, being 5.8 x 10 -6 cm -2 V -1 s -1 (Table III. 1, entry 6), one order of magnitude smaller than for the H-bonded derivatives. The kinetics decay of photoconductivity of HDPPBA-C and HDPPBA-N show that the photo-generated free charge carriers are stable up to more than 10 s. The recombination of charge carriers is slower for HDPPBA-C and HDPPBA-N than for the control molecule, with one order of magnitude longer lifetime: t1/2 equals 2 x 10 -5 s for HDPPBA-C and HDPPBA-N, and 8 x 10 -6 s for HDPPH (Table III. 1, entries 4-6).

1 m e) d) c) b) a) j) i) h) g) f) o) n) m) l) k)
These results highlight the beneficial role of H-bonding in this particular family and in extension, to the rest of the families explored so far. For the moment, the results for HDPPBA-C and HDPPBA-N are very similar since this technique measures photoconductivity at the nanoscale. However, measurements after solvent vapour annealing are being carried out by our collaborators in Kyoto to shed light on the effect of rearrangements in molecular packing after solvent exposure to compare the values to the previously measured families under the same conditions. Simultaneously, the molecular packing is being studied in our group using electron diffraction in cast samples and after thermal and vapor annealing. Once all these results are obtained, it will be possible to rationalize and complete the photoconductivity results. aggregate is more pronounced in all the solvents tested, presumably as a sign of stronger aggregation.

In the case of morphology, for this family there is less variety when compared to previous DPP derivatives, especially for the N-centered derivative that self-assembles in almost identical morphologies in all the tested solvents. It has been hypothesized that the increase of solubility could be the responsible for the different behavior of HDPPBA-C and HDPPBA-N, as well as the change in amide topology in the case of the N-center derivative, which seems to guide the assembly towards smaller aggregates.

The photoconductivities of HDPPBA-C and HDPPBA-N are very similar, but clearly larger than the value found for HDPPH, highlighting the beneficial role of H-bonding in this family and in extension, to the rest of the families explored so far. When comparing to the previously studied families, it can be observed that the recombination of charge carriers is comparable and that the photoconductivity values are lower. Interestingly, the recombination of charge carriers for chiral DPP derivatives is in the same order of magnitude as for the control molecule HDPPH not containing H-bonds in its structure, which indicates how important is to finely-tune the molecular design of H-bonded π-conjugated materials, since the most subtle change can dramatically impact the electronic properties. Interestingly, the photo-generated free charge carriers are stable up to more than 1 ms and more importantly, the recombination of charge carriers for HDPPBA-N was one order of magnitude slower than for the C-centered analogue. For now, our collaborators are following up with these results and the comparison to the rest of the derivatives shown in Chapter II.

III. Experimental

III.1) Materials and methods

All reagents and solvents were obtained from commercial suppliers and purified or dried according to standard procedures. Column chromatography was performed on silica gel (VWR Silica 60, particle size 0.040-0.063 mm). Solvents for spectroscopic studies were of spectroscopic grade and used as received. Elemental analysis was performed on a Thermofischer Scientific Flash 2000. Matrix-assisted laser desorption/ionisation-time of filght (MALDI) was performed in a Bruker Daltonics. 1 H and 13 C spectra were recorded in CDCl3 on a Bruker Avance 400 MHz spectrometer and/or Bruker Avance III HD 500 MHz spectrometer. UV-vis measurements were performed in a conventional quartz cell (light pass 1 mm) on a Cary 5000 UV-Vis-NIR spectrophotometer. TEM measurements were done with a Technai G2 (FEI) microscope with an accelerating voltage of 200 kV. 5 µL of the sample solution were deposited onto a freshly glow discharged carbon-covered grid (400 mesh). The suspension was left for 2 min, and then, the grid was negatively stained with 5 µL of uranyl acetate (2% in water) for another 1 min and finally blotted using a filter paper.

FTIR spectra were recorded with a Vertex 70 from Bruker Optics, equipped with MCT detector and a black-body source. The spectra of the solids were measured by ATR on diamond. The solutions were studied in cells from Specac Pike with KBr NaCl windows. For the VT experiments the solutions were inserted in a home-made cell between two NaCl windows. The cell was inserted in a Linkam heating stage, hold in a horizontal measurement chamber. The spectra were measured with the built-in MCT detector of the Vertex 70. The spectra were compensated from CO2 and moisture with OPUS from Bruker. The solvent intensities were measured separately and subtracted. The spin coated samples were prepared using a Spin 150 spin coater at 2000 rpm using 80 ml of solution on glass slides or silicon wafers.

Charge carrier mobilities were evaluated by FP-TRMC at room temperature. [START_REF] Wang | [END_REF][START_REF] Riede | Reference Module in Materials Science and Materials Engineering[END_REF] The thin films of samples were fabricated by drop-cast method onto quartz substrates (9 × 40 mm 2 , 1 mm thick). Charge carriers were injected into the materials via photo-ionization with a third harmonic generation (λ = 355 nm) of a Spectra Physics model INDI-HG Nd:YAG laser pulses at 10 Hz with a pulse duration of ca. 5 ns. The photon density of a 355 nm pulse was modulated from 4.5 × 10 15 photons cm -2 pulse -1 . The microwave frequency and power were set at ~9.1 GHz and 3 mW, respectively, and guided into a microwave cavity. The Q-factor of the microwave cavity loaded with the sample was 2200, and the substrates with the compound films were set at the point of electric field maximum. The reflected power of the probing microwave, picked up by a diode (rise time < 1 ns), was monitored by a Tektronics model TDS3032B digital oscilloscope after an amplification by Ciao Electronics CA812-304 FET amplifier system. The observed change in the reflected microwave power (ΔPr) was normalised with the steady reflection of the microwave from the cavity (Pr), and converted directly into the product of a photocarrier generation yield (f) and the sum of photo-generated electron/hole mobilities (Sm),

 = 1/(eI0Flight) × (/A) × (Pr/Pr) (1)
where e, A, I0, and Flight are elementary charge, sensitivity factor (S -1 cm), incident photon density of the excitation laser (photon cm -2 ), and filling factor (cm -1 ), respectively. The value of Flight was calculated based on the overlap of the area of photo-carrier injection (presumed to be proportional to the absorbance of excitation light by the sample film) with electric field strength distribution in the cavity derived from a calculation code of CST Microwave Studio from AET Inc.

III.2) Synthetic procedure

2-hexylthiophene (1)

In a 2-neck round bottom flask under inert atmosphere, 400 ml of anhydrous Tetrahydrofuran were added along with a magnetic stirrer. The thiophene (200 mmol, 1 eq, 33.66 g) was then added to form a solution, which was then cooled down to -78 °C for 30 mins by using an isopropanol and dry ice bath. Mixture became white in color, then a 2.3 M solution of n-Buthyl Lithium in hexanes (220 mmol, 1.1 eq, 95.66 ml) was added dropwise while the mixture was still at -78 °C and it was allowed to react for 1h. Finally, 1-bromohexane (220 mmol, 1.1 eq, 72.62 g) was added dropwise and the mixture was allowed to gradually warm up to room temperature by changing to an ice bath that eventually warmed up to room temperature, since the reaction was allowed to occur for 24 h. The flask and the ice bath were covered in aluminum foil to avoid having decomposition products due to light (halides give the solution an orange color). After 24 h, the mixture was cooled down back to 0 °C, diluted and quenched by adding 400 ml of distilled water. Extraction was performed by using diethyl ether (3x300 ml) and the organic phase was washed with 200 ml of a brine solution, the resulting organic phase was dried over anhydrous MgSO4 and filtered. Solvent was then evaporated, and a yellow oil remained as a mixture of 1-bromohexane and the product. Purification was performed by vacuum distillation at 0.4 mbar, a first distillate was recovered at 60 °C, 1bromohexane, temperature was then increased to 100 °C and a second distillate was recovered, compound

2-bromo-5-hexylthiophene (2)

In a 2-neck round bottom flask under inert atmosphere, 150 ml of a mixture of chloroform and acetic acid (1:1, v/v) were added along with a magnetic stirrer. N-bromosuccinimide (180 mmol, 1.1 eq, 32.7 g) was then added to form a solution, which was then cooled down to 0 °C for 30 mins by using an ice bath. Compound 1 (163 mmol, 1 eq, 27.56 g) was so added dropwise while the mixture was at 0 °C and it was allowed to gradually warm up to room temperature, as reaction occurred for 12 h. The flask and the ice bath were covered in aluminum foil to avoid decomposition of the N-bromosuccinimide due to light. After 12 h, the mixture was diluted by adding 150 ml of dichloromethane, the resulting organic phase was washed with a saturated solution of NaHCO3 (3x150 ml) and was dried over anhydrous MgSO4 and filtered. The organic phase was then evaporated. No purification was performed. Yield: dark yellow oil (38.94 g, 95%). In a 3-neck round bottom flask under inert atmosphere, coupled with a reflux apparatus, 600 ml of dimethylsulfoxide were added along with a magnetic stirrer. The copper cyanide (265 mmol, 1.6 eq, 24.25 g) was then added to form a solution, which was then warmed up to 50 °C for 30 mins by using an oil bath to ensure the copper cyanide was dissolved. Then Compound 2 (166 mmol, 1 eq, 38.94 g) was added dropwise while the mixture was still at 50 °C and temperature was increased to 140 °C, allowing it to react overnight. Afterwards, reaction was allowed to cool down to room temperature and 200 ml of a 30% (w/w) ammonia solution were slowly added, since some bubbling and heating occurred. Mixture was so diluted with distilled water to a final volume of 1200 ml and a distinctive dark blue color solution was obtained. This solution was washed several times with ethyl acetate (300 ml per washing), until the ethyl acetate washing was not getting colored (from dark yellow in the first washing to slightly colorless in the last). The organic layers were combined and dried over anhydrous MgSO4 and filtered, then the solvent was evaporated, and a dark brown oil remained. Purification was performed by Column Chromatography, using a mixture of cyclohexane: ethyl acetate (9:1) as the eluent. Yield: Dark yellow oil (16.25 g, 51%). 3,6-bis(5-hexylthiophen-2-yl)-2,5-dihydropyrrolo [3,4-c]pyrrole-1,4-dione (4) In a 3-neck round bottom flask under inert atmosphere, coupled with a reflux apparatus, the potassium t-Butoxide (92 mmol, 2.2 eq, 10.61 g), Compound 3 (84 mmol, 2 eq, 33.66 g) and 120 ml of t-amyl alcohol were added along with a magnetic stirrer. Mixture was stirred and warmed up to 120 °C for 30 mins by using an oil bath. Diethyl Succinate (42 mmol, 1 eq, 7.32 g) was added dropwise while the mixture was still at 120 °C, mixture became dark red in color upon addition of the diethyl succinate, reaction was carried overnight at 120 °C. Mixture was allowed to cool down to room temperature and 10 ml of acetic acid were used to neutralize the excess base, mixture turned dark purple. Purification was performed by filtering the mixture through a P16 fritted glass filter funnel and the solid product was put in the oven to dry overnight. Yield: Dark purple solid (14.24 g, 72%).

N-(5-hydroxypentyl)heptanamide

Heptanoyl chloride (4.1 mL, 26.5 mmol) dissolved in CH2Cl2 (50 mL) is added dropwise using an addition funnel to a solution of 5-amino-1-pentanol (3.1 mL, 27.1 mmol) in 0.2 M NaOH (50 mL). The reaction was vigorously stirred overnight. Next, the crude is extracted with CHCl3 (3x 100 mL). Then, the organic layers were collected and washed with water (2x 50 mL) and saturated brine (50 mL). The organic layer was dried over MgSO4 and the solvent evaporated under reduced pressure. The product is obtained as a white solid which is used in the next step without any further purification (5.4119 g, 91.0%). 1 H NMR (400 MHz, CDCl3) δ[ppm]: 6.20 (t, J = 5.8 Hz, 1Hh), 3.56 (t, J = 6.4 Hz, 2Hg), 3.17 (td, J = 7.0, 5.7 Hz, 2Hf), 2.10 (t, J = 7.7 Hz, 2He), 1.63 -1.41 (m, 6Hd), 1.40 -1.14 (m, 8Hc), 0.87 -0.75 (m, 3Ha).

5-heptanamidopentyl methanesulfonate

Mesyl chloride (1.1 mL, 14.2 mmol) was added dropwise to a solution of N-(5hydroxypentyl)heptanamide (1.5540 g, 7.2 mmol), Et3N (2.0 mL, 14.3 mmol) in dry THF (40 mL) at 0 °C. Then, the solution was let to reach room temperature and stirred for 3 h. After filtration, the solvent was vacuum evaporated, the crude dissolved in CHCl3 (100 mL) and washed with water (2x 100 mL) and saturated brine (100 mL). The organic layer was dried over MgSO4 and the solvent evaporated under reduced pressure. The crude product was purified by column chromatography using a cyclohexane-ethyl acetate (10 up to 100%) mixture. The desired product was obtained as a white solid (1.3103 g, 62.0%). 1 H NMR (400 MHz, CDCl3) δ[ppm]: 5.52 (s, 1Hi), 4.22 (t, J = 6.4 Hz, 2Hh), 3.25 (td, J = 6.9, 5.9 Hz, 2Hg), 3.00 (s, 3Hf), 2.15 (t, J = 7.5 Hz, 2He), 1.83 -1.72 (m, 2Hd), 1.67 -1.38 (m, 6Hc), 1.37 -1.21 (m, 6Hb), 0.87 (t, J = 7.0 Hz, 3Ha). Cs2CO3 (0.8861 g, 2.7 mmol) was added to a suspension of 4 (0.5021 g, 1.1 mmol) in acetonitrile (40 mL) and stirred at 80 °C for one hour under argon atmosphere. Then, the Ccentered amide chain (0.8861 g, 2.7 mmol) dissolved in acetonitrile (10 mL) was added dropwise during 20 min. The solution was stirred overnight at 80 °C. The reaction was allowed to cool to room temperature, the solvent was evaporated under vacuum. The residue was dissolved in CHCl3 (70 mL) and washed with water (3x 100 mL). The organic phase was dried over MgSO4 and filtered. Then, the solvent was vacuum evaporated. The crude product was purified by column chromatography using CHCl3-Methanol (0 up to 10%) as eluent. Finally, the product was recrystallized in a CHCl3-Methanol mixture to obtain HTDPPBA as purple flake-like solids (0.2868 g, 31.0%). In this chapter, the main objective is to explore and evaluate the effect of the position of the H-bond within the main core. Apart from studying the influence of the position of the H-bond moiety, the topology of the amide was evaluated once again. In this new family, the position of the H-bonding units has been changed to the thiophene rings (Figure IV. 1). The thiophene rings on the DPP were functionalized with amide branches, while regular alkyl chains were placed in the lactam rings. In general, thiophene capped DPP derivatives are functionalized in the thiophenes to serve as the starting materials in Pd-catalyzed cross-coupling reactions. Grzybowski et al reviewed the synthesis and reactivities of DPPs, where they discussed the substitutions that can be performed on the thiophene units of DPPs, these include couplings such as Suzuki, Stille, Buchwald-Hartwig and Sonogashira. [1] For instance, Suzuki and Stille couplings are employed most often for the synthesis of DPPbased -conjugated polymers. Such an example is shown in Scheme IV. 1, where a brominated thiophene derivative was used along with tributyl-(4-dodecyl-thiophen-2-yl)stannane under Stille conditions to extend the aromaticity of the DPP core and increase its solubility, to finally yield a polymer with ambipolar charge transport properties. [2] Scheme IV. 1 Summarized synthetic approach of an alkylated bithiophene DPP polymer derivative.

Another way the thiophene units on DPPs are functionalized is by creating oligomers, which is also done by Suzuki and Stille coupling. However, they have a major drawback: both reactions require the pre-activation of the substrates. For instance, the presence of reactive functional groups, such as bromine atoms in one of the species, and boronic or trialkyltin groups in the second component of the reaction. [3] While the introduction of bromine atoms is relatively easy, the synthesis of boronic acids/esters and organotin compounds is more troublesome.

An example with a DPP dimer was reported by Riaño et al, were they synthesized two dicyanovinylene-substituted DPP-oligothiophene semiconductors, DPP-4T-2DCV and 2DPP-6T-2DCV (Figure IV. 2). In these materials, the combination of an extended oligothiophene conjugated skeleton with the strong electron-withdrawing DPP-dicyanovinylene groups results in semiconductors exhibiting ambipolar response with reasonably balanced electron and hole mobilities. [4]

Figure IV. 2 Molecular structures of semiconductors DPP-4T-2DCV and 2DPP-6T-2DCV.

The synthesis of compound 2DPP-6T-2DCV is summarized in Scheme IV. 2. By using a monobromo DPP derivative and bis-tributyltin in refluxing toluene, a DPP dimer was obtained. They also discussed how this dimer can also be obtained by a Suzuki coupling reaction with bis-pinacolate diboron, but the yield was lower.

Scheme IV. 2 Summarized synthetic approach of dimer 2DPP-6T-2DCV.

Subsequently, the bromination of the dimer was performed with NBS in CHCl3, which was then followed by a Stille coupling with a thiophene stannyl derivative to afford an aldehyde DPP derivative after its respective hydrolysis in aqueous acid media. Subsequently, a Knoevenagel reaction with malononitrile yielded 2DPP-6T-2DCV. Following the same methodology, compound DPP-4T-2DCV was also obtained. 3) [5] , which are the closest structures to what we aimed to obtain. One of the pathways they discussed was a succinic cyclization approach that can be summarized as follows:

1) The synthesis of a carbonitrile bithiophene bearing alkyl chains by Stille coupling.

2) The use of the bithiophene in a reaction with diethyl succinate and sodium tert-amyl alkoxide to generate the DPP core.

3) The N-alkylation obtaining of the DPP core.

Scheme IV. 3 Summarized synthetic succinic cyclization approach of an alkylated bithiophene DPP derivative.

Yet, this is not the smallest thiophene alkylated DPP core that one can obtain and there is not a procedure describing such synthesis in the literature; furthermore, the previously discussed examples often contain unfunctionalized alkyl chains, which does not help in our quest of evaluating different flexible H-bonding groups pending on the thiophene.

Fortunately, in chapter III we presented that it is possible to synthesise DPP derivatives with pending alkyl chains on the thiophenes with a good yield. Therefore, we decided to perform the same succinic cyclization approach to synthesize a DPP bearing unfunctionalized alkyl chains on the lactam rings and with amide moieties pending from the thiophene rings.

Consequently, in this chapter a very detailed synthetic approach of two DPP derivatives with different topology and functionalized in the thiophene rings is presented. The synthesis of said derivatives was attempted by two different methods, the first one was inspired by the synthetic approach of Stas et al [5] , while the second one is a more direct approach. It is convenient to mention and discuss all the difficulties encountered for achieving these products.

The self-assembly processes of the N-and C-centered amide-containing DPP derivatives were also followed with different spectroscopy and microscopy techniques. The results are compared to the derivatives described in the previous chapter.

Particularly, I focused on the synthesis of the C-centered amides, optimizing the synthetic method that was then applied for the N-centered analogue synthesized by another student of the group. The synthetic comparison between both compounds will still be done to have a better understanding of the results.

II.

Results and Discussion II.1) Synthesis a) Succinic cyclization approach At first, the direct alkylation of a thiophene molecule with an amide arm having a mesylate functionality was attempted, but this reaction did not yield the desired product (Scheme IV. 4). It seemed that the mesylate group was not a good leaving group for this coupling and we replaced it by an iodine (Scheme IV. 5).

Scheme IV. 4 Failed attempt of a direct alkylation of a thiophene ring with amide arm.

optimized, as can be seen in Scheme IV. 9. The yield was greatly improved, as solubility was better, especially as the temperature increased.

Scheme IV. 9 Optimized conditions for the hydrolysis of the nitrile into a carboxylic acid.

The synthesis of the precursors with different topologies was the same from 4-C to 6-C and 4-N to 6-N, in this case only the C-centered route is shown in Scheme IV. 10.

Scheme IV. 10 Synthetic route of the C-centered thiophene with the pending amide.

The next major issue of this approach was found on the cyclization reactions, where compounds 6-C and 6-N were involved, as the target molecules were not being obtained. For both compounds the reaction mixture became green in color upon addition of the base.

Scheme IV. 16 Alternative DPP cyclization using an azide pending thiophene precursor.

Consequently, another alternative was put into practice, consisting on the cyclization reactions with compounds 16 and 18 as shown in Scheme IV. 15 and Scheme IV. 16 respectively, but the reactions did not work again, concluding that this approach was not suitable for thiophenes that had functional groups at the end of the added alkyl chain, being halogens or azides in these cases.

The reaction using compound 18 gave a white solution with no trace of the targeted DPP. On the contrary, the cyclization reaction using compound 16 gave a violet solid which seemed like DPP and the obtained solid was used to synthesize compound 19 (Scheme IV. 17). This reaction was monitored by IR due to the low solubility of the product and a small signal around 2200 cm -1 , belonging to the azide group, was detected. The intensity of this signal did not increase with longer reaction times. At this point, we concluded the reaction had finished.

Scheme IV. 17 Side chain functionalization of intermediate DPP compounds.

Next, to increase the solubility of product 19, an alkylation with 1-bromohexane was carried out. This reaction resulted in a red-brown solid, which was insoluble in common organic solvents like chloroform, tetrahydrofuran, methanol, cyclohexane (in which compound 20 should be at least partially soluble). It is possible that dimers or tetramers were being obtained by the reaction of the lactam nitrogen with the side chains in the thiophene containing either bromide or azide.

In a parallel reaction, reducing the azide groups in compound 19 was attempted to obtain compound 21, bearing free amines (Scheme IV. 17). Nevertheless, it was not possible to isolate derivative 21. Having exhausted this route, it was decided to change the synthetic strategy.

b) Direct approach

The possibility of performing a Sonogashira coupling to a DPP [8,9] was not yet explored and an attempt by using a dibrominated thiophene-capped DPP (compound 23) as the starting material was performed (Scheme IV. 18). Compound 8-C was obtained after hydrogenation at 60 °C using a mixture of solvents.

Scheme IV. 18 Final and reliable synthetic approach to obtain 8-C.

Similarly, the N-centered amide analogue was obtained following the strategy shown in Scheme IV. 19. In this case, the amide branch 24 was synthesized starting with a Mitsunobu reaction to obtain compound 23, followed by treatment with hydrazine and a coupling with heptanoyl chloride. In a next step, the amide branch (22-N) was coupled to compound 23 by Sonogashira coupling, yielding compound 24-N that was subsequently hydrogenated to the final N-centered DPP amide derivative 8-N.

Scheme IV. 19 Synthetic route towards compound 8-N.

This direct approach proved its versatility and will help in the synthesis of new DPP derivatives with functionalized alkyl chains pending from the thiophene rings.

II.2) Optical and self-assembly properties

The optical and self-assembly properties of 8-C and 24-C were followed with UV-Vis absorption in solution at variable temperature in different solvents and concentrations, and by FTIR. As usual with these derivatives, compound 8-C displays broad absorption bands ranging from 400 to 600 nm at 20 °C in chloroform with absorption maxima at  = 562 nm ( Furthermore, the alkyne precursors 24-C and 24-N are being investigated as well since the presence of the triple bond makes the self-assembly processes different despite having almost the same structure. Therefore, a comparison between compounds 8-C and 24-C was performed. For instance, when UV-Vis spectra of 24-C were measured in CHCl3, unlike for compound 8-C, a band can be observed and remains even upon dilution (Figure IV. 10a), and likewise, the disappearance of this band was not observed upon heating (Figure IV. 10b). Moreover, the color of the solutions was different and for 24-C, the spectra was red shifted and the additional band was observed at lower concentrations than in solutions of 8-C in CHCl3 where concentration was higher but the band was not present (Figure IV. 11). Finally, this band did not disappear upon addition of MeOH (Figure IV. 12). Ultimately, this signal is assumed to be a consequence of the extended conjugation of the DPP core, due to the triple bond next to the thiophene rings, which also gives a more rigid structure to the amide chain, inducing a planarization effect that might have an impact in π-π stacking, and creates stronger aggregates. FTIR spectra of powders at room temperature proved the existence of H-bonds in 8-C and 24-C. The first showed a band at 3295 cm -1 in the NH stretching area attributed to H-bonded amide bonds, whereas the latter showed it at 3299 cm -1 (Figure IV. 13a). In the region between 1600 cm -1 and 1700 cm -1 , both compounds show peaks at 1659 cm -1 , corresponding to the amide functions present in the lactam rings of the DPP core (Figure IV. 13b). Additional peaks at 1641 cm -1 and 1638 cm -1 for 8-C and 24-C, respectively were found in this area, corresponding to amide groups engaged in H-bonding like the peaks at 3295 cm -1 and at 3299 cm -1 . The difference of 3 cm -1 between the amide-containing derivatives indicates the subtle differences in aggregation. Furthermore, the IR also helped to confirm no traces of precursor remained, as the peak corresponding to the stretching of the disubstituted alkyne bond was observed at 2216 cm A FTIR powder spectra comparison between 8-C and HDPPBA-C was also performed, but no major differences were observed. The NH stretching signal attributed to H-bonded amide bonds was red-shifted by 3 cm -1 for 8-C, 3303 cm -1 for HDPPBA-C vs 3299 cm -1 for 8-C (Figure IV. 15a). In the region between 1600 cm -1 and 1700 cm -1 , both compounds show the corresponding peaks belonging to amide functions present in the lactam rings of the DPP core, this time blue shifted by 3 cm -1 (1655 cm -1 for HDPPBA-C and 1658 cm -1 for 8-C), as well as those corresponding to amide groups engaged in H-bonding (Figure IV. 15b). These small shifts may ultimately explain the changes in self-assembly observed by TEM. Nevertheless, these results were obtained in powder samples where the differences in aggregation are not so evident. Currently, the comparison of these derivatives is being done in solution at different solvents and concentrations to obtain more detailed information about the self-assembly process.

II.3) Conclusions

In conclusion, a new family of DPP derivatives with amides pending from the thiophene, as well as bearing different amide topology, were synthesized and are being characterized. More importantly, to our knowledge, we obtained the first derivatives where the basic DPP core bears functionalized alkylated thiophenes.

Furthermore, new DPP derivatives bearing alkyne bonds were also obtained and are being characterized. Like the previously obtained families, some of these new derivatives also aggregate and form J-type aggregates where H-bonds are involved.

The succinic cyclization approach seems to be limited, as it works best for thiophene rings that have alkyl chains without moieties, whereas the direct approach proved its versatility and will help in the synthesis of new and different DPP derivatives.

In the case of morphology, placing H-bonding groups in different positions seems to dramatically change the self-assembly processes, as it was found that these new derivatives were more soluble than the ones described in chapter III. This behavior was also reflected in the absorption spectra, where they show much smaller intensity in the J-aggregation bands.

The aggregates formed by 8-C seem like amorphous material not assembled into well-defined structures, unlike HDPPBA-C which does present well-defined high-aspect ratio structures.

FTIR spectra of powders at room temperature also proved the existence of H-bonds in these new derivatives and provided further proof that there are small spectra shifts, that may ultimately explain the changes in self-assembly.

The complete characterization of this family will be very important, for instance, the photoconductivity measurements and a more complete comparison of the influence of topology, will provide crucial data on future molecular design and elucidate the impact of the position of the H-bond with respect to the conjugated core.

III. Experimental

III.1) Materials and methods

All reagents and solvents were obtained from commercial suppliers and purified or dried according to standard procedures. Column chromatography was performed on silica gel (VWR Silica 60, particle size 0.040-0.063 mm). Solvents for spectroscopic studies were of spectroscopic grade and used as received. Elemental analysis was performed on a Thermofischer Scientific Flash 2000. Matrix-assisted laser desorption/ionisation-time of filght (MALDI) was performed in a Bruker Daltonics. 1 H and 13 C spectra were recorded in CDCl3 on a Bruker Avance 400 MHz spectrometer and/or Bruker Avance III HD 500 MHz spectrometer. UV-vis measurements were performed in a conventional quartz cell (light pass 1 mm) on a Cary 5000 UV-Vis-NIR spectrophotometer. TEM measurements were done with a Technai G2 (FEI) microscope with an accelerating voltage of 200 kV. 5 µL of the sample solution were deposited onto a freshly glow discharged carbon-covered grid (400 mesh). The suspension was left for 2 min, and then, the grid was negatively stained with 5 µL of uranyl acetate (2% in water) for another 1 min and finally blotted using a filter paper.

FTIR spectra were recorded with a Vertex 70 from Bruker Optics, equipped with MCT detector and a black-body source. The spectra of the solids were measured by ATR on diamond. The solutions were studied in cells from Specac Pike with KBr NaCl windows. The spectra were measured with the built-in MCT detector of the Vertex 70. The spectra were compensated from CO2 and moisture with OPUS from Bruker.

III.2) Synthetic procedure

2-(5-bromopentyl)thiophene (Compound 1).

Reaction was performed in two batches to have enough product for the purification step (vacuum distillation). Each batch was prepared as follows: In a 2-neck round bottom flask under inert atmosphere, 50 ml of anhydrous Tetrahydrofuran were added along with a magnetic stirrer. The thiophene (125 mmol, 1 eq, 10.6 g) was then added to form a solution, which was then cooled down to -78 °C for 30 mins by using an isopropanol and dry ice bath. Mixture became white in color, then a 2.3 M solution of n-Buthyl Lithium in hexanes (138 mmol, 1.1 eq, 60 ml) was added dropwise while the mixture was still at -78 °C and it was allowed to react for 1h.

Finally, 1,5-dibromopentane (138 mmol, 1.1 eq, 31.7 g) was added dropwise and the mixture was allowed to gradually warm up to room temperature by changing to an ice bath that eventually warmed up to room temperature, since the reaction was allowed to occur for 24 h. The flask and the ice bath were covered in aluminum foil to avoid having decomposition products due to light (halides give the solution an orange color). After 24 h, the mixture was cooled down back to 0 °C, diluted and quenched by adding 50 ml of distilled water. Both crudes were then combined, and the extraction was performed by using diethyl ether (3x300 ml), the organic phase was then washed with 200 ml of a brine solution. The organic phase was then dried over anhydrous MgSO4 and filtered.

Solvent was then evaporated, and a yellow oil remained as a mixture of 1,5-dibromopentane and the product. Purification was performed by vacuum distillation at 0.4 mbar, a first distillate was recovered at 110 °C, 1,5-dibromopentane, temperature was then increased to 150 °C and a second distillate was recovered, compound 1. Yield: slightly yellow liquid (29.09 g, 50%). ), 2.87 (q, J=7.8 Hz, 2Hd), 1.92 (q, J=9.5 Hz, 2Hc), 1.73 (q, J=10.0 Hz, 2Hb), 1.54 (q, J=10.0 Hz, 2Ha).

6-(thiophen-2-yl)hexanenitrile (Compound 2-C)

In a 2-neck round bottom flask, coupled with a reflux apparatus, 80 ml of DMSO were added along with a magnetic stirrer. The sodium cyanide (70.8 mmol, 1.1 eq, 3.58 g) and the potassium iodide (0.64 mmol, 0.01 eq, 0.11 g) were then added to form a solution, which was then warmed up to 50 °C for 30 mins by using an oil bath to ensure the salts were dissolved.

Compound 1 (64.3 mmol, 1 eq, 15.0 g) was so added dropwise while the mixture was still at 50 °C and then temperature was increased to 120 °C, allowing it to react overnight. Reaction was then allowed to cool down to room temperature, then diluted with distilled water to a final volume of 400 ml. Extraction was performed by using diethyl ether (3x300 ml), the organic phase was then dried over anhydrous MgSO4 and filtered. Solvent was then evaporated and compound 2-C was considered pure enough to follow with the next step. Yield: dark yellow oil (10.96 g, 95%).

6-(thiophen-2-yl)hexanoic acid (Compound 3-C)

In a round bottom flask coupled with a reflux apparatus, potassium hydroxide (175.7 mmol, 5 eq, 11.6 g) and 100 ml of a mixture comprised of Ethylene glycol/H2O (4:1) were added along with a magnetic stirrer to form a solution. Compound 2-C (35.1 mmol, 1 eq, 6.3 g) was then added and mixture was then heated up to 150 °C for 16 h by using an oil bath. Afterwards, reaction was allowed to cool down to room temperature and diluted with distilled water to a final volume of 600 ml. Then, 17.2 ml of 37% (w/w) HCl were slowly added, to neutralize the base. This solution was washed with diethyl ether (3x200 ml) and the organic layers were combined and dried over anhydrous MgSO4 and filtered, then the solvent was evaporated. A dark yellow oil remained, which became a waxy solid when left in the fume hood (during winter). Purification was performed by Column Chromatography, using chloroform as the In a round bottom flask, 100 ml of CH2Cl2 were added along with a magnetic stirrer. Compound 3-C (25.7 mmol, 1 eq, 5.1 g), hexyl amine (25.7 mmol, 1 eq, 3.4 g) and triethyl amine (77.2 mmol, 3 eq, 7.9 g) were then added and mixture was cooled down to 0 °C for 30 mins by using an ice/water bath. Afterwards, SOCl2 (25.7 mmol, 1 eq, 3.1 g) was added dropwise to the mixture, which thickened and became yellow in color, gas was also released upon addition of each drop. Reaction was allowed to continue at room temperature for 1 h. Mixture was diluted with CH2Cl2 to a final volume of 200 ml and the organic phase was then washed as follows: first with 75 ml of a 1 mol/l solution of HCl, then with 75 ml of a 1 mol/l solution of NaOH and finally with 75 ml of a saturated brine solution. Organic phase was then dried over anhydrous MgSO4 and filtered, then the solvent was evaporated. A yellow brownish solid remained. Purification was performed by Column Chromatography, using a mixture of Cyclohexane/Ethyl Acetate mixture (8:2) as the eluent. Yield: Slightly yellow solid (5.1 g, 70%). H NMR (400 MHz, CDCl3): δ 7.12 (dd, J=5.1 Hz, J=1.2 Hz, 1Hl), 6.93 (t, J=4.2 Hz, 1Hk), 6.79 (dd, J=2.8 Hz, J=1.0 Hz, 1Hj), 5.39 (s, 1Hi), 3.25 (q, J=6.9 Hz, 2Hh), 2.85 (t, J=7.8 Hz, 2Hg), 2.18 (t, J=7.6 Hz, 2Hf), 1.71 (m, J=10.2 Hz, 4He), 1.50 (t, J=6.5 Hz, 2Hd), 1.41 (q, J=5.8 Hz, 2Hc), 1.31 (m, 6Hb), 0.91 (t, J=6.2 Hz, 3Ha)

6-(5-bromothiophen-2-yl)-N-hexylhexanamide (Compound 5-C)

In a 2-neck round bottom flask under inert atmosphere, compound 4-C (11.4 mmol, 1 eq, 3.21 g) and 40 ml of a mixture of chloroform and acetic acid (1:1, v/v) were added along with a magnetic stirrer, mixture was then cooled down to 0 °C for 30 mins by using an ice-cold water bath. N-bromosuccinimide (12.6 mmol, 1.1 eq, 2.28 g) was then added at once while the mixture was at 0 °C and it was allowed to gradually warm up to room temperature, as reaction After 12 h, the mixture was diluted with CH2Cl2 to a final volume of 300 ml, the resulting organic phase was washed with a saturated solution of NaHCO3 (3x100 ml), extraction funnel was shaken carefully and properly vented, as gas is generated due to the neutralization of the acid. The organic phase was dried over anhydrous MgSO4 and filtered, then solvent was evaporated. No purification was performed as not many impurities were seen in the NMR spectrum. Yield: light brown solid (3.91 g, 95%).

6-(5-cyanothiophen-2-yl)-N-hexylhexanamide (Compound 6-C)

In a 3-neck round bottom flask under inert atmosphere, coupled with a reflux apparatus, 30 ml of DMSO were added along with a magnetic stirrer. The copper cyanide (16.1 mmol, 1.6 eq, 1.48 g) was then added to form a solution, which was then warmed up to 50 °C for 30 mins by using an oil bath to ensure the copper cyanide was dissolved. Then compound 6-C (10.1 mmol, 1 eq, 2.84 g) was dissolved in 10 ml of DMSO and this solution was added dropwise while the mixture was still at 50 °C, temperature was increased to 150 °C afterwards, allowing it to react overnight.

Afterwards, reaction was allowed to cool down to room temperature and 38 ml of a 30% (w/w) ammonia solution were slowly added, since some bubbling and heating occurred. Mixture was so diluted with distilled water to a volume of 200 ml, this solution was further diluted with brine solution to a final volume of 500 ml to avoid having emulsification. This aqueous solution had a distinctive dark blue color. This solution was washed several times with diethyl ether (150 ml per washing), until the diethyl ether washing was not getting colored (from dark yellow in the first washing to slightly colorless in the last). The organic layers were combined and dried over anhydrous MgSO4 and filtered, then the solvent was evaporated, and a dark oil remained. Purification was performed by Column Chromatography, using a gradual mixture of cyclohexane/ ethyl acetate (8:2) → (6:4) as the eluent. Yield: Dark yellow solid (1.88 g, 60 %). 1 H NMR (400 MHz, CDCl3): δ 7.45 (d, J=3.8 Hz, 1Hk), 6.79 (dt, J=3.8 Hz, J=0.9 Hz, 1Hj), 5.42 (s, 1Hi), 3.24 (dd, J=13.7 Hz, J=6.3 Hz, 2Hh), 2.85 (t, J=7.6 Hz, 2Hg), 2.16 (t, J=7.4 Hz, 2Hf), 1.70 (m, J=10.8 Hz, 4He), 1.48 (t, J=7.9 Hz, 2Hd), 1.40 (q, J=7.9 Hz, 2Hc), 1.29 (m, 6Hb), 0.89 (t, J=6.9 Hz, 3Ha)

6,6'-((3,6-dioxo-2,3,5,6-tetrahydropyrrolo[3,4-c]pyrrole-1,4-diyl)bis(thiophene-5,2-diyl))bis(Nhexylhexanamide) (Compound 7-C)

In a 2-neck round bottom flask coupled with a reflux apparatus, a solution of Compound 6-C (4.2 mmol, 2 eq, 1.30 g) and potassium tert-butoxide (4.7 mmol, 2.2 eq, 0.53 g) was stirred under argon atmosphere in tert-amyl alcohol. Mixture was heated up for 1 hour to 120°C by using an oil bath. Diethyl succinate (2.1 mmol, 1 eq, 0.37 g) was then added dropwise while the mixture was at 120°C. Mixture became dark red in color after 1 h and the solution was stirred at 120 °C overnight, and then cooled down to room temperature. The base was neutralized with 5 ml of concentrated acetic acid, upon this addition mixture thickened and changed to a dark purple color. The mixture was vigorously stirred for 2 hours at room temperature. The crude was filtered through a type 4 fritted glass funnel and washed several times with ice cold MeOH and dried to afford a dark purple solid. Purification was attempted In a round bottom flask coupled with a magnetic stirrer, Compound 3-C (6.8 mmol, 1 eq, 1.32 g), ethanol (13.7 mmol, 2 eq, 0.64 g) and 4-Dimethylaminopyridine (DMAP) (11.0 mmol, 1.6 eq, 1.3532 g) were dissolved in 30 ml of CH2Cl2. Mixture was then cooled down to 0 °C for 1 hour by using an ice-cold water bath, then a solution comprised of Dicyclohexylcarbodiimide (DCC) (15.1 mmol, 2.2 eq, 3.14 g) dissolved in 10 ml of CH2Cl2 was added dropwise at 0 °C. a b Reaction was allowed to happen for 3h at room temperature. A white precipitate formed, which was removed by filtration; the filtrate was diluted with diethyl ether to a final volume of 100 ml. The organic phase was washed with 2 N HCl (1x50 ml), water (1x50 ml), and brine (1x50 ml) and was then dried over anhydrous MgSO4 and filtered. After the solvent was removed, a slightly yellow powder remained. Purification was performed by Column Chromatography, using a mixture of Cyclohexane/Ethyl Acetate mixture (8:2) as the eluent. Yield: White powder with a faint yellow color (1.27 g, 82%). Hz, 1Hh), 6.80 (dd, J=3.1 Hz, J=0.9 Hz, 1Hg), 4.13 (q, J=7.2 Hz, 2Hf), 2.84 (t, J=7.7 Hz, 2He), 2.31 (t, J=7.5 Hz, 2Hd), 1.67 (m, J=7.4 Hz, 4Hc), 1.42 (q, J=7.6 Hz, 2Hb), 1.25 (t, J=7.2 Hz, 3Ha).

Ethyl 6-(5-bromothiophen-2-yl)hexanoate (Compound 11)

In a 2-neck round bottom flask under inert atmosphere, compound 10 (5.62 mmol, 1 eq, 1.27 g) and 20 ml of a mixture of chloroform and acetic acid (1:1, v/v) were added along with a magnetic stirrer, mixture was then cooled down to 0 °C for 30 mins by using an ice-cold water bath. NBS (6.18 mmol, 1.1 eq, 1.12 g) was then added at once while the mixture was at 0 °C and it was allowed to gradually warm up to room temperature, as reaction occurred for 12 h. The flask and the ice bath were covered in aluminum foil to avoid decomposition of the Nbromosuccinimide due to light. After 12 h, the mixture was diluted with CH2Cl2 to a final volume of 100 ml, the resulting organic phase was washed with a saturated solution of NaHCO3 (3x50 ml), extraction funnel was shaken carefully and properly vented, as gas is generated due to the neutralization of the acid. The organic phase was dried over anhydrous MgSO4 and filtered, then solvent was evaporated. No purification was performed as not many impurities were seen in the NMR spectrum. Yield: light brown solid (1.7 g, 99%). 1 H NMR (400 MHz, CDCl3): δ 6.84 (d, J=3.7 Hz, 1Hh), 6.53 (dt, J=3.8 Hz, J=0.8 Hz, 1Hg), 4.13 (q, J=7.2 Hz, 2Hf), 2.74 (q, J=8.5 Hz, 2He), 2.30 (t, J=7.5 Hz, 2Hd), 1.65 (m, J=6.8 Hz, 4Hc), 1.38 (q, J=4.5 Hz, 2Hb), 1.26 (t, J=7.2 Hz, 3Ha).

Ethyl 6-(5-cyanothiophen-2-yl)hexanoate (Compound 12)

In a 3-neck round bottom flask under inert atmosphere, coupled with a reflux apparatus, 20 ml of DMSO were added along with a magnetic stirrer. The copper cyanide (16.1 mmol, 1.6 eq, 1.48 g) was then added to form a solution, which was then warmed up to 50 °C for 30 mins by using an oil bath to ensure the copper cyanide was dissolved. Then compound 11 (5.6 mmol, 1 eq, 2.84 g) was dissolved in 10 ml of DMSO and this solution was added dropwise while the Afterwards, reaction was allowed to cool down to room temperature and 26 ml of a 30% (w/w) ammonia solution were slowly added, since some bubbling and heating occurred. Mixture was so diluted with distilled water to a volume of 200 ml, this solution was further diluted with brine solution to a final volume of 500 ml to avoid having emulsification. This aqueous solution had a distinctive dark blue color. This solution was washed several times with diethyl ether (150 ml per washing), until the diethyl ether washing was not getting colored (from dark yellow in the first washing to slightly colorless in the last). The organic layers were combined and dried over anhydrous MgSO4 and filtered, then the solvent was evaporated, and a dark oil remained. Purification was performed by Column Chromatography, using a gradual mixture of cyclohexane/ ethyl acetate (8:2) → (6:4) as the eluent. Yield: Dark yellow solid (0.35 g, 25 %). In a round bottom flask, 15 ml of CH2Cl2 were added along with a magnetic stirrer. Hex-5ynoic acid (8.7 mmol, 1 eq, 5.1 g), hexyl amine (8.7 mmol, 1 eq, 3.4 g) and triethyl amine (26.1 mmol, 3 eq, 7.9 g) were then added and mixture was cooled down to 0 °C for 30 mins by using an ice/water bath. Afterwards, SOCl2 (8.7 mmol, 1 eq, 3.1 g) was added dropwise to the mixture, which thickened and became yellow in color, gas was also released upon addition of each drop. Reaction was allowed to continue at room temperature for 1 h. Mixture was diluted with CH2Cl2 to a final volume of 100 ml and the organic phase was then washed as follows: first with 25 ml of a 1 mol/l solution of HCl, then with 25 ml of a 1 mol/l solution of NaOH and finally with 25 ml of a saturated brine solution. Organic phase was then dried over anhydrous MgSO4 and filtered, then the solvent was evaporated. A yellow brownish oil remained. Purification was performed by Column Chromatography, using a mixture of Cyclohexane/Ethyl Acetate mixture (1:1) as the eluent. Yield: Slightly yellow oil (0.77 g, 45%). (2,5-dihexyl-3,6-dioxo-2,3,5,6-tetrahydropyrrolo[3,4-

c]pyrrole-1,4-diyl)bis(thiophene-5,2diyl))bis(N-hexylhex-5-ynamide) (Compound 24-C)

In a 2-neck round bottom flask coupled with a reflux apparatus, Compound 23 (0.16 mmol, 1 eq, 0.10 g), N-hexylhex-5-ynamide (0.33 mmol, 2.1 eq, 0.065 g), (PPh3)2PdCl2 (0.02 mmol, 0.14 eq, 0.016 g) and CuI (0.01 mmol, 0.062 eq, 0.065 g), along with a magnetic stirrer, were dissolved in 10 ml of a mixture of THF/Diisopropylamine (4:1). Reaction was performed under argon atmosphere at 60°C. The mixture was stirred overnight and was then cooled down to room temperature. Mixture was diluted in 30 ml of distilled water and was then washed with CHCl3 (3x50 ml) and the organic phase was dried over MgSO4, filtered and the solvent was removed under vacuum. A dark bluish-purple solid remained, which was purified as follows: gradual column chromatography using CHCl3 as the eluent, then polarity was increased using a mixture of CHCl3/MeOH (99:1) as the eluent. The fractions containing what was suspected to be the product was kept apart, solvent was evaporated, and a dark bluish-purple solid remained. Upon 1 H-NMR product was confirmed but still had impurities, so a purification by precipitation was performed. Enough CHCl3 was used to solubilize most of the solid and when a large excess of MeOH was added, a precipitate formed, suspension was left in the fridge overnight and the precipitate was filtered and dried, yielding a dark bluish-purple solid (64 mg, 47%). (s, 2Hk); 4.04 (t, J = 7.7Hz, 4Hj); 3.27 (q, J = 6.7 Hz, 4Hi); 2.58 (t, J = 6.9 Hz, 4Hh); 2.36 (t, J = 7.4Hz, 4Hg); 1.99 (quin, J = 7.0Hz, 4Hf) 1.73 (quin, J=7.8 Hz, 4He); 1.54-1.48 (t, J = 6.7Hz, 4Hd), 1.46-1.40 (t, J = 7.7Hz, 4Hc); 1.37-1.29 (m, J = 4.5Hz, 20Hb); 0.89 (tq, J = 7.0 Hz, J=1.0 Hz, 12Ha).

6,6'-((2,5-dihexyl-3,6-dioxo-2,3,5,6-tetrahydropyrrolo[3,4-c]pyrrole-1,4-diyl)bis(thiophene-5,2diyl))bis(N-hexylhexanamide) (Compound 8-C)

Succinic cyclization approach

In a 2-neck round bottom flask coupled with a reflux apparatus, a suspension of cesium carbonate (1.04 mmol, 3 eq, 0.35 g) and Compound 7-C (0.35 mmol, 1 eq, 0.24 g) in 20 ml of acetonitrile was stirred under argon atmosphere at 82°C. The mixture was stirred for 1h at , then hexyl bromide (1.04 mmol, 3 eq, 0.18 g) was added dropwise. The solution was stirred overnight at 82°C and was then cooled down to room temperature. Solvent was evaporated from the crude, leaving a dark purple paste behind which was then dissolved in 200 ml of CHCl3.

Mixture was washed with distilled water (3x75 ml) and the organic phase was dried over MgSO4, filtered and the solvent was removed under vacuum. A dark purple solid remained, which was purified follows: column chromatography using a Toluene/MeOH (96:4) mixture as the eluent. The fraction containing what was suspected to be the product was kept apart, solvent was evaporated, and a dark purple solid remained. Upon 1 H-NMR product was confirmed but still had impurities, so a purification by precipitation was performed. Enough CHCl3 was used to solubilize most of the solid and when a large excess of MeOH was added, a precipitate formed, suspension was left in the fridge overnight and the precipitate was filtered and dried, yielding a purple solid (17.4 mg, 6%).

Direct approach

In a 3-neck round bottom flask Compound 24-C (0.05 mmol, 1 eq, 0.04 g) and 10% weight Pd/C (0.005 mmol, 0.1 eq, 0.005 g) were dissolved in 100 ml of a mixture consisting of Toluene/EtOH (1:1). Reaction was carried under hydrogen atmosphere at 60°C. The mixture was stirred for 2h at 60°C, and once it cooled down to room temperature, filtered through cotton with CHCl3 to remove the catalyst. Solvent was evaporated from the crude, leaving a dark purple solid behind, which was purified by column chromatography using a mixture consisting of CHCl3/EtOH (99:1) as the eluent. Product was recovered as a dark purple solid (48.4 mg, 90%). In the previous chapters we have shown the beginning of the comparative and systematic studies done on H-bonded -conjugated materials based on DPP. These initial families are guiding us towards the next steps in the molecular design of new components. So far, we have found that even subtle differences in the molecular structure among DPP families and the different self-assembly processes can impact the optoelectronic properties. Furthermore, other parameters such as sample preparation, solvent chosen, concentration and temperature can influence the H-bonding ability, making the optimization process very complex. In this sense, we are starting to work on the in-situ control over the morphology and electric properties to gather as much information as possible and build up a screening protocol.

We have shown the different morphologies observed in the H-bonded DPP systems depend on the conditions. In addition, morphology transformations in solution as well as on thin films have been reported by other groups, as demonstrated in electroluminescent self-assembled systems, [1][2][3] opening a new platform to study morphology conversion in different types of devices. However, the use of H-bonds has been minimally employed in electronic devices despite the positive results found, [4][5][6][7] possibly due to the time consuming process needed to find first, the best supramolecular structures and second, the optimal device conditions. Therefore, the long-term goal of this project is to measure device efficiency in real time while simultaneously changing the morphology using stimuli such as solvent vapour (Figure V. 1).

Figure V. 1 Real-time efficiency setup. A) First the donor-acceptor solution is deposited; B) Next, the morphology is changed continuously using solvent vapour, while measuring the energy conversion efficiency in real-time. C) Expected efficiency vs time output that will be used to identify the most efficient morphology.

The advantage of this approach over traditional device fabrication and testing cycles is that a great number of data points, such as efficiency vs. morphology, can be collected in a shorter time. Traditionally, many devices must be made, which is time consuming and only provides few scattered data points. This process can be even more tedious when testing completely new systems. In our case, the H-bonded groups will guide self-assembly into different morphologies, forming nanostructures in solution that subsequently will be deposited to form thin films.

The resulting films will be exposed to different solvents to provoke a change in film morphology as has been observed in previously reported work. [8][9][10] Specifically, we intend to use substrates with interdigitated electrodes of cathode and anode and drop cast solutions of Hbonded molecules. In this way, we can characterize device performance, without applying a top electrode (Figure V. 1). We note that this will not be the best arrangement to optimize output characteristics, but at this stage our device structure is aimed at getting good correlations, not the best performance.

Practically, the substrate coated with the film consisting of nanostructures will be placed in a container with a gas inlet and outlet. After a defined period of time, the vapour pressure is reduced, and device performance is quantified. The process (i.e., vapour in → vapour out → measure) can be programmed and run dozens of times, resulting in high fidelity data. It will be interesting to see the device performance during a large morphological change, for instance, when going from vesicles to interconnected films or from nanobelts to twisted fibres. This setup has been previously used by our team to control polymer crystallization on thin films using controlled solvent vapor annealing. [11] For instance, highly crystalline poly{[4,4-bisalkyl-cyclopenta-(2,1-b;3,4-b′)dithiophen]-2,6-diyl-alt-(2,1,3-benzo-thiadiazole)-4,7-diyl} (PCPDTBT) films were prepared by exposing them to either chlorobenzene or carbon disulphide, in a controlled solvent vapor annealing protocol. Both, chlorobenzene and carbon disulphide annealing induced the formation of a polymorph of PCPDTBT, only differing in the orientation of the polymer chains on the substrate. The electron diffraction patterns and the structural model of the polymorph did not give evidence for any efficient π-stacking and differed from the reflections reported in literature for films deposited by traditional device protocols.

These solvent-annealed films seemed to be quasi-equilibrated and were highly stable up to the melting point of the material. The difference in crystal structure was also reflected by the differing absorption spectra between the solvent-annealed and non-solvent annealed films. Furthermore, the potential of solvent vapor crystallization as an approach applicable to semicrystalline materials was highlighted. Lastly, the use of low boiling point solvents, demonstrated that it is possible to control the crystallization behaviour and to establish structure function relationships.

In this regard, our intention is to upgrade the setup by adding a properties analyser so we could choose an electronic parameter of interest. Nevertheless, before moving to our studies using this setup, we have studied several H-bonded DPP systems individually before and after exposure to solvent vapour and temperature. Particularly loss by 300 °C. This difference was attributed to the fact that HDPPH does not possess Hbonds and to the electron donating character of the alkyls chains. In fact, the introduction of hexyl chains to the nitrogen atoms breaks the planarity of the molecule, which upon heating causes easier defragmentation of the molecule. [12,13] Additionally, these derivatives do not seem to display polymorphism since the DSC traces of the three compounds only show one peak, which is unusual as it has been reported that symmetrical DPP derivatives with long alkyl chains attached to the lactam ring have a tendency to form different crystalline forms, resulting in occurrence of multiple peaks in DSC. [13] It is also possible that the DPP molecular skeleton has an influence on the alkyl chains via van der Waals interactions. In fact, the first carbons of an alkyl chain can be affected by the presence of a neighboring electron acceptor atom, having a great influence on the molecular motion of the whole chain. On the other hand, it is possible that the molecular motion is influenced by the whole DPP skeleton, and the hexyl chain length is not long enough to overcome the electrostatic interactions between adjacent DPP molecules. In this sense, further measurements at slower cooling/heating rates (i.e., 1 °C/min), as well as starting the DSC measurements at lower temperature (i.e., -80 °C) could shed more light on possible crystalline forms.

These results lay the groundwork for the next measurements, as thin films of these derivatives were studied under melting conditions.

II.2) Oriented thin films study

To have a better understanding on the assemblies formed by these derivatives, thin films were studied. Particularly, the structural orientation of the self-assembled molecules was followed by electron diffraction (ED) preparing films on different substrates. The first set of experiments consisted of drop casting these derivatives from a chlorobenzene solution at a concentration of 2.5 mg/ml, the samples were casted onto carbon TEM grids and blotted to remove excess of solvent.

The first derivative that was analyzed was HDPPBA-C, finding that the stacking direction of the DPP molecules is parallel to the fiber axis (Figure V. 6). Additionally, it was observed that the molecules form columns and are tilted with respect to the fiber axis. The diffractogram shows the periodicity of H-bonded amides as the typical distance of 4.9 Angstroms (Å). The next experiment that was performed aimed to see the impact that melting and recrystallization has on the orientation of the H-bonded aggregates. In this case the film was prepared on a polytetrafluoroethylene (PTFE) substrate by drop casting from solution and then In this case, the electron diffractograms showed that the fibers had the same structure as the drop cast samples previously studied, but the crystallization was better as there are noticeable stronger reflections (Figure V. 7).

As it was observed that it is possible to control the orientation of these aggregates through melting, the impact of solvent vapor on the orientation was also evaluated. For this experiment, drop cast thin films were subjected to chloroform vapor annealing (SVA) for 1 hour. HDPPBA-C displayed the same structure as the drop cast samples, but the films showed stronger reflections as a sign of better crystallization and orientation, with no streaking of reflections (Figure V. 8).

Another ED pattern taken from the same sample shows additional reflections from crystals with different contact planes (Figure V. 9). In this case, more streaking is observed on the l=1 layer line, indicating some disorder in the arrangement of columns. Interestingly, the minimization yielded a structure that is stable and shows nice H-bonds in the c-axis direction. This is fully consistent with the 4.9 Å periodicity along the stacking direction and explains why the DPP plane is tilted to the c-axis.

Furthermore, ED patterns for this model were calculated for planes [100] In the third ED pattern, the stacking direction of molecules is parallel to the PTFE chain direction and the structure is very close to that of HBDPPA-C (Figure V. 16). Additionally, the presence of Scherrer rings indicates the presence of mis-oriented material.

The presence of a dominant (100) contact plane with CDPP//CPTFE is somehow equivalent to edge-on orientation with respect to the substrate with the -stacking in plane and the amideside chains perpendicular to the substrate plane.

Lastly, HDPPH films were also studied, observing that crystals are formed and that the ED presents sharp reflections and high order (Figure V. 17), although no orientation was observed on the PTFE substrates. The diffraction pattern is similar to the H-bonded derivatives, and reticular distances are only slightly different. The ED pattern corresponds to edge-on crystals with side-chains normal to the substrate (100) contact plane. The similarity of ED with amides suggests that the packing is essentially driven by van der Waals interactions. In a next step, the orientation of the aggregates on thin film was evaluated placing the films under the polarized optical microscope (POM). The preparation protocol for the samples is described in (Figure V. 18).

The procedure consisted of two steps, first an isotropic solution of the DPP molecules in a given solvent was spread between the PTFE/glass substrate and a cover slip by capillarity. In this step it is important to make sure the molecules are completely solubilized; hence, the solution was heated above the isotropic temperature to reach dissolution of all aggregates. Lastly, the sample was moved to a colder surface to initiate the growth by reaching supersaturation, where heterogeneous nucleation occurs on the PTFE substrate and the orientation of DPP occurs. All three derivatives were used to prepare films on PTFE substrates, samples for HDPPBA-C and HDPPBA-N were prepared departing from a 2.5 mg/ml solution in chlorobenzene. The dichroic ratio (DR) value was 1.7 at 618 nm and it can be seen that not all features are equally polarized, for instance at 467 nm components are less polarized. Its contribution may add with the component at 618nm, hence reducing the apparent DR value. Nevertheless, low DR does not mean poor alignment. The transition dipole is certainly tilted to the stacking axis and this is why DR is small, similar to form beta of phthalocyanines. UV-vis measurements were also performed for thermally annealed films (Figure V. 30), in this case a change in the relative absorbance of the 637 nm band vs 497 nm band is observed, which explains the change in color when exposed to polarized light. This situation is similar to other DPPs studied by Genevaz et al. [14] In this case, it is assumed that the J-aggregate band at 637 nm is mostly polarized parallel to the PTFE chains and in strong contrast, the H-like band at 497 nm is weakly polarized along the PTFE, highlighting the fact that the two bands must have a different electronic origin. at a higher concentration, such as 10 mg/ml, which might also be used to do inverted OFETs on the oriented films and help us with the first experiments on the in-situ morphology control setup presented in the introduction of this chapter.

Furthermore, atomic force microscopy measurements of oriented HDPPBA-N films must be performed to check the morphology of the fibers before and after melt-crystallization. Additionally, to get out-of-plane structural information, grazing-incidence wide-angle X-ray scattering can be performed.

Moreover, adapting the protocol for the oriented growth on PTFE of HDPPBA-N from solution to other solvents, such as toluene and ethyl acetate, would help to evaluate the impact of different solvents.

Finally, performing the same type of experiments and analysis to the thiophene functionalized DPP derivatives that were described in Chapter IV would also help and complement these results, which will ultimately pave the way for real-time screening of organic electronic devices.

IV. Experimental

IV.1) Materials and methods TGA was performed by using a TGA 2 Mettler Toledo instrument, the sample was heated from 25 °C to 300 °C at a rate of 5 °C/min under nitrogen atmosphere at a flowrate of 20 ml/min. DSC was performed by using a DSC 8500 Perkin Elmer instrument, a first heating-cooling cycle was performed to remove any potential thermal history, then a second cycle was performed to measure the properties of each sample. The samples were heated from -10 °C to 300 °C at a rate of 5 °C/min under nitrogen atmosphere at a flowrate of 20 ml/min, and the cooling down was performed under the same rates and conditions. The film orientation was investigated by using a LEICA DM-2700 P microscope. The films were studied in bright field and diffraction modes with a 120 kV Philips CM12 electron microscope equipped with a MVIII charge-coupled device camera. UV-vis measurements were performed on a Cary 5000 UV-Vis-NIR spectrophotometer.

V.

In summary, in my thesis I have expanded the library of DPP molecules for the systematic and comparative studies based on DPP as a model (Figure 38, highlighting in light blue the families I have directly worked on). Parameters such as solubility, chirality, topology and position of the H-bonding functionality with respect to the DPP core were also investigated. Several characterization techniques were used to have a better understanding on the behaviour and properties of these molecules. For instance, UV-visible spectra revealed the formation of aggregates, usually attributed to J-type aggregates, depending on the nature of the solvent, concentration and temperature. Moreover, experiments were MeOH was added, and FTIR spectra confirmed the formation of H-bonds and their involvement in the aggregate formation. In the case of the amide containing DPP derivatives presented in chapter II, all three derivatives aggregate and form J-type aggregates, where H-bonds are involved (Figure 39). The aggregation is particularly strong in the chiral derivatives, which show aggregate signals in solvents where the achiral DPP is fully dissociated.

The photoconductivity measurements performed using FP-TRMC indicate that the achiral derivative has superior values of photoconductivity as well as slower recombination of the charge carriers.

As for the derivatives presented in chapter III, despite having mostly the same structure, but different amide topology and increased solubility, it was observed that the recombination of charge carriers and the photoconductivity values are comparable to the previously studied families.

Remarkably, the recombination of charge carriers for chiral DPP derivatives is in the same order of magnitude as for the control molecule HDPPH, containing no H-bonds in its structure, which indicates how important is to finely-tune the molecular design of H-bonded π-conjugated materials, since the most subtle change can dramatically impact the electronic properties.

Slight differences were observed for changes in topology, the C-centered derivative presents a bathochromic shift in all the solvents compared to N-centered derivative, and the Jaggregate is more pronounced in all the solvents tested, presumably as a sign of stronger aggregation. The photoconductivities of HDPPBA-C and HDPPBA-N are very similar, but clearly larger than the value found for HDPPH, highlighting the beneficial role of H-bonding in this family and in extension, to the rest of the families explored so far (Figure 40).

The family of DPP derivatives described in chapter IV is to our knowledge, the first derivatives where the basic DPP core bears functionalized alkylated thiophenes. The succinic cyclization approach seems to be limited, as it works best for thiophene rings that have alkyl chains without moieties, whereas the direct approach proved its versatility and will help in the synthesis of new and different DPP derivatives (Figure 41).

Figure 41

Final and reliable synthetic approach to obtain 8-C.

In the case of morphology, placing H-bonding groups in different positions seems to dramatically change the self-assembly processes. This behavior was also reflected in the absorption spectra, where they show smaller bands in the J-aggregate regions.

FTIR spectra of powders at room temperature also proved the existence of H-bonds in these new derivatives and provided further proof that there are small spectra shifts, that may ultimately explain the changes in self-assembly.

The complete characterization of this family will be very important, as it will provide crucial data on future molecular design and elucidate the impact of the position of the H-bond with respect to the conjugated core.

In chapter V, we have reported the first successful orientation of a self-assembled molecule on PTFE from solution. Additionally, from the obtained diffraction patterns, it was possible to construct a very simple model of the structures formed by these aggregates (Figure 42).

However, more studies such as AFM or GIWAXS are needed to complement and expand the scope of the results. Moreover, preparing thicker and continuous films might also be done to

Figure 3

 3 Figure 3 Représentation simplifiée d'une chaîne carbonée linéaire connectée par des liaisons  et .

Figure 6

 6 Figure 6 Exemples où des matériaux utilisés pour la fabrication des cellules solaires organiques portant de liaisons-H sont nuisibles (A et B) ou bénéfiques (C et D).

Figure 8

 8 Figure 8 Familles de DPPs portant des liaisons-H synthétisés jusqu'à présent dans l'étude systématique des DPPs comme système modèle.

Figure 9

 9 Figure 9 Comparaison structurelle entre la famille semicarbazone et la famille des bisamides.

Schéma 1

 1 Approche synthétique pour produire DPPBA, (S)-DPPBA et (R)-DPPBA. iii) Irradiation par micro-onde (P = 150 W, DMF, 2 h, 120 ºC pour (S)-DPPBA et P = 150 W, DMF, 2h, 70 ºC pour (R)-DPPBA). Une fois les molécules synthétisées, on a procédé à l'étude des propriétés optiques et d'autoassemblage. En particulier, on a utilisé les techniques spectroscopiques d'absorption d'UV/vis, d'infrarouge et de dichroïsme circulaire, en solution et à l'état solide, pour comprendre les processus d'assemblage des trois dérivés. La microscopie électronique en transmission (MET) a aussi été utilisée pour étudier la formation des structures supramoléculaires.

Figure 10 a

 10 Figure 10 a) Spectre d'absorption en chloroforme pour DPPBA, (S)-DPPBA et (R)-DPPBA. La concentration est de 2,5 mg/ml dans tous les trois cas. Spectres d'absorption dans différents solvants pour b) DPPBA ; c) (S)-DPPBA ; et d) (R)-DPPBA, la concentration est de 2,5 mg/ml pour tous les solvants, sauf pour le chloroforme (1.6 mg/ml) dans les figures c) et d).

  additionnelle à des énergies plus basses, vers 600 nm (Figure10a, lignes rouge et bleue).

Figure 11 Spectre

 11 Figure 11 Spectre IRTF à température ambiante dans du chloroforme deutéré pour (S)-DPPBA, (R)-DPPBA et DPPBA.

  qui met l'accent sur la formation d'agrégats, même à haute température (Figure12).

Figure 12

 12 Figure 12 Spectres d'absorption pour DPPBA dans le chlorobenzène, et pour (S)-DPPBA et (R)-DPPBA dans le toluène, lors de l'augmentation en température. La concentration dans tous les cas est de 2,5 mg/ml.

Figure 13

 13 Figure 13 Spectre de dichroïsme circulaire pour (S)-DPPBA et (R)-DPPBA dans une solution de toluène. [(S)-DPPBA] = [(R)-DPPBA] = 2,5 mg/ml. La Figure 13 montre un spectre de dichroïsme circulaire pour (S)-DPPBA et (R)-DPPBA à température ambiante. Des forts signaux ont été trouvés, spécialement à la longueur d'onde de l'agrégat J, indiquant un transfert de chiralité à travers les agrégats.

Figure 14

 14 Figure 14 Clichés de MET pour DPPBA (a-d), (S)-DPPBA (e-h) et (R)-DPPBA (i-l) dans chlorobenzène, toluène, cyclohexane et acétate d'éthyle respectivement. Après avoir exploré la capacité d'agrégation de ces molécules, leurs propriétés électriques ont été examinées. Les propriétés de photoconductivité ont été explorées en utilisant une technique sans électrodes basée sur la conductivité de micro-ondes (FP-TRMC). Ces mesures indiquent que DPPBA possède des valeurs supérieures de photoconductivité, ainsi qu'un temps de recombinaison des transporteurs de charge plus lent. Les mesures cinétiques de photoconductivité sont représentées sur la Figure 15 et les valeurs de la photoconductivité déduite sont reportées dans le Tableau 1.

Figure 15

 15 Figure 15 Cinétiques de la photoconductivité pour DPPBA (a), (S)-DPPBA (b) et (R)-DPPBA (c) échantillons déposés à partir du chloroforme. Cinétiques de photoconductivité pour DPPBA avant et après recuit en présence de vapeur d'acétate d'éthyle (d), avant et après recuit en présence de vapeur de méthanol (e) et après l'avoir immergé dans du méthanol (f).Tableau 1 Valeurs de photoconductivité des trois dérivés avant et après recuit en présence de vapeur de solvant.

Figure 17

 17 Figure 17 Spectres d'absorption en chloroforme à différentes concentrations et températures pour a), d) HDPPBA-C ; b), e) HDPPBA-N et c), f) HDPPB.

Figure 18

 18 Figure 18 Spectres d'absorption pour a) HDPPBA-C, b) HDPPBA-N et c) HDPPH à température ambiante dans différents solvants (chloroforme, chlorobenzène, toluène et acétate d'éthyle). Le spectre IRTF en poudre à température ambiante prouve l'existence des liaisons-H pour les dérivés amide. HDPPBA-C et HDPPBA-N présentent une bande vers 3303 cm -1 , attribué à l'élongation des groupes NH des amides. Cette fréquence révèle que les amides forment des liaisons-H (Figure 19 à gauche). Dans la région entre 1600 cm -1 et 1700 cm -1 , les composés amide et la molécule de contrôle, présentent un pic vers 1655 cm -1 , ce qui correspond à la bande amide I des lactames du noyau DPP. Dans cette même région, les pics vers 1641 cm - 1 et 1637 cm -1 pour HDPPBA-C et HDPPBA-N respectivement, correspondent à des groupes amide engagés dans des liaisons-H (Figure 19 à droite). Les bandes amide II se trouvent vers 1550 cm -1 et 1548 cm -1 pour HDPPBA-C et HDPPBA-N respectivement, ce qui démontre également que les groupes amide forment des liaisons-H. Ces bandes chevauchent la bande amide II du lactame, visible vers 1553 cm -1 pour HDPPH. La différence de 4 cm -1 entre les dérivés amide indique une légère différence dans la force des liaisons-H, ce qui peut induire de faibles différences d'agrégation.

Figure 19 SpectreFigure 20

 1920 Figure 19 Spectre IFTR en poudre de HDPPBA-C, HDPPBA-N et HDPPH. La morphologie de HDPPBA-C, HDPPBA-N et HDPPH a été étudiée par MET dans différents solvants (Figure III. 12). Des différences significatives sont observées lorsqu'on compare les dérivés capables de former des liaisons-H avec la molécule de contrôle. Tandis que HDPPBA-C et HDPPBA-N s'auto-assemblent dans des structures à haut rapport d'aspect, HDPPH forme des cristallites courtes d'approximativement 2 m en longueur, en se chevauchant les uns aux autres pour tous les solvants utilisés, sauf dans le cas du cyclohexane, où les structures sont plus étroites et élongées.

Figure 21

 21 Figure 21 Cinétique de photoconductivité pour HDPPBA-C, HDPPBA-N et HDPPH déposés à partir de solutions de chloroforme/toluène.

Figure 22

 22 Figure 22 Comparaison structurale pour le changement de la position du groupe amide dans les dérivés de DPP.

Figure 24 Figure 25

 2425 Figure 24 Spectres d'absorption de 8-C à température ambiante dans différents solvants. [8-C] = 0,5 mg/ml pour tous les solvants.

Figure 26 Figure 27

 2627 Figure 26 Spectres d'absorption pour 8-C pour lesquels la bande d'agrégats J disparaît lorsqu'on chauffe dans a) le chlorobenzène, b) le toluène et c) l'acétate d'éthyle. [8-C] = 0,5 mg/ml pour tous les solvants. A ce stade, bien que la caractérisation des molécules 8-C et 8-N ne soit pas complète, il ressort de la comparaison des résultats obtenus avec le dérivé HDPPBA-C (chapitre III) et la molécule 8-C, que la position de l'amide dans la structure moléculaire est fortement modifiée. Il a été observé également que les molécules ont un comportement différent pour la spectroscopie d'absorption UV-Vis, ainsi que pour la morphologie. Bien que les propriétés optiques du produit 8-C suivent un comportement similaire par rapport au reste des DPPs dé à étudiés, en présentant notamment des bandes d'agrégats de type J dans les solvants comme le chlorobenzène et le toluène (Figure 27, ligne bleue), il a été observé que 8-C est plus soluble que HDPPBA-C dans tous les solvants utilisés.

Figure 28

 28 Figure 28 Clichés par MET dans différent solvants pour HDPPBA-C (a-c) et 8-C (d-f).Les précurseurs alcynes 24-C et 24-N sont encore en cours d'étude, parce que la présence de la triple liaison change le processus d'auto-assemblage, même si la structure moléculaire est pratiquement la même.

  Figure 30 ATG pour a) HDPPBA-C b) HDPPBA-N et c) HDPPH.

Figure 31

 31 Figure 31 DSC pour a) HDPPBA-C b) HDPPBA-N et c) HDPPH.

Figure 32 À

 32 Figure 32 À gauche : Cliché de DE d'un film de HDPPBA-C déposé par goutte, à partir d'une solution de chlorobenzène, sur une grille de carbone pour MET. À droite : Cliché MET du film étudié.

Figure 33 À

 33 Figure 33 À gauche : Cliché de DE d'un film de HDPPBA-C qui a été recuit en présence de vapeur de chloroforme sur un substrat de PTFE. À droite : Cliché MET du film étudié.

Figure 34

 34 Figure 34 Structure générée par modélisation en utilisant les données obtenues des clichés de DE.

  les clichés de DE pour ce modèle ont été indexés pour les plans [100] et [010], et sont en accord avec les données expérimentales. Les mêmes expériences ont été réalisées pour HDPPBA-N et HDPPH. Dans l'étape suivante, l'orientation des agrégats sur des films à couche mince a été étudiée par microscopie optique polarisé (MOP). Les trois composés ont été utilisés pour préparer des films sur des substrats de PTFE, les échantillons de HDPPBA-C et HDPPBA-N ont été préparés en partant d'une solution de chlorobenzène à 2,5 mg/ml.

Figure 35

 35 Figure 35 Clichés d'un film de HDPPBA-N orienté sur du PTFE observé par MOP.Après un processus de fonte-recristallisation, les films ont été étudiés par DE à 4°C. Pour le film préparé sur du PTFE à 4°C, les clichés de DE présentent une diffraction étroite sur le plan (010), ce qui indique un degré d'alignement très élevé (Figure36). En plus, les films présentent des fibres orientées le long de la direction des chaînes du PTFE, ce qui signifie que la direction de l'empilement de HDPPBA-N est parallèle à CPTFE.

Figure 36 aFigure 37

 3637 Figure 36 a) Cliché de DE d'un film de HDPPBA-N formé sur du PTFE à 4°C et b) cliché obtenu par MET du film étudié.Après un recuit thermique, l'orientation est maintenue, et il n'y a pas de changement observé sur le plan de contact (Figure37). Les stries sur la couche de la ligne l=1 sont fortement réduites après le recuit. En outre, des réflexions plus nettes sont observées, ce qui implique une organisation des colonnes moléculaires adjacentes ainsi que les changements des spectres UV-Vis. La même séquence d'expériences a été réalisée pour HDPPBA-C et HDPPH.

Figure I. 2

 2 Figure I. 2 Simplified process flow chart of a typical PWR used to produce nuclear energy into electricity.Reproduced.[18]

Figure I. 4

 4 Figure I. 4 Cross section of the Earth's interior describing each layer.*Adapted.[35]

Figure I. 5

 5 Figure I. 5 How a silicon based photovoltaic cell works.*Adapted.[44]

Figure I. 11 .

 11 The anti-dibenzothienopyrrole (anti-DBTP) showed a 50 fold decrease in mobility in vacuum deposited organic field transistor devices (OFETs) when compared to its sulfur counterpart, dibenzo[d,d′]thieno[3,2-b;4,5-b′]dithiophene (D TDT);

Figure I. 15

 15 Figure I. 15 Schematic representations of the DPC method. (a) An organic semiconductor droplet pinned by a silicon wafer. As the solvent evaporates slowly, the crystals of the organic semiconductors nucleate near the contact line of the droplet. Subsequently, the nuclei grow along the receding direction (toward the center) of the droplet. (b) A magnified view of a white-marked area in (a), highlighting the contact line where a high nucleation density (right side) leads to unidirectional crystallization along the receding direction of the droplet, while a low nucleation density (left side) results in nondirectional crystallization. (c) DPC can be scaled up by using multiple pinners with larger sizes. Elongation of the pinner leads to unidirectional parallel alignment of the crystals.*Reproduced.[114]

3 Δ

 3 Figure I. 19 a) Molecular structures of oligothiophenes. b) Schematic representation of non-solvent vapor-induced crystallization in combination with lithographically controlled wetting.*Reproduced.[START_REF] Gentili | [END_REF]

  example of H-bonds are the natural building blocks of nucleic acids; therefore, H-bonds have always been considered very relevant interactions in biological processes, as molecular recognition between purine and pyrimidine bases in deoxyribonucleic acid (DNA)(Figure I. 22)

  Figure I. 25 Example of detrimental (A and B) and beneficial (C and D) cases of Hbonded materials in the fabrication of organic solar cells.

  the other hand, although the molecular structures of the examples shown in Figure I. 25C and Figure I. 25D are very different from the similar design of the previous two examples,

)

  Figure I. 27 The possible product structures in the alkylation of DPPs.

  3) H-bonding in DPP IV.3.1) Hydrogen-bonded DPP with unsubstituted lactam rings a) Structural characterization, crystallization, and optical properties 1,4-diketo-3,6-diaryl-pyrrolo-[3,4-c]-pyrrole as synthesized contains two unsubstituted lactams with ability to form H-bonds (Figure I. 26). In the solid state, there are chains of NH•••O intermolecular H-bonds between the NH group of one molecule and the O atom of the neighboring molecule forming linear chains. These H-bonds are necessary to align the transition dipole in a "head-to-tail" mode that results in a bathochromic shift of the absorption band when transitioning from the solution state to the solid state.

Figure I. 28

 28 Figure I. 28 Projection of the crystal structure of DPP a) onto the plane (b,c), b) onto the (a,c) plane.*Reproduced.[230]

Figure I. 29

 29 Figure I. 29 Absorption spectra of DPP-Ph in dimethyl sulfoxide (DMSO) solution and on evaporated thin film.*Reproduced.[230]

  6 x 10 -3 cm 2 /(V•s) were fabricated. The optical properties of NH BTTDPP1 and NH BTTDPP2 change dramatically when comparing solution to thin films (Figure I. 32b and c), initially just by spin coating and subsequently, by thermally annealing and cleaving the t-Boc groups. A bathochromic shift of 80 nm is observed in the absorption onset of NH BTTDPP1, while in NH BTTDPP2 the absorption onset red-shifts more than 200 nm.

Figure I. 32

 32 Figure I. 32 a) Molecular structures of NH BTTDPP1 and NH BTTDPP2. b) UV-Vis spectra of Boc-proteted NH BTTDPP1 in solution (green trace), thin film (blue trace), and NH BTTDPP1 (red trace). c) UV-Vis spectra of Boc-protected NH BTTDPP2 in solution (green trace), thin film (blue trace), and NH BTTDPP2 (red trace).*Reproduced.[253]

Furthermore, ambipolar

  behavior was reported for the three hydrogen-bonded DPP derivatives shown, being μh = μe = 0.01 cm 2 /(V•s) for DPP-Ph, μh of 0.03 and μe of 0.01 for the p-Cl DPP and μh of 0.06 and μe of 0.02 for p-Br DPP. The crystalline structures obtained are very important to understand the differences in mobility values. While in the phenyl derivative, the H-bonded chains are parallel to one another (Figure I. 33b) and parallel to the plane, which was the same for the para-halogenated DPPs but the chains were staggered relative to each other making two linear H-bonded chains run along the [001] plane, and other two chains run along the [002] plane, with a tilt with respect to the first chain (Figure I. 33c). The crystal structures were described as pseudo brick-wall π-π stacking. While no discrepancies in charge transport were expected for the three derivatives described, a difference in crystallite size was found. DPP-Ph formed crystal grains between 100-200 nm with clearly defined boundaries, p-Cl DPP had similar crystallites but oblong in shape, and p-Br DPP had smaller grains making very smooth films and more continuous. The higher mobility values found for p-Br DPP might be explained according to this morphology.

Figure I. 33

 33 Figure I. 33 Molecular structures of a) DPP, b) p-Cl DPP and c) p-Br DPP.[238]

Figure I. 35

 35 Figure I. 35 a) Thermo-cleavable polymer based on DPP. (b) Schematic illustration of solution-shearing technique.*Reproduced.[260]

  Figure I. 37A to C).

Figure I. 37

 37 Figure I. 37 Schematic representation of the preparation pathways used for device fabrication. Pathway 1 (top) shows the single step self-assembly of DPPPHP and PC71BM. Route 2 (bottom) shows the stepwise self-assembly of DPPHP prior to the addition of PC71BM. Cryo-TEM image of a DPPHP solution in toluene prepared following the stepwise self-assembly pathway. [DPPHP] = 7 mg ml -1 a). Cryo-TEM image of a DPPHP:PC71BM blend in a 1 : 1 ratio mixed for 30 seconds. [DPPHP] = 7 mg ml -1 and [PC71BM] = 27 mg ml -1b). AFM image of the active layer of a device fabricated by the stepwise self-assembly pathway c).*Reproduced.[188]

  Figure I. 40b). Such attenuation was not due to ground state charge transfer since the absorption spectrum of the DPP-Amide: PC71BM mixture did not show any additional bands, being the sum of the spectral features of both components (Figure I. 40a). These results indicate that the self-assembled structures of DPP-Amide are necessary to immobilize PC71BM aggregates and to facilitate the electron transfer process. Flash-photolysis time resolved microwave conductivity (FP-TRMC) was used to study charge carrier mobility and photovoltaic performance, which can be predicted by plotting transient photoconductivity vs different blending ratios of acceptor material. FP-TRMC measurements were performed on assembled (toluene) and disassembled samples (chloroform) of DPP-Amide using different ratios of PC71BM, finding a 5-fold increase in intrinsic conductivity for self-assembled films of DPP-Amide:PC71BM in 1.5:1-1:1.5 ratio (Figure I. 40c). No enhancement in conductivity was observed in DPP-Ester: PC71BM films.

Figure I. 40

 40 Figure I. 40 a) Absorption spectra of DPP-Amide aggregates (orange, dash), PC71BM (black, solid) and DPP-Amide : PC71BM (1 : 1 wt. ratio) hybrid assembly (red, dashdot). b) Emission spectra of DPP-Amide in toluene (λex=680 nm) with different blend ratio of PC71BM. c) The plot showing increase in photoconductivity of DPP-Amide and DPP-Ester upon addition of PC71BM(1 : 1 wt. ratio).*Adapted.[273]

Figure I. 42

 42 Figure I. 42 FP-TRMC transients of a) DPP-Amide, DPP-Amide:P3HT, and DPP-amide:PC71BM; b) DPP-Ester, DPP-Ester:P3HT, and DPP-Ester:PC71BM; and c) DPP-DCV, DPP-DCV:P3HT, and DPP-DCV:PC71BM. d) Comparison of ϕΣμ values of all the DPP derivatives in the absence and presence of P3HT and PC71BM.*Reproduced.[275]

Figure I. 44 DPP

 44 Figure I. 44 DPP derivatives whose aggregation was studied by Braunschweig et al.[282]

Figure I. 46

 46 Figure I. 46 a) Molecular structure of DPP-11a. b) Time-dependent absorption spectra of DPP-11a.*Adapted.[284]

Figure

  Figure I. 47 a) Chemical Structure of PDPP4T-T; Thymine groups are randomly connected to the conjugated backbone and the illustration of T-T Intermolecular Hbonding and the coordination with Pd(II) and Hg(II).*Reproduced.[285] b) Chemical Structures of pDPP4T-1, pDPP4T-2, pDPP4T-3, and pDPP4T, and illustration of the design rationale for the incorporation of urea groups in the side chains of conjugated D-A polymers.*Reproduced.[287] c) Chemical structures of DPP polymers containing lysine residues.*Reproduced.[288]

  DPP polymers based on DPP3T (dithienyl-DPP) containing different number of lysine derivatives (Figure I. 47c) were synthesized.

Figure I. 48

 48 Figure I. 48 Thiophene-capped DPP main structure, parameters to study and state-ofthe-art semiconductors.

  Apply to state-of-the art derivatives Diketopyrrolopyrrole

Figure I. 49 H

 49 Figure I. 49 H-bonded DPP families synthesized so far in the DPP model system study.

A

  (Figure II. 4a) forms one-dimensional supramolecular polymers, possibly by connecting via intermolecular H-bonding and π-π interactions. The CD spectra of C3 derivatives (Figure II. 4b), showed the formation of one-handed supramolecular helices under the same conditions.

Figure

  Figure II. 4 a) Chemical structures of propeller-shaped TPA derivatives. (b) Schematic illustration of the self-assembly of TPA monomers into supramolecular helices and chiral amplification through the sergeants and soldiers experiment. The green TPA monomer corresponds to a sergeant.

2 Figure II. 6

 26 Figure II. 6 Chemical structure of a triad DPP-helicene derivative.

Figure II. 7

 7 Figure II. 7 Chemical structure of the disubstituted myrtenal DPP derivative.

Figure II. 8

 8 Figure II. 8 a) Absorption spectra in chloroform of DPPBA, (S)-DPPBA and (R)-DPPBA. The concentration is 2.5 mg/ml in all cases. Absorption spectra in different solvents of b) DPPBA; c) (S)-DPPBA; and d) (R)-DPPBA. The concentration is 2.5 mg/ml for all solvents, except for chloroform (1.6 mg/ml).Initially we measured the compounds in chloroform (2.5 mg/mL), observing broad absorption bands ranging from 415 to 600 nm for the three derivatives at 20 °C (Figure II. 8a). The chiral derivatives showed an additional absorption band at lower energy at 600 nm (Figure II. 8a, traces red and blue). This band was not observed for DPPBA, even in saturated solutions (Figure II. 8a). This band could be attributed to the formation of J-type aggregates, as for other H-bonded DPP derivatives, including semicarbazone-containing DPPs reported earlier by our group.[10,47,48] This signal is related to the formation of H-bonds since it disappears when methanol, an H-bonding competing solvent, is added to (S)-DPPBA and (R)-DPPBA(Figure II. 9). So far, it was the first time that we observed aggregation bands in chloroform, which is normally a good solvent for the H-bonded DPP derivatives we have reported until the moment. The presence of such a band, already indicates the stronger aggregation tendency of the chiral derivatives in comparison to the achiral.

Figure II. 9

 9 Figure II. 9 Absorption spectra of (S)-DPPBA in chloroform (black trace) and after the addition of 4% volume of methanol (red trace).

  Figure II. 8 b to d).A shoulder band appears at approximately 480 nm in several solvents, attributed to the formation of H-type aggregates. It is particularly intense in chlorobenzene, toluene and cyclohexane. For (S)-DPPBA and (R)-DPPBA, the J-aggregate signal (λ = 600 nm) is the predominant one in toluene, cyclohexane and ethyl acetate, showing the strong formation of H-bonds in these conditions. In these solvents, like in the case of chloroform, the J-aggregate band disappears when methanol is added (Figure II. 12).

Figure

  Figure II. 10 a) FTIR spectra in deuterated chloroform at room temperature of (S)-DPPBA, (R)-DPPBA and DPPBA. b) CD spectra (S)-DPPBA and (R)-DPPBA in toluene solution. [(S)-DPPBA] = [(R)-DPPBA] = 2.5 mg/ml. Variable temperature CD spectra in toluene of (c) (S)-DPPBA and (d) (R)-DPPBA. c = 2.5 mg/ml.

Figure II. 11 FTIR

 11 Figure II. 11 FTIR spectra of (S)-DPPBA in deuterated chloroform at different temperatures. From 27 ºC to 59 ºC (red trace).

Figure II. 12

 12 Figure II. 12 Absorption spectra of (S)-DPPBA in chlorobenzene and (R)-DPPBA in toluene upon the addition of methanol (in vol %).

Figure II. 13

 13 Figure II. 13 a) Absorption spectra of (S)-DPPBA in toluene at different concentrations. b) Absorption spectra of (S)-DPPBA in chloroform at different concentrations. c) Absorption spectra of (R)-DPPBA in chloroform at different concentrations.

  us, with very simple semiconducting segments, to control the properties through aggregation.Dilution series and variable temperature measurements were performed to keep on exploring the aggregation process. The J-aggregate bands were observed upon diluting, still appearing at low concentrations in solvents that promote the formation of strong H-bonds (Figure II. 13). When the temperature increases, the J-aggregate band is still present, emphasizing the formation of aggregates even at high temperature(Figure II. 14).

Figure II. 14

 14 Figure II. 14 Absorption spectra of DPPBA in chlorobenzene, (S)-DPPBA and (R)-DPPBA in toluene upon increasing the temperature. The concentration is of 2.5 mg/ml in all cases.

Figure

  Figure II. 15 Absorption spectra of thin films of DPPBA, (S)-DPPBA and (R)-DPPBA drop cast from chloroform solutions at room temperature.

  To explore the chiral derivatives, CD spectroscopy in solution was used, finding signals with strong Cotton effect for the chiral derivatives, while no signal was observed for DPPBA even in aggregation conditions (FigureII. 16). Figure II. 10b shows the CD spectra in toluene for (S)-DPPBA and (R)-DPPBA at room temperature, where strong signals are found, especially at the J-aggregate wavelength as a sign of chirality transfer through the aggregates. Variable temperature CD was performed in several solvents, finding strong signals at low temperature that gradually disappear upon heating. The CD signal can be observed up to high temperatures, reaching 60-80 ºC, as evidenced in Figure II. 10c and d and Figure II. 17, where the variable temperature spectra in toluene were recorded.

Figure II. 16

 16 Figure II. 16 CD spectrum of DPPBA in chloroform, chlorobenzene, toluene, ethyl acetate and cyclohexane. [DPPBA] = 2.5 mg/ml.

Figure II. 17

 17 Figure II. 17 Variable temperature CD signal followed at 610 nm for (S)-DPPBA and (R)-DPPBA in toluene. [(S)-DPPBA] = [(R)-DPPBA] = 2.5 mg/ml.

Figure II. 18 Figure

 18 Figure II. 18 TEM images of chloroform prepared samples of a) DPPBA, b) (S)-DPPBA and c) (R)-DPPBA.

Figure II. 20

 20 Figure II. 20 TEM image of (S)-DPPBA in ethyl acetate.

Figure II. 21

 21 Figure II. 21 Sample preparation for the DPP bisamide derivatives. All the films are drop cast from chloroform (at a concentration of 5 mg/ml) to be subsequently exposed to ethyl acetate and methanol. The observed kinetic traces of conductivity transients are shown on Figure II. 22. The photoconductivity of DPPBA is evidently larger than those of (S)-and (R)-DPPBA (the values can be found in TableII. 1), even though photoconductivity (ΦΣµ) depends on the photo generation yield Φ. The kinetics decay of photoconductivity of DPPBA shows that the photogenerated free charge carriers are stable up to 10 μs. The recombination of charge carriers is slower in DPPBA than in (S)-and (R)-DPPBA, with one order of magnitude longer lifetime:

. 1 )

 1 was recorded in DPPBA after solvent annealing in ethyl acetate (Figure II. 22d), suggesting an efficient promotion of aggregated states of the molecule.

6 Figure II. 22

 622 Figure II. 22 Kinetic traces of photoconductivity transients of DPPBA (a), (S)-DPPBA (b) and (R)-DPPBA (c) cast from chloroform. Kinetic traces of photoconductivity traces of DPPBA before and after ethyl acetate vapor annealing (d), before and after methanol vapor annealing (e) and after soaking in methanol (f).

  Figure II. 23 Kinetic traces of photoconductivity transients of (S)-DPPBA (a) and (b) and (R)-DPPBA (c) and (d) before and after ethyl acetate (a) and (c) and methanol vapor annealing (b) and (d).

1 H

 1 -NMR (400 MHz, CDCl3): δ [ppm] 5.6 (s, 1Hj), 3.64 (td, J= 6.5 Hz, 5.1 Hz, 2Hi), 3.22 (td, J= 7.3 Hz, 5.7 Hz, 2Hh), 2.17 (t, J=7.5 Hz, 2Hg), 1.95 (t, J= 5.1 Hz, Hf),1.66 (quint, J= 7.6 Hz, 2He), 1.58 (quint, J= 7.0 Hz, 2Hd), 1.53-1.35 (m, 4Hc), 1.34-1.21 (m, 6Hb), 0.88 (t, J= 6.6 Hz, 3Ha).

1 H

 1 -NMR (400 MHz, CDCl3): δ [ppm] 5.48 (s, 1 Hj), 4.23 (t, J= 6.4 Hz, 3 Hi), 3.23 (td, J= 7,2 Hz, 5.8 Hz, 2Hh), 3.00 (s, 3 Hg), 2.17 (t, J= 7.4 Hz, 2 Hf), 1.78 (m, J= 7.1 Hz, 2He), 1.69 (m, J= 7.8 Hz, 2Hd), 1.47 (m, J= 7.4 Hz, 4Hc), 1.29 (m, 6 Hb) 0.89 (t, J= 6.5 Hz, 3Ha).

1

 1

1 H

 1 -NMR (400 MHz, CDCl3): δ [ppm] 5.21 (d, J= 7.9 Hz, 1Hk), 4.23 (t, J= 6.5 Hz, 2Hg), 3.97 (dtq, J = 8.6 Hz, 6.8 Hz, 6.4 Hz, 1Hj), 3.01 (s, 3Hh), 2.16 (t, J= 7.4 Hz, 2Hg), 1.78 (dq, J= 8.2 Hz, 6.5 Hz, 2Hf), 1.69 (t, J= 7.8 Hz, 2He), 1.44 (m, J= 7.3 Hz, 4Hd), 1.34-1.25 (m, 6Hc), 1.12 (d, J= 6.5 Hz, 3Hb), 0.88 (t, J= 6.6 Hz, 3Ha).

1 H

 1 -NMR (400 MHz, CDCl3): δ [ppm] 5.39 (d, J = 7.3 Hz, 1Hk), 3.95 (ddm, J = 8.5 Hz, 7.3 Hz, 6.3 Hz, 1Hj), 3.62 (t, J=6.5 Hz, 2Hi), 2.14 (td, J=7.4 Hz, 3.8 Hz, 2Hh), 1.75 (d, J= 4.3 Hz, 1Hg), 1.64 (m, J= 7.4 Hz, 2Hf), 1.57 (m, J= 6.9 Hz, 2He), 1.39 (dqd, J= 9.6 Hz, 6.7 Hz, 2.7 Hz, 4Hd), 1.29-1.24 (m, 6Hc), 1.09 (d, J= 6.6 Hz, 3Hb), 0.86 (t, J= 6.6 Hz, 3Ha).

1 H

 1 -NMR (400 MHz, CDCl3): δ [ppm] 5.21 (d, J= 7.9 Hz, 1Hk), 4.23 (t, J= 6.5 Hz, 2Hg), 3.97 (dtq, J = 8.6 Hz, 6.8 Hz, 6.4 Hz, 1Hj), 3.01 (s, 3Hh), 2.16 (t, J= 7.4 Hz, 2Hg), 1.78 (dq, J= 8.2 Hz, 6.5 Hz, 2Hf), 1.69 (t, J= 7.8 Hz, 2He), 1.44 (m, J= 7.3 Hz, 4Hd), 1.34-1.25 (m, 6Hc), 1.12 (d, J= 6.5 Hz, 3Hb), 0.88 (t, J= 6.6 Hz, 3Ha).

1 H

 1 -NMR (400 MHz, DMSO) δ [ppm]: 11.10 (s, 2Hd), 8.22 (d, J = 3.3 Hz, 2Hc); 7.88 (d, J = 4.7 Hz, 2Hb); 7.27 (t, J = 4.7 Hz, 2Ha).

13 C

 13 -NMR (400 MHz, CDCl3) δ [ppm]: 172.8 (2C13), 161.6 (2C12), 140.2 (2C11), 135.5 (2C10), 131.1 (2C9), 129.9 (2C8), 128.8 (2C7), 107.9 (2C6), 42.0 (2C5), 39.7 (2C4), 36.7 (2C3), 31.6, 29.8, 29.7, 26.7, 26.5, 25.4, 22.7 (2C2), 14.2 (2C1). HRMS (ESI) m/z 695.3659 (MH + ) Elemental analysis. Found: C, 64.88 %; H, 7.88 %; N, 8.06 %. Calculated: C, 65.67 %, H, 7.83 %; N, 8.06 %.

13 C

 13 -NMR (500 MHz, CDCl3) δ [ppm]: 171.9 (2C15), 161.4 (2C14), 140.0 (2C13), 135.3 (2C12), 130.8 (2C11), 129.7 (2C10), 128.7 (2C9), 107.7 (2C8), 45.3 (2C7), 42.0 (2C6), 37.0 (2C5), 36.8 (2C4), 31.8, 29.7, 26.5, 25.9, 25.5, 22.6 (2C3), 21.1 (2C2), 14.1 (2C1). HRMS (ESI) m/z 723.3972 (MH + ) Elemental analysis. Found: C, 66.01 %; H, 8.07 %; N, 7.63 %. Calculated: C, 66.45 %; H, 8.09 %; N, 7.75 %.

  dioxo-3,6-di(thiophen-2-yl)pyrrolo[3,4-c]pyrrole-2,5

13 C

 13 -NMR (400 MHz, CDCl3) δ [ppm]: 172.1 (2C15), 161.4 (2C14), 140.0 (2C13), 135.4 (2C12), 130.9 (2C11), 129.7 (2C10), 128.7 (2C9), 107.7 (2C8), 45.2 (2C7), 41.9 (2C6), 37.0 (2C5), 36.8 (2C4), 31.8, 29.7, 26.5, 25.9, 25.5, 22.6 (2C3), 21.0 (2C2), 14.1 (2C1). HRMS (ESI+) m/z: 723.3947 (MH+)

Figure III. 5 )

 5 . The three derivatives do not show any sign of aggregation in chloroform at 20 °C and the absorption bands do not change upon heating or changing the concentration (Figure III. 6 a-f). Additional absorption bands appeared at lower energy when HDPPBA-C and HDPPBA-N were measured in different solvents, such as chlorobenzene, toluene and ethyl acetate (Figure III. 7a and b) with max at 620 nm in chlorobenzene and toluene, and at 630 nm in ethyl acetate for HDPPBA-C, and max at 617 nm in chlorobenzene, 620 nm in toluene and 624 nm in ethyl acetate for HDPPBA-N. Interestingly, this band at lower energy was not observed for the control molecule HDPPH, which displayed equal spectra in all the solvents (Figure III. 7c).

Figure III. 5

 5 Figure III. 5 Absorption spectra of HDPPBA-C, HDPPBA-N and HDPPBH in chloroform solution at room temperature.

Figure III. 6

 6 Figure III. 6 Absorption spectra in chloroform at different concentrations and temperatures of HDPPBA-C ((a) & d)), HDPPBA-N ((b) & e)) and HDPPBH ((c) & (f)).

  , 0.5 mg/ml, CHCl 3 obtained from electron diffraction will be presented in chapter V, showing the molecular packing of the different H-bonded DPPs.

Figure III. 7

 7 Figure III. 7 Absorption spectra of a) HDPPBA-C, b) HDPPBA-N and c) HDPPH at room temperature in different solvents (chloroform, chlorobenzene, toluene and ethyl acetate).

Figure III. 8

 8 Figure III. 8 Absorption spectra for HDPPBA-C showing disappearance of the Jaggregate band upon addition of methanol at room temperature. [HDPPBA-C] = 0.625 mg/ml.

Figure III. 9

 9 Figure III. 9 Absorption spectra of HDPPBA-C, HDPPBA-N and HDPPH in chlorobenzene at room temperature and digital pictures of the solutions measured.

Figure III. 10

 10 Figure III. 10 Absorption spectra in chlorobenzene at different concentrations and temperatures of a) c) HDPPBA-C and b) d) HDPPBA-N.

  The amide II bands are located at 1550 and 1548 cm -1 for HDPPBA-C and HDPPBA-N respectively, which also shows the amide groups are H-bonded. These large bands overlap with the amide II band of the lactam, visible at 1553 cm -1 for HDPPH. The difference of 4 cm - 1 between the amide-containing derivatives indicates a slight difference in the strength of the H-bonds that can induce subtle differences in aggregation.

Figure III. 11

 11 Figure III. 11 FTIR powder spectra of HDPPBA-C, HDPPBA-N and HDPPH. The morphology of HDPPBA-C, HDPPBA-N and HDPPH was studied using TEM in different solvents (Figure III. 12). Clear differences were found when comparing the H-bonded derivatives to the control molecule. While HDPPBA-C and HDPPBA-N self-assemble into high aspect-ratio structures, HDPPH forms short tape-like crystallites of approximately 2 µm in length overlapping with each other in all the solvents tested except for cyclohexane, where the tape-like structures are narrower and longer (Figure III. 12k-o).

Figure III. 12

 12 Figure III. 12 TEM images of HDPPBA-C (a-e), HDPPBA-N (f-j) and HDPPH (k-o) in chloroform, chlorobenzene, toluene, ethyl acetate and cyclohexane, respectively. The samples were prepared by drop casting solutions at a 2.5 mg/ml onto carbon grids and blotting to eliminate the excess of solvent to avoid drying effects. Time dependent-DFT calculations were performed to rationalize the behavior of the amidecontaining derivatives, showing that the dihedral angles of HDPPBA-C and HDPPBA-N are different, the N-centered derivative being more like the control molecule (Figure III. 13).The control molecule is quite planar, with angles between the DPP core and the thiophenes of 5° and 15°, HDPPBA-N is very dissymmetrical, with angles of 0° and 20°. In contrast, the Ccentered derivative is the least planar of the three, with both angles of 20°. These results could rationalize the different molecular packing among these derivatives.

Figure III. 13 15 -

 1315 Figure III. 13 DFT calculations data. Minimized energy configurations and HOMO-LUMO topology.

Figure

  Figure III. 14 Kinetic traces of photoconductivity transients of HDPPBA-C, HDPPBA-N and HDPPH cast from chloroform/toluene solutions.

  Figure III. 15 Free charge carrier stability over time of HDPPBA-C and HDPPBA-N.

1 H

 1 NMR (400 MHz, CDCl3): δ 6.86 (d, 1Hf), 6.56 (d, 1He), 2.77 (t, 2Hd), 1.66 (q, 2Hc), 1.34 (m, 6Hb), 0.93 (t, 3 Ha).

1 H

 1 NMR (400 MHz, CDCl3): δ 7.44 (d, 1Hf), 6.79 (d, 1He), 2.84 (t, 2Hd), 1.68 (q, 2Hc), 1.31 (m, 6Hb), 0.89 (t, 3 Ha).

1 H

 1 NMR (400 MHz, DMSO-d6): δ, 8.0 (d, J = 3.8 Hz, 2Hf), 7.02 (d, J = 3.8 Hz, 2He), 2.88 (t, J=7.6 Hz, 4Hd), 1.68 (quin, J= 7.2 Hz, 4Hc), 1.32-1.26 (m, 12Hb), 0.87 (ddt, J=7.1 Hz, 4.7 Hz, 6 Ha).

  -(3,6-bis(5-hexylthiophen-2-yl)-1,4-dioxopyrrolo[3,4-c]pyrrole-2,5(1H,4H)-diyl)bis(Nhexylhexanamide) (HDPPBA-C)

1 H 13 C

 113 NMR (400 MHz, CDCl3) δ[ppm]: 8.72 (d, J = 3.9 Hz, 2Hk), 6.96 (d, J = 4.0 Hz, 2Hj), 5.47 (s, 2Hi), 4.05 (t, J = 7.6 Hz, 4Hh), 3.22 (dd, J = 7.3, 5.8 Hz, 4Hg), 2.90 (t, J = 7.6 Hz, 4Hf), 2.17 (t, J = 7.5 Hz, 4He), 1.82 -1.65 (m, 12Hd), 1.51 -1.35 (m, 12Hc), 1.35 -1.23 (m, 20Hb), 0.91 -0.85 (m, 12Ha). NMR (101 MHz, CDCl3) δ[ppm]: 172.78 (2C13), 161.55 (2C12), 153.06 (2C11), 139.84 (2C10), 135.71 (2C9), 127.41 (2C9), 126.25 (2C7), 107.14 (2C6), 41.90 (2C5), 39.67 (2C4), 36.77 (2C3), 31.62, 31.59, 30.48, 29.79, 29.72, 28.93, 26.73, 26.53, 25.43, 22.70 (4C2), 14.15 (4C1). Theoretical m/z: 862.5464, HR-MS (ESI-TOF): 885.5358 [M+Na] + .Elemental analysis for C50H78N4O4S2: calculated: C, 69.56 %; H, 9.11 %; N, 6.49 %. Found: C, 69.03 %; H, 9.17 %; N, 6.49 %.

  Theoretical m/z: 862.5464, HR-MS (ESI-TOF): 863.5537 [M + H] + .

Figure IV. 1

 1 Figure IV. 1 Structural comparison for the change in position of the amide group in DPP derivatives.

Figure IV. 3

 3 Figure IV. 3 Structure of a DPP core bearing functionalized alkylated chains directly attached to the thiophenes of the core. It has been shown that examples including functionalization of the thiophenes in the DPP core exist in literature. Although, most of these approaches are generally used to extend the conjugated DPP core by adding more thiophene rings, while examples where the basic DPP core bears functionalized alkylated thiophenes (Figure IV. 3) are non-existent in the literature.Stas et al discussed and optimized several synthetic approaches to obtain DPPs bearing bithiophene moieties (Scheme IV. 3)[5] , which are the closest structures to what we aimed to obtain. One of the pathways they discussed was a succinic cyclization approach that can be summarized as follows:

Figure IV. 4 )

 4 ; although it did not show any sign of aggregation in chloroform at 20 °C and the absorption bands did not change upon increasing the concentration (Figure IV. 5a). Additional absorption bands appeared at lower energy when 8-C spectra were measured in different solvents, such as chlorobenzene, toluene, and ethyl acetate. In chlorobenzene, the max of this band was at 621 nm in toluene, at 622 nm in chlorobenzene, and at 629 nm in ethyl acetate (Figure IV. 4). This band was attributed to the formation of J-type aggregates and its intensity decreased upon dilution and heating, like for the previously described families of H-bonded DPPs (Figure IV. 5b-d and Figure IV. 6, respectively); this was once again confirmed by measuring spectra upon the addition of methanol, finding the disappearance of the band in the same way as for the other H-bonded DPPs already described (Figure IV. 7).

Figure IV. 4

 4 Figure IV. 4 Absorption spectra of 8-C at room temperature in different solvents. [8-C] = 0.5 mg/ml in all solvents.

Figure IV. 5

 5 Figure IV. 5 Absorption spectra of 8-C at different concentrations, at room temperature in a) chloroform, b) chlorobenzene, c) toluene and d) ethyl acetate.

Figure IV. 6 Figure IV. 7

 67 Figure IV. 6 Absorption spectra of 8-C showing the disappearance of the J-aggregate band upon heating in a) chlorobenzene, b) toluene and c) ethyl acetate. [8-C] = 0.5 mg/ml for all solvents.

Figure IV. 8

 8 Figure IV. 8 Absorption spectra of HDPPBA-C and 8-C in toluene and chlorobenzene at the same concentration at room temperature.

Figure IV. 9

 9 Figure IV. 9 TEM images in different solvents of HDPPBA-C (a-c) and 8-C (d-f).

Figure IV. 10

 10 Figure IV. 10 Absorption spectra for compound 24-C in CHCl3 at different a) concentrations and b) temperatures.

Figure

  Figure IV. 11 Spectra comparison between 8-C and 24-C. [8-C] = 0.5 mg/ml vs [24-C] = 0.31 mg/ml.

Figure IV. 12

 12 Figure IV. 12 Absorption spectra for 24-C upon addition of methanol at room temperature. [24-C] = 1.25 mg/ml in CHCl3.

  -1 only for 24-C (Figure IV. 14).

Figure IV. 13 FTIR powder spectra of 8 -C and 24 - 1 )

 138241 Figure IV. 13 FTIR powder spectra of 8-C and 24-C.

Figure IV. 15 FTIR

 15 Figure IV. 15 FTIR powder spectra of 8-C and HDPPBA-C.

1 H

 1 NMR (400 MHz, CDCl3): δ 7.13 (dd, J=5.2 Hz, 1.0 Hz, 1Hg), 6.93 (dd, J=5.4 Hz, J=5.4 Hz, 1Hf), 6.80 (dt, J = 2.2 Hz, 1.8 Hz, 1He), 2.87 (t, J=7.4 Hz, 2Hd) , 2.35 (t, J=7.3 Hz, 2Hc), 1.72 (m, J=4.5 Hz, 4 Hb), 1.54 (m, J=7.6 Hz, 2 Ha).

13 C-NMR. 1 H 13 C

 13113 : Slightly yellow oil/ wax (5.58 g, 80%). Product was confirmed by 1 H NMR and NMR (400 MHz, CDCl3): δ 11.49 (s, 1Hh), 7.12 (dd, J=5.1 Hz, J=1.1 Hz, 1Hg), 6.93 (t, J=4.3 Hz, 1Hf), 6.80 (dd, J=3.3 Hz, J=0.9 Hz, 1He), 2.85 (t, J=7.7 Hz, 2Hd), 2.37 (t, J=7.5 Hz, 2Hc), 1.70 (m, J=8.8 Hz, 4Hb), 1.44 (m, J=7.8 Hz, 2Ha). NMR δ 179.4 (1C10), 145.3 (1C9), 126.7 (1C8), 124.1(1C7), 122.9 (1C6), 33.8 (1C5), 31.4 (1C4), 29.7 (1C3), 28.5 (1C2), 24.5 (1C1). -6-(thiophen-2-yl)hexanamide (Compound 4-C)

  h. The flask and the ice bath were covered in aluminum foil to avoid decomposition of the N-bromosuccinimide due to light.

1 H

 1 NMR (400 MHz, CDCl3): δ 6.84 (d, J=3.7 Hz, 1Hk), 6.53 (dt, J=3.5 Hz, J=0.6 Hz, 1Hj), 5.44 (s, 1Hi), 3.23 (dd, J=13.1 Hz, J=7.1 Hz, 2Hh), 2.75 (t, J=7.6 Hz, 2Hg), 2.15 (t, J=7.6 Hz, 2Hf), 1.65 (m, J=8.7 Hz, 4He), 1.48 (t, J=7.5 Hz, 2Hd), 1.38 (q, J=8.4 Hz, 2Hc), 1.29 (m, 6Hb), 0.89 (t, J=6.8 Hz, 3Ha)

1 H

 1 using a CHCl3/MeOH (98:2) mixture. A purple solid was obtained (0.10 g, 7 %) which was assumed to be the product by the 1 H NMR spectrum, as the expected aromatic signals from the protons in thiophenes could be observed. Product was used like this for the next step (despite the integration of signals in the aliphatic region of the spectrum did not match with what was expected). NMR (400 MHz, CDCl3): δ 7.81 (d, J=3.8 Hz, 1Hb), 6.94 (dt, J=3.8 Hz, J=0.9 Hz, 1Ha) Ethyl 6-(thiophen-2-yl)hexanoate (Compound 10)

1 H

 1 NMR (400 MHz, CDCl3): δ 7.11 (dd, J=5.1 Hz, J=1.1 Hz, 1Hi), 6.92 (dd, J=5.2 Hz, J=3.4

  at 50 °C, temperature was increased to 150 °C afterwards, allowing it to react overnight.

1 H

 1 NMR (400 MHz, CDCl3): δ 7.48 (d, J=3.8 Hz, 1Hh), 6.82 (dt, J=3.7 Hz, J=0.9 Hz, 1Hg), 4.15 (q, J=7.1 Hz, 2Hf), 2.88 (t, J=7.6 Hz, 2He), 2.33 (t, J=7.4 Hz, 2Hd), 1.71 (m, J=8.7 Hz, 4Hc), 1.4 (q, J=3.7 Hz, 2Hb), 1.27 (t, J=7.1 Hz, 3Ha), -5-ynamide (Compound 22-C)

1 H

 1 NMR (400 MHz, CDCl3): δ 5.64 (s, 1Hi), 3.23 (td, J=7.2 Hz, J=5.8 Hz, 2Hh), 2.29 (t, J=7.4 Hz, 2Hg), 2.25 (td, J=6.4 Hz, J=2.8 Hz, 2Hf), 1.96 (t, J=2.7 Hz, 1He), 1.85 (m, J=7.2 Hz, 2Hd), 1.48 (md, J=7.1 Hz, J=2.2 Hz, 2Hc), 1.32-1.25 (m, 6Hb), 0.87 (t, J=6.9 Hz, 3Ha).

1 H

 1 -NMR (400 MHz, CDCl3) δ [ppm]: 8.85 (d, J = 4.1 Hz, 2Hm); 7.25 (d, J = 4.2 Hz, 2Hl), 5.47

1 H

 1 -NMR (400 MHz, CDCl3) δ [ppm]: 8.68 (d, J = 3.9 Hz, 2Hk); 6.93 (d, J = 3.9 Hz, 2Hj); 5.38 (s, 2Hi); 4.00 (t, J = 7.9Hz, 4Hh); 3.21 (dt, J = 7.7 Hz, 6.1 Hz, 4Hg); 2.89 (t, J = 7.6 Hz, 4Hf); 2.14 (t, J = 7.6Hz, 4He); 1.76-1.65 (m, J=7.1 Hz, 8Hd); 1.45-1.42 (m, J = 3.6 Hz, 4Hc); 1.34-1.20 (m, J=8.1 Hz, 32Hb); 0.86 (t, J = 7.9Hz, 12Ha).

  At the moment, we have a similar setup in our group (made by Dr. Martin Brinkmann and Laurent Herrmann) that will allow us to observe in real time the morphology changes upon solvent vapor annealing and temperature (Figure V. 2).

Figure V. 2

 2 Figure V. 2 Solvent vapor annealing setup connected to an optical microscope and a Keithley machine.

  , we have explored the DPP derivatives presented in chapter III: HDPPH, HDPPBA-C and HDPPBA-N (Figure V. 3). The work shown in this chapter is the fruit of a collaboration with Dr. Martin Brinkmann from our group, an expert on alignment techniques and electron diffraction.

Figure V. 3

 3 Figure V. 3 Chemical structure of the studied derivatives in this chapter.

Figure V. 4

 4 Figure V. 4 TGA of a) HDPPBA-C b) HDPPBA-N and c) HDPPH. From the data collected from these experiments, it was possible to determine the conditions required to perform the differential scanning calorimetry (DSC). This measurement aimed to determine the melting behavior of these derivatives. The DSCs of HDPPBA-C, HDPPBA-N and HDPPH are shown in Figure V. 5, the first two compounds had melting points of 218 °C (Figure V. 5a) and 204 °C (Figure V. 5b) respectively, while the HDPPH had a substantially lower melting point of 159 °C (Figure V. 5c).Interestingly, there is a difference of 14 degrees in the melting temperature of the H-bonded derivatives, suggesting that the C-center derivative is more stable than the N-centered. It is probably due to the stronger aggregation character of HDPPBA-C, as we have shown in Chapter III. Once again, there was a big difference when comparing to the control molecule, attributed to the lack of H-bonds.

Figure V. 5

 5 Figure V. 5 DSC of a) HDPPBA-C b) HDPPBA-N and c) HDPPH.

Figure V. 6

 6 Figure V. 6 Left: ED pattern of a drop casted film from a chlorobenzene solution of HDPPBA-C onto carbon TEM grids. Right: TEM image of the studied film.

  heating up the film to 240 °C during 1 min to ensure HDPPBA-C was melted. Next, the sample was cooled down to room temperature.

Figure V. 7

 7 Figure V. 7 Left: ED pattern of a melted and recrystallized film of HDPPBA-C in a PTFE substrate. Right: TEM image of the studied film.

Figure

  Figure V. 8 Left: ED pattern of a film of HDPPBA-C that was annealed with vapor of chloroform in a PTFE substrate. Right: TEM image of the studied film.

Figure V. 9 A

 9 Figure V. 9 A different ED pattern of HDPPBA-C showing additional reflections with different contact planes.

Figure V. 10

 10 Figure V. 10 Modeling of the structure based on the obtained electron diffraction patterns. The parameters of this model are as follows: a= 28.7 Å, b=8.9 Å and c=4.95 Å, == =90°, where there is only one molecule per unit cell and possibly belonging to P-1 space group. The original ED pattern was further minimized in energy, but assuming the molecular conformation shown in Figure V. 10.

  and [010] as depicted in Figure V. 11, which are in good agreement with the obtained experimental ED patterns.

Figure V. 11

 11 Figure V. 11 Calculated ED patterns for the proposed model of aggregation for planes [100] and [010].The same sets of experiments were performed for HDPPBA-N, where the drop cast ED pattern shows the typical reflections as for its C-centered counterpart (Figure V. 12). The periodicity of H-bonded amides was observed once again. Additionally, ill-defined morphology of aggregates was observed in the film, with twisted lamellar objects and with very thin fibrils at extremities. These results agree with the morphology reported in chapter III for HDPPBA-N.

Figure V. 12

 12 Figure V. 12 Left: ED pattern of a drop casted film from a chlorobenzene solution of HDPPBA-N onto carbon TEM grids. Right: TEM image of the studied film.

Figure V. 13

 13 Figure V. 13 Left: ED pattern of a melted and recrystallized film of HDPPBA-N in a PTFE substrate. Right: TEM image of the studied film.For the melted and recrystallized film experiment, the ED pattern of HDPPBA-N shows a unique orientation of crystals (edge-on) with (100) contact plane and it was observed that the c-axis of the aggregates formed by the DPP core are parallel to the c-axis of the oriented PTFE substrate (CDPP//CPTFE) (Figure V. 13). Additional reflections can be seen due to the presence of a few domains with slightly different orientation on the substrate plane. This may also indicate that the unit cell is slightly monoclinic.

  Figure V. 14 Left: ED pattern of a film of HDPPBA-N that was annealed with vapor of chloroform in a PTFE substrate. Right: TEM image of the studied film. On the other hand, for the SVA experiment three different ED patterns were obtained. The first ED pattern is shown in Figure V. 14, where domains have a (010) contact plane and CDPP//CPTFE. Furthermore, the ED pattern is better defined and it is obvious that orientation was induced by epitaxy of the PTFE substrate because in this case the HDPPBA-N molecular columns run parallel to the PTFE chains. The second ED pattern was taken from a sample where the stacking direction of molecules is perpendicular to the PTFE chain direction (Figure V. 15). This is a perfect example of 1D epitaxy induced by PTFE. A dominant (010) DPP contact plane on PTFE with aDPP // cPTFE was obtained.In this case the epitaxial condition (d001)DPP ≈ (d100)PTFE ≈ 4.9 Å and the l=1 layer line show strong streaking, indicating disorder in the packing of adjacent columns of molecules.

Figure V. 15

 15 Figure V. 15 Left: ED pattern of a SVA film of HDPPBA-N that has perpendicular orientation to CPTFE. Right: TEM image of the studied film.

  Figure V. 16 A different ED pattern of HDPPBA-N showing Scherrer rings.

Figure V. 17

 17 Figure V. 17 Left: ED pattern of a melted and recrystallized film of HDPPH in a PTFE substrate. Right: TEM image of the studied film.

Figure V. 18

 18 Figure V. 18 Protocol to prepare oriented self-assembled DPP systems on PTFE substrates.

Figure V. 19

 19 Figure V. 19 Oriented HDPPBA-N on PTFE observed in the POM under crossed polarizers.

Figure V. 20

 20 Figure V. 20 UV-vis of a film of HDPPBA-N grown from solution in chlorobenzene at room temperature, black trace: parallel orientation, red trace: perpendicular orientation.

Figure V. 21

 21 Figure V. 21 UV-vis comparison of a film of HDPPBA-N grown at 4 °C and upon melting and recrystallizing of the film.Another film was measured by depositing HDPPBA-N from solution on a PTFE substrate at 70°C and cooled down to 4 °C. Absorption spectra were taken and then the film was melted by heating it up at 210 ⁰C for 1 min. Then recrystallization was allowed by cooling the film to room temperature, taking UV-vis spectra subsequently (Figure V. 21). It was observed that the melting-recrystallization process modifies the vibronic structure of the spectra. In this case, the 0-0 becomes weaker than the 0-1 and shifts to the blue from 619 nm to 604 nm, although the alignment was almost not affected (Figure V. 21).The films were then studied by ED at 4 °C and after the melting-recrystallization process. When the film was grown on PTFE at 4°C, the ED pattern shows very narrow (010) diffraction, indicating very high in-plane alignment(Figure V. 22). Additionally, the films show oriented tapes or fibers along the PTFE chain direction, meaning that the stacking direction of HDPPBA-N is parallel to CPTFE. The ED pattern also shows that the (011) is strongly streaked and overlaps with the (001). The streaking in l=1 layer indicates disorder between adjacent molecular columns.

Figure V. 22

 22 Figure V. 22 a) ED pattern of HDPPBA-N film grown on PTFE at 4°C and b) TEM image of the studied film.

Figure

  Figure V. 23 a) ED pattern of HDPPBA-N film after thermal annealing and b) TEM image of the studied film.

Figure V. 24 Oriented

 24 Figure V. 24 Oriented HDPPBA-C on PTFE observed in the POM under crossed polarizers. Next, the UV-vis measurements of films cooled down to 4 °C and after thermal annealing were performed (Figure V. 25). No clear anisotropy in UV-vis was seen in the first part of the experiment, whereas upon thermal annealing an improvement of alignment was observed. In fact, there was no change in the positions of the bands, contrary to what happened with HDPPBA-N. The vibronic structure was maintained, as well as the relative intensities of the

Figure V. 25

 25 Figure V. 25 UV-vis comparison of a film of HDPPBA-C grown at 4 °C and upon thermal annealing of the film.

Figure V. 26 Figure V. 29

 2629 Figure V. 26 a) ED pattern of HDPPBA-C film grown on PTFE at 4°C and b) TEM image of the studied film.

Figure V. 30

 30 Figure V. 30 UV-vis spectrum of HDPPH upon thermal annealing. Lastly, the ED pattern of the thermally annealed sample of HDPPH is almost identical to the amide-containing molecules (Figure V. 31). Dominant reflections are observed at 4.96 Å, 4.26Å and 9.46Å. The angle *=85° corresponds to a slightly monoclinic (or triclinic) crystalline lattice, where c* is along the crystal long axis (stacking direction) and one population of HDPPH crystals is defined by CHDPPH // CPTFE.

Figure V. 31

 31 Figure V. 31 ED pattern of a HDPPH film after thermal annealing.

Figure V. 32

 32 Figure V. 32 Comparison of the UV-vis spectra of all three derivatives.

Figure 38 H

 38 Figure 38 H-bonded DPP families synthesized so far in the DPP model system study, the families studied in this thesis are highlighted in light blue.

Figure 39 FTIR

 39 Figure 39 FTIR spectra in deuterated chloroform at room temperature of (S)-DPPBA, (R)-DPPBA and DPPBA.

Figure 40

 40 Figure 40 Kinetic traces of photoconductivity transients of HDPPBA-C, HDPPBA-N and HDPPH cast from chloroform/toluene solutions.

Expansion de la famille bisamide : influence de la topologie et de la solubilité

  Pour optimiser la conception de dérivés à liaisons-H et compléter notre bibliothèque, nous avons testé d'autres paramètres ayant un impact sur la formation de liaisons-H. Pour cela, nous avons d'abord choisi d'augmenter la solubilité des dérivés présentés au chapitre II. Nous avons également examiné l'impact de la topologie des amides sur l'auto-assemblage et sur les propriétés électroniques.Pour améliorer la solubilité des DPPs, les thiophènes du noyau ont été fonctionnalisés avec des chaînes hexyl et les bras amides ont été placés sur les lactames (Figure16). carbonitrile (3), qui en présence de diéthyl succinate et t-butoxide de potassium réagi pour produire un DPP fonctionnalisé sur les thiophènes, le dérivé 4, avec un rendement de 72%. Dans l'étape finale, les lactames sont alkylés avec des groupes amides, qui ont été synthétisés en parallèle et qui présentent des topologies différentes. , les deux dérivés amide et la molécule de contrôle absorbent entre 400 et 600 nm à 20 °C.Les trois molécules ne montrent aucun signal d'agrégation dans le chloroforme à 20 °C et les bandes d'absorption ne changent pas lorsque la solution est chauffée, ou lorsque sa concentration est modifiée (Figure

	Chapitre III :
	Before ethyl acetate	Before methanol	Annealed in ethyl acetate
	After ethyl acetate	After methanol	Soaking in methanol
			xxii

Figure 16 Structure chimique d'un DPP bisamide alkylé sur les thiophènes.

Deux dérivés de DPP contenant des groupes amide attachés aux lactames, avec une topologie centrée sur l'azote (centré-N) ou le carbone (centré-C), et portant des chaînes alkyles sur les thiophènes ont été synthétisés. Une comparaison entre ces deux nouvelles molécules a été réalisée, ainsi qu'une comparaison de cette nouvelle famille à la famille présentée au chapitre II. Avec ces deux nouveaux dérivés, une molécule de DPP ne portant que des chaînes hexyle, sur les lactames et les thiophènes, a également été synthétisée comme une molécule de contrôle qui ne peut pas former des liaisons-H.

Les processus d'auto-assemblage des DPPs centré-N et centré-C ont été suivis à nouveau par des techniques de spectroscopie et de microscopie. Les propriétés de transport de charges ont été étudiées par FP-TRMC et les résultats ont été comparés aux résultats obtenus avec la molécule de contrôle, ce qui met en évidence l'impact positif des liaisons-H sur les propriétés électroniques.

Dans ce cas, une approche de cyclisation succinique a été conçue, elle consiste à alkyler un thiophène et le fonctionnaliser pour enfin réaliser la réaction de cyclisation normalement utilisée lorsqu'on obtient un noyau de DPP.

Les molécules

HDPPBA-C et HDPPBA-N ont été synthétisées via l'approche de cyclisation succinique (Schéma 2). Un thiophène est d'abord alkylé avec du bromure d'hexyle pour produire le dérivé 1 avec un rendement de 82%, puis, un atome de brome est introduit en position 5 pour produire 2. Ensuite, le brome est remplacé par un nitrile, pour produire le 5xxiii hexylthiophene-2-Schéma 2 Approche synthétique pour obtenir HDPPBA-C et HDPPBA-N. Schéma 3 Alkylation de 4 pour obtenir HDPPH. La molécule de contrôle HDPPH a été synthétisée en suivant la même stratégie, mais les lactames sont ici alkylés avec du bromure d'hexyle (Schéma 3). Les propriétés optiques et d'autoassemblage de HDPPBA-C, HDPPBA-N et HDPPH ont été suivies par spectroscopie d'absorption UV-vis, en solution et en couche mince, à température variable pour différents solvants en fonction de la concentration, ainsi que par IRTF. En xxiv présence de chloroforme

  Plusieurs exemples où la fonctionnalisation est effectuée sur les thiophènes du noyau DPP existent dans la littérature, cependant, la majorité de ces approches sont généralement utilisées pour étendre le noyau conjugué de DPP, en rajoutant plus de thiophènes, tandis que le cas où l'unité DPP de base porte des thiophènes alkylés et fonctionnalisés (Figure23) n'est pas mentionné dans la littérature. sur la synthèse de dérivés centrés-C. Dans le manuscrit final, cette synthèse a été comparée à la synthèse des analogues centrés-N, effectuées au laboratoire. Elle ne sera pas évoquée dans ce qui suit. Cette comparaison synthétique a été faite pour avoir une meilleure compréhension des résultats.

	Figure 23 Structure d'un noyau DPP portant des chaînes alkyles fonctionnalisées
	directement attachées sur les thiophènes du noyau.

Cependant, dans le chapitre III, la synthèse de dérivés de DPP avec des chaînes alkyles sur les thiophènes, avec des bons rendements, a été mis en évidence. Par conséquent, il a été décidé d'utiliser la même approche de cyclisation succinique pour produire un DPP qui porte des chaînes alkyl non-fonctionnalisées sur les lactames et portant des amides sur les thiophènes.

Dans ce chapitre, une approche synthétique détaillée de deux dérivés de DPP, avec différentes topologies et fonctionnalités sur les thiophènes, est présentée. La synthèse de ces composés a été envisagée selon deux voies différentes.

Schéma 4 Retro synthèse pour obtenir le composé 8-C.

xxix Ce chapitre porte Une rétro-synthèse a été faite (Schéma 4). En principe, ce schéma versatile est applicable à la synthèse des dérivés de DPP avec une topologie inversée, la clé se trouvant sur le précurseur 1. La synthèse des précurseurs avec différentes topologies est la même à partir des produits 4-C usqu'à 6-C et pour 4-N usqu'à 6-N, dans ce cas seulement la route du produit centré-C est montrée sur le Schéma 5.

Schéma 5 Route synthétique pour le thiophène portant une amide C-centré.

L'étape suivante est la réaction de cyclisation où les composés 6-C et 6-N sont engagés, cependant des rendements bas ont été obtenus (Schéma 6). Par conséquent, cette approche a été considéré comme inadéquate pour obtenir ce type de produit, ce qui a entraîné à la proposition de routes alternatives pour obtenir un DPP avec des thiophènes portant des chaînes amides. Therefore, this approach was considered not suitable to obtain this type of products, leading to the proposal of alternative routes to obtain the DPP functionalized with an amide chain in the thiophene rings.

xxx

Schéma 6 Étapes finales dans l'approche synthétique par cyclisation succinique pour obtenir le produit 8-C. Plusieurs modifications ont été essayées pour essayer d'améliorer le rendement de cette réaction. En l'absence de rendement élevé, il a été décidé de changer la stratégie de synthèse, étant donné que l'obtention du composé 8-C par cette voie était trop difficile. Schéma 7 Approche synthétique finale et fiable pour obtenir 8-C.

  n'avait pas encore été testé et un essai en utilisant un dérivé DPP dibromé (produit 23) comme produit de départ a été effectué (Schéma 7). Le composé 8-C a été obtenu par hydrogénation à 60 °C en utilisant un mélange de solvant.De la même façon, le produit N-centré a été obtenu via cette approche, qui est très directe et a prouvé sa versatilité. Elle servira dans la synthèse de nouveaux dérivés de DPP portant des chaînes alkyl fonctionnalisées sur le thiophène. Les propriétés optiques et d'autoassemblage de 8-C et 24-C ont été suivies par spectroscopie d'absorption UV-Vis en solution, à température variable pour différents solvants et concentrations, et par IRTF. Comme d'habitude pour ces dérivés, le composé 8-C présente des larges bandes d'absorption entre 400 et 600 nm à 20 °C dans le chloroforme, avec un maximum d'absorption vers = 562 nm (Figure 24, tracée bleue). Il ne présente pas cependant des signaux d'agrégation et les bandes d'absorption ne changent pas lorsque la concentration de la solution est augmentée (Figure 25a).

	0.0 Des 300 0.2 0.4 Normalized 0.6 0.8 1.0 absorbance	400	500	600	700 Toluene Chlorobenzene 800 Chloroform Ethyl Acetate
			 (nm)

bandes d'absorption supplémentaires sont observées à des énergies plus faibles lorsque les spectres de 8-C sont mesurés dans différents solvants, comme le chlorobenzène, le toluène et l'acétate d'éthyle. Dans le chlorobenzène, la valeur de max est de 621 nm dans le toluène, vers 622 nm dans le chlorobenzène, et vers 629 nm dans l'acétate d'éthyle (Figure

24

).

Cette bande a été attribuée à la formation d'agrégats J et son intensité diminue lorsqu'on chauffe ou on dilue la concentration de la solution, comme pour les familles de DPPs décrites précédemment (Figure

25b

-d et Figure

26

, respectivement). La formation de ces agrégats a été confirmé à nouveau en réalisant des mesures lorsqu'on ra oute du méthanol.

Chapitre V : Perspectives : Ouvrir la voie à un processus de criblage en temps-réel pour des dispositifs électroniques organiques Dans

		a)					b)
		1.05					1.00
	Transmittance	1.00 0.85 0.90 0.95			24-C 8-C	Transmittance	0.55 0.70 0.85
							0.40
		0.75 0.80					0.25		8-C 24-C
		3500	3400	3300	3200		1800	1700	1600	1500
			Wavenumber (cm -1 )			Wavenumber (cm -1 )

Figure 29 Spectres IRTF en poudre pour 8-C et 24-C.

Une comparaison des spectres IRTF en poudre entre 8-C et HDPPBA-C a aussi été faite, mais aucune différence ma eure n'a été observée. Toutefois, ces résultats ont été obtenus sur des poudres, pour lesquelles les différences d'agrégation ne sont pas trop évidentes. La comparaison de ces dérivés est toujours en cours. Des mesures de spectres dans différents solvants et à différentes concentrations devraient conduire à des informations plus détaillées sur les processus d'auto-assemblage.

La caractérisation complète de cette famille est très importante. En particulier, les mesures de photoconductivité et une comparaison plus complète de l'influence de la topologie devraient fournir des données essentielles pour les futures conceptions moléculaires envisagées et également pour élucider l'impact de la position de la liaison-H par rapport au noyau conjugué. les chapitres précédents, on a montré le début d'études comparatives et systématiques faites sur des matériaux  conjugués portant des liaisons-H basées sur le DPP. Ce travail devait permettre d'aider à la conception moléculaire de nouveaux composants. Jusqu'à présent, il avait été observé que des faibles différences dans la structure moléculaire des DPPs ou des différences dans le processus d'auto-assemblage pouvaient avoir un impact ma eur les propriétés optoélectroniques. En plus, d'autres paramètres comme la méthode de préparation de l'échantillon, le solvant choisi, la concentration et la température pouvaient influer la capacité de formation des liaisons-H, compliquant par suite leur optimisation. C'est pourquoi nous avons commencé à travailler sur le contrôle in situ de la morphologie et des propriétés électroniques, pour recueillir un maximum d'information et créer un protocole de criblage.

xxxv Le travail qui suit a eu précisément pour but d'examiner les propriétés de différents systèmes de DPP portant des liaisons-H, avant puis après exposition à une vapeur de solvant ou/et à des traitements thermiques. Cette étude a été effectuée pour les dérivés DPP présentés au chapitre III : HDPPH, HDPPBA-C et HDPPBA-N.

F

  FF ...................................................................... fill factor FP-TRMC ........ Flash-photolysis time resolved microwave conductivity G GIWAXS .... grazing incidence wide-angle X-ray scattering GIXD ........................... grazing incidence X-ray diffraction GW .................................................................... Gigawatts H H-bonded ............................................. hydrogen bonded H-bonding ........................................... hydrogen bonding H-bonds ................................................... hydrogen bonds HTL ............................................... hole-transporting layer ........................................................................... meter MD .................................................... molecular dynamics Mtoe ............................... million tonnes of oil equivalent MW ................................................................. Megawatts OFETs ............................... organic field transistor devices OLED ................................... organic light emitting diodes OPVs .................................... organic photovoltaic devices OTFTs .................................... organic thin film transistors P3HT............................................ poly (3-hexylthiophene) PBI ......................................................HA ..................................... hydrogen acceptor polymer POM .................................... polarized optical microscope PSCs .................................................... polymer solar cells PTFE ........................................... polytetrafluoroethylene PV ................................................................. photovoltaic PWR ....................................... Pressurized Water Reactor S SDS ............................ Sustainable Development Scenario SEM ................................... scanning electron microscopy SF ............................................................... singlet fission STEPS ........................................... Stated Policies Scenario STM ................................. scanning tunneling microscopy SVA ............................................. solvent vapor annealing syn-DBTP .......................... syn-dibenzothieno[b,d]pyrrole T TAT .............................................................. triazatruxene t-Boc .................................................. tert-butoxycarbonyl TClT ................................. 5,6,11,12-tetrachlorotetracene TFA ........................................................ trifluroacetic acid TGA ....................................... thermogravimetric analysis TPA ........................................................... triphenylamine TTF ....................................................... tetrathiofulvalene

	I.	World's Energetic consumption
	II.1) Current situation and forecast
		. perylene bisimides
	PC71BM ........ phenyl [6,6]-Phenyl C71 butyric acid methyl
	ester
	PCBM ............ [6,6]-phenyl-C61-butyric acid methyl ester
	PCE ....................................... power conversion efficiency
	p-ClDPP .......................................... "Ferrari red" pigment
	PCPDTBT .......... poly{[4,4-bis-alkyl-cyclopenta-(2,1-b;3,4-
	b′)dithiophen]-2,6-diyl-alt-(2,1,3-benzo-thiadiazole)-
	4,7-diyl}
	PDMS .............................................. polydimethylsiloxane
	PEDOT
	PSS ..... Poly(3,4-ethylenedioxythiophene) polystyrene
	sulfonate
	I P-INTRODUCTION
			ICZ ................................................... indo[3,2-b]carbozole
			IR ........................................................................ infrared
			ITO .......................................................... Indium Tin Oxide
			L
			LDA ........................................................ diisopropylAmide
			M
			N
			NBS .................................................. N-Bromosuccinimide
			NFAs ........................................... non-fullerene acceptors
			NMP ................................................ N-methylpyrrolidone
			O
	CHAPTER	I

m xlv P

Table II

 II

	. 3 Rate constant (calculated after 3 µs after pulse excitation) and half lifetime
	values for DPPBA.
	DPPBA	Anneal ethyl acetate	Soaking in methanol
	k (s -1 )	4 × 10 4	1 × 10	5
	t1/2 / s	2 × 10

  1. Yield: colorless oil (27.56 g, 82%).

	1 H NMR (400 MHz, CDCl3): δ 7.16 (dd, J=6.2 Hz, 3.0 Hz, 1Hg), 6.99 (t, 1Hf), 6.85 (dd, J =
	3.9Hz, 3.7Hz, 1He), 2.90 (t, 2Hd), 1.75 (m, 2Hc), 1.4 (m, 6 Hb), 0.98 (t, 3Ha).

  NMR (101 MHz, CDCl3) δ[ppm]: 173.32 (2C13), 161.68 (2C12), 153.23 (2C11), 139.89 (2C10), 135.86 (2C9), 127.32 (2C8), 126.27 (2C7), 107.06 (2C6), 41.60 (2C5), 39.42 (4C4), 36.95 (2C3), 31.72, 31.62, 31.59, 30.47, 29.75, 29.11, 29.04, 28.93, 25.92, 24.11, 22.69 (4C2), 14.19 (4C1).

	1 H NMR (400 MHz, CDCl3) δ[ppm]: 8.75 (d, J = 3.8 Hz, 2Hk), 6.95 (d, J = 3.7 Hz, 2Hj), 5.62 (s,
	2Hi), 4.06 (t, J = 7.1 Hz, 4Hh), 3.25 (q, J = 6.4 Hz, 4Hg), 2.90 (t, J = 7.6 Hz, 4Hf), 2.12 (t, J =
	7.5 Hz, 4He), 1.82 -1.66 (m, 8Hd), 1.48 -1.17 (m, 28Hb and 8Hc), 0.92 -0.83 (m, 12Ha).

13 C

m 2 m 50 nm

Acknowledgements

"What we know is a drop, what we don't know is an ocean." -Sir Isaac Newton IV.

IV.

EXPLORING THE AMIDE FUNCTION:

Impact of chirality and solubility

CHAPTER II

When comparing to the previously studied families, it can be observed that the recombination of charge carriers of HDPPBA-C and HDPPBA-N are comparable to DPPBA (Table III. 1, entry 1), the achiral derivative previously studied containing unfunctionalized thiophene rings, and that the photoconductivity values are lower (Table III. 1, entry 1 vs entries 4 and 5), but like those of the chiral compounds, (S)-and (R)-DPPBA (Table III. 1, entries 2 and 3 vs entries 4 and 5). The recombination of charge carriers is equal than DPPBA (entries 1, 4 and 5), being in this case one order of magnitude slower than the chiral derivatives (S)-and (R)-DPPBA previously studied (entries 2 and 3 vs entries 4 and 5). Interestingly, the recombination of charge carriers for (S)-and (R)-DPPBA is in the same order of magnitude as for the control molecule HDPPH not containing H-bonds in its structure. These results indicate how important is to finely-tune the molecular design of H-bonded -conjugated materials, since the most subtle change can dramatically impact the electronic properties.

Table III. 1 Photoconductivity (ϕΣμ) values for

II.4) Conclusions

In conclusion, three new DPP derivatives were synthesized and characterized, with two of them having mostly the same structure, but different amide topology. Furthermore, a very soluble DPP derivative that has no H-bond functionality was obtained and used as a control molecule for comparison. The two amide DPP derivatives aggregate and form J-type aggregates, where H-bonds are involved, whereas the control does not display J-aggregation.

Furthermore, the synthetic approach seems to provide higher regioselectivity towards the N,N'-alkylated products, as the typical isomers that are usually obtained in DPP alkylation were not present. This might be explained by the combination of multiple factors: improved solubility of the starting material, the steric hindrance provided by the hexyl chains with respect to the DPP carbonyl groups, the lower reaction temperature and the based used to deprotonate the lactam. The improved regioselectivity also resulted in higher yields for the alkylation reactions in the lactams, reaching 30%.

Slight differences were observed for changes in topology, the C-centered derivative presents a bathochromic shift in all the solvents compared to N-centered derivative, and the J-2,5-dihexyl-3,6-bis(5-hexylthiophen-2-yl)-2,5-dihydropyrrolo [3,4-c]pyrrole-1,4-dione (HTDPPH) Cs2CO3 (0.7160 g, 2.1 mmol) was added to a suspension of HTDPP (0.4155 g, 0.9 mmol) in acetonitrile (25 mL) and stirred at 80 °C for one hour under argon atmosphere. Then, 1bromohexane (0.3 mL, 2.1 mmol) was added dropwise during 20 min. The solution was stirred overnight at 80 °C. The reaction was allowed to cool to room temperature, the solvent was evaporated under vacuum. The residue was dissolved in CHCl3 (70 mL) and washed with water (3x 100 mL). The organic phase was dried over MgSO4 and filtered. Then, the solvent was vacuum evaporated. The crude product was purified by column chromatography using toluene as eluent. The desired product was obtained as a purple solid (0.1790 g, 33.7%).

EXPANDING THE BISAMIDE FAMILY:

Influence of amide position and topology

CHAPTER IV

Scheme IV. 5 Replacement of the mesylate function by an Iodine.

Another alkylation reaction was attempted with this new amide arm, but again the desired product was not obtained. The amide functionality seemed to be undergoing another side reaction and therefore, the alkylation by this approach was discarded. An organometallic approach was also attempted, but the amide arm was also not suitable for this type of coupling.

Therefore, a retro-synthetic approach was made (Scheme IV. 6). On paper, this versatile pathway also allowed the synthesis of DPP derivatives with amide arms grafted to the thiophene rings with an inverted topology, the key precursor was compound 1 and the subsequent derivatives are shown in Scheme IV. 7. While the synthesis of the N-centered amide derivative had its own challenges, the C-centered amide derivative presented a major bottle neck on the synthetic step leading to compound 3-C.

Scheme IV. 6 Retro-synthetic approach for compound 8-C.

Scheme IV. 7 Precursors to obtain a DPP derivative with inverted amide topology.

The hydrolysis of the nitrile to a carboxylic acid seemed easy and straight on paper, however, it was very challenging. Acidic hydrolysis of nitriles has been extensively described in the literature [6] , where strong acid and heat are sufficient to lead to a carboxylic acid with water as the solvent. However, the attempted reactions were unsuccessful.

Some protocols claim to have used few drops of concentrated sulfuric or hydrochloric acid, others use water/acid mixtures in a 1:1 ratio. Several attempts were performed but only the most relevant ones are commented.

Scheme IV. 8 First successful attempt of the hydrolysis of compound 2-C.

When water/acid mixtures in a 1:1 ratio were used, no reaction was occurring at room temperature, so the next step was to increase the temperature and see its impact. The reactions started to occur at temperatures above 40 °C for the mixture consisting of H2O/H2SO4 (1:1), where the crude started to become black in color, and degradation of the starting material was confirmed by 1 H-NMR and TLC. For the H2O/HCl (1:1) mixture, several attempts at different temperatures were performed but the hydrolysis was not occurring, and when the temperature was increased to 70 °C, the degradation reaction started.

Therefore, it was decided to play with the water/acid ratios, until finally, working conditions that led to the carboxylic acid were found. The first conditions that yielded compound 3-C are shown in Scheme IV. 8, the major inconvenient of this approach was the solubilization of the starting material in the solvent mixture as it is insoluble in water, which ultimately impacted the yield. Later, this synthetic step was completely changed to a basic hydrolysis procedure [7] and Scheme IV. 11 Cyclization reaction with compound 6-N.

Several cyclization reactions (Scheme IV. 11) were done changing parameters such as the number of equivalents of potassium tert-butoxide, nitrile 6-N and diethyl succinate, and the order of addition of the reagents. This was performed with N-centered derivatives by another PhD student, who will provide details on their synthesis in his manuscript.

In some trials with the C-centered derivative, the reaction mixture was getting the characteristic intense red color of DPP derivatives, but when trying to characterize the products from these reactions, the cyclization seemed to be more a parasitic reaction rather than the main one. The crude of this reaction was purified by column chromatography and used on an alkylation reaction, finally obtaining compound 8-C, although the yield was low (Scheme IV. 12). Therefore, this approach was considered not suitable to obtain this type of products, leading to the proposal of alternative routes to obtain the DPP functionalized with an amide chain in the thiophene rings.

Scheme IV. 14 Ester thiophene derivative cyclization intended approach.

The amide moiety was considered the main issue in the failure of the cyclization and a new approach was envisioned (Scheme IV. 14). For this approach, instead of performing the cyclization on an amide functionalized thiophene, it was done on an ester that would later be converted into an amide. Nevertheless, the cyclization with compound 12 did not lead to a DPP cycle. It was inferred that the carbonyl group was undergoing a nucleophilic substitution and interfering in the cyclization mechanism.

Scheme IV. 15 Cyclization reaction starting from a bromide-pending thiophene carbonitrile. Lattice parameters for 010, 011 and 001 are similar for the three molecules, suggesting quite similar packing, despite the presence of amides for HDPPBA-N and HDPPBA-C.

In fact, only HDPPBA-N presents a significant change in the parameters, especially of d010 after thermal annealing, where it goes from 8.66 Å to 8.93 Å. This is consistent with the changes in UV-vis spectra with a shift of the 0-0 from 619 nm to 604 nm after thermal annealing.

This means the DPP packing is more robust compared against the H-bonding packing of amides in the side chains. Finally, HDPPH shows the largest value of d010=9.46 Å, hinting that this parameter seems to be affected by the molecular structure, in other words, by the presence of the amide group.

III. Conclusions and perspectives

We have reported the first successful orientation of a self-assembled molecule on PTFE from solution, which provides evidence for oriented growth and heterogeneous nucleation on PTFE. Moreover, a clear difference in the orientation between HDPPBA-N and HDPPBA-C on PTFE was observed. For instance, excellent alignment was obtained for HDPPBA-N, whereas HDPPBA-C does not tend to orient on PTFE.

The change in color from blue (when exposure is done in parallel to CPTFE) to orange (when the exposure es perpendicular to CPTFE) of the polarized UV-vis spectra is due to the balance of absorbance between 610-620 nm vs 500 nm, as the band at 500 nm is less polarized.

The UV-vis spectra of the three derivatives when samples were annealed are quite similar, although differences between grown and annealed films were observed for HDPPBA-N, which is the one that orients on PTFE. The TEM ED patterns showed that annealing of HDPPBA-N improves ordering between columns as there was loss of streaking. This means that the aggregates could be undergoing a transformation from columnar 1D order to more 3D order. This results in a shift of the 0-0 absorption band and lattice expansion along the b axis. On the other hand, films made of HDPPBA-C do not seem to change much their structure between solution-grown and melt-recrystallized. This indicates the less dynamic character of the aggregates formed by this derivative, as evidenced in chapter III.

In order to complement and expand these studies, thicker films for HDPPBA-N could be grown, to have more continuous thin films. This can be done by preparing films from solutions

SUMMARY AND GENERAL CONCLUSIONS

produce inverted OFETs that will help us with the first experiments on the in-situ morphology control.

In this sense, the results presented in this thesis will help in the development of the in-situ control over the morphology and electric properties of H-bonded organic electronic materials, ultimately gathering as much information as possible and helping to build a screening protocol.

Summary

Organic semiconductors combine the electronic advantages of semiconducting materials with the chemical and mechanical benefits of organic compounds. When non-covalent interactions such as hydrogen bonds (Hbonds) are added, some studies have demonstrated they improve efficiency in different electronic devices; while others report they are detrimental. This has led to a lack of consensus regarding the incorporation of Hbonds in semiconductors. The aim of this PhD is to elucidate their impact in the optoelectronic properties of organic semiconductors, as well as screening the required conditions needed to fabricate efficient electronic devices. For this purpose, systematic and comparative studies have been done using a conjugated molecule as a model system, more precisely, diketopyrrolopyrrole (DPP). Three different DPP families were studied, evaluating the effect of varying parameters such as functionality, topology, and position of the H-bonds. These studies have brought more light on the role of H-bonds in organic electronics and will serve as a basis to successfully develop processing techniques to obtain high performing organic electronic devices in the future.