Trop) Zn(Op) 2 C Crystal Refinement Data D Concentration Dependence Emission

Résumé Substantiel

De nos jours, la micro-électronique est en grande partie basée sur les semi-conducteurs inorganiques tels que le silicium et le germanium. Vers le milieu du siècle dernier, les semiconducteurs organiques (en anglais: organic semiconductors -OSCs) éveillèrent l'intérêt de la communauté scientifique ainsi que des industriels. En effet, cette nouvelle classe de matériaux est prometteuse, non seulement pour la fabrication de circuits électroniques étendus, à bas cout et imprimables mais aussi pour des applications en opto-électronique. Les OSCs se divisent en deux catégories: d'une part ceux de faible poids moléculaire et d'autre part les polymères. Tous ont en commun d'avoir un système conjugué π sur une chaine formée de structures d'atomes de carbone liés entre eux par des liaisons σ. La structure de la molécule d'éthylène montrée en Figure 1 illustre bien cette caractéristique des OSCs. Les propriétés optiques des OSCs sont dues aux électrons π qui participent à des transitions ππ * ayant lieu dans le système conjugué π délocalisé. Du point de vue des propriétés électroniques, les OSCs sont des isolants intrinsèques. En effet, pour qu'il y ait conduction électronique dans un OSC, des porteurs de charge externes doivent être injectés par des électrodes. Ceux-ci se déplacent dans la couche de matériau organique en passant d'un état localisé à un autre, HO (haute occupée, en anglais: higher occupied molecular orbital -HOMO) et BV (basse vacante, en anglais: lower unoccupied molecular orbital -LUMO), qui sont respectivement l'orbitale liante π et l'orbitale anti-liante π * . Un des principaux intérêts des OSCs réside dans la possibilité de pouvoir modifier leurs propriétés optiques et électroniques par le biais de modifications chimiques de la chaine carbonée et du système conjugué π.

La molécule de Alq 3 (tris-(8-hydroxyquinoline)aluminum) constitue l'exemple le plus connu parmi les OCSs, en particulier parmi ceux de poids moléculaire faible. Cette molécule est formée par un ion central Al 3+ chélaté par trois quinolinates bidentées, assurant la neutralité du complexe. Le complexe Alq 3 a deux isomères géométriques: mer-et fac-Alq 3 (voir Figure 2) qui présentent des propriétés différentes. Mais c'est principalement l'isomère méridional qui se forme lors des synthèses conventionnelles. Ses niveaux énergétiques de HOMO et de LUMO, sa stabilité thermique, sa capacité à former des couches minces ainsi que ses mobilités de porteurs de charge élevée (électrons: 10 -5 -10 -6 cm 2 V -1 s -1 ; trous: 10 -8 -10 -9 cm 2 V -1 s -1 ) font du complexe Alq 3 un OSC utilisé dans de nombreuses applications. Les diodes électroluminescentes organiques (en anglais: organic light emitting devices -OLEDs) constituent l'un des tout premiers champs d'application du complexe Alq 3 en tant que matériau assurant la conduction électrique, l'émission de photons et de matrice. Depuis la première utilisation dans v Figure 2: Représentation de la structure moléculaire de l'isomère méridional (mer-Alq 3 ) (à gauche) et de celle de l'isomère facial (fac-Alq 3 ) (à droite). ce domaine, le complexe Alq 3 ainsi que ses dérivés modifiés chimiquement furent l'objet de nombreuses études afin d'améliorer les performances des OLEDs. Le complexe Alq 3 fut utilisé également dans le processus de fabrication de cellules photovoltaïques organiques (en anglais: Organic Photovoltaic -OPVs) comme matériau assurant le transport électronique et le blocage des trous. De plus, ce complexe est, de nos jours, l'un des OSCs les plus étudiés dans le domaine de la spintronique organique. En effet, les dispositifs spintroniques organiques (en anglais: organic spintronic devices -OSPDs) basés sur ce complexe présentent des résultats reproductibles prometteurs. Enfin, la fabrication de transistors organiques à effet de champ (en anglais: organic field-effect transistors -OFETs) ambipolaires et de transistors organiques électroluminescents à effet de champ (en anglais: light-emitting organic field-effect transistor -LE-OFETs ) constituent un domaine supplémentaire d'application du complexe Alq 3 en tant que matériau actif.

Élaboration, synthèse et caractérisation des OSCs étudiés

Lors de ma thèse, j'ai synthétisé et analysé des OSCs contenant de l'aluminium, afin de comprendre le lien entre la structure chimique et les propriétés opto-électroniques. La première étape consista à établir, sélectionner et synthétiser une librairie de ligands pouvant être utilisés dans la fabrication des séries de complexes d'aluminium étudiés (voir Table 1 pour la liste de ces nombreux ligands). Les ligands et les complexes furent caractérisés par spectroscopie et par des méthodes électrochimiques. Le complexe Al(Op) 3 (tris-(1-oxo-1H-phenalen-9-olate)aluminum) fut le premier OSC synthétisé lors de mon travail. Ce complexe a une structure symétrique et a des ligands qui présentent un système aromatique étendu par rapport au complexe Alq 3 . Par la suite, deux séries de dérivés halogenés et substitués du complexe Al(Op) 3 furent synthétisées: Al(Op-X) 3 et Al(Op-R) 3 . De plus, l'extension du système aromatique de Al(Op) 3 me permit de former un autre complexe d'aluminium, le complexe Al(Oba) 3 (tris-(7-oxo-7Hbenzo(de)anthracen-6-olate)aluminum). En raison de leurs caractéristiques structurelles, il me parut intéressant de synthétiser et d'analyser deux autres complexes: le complexe Al(Op-py) 3 (tris-(2-(pyridin-2-yl)phenolate)aluminum) dont la structure est similaire à celle du complexe Alq 3 ainsi que le complexe Al(Trop) 3 (tris-(7-oxocyclohepta-1,3,5-trienolate)aluminum) qui lui présente une structure symétrique et trois cycles carbenés insaturés. Trois séries supplémentaires de complexes à ligands mixtes furent obtenues en échangeant un quinolate respectivement par Acac (4-hydroxypent-3-en-2-one), HOp (9-hydroxy-1H-phenalen-1-one) et tropolone Table 1: Liste des ligands et des (nouveaux) OSCs étudiés. R: phenyl, naphthalenyl, phenylethynynl. X: F, Cl, Br, I. (2-hydroxycyclohepta-2,4,6-trien-1-one). Enfin, j'ai synthétisé le complexe plan Zn(Op) 2 (bis-(1-oxo-1H-phenalen-9-olate)zinc), le premier d'une série de complexes plans contenant du zinc. Les complexes furent caractérisés par résonance magnétique nucléaire (en anglais: nuclear magnetic resonance -NMR), par analyse élémentaire, par les méthodes de spectrométrie de masse désorption-ionisation laser assistée par matrice-temps de vol (en anglais: matrix assisted lased desorption ionization-time of flight -MALDI-TOF) et ionisation par électronébuliseur-temps de vol (en anglais: electrospray ionization-time of flight -ESI-TOF) ainsi que par diffractométrie de rayons X. a λ abs max = absorption maximum de la première bande de transition π → π * ainsi que son coefficient d'extinction (ǫ). b λ emi max = émission maximum. c Φ = rendement quantique de photoluminescence, determiné en utilisant la molécule de rhodamine 6G comme standard. d τ = durée de vie photonique de luminescence.

Les propriétés photo-physique du complexe Al(Op) 3 furent mesurées en solution et lorsqu'il est déposé en couche mince. Ces résultats furent comparés à ceux obtenus pour le complexe Alq 3 (voir Figure 3).

Les analyses montrent que, à l'état solide , le complexe Al(Op) 3 forme des excimères et exhibe par conséquent des propriétés photo-physiques très différentes qu'il soit en solution (λ emi max = 458 nm, Φ= 0.027 et τ = 0.7 ns) ou bien déposé en couche mince (λ emi max = 583 nm, Φ= 0.014 et τ = 7.1 ns), comme indiqué dans la Figure 3. Les spectres d'absorption et d'émission des complexes halogènés et substitués Al(Op-X) 3 et Al(Op-R) 3 ne montrent que peu de variations par rapport à ceux du complexe Al(Op) 3 pur. Un point intéressant à souligner est l'émission phosphorescente (≈600 nm), due à l'effet des atomes lourds, observée pour le complexe Al(Op-I) 3 . Par ailleurs, malgré son substituent massif, le complexe Al(Op-p) 3 forme des exciméres lorsqu'il est déposé en couche mince (λ emi max = 537 nm). En raison de son noyau de phenalenyl, le complexe Al(Oba) 3 présente des spectres d'absorption et d'émission similaires à ceux du complexe Al(Op) 3 . De plus, il forme des excimères à l'état solide (λ emi max = 591 nm). Au contraire, le complexe Al(Op-py) 3 qui est insoluble dans tous les solvants, est caractérisé à l'état solide par une émission (λ emi max = 445 nm) déplacée vers le bleu par rapport au complexe Alq 3 (λ emi max = 523 nm). Il résulte de la structure particulière du complexe Al(Trop) 3 , que ses spectres ne sont pas comparables à ceux des complexes Alq 3 et Al(Op) 3 . Cependant, les bandes d'absorption du complexe Al(Trop) 3 purent être identifiées à leur transitions respectives et une émission fluorescente dans le bleu fut détectée (λ emi max = 456 nm). Les spectres d'absorption et d'émission des complexes à ligands mixtes Al(q 2 Acac), Al(q 2 Op) et Al(q 2 Trop) sont le résultat de la combinaison des spectres des groupes fonctionnels formant ces complexes. Puisque Acac n'émet pas, l'emission du complexe Al(q 2 Acac) (λ emi max = 512 nm) est pratiquement similaire à celle observée pour le complexe Alq 3 . En revanche, dans le cas du complexe Al(q 2 Op) puisque les groupes fonctionnels quinolinate et phenalenyl émettent, le spectre d'émission est une combinaison des spectres des groupes fonctionnels. Les deux groupes fonctionnels peuvent être excités de façon sélective, permettant ainsi d'observer une émission du complexe Al(q 2 Op) différente suivant la longueur d'onde d'excitation. Le même effet fut observé pour le complexe Al(q 2 Trop). Cepedant, puisque le domaine d'absorption des groupes fonctionnels quinolinate et tropolonate se superposent, l'excitation sélective d'un seul groupe fonctionnel se revela être impossible dans ce cas. Dans le cas du complexe Zn(Op) 2 , dernier complexe analysé dans ce travail, les spectres d'absorption et d'émission dérivent des ligands phenalenyl, et ceux, en dépit de la structure plane du complexe.

La réduction électrochimique simple et irréversible du complexe Alq 3 a lieu pour des potentiels viii ix relativement négatifs (-1.79 V). Ceci contraste avec le complexe Al(Op) 3 qui peut subir trois réductions (-1.63 V, -1.84 V et -2.07 V) , chacune quasi-réversible, la première de ces réductions ayant lieu pour un potentiel moins négatif que dans le cas de la molécule de Alq 3 . La Figure 4 montre les courbes de voltammétrie cyclique (en anglais: cyclic voltammetry -CV) pour les complexes Alq 3 et Al(Op) 3 . De part leur similarité structurelle avec le complexe Al(Op) 3 , le même comportement put être observé pour les complexes halogenés et substitués Al(Op-X) 3 , Al(Op-R) 3 et Al(Oba) 3 (voir Table 3). En raison de sa petite structure aromatique, le complexe Al(Trop) 3 est réduit pour un potentiel fortement négatif (-2.10 V). La réduction des complexes Al(q 2 Acac), Al(q 2 Op) et Al(q 2 Trop) est rendue possible grâce leurs groupes fonctionnels électro-actifs. Plus précisément, la réduction du complexe Al(q 2 Acac) (-1.80 V) a lieu sur les quinolinates, celle du complexe Al(q 2 Op) (-1.58 V) sur le phenalenyl et la réduction du complexe Al(q 2 Trop) (-2.08 V) sur le tropolonate. Le complexe Zn(Op) 2 est, quant à lui, caractérisé par trois réactions de réduction (-1.50 V, -1.

Étude théorique et résultats expérimentaux préliminaires concernant les (nouveaux) OSCs

En collaboration avec: Dr. Velimir Meded and Pascal Friederich (INT-KIT, Karlsruhe, Germany); Dr. Timo Strunk (Nanomatch, Eggenstein-Leopoldshafen, Germany), Dr. Xiangnan Sun and Prof. Luis E. Hueso (CIC nanoGUNE, Donostia-San SebastiÃąn, Spain); Dr. Valeria Fattori and Dr. Francesca Tinti (ISOF-CNR, Bologna, Italy)

La mobilité des porteurs de charge dans les OSCs fut étudiée en se basant aussi bien sur des méthodes théoriques tout comme sur des méthodes expérimentales. Tout d'abord, les niveaux HOMO et LUMO ainsi que les moments dipolaires des différents OSCs furent calculés pour des systèmes dans le vide (voir Table 4). Les calculs effectués montrèrent que la localisation des orbitales HOMO et LUMO dépend de la symétrie des ligands. Ce phénomène est illustré pour les complexes mer-Alq 3 et Al(Op) 3 dans la Figure 5. La présence de ligands asymétriques, qui forment les complexes mer-Alq 3 and mer-Al(Op-py) 3 , a pour conséquence des orbitales HOMO et LUMO localisées. Ces OSCs présentent ainsi un moment dipolaire élevé (4. 45 D et 4.79 D respectivement). En revanche, la présence de ligands symétriques, qui forment les complexes Al(Op) 3 , Al(Trop) 3 et Al(Acac) 3 , conduit à des orbitales HOMO et LUMO équitablement reparties et donc à un moment dipolaire faible (0.086 D, 0.12 D, et 0.053 D respectivement).

Les orbitales HOMO et LUMO du complexe à ligands mixtes pseudofac-Al(q 2 Acac) sont localisées exclusivement sur le groupe fonctionnel quinolinate. Cette configuration contraste avec celle des complexes pseudofac-Al(q 2 Op) et pseudomer-Al(q 2 Trop), dont les orbitales HOMO et x LUMO sont reparties alternativement sur les groupes fonctionnels quinolinate et phenalenyle ou tropolonate, ce qui conduit à un moment dipolaire elevé (6.52 D et 5.49 D respectivement). En utilisant la méthode "Quantum Patch" développée récemment, une série de paramètres microscopiques purent être déterminés pour les couches minces formées par les différents OSCs. Nous nous sommes plus particulièrement intéressés à l'énérgie de désordre (σ(E)), à l'énergie de réorganisation (λ) et à l'énergie de couplage (J 2 r 2 ). Les valeurs de ces grandeurs ont été utilisées pour calculer les mobilités des porteurs de charge µ dans les OSCs déposés en couches mince (voir liste Table 5). La valeur élevée de la mobilité des porteurs de charge obtenue pour le complexe Al(Acac) 3 en utilisant la méthode Quantum Patch indique que cette méthode nécessite encore des ajustements. Cependant, la méthode fournit des résultats tout à fait satisfaisants et en bon accord avec les mesures expérimentales dans le cas des complexes suivants: mer-Alq 3 , pseudofac-Al(q 2 Acac) et Al(Op) 3 . Il est cependant nécessaire, pour un calcul réaliste de la mobilité électronique, de prendre en compte la formation d'excimères à l'état solide dans les molécules telles que Al(Op) 3 . Parmis les OSCs, les complexes mer-Alq 3 , mer-Al(Op-py) 3 , Al(Trop) 3 et pseudofac-Al(q 2 Acac) ont des mobilités électroniques calculées similaires. Leur mobilité de trous, en revanche, présente des variations jusqu'à cinq ordre de magnitude. Les complexes à ligands mixtes pseudofac-Al(q 2 Op) et pseudomer-Al(q 2 Trop) ont quant à eux les mobilité d'électrons et de trous les plus faibles de tous les complexes étudiés.

Table 5: Mobilités des porteurs de charge µ dans les OSCs etudiés (Valeurs calculées avec la méthode "Quantum Patch").

Composé Mobilité [cm 2 V -1 s -1 ] Trous électrons mer-Alq 3 3.26 × 10 -8 9.23 × 10 -8 Al(Op) 3 1.42 × 10 -4 9.49 × 10 -6 mer-Al(Op-py) 3 5.67 × 10 -7 6.64 × 10 -8 Al(Trop) 3 4.70 × 10 -10 2.62 × 10 -8 Al(Acac) 3 8.57 × 10 -3 6.31 × 10 -4 pseudofac-Al(q 2 Acac) 1.59 × 10 -5 4.68 × 10 -6 pseudofac-Al(q 2 Op) 8.32 × 10 -12 2.43 × 10 -13 pseudomer-Al(q 2 Trop) 2.64 × 10 -11 3.27 × 10 -10 xii Le complexe Al(Op) 3 fut utilisé comme matériau pour fabriquer un transistor en couches minces (en anglais: thin film-transistor -TFT), rendant possible la mesure de la mobilité d'effet de champ. Pour les trous, une mobilité entre 0.6 and 2.1 × 10 -6 cm 2 V -1 s -1 a été observée tandis que pour les électrons aucun mobilité ne fut détectée. De plus, le ratio On/Off constaté est d'environ 104 et les tensions seuils se situent entre -35 et -45 V pour ce TFT à base de Al(Op) 3 . En revanche, en ce qui concerne le complexe Al(Op) 3 , il fut impossible de mesurer une quelconque mobilité de porteurs de charge que ce soit en temps de vol (en anglais: time of flight -TOF) ou bien en spectroscopie d'admittance (en anglais: admittance spectroscopy -AS). Il en résulte que la conception des dispositifs intégrant ces complexes doit encore être optimisée, afin de pouvoir obtenir des résultats probants en utilisant les deux méthodes précédemment citées.

Étude des interfaces hybrides OSCs/Co

En collaboration avec: Dr. Mirko Cinchetti and Nicolas Großmann (Department of Physics and Research center OPTIMAS, University of Kaiserslautern, Kaiserslautern, Germany) Lors de ma thèse, j'ai étudié le complexe Al(Op) 3 dans l'optique de développer une nouvelle génération de OSCs pouvant être utilisés pour fabriquer des interfaces hybrides et exploiter la flexibilité des semi-conducteurs organiques. Puisque les ligands du complexe Al(Op) 3 sont de plus grande taille que ceux du complexe Alq 3 , la chemisorbtion de ces deux complexes sur une surface de cobalt diffère. Par conséquent, les propriétés dépendantes du spin électronique de l'interface hybride Co/Al(Op) 3 diffèrent de celles de l'interface hybride Co/Alq 3 . En raison des propriétés électroniques hétérogènes exhibées par les OCSs déposés sur un substrat de cobalt, l'interaction entre le complexe et le substrat ferromagnétique présente une grande diversité, que cela soit dans leur nature ou dans leur intensité. Le type d'interaction affecte directement les propriétés quantiques du spin des électrons et, par conséquence, les applications en spintronique de ces interfaces hybrides. L'interface hybride Co/Al(Op) 3 fut analysée en utilisant les méthodes de spectroscopie de photoélectrons (en anglais: photoemission spectroscopy -PES) suivantes: la spectroscopie de photoélectrons UV (en anglais: ultraviolet photoemission spectroscopy -UPS), NT-PS (en anglais: near-threshold photoemission spectroscopy) et la spectroscopie de photoélectrons à Les résultats fournis par les analyses NT-PS pour l'interface Co/[1.5 nm]Al(Op) 3 sont présentés dans le Figure 8. Les deux états hybrides pour cette interface (en anglais: hybrid interface state -HIS) d'énergie respectives E -E F = -0.9 eV et E -E F = -1.6 eV y sont indiqués. Le HIS1 présente une polarisation du spin (en anglais: spin polarization -SP) 8% plus élevé que celui du cobalt, tandis que le HIS2 est caractérisé par un SP 4% plus bas que celui du cobalt. Les OSCs peuvent être modifiés chimiquement afin de changer les propriétés électroniques des interfaces qu'ils forment avec des métaux. Le niveau HOMO dans le coeur des complexes Al(Op) 3 , Al(Op-py) 3 et Alq 3 est respectivement de -3.3 eV, -3.5 eV et -2.7 eV lorsque ces complexes sont déposés sur du cobalt. Les moments dipolaires d'interface des ces trois composés sont quant à eux pratiquement identiques: ∆= -1.5 eV, ∆= -1.8 eV and ∆= -1.5 eV respectivement. Enfin, les mesures 2PPE résolues en spin et en temps montrent qu'aucun état d'énergie d'interface inoccupé (uHISs) n'est présent pour l'interface Co/Al(Op) 3 . Cependant, le niveau LUMO du complexe Al(Op) 3 put être détecté lors des mesures. Puisque le niveau LUMO n'est pas influencé par le SP du substrat de cobalt, la durée de vie des électrons spin-up (τ e up ) et de ceux spin-down (τ e down ) sont identiques.

Aimants mono-moléculaires à base de phenalenyl

En collaboration avec: Dr. Yanhua Lan (INT-KIT, Karlsruhe, Germany) J'ai, par ailleurs, analysé les conditions pour lesquelles les ligands HOp chélatent des atomes xiv paramagnétiques pour former des aimants mono-moléculaires (en anglais: single-molecule magnets -SMMs). Les SMMs ont pour propriété élémentaire de conserver leur magnétisation sur de longues périodes et ce en l'absence de champ magnétique externe. Les lanthanides les plus utilisés pour la fabrication de SMMs sont les suivants: le terbium(III), le dysprosium(III), l'erbium(III)et l'holmium(III). La synthése des complexes à base de dysprosium et de terbium contenant des ligands HOp put être realisée ainsi que la détermination de leurs structures en utilisant les méthodes 1 H-NMR, MALDI-TOF et spectrophotométrie UV-Vis. J'ai fait croitre des mono-cristaux de [Dy(Op) 2 Cl(HOp)(EtOH)] et des mono-co-cristaux de [Dy(Op) 3 (HOp)] et [Dy(Op) 3 (EtOH)], permettant de déterminer leur structure moléculaire de façon inéquivoque (voir Table 6).

Table 6: Structure chimique des complexes de lanthanides à base de phenalenyl. Résultats obtenus par diffractométrie de rayons X. Les résultats obtenus lors des mesures des propriétés magnétiques du complexe [Dy(Op) 2 Cl(HOp)(EtOH)] tendent à montrer que ce complexe est un SMM exhibant, pour un champ statique externe nul, un barrière anisotropique ∆ de 43.8 K et un temps de relaxation quantique de ≈5 × 10 -4 s . Par ailleurs, les même mesures furent répétées en appliquant un champ externe de 200 Oe et permirent d'observer dans ce cas un barriére anisotropique ∆ de 49.4 K et un temps de relaxation quantique de ≈1 × 10 -3 s. Ces résultats permettent de conclure que l'effet tunnel quantique n'est pas très prononcé dans ce composé. Puisque la séparation des deux complexes l'un de l'autre s'avére impossible à réaliser, les mesures des propriétés magnétiques furent réalisées en utilisant les co-cristaux de [Dy(Op) 3 (HOp)] et de [Dy(Op) 3 (EtOH)]. Lorsque aucun champ magnétique statique externe n'est appliqué, la susceptibilité ne présente pas de déphasage, ce qui pourrait être du à une forte résonance de l'effet tunnel quantique. Les mesures furent répétées pour des champ magnétique statiques externes de 1500 Oe et 3000 Oe. Pour un champ magnétique externe de 1500 Oe, le temps de relaxation calculé suit un activé comportement et le gap d'énergie est de ∆ 14.1 K tandis que pour un champ externe de 3000 Oe la barrière anisotropique ∆ est de 7.6 K lors de la relaxation à haute fréquence. De plus, j'ai pu synthétiser et caractériser d'autres complexes de dysprosium et de terbium. Par exemple, en condition anhydre, j'ai pu obtenir et sublimer des complexes de dysprosium et de terbium à base de phenalenyl. La synthèse de ces composés pourrait permettre de réaliser la déposition de complexes de lanthanides à base de phenalenyl sur des substrats. Cela permettrait ainsi d'ouvrir la porte à leur étude, sous réserve d'obtenir des mono-cristaux condition nécessaire pour connaitre leur structure exacte.

Lors de ma thèse, j'ai conduit et présenté une analyse systématique de nouveaux materiaux OSCs très prometteurs. J'ai pu mettre en évidence ainsi le lien entre la structure chimique et les propriétés électroniques de ces matériaux. La première étape de mon travail consista à synthétiser les OSCs ainsi qu'à caractériser leur structure. Les analyses photo-physiques et électrochimiques réalisées permirent de déterminer les propriétés électroniques de ces nouveaux matériaux. Les résultats obtenus se révélÃĺrent être en bon accord avec les calculs théoriques. Par ailleurs, les mobilités des porteurs de charge purent être calculées en faisant appel à des méthodes de calcul développées récemment telles que DEPOSIT et Quantum Patch. En ce qui concerne les mesures expérimentales des mobilités, de premiers résultats probants furent obtenus pour le complexe Al(Op) 3 en utilisant la méthode FET. En mÃłme temps que l'analyse systématique des complexes OSCs simples, j'ai pu étendre l'analyse à quelques interfaces hybrides OSC/cobalt . Par exemple, l'analyse de la surface hybride Co/Al(Op) 3 par PES montra la formation de HISs.

Parallèlement à mon projet principal, je présente dans ma thèse les premiers résultats obtenus pour des SMMs de lanthanides à base de phenalenyl. Ces résultats préliminaires sont très encourageants puisqu'ils mettent en évidence que les complexes de dysprosium exhibent un comportement caractéristique de SMMs. Par ailleurs, l'obtention de complexes se laissant sublimer ouvre la porte à la déposition de ces molécules sur des substrats par évaporation et, ainsi, à de futures applications en spintronique. xvi

Introduction

I would begin the thesis clarifying what is the meaning of its title: "Multifunctional Complexes for Molecular Devices". Firstly, what is a multifunctional complex?. The Oxford English Dictionary [1] defines "multifunctional" as: "having or fulfilling many functions", while the substantive "complex" is defined as: "a substance formed by the combination of simpler substances, especially one in which the bonds between the substances are weaker than or of a different character from those between the constituents of each substance". Hence, a coordination compound such as a metal chelate, which can accomplish a variety of functions, can be considered as a "multifunctional complex". Secondly, what is a molecular device? The definition of "molecular" is: "pertaining to, consisting of, or concerned with molecules". One of the many definitions of "device" is: "the result of contriving; something devised or framed by art or inventive power; an invention, contrivance; especially a mechanical contrivance (usually of a simple character) for some particular purpose". In other words, a molecular device is an invention (a tool or an instrument) based on one, or more molecules developed and built to fulfill specific intentions.

In this thesis, we have studied metal complexes belonging to the class of materials known as organic semiconductors (OSCs), which are molecules able to transport charge carriers (electrons and/or holes), but also to exhibit photo-and electro-luminescence, and, as described in the succeeding sections, many more interesting properties.

Around the middle of the last century, the invention of the transistor gave rise to the era of inorganic semiconductors such as silicon and germanium. Contemporaneously, the substitution of vacuum tube based electronics by solid state devices led to the semiconductor microelectronics we experience in our everyday life. The first promise of OSCs was to realize large area, flexible, printed and low cost electronic and optoelectronic devices. First studies on mere conductivity and photoconductivity of anthracene crystals were published in the beginning of the 20th century by Koenigsberger et al. and Volmer [2,3]. With the discovery of electroluminescence (EL) in the 1960s [4,5], and the work of many researchers, the basic processes involved in optical excitation and charge carrier transport were established [6,[START_REF] Pope | Electronic processes in organic crystals and polymers[END_REF]. The successful synthesis and controlled doping of conjugated polyacetylene polymers (see Figure 1.1) in the 1970s [8] opened the way for a new class of OSCs, which was awarded with the Nobel Prize in Chemistry in the year 2000. Finally, the demonstration of high-performance OLEDs (Organic Light Emitting Diodes) based on vacuum-deposited molecular films [9,10] and on conjugated polymers [11,12] revived the interest in undoped OSCs. Besides OLEDs, OSCs are nowadays implemented in a variety of devices such as organic photovoltaic cells (OPVs) [13,14], organic spintronic devices (OSPDs) [15] and organic field-effect transistors (OFETs) [16].

"The exciting idea of being able to combine the flexibility and low weight of plastics with the electric properties of metals has stimulated scientists all over the world, resulting in a novel research field bordering physics and chemistry. Various theoretical models and new conductive, but also semi-conductive, polymers followed during the 1980s in the wake of the first discoveries. Today we can see several possible applications. How about electrically luminous plastic that may

Figure 1.1: Polyacetylene polymers studied in reference [8]. Left: trans-polyacetylene. Right: cis-polyacetylene.

be used for manufacturing mobile phone displays or the flat television screens of the future? Or the opposite -instead using light to generate electric current: solar-cell plastics that can be unfolded over large areas to produce environmentally friendly electricity. Finally, lightweight rechargeable batteries may be necessary if we are to replace the combustion engines in today's cars with environmentally friendly electric motors -another application where electrical polymers might find use.

In parallel with the development of conducting polymers, there is an ongoing development of what we might call "molecular electronics," where the very molecules perform the same tasks as the integrated circuits we just heard about in the Nobel Prize in Physics, with the difference that these could be made incomparably smaller.

Organic semiconductors (OSCs)

Figure 1.2: σ-and π-bonds in ethene as an example for the simplest conjugated π-electron system. On the right-hand side are depicted energy levels and lowest electronic excitation of ethene. Source: [START_REF]Physics of organic semiconductors[END_REF].

In solid state physic it is convenient to distinguish between three different material classes by means of electrical properties: metals (conductors), semiconductors, and insulators. In general, they are defined by the value of their energy band gap between valence and conduction bands and by the position of the Fermi energy. We will focus on the class of OSCs briefly explaining the main features of these materials (for a review on OSCs see [START_REF]Physics of organic semiconductors[END_REF][START_REF][END_REF][START_REF] Schwoerer | Organic molecular solids[END_REF]).

There are two main classes of OSCs: low molecular weight (small molecules) and polymers.

Both have in common a conjugated π-electron system formed by the p z -orbitals of sp 2 -hybridized carbon atoms. The most important difference between the two classes of OSCs is the processing method to form thin films. Low molecular weight OSCs are usually deposited from the gas phase by sublimation or evaporation in vacuum. Polymeric OSCs are processed by solutionbased methods such as spin-coating or printing techniques. For both, the controlled growth of high quality films is crucial for the applications in devices [START_REF] Faupel | [END_REF]. In both classes of OSCs, carbon atoms are bonded with strong σ bonds, which form the backbone of the molecule, and significantly weaker π bonds (see Figure 1.2). As a consequence, the lowest electronic excitation of conjugated molecules are π -π * transitions with an energy gap (calculated from the main absorption band) between 185 and 580 nm resulting in absorption and emission ranging from UV to visible wavelengths. As illustrated in Table 1.1, it is possible to tune the energy gap by increasing the degree of conjugation of polyenes and polyacenes. This is an example on how chemistry tools are used to significantly modify the electronic properties of OSCs. The fundamental interaction between different molecules in organic crystals or in amorphous films are the van-der-Waals forces. Hence, due to the weak electronic delocalization between adjacent molecules, electronic and optical properties of isolated molecules are similar to those of molecules in solid state. All the basic optical energy conversion processes of an organic molecule or solid are exemplified in the Jablonsky diagram shown in Figure 1.3. Optical excitation processes take place between the singlet ground state S 0 (HOMO) and singlet excited states S 1 (LUMO), S 2 , ... , S n ; singlet states have multiplicity equal to 1. The radiative decay process between S 1 and S 0 is called fluorescence, however, S 1 can experience also non-radiative decays (thermal decay, quenching, ...). Higher singlet excited states undergo a very fast non-radiative internal conversion process to S 1 , and thus, normally, no radiative processes are observed between S 2 , ... , S n and S 0 [START_REF][END_REF]. Triplet states T n have multiplicity equal to 3, as a result, due to the quantum mechanical selection rules, the radiative decay from triplet states to S 0 (phosphorescence) is strictly forbidden if no spin-orbit coupling is present in the molecule [START_REF][END_REF]. Triplet emission of molecules constituted from carbon and hydrogen is weak, in contrast, when heavy atoms with a strong spin-orbit coupling are introduced, the phosphorescence process can occur. The triplet state T 1 is formed by intersystem crossing from S 1 rather than by a direct optical excitation S 0 -T 1 . Intersystem crossing processes are triggered by the spin-orbit coupling resulting in a spin-flip from S 1 to T 1 . Higher triplet states are formed by triplet-triplet annihilation processes, in which two triple states fuse generating a ground state S 0 and higher triplet states T 2 , ... ,T n . These states transform in singlet states by intersystem crossing resulting in a delayed fluorescence [START_REF] Kondakov | [END_REF]. Rates of absorption k and radiative Γ r and non-radiative Γ nr decays depend from the overlap between the wavefunctions of initial i and final f states, which are determined by the transition matrix elements, if one of the three factors is zero, the transition is forbidden with a null probability P i→f to occur.

Optical properties of OSCs

P 2 i→f ∝| Ψ f | p|Ψ i | 2 ∝| Ψ el,f | p|Ψ el,i | 2 • | Φ vib,f |Φ vib,i | 2 • | χ spin,f |χ spin,i | 2 (1.1)
In Equation 1 The last parameter to take in account, | χ spin,f |χ spin,i |, concerns the spin selection rule of an electronic transition. Basically, transitions between spin states with different multiplicities are forbidden. Therefore, only transitions between singlet states, such as fluorescence, are allowed.

Introduction

However, in case of spin-orbit coupling, induced by heavy atoms, transitions between singlet and triplet states, such as phosphorescence, are allowed.

Electrical properties of OSCs

Macroscopically, the current through a material is given by the charge carrier density n and the carrier drift velocity ν, which can be expressed by the mobility µ and the electric field F [START_REF]Physics of organic semiconductors[END_REF]:

j = qnν = qnµF (1.2)
where, j is the current density and q is the elementary electric charge. In general, the charge carrier mobility exhibits a non-linear behavior and depends on the charge carrier density n, the temperature T , and the electric field F . The intrinsic charge carrier density in a semiconductor is given by:

n = N 0 exp - E gap 2k b T (1.3)
where, N 0 is the density of organic molecules, E gap is the HOMO-LUMO gap, k b is the Boltzmann constant, and T is the temperature. For a typical organic molecular solid, with E g = 2.5 eV and N 0 = 10 × 10 21 cm -3 , at room temperature the charge carrier density is n= 1 cm -3 (silicon n= 10 10 cm -3 ) [START_REF]Physics of organic semiconductors[END_REF]. As a result, OSCs are characterized by extremely low conductivity if no additional free charge carriers are created. To increase the carrier density in molecular solids, different means can be applied, which are the fundamental processes involved in OSCsbased devices. OLEDs are governed by the injection of charge carriers from electrodes into organic layers. Similarly, in OSPSs, charges (spins) are injected from ferromagnetic electrodes into non-magnetic organic materials. In contrast, in OPVs charge carriers are photogenerated by absorption of light. In OFETs, the density of charge carriers, which are injected from source and drain electrodes, is controlled by the applied gate voltage across the dielectric. films, only the hopping mechanism is discussed in the following. The motion of a charge between two localized energy levels under an applied field is described by the hopping transport mechanism [23]. OSCs in amorphous films, due to a statistical alignment of molecules during the film growth, are characterized by distributed energy levels resulting in shifted HOMO and LUMO energies [START_REF] Pope | Electronic processes in organic crystals and polymers[END_REF][24][25][26], as illustrated in Figure 1.5. HOMO and LUMO energies are shifted compared to those of an isolated molecule owing to interactions with the surrounding environment. Considering a statistical number of molecules in an amorphous film, a Gaussian distribution of energy, with typical width (σ h and σ e ) of 75-100 mV, is assumed [23]. As a result, the hopping of charge carriers must be thermally activated to overcome the energetic barriers between localized states. Lastly, the presence of trap states, which can be a very low LUMO or a very high HOMO, influences the charge transport resulting in low charge carrier mobilities, and thus, poor performance of devices. Alq 3 is, beyond any doubt, a multifunctional complex implemented in a multitude of molecular devices. The very first application of quinolin-8-ol metal chelates was in analytical chemistry for the gravimetric determination of metal cations in solution [28]. Since its first application in an electroluminescent device [9], Alq 3 is one of the most widely known OSC [START_REF] Li | Organic Light-Emitting Materials and Devices[END_REF]. Before describing in detail the applications of Alq 3 in molecular devices, we will focus our attention on the chemical structure of Alq 3 , which is at the origin of its properties.

Alq 3 is formed by three bidentate anions, quinolinates, which fill the coordination sites of the central metal ion, Al 3+ . The resulting net charge of the complex is zero. Alq 3 is also well known to be a MN 3 O 3 octahedral complex, where M is a trivalent metal, whereas N and O stand for the nitrogen and oxygen atoms, respectively, in the quinoline ligand. These octahedral complexes can occur in two different geometric isomers, the meridianal and the facial isomer, which are illustrated in Figure 1.6 [27,[START_REF] Kauffman | [END_REF]. In the facial isomer, the three oxygens face the three nitrogens. Diversely, in the meridianal isomer, two oxygens are opposite to each other as well as two nitrogens and one oxygen faces one nitrogen.

The conventional synthesis of Alq ] mer-Alq 3 Al1-O1 1.8789(10) O1-Al1-O2 167.98(5) O2-Al1-N3 95.28(5) Al1-O2 1.8553(10) O1-Al1-O3 96.35 (5) O3-Al1-N1 90.17 [31]. On the contrary, fac-Alq 3 has been difficult to isolate for its relatively short lifetime in solution [32]. Nevertheless, by the solid-state synthetic procedure described by Katakura et al., it is possible to efficiently produce the fac-isomer [33]. Since fac-Alq 3 has quite distinct properties compared to those of mer-Alq 3 , it has been extensively studied [27]. The molecular structure of mer-Alq 3 , obtained by single crystal X-ray diffraction, was first reported for single crystals grown in methanol [34] and in ethyl acetate [35]. We have grown single crystals of mer-Alq 3 in ethanol; the molecular structure obtained by single crystal X-ray diffraction is illustrated in Figure 1.7, in addition, selected bond distances and angles are listed. An intrinsic asymmetry, caused by the positions of the six chelating atoms, characterizes mer-Alq 3 . In detail, O1 faces O2 and N1 faces N3, in contrast, O3 is opposite to N2. This results in an elongation of the bond Al-N2 (2.0637 Å) compared to the bonds Al-N1 and Al-N3 (2.0238 Å and 2.0421 Å, respectively), and a shrinking of the bond Al-O3 (1.8384 Å) compared to the bonds Al-O1 and Al-O2 (1.8789 Å and 1.8553 Å, respectively). In addition, the narrow bite angle of Hq and the electrostatic repulsion between nitrogens and oxygens, induce a distorted octahedral geometry of the six chelating atoms, with bond angles of 82.14 Due to the electron deficient quinoline, Alq 3 is characterized by high LUMO and HOMO, ≈-3.0 eV and ≈-6.0 eV, respectively [36][37][38] (-3.01 eV and -5.83 eV experimentally estimated in Section 3.6). As a consequence of its good thermal stability [39], Alq 3 can be deposited by vacuum evaporation forming amorphous pinhole-free thin films [40], which are likely containing both the mer-Alq 3 and fac-Alq 3 [41]. In addition, Alq 3 in amorphous thin film is characterized by electron and hole mobilities of 10 -5 -10 -6 cm 2 V -1 s -1 and 10 -8 -10 -9 cm 2 V -1 s -1 , repectively [42][43][44][45][46][47][48][49]. All these characteristics make Alq 3 and ideal material for applications in OSCs-based devices.

Alq 3 in OLEDs

OLEDs are devices in which the light emission originates by the radiative recombination of charge carriers in organic layers (for a review on OLEDs see [START_REF][END_REF]). An elementary OLED can consist of a single organic layer sandwiched between two electrodes [11], however, to improve the device efficiency, multilayer OLEDs, in which each organic layer fulfill a specific function, are preferred. In a simple configuration, an OLED is composed by three organic layers: the electron transport layer (ETL), the hole transport layer (HTL), and the emission layer (ETL). As illustrated in Figure 1.8, the working principle of OLEDs is described by four main processes:

(1) injection of electrons from the cathode into the LUMO of the ETL and injection of holes In the schematic energy diagram shown in Figure 1.8, the barriers for the injection of electrons and holes into the organic materials are illustrated. At first it is important to define the built-in potential Φ BI , which is the difference between the work functions Φ A and Φ C of anode and cathode, respectively. As a consequence, to inject charge carriers into the organic layer, it is necessary to apply a voltage V higher than: V BI = (1/e)(Φ A -Φ C ). Additional injection barriers for holes and electrons, Φ h and Φ e , respectively, are defined by the Fermi energy of the metals and the HOMO and LUMO of the organic materials. In detail, for holes, Φ h = E HOM O -Φ A , and for electrons, Φ e = E LU M O -Φ C . To minimize the injection barriers, it is fundamental to choose electrodes and organic materials with an as low as possible mismatch between work 1.2 Tris-(8-hydroxyquinoline)aluminum (Alq 3 ) function and the energy of HOMO and LUMO.

To measure the performance of OLEDs, the most important parameter is the electroluminescence quantum efficiency η EQE . It is defined as the ratio between the number of emitted photons and injected charges [50]:

η EQE = γη S/T q ef f η out (1.4)
where, γ is the charge balance factor describing what fraction of electrons and holes injected recombine. The fraction of excitons that is allowed to decay radiatively by spin statistic is given by η S/T . The factor q ef f indicates how many spin-allowed excitons decay radiatively. At last, η out is known as the outcoupling factor which measure the fraction of generated photons escaping the device. Another important parameter is the luminous efficacy η P [lm W -1 ], which is defined as the luminous flux Φ L [lm] at given drive conditions (voltage V and current I):

η P = Φ L V I ; Φ L = K m 780nm 380nm V (λ)Φ R (λ)dλ (1.5)
The luminous flux Φ L quantify the amount of visible light produced by an OLED considering the sensitivity of the human eye. It is calculated by the integration over the whole visible spectra of the spectral flux of radiation Φ R [W nm -1 ] and the response curve of the eye (photopic curve) V (λ) [START_REF] Diekmann | white paper on the necessity of luminous efficacy measurements standardization of OLED light sources[END_REF]. In the first demonstration of a double-layer OLED based on low molecular weight OSCs by Tang and VanSlyke, the hole-transporting materials was TAPC (1,1-bis4-[di(p-tolyl)amino]phenylcyclohexane), the electron-transporting and emitting material was Alq 3 , and the electrodes were ITO (indium tin oxide) and an alloy of silver and magnesium [9]. In this experiment, an external quantum yield η EQE of 1%, a luminous efficacy η P of 1.5 lm W -1 , and ) by two orders of magnitude compared to the single-layer device, as a result of the enhanced charge balance [52]. Several attempts to improve the properties of Alq 3 by structural modifications were made, as an example, other metal chelates containing two or three quinolines were investigated (see Figure 1.10) [53][54][55][56][57]. As emitting material, Gaq 3 -based devices resulted in similar external quantum yield η EQE and 50% higher luminous efficacy η P compared to those of Alq 3 -based devices [53]. On the other hand, Inq 3 was superior as electron-transporting material, probably due to its lowered LUMO ≈-3.4 eV and improved electron mobility with the increase in size of the central metal ion [54]. OLEDs based on Znq 2 yielded a higher luminance 16 200 cd m -2 and required lowered operating voltages indicating improved electron injection and transport, compared to those of Alq 3 -based devices [55,56]. Another strategy, exploited to improve the properties of Alq 3 , was to chemically modify the ligand Hq. Examples among the multitude of reports on structurally modified Alq 3 are: AlOq 3 and Alq(Clq) 2 (see Figure 1.11) [58,59]. AlOq 3 is reported to form super molecular structures in the thin film, due to the hydroxymethyl groups which form hydrogen bonds, yielding luminous efficacy η P three times higher than similar Alq 3 -based OLEDs [58]. Diversely, Alq(Clq) 2 -based OLEDs showed a red-shifted emission compared to that of Alq 3 -based devices.

N O N O N O Al N O N O N O Al R 2 R 2 R 2 R 1 R 1 R 1 Figure 1.
12: Chemical structures of the 5-substituted Alq 3 . In the left hand side complex the electron-rich and -poor substituents are bonded to the quinolinate by an ethynyl bridge. In the right hand side complex the electron-rich and -poor substituents are directly bonded to the quinolinate. Source: [38].

At last, in a comprehensive work of Montes et al., series of electron-poor and -rich functionalities were used to substitute the 5-position of Hq (see Figure 1.12) [38]. It was found that the HOMO was effectively manipulated while the LUMO was largely unaffected. From the characterization of OLEDs based on modified Alq 3 's, the tunability of the electroluminescence spectra was demonstrated with emission ranging from blue to red. However, the external quantum yield η EQE and the maximum ratio between luminance and current density through the device [cd A -1 ] of the OLEDs were, in the best case, similar, but normally lowered compared to those of OLEDs based on pristine Alq 3 . The reported examples are only few among the vast number of works on Alq 3 derivatives, however, the review of all the literature is exceeding the purpose of this introduction.

Alq 3 in OPVs

In organic photovoltaic devices (OPVs) the light energy is directly converted into electrical energy, in a reverse way of what happens in OLEDs (for a review on OPVs [13,14,[START_REF][END_REF]). As illustrated in Figure 1.13, OPVs can be made of a single organic thin layer sandwiched between two electrodes (ITO and silver in the figure). Since the work function of the two conductors are different, electrons will flow from the conductor with the highest work function to that with the lowest work function until they reach the same chemical potential. The charge that builds up in the two electrodes generates an electric field across the semiconductor. When light is absorbed by the OSC, an exciton (electron-hole pair) is formed, and the electric field pulls the electrons toward the positive electrode and the holes toward the negative electrode resulting in a net electric current. However, due to the strong binding energy of excitons, single layer OPVs yield poor performance. By adding a second OSC layer, a so-called pn-heterojunction is formed. Generally, p-type and n-type OSCs stand for electron-donating and -accepting organic semiconductors, respectively [61]. When the exciton is formed near the pn-heterojunction, the charge separation takes place more efficiently. In detail, electrons can easily transfer from the electron-donating to the electron-accepting material toward the positive electrode, and holes travel in the opposite way to the negative electrode. To further increase the efficiency of OPVs, p-and n-OSCs were interpenetrated aiming to extend the pn-heterojunction, and thus, favor the charge separation of excitons [62,63]. The latter type of OPV is called bulk heterojunction cell. The main processes occurring in bulk heterojunction OPVs are illustrated in Figure 1.14: (1) light absorption and excitons generation, (2) diffusion of excitons to the heterojunction, (3) charge transfer of electrons into the electron-accepting material and of holes into the holeaccepting material, (4) exciton dissociation, and (5) holes and electrons transport to the electrodes leading to the photocurrent. Side processes can occur: (i) recombination of excitons before reaching the heterojunction, and (ii) recombination of excitons at the heterojunction. Performance of OPVs is estimated by the power conversion efficiency η p , which is defined as the ratio between the maximum power P max delivered by the device and the incident power of the light source P in . The maximum power P max is equal to J m V m , where J m and V m are the current and voltage at the maximum power point, respectively.

η p = (J m V m ) P in = J SC V OC F F/P in (1.6)
where, J SC is the short-circuit photocurrent density, V OC is the open circuit voltage (see Fig- 14), and F F is the fill factor. The latter is an indication of the diode quality and is mainly influenced by the charge carrier transport and recombination. Extensive studies on OPVs have been triggered by the demonstration of a planar pn-heterojunction based on copper phthalocyanine (CuPc) and perylene sandwiched between ITO and silver electrodes, reported by Tang [66]. A power conversion efficiency η of about 1% and a fill factor F F of 0.65 were recorded under simulated AM2 white light at 75 mW cm -2 .

1 Introduction ure 1.
OPVs implement active materials such as porphyrins, phthalocyanines, perylenes, fullerenes, polymer hybrid structures and more [13,14]. However, Alq 3 was successfully utilized as buffer layer between cathode and active layer in bulk heterojunction devices [64,65] (see Figure 1.15). In the work of Song et al., Alq 3 was used as electron-transporting and hole-blocking material to carry electrons and, simultaneously, to prevent the leakage of holes to the cathode, resulting in a power conversion efficiency η p = 2.11% [64]. As a main result, the lifetime of OPVs including Alq 3 was ≈150 times longer than that of OPVs implementing BCP (2,9-dimethyl-4,7diphenyl-1,10-phenanthroline), which is the most widely used interfacial layer on the cathode side [13]. The increased stability is attributed to the formation of a superior barrier against oxygen, water molecules, and metal atom diffusion from the cathode to the active layers. Similarly, in the work of Yu et al., Alq 3 was introduced between C60 and the aluminum electrode as electron transport layer and, in addition, to avoid the damage of C60 during the deposition of cathode [65]. However, this study aimed to investigate SnCl 2 Pc and F 16 CuPc (tin phthalocyanine dichloride and copper hexadecafluorophthalocyanine, respectively) as connecting units in tandem cells. Despite the few examples of OPV implementing Alq 3 , it is clear that, due to its easy processability to form uniform and stable films, and its convenient HOMO and LUMO energy levels, which make Alq 3 a good electron-transport and hole-blocking material, Alq 3 can be utilized in OPVs. The study of the transport of electrons, depending on the spin degree of freedom, through metallic and semiconducting devices is called spintronics (for a review [15,[START_REF][END_REF]). Spin valves are

Alq 3 in OSPDs

1.2 Tris-(8-hydroxyquinoline)aluminum (Alq 3 )
the typical OSPD consisting of, in the simplest form, two ferromagnetic electrodes separated by a nonmagnetic (organic) spacer. Since the electrodes are characterized by two distinct switching fields, the device can switch from a parallel to an antiparallel magnetization configuration applying an external magnetic field. The significant difference between the two configurations is called giant magnetoresistance (GMR) (see Figure 1.16); for the work on GMR, Fert and Gründberg were awarded with the Nobel prize in 2007 [http://www.nobelprize.org/nobel _prizes/physics/laureates/2007/]. When a thin layer of insulator is sandwiched between the two ferromagnetic electrodes, the corresponding effect is called tunneling magnetoresistance (TMR) [67,68]. OSCs represent an interesting material class for spintronics, due to the little spin-orbit coupling of light atoms and the versatility of organic materials [15]. ferromagnetic electrodes into an organic layer of sexithiophene (6T) [70]. A strong MR up to 30% was measured on nanostructured planar hybrid junctions LSMO/T-6/LSMO. In addition, spin diffusion length and spin relaxation time in T6 were estimated in about 200 nm and 1 µs, respectively. Among OSCs, Alq 3 is the most implemented material in OSPDs, mainly due to its processability, electron mobility, and reproducibility of results [15]. The first example of an Alq 3 -based OSPD, in which Alq 3 was sandwiched between LSMO and cobalt ferromagnetic electrodes in a vertical architecture, was reported by Xiong et al. [69] (see Figure 1.17). A MR of ≈40% was measured at 11 K, in addition, the MR was still detectable up to 200 K. Moreover, the device showed an inverse magnetization, in which a lowered MR was detected for an antiparallel magnetization of the electrodes. These results have been confirmed in a reproducible way in several other experiments [71][72][73].

TMR was detected in Alq 3 -based OSPD by Barraud et al. [74]. A thin layer of Alq 3 (2 nm) was sandwiched between LSMO and cobalt ferromagnetic electrodes with a nanoindentation technique, as illustrated in Figure 1.18. As a result, a TMR up to 300% was detected at 2 K.

In contrast to the Alq 3 -based OSPDs previuosly described, which show a negative MR, in this case, a positive MR is observed. In a recent communication by Prezioso et al., Alq 3 -based OSPDs showed memristance behavior [75]. In few words, the defining property of a memristor is the non-volatile variation of its resistance (memristance), which depends on the history of the applied current or voltage.

19).

The origin of MR is ascribed to the hybridization between the ferromagnetic cobalt surface and the planar structure of ZMP, which creates an anionic radical with a net momentum. Source: [61].

Organic field-effect transistors (OFETs), in the thin film transitor (TFT) architecture, are formed by three conducting electrodes (source, drain and gate), a gate dielectric (insulator), and an OSC as active material (for a review see [16]). Generally, OFETs are built in a top-or bottom-contact configuration, as illustrated in Figure 1.20. Depending on the voltage applied to the gate electrode there are two states in which OFETs can be. The off-state is referred to the state when no voltage is applied to the gate electrode and only small currents flow between source and drain electrodes. In contrast, the on-state is referred to the state when voltage is applied to the gate electrode and there are consistent current flows between source and drain electrodes. In more detail, when a negative voltage is applied to the gate electrode, hole carriers accumulate at the interface between OSC and gate dielectric, and thus, hole currents occur from the source to the drain electrode. This kind of OFET is called p-channel device. In the opposite way, a n-channel device is characterized by electron currents between source and drain electrodes resulting from the accumulation of electrons at the interface between gate dielectric and OSC induced by a positive voltage applied to the gate electrode. In addition to p-and n-channel devices (unipolar OFETs), ambipolar OFETs, in which the simultaneous transport of holes and electrons occurs, can be obtained. The best performance is obtained for p-channel devices based on single crystals of pentacene, rubrene and copper phthalocyanine [61]. On the contrary, n-channel devices display lowered stability and performance with the best results obtained for OFETs based on fullerenes and fullerene derivatives [61]. Due to its relatively low charge carrier mobilities, Alq 3 is not among the most implemented OSCs in OFETs. Nonetheless, it was successfully integrated in two specific classes of OFETs: ambipolar OFETs and LE-OFETs (light-emitting OFETs). In few words, LE-OFETs (light-emitting OFETs) combine functions of OLEDs and OFETs. Strictly speaking, electrical switching is enabled by modulation of the current flow between the source and drain electrodes under tuned gate bias voltage, whereas electroluminescence takes place by electron-hole recombination in the transistor channel [77].

In the example reported by Sakanoue et al., Alq 3 was utilized as organic material in singlecomponent ambipolar OFETs [78] (see Figure 1.21). The FET electron mobility µ obtained for the n-channel device, built with calcium electrodes, was 5.5 × 10 -7 cm 2 V -1 s -1 with a thresh- old voltage V T of 64 V. To measure the hole mobility, a bottom-contact configuration, with interdigital electrodes of Au/Cr (L= 76 mm, W = 25 µm) on a HMDS (hexamethyldisylazane) treated substrate, was used to enhance the drain current. As a result, for the p-channel device, the measured FET electron mobility µ was 1.6 × 10 -7 cm 2 V -1 s -1 with a threshold voltage V T of -43 V. [79]. By implementing the uncommon fabrication strategy illustrated in Figure 1.22, the authors could form heterojunctions between pentacene (chemical structure in Table 1.1) and Alq 3 . A hole mobility µ between 1.8 × 10 -3 and 2.1 × 10 -3 cm 2 V -1 s -1 , a threshold voltage V T of -10 V, and a on/off current ratio between 10 3 and 10 4 were measured. For electrons, the mobility µ was 1.6 × 10 -6 cm 2 V -1 s -1 , the threshold voltage V T was 20 V, and the on/off current ratio was 10 3 . Additionally, for the device built with gold as source electrode, and lithium fluoride (LiF) as drain electrode, emission of light was detected. Here, the light-emitting layer, formed by Alq 3 doped with DCM1 (chemical structure in Figure 1.9), was inserted between p-type (DH-4T) and n-type (DFH-4T) layers [80]. In this device, electroluminescence spread over the entire channel was detected. The measured external quantum efficiency, η EQE = 5%, exceeds the best OLED based on the same emitting layer and optimized transport layers (η EQE = 2.2%) [81].

Theoretical and experimental techniques implemented to study the (novel) OSCs

In this thesis we have synthesized and studied a series of (novel) OSCs. Chapter 3 outlines synthetic strategies and characterization results. Firstly, the (novel) OSCs were structurally characterized by means of proton and carbon nuclear magnetic resonance (NMR), matrix-assisted laser desorption/ionization-time of flight (MALDI-TOF), electro-spray ionization-time of flight (ESI-TOF), elemental analysis, and single crystal X-ray diffraction. Secondly, the photophysical and electrochemical properties of the OSCs were determined. The photophysical characterization was carried out measuring absorption, emission and (in some cases) excitation spectra of the (novel) OSCs. Photophysical measurements are fundamental to investigate molecular orbitals and main transitions between ground and excited states of the OSCs. In addition, from the absorption spectra it is possible to estimate HOMO-LUMO gaps. Electrochemical studies, by means of cyclic voltammetry (CV), were performed to measure the reduction potential (electron affinity) of the OSCs, and thus, to evaluate their LUMO energy levels. Moreover, for Alq 3 and Al(Op) 3 a complete photophysical characterization was carried out to measure the fluorescence quantum yield and the excited state lifetime in solution and in thin film. Lastly, we have determined the HOMO and LUMO energy levels, which are fundamental to assess the possible implementation of the (novel) OSCs in devices. The LUMO energy level was calculated from the reduction potential measured in solution CV, and the HOMO-LUMO gap was estimated from the first absorption band in the absorption spectrum. Knowing the LUMO energy and the HOMO-LUMO gap, the HOMO energy level was computed easily.

Introduction on the theoretical methods

In the first part of Chapter 4, the most interesting OSCs synthesized in Chapter 3 were studied by means of newly developed theoretical methods. A brief introduction on the theoretical methods is given in the following. To start with, all the quantum chemical characterizations in Section 4.2.1 were done with TURBOMOLE [82] on a B3-LYP [83] /SV(P) [84] level of theory.

The atomistic morphologies, presented in Section 4.2.2 were generated with a Monte Carlo based simulated annealing method [85]. The method starts with a set of initial coordinates { r i (t 0 )} and make use of random guesses for new coordinates { r i (t 1 )} for one atom. The total energy E 1 of the new system is evaluated and compared to the initial total energy E 0 . The new step is accepted to a certain possibility, the Metropolis-criterion in Equation 1. [START_REF] Pope | Electronic processes in organic crystals and polymers[END_REF].

ω(0→1) =    1 if E 1 ≤ E 0 exp -E 1 -E 0 k b T if E 1 > E 0 (1.7)
In the DEPOSIT code, molecules are sequentially added to the simulation box. For each molecule, a certain number of Monte Carlo steps is performed in order to find an energetically favorable position and configuration of the molecule. The deposition is repeated and the final position with the lowest energy is chosen. Afterward, a simulated annealing process is possible to relax the local environment of the new molecule.

Microscopic properties, such as energetic disorder, reorganization energy and electronic coupling, described in Section 4.2.3, were calculated with the Quantum Patch method as described by Friederich et al. [START_REF] Friederich | Simulation of energetic disorder and charge transport in amorphous organic semiconductors[END_REF][START_REF] Friederich | [END_REF]. These microscopic parameters were used in an analytic Marcusrate [88] based effective medium approach [89] in order to estimate charge carrier mobilities for electrons and holes for zero-field and low carrier concentration. All quantum chemical calculations involved directly into the multi-scale work-flow, as well as any additional quantum chemical characterization were done with TURBOMOLE [82] on a B3-LYP [83] /SV(P) [84] level of theory. For reorganization energies, a def2-TZVP [90] basis set was used.

When modeling charge transport in disordered organic material, where charges propagate by a succession of leaping processes between neighboring localized sites, the hopping transport formalism is a common starting point. In the case of weakly coupled sites [91] and time scale of local charge reorganization smaller than the time scale of a single hopping process, Marcus theory [88] is widely used for the calculation of charge hopping rates.

k if = 2π |J if | 2 1 4πλ if k B T exp - (λ if + ∆G if ) 2 4λ if k B T (1.8)
where k if is the hopping rate, is the Plank constant, J if is the electronic coupling, λ if is the reorganization energy, k B is the Boltzmann factor and ∆G if is the Gibbs free energy difference of initial and final states. Materials specific parameters can be mapped onto transport models, which can then be used for the calculation of charge carrier mobility and other experimentally relevant quantities in master equation approaches [92][93][94].

In the quantum patch approach, the Hamiltonian operator for a system of N weakly coupled molecules with the total density n(r) is approximated by:

Ĥ = diag(H 1 [n tot ( r)], ..., H N [n tot ( r)]) (1.9)
neglecting inter-molecular contributions to kinetic energy and exchange interactions. This approximation is reported in many embedding methods for weakly coupled molecules [95][96][97]. As a result, under the condition that the total charge density is known, the Hamiltonian for each molecule con be solved separately. To iteratively solve the electronic structure of the system we partition the total charge density n tot (r) into a sum of charge densities of single molecules. To calculate the charge density for the molecule i, the charge densities n j =i (r) of the neighboring molecules are replaced by a set of point charges where k is the index of the respective atom at the position R j,k .

n µ tot ( r) = n µ i ( r) + j =i,k q µ j,k δ( r -R j,k ) (1.10)
Intermolecular electrostatic interactions are taken into account by employing partial charges fitted with the Merz-Singh-Kollman scheme (ESP-charges) [98] which are specifically designed to reproduce the electrostatic field of a molecule. The process begins by guessing the initial partial charges q 0 j,k , using vacuum partial charges, for each molecule, and then, solve the Schrödinger equation for each molecule self-consistently. Subsequently, the partial charges are recalculated on the basis of the new electron densities n µ i = j |Φ µ i,j (r)| 2 for the molecule i, with Kohn-Sham orbitals Φ i,j . These densities are used in the calculations for the other molecules, such that µ denotes the iteration step. This procedure is iterated for all the molecules in the system of interest until the convergence, as shown in Figure 1.24.

Figure 1.24: Schematic description of the algorithm used for the calculation of energy disorder. In the first step, partial vacuum partial for each molecule are calculated. Afterward, an additional charge is assigned to a certain molecule. Partial charges of this, as well as of the neighboring molecules within a certain cut-off distance, are self-consistently re-evaluated using a cloud of point charges that are iteratively improved until convergence in total energy of the charged molecule is reached. This procedure is repeated for positive and negative additional charges on each molecule in the system.

In order to calculate hopping rates of electrons and holes, as described in Equation 1.8, ∆G if of charged hopping sites is needed as input. In absence of external field and entropic effects,

1 Introduction
∆G if is approximated by the total energy of difference ∆E if between final and initial states [97,99]. These energy differences are calculated for each pair of hopping sites with the method aforementioned, using an environment of self-consistent point charges surrounding the single monomers. Polaron effects are described by assigning an additional charge to the molecule i, and thus, its vacuum partial charges and the total energy of the system are calculated. Formally, this approach is an approximation of the frozen density embedding method [100-102] including polarization effects due to explicit additional charges in the system. The procedure is repeated by putting an additional charge on the target molecule f of the hopping process. The result is the energy E - f (E + f ), for which the energy differences for electron (hole) transport ∆E electron (∆E hole ) are computed. These energies differences, averaged over samples of sufficient size, yield the energy disorder distribution σ(∆E) = (1/(N pairs -1) ∆E 2 ) 1/2 , computed for all the nearest-neighboring pairs in the morphology. To estimate charge carrier mobilities, we employ the analytic solution of the master equation for Marcus rates in a homogeneous medium by Rodin et al. (unpublished):

µ = eβ n √ λ πβ 1 + βσ 2 λ exp - βσ 2 4 -β λ 4 M J 2 R 2 (1.11)
Consistently with our microscopic energy disorder, Rodin et al. use a local disorder parameter σ(E), which inherently includes energy correlations and show their thusly modified effective medium approach to work well for materials with both strong and weak disorder. β = 1/k B T is the inverse temperature, n the dimension and M the mean number of nearest neighboring molecules. Electronic coupling constants were calculated with a Löwdin orthogonalization method [103], using dimer Fock-and overlap matrices and frontier orbitals of uncharged monomers, within a self-consistently evaluated point charge environment. The inner part of the reorganization energy was calculated in geometry optimizations of charged molecules starting from the optimized geometry of the neutral molecule and vice versa.

Introduction on the experimental techniques

In the second part of Chapter 4, we present a preliminary study on the experimental charge carrier mobility of the (novel) OSCs. In particular, we have made use of three methods to determine the mobilities: field-effect transistor (FET), time of flight (TOF), and admittance (impedance) spectroscopy (AS). In the following, a brief description of these methods is given (for a review [61,[104][105][106]).

Field-effect transistor (FET).

A common measure used to determine the processing speed of FETs is the field-effect mobility, which is the average charge carrier drift velocity per unit electric field. A large field-effect mobility is the key to obtain large on-currents for a given device geometry and gate dielectric [61,104,105]. Typical device configuration and source-drain current I SD , in function of sourcedrain voltage V SD and gate voltage V G , are illustrated in Figure 1.20. OSCs are essentially electrical insulators, and thus, charge carries are supplied by injection from the source electrode into the organic spacer. The current flow between source and drain electrodes I SD is modulated by gate V G and source-drain V SD voltages. As illustrated in Figure 1.20, the current I SD , at a given gate voltage V G , increases almost linearly with increasing source-drain voltage V SD till saturation. In the linear regime the current I SD is calculated by the equation:

1.3 Theoretical and experimental techniques implemented to study the (novel) OSCs

I SD,lin = W µC i L (V G -V T )V SD (1.12)
where, W and L are the channel width and length, respectively, µ is the charge carrier mobility (field-effect mobility), C i is the capacitance per unit area of the dielectric, and V T is the threshold voltage, which is the voltage for which the channel conductance is equal to that of the whole semiconducting layer. In other words, the threshold voltage V T is the gate voltage needed to create a conducting path between source and drain terminals. In the saturation regime the current I SD is described by the equation:

I SD,sat = W µC i 2L (V G -V T ) 2 (1.13)
The field effect mobility µ can be calculated from the slope of a linear plot of I 1/2 SD,sat versus V G . As an example, a linear plot of I TOF is, perhaps, the most general technique to measure charge carrier mobilities of OSCs [107].

In TOF, free charge carriers are photogenerated by a pulsed laser. The mobility is determined by the transit time τ of the leading charge carrier transporting through the organic film. Since charge carriers are photogenerated, the problem of charge injection can be neglected. In a typical TOF experiment, a few µm thick film of OSC is grown between two electrodes (at least one semitransparent). The sample is excited at t 0 photogenerating carriers of both signs (electrons and holes) near one electrode. Depending on the applied field F , one type of carriers recombine instantaneously at the close electrode (electrons in Admittance spectroscopy (AS) is known to be a powerful method to measure charge carrier mobilities [108], moreover, for dispersive materials, it is considered superior to TOF techniques [106]. Illustrative experimental setup, which has a simple structure anode/OSC/cathode, and signal are displayed in Figure 1.26. To measure AS hole mobility, an ohmic contact between anode and OSC is necessary, as well as an electron blocking layer, which prevents the injection of electrons from the cathode. On the contrary, for AS electron mobility, an ohmic contact between cathode and OSC is required, additionally, a hole blocking layer to impede the injection of holes from the anode is crucial. In AS, the relaxation of the charge density of the sample is monitored under a dc biased voltage V dc superimposed with a small ac excitation v ac with frequency f . Experimentally, the ac current response i ac is measured and the complex admittance Y is obtained as

Y (ω) = i ac /v ac = G + iB = iωC, where i 2 = 1, ω = 2πf ,

Introduction on the photoemission spectroscopy techniques (PES)

In Chapter 5, hybrid interfaces formed by OSCs and cobalt were investigated. In the study, three techniques were implemented: ultraviolet photoemission spectroscopy (UPS), near threshold photoemission spectroscopy (NT-PS), and two-photon photoemission spectroscopy (2PPE). Here, a brief introduction of these techniques is given. UPS is based on the measurement of the kinetic energy spectra of photoemitted electrons originating from molecules which have absorbed ultraviolet photons. In other words, UPS measures the ionization potential of molecular orbitals. UPS is, together with XPS (X-ray photoemission spectroscopy), which uses X-ray photons, one of the basic photoemission spectroscopy techniques (PES). Through the simple relation E kin = hν -IP , where h is the Plank's constant, ν is the frequency of the ionizing light, and IP is the ionization energy, which can be identified as the energy of an occupied molecular orbital (Koopmans' theorem) [110]. UPS determines experimentally the energy of the highest occupied molecular orbitals of molecules absorbed on metal surfaces, in contrast, XPS gives information on the core occupied molecular orbitals. Strictly speaking, the working principle of NT-PS is identical to UPS, the only difference is the photon energy: 21.2 eV for UPS, and 5.95 eV for NT-PS [111,112]. With the lowered photon energy, NT-PS is capable of probing electronic states close to the Fermi energy E F . A schematic view of UPS and NT-PS is illustrated in Figure 1.27. In our experiments, we have monitored the changes in the work function and in the energetic position of the molecular orbitals, which give information on the energy level alignment, the spin polarization (SP), and the origin of the electronic states at the interface. In particular, to detect the SP polarization 3.5 nm thin cobalt films were deposited by electron beam epitaxy on a Cu(001) single crystal. Afterwards, the substrate was annealed at 370 K. This results in a metastable tetragonally distorted Co 1 Introduction fcc structure with an in-plane magnetic uniaxial anisotropy along the (110) direction of copper [113,114]. The Co/Cu(001) was then progressively covered with the OSC to form the hybrid interface. The photoemitted electrons were analyzed in a normal emission geometry in an ultrahigh vacuum system equipped with a commercial cylindrical sector energy analyzer (CSA) and a spin detector (SPLEED), which are schematically illustrated in Figure 1.28. A 2PPE spectrum represents the energy distribution curve of photoemitted electrons measured in function of their kinetic energy E kin (and emission angle). A peak in the 2PPE spectrum can be assigned to an initial or intermediate state depending on the peak shift relative to the energy of the pump and probe photons hν pu and hν pr , respectively. When a coherent two-photon excitation from an occupied state E i , below the Fermi energy E F , brings an electron above the vacuum energy E vac , the kinetic energy of the photoemitted electron is E kin = hν pu + hν pr + E i (process (b) in Figure 1.30). On the other hand, when 2PPE is given by two independent processes: transient population of an intermediate state E j caused by the pump photon with energy hν pu , and consequent excitation above the vacuum energy E vac caused by the probe photon with energy hν pr , the kinetic energy of the photoemitted electron is E kin = hν pr + E j (process (a) in Figure 1.30).

Ultraviolet photoemssion spectroscopy (UPS) and near threshold photoemission spectroscopy (NT-PS).

In our experiments, the 2PPE technique was used in two modes. In the static mode, which is the 2PPE spectroscopy, the time delay between the two photons is fixed, ∆t= 0(1) fs, whereas the photon energy was varied between 2.91 and 3.31 eV. In the time-resolved mode, the time delay between the two laser pulses varies from ∆t= -9 to ∆t= 9 ps, whereas the photon energy is tuned to 3.25 eV. In this mode, the determination of the lifetime of hot electrons in the intermediate states populated in the 2PPE process is possible [116]. As illustrated in Figure 1.27 for UPS and NT-PS, the photoemitted electrons were analyzed in a normal emission geometry in an ultrahigh vacuum system equipped with a cylindrical sector energy analyzer (CSA) and a spin detector (SPLEED).

Single-molecule magnets (SMMs)

Mainly, this thesis is focused on the synthesis and characterization of (novel) OSCs implementing the ligands listed in Table 3.1. These ligands can also easily chelate lanthanides to form stable complexes. Since lanthanides are widely used to form single-molecule magnets (SMMs), we have initiated a study on phenalenyl-based SMMs formed with dysprosium and terbium. Preliminary results are shown in Chapter 6. Here, we present a summary on SMMs and their magnetic characterization, for a review on this class of materials see references [117][118][119][120][121]. In general, the properties of SMMs are evaluated by measuring three parameters. First, the magnetic blocking temperature T B is the highest temperature at which a SMM displays hysteresis in plots of magnetization M versus magnetic field H. Second, the coercive magnetic field H c is the strength of the magnetic field needed to drive the magnetization of an SMM back to zero following saturation. Last, the effective energy barrier to reversal of the magnetization (or anisotropy barrier) U ef f (or ∆), is the energy required to convert a SMM back into a simple paramagnet. Due to the strong angular dependence of the 4f orbitals, the electronic structures of Tb(III) and Dy(III) ions possess substantial axial anisotropy.

Magnetic characterization of SMMs

SMMs are generally characterized in crystalline forms using conventional SQUID (superconducting quantum interference device) magnetometers. In the standard experiment, the magnetic susceptibility χ is measured using a very small alternating current (ac) with a magnetic field of about 1-5 Oe across a temperature range between 1-50 K. The frequency ν of the ac field can be varied in the range of 1-1500 Hz resulting in a time dependent magnetic moment, which can be characterized by a relaxation time τ at a given temperature. Since individual SMMs have their own magnetic moment, the magnetization of the SMM will lag behind the driving ac field as it alternates across the sample, and thus, the measured magnetic susceptibility contains a phase shift. By this experiment, the so-called in-phase and out-of-phase susceptibilities, χ′ and χ′′, respectively, are measured.

To identify SMM behavior, the dependence off χ′ and χ′′ versus the temperature is investigated at different frequencies ν. When the temperature decreases, if the plot of χ′′ gradually increases till a maximum and then decreases at lower temperatures, this indicates that the reversal of the spin has been blocked. Furthermore, changing the ac frequency ν, the maximum in the χ′′(T ) plot also changes. In contrast, the absence of maxima in the χ′′(T ) plots, or the lack of frequency dependent χ′′ in zero fields, originates ambiguity on the SMM behavior. Another experiment implemented to characterize SMMs are the plots of χ′ and χ′′ versus the ac frequency ν at different temperatures. Plots of χ′′(ν) isotherms permit to determine the anisotropy barrier U ef f . Strictly speaking, from each χ′′(ν) curve, an average relaxation time τ , at a given temperature T , can be determined. Hence, through the Arrhenius-type relationship:

τ = τ 0 exp U ef f k b T (1.14)
the anisotropy barrier U ef f can be calculated from the slope of ln τ versus T -1 . When the graph is linear and τ is temperature dependent, the magnetization in the SMM is relaxing via a thermally assisted mechanism. On the contrary, when τ is temperature independent, the relaxation of the magnetization occurs via quantum tunneling (QTM). In many cases, thermal and QTM relaxation of the magnetization take place concurrently, as a result, the Arrhenius plot shows a curvature of ln τ versus T -1 . A schematic illustration of the relaxation processes is given in Figure 1.32.

Monometallic lanthanide-based SMMs

In our study, we synthesized exclusively mononuclear lanthanide-based SMMs, and thus, a brief overview is given only on this specific class of SMMs. Mononuclear lanthanide-based SMMs show slow relaxation of the magnetization although they contain only one single metal ion (for a review [117]). SMMs was synthesized, however, besides the characterization of the magnetic properties, they were not applied in any device. Therefore, in our study, we aim to synthesize phenalenyl-based lanthanide SMMs to investigate their magnetic properties and eventually to be deposited on surfaces by vacuum evaporation. This would be the first step towards the implementation of such molecules in devices.

Aim of the Thesis

In the last two decades, a huge amount of reports related to OSCs has been published. In most cases, the studies aimed to produce materials with enhanced performance in respect to the previously reported OSCs. However, there is still a lack of knowledge about the exact relationship between the molecular structure of an OSC and its electronic properties when it is implemented in devices. Together with our collaborators, we started a study on the low molecular weight class of OSCs. Our work on OSCs can be divided in three main parts:

1. Rational design, synthesis and structural characterization of a series of OSCs utilizing Alq 3 as "leitmotif". Systematic photophysical and electrochemical characterization in solution of the OSCs to determine the influence of the chemical structure on the electronic properties, i.e HOMO and LUMO energy levels.

2. Theoretical and experimental studies on the charge carrier mobility of the (novel) OSCs.

Theoretically the OSCs were studied in vacuum and in generated morphologies to determine the charge carrier mobility of electrons and holes. Preliminary experimental measurements have been performed in comparison.

3. Photoemssion spectroscopy studies on the OSCs deposited on cobalt substrates. The spin dependent properties OSC/Co were investigated in comparison with the prototypical Alq 3 /Co interface.

In addition, we have synthesized and characterized phenalenyl-based lanthanide complexes. This study aimed to examine the SMM behavior of such molecules and the possible deposition of those materials on substrates for surface studies.

Design, Synthesis and Characterization of (novel) OSCs

Introduction

In Section 1.1, the principal characteristics of OSCs are described. All OSCs are based on a backbone formed by carbon atoms bonded through σ bonds and a delocalized π electron system, which derives from the weaker π-electron of the p z -orbitals of sp 2 -hybridized carbon atoms. Alq 3 is the most known semiconductor among the class of low molecular weight OSCs.

As explained in Section 1.2, Alq 3 is formed by three quinolinate ligands chelating the central aluminum atom. Due to the asymmetric structure of Hq, two geometrical isomers, mer-Alq 3 and fac-Alq 3 , can be formed. In addition, the electronic properties of Alq 3 are mainly resulting from the ligands. Attempts to ameliorate the electronic properties of Alq 3 , chemically modifying Hq or substituting the aluminum with other metals, are presented in Section 1.2.1. In this study, we have investigated (novel) OSCs affine to Alq 3 . Our strategy was to tune the electronic properties (HOMO and LUMO energy levels) of aluminum-based OSCs mutating the following three parameters:

• Extension of the aromatic system

• Symmetry of the ligand

• Symmetry of the complex

The first part of the study was to design and synthesize, when necessary, ligands. Due to their features we selected the ligands listed in Table 3.1, which were utilized to form the aluminum complexes listed in Table 3.2. Additionally, after the report of a phenalenyl-based zinc complex in organic spintronic devices (see Section 1.2.3), we studied a zinc complex for a better understanding of this class of OSCs. The (novel) OSCs were synthesized, purified and structurally characterized by means of elemental analysis, NMR spectroscopy, mass spectrometry, and single crystal X-ray diffraction. In the second part, a photophysical characterization of the ligands and (novel) OSCs in solution is presented. In addition, we have developed a study with Dr. Fattori (ISOF-CNR, Bologna) which investigates the photophysical properties of the complexes evaporated onto quartz substrates. Electrochemical investigations on ligands and (novel) OSCs were carried out to determine the reduction potentials. At last, the HOMO and LUMO energy levels were determined and related to the structure of the ligands and of the (novel) OSCs. The detailed description of the reaction procedures and the analytical characterization of the OSCs as well as of the intermediates are reported in Section 8.2. • 2 fused aromatic rings

• Asymmetric

• mer-and fac-Al complex

HOp

OH O

• 3 fused aromatic rings

• Symmetric (fast proton transfer) • 1 aromatic ring

• Symmetric complex HOp-X OH O X • 3
• Symmetric (fast proton transfer)

• Symmetric complex Acac OH O • Non-aromatic
• Symmetric (fast proton transfer)

• Symmetric complex • Asymmetric

• mer-and fac-isomer

• Homoleptic Al(Op) 3 O O O O O O Al • Symmetric • No isomers • Homoleptic Al(Op-X) 3 O O O O O O Al X X X • Symmetric plus halogen • No isomers • Homoleptic Al(Op-R) 3 O O O O O O Al R R R • Symmetric plus substituent • No isomers • Homoleptic Al(Oba) 3 O O O O O O Al

• Asymmetric

• mer-and fac-isomer

• Homoleptic Al(Op-py) 3 N O N O N O Al • Asymmetric
• mer-and fac-isomer

• Homoleptic Al(Trop) 3 O O O O O O Al • Symmetric • No isomers • Homoleptic Al(q 2 Acac) N O N O Al O O • Asymmetric
• pseudomer-and pseudofac-isomer

• Heteroleptic Al(q 2 Op) O O Al O N O N • Asymmetric
• pseudomer-and pseudofac-isomer

• Heteroleptic Al(q 2 Trop) Al O N O N O O • Asymmetric
• pseudomer-and pseudofac-isomer

• Heteroleptic Zn(Op) 2 O Zn O O O • Symmetric (flat)
• No isomers

• Homoleptic

Experimental techniques and instrumentation

All the reactions were carried out under argon inert atmosphere using standard Schlenk techniques. All the purchased chemicals and solvents for the synthesis and column chromatography were used as received without any further purification unless otherwise stated. Elemental analysis of carbon, hydrogen, and nitrogen were carried out in a Vario Micro Cube. 1 H-NMR and 13 C-NMR were recorded in a Bruker FT-NMR Avance III 500 MHz with deuterated solvents as internal standards for proton and carbon signals. MALDI-TOF mass spectrometric data were acquired on a MALDI-TOF Synapt G2-S HDMS with no additional matrix compound other than the sample itself. ESI-TOF mass spectrometric analytical data were acquired on a Bruker microOTOF-Q II equipped with a nanospray source. Single crystal X-ray diffraction data were collected on a STOE IPDS II diffractometer with graphite monochromated Mo Kα radiation (0.710 73 Å). Structure solution and refinement against F 2 were carried out using shelxs and shelxl software. Refinement was performed with anisotropic temperature factors for all nonhydrogen atoms (disordered atoms were refined isotropically); hydrogen atoms were calculated on idealized positions.

Absorption spectra were acquired at room temperature for diluted solutions of the ligands and complexes (8.0 × 10 -6 M) on a Cary 500 Scan UV-Vis-NIR spectrophotometer using a 1 cm quartz cell. Photoluminescence, emission and excitation spectra were recorded at room temperature for diluted solutions of the ligands and complexes (8.0 × 10 -6 M) on a Cary Eclipse Fluorescence spectrophotometer using a 1 cm quartz cell. The photoluminescence quantum yield in solution was computed using rhodamine 6G as reference [131,132]. Cyclic voltammetry studies were performed using an Autolab PGSTAT10 potenziostat in a three-electrode singlecompartment cell with a glassy carbon working electrode, Ag/AgCl reference electrode, and a platinum wire as auxiliary electrode in an inert argon atmosphere. Tetrabutylammonium hexafluorophosphate (TBAPF 6 ) was used as supporting electrolyte (0.1 M) and DCM was used as solvent (except for the zinc complex). The concentration of the ligands and complexes was 1.0 × 10 -4 M; the solutions were degassed with argon prior to the measurements. A scan rate of 100 mV s -1 was employed. Ferrocene was used as internal standard to calculate the corrected reduction potential [133]. The evaporation of the OSCs onto quartz substrates was carried out in an Edwards Auto 306 evaporator equipped with a high vacuum chamber (10 -6 mbar) and a frequency thickness monitor (FTM) to check the evaporation rate. The complexes were grown at a deposition rate of 0.5 nm s -1 with a final thickness of 80 nm. The solid state absorption spectra were recorded on a Perkin-Elmer Lamba 900 UV-Vis-NIR spectrophotometer. The solid state photoluminescence spectra were acquired on a Spex Fluorolog 2 (the spectra are corrected to compensate the nonlinear response of the photomultiplier Hamamatsu R28). The photoluminescence quantum yield in thin film was determined using the integrating sphere absolute method [134] on a Spex Fluorolog 2 (the spectra are corrected to compensate the nonlinear response of the photomultiplier Hamamatsu R28). The lifetimes, in solution and solid state, were obtained on a TCSPC (time correlated single photon counter) equipped with a NanoLED source and a Horiba Jobin-Yvon Fluorohub for the data elaboration. were grown by slow evaporation of a chloroform solution at room temperature. The molecular structure obtained by single crystal X-ray diffraction is illustrated in Figure 3.2, in addition, selected bond lengths and angles are listed. The crystal refinement data is reported in Table C. The high chemical shift indicates that the hydrogen is between the two oxygens rather than being localized on one oxygen. In other words, the proton transfer at room temperature is faster In contrast, the resonances corresponding to the aromatic hydrogens of the phenalenyl experience a considerable shift in relation to the halogen atom. As an example, the shift of the proton H4, which is in the vicinity of the halogen atom, is the most significant. It moves progressively from low to high chemical shift, beginning with the fluoro derivative towards the iodo derivative. In detail, for HOp-F 5a, the chemical shift of H4 is 7.74 ppm, whereas for HOp-I 5d it is 8.31 ppm. Due to the coupling between 1 H and 19 F, the resonance of H4 in HOp-F 5a is a doublet [155]. Conversely, protons H1 and H2 move from high to low chemical shift going from HOp-F 5a to HOp-I 5d. However, the shifts of H1 and H2 are not as appreciable as the shift of H4. In detail, H1 and H2 of HOp-F 5a are at 7.22 ppm and 8.05 ppm, respectively, whereas in HOp-I 5d they are at 7.17 ppm and 7.99 ppm, respectively. The same trend is observed in the 1 H-NMR spectra of the complexes Al(Op-X) 3 6a-d. As a result, in the 1 H-NMR spectra of Al(Op-X) 3 6a-d, illustrated in Figure 3.7, the resonance corresponding to the proton H4 moves from low, 7.68 ppm for Al(Op-F) 3 6a, to high, 8.24 ppm for Al(Op-I) 3 6d, chemical shift. In contrast, the resonance of H1 moves from high, 7.17 In conclusion, the formation of the halogenated complexes Al(Op-X) 3 6a-d is proved unambiguously by the structural characterization. However, we were unable to grow high quality single crystals suitable for single crystal X-ray diffraction. The most probable reason is that the halogen atom in the 5-position prevents the correct orientation of the molecules during the crystallization process. A series of novel ligands and aluminum complexes was synthesized by exchanging the hydrogen in the 5-position with aromatic functionalities. 2-Methyl-and 5-methyl-HOp were previously synthesized and characterized. However, the effect on the absorption spectra was negligible [135]. As a consequence, we have implemented bulky aromatic molecules aiming to significantly modify the electronic properties of Al(Op) 3 4. The procedures to obtain the substituted ligands HOp-R 15a-c and complexes Al(Op-R) 3 16a-c are detailed in Scheme 3.4. The synthesis of the three substituted ligands HOp-R 15a-c takes place starting from the methoxy derivative 11 by coupling reactions with phenyl boronic acid 12, naphthalen boronic acid 13 and ethynylbenzene 14. The hydrolysis of the methoxy group is efficiently carried out with BBr 3 . Although this strategy involves two steps more than direct coupling with HOp-Br 5c, overall yields and purities were higher. To form the substituted complexes Al(Op-R) 3 16a-c, the ligands HOp-R 15a-c were reacted with AlCl 3 . In more detail, starting from 2-bromo-6-methoxynaphthalene 7, the overall yield of the synthesis of 9-hydroxy-5-phenyl-1H-phenalen-1-one (HOp-p) 15a is ≈38% and tris-(1-oxo-5-phenyl-1H-phenalen-9olate)aluminum (Al(Op-p) 3 ) 16a was obtained with a yield of ≈32%. The yield to form (9-hydroxy-5-(naphthalen-1-yl)-1H-phenalen-1-one (HOp-n) 15b is ≈39% and to form tris-(5-(naphthalen-1-yl)-1-oxo-1H-phenalen-9-olate)aluminum (Al(Op-n) 3 ) 16b it is ≈26%. At last, the yield of the synthesis of 9-hydroxy-5-(phenylethynyl)-1H-phenalen-1-one (HOp-pe) 15c is ≈26% and tris-(1-oxo-5-(phenylethynyl)-1H-phenalen-9-olate)aluminum (Al(Op-pe) 3 ) 16c is obtained with a yield of ≈22%. Due to the presence of bulky substituents, which prevents the correct orientation of the phenalenyl ligands, we were unable to grow high quality single crystals of the substituted complexes Al(Op-R) 3 16a-c for single crystal X-ray diffraction. However, we have grown single crystals of the ligand HOp-pe 15c to investigate the effect of the ethynyl bridge on the electronic coupling between the phenalenyl core and the phenyl substituent. The molecular structure obtained by single crystal X-ray diffraction is illustrated in 7.17 8.17 8.17 Al(Op-pe) 3 6c 7.09 8.08 8.18 are almost identical for HOp-p 15a and HOp-n 15b, ≈7.23 ppm and ≈8.20 ppm, respectively, whereas for HOp-pe 15c are shifted to 7.17 ppm and 8.06 ppm, respectively. The same resonances, recorded for the ligands HOp-R 15a-c, are observed in the 1 H-NMR spectra of the substituted complexes Al(Op-R) 3 16a-c illustrated in Figure 3.11. Interestingly, the resonance of H4 is almost identical for the three complexes, ≈8.17 ppm. In addition, the resonance of H1 is similar for Al(Op-p) 3 16a and Al(Op-n) 3 16b, ≈7.17 ppm, and it is shifted to 7.09 ppm for Al(Op-pe) 3 16c. In contradiction, the resonance of H2 is comparable for Al(Op-p) 3 16a and Al(Op-pe) 3 16c, ≈8.08 ppm, and shifted to 8.17 ppm for Al(Op-n) 3 16b. Despite the asymmetric nature of the ligand HOba 18, the resonance of H18 in its

Synthesis of the (novel) OSCs

5-Substituted Al(Op)

3 : Al(Op-R) 3 (16a-c) OMe O Br O O R O O O O O O Al R R R B(OH) 2 B(OH) 2 (a) (b) (c) (d)

Tris-(2-(pyridin-2-yl)phenolate)aluminum (Al(Op-py) 3 ) (23)

The ligand 2-(pyridin-2-yl)phenol (HOp-py) 22 was selected due to its similarity to Hq. In can be considered as an extension of Hq where the two chelating atoms (nitrogen and oxygen) are inserted in two separated aromatic rings. HOp-py 22 was previously studied to investigate the intramolecular proton transfer in excited state by Basaric et 24 no resonance relative to the proton between the two oxygen was recorded. Carbon and hydrogen content measured by elemental analysis, C= 64.57% and H= 3.83%, matches the calculated one, C= 64.61% and H= 3.88% (see Table 3.3). At last, the MALDI-TOF spectrum, shown in Figure 3.15, is characterized by a series of peaks. The most intense peak corresponds to the fragment [Al(Trop) 2 ] + (m/z= 269). Additionally, the binuclear fragment [Al 2 (Trop) 5 ] + (m/z= 659), most probably produced during the MALDI process, was identified. In order to further understand the relationship between OSCs structure and their electronic properties, we have replaced one quinolinate in Alq 3 with 4-hydroxypent-3-en-2-one (also known as acetyl acetonate, Acac) 27. The mixed-ligand aluminum complex formed, Al(q 2 Acac) O3-Al1-O4 91.74(6) Al1-O3 1.8765(14) O1-Al1-O4 97.96 (6) O3-Al1-N1 173.02(7) Al1-O4 1.8816(14) O1-Al1-N1 82.67 (6) O3-Al1-N2 90.33(6) Al1-N1 2.0464(16) O1-Al1-N2 89.38 (6) O4-Al1-N1 89.17(6) Al1-N2 2.0738(17) O2-Al1-O3 95.58 (6) O4-Al1-N2 172.36(7) O2-Al1-O4 90.16 (6) N1-Al1-N2 89.67(6) O2-Al1-N1 91.33(6) The 1 H-NMR spectrum of Al(q 2 Acac) 28, illustrated in Figure 3.17 in comparison with the spectra of Hq 26 and Acac 27, is composed by two sets of resonances. Between 7.00 and 8.52 ppm are the resonances of the aromatic hydrogens of quinolinate, whereas the resonances at 5.64 ppm and 1.94 ppm are relative to the hydrogens of acetyl acetonate. The elemental analysis on Al(q 2 Acac) 28, C= 65.98%, H= 4.38% and N= 6.55%, fairly matches the expected values, C= 66.66%, H= 4.63% and and N= 6.76% (see Table 3.3). Mass spectrometry experiments were carried out by ESI-TOF and MALDI-TOF measurements. The main fragment in the ESI-TOF spectrum is relative to the fragment [Al(q 2 Acac)H] + (m/z= 415.12), where an additional hydrogen forms the cation (see Figure B.55). Moreover, a series of peaks corresponding to various combinations of the ligands are observed: [Al(qAcac 2 )H] + (m/z= 370.12), [Al(q 2 )] + (m/z= 315.07), and [Al(qAcac)] + (m/z= 270.07). In the same manner, the MALDI-TOF spectrum displays a series of peaks relative to different combinations between the ligands (see Figure 3.21). The most intense peak corresponds to the fragment [Al(q 2 )] + (m/z= 315). In addition, the fragment [Al(qAcac)] + (m/z= 270) and two dinuclear fragments, [Al 2 (q 4 Acac)] + (m/z= 729) and [Al 2 (q 3 Acac 2 )] + (m/z= 684), were detected. The novel aluminum complex Al(q 2 Op) 29 was obtained by the substitution of acetyl acetonate in Al(q 2 Acac) 28 with a phenalenyl ligand. As illustrated in Scheme 3.9, Al(q 2 Op) 29 is formed by the reaction between Al(q 2 Acac) 28 and HOp 3 with a yield of ≈73%. High quality single crystals were grown for single crystal X-ray diffraction measurements. Hence, for the first time, the crystal structure of Al(q 2 Op) 29 was resolved (crystal refinement data is reported in Table C.5). Similarly to Al(q 2 Acac) 28, Al(q 2 Op) 29 can form two geometrical isomers: the pseudomer-isomer, where the two nitrogens are facing each other, and the pseudofac-isomer, where the two nitrogen are facing two oxygens. From the molecular structure, shown in Figure 3.18, it can be seen that the two nitrogens occupies neighboring positions in a pseudofac geometry. Due to the similar bite angle of HOp 3 and Acac 27, pseudofac-Al(q 2 Op) 29 is characterized by similar bond angles, 81.9-94.7 • and 172.4-174.0 • , in respect to those of pseudofac-Al(q 2 Acac) 28 (see Section 3.3.7). Accordingly, the bond distances between the chelating atoms of quinolinate and aluminum, Al-O1 (1.844 Å), Al-O2 (1.864 Å), Al-N1 (2.050 Å), and Al-N2 (2.036 Å), are similar to those of Al(q 2 Acac) 28 and mer-Alq 3 (see Section 1.2). Furthermore, the bond lengths between the oxygens of phenalenyl and aluminum, Al-O3 (1.867 Å) and Al-O4 (1.861 Å), are analogous to those of Al(Op) 3 4 (see Section 3.3.1). In the crystal lattice, the : selected bond distances and angles for Al(q 2 Op) 29. molecules of pseudofac-Al(q 2 Op) 29 are oriented to maximize the interaction between quinolinates and phenalenyls. Interestingly, it can be noted that the quinolinates are only facing between themselves as well as the phenalenyls.

Bis-(quinolin

Compound

Resonances In the 1 H-NMR spectrum of Al(q 2 Op) 29, illustrated in Figure 3.19 together with the spectra of HOp 3 and of Hq 26, two sets of resonances are clearly visible. One set (H1, H2, H3, H5, H6, H7) is corresponding to the hydrogens of quinolinate. On the other hand, the second set (H10, H11, H13, H14) is relative to the hydrogens of phenalenyl. The elemental analysis of carbon, hydrogen and nitrogen, C= 72.17% H= 3.97% and N= 5.31%, matches the expected values, C= 72.93% H= 3.76% and N= 5.49% (see Table 3 At last, we have exchanged the acetyl acetonate of Al(q 2 Acac) 28 with a tropolonate to synthesize the unprecedented Al(q 2 Trop) 30. As illustrated in Scheme 3.10, the reaction takes place by mixing Al(q 2 Acac) 28 and tropolone 24 in ethanol with a yield of ≈68%. High quality single crystals suitable for single crystal X-ray diffraction were grown, and thus, the molecular structure of Al(q 2 Trop) 30, depicted in Figure 3.20, was resolved (crystal refinement data is reported in Table C.6). Unexpectedly, in the molecular structure of Al(q 2 Trop) 30, the two nitrogens are facing each other in a pseudomer geometry. This is most surprising because the starting material Al(q 2 Acac) 28 is characterized by a pseudofac geometry. Most probably, during the reaction between Al(q 2 Acac) 28 and tropolone 24, a rearrangement of the ligands takes place resulting in pseudomer-Al(q 2 Trop) 30. It might be also possible that the pseudomer-isomer has a higher tendency to crystallize than the pseudofac-isomer, and thus, we could grow only single crystals of pseudomer-Al(q 2 Trop) 30 out of a mixture of both isomers. In pseudomer-Al(q 2 Trop) mer-Alq 3 (see Section 1.2), pseudofac-Al(q 2 Acac) 28 and pseudofac-Al(q 2 Op) 29. In the crystal lattice, pseudomer-Al(q 2 Trop) 30 is oriented to maximize the interaction between quinolinates and tropolonates. In particular, quinolinates are exclusively facing each other as well as the tropolonates.

Al(q 2 Trop) 30 was partially characterized by ESI-TOF, MALDI-TOF and elemental analysis. In the ESI-TOF spectrum, illustrated in The last consideration on the zinc complex Zn(Op) 2 31 is concerning the presence of water molecules which complete the coordination sphere. These water molecules can affect the thermal stability of the complex during the vacuum evaporation process. In order to achieve a waterfree zinc complex, reactions have to be carried out in a controlled environment, such as a glove-box using anhydrous starting materials. However, due to the nature of zinc, a waterfree zinc complex would be characterized by a tetrahedral geometry. Nonetheless, in principle, all the ligands listed in Table 3.1 can be utilized to form zinc complexes for further studies. Moreover, it might be possible to obtain complexes with mixed-ligands in a similar fashion to that presented in Section 1.2.3.

(a) (b) (c) Bond Length [Å] Bond angle Angle [ • ] Bond angle Angle [ • ] Zn(Op) 2 • 2 H 2 O

Spectroscopic characterization

Ligands (see Table 3.1) and complexes (see Table 3.2), synthesized in Section 3.3, were photophysically characterized. At first, a complete photophysical investigation has been carried out for Al(Op) 3 4 in solution and in thin film, in comparison with the benchmark Alq 3 . For all the other OSCs synthesized, the absorption and emission spectra have been recorded. Additionally, some of the OSCs have been grown on quartz substrates to measure their spectra in thin film.

The findings (absorption maxima and their extinction coefficient and emission maxima) are listed in Table 3.5 for the ligands and in Table 3.6 for the OSCs. By measuring absorption and emission spectra, important information on the frontier orbitals and electronic transitions of the molecules can be inferred [174]. Furthermore, from the onset of the first band in the absorption spectra it is possible to calculate the optical HOMO-LUMO gaps listed in Table 3.7 and Table 3.8.

Photophysical characterization of Al(Op) 3 (4) in comparison with Alq 3

The photophysical properties of Al(Op) 3 4 were determined by measuring the absorption and emission spectra in solution and in thin film. Additionally, photoluminescence quantum yield and luminescence lifetime were estimated. The results are reported in Table 3.4.

(ǫ) λ emi max b Φ c τ d [nm] ([M -1 cm -1 ]) [nm]
[ns] Alq and in thin film deposited onto a quartz substrate of Alq 3 . There are two bands in the absorption spectrum of Alq 3 , which are at 385 nm and at 250 nm. These bands correspond to π → π * transitions localized on the quinolinate moiety [175,176]. As a consequence, Hq shows the same bands shifted at lowered wavelength [177]. On the contrary, the band between 300 and 350 nm, which is not visible for the free ligand, is attributed to a charge transfer metal to ligand (MLCT). In addition, since Alq 3 is formed by three quinolinates, its extinction coefficient ǫ is about threefold compared to the extinction coefficient ǫ of Hq. As an example, the extinction coefficient of the first absorption band of Alq 3 is ǫ 385 = 1.1 × 10 4 M -1 cm -1 and that of the first absorption band of Hq is ǫ 314 = 3.1 × 10 3 M -1 cm -1 . The absorption spectrum of Alq 3 in thin film is similar to that in solution, which confirms that the complex was successfully deposited onto the substrate. The slight shift of the peaks is caused by the solvatochromic effect [178,179]. Furthermore, the emission spectrum of the film is almost identical to that in solution; the emission maximum λ emi max in solution is 517 nm and in thin film is 523 nm, only 6 nm shifted. In solution and in thin film, Alq 3 is characterized by comparable photophysical properties. In detail, the photoluminescence quantum yield Φ in solution and in solid state is 0.13 and 0.17, respectively, and the luminescence lifetime τ , extracted from the photoluminescence decay, illustrated in Figure 3.27, is 16.2 ns and 12.5 ns, respectively. In both cases the photoluminescence decay is mono-exponential. In contrast, the emission spectrum in solid state is dramatically red-shifted and broadened. As a result, the emission maximum λ emi max in solution occurs at 458 nm and in thin film at 583 nm. The formation of excimers (collision complexes at the excited state), which is well-known for molecules such as pyrene [181], is assumed to have occurred. Normally an excimer is caused by a charge-transfer interaction between an electronically excited species and a ground state molecule. Often, the excimer possesses observable properties quite distinct from those of the single molecule [180,182]. That becomes clear observing the photoluminescence quantum yield Φ and lifetime τ of Al(Op) 3 4 in solution and in thin film. In solution, the quantum yield Φ is 0.027 and in thin film is 0.014. Moreover, as it can be seen in Figure 3.27, the lifetime τ in solution is considerably shorter than in thin-film. In solution, Al(Op) 3 4 is characterized by a mono-exponential decay with a lifetime τ = 0.7 ns. On the contrary, the decay in thin film is multi-exponential and the average lifetime estimated is τ = 7.1 ns. Interestingly, was impossible to solely detect the emission from excimers in concentrated solutions of HOp 3 and Al(Op) 3.6). In addition, the florescence quantum yield Φ in solution of Alq 3 (0.13) is considerably larger than that of Al(Op) 3 4 (0.027). In the same way, the fluorescence lifetime τ in solution of Alq 3 (16.2 ns) is substantially longer than that of Al(Op) 3 4 (0.7 ns). Low fluorescence quantum yield and short fluorescence lifetime in solution suggest that fast non radiative decay processes take place in Al(Op) 3 4. Both the complexes were successfully deposited onto quartz substrates to measure the photophysical properties in thin film, as proved by the equivalent absorption spectra. The emission spectra of Alq 3 in solution and thin film are almost identical. In addition, fluorescence quantum yield Φ and lifetime τ of Alq 3 in thin film, 0.17 and 12.5 ns, respectively, are comparable to those in solution. In contrast, the emission spectra of Al(Op) 3 4 in thin film is substantially different from that in solution. As a result, fluorescence quantum yield Φ and lifetime τ of Al(Op) 3 4 in thin film, 0.014 and 7.1 ns, respectively, heavily deviate from those in solution, 0.027 and 0.7 ns. The origin of the discordant photophysical properties of Al(Op) 3 4, in solution and in thin film, is the formation of excimers in the solid state (see Figure 3.28). The extended flat aromatic system of HOp 3 is presumably the cause of the excimer formation. Conversely, the small hetero aromatic system of Hq is preventing the excimers generation in thin films of Alq 3 .

Characterization of the (novel) OSCs

Absorption and emission spectra of the (novel) OSCs have been measured. To explain the features of the spectra of the (novel) OSCs, the photophysical characterization of Alq 3 and Al(Op) 3 4, described in the previous section, has been used as a reference . In the region between 325 and 475 nm transitions localized on the phenalenyl take place. On the contrary, in the UV region, the absorption spectra of the substituted derivatives present entirely different profiles, due to π → π * transitions localized on the aromatic substituents. In addition, the bulky substituents influence the structure of the peaks in the absorption and emission spectra. As a result, all the bands are less structured and slightly red-shifted. Out of the three substituted complexes, only Al(Op-p) 3 16a was grown onto a quartz substrate to investigate the effect of the bulky phenyl substituent on the excimers formation. The absorption spectrum in thin film resemble the spectrum in solution, confirming that the complex was deposited successfully onto the quartz substrate. In contrast, the emission in thin film is dominated by a band originating from excimers with a maximum The absorption spectra in solution and in thin film are identical, confirming that the molecule was deposited on quartz successfully. On the other hand, the emission spectrum of Al(Oba) 3 19 is dominated by a red-shifted emission, with a maximum at 591 nm, arising from excimers. In spite of the asymmetric geometry of HOba 18, the excimers formation is not hindered in Al(Oba) 3 19 thin film. Figure 3.33 illustrates the absorption and emission spectra of Al(q 2 Acac) 28 in solution. The absorption spectrum of Al(q 2 Acac) 28 is identified by quinolinate centered bands. In detail, the first band is observed at 380 nm and the second band at 260 nm. Both the bands correspond to π → π * transitions localized on the quinolinate. An additional band is observed at 300 nm. This band is assigned to a n → n * transition localized on the acetyl acetonate moiety. The emission spectrum of Al(q 2 Acac) 28 shows an intense fluorescence band with a maximum at 508 nm.

In Figure 3.34 are illustrated the absorption, emission and excitation spectra of Al(q 2 Op) 29 in solution. The absorption spectrum is characterized by the characteristic absorption bands of Hq 26 and HOp 3. Between 400 and 475 nm and between 325 and 375 nm is visible the phenalenyl absorption profile. In addition, between 375 and 400 nm and at 250 nm, the absorption of the quinolinates can be observed. Interestingly, as a result of the insertion of the phenalenyl, the emission profile of Al(q 2 Op) 29 depends from the excitation wavelength. This is clear when the molecule is excited at 430 nm. Here, solely the phenalenyl moiety absorbs the excitation light, and thus, the emission pattern resembles the emission of HOp 3 and Al(Op) 3 4. At lower wavelengths both ligands absorb the incident light, hence, the overall emission arises from a combination between the emission of the quinolinate and the phenalenyl. Indeed, in the excitation spectra, at wavelengths higher than 550 nm, the emission origins only from the quinolinate, and thus, the absorption of the phenalenyl disappears. 300 and 350 nm are localized on the tropolonate. On the contrary, the small absorption at 400 nm is localized on the quinolinates. The emission spectrum of Al(q 2 Trop) 30 remains almost constant in relation to the excitation wavelength. Due to the superimposition of the quinolinate and tropolonate absorption spectra, it was impossible to excite selectively one of the ligands. Therefore, the emission spectra of Al(q 2 Trop) 30 are a combination between the emission of both moieties. In the resulting excitation spectra, the absorption bands exhibit only a slight variation of the relative intensities in function of the emission wavelength. In Table 3.5 are listed absorption peaks λ abs max with their extinction coefficient ǫ and emission peaks λ emi max of the ligands used in the synthesis of the (novel) OSCs. Comparing the absorption peaks of the halogenated ligands HOp-X 5a-d with the peaks of HOp 3, only minor differences can be noticed. The absorption peaks are few nm shifted toward higher wavelengths, and, in addition, their extinction coefficients ǫ have the same order of magnitude. As an example the extinction coefficient of the first absorption peak of the halogenated ligands HOp-X 5a-d (ǫ HOp-F 451 , ǫ HOp-Cl 451 , ǫ HOp-Br 450 , and ǫ HOp-I

452

) is between 6.9 × 10 3 and 1.0 × 10 4 M -1 cm -1 , close to that of HOp 3, ǫ 439 = 9.0 × 10 4 M -1 cm -1 . Similarly, the extinction coefficient of the first absorption peak of the substituted ligands HOp-R 15a-c (ǫ HOp-p 454 , ǫ HOp-n 448 , and ǫ HOp-pe

448

) is between 7.6 × 10 3 and 7.9 × 10 3 M -1 cm -1 , comparable to that of ǫ of HOp 3, ǫ 439 = 9.0 × 10 4 M -1 cm -1 . However, the absorption peaks of the substituted ligands HOp-R 15a-c below 300 nm originate from the substituent, and thus, their extinction coefficient ǫ is not comparable with HOp 3. Obviously, the halogenation and substitution of HOp 3 is not strongly affecting the absorption transitions localized of the phenalenyl-based ligands.

The absorption peaks of HOba 18, in the region between 350 and 460 nm, have similar extinction coefficients ǫ to those of HOp 3 in the same region. As an example, the first absorption peak at 459 nm has an extinction coefficient, ǫ 459 = 9.1 × 10 3 M -1 cm -1 , which is virtually identical to the extinction coefficient, ǫ 439 = 9.0 × 10 3 M -1 cm -1 , of the first absorption peak at 439 nm of HOp 3. This means that the absorption transition is probably located on the phenalenyl core of HOba 18. In contrast, the peak at 235 nm has an extinction coefficient, Table 3.5: List of the absorption and emission peaks of the studied ligands. In the parenthesis is reported the extinction coefficient ǫ relative to the absorption peak.

Compound

λ abs max (ǫ) ǫ 235 = 4.9 × 10 4 M -1 cm -1 , about two times higher than the extinction coefficient of the same absorption peak of HOp 3, ǫ 235 = 2.6 × 10 3 M -1 cm -1 . Hence, these absorption transitions might have a different origin. The extinction coefficient of the absorption peak of HOp-py 22 at 320 nm, ǫ 320 = 2.7 × 10 3 M -1 cm -1 , is comparable to the extinction coefficient of the corresponding absorption peak of Hq 26 at 314 nm, ǫ 314 = 3.1 × 10 3 M -1 cm -1 . Conversely, the extinction coefficient of the absorption peak of HOp-py 22 at 257 nm, ǫ 257 = 3.7 × 10 3 M -1 cm -1 , is one order of magnitude lower than the the extinction coefficient of the corresponding absorption peak of Hq 26 at 243 nm, ǫ 243 = 4.7 × 10 4 M -1 cm -1 . This suggests that the first absorption transitions of HOp-py 22 and Hq 26 have similar pathways. In contrast the second absorption transition has a different origin. At last, the extinction coefficient ǫ of the absorption peaks of tropolone 24 are ranging between 5.3 × 10 3 and 9.5 × 10 3 M -1 cm -1 , comparable with those of the other studied ligands. However, due to the different structure of tropolone 24, a direct comparison between its extinction coefficients ǫ and those of the other ligands is impossible.

λ emi max [nm] ([M -1 cm -1 ]) [nm
Table 3.6 lists all the absorption peaks with their extinction coefficient ǫ and the emission peaks λ emi max of the (novel) OSCs. The comparison between the extinction coefficients ǫ of the halogenated and substituted complexes, Al(Op-X) 3 6a-d and Al(Op-R) 3 16a-c, and of Al(Op) 3 4 yields to the same observation described for the halogenated and substituted ligands, HOp-X 5a-d and HOp-R 15a-c, and HOp 3. Similarly, the observations on the extinction coefficients ǫ of the peaks for the ligands HOba 18 and tropolone 24 are identical to those for Al(Oba) 3 19 and Al(Trop) 3 25.

Comparing the two tables, Table 3.5 and Table 3.6, it can be noted that the extinction coefficient ǫ of an absorption peak of a complex is about 3-5 times that of the corresponding absorption peak of its ligand. Since a complex is formed by three ligands, its extinction coefficient ǫ is roughly the sum of the extinction coefficient ǫ of three ligands. As an example the first absorption peak of Alq 3 has an extinction coefficient, ǫ 385 = 1.1 × 10 4 M -1 cm -1 , which is 3.5 times the extinction coefficient of the first absorption peak of Hq 26, ǫ 314 = 3.1 × 10 3 M -1 cm -1 . For Al(Op) 3 4, the extinction coefficient of the first absorption peak, ǫ 454 = 4.4 × 10 4 M -1 cm -1 , is about 4.9 times the extinction coefficient of the first absorption peak of HOp 3, ǫ 439 = 9.0 × 10 3 M -1 cm -1 . The same trend is observable for the halogenated complexes Al(Op-X) 3 6a-d, which have extinction coefficient of the first absorption peak (ǫ

Al(Op-F ) 3 469 = 5.1 × 10 4 M -1 cm -1 , ǫ Al(Op-Cl) 3 467 = 4.8 × 10 4 M -1 cm -1 , ǫ Al(Op-Br) 3 467 = 4.6 × 10 4 M -1 cm -1 ,

and ǫ

Al(Op-I) 3 468 = 4.8 × 10 4 M -1 cm -1 ) between 4.6 and 7.4 times that of the corresponding absorption peak of their respective ligands (ǫ HOp-F 451 = 6.9 × 10 3 M -1 cm -1 , ǫ HOp-Cl 451 = 8.2 × 10 3 M -1 cm -1 , ǫ HOp-Br 450 = 1.0 × 10 4 M -1 cm -1 , and ǫ HOp-I 452 = 8.9 × 10 3 M -1 cm -1 ). The extinction coefficient ǫ of the first absorption peak of the substituted complexes Al(Op-R) 3 16a-c (ǫ

Al(Op-p) 3 470 = 3.0 × 10 4 M -1 cm -1 , ǫ Al(Op-n) 3 464 = 2.9 × 10 4 M -1 cm -1 ,

and ǫ

Al(Op-pe) 3 475 = 3.6 × 10 4 M -1 cm -1 ) is between 3.7 and 4.6 times that of the corresponding absorption peaks of their respective ligands (ǫ HOp-p 454 = 7.6 × 10 3 M -1 cm -1 , ǫ HOp-n 448 = 7.9 × 10 3 M -1 cm -1 , and ǫ HOp-pe 448 = 7.9 × 10 3 M -1 cm -1 ). In the case of Al(Oba) 3 19 the extinction coefficient of the first absorption peak, ǫ 452 = 5.1 × 10 4 M -1 cm -1 , is about 5.6 times higher than the extinction coefficient of the same peak of HOba 18, ǫ 459 = 9.1 × 10 3 M -1 cm -1 . In the same way, the extinction coefficient of the first absorption peak of Al(Trop) 3 25, ǫ 384 = 2.9 × 10 4 M -1 cm -1 , is about 5.5 times higher than that of the first absorption peak of tropolone 24, ǫ 370 = 5.3 × 10 3 M -1 cm -1 .

The mixed ligands Al(q 2 Acac) 28, Al(q 2 Op) 29 and Al(q 2 Trop) 30 are characterized by absorption spectra which are a combination between the absorption of their ligands. As an example, the spectra of Al(q 2 Acac) 28 is composed by the absorption of the two quinolinates plus the absorption of the acetyl acetonate. Hence, the extinction coefficient ǫ of a peak in Alq 3 should be Table 3.6: List of the absorption and emission peaks of the (novel) OSCs. In the parenthesis is reported the extinction coefficient of the absorption peak.

Compound

λ abs max (ǫ) .

λ emi max [nm] ([M -1 cm -1 ]) [nm
a Excitation at 350 nm about 1.5 times higher of the extinction coefficient ǫ of the same peak in Al(q 2 Acac) 28. As an example, the peak at 385 nm has an extinction coefficient for Alq 3 , ǫ 385 = 1.1 × 10 4 M -1 cm -1 , which is 1.38 times higher the extinction coefficient of the same peak at 384 nm for Al(q 2 Acac) 28, ǫ 384 = 8.0 × 10 3 M -1 cm -1 . Similarly, for Al(q 2 Op) 29 and Al(q 2 Trop) 30, the extinction coefficient ǫ of the peaks deriving from the absorption of the phenalenyl and tropolonate is about one third of that of the corresponding peaks for Al(Op)

Electrochemical characterization

Solution electrochemistry methods are known to prove insight into electron-transfer reactions in the condensed phase [184]. We have measured the cyclic voltammetries (CVs) of the ligands (see Table 3.1) and complexes (see Table 3.2) in solution to determine their reduction potentials E red 1/2 . CVs of the phenalenyl-based OSCs show clear reduction waves, however, no oxidation processes were recorded. Therefore, in order to compare the results we have illustrated and discussed only the cathodic processes of the CVs. In addition, from the reduction potential it is possible to estimate the LUMO energy levels. The values of the reduction potentials E red 1/2 and the LUMO energies E LU M O are listed in Table 3.7 andTable 3. -

2,4 -2,2 -2,0 -1,8 -1,6 -1,4 -1,2 -1,0 -3,0 -2,0 -1,0 0,0 1,0 Al(Oba) 3 ( 19
)
HOba ( 18) The cathodic cyclic voltammograms of tropolone 24 and Al(Trop) 3 25, illustrated in Figure 3.42, are characterized by single reduction waves at -2.06 V and -2.10 V, respectively. As expected, due to its small aromatic system, tropolone 24 has the most negative reduction potential. Moreover, the reduction potentials of the free ligand and the complex are almost identical. This indicates that the electro-active species in Al(Trop) 3 25 is the tropolonate. Successive reductions of the complex, if any, would occur at potentials out of the redox window of our electrochemical system, and thus, they were impossible to record.

Current ( A) Potential (V vs Fc/Fc + ) (a) -2,4 -2,2 -2,0 -1,8 -1,6 -1,4 -1,2 -
Figure 3.42 shows the cathodic cyclic voltammogram of Al(q 2 Acac) 28. Al(q 2 Acac) 28 is characterized by a single irreversible reduction process with an onset of -1.80 V. Since the electro-active species in Al(q 2 Acac) 28 is the quinolinate, its reduction potential is almost identical to that of Alq 3 . Hence, we can conclude that the effect of the acetyl acetonate moiety on the electrochemical properties of Al(q 2 Acac) 28 is negligible. The cathodic cyclic voltammogram of Al(q 2 Op) 29, shown in Figure 3.43, is characterized by a single quasi-reversible reduction wave at -1.58 V and an irreversible wave with an onset of -2.08 V. Since Al(q 2 Op) 29 is formed by two quinolinates and one phenalenyl, which are both

Electrochemical characterization

electro-active, we can discriminate on which moiety are localized the reduction processes. The first quasi-reversible reduction process occurs at -1.58 V, similar to the first reduction process of Al(Op) 3 4. The shape and the potential of the wave strongly suggest that this reduction process is localized on the phenalenyl. Therefore, the second reduction process is localized on one of the two quinolinates. Its extremely negative reduction potential, compared to the reduction of Alq 3 , is caused by the formation of the mono-anion during the first reduction process, which shifts the second reduction process toward more negative potential.

The cathodic cyclic voltammogram of Al(q 2 Trop) 30 is illustrated in Figure 3.43. A single quasireversible reduction wave at -2.08 V is recorded. Since, as previously described for Al(q 2 Op) 29, Al(q 2 Trop) 30 is formed by two electro-active species, we would expect to record two distinct reduction processes. However, only one quasi-reversible wave is observed. The evidence that the wave is quasi-reversible indicates that, most probably, the reduction process takes place on the tropolonate. In addition, the reduction potential of Al(q 2 Trop) 30 at -2.08 V is almost identical to the reduction potential of Al(Trop) 3 (-2.10 V). Nevertheless, due to the negative potential, the simultaneous reduction of one of the two quinolinate can occur. The reduction potentials of the ligands and complexes are listed in Table 3.7 and Table 3.8. Among the studied ligands, due to their small aromatic structures, tropolone 24 and HOp-py 22 have the most negative reduction potentials, -2.06 V and -1.94 V, respectively. Similarly, the reduction of Hq 26 occurs at -1.87 V. Phenalenyl-based ligands are characterized by extended aromatic systems, and thus, their reduction occurs at a more positive potential. The reduction of HOp 3 takes place at -1.60 V. The halogenated and substituted ligands, HOp-X 5a-d and HOp-R 15a-c, have reduction potentials between -1.47 and -1.57 V, slightly more positive than that of HOp 3. Lastly, the reduction of HOba 18 is at -1.71 V. The same trend is confirmed by the reduction potentials of the (novel) OSCs studied. Al(Trop) 3 25 is characterized by the most negative reduction potential, -2.10 V. This value is similar to that of Al(q 2 Trop) 30, -2.08 V, since the electro-active species is the tropolonate. The quinolinate is the electro-active species in Alq 3 and Al(q 2 Acac) 28, and thus, they present virtually identical reduction potentials, -1.79 V and -1.80 V, respectively. Three reduction processes are recorded for Al(Op) 3 4 at -1.63 V, -1.84 V and -2.07 V. All the halogenated and substituted derivatives, Al(Op-X) 3 6a-d and Al(Op-R) 3 16a-c, show the same three reduction processes. The effect of the halogenation and substitution of the phenalenyl leads to slightly more positive reduction potentials compared to those of Al(Op) 3 4. On the contrary, the three reductions of Al(Oba) 3 19, -1.75 V, -1.93 Vand -2.15 V, are at more negative potential than those of Al(Op) 3 4. Al(q 2 Op) 29 is reduced two times at -1.58 V and -2.08 V. The first reduction occurs on the phenalenyl, hence, its value is close to the first reduction of Al(Op) 3 4, while the second reduction process involves the quinolinates. At last, Zn(Op) 2 31 presents three reduction processes at -1.50 V, -1.81 Vand -2.04 V which occur on the phenalenyls and, most probably, on the zinc.

HOMO and LUMO energy levels

HOMO and LUMO energy levels of OSCs play a decisive role in organic-based devices [61,104,190]. As described in the introduction of this thesis, the injection of charge carriers from the electrodes into organic layers is strongly affected by the mismatch between HOMO or LUMO and the work function of the electrode (anode or cathode). A large mismatch between HOMO energy level and work function of the anode results in a poor injection of holes. Similarly, a large mismatch between LUMO and work function of the cathode yields a poor injection of electrons. Additionally, in multi-layer devices, hole-and electron-transporting materials also prevent the diffusion of electrons and holes, respectively, acting as electron-and hole-blocking materials. Hence, we have estimated the HOMO and LUMO levels of the ligands and of the OSCs to investigate the relation between their molecular structure and their electronic properties. LUMO levels are computed with the empirical relation

HOMO and LUMO energy levels

E LU M O = -(E red + 4.8) eV
, where E red is the onset of the first reduction wave in the cyclic voltammogram corrected accordingly to the reduction potential of ferrocene [191]. From the onset of the first band in the absorption spectrum, the optical HOMO-LUMO gap is determined. The onset is defined as the intersection between the baseline and a tangent line that touches the point of inflection. Lastly, HOMO levels are determined by the simple relation E HOM O = E LU M O -E gap . Calculated HOMO and LUMO energy levels and HOMO-LUMO gaps are listed in Table 3.7 and Table 3.8 and graphically compared in Figure 3.45.

At first we discuss the relation between structure and HOMO and LUMO energy levels of the ligands listed in Table 3.1. Ligands formed by small aromatic systems, such as Hq 26, HOp-py 22 and tropolone 24, have considerably higher LUMO energies than ligands formed by bigger aromatic systems, such as HOp 3 and HOba 18. Due to its single aromatic system, tropolone 24 has the highest LUMO at -2.74 eV. HOp-py 22 and Hq 26 are structurally similar, and thus, their LUMOs are close, -2.86 eV and -2.93 eV, respectively. HOp 3 and HOba 18 have LUMOs at -3.25 eV and -3.16 eV, respectively. As expected, the extended aromatic system shifts the LUMO at a lowered energy. Surprisingly, HOba 18 has a higher LUMO than HOp 3. Hq 26 and HOp-py 22 have the lowest HOMOs, -6.42 eV and -6.35 eV, respectively. On the other hand, HOp 3, HOba 18 and tropolone 24 are characterized by comparable HOMOs, between -5.84 and -6.01 eV. Presumably, the carbonyl group, which characterizes the three ligands, is the reason of increased HOMOs. Halogenated and substituted ligands, HOp-X 5a-d and HOp-R 15a-c, have similar HOMO and LUMO compared to those of the pristine HOp 3.

Both series have slightly lowered LUMOs. The HOMO of the halogenated ligands HOp-X 5a-d is slightly lowered compared to that of HOp 3. On the contrary, the HOMO of the substituted ligands HOp-R 15a-c is slightly increased compared to that of HOp 3.

In collaboration with the group of prof. Willem Klopper (INT-KIT, Karlsruhe), the HOMO and (a) LUMO energy levels of the ligands have been calculated at the B3-LYP [83]/def2-TZVPP [90] level of theory. The aim of this study was to evaluate the ability of the studied ligands to sensitize the emission of lanthanides. Calculated HOMO and LUMO energy levels, determined in the preliminary studies, are compared to those estimated experimentally in Table 3.7. Despite the difference between the absolute values, a general trend is identified. The calculated HOMO and LUMO energies of HOp 3, -6.28 eV and -2.71 eV, respectively, are lowered compared to those of Hq 26, -5.97 eV and -1.72 eV, respectively. This matches the experimental results for the LUMO, whereas the experimental HOMO of HOp 3 is higher than that of Hq 26. As observed experimentally, HOba 18 is characterized by a calculated LUMO, -2.53 eV, lowered in respect to that of HOp 3. Conversely to the experimental results, the theoretical HOMO level of HOba 18, -6.08 eV, is higher compared to that of HOp 3. Likewise, the calculated LUMO of tropolone 24, -2.21 eV, is higher than that of HOp 3, whereas the theoretical HOMO, -6.37 eV, is lowered compared to that of HOp 3. In accordance with the experimental data, the HOMO and LUMO levels of HOp-py 22, -5.88 eV and -1.57 eV, respectively, are higher than those of Hq 26.

H q H O p H O p -F H O p -C l H O p -B r H O p -I H O p -p H o p -n H o p -p
A lq 3 A l( O p )3 A l( O p -F )3 A l( O p -C l) 3 A l( O p -B r )3 A l( O p -I )3 A l( O p -p )3 A l( O p -n )3 A l( O p -p e )3 A l( O b a )3 A l( T r o p )3 A l( q 2 A c a c ) A l( q 2 O p ) A l( q 2 T r o p ) Z n (O p )2
Lastly, the calculated HOMO and LUMO of the halogenated ligands HOp-X 5a-d, between -6.32 and -6.37 eV and between -2.91 and 2.94 eV, respectively, are both lowered compared to those of HOp 3, as determined experimentally. In addition, accordingly to the experimental results, the substituted ligands HOp-R 15a-c are characterized by slightly lowered calculated LUMO, between -2.71 and -2.79 eV, and higher calculated HOMO, between -5.92 and 6.09 eV, compared to those HOp 3. In conclusion, the experimental HOMO and LUMO levels have been confirmed theoretically, besides few discrepancies concerning the HOMO levels. Theoretical studies on the (novel) OSCs are presented in Chapter 4.2, and thus, here, only the experimental HOMO and LUMO energy levels are discussed in the following.

HOMO and LUMO energy levels of Alq 3 reported in literature, -5.95 eV and -3.01 eV, respectively [36,38], are in a fairly good agreement with the HOMO and LUMO energy levels estimated in this study, -5.83 eV and -3.01 eV, respectively. Unexpectedly, all the aluminum complexes have similar HOMOs ranging between -5.80 and -5.97 eV. On the contrary, the LU-MOs follow the same trend described for those of the ligands. As an example, Al(Trop) 3 25 is characterized by the highest LUMO, -2.78 eV, followed by that of Alq 3 , -3.01 eV. The LUMOs of Al(Op) 3 4 and Al(Oba) 3 19 are -3.26 eV and -3.12 eV, respectively. HOMOs and LUMOs of the mixed-ligands aluminum complexes exhibit quite interesting features. Al(q 2 Acac) 28

presents HOMO and LUMO, -5.87 eV and -3.00 eV, respectively, almost identical to those of Alq 3 . This is expected considering that the electro-and photo-active species in Al(q 2 Acac) 28 is the quinolinate, whereas the effect of the acetyl acetonate is negligible. In Al(q 2 Op) 29 the predominant electro-and photo-active species is the phenalenyl, and thus, its HOMO and LUMO, -5.98 eV and -3.31 eV, respectively, are similar to those of Al(Op) 3 4. At last, Al(q 2 Trop) 30 is identified by HOMO and LUMO, -5.95 eV and -2.84 eV, respectively, almost identical to those of Al(Trop) 3 30, indicating that the predominant electro-and photo-active moiety is the tropolonate. The halogenated and substituted aluminum complexes, Al(Op-X) 3 6a-d and Al(Op-R) 3 16a-c, present the same behaviors described for the halogenated and substituted ligands HOp-X 5a-d and HOp-R 15a-c. The LUMO of the halogenated and substituted aluminum complexes, Al(Op-X) 3 6a-d and Al(Op-R) 3 16a-c, in the range between -3.31 and -3.37 eV, are lowered compared to that of Al(Op) 3 4. In addition, the halogenated complexes Al(Op-X) 3 6a-d show also a lowered HOMO, between -5.94 and -5.97 eV, compared to that of Al(Op) 3 4. On the contrary, the substituted complexes Al(Op-R) 3 16a-c exhibit a higher HOMO, ranging between -5.80 and -5.89 eV, compared to that of Al(Op) 3 4.

Lastly, the HOMO and LUMO energy levels of Zn(Op)

Conclusions

In conclusion, we have designed, synthesized and characterized a series of (novel) OSCs. The goal was to determine the relationship between molecular structure and electronic properties of the (novel) OSCs in comparison to the benchmark Alq 3 . The ligands and complexes involved in this study are listed in Table 3.1 and Table 3.2.

The first OSC synthesized was Al(Op) 3 4, which is characterized by a symmetrical structure and ligands with an extended aromatic system compared to Alq 3 . Its molecular structure was, for the first time, resolved. Additionally, two series of halogenated and substituted derivatives of Al(Op) 3 4 were synthesized, namely, Al(Op-X) 3 6a-d and Al(Op-R) 3 16a-c. The aromatic system of Al(Op) 3 4 was further extended to form the aluminum complex Al(Oba) 3 19. Due to its structural similarity to Alq 3 , Al(Op-py) 3 23 was synthesized and studied. Because of its 7-membered aromatic backbone and its symmetrical structure, Al(Trop) 3 25 was formed and investigated. The three mixed-ligands complexes Al(q 2 Acac) 28 , Al(q 2 Op) 29, and Al(q 2 Trop) 30 were obtained by the exchanging one quinolinate of Alq 3 with Acac 27, HOp 3 and tropolone 24, respectively. The molecular structure of the unprecedented Al(q 2 Op) 29 and Al(q 2 Trop) 30 was resolved by single crystal X-ray diffraction. At last, the flat complex Zn(Op) 2 31 was synthesized as the first member of a series of complexes based on zinc, and its exact molecular structure was resolved by single crystal X-ray diffraction.

A complete photophysical characterization of Al(Op) 3 4 in solution and in thin film was carried out. The results were compared to the photophysical properties of Alq Moreover, it was demonstrated that, in spite of the bulky substituent, Al(Op-p) 3 16a forms excimers in thin film. As a consequence of its phenalenyl core, Al(Oba) 3 19 presents absorption and emission spectra similar to those of Al(Op) 3 4. Moreover, it forms excimers in solid state. On the contrary, Al(Op-py) 3 23, which is insoluble in all the solvents, in solid state is characterized by an emission blue-shifted compared to the emission of Alq 3 . As a result of its particular structure, the spectra of Al(Trop) 3 25 are not comparable to those of Alq 3 and Al(Op) 3 4. However, the absorption bands of Al(Trop) 3 25 were assigned to their respective transitions and a blue fluorescence emission was detected. Absorption and emission spectra of the mixed-ligands complexes Al(q 2 Acac) 28, Al(q 2 Op) 29, and Al(q 2 Trop) 30 result from the combination of the absorption and emission of the two moieties forming the complexes. Since Acac is not emitting, the emission of Al(q 2 Acac) 28 is almost identical to that of Alq 3 . On the contrary, the emission of Al(q 2 Op) 29 is a combination between the emission of the quinolinate and the phenalenyl. It was possible to excite selectively one of the two moieties, and, as a result, the emission of Al(q 2 Op) 29 depends from the excitation wavelength. The same effect was observed for Al(q 2 Trop) 30, however, since the absorption of the quinolinate and of the tropolonate are superimposed, it was impossible to excite selectively one of the two ligands. Lastly, absorption and emission spectra of Zn(Op) 2 31 derive from the phenalenyl ligands and the flat structure of the complex has a negligible effect on its spectra.

The single irreversible electrochemical reduction of Alq 3 occurs at a quite negative potential. In contrast, Al(Op) 3 4 can be reduced quasi-reversibly three times at more positive potentials.

As a consequence of their structural affinity with Al(Op) 3 4, the same behavior was observed for the halogenated and substituted complexes Al(Op-X) 3 6a-d and Al(Op-R) 3 16a-c and for Al(Oba) 3 19. Due to its small aromatic structure, Al(Trop) 3 25 is characterized by a single quasi-reversible reduction at a considerably negative potential. The reduction of Al(q 2 Acac) 28, Al(q 2 Op) 29, and Al(q 2 Trop) 30 is caused by their electro-active moieties. In detail, the reduction of Al(q 2 Acac) 28 occurs on the quinolinates, the (first) reduction of Al(q 2 Op) 29 takes place on the phenalenyl and the reduction of Al(q 2 Trop) 30 involves the tropolonate. Zn(Op) 2 31 is characterized by three reduction processes which occur on the two phenalenyl and, most probably, on the zinc.

From the photophysical and electrochemical characterization the HOMO and LUMO energy levels of the (novel) OSCs were estimated. Al

Theoretical and preliminary experimental studies on the (novel) OSCs

Introduction

In this chapter, we have studied the charge carrier mobilities of the (novel) OSCs by means of theoretical and experimental methods. At first, the (novel) OSCs, Al(Op) 3 , Al(Op-py) 3 , Al(Trop) 3 , Al(q 2 Acac), Al(q 2 Op), and Al(q 2 Trop), synthesized and characterized in Chapter 3, were investigated with newly developed theoretical methods. Alq 3 was included as a benchmark. Additionally, due to its non-aromatic structure, Al The theoretical investigation was carried out in three parts. In the first part, HOMO and LUMO energy levels and electrical dipole moment of the (novel) OSCs were investigated in vacuum. Additionally, the HOMO and LUMO energy levels computed have been compared with those obtained experimentally in Section 3.6. In the second part, morphologies of the OSCs were generated to simulate amorphous films. In the last section of the theoretical studies, implementing the morphologies in a newly developed method, the charge carrier mobility of the OSCs has been calculated. The obtained data has been compared with the structure of the OSCs aiming to infer a relation between properties and chemical structure. An additional preliminary study on the experimental charge carrier mobility of Al(Op) 3 is presented. In detail, the mobilities were estimated by means of field-effect transistors (FET), time of flight (TOF), and admittance spectroscopy (AS). Although the results are still inconclusive and partially unsatisfactory, sample preparation and measurement are reported.

Theoretical studies on the (novel) OSCs

Theoretical studies in collaboration with: Dr. Velimir Meded, Pascal Friederich INT-KIT, Karlsruhe, Germany and Dr. Timo Strunk Nanomatch, Eggenstein-Leopoldshafen, Germany

Frontier orbitals and electrical dipole moment in vacuum

In this section we have studied the complexes in vacuum with the aid of density function theory (DFT) based calculations implementing TURBOMOLE [82] on a B3-LYP [83] /SV(P) [84] level of theory. The crystal structure of the complexes, except for Al(Op-py) 3 , was used as starting point for the atomic coordinates. HOMO and LUMO energy levels and the electrical dipole moment of the OSCs in vacuum were computed. Studies on the geometry and the electronic properties of Alq 3 , in neutral and charged states, as well as the bonding characteristics in metal-Alq 3 complexes, have been carried out by Andreoni and co-workers [192][193][194]. As reported in Section 1.2, the meridianal isomer, mer-Alq 3 , was found to be the preferred form of Alq 3 , being energetically favored than the facial isomer, fac-Alq 3 . Therefore, we have only studied the HOMO and LUMO of the mer-isomer. A number of theoretical studies on the electronic structure of Alq 3 has been reported [192,[194][195][196][197][198][199], which complements the extensive experimental studies carried out using optical and ultraviolet photoelectron spectroscopies [195,198,[200][201][202]. Frontier orbital levels of mer-Alq 3 consist of sets of closely spaced triplets. HOMOs and LUMOs largely preserve the electronic structure of the individual quinolin-8-ol (Hq) ligand with little contribution from the central aluminum.

Due to the loss of symmetry of the meridianal isomer, the highest HOMO, -5.14 eV, and the lowest LUMO, -1.91 eV, depicted in Figure 4.2, are mainly localized on a single ligand. A detailed analysis reveals that the HOMO is principally localized on the phenoxide side of the quinolinate, whereas the LUMO is primarily localized on the pyridyl side. The localization of the orbitals is caused by the loss of symmetry resulting in an elongation, or shrinking, of the distances between the central aluminum and the nitrogens or oxygens. As a result, in mer-Alq Al(Op-py) 3 is formed by three asymmetrical HOp-py ligands (see Table 3.1). As described in Section 3.3.5, due to the asymmetrical structure of the ligand, two geometrical isomers can be formed fac-Al(Op-py) 3 and mer-Al(Op-py) 3 . In Section 3.3.5, we have presumed that the merisomer is more stable, and thus, we have studied the HOMO and LUMO distribution exclusively of mer-Al(Op-py) 3 . Both HOMO and LUMO, illustrated in Figure 4.4, are strongly localized.

In more detail, the HOMO is mostly localized on the phenoxide part of one ligand, whereas the LUMO is confined unevenly on the pyridyl side of two ligands. As a result, the ground state vacuum dipole moment of mer-Al(Op-py) 3 is 4.79 D. The calculated HOMO energy, -5.07 eV, is comparable to that of mer-Alq 3 . In contrast, the LUMO energy, -1.55 eV, is quite higher than that of mer-Alq 3 . The localization of the orbitals is caused by the loss of symmetry resulting in an elongation or shrinking of the distances between the central aluminum and the oxygen and nitrogen atoms. In mer-Al(Op-py) that of Al(Op) 3 . Despite its seven-membered aromatic structure, tropolone is a symmetric molecule (see Table 3 In Al(q 2 Acac) a quinolinate is replaced by Acac, which introduces a plane of symmetry. Hence, the two quinolinate ligands are identical. In Section 3.3.7, we have observed that Al(q 2 Acac) occurs in a pseudofac-geometry, for that reason, we have solely computed the HOMO and LUMO of this isomer. HOMO and LUMO, illustrated in Figure 4.7, are localized equally on the two quinolinates, giving rise to a ground state dipole moment of 1.47 D, lowered in comparison to that of mer-Alq 3 . However, as previously described for mer-Alq 3 , the HOMO is mainly localized on the phenoxide side of the quinolinates, whereas the LUMO is principally localized on the pyridyl side. Moreover, either the HOMO, -5.29 eV, either the LUMO, -1.74 eV, have lowered energies compared to those of mer-Alq 3 . Due to the different nature of the ligands, the six chelating atoms of pseudofac-Al(q 2 Acac), two nitrogens and four oxygens, are not equivalent.

Bond Length [Å] Bond Length [Å] Al-O1 In detail, O1 is facing N1 and O2 is facing N2, while O3 is facing O4. As a consequence, the bonds Al-O1 and Al-O2, 1.892 and 1.893 Al(q 2 Op) is formed by the substitution of Acac in Al(q 2 Acac) with HOp. In Section 3.3.8, we have obtained the molecular structure of pseudofac-Al(q 2 Op) by single crystal X-ray diffraction, and thus, we have studied only the HOMO and LUMO orbitals of this geometry. The HOMO is localized uniformly on the two quinolinate moieties with a higher density on the phenoxide side. However, the LUMO is exclusively localized on the phenalenyl. The strong localization of the molecular orbitals results in a ground-state dipole moment of 6.52 D, which is the highest among all the studied OSCs. Additionally, the HOMO energy, -4.99 eV, is close to that of mer-Alq 3 , whereas and the LUMO energy, -2.71 eV, is closer to that of Al(Op) 3 . For the sake of understanding, we have calculated and plotted lower HOMOs and higher LUMOs of pseudofac-Al(q 2 Op). It can be seen that the HOMO-1, HOMO, LUMO+1 and LUMO+2 are centered on the quinolinates, whereas the HOMO-2 and LUMO on the phenalenyl. The HOMO-LUMO gap of Al(q 2 Op) is -2.28 eV, considerably lowered compared to that of all the other studied OSCs. However, the gap between HOMO and LUMO+1 (both centered on the quinolinates) and between the HOMO-2 and LUMO (both centered on the phenalenyl) are 3.44 eV and 3.47 eV, respectively. These values are comparable to the HOMO-LUMO gaps of mer-Alq 3 and Al(Op) 3 .

Due to the different nature of the ligands in pseudofac-Al(q 2 Op), the bonds O(phenalenyl)- In Al(q 2 Trop), Acac is replaced with tropolone. As described in Section 3.3.9, by X-ray single diffraction, we have determined that Al(q 2 Trop) assumes a pseudomer-geometry. Hence, we have studied the HOMO and LUMO orbitals of pseudomer-Al(q 2 Trop). Figure 4.9 illustrates the molecular orbital surfaces of pseudomer-Al(q 2 Trop) from HOMO-2 to LUMO+2. The HOMO is localized uniformly on the two quinolinates with a higher density on the phenoxide side. However, the LUMO is exclusively localized on the tropolonate. The strong localization of the orbitals leads to a high ground state dipole moment of 5.49 D. Whilst the HOMO-1, HOMO and LUMO+1 are localized on the two quinolinates, the HOMO-2, LUMO and LUMO+1 are centered on the tropolonate. Since the HOMO energy level is -5.09 eV and the LUMO energy level is -2.07 eV, the resulting HOMO-LUMO gap is 3.02 eV. However, the gap between HOMO-2 and LUMO, both localized on the tropolonate, is 4.09 eV, which is similar to that of Al(Trop) 3 .

On the contrary, the gap between HOMO-2 and LUMO, both localized on the quinolinates, is 3.47 eV, which is comparable to that of mer-Alq 3 and of pseudofac-Al(q 2 Acac), furthermore, it is identical to that between HOMO-2 and LUMO of Al(q 2 Op). The bonds O(tropolonate)-Al, 1.946 Å, are longer than those O(quinolinate)-Al, 1.864 Å. In addition, the N(quinolinate)-Al bond lengths, 2.066 Å, are similar to those of pseudofac-Al(q 2 Op) and shorter than those of Figure 4.12 shows the comparison between HOMO and LUMO energy levels estimated experimentally in Section 3.6 and calculated theoretically. Despite a shift of the values, caused by the underestimation of the experimental HOMO and LUMO energy levels measured by the solutionbased methods, the trend of experimental and calculated HOMO and LUMO energy levels are comparable. The major differences are observed for the HOMO and LUMO energy levels of the mixed ligands complexes pseudofac-Al(q 2 Op) and pseudomer-Al(q 2 Trop). Experimentally, the phenalenyl and tropolonate are the photo-and electrochemical-active moieties resulting in HOMO and LUMO energy levels almost identical to those of Al(Op) 3 and Al(Trop) 3 . On the contrary, the theoretical studies demonstrate that the HOMO orbitals are localized on the quinolinates, whereas the LUMO orbitals are centered on the phenalenyl or the tropolonate, as illustrated in Figure 4.8 and in Figure 4.9. As a consequence, the HOMO levels estimated experimentally are considerably underestimated than those calculated theoretically.

In silico morphologies

The DEPOSIT code, developed by Neumann et al. [85], was implemented to generate realistic morphologies based on the OSCs aforementioned. Morphologies are used to predict the microscopic parameters presented in Section 4.2.3. In addition, the degree of order of the morphologies is evaluated through the pair correlation function g(r) extracted from the calculations. The prevalent morphology of a layer, produced by vapor deposition of OSCs, is an amorphous film [91,190,204]. The disorder in the morphology and the weak electronic coupling between the molecules lead to states described by quantum-mechanical wave functions localized on single molecules. As a result, the charge transport occurs by hopping of charge carriers from one molecule to another. Hopping probabilities depend strongly on the overlap between molecular orbitals on adjacent sites [104,205]. Thus, the charge transport properties are extremely sensitive to the morphology of the film [206]. Morphologies have been generated using a deposition protocol that emulates vapor deposition of molecular films. In detail, the protocol consists of two steps: the first step is the deposition of a single molecule on a partially formed film, the second step consists of the selection of a neighborhood around the deposited molecule and its post-deposition relaxation via an annealing method. To reduce the trapping of the system in metastable configurations, a basing hopping approach [207-209], which comprises several simulated annealing processes [START_REF]Bond angle Angle[END_REF], was used.

The setting of the DEPOSIT code, implemented to generate the morphologies, includes: 1000 molecules per morphology with the input structure of the molecules plus the partial charges (ESP) calculated as described in 4.2.1. During the simulation, standard van der Walls interaction were taken in account using the Lennard-Jones potential as an approximation. 10 simulated annealing steps for the deposited molecules were calculated. Each simulated annealing process starts at 4000 K, where the molecule can easily transverse the energy barriers separating local minima. The temperature is lowered gradually during the simulation over 60000 steps to a final temperature of 300 K. The morphologies obtained, with a size of 22 nm x 22 nm x 100-160 nm, were extended periodically in x-and y-direction to a final dimension of 9000 molecules. Three examples of the generated morphologies are shown in Figure 4.10.

The parameter, which can be extracted from the morphologies, is the so-called pair correlation function (or radial distribution function) g(r), that represents the short-range order in amorphous materials. It describes the variation of the density as a function of distance from a reference particle (molecule). In other words, it is a measure of the probability of finding a particle (molecule) at a distance r away from a given reference particle (molecule). For amorphous films, which are anisotropic structures, the pair correlation function is an indication of the packing of the molecules in the film. In Figure 4.11, the pair distribution function g(r) for all the generated morphologies is plotted. From the data, we can infer some relations between the structure (see Table 3.2) and the electrical dipole moment (see Table 4.1) of the OSCs and the degree of order of the generated films. As an example, mer-Alq 3 and mer-Al(Op-py) 3 are characterized by similar structures and dipole moments resulting in almost identical pair distribution functions g(r), sharply peaked at nearly 10 Å. This indicates that the films have a high degree of order and the molecules are closely packed. Similarly, pseudofac-Al(q 2 Acac), which is characterized by a similar structure and a lower dipole moment than those of mer-Alq 3 , has a sharp pair distribution function g(r). Al(Acac) 3 is formed by non-aromatic small ligands, as a consequence, its pair distribution function g(r) is sharply peaked at ≈8 nm. The negligible dipole moment and the extended ligands of Al(Op) 3 result in a broad pair distribution function g(r). Likewise, the pair distribution function g(r) of Al(Trop) 3 , although the peak is at 10 Å, is broadly distributed. The broad pair distribution function g(r) of pseudofac-Al(q 2 Op) and pseudomer-Al(q 2 Trop), despite their high dipole moment, is induced by the introduction of bulky phenalenyl and tropolonate.

Calculated charge carrier mobility

In this section, the morphologies generated in Section 4.2.2 are implemented in the Quantum Patch method [START_REF] Friederich | Simulation of energetic disorder and charge transport in amorphous organic semiconductors[END_REF][START_REF] Friederich | [END_REF]. Firstly, the HOMO and LUMO energy levels of the OSCs were re-calculated in the morphology. Subsequently, the microscopic parameters, included in the Equation 1.11, were computed. Lastly, the charge carrier mobility (for holes and electrons) of the OSCs was determined. Table 4.1 lists the HOMO and LUMO energy levels of the studied OSCs calculated in vacuum and in the morphologies. Additionally, Figure 4.12 illustrates the comparison between the HOMO and LUMO energy levels estimated experimentally in Section 3.6 and those calculated in vacuum and in the morphology. It can be noted that HOMO and LUMO energy levels in vacuum and in the environment (amorphous film) are substantially similar. The effect of the neighboring molecules in the generated morphologies slightly shifts the orbitals to higher energies. Reminding that HOMO and LUMO energy levels are fundamental parameters for OSCs, because they affect the charge injection from the electrodes into the organic layers and the charge transport between the layers [61,104,190]. The indication that in vacuum and in amorphous film their values are comparable is most important for applications. The symmetry breaking, caused by the neighboring molecules in the morphology causes a rise in the ground state dipole moment of all the OSCs. This can be understood as a stronger localization of the molecular orbitals when the molecules are embedded in an anisotropic film.

A l q 3 A l ( O p ) 3 A l ( O p -p y ) 3 A l ( T r o p ) 3 A l ( A c a c ) 3 A l ( q 2 A c ) A l ( q 2 O p ) A l ( q 2 T
In order to calculate µ (charge carriers mobility) of the different OSCs, as described in Equation 1.11, the microscopical parameters σ(E) (energetic disorder), λ (reorganization energy) and J 2 r 2 (electronic coupling) have to be computed first. All the results for holes and electrons are listed in Table 4.2. In addition, the value of the electron and hole mobilities are summarized in Table 4.3. All the microscopic parameters are graphically compared in Figure 4.13.

The resulting mobility µ is highly sensitive to changes of the width of the density of states, or energy disorder σ(E), as it enters the functional form in a quadratic fashion [23,211,212]. The energy disorder σ(E) is defined as the width of the local on-site energy distribution of the system. It originates from the disorder of the local electronic states induced by the amorphous structure of the materials. In disordered materials, energetic disorder σ(E) is introduced in two different ways: one effect is that molecules in amorphous structures are individually bent in a trade-off for a better alignment with other molecules, which leads to lowered intermolecular energies. The second effect is related to environmental causes. Each molecule is embedded into an individual, mainly electrostatic, environment created by all other molecules. The structure-related part is considered to be much smaller than the one caused by the electrostatic interactions with the environment [96]. Modest differences in the value of energy disorder σ(E) lead to dramatic variation of the charge carrier mobility µ. OSCs with small energy disorder, such as Al(Acac) 3 and pseudofac-Al(q 2 Acac), are characterized by high mobilities µ. Whereas, molecules with high energy disorder σ(E), as pseudofac-Al(q 2 Op) and pseudomer-Al(q 2 Trop), yield poor mobilities µ. A relation between the dipole moment of the OSCs (see Table 4.1) and the energy disorder σ(E) can be inferred. It appears clear that molecules characterized by low dipole moment have low energy disorder σ(E) and vice versa. This is true for Al(Acac) 3 , Al(Op) 3 and pseudofac-Al(q 2 Acac), characterized by both low dipole moment and energy disorder σ(E). In addition, mer-Alq 3 , mer-Al(Op-py) 3 , pseudofac-Al(q 2 Op) and pseudomer-Al(q 2 Trop) are characterized by both high dipole moment and energy disorder σ(E). In contradiction, Al(Trop) 3 , which has a negligible dipole moment, presents a high energy disorder σ(E). The reorganization energy λ is the energy obtained during the ionic relaxation of the donor and acceptor molecules as well as their environment after the charge transport process. It is usually separated in two parts: (i) the inner part λ i includes the relaxation of the donor and acceptor, (ii) the outer part λ o includes the relaxation of the environment. The outer part λ o is assumed to be much smaller than the inner part λ i , because the additional charge will cause much stronger conformational changes to the charged molecule than to the molecules in its environment. It can be noted that small differences in the reorganization energy λ do not critically affect the charge carrier mobility µ. Nonetheless, it is clear that the reorganization energy λ is related to the dipole moment of the OSCs (see Table 4.1). Molecules with a low dipole moment, such as Al(Acac) 3 , Al(Op) 3 , Al(Trop) 3 and pseudofac-Al(q 2 Acac), have a low reorganization energy λ. On the contrary, molecules with a high dipole moment, such as mer-Alq 3 , mer-Al(Op-py) 3 , pseudofac-Al(q 2 Op) and pseudomer-Al(q 2 Trop), have also a high reorganization energy λ.

A lq 3 A l( O p )3 A l( O p -p y )3 A l( T r o p )3 A l( A c a c )3 A l( q 2 A c ) A l( q 2 O p ) A l( q 2 T r o p ) 0,
A lq 3 A l( O p )3 A l( O p -p y )3 A l( T r o p )3 A l( A c a c )3 A l( q 2 A c ) A l( q 2 O p ) A l( q 2 T r o p ) 0,0 0,1 0,2 0
A lq 3 A l( O p )3 A l( O p -p y )3 A l( T r o p )3 A l( A c a c )3 A l( q 2 A c ) A l( q 2 O p ) A l( q 2 T r o p ) 1E-3 0,01 Electronic coupling j 2 r 2 (eV 2 Å 2 )
Holes Electrons (c) The last parameter to be considered is the electronic coupling J 2 r 2 . As the charge carrier mobility µ depends only linearly on the electronic coupling J 2 r 2 , its variations are of a minor importance. The electronic coupling J 2 r 2 fluctuates for all the OSCs in a narrow range between 4.4 × 10 -3 and 1.1 × 10 -2 eV 2 Å 2 . In addition, no direct relation between the electronic couplings J 2 r 2 and the OSCs structure and/or dipole moment can be inferred from the data.

A lq 3 A l( O p )3 A l( O p -p y )3 A l( T r o p )3 A l( A c a c )3 A l( q 2 A c ) A l( q 2 O p ) A l( q 2 T
Charge carrier mobilities µ, estimated for all the studied OSCs, are summarized in Table 4.3.

For mer-Alq 3 and pseudofac-Al(q 2 Acac) it is possible to compare the results with the experimentally determined charge carrier mobilities. In addition, the hole mobility of Al(Op) 3 , measured in thin film transistor devices (TFTs), is reported in Section 4.3.1. However, as far as the author is aware, the charge carrier mobility of the other OSCs is not reported in literature. The mobility of electrons and holes of Alq 3 has been widely studied experimentally by means of several techniques [42][43][44][45][46][47][48][49]. It has been found that the electron mobility is 10 -5 -10 -6 cm 2 V -1 s -1 and the hole mobility is 10 -8 -10 -9 cm 2 V -1 s -1 . The calculated electron mo-bility, 9.23 × 10 -8 cm 2 V -1 s -1 , results one order of magnitude lowered than the experimental. On the other hand, the calculated hole mobility, 3.26 × 10 -8 cm 2 V -1 s -1 , fairly agrees with the experimental value. The experimental electron mobility of pseudofac-Al(q 2 Acac), measured via transient electroluminescence, is 2.7-4.4 × 10 -6 cm 2 V -1 s -1 [167], which matches the theoretical value of 4.68 × 10 -6 cm 2 V -1 s -1 . However, no hole mobility was measured for pseudofac-Al(q 2 Acac). The hole mobility of Al(Op) 3 , measured in TFTs devices (see Section 4.3.1), is 0.6-2.1 × 10 -6 cm 2 V -1 s -1 . In contrast, no obvious electron mobility was detected. The calculated hole mobility, 1.42 × 10 -4 cm 2 V -1 s -1 , is two order of magnitude higher than the experimental. In addition, with the Quantum Patch method, an electron mobility of 9.49 × 10 -8 cm 2 V -1 s -1 was computed. Obviously, the electron mobility in amorphous film of Al(Op) 3 is impeded by the formation of excimers in the solid state, described in Section 3.4.1. Excimers are known to be electron traps. Therefore, to obtain more realistic data on the electron mobility, the formation of excimers must be taken in account in the Quantum Patch method.

Among the studied OSCs, pseudofac-Al(q 2 Acac) has a slightly higher electron mobility than mer-Alq 3 . In addition, the electron mobility of mer-Al(Op-py) 3 and Al(Trop) 3 is comparable to that of mer-Alq 3 . The mixed-ligands pseudofac-Al(q 2 Op) and pseudomer-Al(q 2 Trop) have a poor mobility of both electrons and holes. The high charge carriers mobility of Al(Acac) 3 is caused by its extremely low energy disorder, most probably, due to the strong localization of the orbitals on the non-aromatic ligands. However, this result is unrealistic considering that the charge transport occurs by hopping on the π orbitals of the molecules. Nevertheless, this result is most useful to further improve the Quantum Patch approach.

Experimental charge carrier mobilities

FET in Al(Op) 3 -based TFTs

In this preliminary study, we have measured the charge carriers mobilities of Al(Op) 3 in fieldeffect transistors (FETs). This is most important to confirm the results obtained theoretically, and, in addition, to evaluated the performance of Al(Op) 3 as semiconductor (see Section 1.1).

In order to do so, we have built and characterized a series of thin film transistors (TFTs) to determine the charge carriers mobility in Al(Op) 3 [16]. TFTs were built in a bottom contact configuration (see Section 1.2.4), using SiO 2 as gate dielectric, which was thermally grown onto the gate electrode of silicon. Source and drain electrodes of gold were deposited and patterned onto the gate dielectric. The OSC-based active layer was thermally evaporated onto the gate and between the source and drain electrodes, after adding a layer of trichloro(octadecyl)silane (OTS) to increment the charge carrier mobility detectability. To measure the field-effect mobility, a series of Al(Op) 3 -based TFTs based were fabricated with channel lengths ranging from 10 to 100 µm. Transfer curves were obtained by the electrical characterization of the devices. Figure 4.14 illustrates the holes transfer curve relative to the TFT device with a channel length of 100 µm. When a negative voltage is applied to the gate electrode, the hole carriers in the organic semiconductor layer accumulate at the interface with the gate dielectric. Hence, hole transport takes place from the source to the drain electrode. The injection of the charge carriers in the organic layer is provided by a source-drain voltage (V DS ) of -70 V. The threshold voltage V T , necessary to measure the hole mobility, is between -35 and -45 V. In addition, the on/off current ratio measured for the curve in Figure 4.15 is about 104. The on/off current ratio is defined as the ratio between the current when the TFT is in the on-state and the current when the TFT is in the off-state. The off-state is when voltage is not applied to the gate electrode and only small currents flow between source and drain electrodes. The on-state is when a negative voltage is applied to the gate electrode and hole transport takes place from the source to the drain electrode. The hole mobility is determined by the slope of the curve of |I DS | 1/2 versus the gate voltage illustrated in Figure 4.14. From the characterization of the Al(Op) 3 -based TFTs a hole mobility between 0.6 and 2.1 × 10 -6 cm 2 V -1 s -1 was determined. As previously reported, this value is two order of magnitude lower than the hole mobility calculated in Section 4.2.3, 1.42 × 10 -4 cm 2 V -1 s -1 . No obvious electron mobility was detected, most probably, as a consequence of the excimer formation in amorphous thin films of Al(Op) 3 , which is described in Section 3.4.1.

The hole mobility measured in Al(Op) 3 -based TFTs is comparable to the hole mobility measured for the well-know hole transporting material α-NPD [213]. In detail, α-NPD is characterized by a hole mobility of 6.1 × 10 -5 cm 2 V -1 s -1 [214], only one order of magnitude higher than that of Al(Op) 3 . However, the on/off current ratio, 3.5 × 10 3 (V SD = -60 V) of the α-NPDbased devices is significantly higher compared to that of Al(Op) 3 -based TFTs. In addition the threshold voltage V T , -4.4 V, is considerably lowered. Surprisingly, as far as the author is aware, the only report on field-effect charge carriers mobilities of Alq 3 was reported by Sakanoue et al. [78] (see Section 1.2.4). The measured hole mobility was 1.6 × 10 -7 cm 2 V -1 s -1 with a threshold voltage V T of -43 V, which is comparable to that obtained for the Al(Op) 3 -based devices. In addition, the measured electron electron mobility was 5.5 × 10 -7 cm 2 V -1 s -1 with a threshold voltage V T of 64 V.

Experimental techniques and instrumentation

Al(Op) 3 based TFTs were fabricated with a bottom-gated bottom contact geometry. In these devices, highly doped p-type silicon, which has a 150 nm thermal-growth SiO 2 layer on the top, was employed as substrate and bottom gate electrode. Source and drain electrodes were patterned on the Si-SiO 2 substrates by electron beam lithography (Raith 150) method. These electrodes were deposited in high vacuum (Oerlikon evaporator) with an architecture composed by a bottom part of 1.2 nm titanium and a top part of 42 nm gold. Before depositing the organic layer, the substrate was cleaned by oxygen plasma for 5 min and modified with OTS (Purity 90% from Aldrich) by vapor-phase modification method. This process was carried out in a vacuum oven placed inside a glove box, which has an inert N 2 atmosphere (H 2 O and O 2 concentration <0.1 ppm). Finally, a 40 nm Al(Op) 3 layer was deposited on the OTS-modified substrate in a ultra-high vacuum evaporator (dual-chamber Theva system). The thickness of the Al(Op) 3 film in TFTs was calibrated by X-ray reflectivity (XRR) measurements. Al(Op) 3based TFTs were characterized in a Lake Shore probe station with Keithley 4200 semiconductor characterization system. All the electrical measurements on TFTs were carried out in vacuum, at room temperature and in the dark, to avoid the decomposition of the organic material.

Preliminary TOF and AS studies

To measure the charge carrier mobilities of the (novel) OSCs, we have initiated a study implementing the well-known time of flight (TOF) and admittance spectroscopy (AS) techniques. Here, we present preliminary results obtained on Alq 3 and Al(Op) 3 . A optimized configuration of the device is needed to estimate accurately the charge carrier mobilities. So far, the measurements with both the techniques were unsatisfactory. However, a description of the experiments is reported.

We prepared a series of samples with the configuration illustrated in Figure 4.17. Samples were constructed by thermal evaporation on quartz/ITO substrates using FI3 (ter(9,9'-diethylfluorene)) as CGL (charge generation layer) [215]. Due to the high absorption coefficient of FI3 at 337 nm, which is the emission wavelength of the used N 2 laser, the CGL allowed to deposit lowered layer thickness of the aluminum complexes. A CGL 200 nm thick is needed to absorb 99.6% of the incident light, thus, the Al-complex layer must be not less than 2 µm thick. This configuration should lead to fairly good results since the Al-complex layer is ten times thicker than the CGL. The charge carriers mobilities obtained for Alq 3 (electrons: 2.89 × 10 -5 -6.11 × 10 -5 cm 2 V -1 s -1 ; holes: 1.52 × 10 -9 -2.02 × 10 -9 cm 2 V -1 s -1 ), illustrated in Figure 4.19, are in good agreement with the reported data in Section 1.2, 10 -5 -10 -6 cm 2 V -1 s -1 (electrons) and 10 -8 -10 -9 cm 2 V -1 s -1 (holes) [42][43][44][45][46][47][48][49]. Implementing the same sample configuration, preliminary results on Al(Op) 3 were unsatisfactory. Since TOF is capable to measure low charge carrier mobilities, we expected to detect, at least, the hole mobility of Al(Op) 3 , which was measured by FET in the previous section. In order to improve the results, a different sample configuration might be necessary.

The configuration of the samples for the AS measurements is illustrated in Figure 4.18. For holes, MoO x was used as injecting material together with a silver cathode to prevent the electron diffusion into the organic layer. For electrons, a calcium cathode was utilized to inject the Applied field F for electron mobility: 4.0 × 10 5 V cm -1 -6.5 × 10 5 V cm -1 ; for hole mobility: 4.0 × 10 5 V cm -1 -6.0 × 10 5 V cm -1 . carriers together with an aluminum anode to exclude the hole diffusion into the organic layer. Preliminary studies were unsuccessful in measuring charge carrier mobilities of both Alq 3 and Al(Op) 3 . The reason is, most probably, a wrong choice of electrodes. Therefore, in the future measurements, different electrodes will be implemented.

Conclusions

In this chapter, we have studied, by means of theoretical and experimental methods, the charge carrier mobility of the (novel) OSCs.

In the first part, the frontier orbitals and the dipole moment were computed in vacuum. It has been shown that the localization of the HOMO and LUMO depends from the symmetry of the ligand. Asymmetric ligands, which form mer-Alq 3 and mer-Al(Op-py) 3 , lead to localized HOMO and LUMO, and thus, to OSCs with a high dipole moment. Conversely, symmetric ligands, which form Al(Op) 3 , Al(Trop) 3 and Al(Acac) 3 , result in equally distributed HOMO and LUMO, and thus, to low dipole moments. HOMO and LUMO of the mixed-ligands complex pseudofac-Al(q 2 Acac) are localized exclusively on the quinolinates. On the contrary, HOMO and LUMO of pseudofac-Al(q 2 Op) and pseudomer-Al(q 2 Trop) are strongly and alternatively localized on the different ligands yielding high dipole moments.

Via the DEPOSIT code, morphologies of the OSCs were generated. Pair distribution functions g(r) of the films were plotted. Due to its small and symmetric structure, Al(Acac) 3 forms the most ordered and packed film. Similarly, mer-Alq 3 , mer-Al(Op-py) 3 and pseudofac-Al(q 2 Acac), due to their dipole moment and small ligands, form ordered and packed films. On the other hand, as a consequence of their negligible dipole moments, Al(Op) 3 and Al(Trop) 3 form quite disordered films. Likewise, Al(q 2 Op) and Al(q 2 Trop), despite their high dipole moment, as a result of the bulky phenalenyl and tropolonate, form disordered films.

Through the newly developed Quantum Patch method, a number of microscopical parameters were computed. In particular we focused our attention on: energy disorder (σ(E)), reorganization energy (λ), and electronic coupling (J 2 r 2 ). These quantities were used to calculate the charge carrier mobilities µ of the OSCs in film. The theoretical and experimental data for mer-Alq 3 , pseudofac-Al(q 2 Acac) and Al(Op) 3 are in a good agreement. Nevertheless, it is necessary to take in account the formation of excimers in solid state for molecules such as Al(Op) 3 , to compute realistic electron mobilities. In addition, as shown by the high charge carrier mobility of Al(Acac) 3 , the Quantum Patch method needs further improvement in case of small non-aromatic molecules. Among the OSCs, mer-Alq 3 , mer-Al(Op-py) 3 , Al(Trop) 3 and pseudofac-Al(q 2 Acac) have similar calculated electron mobility. On the contrary, the calculated hole mobility fluctuates between five orders of magnitude. The mixed-ligands pseudofac-Al(q 2 Op) and pseudomer-Al(q 2 Trop) have the lowest calculated electron and hole mobilities.

In the second part, Al(Op) 3 was implemented in TFTs devices to measure the field-effect mobility. A hole mobility between 0.6 and 2.1 × 10 -6 cm 2 V -1 s -1 was determined. However, due to the excimer formation, no obvious electron mobility was detected. Additionally, a on/off current ratio of about 104 and a threshold voltage between -35 and -45 V were obtained for the Al(Op) 3 -based TFTs. In contrast, was impossible to measure the charge carrier mobility of Al(Op) 3 by TOF and AS. To improve the measurements, it is necessary to reconsider the architecture of the devices.

Experimental techniques and instrumentation

All the spectroscopic measurements were performed with an UHV-system consisting of one spectrometer chamber and two evaporator chambers. The base pressure in the spectrometer chamber was 4 × 10 -11 mbar. The evaporator chamber enabled us to produce the hybrid interfaces in situ, which is crucial to obtain a clean and high quality surface. Cobalt was evaporated by an Omicron EFM 3 evaporator at a pressure of 10 -10 mbar. OSCs were deposited with a Knudsen cell from Kentax Gmbh at a pressure of 9 × 10 -10 mbar. The deposition rates were monitored by a quartz crystal balance calibrated with ellipsometry. The 3.5 nm thin cobalt films were deposited by electron beam epitaxy on a Cu(001) single crystal. Afterward, the substrate was annealed at 370 K. This resulted in a metastable tetragonally distorted Co fcc structure with an in-plane magnetic uniaxial anisotropy along the (110) direction of copper [113,114]. The Co/Cu(001) was then progressively covered with OSC to form the hybrid interface.

To detect the occupied manifold of the Co/OSCs systems, we performed UPS and NT-PS [111,112]. UPS was performed by using an Omicron HIS 13 vacuum ultraviolet lamp, which operates at the He I line (hν=21.2 eV). The excitation source for NT-PS is a Ti:sapphire laser system with a central wavelength of 800 nm, 82 MHz repetition rate, a pulse power of 1.5 W, and a pulse duration of 100 fs. The output is frequency quadrupled, by using two β-barium borate crystals, leading to the fourth harmonic with a photon energy of 5.95 eV. For both UPS and NT-PS the light incident angle was 45 • . The emitted photoelectrons were energy and spin selected by a spin detector based on spin polarized low-energy electron diffraction (Focus SPLEED) mounted on a commercial cylindrical sector analyzer (Focus CSA). The acceptance angle of the detector system is ±13 • and its energy resolution is 0.22 eV. All the measurements were performed at room temperature.

For static and dynamic detection of unoccupied electronic states we used spin-and time-resolved 2PPE. The experimental set-up for the 2PPE experiments was similar to that described by Cinchetti et al [220]. The pulsed light source was a Ti:sapphire laser system similar to that for NT-PS. The system delivers sech 2 -shaped pulses of up to 10 nJ pulse -1 with a duration of approximately 40 fs at a repetition rate of 80 MHz and a varying central wavelength tunable from 750 to 850 nm. The linearly polarized laser output is frequency doubled in a 0.2 mm-thick β-barium borate crystal, to produce ultraviolet pulses at photon energy tunable between 2.91 and 3.31 eV. The frequency doubled beam is divided with a beam splitter into two equally intense p-polarized beams (Mach-Zehnder interferometer design). One of the beams is guided to a mechanical delay stage where ∆t, with respect to the second beam, can be adjusted in steps of 0.67 fs, which corresponds to a change of the beam path length of 0.2 µm. Using a second beam splitter the two beams are made collinear again. The 2PPE technique was used in two modes. In the static mode, which is the 2PPE spectroscopy, the time delay between the two photons is fixed, ∆t= ±1 fs, whereas the photon energy was varied between 2.91 and 3.31 eV. In the time-resolved mode, the time delay between the two laser pulses varies from ∆t = -9 to ∆t = +9ps, whereas the photon energy is tuned to 3.25 eV. In this mode, it is possible to determine the lifetime of hot electrons in the intermediate states populated in the 2PPE process [116]. As described for UPS and NT-PS, the light incident angle was 45 • . The photoemitted electrons were analyzed in a normal emission geometry in an ultrahigh vacuum system equipped with a commercial cylindrical sector energy analyzer (Focus CSA) and a spin detector (Focus SPLEED).

Co/Al(Op) 3 UPS studies

Al(Op) 3 was progressively grown on a freshly deposited cobalt thin film with coverage ranging between 0.5 and 5 nm. The occupied manifold of the interfaces was investigated by UPS. For every growth step, the changes in the work function and the energetic position of the molecular orbitals, giving information about the energy level alignment, were monitored. The UPS spectra of the Co/[x nm] Al(Op) 3 system for x= 0 nm, 0.5 nm, 1 nm, 1.5 nm, 2 nm, 3 nm and 5 nm are shown in Figure 5.1. From the position of the low-energy cut-off (E cutof f ), in the left panel, the work function (Φ= 21.2-E cutof f eV) is extracted. The variation of the work function with increasing Al(Op) 3 coverage, obtained from the UPS spectra, is plotted in the inset. In detail, we observe a reduction of the work function with increasing Al(Op) 3 coverage up to 1.5 nm, caused by a negative interface dipole moment with strength ∆= -1.5 eV. Interface dipole moments of Al(Op) 3 and of Alq 3 are virtually identical (∆= -1.5 eV) [218]. In contrast, the calculated molecular dipole moment of Al(Op) 3 and of mer-Alq 3 is rather different either in vacuum, 0.086 D and 4.45 D, respectively, either in amorphous film, 1.52 D and 5.55 D, respectively (see Table 4.1). The identical dipole moment, detected in the UPS measurements, is caused by the symmetry breaking of the interface. The symmetry can be broken in two distinct mechanisms: firstly, interface charge transfer and hybridization, and secondly, by substantial environment symmetry lowering. The work function is almost constant for coverages above 1.5 nm, suggesting that at this nominal coverage the cobalt is completely covered by a monolayer of Al(Op) 3 [221,222]. The right panel shows the magnified UPS spectra in the HOMO region. A progressive shift of the HOMO toward lower energies with increasing Al(Op) 3 coverage is observed (plotted in the inset as a dashed red line). The HOMO position ranges from -2.6 eV at x= 0.5 nm to -3.3 eV at x= 5 nm. In addition, the shift is almost linear in function of the Al(Op) 3 coverage. The shift in energy of the HOMO position is probably due to the different conditions experienced by the Al(Op) 3 molecules in the submonolayer, monolayer, and bulk molecular film regime, as described by Hill et al [223]. Strictly speaking, the surrounding potential of the cobalt film, of neighboring molecules, and of the vacuum will vary with coverage. Since the UPS technique is surface sensitive, the UPS spectra mainly contain information about the first monolayer of organic molecules. Nonetheless, a non-vanishing contribution from the Co/Al(Op) 3 interface is preserved in the spectra for 2 and 3 nm Al(Op) 3 coverages (the cobalt Fermi energy is still slightly visible in the UPS spectra). Conversely, for 5 nm coverage we solely detect the signal of the surface of the molecular film, with contributions from the underlying molecules in the bulk. The UPS spectrum of the Co/[5 nm] Al(Op) 3 system, after subtracting the inelastic electron background function [224], is shown in Figure 5.2. The eight occupied states have been determined by approximating the spectrum with a multi-peak function. The molecular orbitals, determined by UPS on the Co/[5 nm] Al(Op) 3 system, can be compared with the occupied manifold of a free Al(Op) 3 molecule, since the electrons originating from the cobalt substrate and from the Co/Al(Op) 3 interface cannot be photoemitted anymore.

DFT calculations, in collaboration with Dr. Droghetti A. and Prof. Sanvito S. (Trinity College Dublin, Dublin, Ireland), in addition to the theoretical studies reported in Section 4.2.1, have been carried out to compare the experimental UPS spectrum of the Co/[5 nm] Al(Op) 3 system with the DFT-B3LYP spectrum (see Figure 5.2). The NWCHEM [225] quantum chemistry package has been implemented with the exchange correlation functional B3LYP [82] and the 6-31G* basis sets. B3LYP and other hybrid functional have been successfully employed in the description of free Alq 3 [226,227] and, in that case, the density of states compares quantitatively with the UPS spectrum [227,228]. Furthermore, hybrid functionals often improve the description of molecular spectra, by partially correcting the inherent self-interaction error of local and semi-local functionals [229]. The HOMO energy computed with the ∆SCF method [230] is -6.6 eV, which is in good agreement with the HOMO position, -6.9 eV with respect to the vacuum energy, inferred from the UPS spectrum of the Co/[5 nm] Al(Op) 3 system. Simi-5.4 Co/Al(Op) 3 NT-PS studies larly, through the ∆SCF method, the calculated LUMO is -1.25 eV and the transport gap is equal to 5.35 eV, i.e. about 0.5 eV smaller than the computed Alq 3 transport gap [226]. In the DFT-B3LYP spectrum, shown in Figure 5.2, the eight-peak structure is clearly recognizable, although some differences between theoretical and experimental results are present.

Co/Al(Op) 3 NT-PS studies

The normalized NT-PS spectra of the Co/[x nm] Al(Op) 3 system (x= 0 nm, 0.5 nm, 1 nm, 1.5 nm, 2 nm, 3 nm and 5 nm) are shown in Figure 5. To compare the the spin polarization (SP) of cobalt with that of the HISs over the complete energy range of the NT-PS measurements, caesium was used to lower the work function of cobalt [114]. The SP polarization of caesiated cobalt (CsCo) ranges between 30 and 40%, in agreement with references [114,231]. Figure 5.4 illustrates the relative SP of the Co/[x nm] Al(Op) 3 system (x= 0 nm, 0.5 nm, 1 nm, 1.5 nm, 2 nm and 3 nm). The relative SP is is calculated by normalizing the SP of Co/[x nm] Al(Op) 3 to the SP of CsCo. Clearly, the SP for x= 1.5 nm deviates from the SP measured for the other Al(Op) 3 coverages. At x= 1.5 nm the true spinterface formed in the Co/Al(Op) 3 is investigated. In detail, for x< 1.5 nm the interface dipole, and thus, the HISs are not completely formed, and as a consequence, their spectral weight is low. On the contrary, for x> 1.5 nm, the spectral weight of the spin-polarized electrons originating from the spinterface is much lower than the spectral weight of the unpolarized electrons excited from the HOMO in bulk Al(Op) 3 . The measured SP of both HISs is also reduced with increasing Al(Op) 3 coverage, in consequence of the spin-flip processes experienced by the spin-polarized electrons, photoexcited at the Co/Al(Op) 3 interface, while they travel through the Al(Op) 3 before being photoemitted.

The relative SP for x= 1.5 nm at the energetic position of the HIS1 is up to 10% higher that the SP of cobalt. Averaged over the energetic region of HIS1 the observed enhancement of the SP is 8%. At the energetic position of HIS2, on average, the SP is 4% lower than the SP of cobalt. Thereby, we conclude that HIS1 has a SP parallel to the cobalt magnetization. Conversely, HIS2 is either unpolarized or polarized antiparallel to the cobalt magnetization.

Co/Al(Op) 3 2PPE studies

In Figure 5.5 is illustrated the 2PPE spectra of the Co/[2 nm] Al(Op) 3 system, measured for photon energy ranging from 3.02 to 3.30 eV. The kinetic energy of the photoemitted electrons is chosen as energy scale. The main feature visible in the spectra, beside the secondary electron peak (SEP) at kinetic energies between 0 and 1 eV, is the LUMO peak. The origin of the LUMO peak is verified by evaluating its energetic shift as a function of the photon energy. This is shown in the inset of Figure 5.5. Clearly, the LUMO energy shifts linearly with hν, and thus, we can conclude that indeed we are probing an intermediate state (the energy of an initial state shifts with 2hν, as described in Section 1.3.3) [218]. The energy dependent behavior of the unoccupied state is similar to a molecular resonance effect, resulting from a resonant excitation from an occupied state into an unoccupied molecular state (exciton). With a maximum excitation energy of 3.30 eV, no initial states in Al(Op) 3 exist for direct excitations into this unoccupied state, i.e. this possibility is discarded. x nm] Al(Op) 3 systems (x= 0.5 nm, 1 nm, 1.5 nm, 2 nm, 3 nm and 5 nm), measured with a photon energy of 3.1 eV. The detected LUMO lies 1.2 eV above the Fermi energy. Moreover, as plotted in the inset of Figure 5.6, the spectral intensity of the LUMO increases almost linearly with increasing Al(Op) 3 coverage. In contrast to the Co/Alq 3 interface, no unoccupied hybrid interface state (uHIS), which is visible only at low coverages (monolayer) and vanishes with increasing coverage (bulk), is detected [218]. Once again, the structural difference, between Alq 3 and Al(Op) 3 (see Table 3.2), results in divergent electronic properties of Co/Alq 3 and Co/Al(Op) 3 hybrid interfaces.

Spin-and time-resolved measurements were carried out on the Co/[2 nm] Al(Op) 3 system in the E * -E F energies range between 0.4 and 2.0 eV. As an example, Figure 5.7 shows the spinand time-resolved data, recorded with a photon energy of 3.9 eV and delays varying between -10 000 fs and 10 000 fs, representing the population decay of the spin-up (N U P ) and spin-down (N DOW N ) electrons excited from cobalt into the LUMO of Al(Op) 3 . The lifetime of electrons in the LUMO, extracted from the energy-spin-and time-resolved 2PPE measurements, is illustrated in Figure 5.8. It ranges between a maximum of ≈1 ps at E * -E F = 0.4 eV to a minimum of ≈0.2 ps at E * -E F = 2.0 eV, which is long-lived for typical metal-organic interfaces [232]. Since the LUMO orbital is not affected by the SP of the cobalt substrate as an uHIS, the lifetime of the spin-up (τ e down ) and spin-down (τ e up ) electrons is virtually identical (in the error range).

Co/Al(Op-py) 3 preliminary UPS studies

Results of the preliminary UPS studies on the Co/Al(Op-py) 3 hybrid interface are shown in Figure 5.9. Al(Op-py) 3 was progressively grown onto the cobalt surface with coverage ranging from 0.7 to 2.8 nm. Every growth step was monitored with UPS, to measure the work function and the energetic position of the molecular orbitals. The variation of the work function with increasing Al(Op-py) 3 coverage is illustrated in the inset of Figure 5.9. The work function decreases, with increasing Al(Op-py) 3 coverage, up to about 2 nm. An interface dipole moment with strength of ∆= -1.8 eV was measured. This value is slightly higher than the interface dipole moment observed for Alq 3 [218] and Al(Op) 3 on cobalt (see Section 5.3). Accordingly, the calculated dipole moment of mer-Al(Op-py) 3 , in vacuum and in thin film, is higher than that of mer-Alq 3 and of Al(Op) 3 (see Table 4.1). In addition, the work function is almost constant for coverages above 2 nm, and thus, we can estimate that at this nominal coverage the cobalt substrate is completely covered by a Al(Op-py) 3 monolayer [221, 222]. As described for Al(Op) 3 in Section 5.3, a progressive shift of the HOMO to lower energies, with increasing coverage, is observed in the UPS spectra. Moreover, a nonvanishing contribution of the Co/Al(Op-py) 3 interface is evident for all the coverages (the cobalt Fermi energy is still slightly visible in the UPS spectra). Further studies are needed to extract accurately the occupied manifold of Al(Op-py) 3 . In addition, NT-PS and 2PPE studies on the Co/[x nm] Al(Op-py) 3 system (x= 0.7 nm, 1.4 nm, 2.1 nm and 2.8 nm) will give an insight on the formation of HISs states and their SP. As a result of the aromatic backbone of the HOp-py ligand (see Table 3.1), a different chemisorption on the cobalt substrate is expected, resulting in distinct HISs formation and SP properties.

Conclusions

The findings for the Co/[5 nm] Al(Op) 3 system, obtained with UPS and 2PPE, and the findings for the Co/[2.8 nm] Al(Op-py) 3 system, extracted by UPS, are summarized in The results of the NT-PS measurements on the Co/[1.5 nm] Al(Op) 3 system are shown in Figure 5.12. The two HISs with energy E -E F =-0.9 eV and E -E F = -1.6 eV, formed at the Co/Al(Op) 3 interface, are indicated. HIS1 presents a SP 8% higher than the SP of cobalt, whereas HIS2 is characterized by a SP 4% lower than the SP of cobalt.

The chemical tailoring of the OSCs induces different electronic properties of the metallo/organic interfaces. The HOMO of bulk Al(Op) 3 , Al(Op-py) 3 and Alq 3 , deposited on cobalt, is at -3.3 eV, -3.5 eV and -2.7 eV below the Fermi energy E F , respectively. Conversely, the interface dipole moment is almost identical: ∆= -1.5 eV, ∆= -1.8 eV and ∆= -1.5 eV, respectively.

At last, the spin-and time-resolved 2PPE measurement revealed that no unoccupied interface states (uHISs) are formed in the Co/Al(Op) 3 system. However, the LUMO of Al(Op) 3 was detected. Since the LUMO is not affected by the SP of the cobalt substrate, the lifetime of the spin-up (τ e up ) and spin-down (τ e down ) electrons is identical.

Phenalenyl-based SMMs

In collaboration with:

Dr. Yanhua Lan INT-KIT, Karlsruhe, Germany

Introduction

In this chapter, we have explored the capability of the ligand 9-hydroxy-1H-phenalen-1-one (HOp) 3 to chelate paramagnetic atoms, i.e. dysprosium and terbium, to form single-molecule magnets (SMMs). As described in the Section 1.4.2 of the introduction, many lanthanide SMMs were synthesized with β-diketonate ligands. Strictly speaking, HOp 3 has the same chelating atoms and geometry of β-diketonates with the two oxygens embedded in an aromatic backbone, as illustrated in Figure 6 By reacting HOp 3 with dysprosium and terbium salts we could synthesize stable complexes, which were characterized by means of paramagnetic 1 H-NMR, MALDI-TOF spectrometry, and UV-Vis spectrophotometry. Additionally, implementing a synthetic strategy in anhydrous conditions, we were able to form sublimable phenalenyl-based dysprosium and terbium complexes. These complexes were characterized prior and after the sublimation process.

To investigate the SMM behavior of the phenalenyl-based lanthanide complexes, magnetic measurements by SQUID are, generally, carried out on crystalline materials, and thus, at first we have grown single crystals of the complexes. In detail, single crystals of two dysprosium complexes were obtained and their exact structure was solved. The preliminary magnetic properties of these two complexes where recorded, indicating that, indeed, they might show SMM behavior. Further studies to investigate the structure of phenalenyl-based lanthanide complexes and their magnetic properties are currently ongoing.

Experimental techniques and instrumentation

All the purchased chemicals and solvents were used as received without any further purification unless otherwise stated. The reactions involving water sensitive materials were carried out with distilled THF (over Na) and implementing standard Schlenck techniques; the glassware was kept in oven at 80 • C and evacuated with argon prior use. The elemental analysis of carbon and hydrogen, was carried out in a Vario Micro Cube. Paramagnetic 1 H-NMR spectra were recorded in a Bruker FT-NMR Avance III 500 MHz with deuterated solvents as internal standards. Matrixassisted laser desorption/ionization-time of flight (MALDI-TOF) mass spectrometric data were acquired on a MALDI-TOF Synapt G2-S HDMS with no additional matrix compound other than the sample itself. The absorption spectra were acquired at room temperature for diluted DMSO (spectrophotometric grade) solutions on a Cary 500 Scan Uv-Vis-NIR spectrophotometer using a 1 cm quartz cell. Emission spectra were recorded at room temperature for diluted DMSO (spectrophotometric grade) solutions on a Cary Eclipse Fluorescence spectrophotometer using a 1 cm quartz cell. Magnetic measurements were obtained with a Quantum Design SQUID magnetometer MPMS-XL. dc susceptibility measurements were carried out over the temperature range 1.8-300 K under applied an applied field of 0.1 T. Magnetization measurements were made at low temperatures with applied dc fields from 0 to 70 kOe. ac susceptibility measurements were measured in zero dc field with an oscillating ac field of 3 Oe and ac frequencies ranging from 1 to 1500 Hz. Measurements were performed on polycrystalline samples. The ground powder was restrained in Apiezon grease. The magnetic data were corrected for the sample holder. Single crystal X-ray diffraction data were collected on a STOE IPDS II diffractometer with graphite monochromated Mo Kα radiation (0.710 73 Å). Structure solution and refinement against F 2 were carried out using shelxs and shelxl software. Refinement was performed with anisotropic temperature factors for all non-hydrogen atoms (disordered atoms were refined isotropically); hydrogen atoms were calculated on idealized positions.

Synthesis of phenaleny-based Dy and Tb SMMs

The synthesis of phenalenyl-based lanthanide complexes was reported by Van Deun et al. [233,234]. The authors described the synthesis of 1:3 metal-to-ligand ratio complexes using ammonia as a base, and the synthesis of 1:4 metal-to-ligand ratio complexes using a stronger base, such as NaOH. A similar approach was implemented to form phenalenyl-based europium complexes [235]. In addition, phenalenyl-based europium and gadolinium nonanuclear complexes were obtained using Et 3 N as a base and a 1:1.8 metal-to-ligand ratio [236]. In view of these works, to obtain phenalenyl-based mononuclear dysprosium complexes, we have implemented the synthetic procedures illustrated in Scheme 6.1 and described in Section 8.3. When NaH was used as a base to deprotonate HOp in a 1:3 Dy/HOp stoichiometry , the complex bis-(1oxo-1H-phenalen-9-olate)dysprosium chloride ([Dy(Op) 2 Cl(HOp)(EtOH)]) 32 was formed. In [Dy(Op) 2 Cl(HOp)(EtOH)] 32, the coordination sphere of the dysprosium atom is completed by HOp 3 and EtOH. Conversely, using diisopropyl amine as a base, the 1:3 metal-to-ligand ratio complex was obtained. The coordination sphere of the dysprosium atom in the tris-(1-oxo-1Hphenalen-9-olate)dysprosium is filled by HOp , yielding [Dy(Op) 3 (HOp)] 33, or ethanol, yielding [Dy(Op) 3 (EtOH)] 34. The exact structure of those complexes, which is discussed in Section 6.4, was determined by single crystal X-ray diffraction experiments on single crystals grown from slow evaporation of EtOH solutions. Due to their similar structure, [Dy(Op) 3 (HOp)] 33 and [Dy(Op) 3 (EtOH)] 34 co-crystallized in single crystals. Since it was impossible to separate the two complexes by standard techniques, the two complexes were characterized simultaneously. we synthesized a sublimable phenalenyl-based dysprosium complex 36. The synthetic procedure, illustrated in Scheme 6.2, was carried out in anhydrous conditions, implementing standard Schlenk techniques, carefully distilled THF, anhydrous starting materials and oven-dried glassware. So far, single crystals of the dysprosium complex, obtained with this procedure, could not be grown, and thus, its exact structure it is unknown. Nevertheless, it was fully characterized by NMR spectroscopy, mass spectrometry and UV-Vis spectrophotometry. In addition, it was successfully sublimated at ≈300 • C in high vacuum (10 -6 mbar). To confirm the thermal stability, the dysprosium complex 36 was characterized also after the sublimation process. Phenalenyl-based terbium complexes were synthesized adopting the same synthetic strategies described to form the mononuclear phenalenyl-based dysprosium complexes. As illustrated in Scheme 6.3, at first, we have reacted the ligand HOp 3 with a terbium salt in EtOH, using diisopropylamine as base. The second procedure implemented was carried out in anhydrous conditions, using distilled THF as a solvent, anhydrous starting materials and oven-dried glassware. Single crystals of the phenalenyl-based terbium complexes 37 and 38 could not be grown, and thus, their exact structure could not be solved. Nonetheless, a structural characterization, by means of NMR spectroscopy, mass spectrometry and Uv-Vis absorption spectrophotometry was carried out. In addition, the terbium complex 38 was sublimed at ≈300 • C in high vacuum (10 -6 mbar); the sublimated material was additionally characterized.

Molecular structure of the dysprosium complexes

The molecular structure of [Dy(Op) 2 Cl(HOp)(EtOH)] 32 is illustrated in Figure 6.2 (refinement data in Table C.8). The central dysprosium is coordinated by seven atoms, six oxygens and one chloro, resulting in a mono-capped trigonal prism geometry with a symmetry lower than D 5h (see Table 6.1 for selected bond lengths and angles). First we discuss the bond lengths and angles between the dysprosium and the oxygen of the deprotonated phenalenyls. The bond lengths Dy-O1, Dy-O2, Dy-O3 and Dy-O4 are between 2.25 and 2.28 Å, in addition, the bond angles Dy-O1-C1, Dy-O2-C3, Dy-O3-C14, and Dy-O4-C16, are ranging between 136.8 • and 138.8 • . This indicates that, although the molecule is asymmetric, the two deprotonated phenalenyls are identical. On the contrary, the bond length Dy-O5 (of the protonated phenalenyl) is considerably longer, 2.38 Å, and the angle Dy-O5-C27 is wider, 148.3 • . Due to the presence of HOp 3 and EtOH, [Dy(Op) 2 Cl(HOp)(EtOH)] 32 forms intramolecular and intermolecular hydrogen bonds. In detail, there are two intramolecular hydrogen bonds, between O6H6 and O2 (2. 52 Å) and between O6H6 and O5 (1.90 Å), involving HOp, and an intermolecular hydrogen bond between O7H7 and Cl1 (2.49 Å) involving EtOH. Clearly, the intermolecular hydrogen bonds, together with the interaction between the phenalenyls, drive the molecular packing in the crystal lattice.

In an asymmetric unit, the two dysprosium complexes [Dy(Op) 3 (HOp)] 33 and [Dy(Op) 3 (EtOH)] 34 co-crystallized with two additional EtOH, as illustrated in Figure 6.3 (refinement data in Table C.9). In both the complexes, the central dysprosium is coordinated by seven oxygens in a mono-capped trigonal prism geometry (see Table 6.1 for selected bond lenghts and angles). In [Dy(Op) 3 (HOp)] 33, the bond lengths between the dysprosium and the oxygens of the deprotonated phenalenyls, Dy1-O1, Dy1-O2, Dy1-O3, Dy1-O4, Dy1-O5, Dy1O6, are varying between 2.280 and 2.309 Å. The bond angles, Dy1-O1-C1, Dy1-O2-C3, Dy1-O3-C14, Dy1-O4-C16, Dy1-O5-C27 and Dy1-O6-C29, have similar values between 135.3 • and 139.1 • . Similar bond lengths and angles indicate that the deprotonated phenalenyls are almost identical, despite the asymmetric geometry of [Dy(Op) 3 (HOp)] 33. In contrast, the bond length between Dy1 and O7 in [Dy(Op) 3 (HOp)] 33 is 2.381 Å, similar to Dy-O5 in [Dy(Op) 2 Cl(HOp)(EtOH)] 32. Two intramolecular hydrogen bonds are formed: O8H8-O4 (2.39 Å) and O8H8-O7 (1. 86 Å). The bond lengths between the deprotonated phenalenyls and the central dysprosium in [Dy(Op) 3 (EtOH)] 34, Dy2-O9, Dy2-O10, Dy2-O11, Dy2-O12, Dy2-O13, Dy2O14, which vary between 2.249 and 2.324 Å, are virtually identical to those in [Dy(Op) 3 (HOp)] 33. Furthermore, also the bond angles, Dy2-O9-C53, Dy2-O10-C55, Dy2-O11-C66, Dy2-O12-C68, Dy2-O13-C79 and Dy2-O14-C81, which are ranging between 137.5 • and 139.1 Interestingly, the same peaks were observed in the spectra of the terbium phenalenyl-based complex 38 illustrated in Figure 6.5. In addition, we were able to record a clear paramagnetic 6.6 MALDI-TOF studies 1 H-NMR spectrum of 38 after the sublimation process. Surprisingly, the peaks between 4 and 8 ppm are the only peaks detected after the sublimation process. The origin of the peaks at a low chemical shift, for the dysprosium complex 36 and the terbium complex 38, is still unclear. However, the formation of the complexes was confirmed by MALDI-TOF measurements (see Section 6.6), UV-Vis spectrophotometry (see Section 6.7) and elemental analysis (see Section 8.3). At last, in the phenalenyl-based terbium complexes 37 and 38 a sets of resonances is detected between 22 and 36 ppm. These resonances are assigned to the phenalenyls in the complexes. However, for a complete and exact assignment of the peaks, the exact structure of the complexes, obtained from single crystal X-ray diffraction, must be solved. The MALDI-TOF spectra (positive mode) of the terbium complexes 37 and 38, before and after the sublimation process, are shown in Figure 6.7. In all the spectra, the most intense peak is relative to the fragment [Tb(Op) 2 ] + (m/z= 549). This is an indication, as previously described for the dysprosium complexes, that the terbium is coordinated by at least two phenalenyls. The second peak observed is corresponding to the fragment [Tb(Op) 3 (H 2 O)] + (m/z= 567), where a molecule of water is absorbed during the preparation and measurement of the samples. The peak of the [Tb(Op) 3 Li] + fragment (m/z= 567) is also observed. Interestingly, this peak has a very high intensity in the MALDI-TOF spectrum of the terbium complex 38 after the sublimation process. This can be interpreted as an indication that the sublimable terbium complex is formed by three phenalenyls. The di-nuclear fragment [Tb 2 (Op) 5 ] + (m/z= 1293), detected in the MALDI-TOF measurements, is most probably resulting from the aggregation of fragments with smaller m/z. At last, in the spectra of 37 and 38 there are two peak at m/z= 937 and at m/z= 1681 which are unassigned. However, their m/z value is very close to that of [Tb(Op) 3 (H 2 Op)] + (m/z= 941) and [Tb 2 (Op) 6 (H 2 Op)] + (m/z= 1685), respectively. are almost identical in the three spectra. However, an attentive observation of the absorption band between 300 and 375 nm reveals that this band is quite different in the spectra. The maximum of the spectrum of [Dy(Op) 3 (HOp)] 33-[Dy(Op) 3 (EtOH)] 34 is at 349 nm, whereas the maximum of the spectra of the dysprosium complex 36 before and after the sublimation process is at 341 nm. Nevertheless, the spectra of 36, before the sublimation, has a shoulder at 349 nm, which is less pronounced after the sublimation process. Considering that the bands between 300 and 375 nm are associated to π → π * transitions centered on the phenalenyls (see Section 3.4.1), the shift of the band can result from slight differences in the structure of the complexes. As a consequence of the few mg of material obtained by the sublimation process, we were unable to compare the extinction coefficients of the complexes. The absorption spectra of the phenalenyl-based terbium complexes 37 and 38, before and after the sublimation process, are plotted in Figure 6.9. Comparing the spectra with the spectrum of HOp 3, we can conclude that the absorption spectra are not caused by the free ligand.

Paramagnetic 1 H-NMR studies

MALDI-TOF studies

Photophysical studies

As observed for the dysprosium complexes, the absorption band between 375 and 500 nm, related to n → π * transitions centered on the phenalenyls (see Section 3.4.1), is almost identical in the three spectra. On the contrary, the phenaleny-centered π → π * band, between 300 and 375 nm (see Section 3.4.1), presents considerable shifts. The absorption maximum for the terbium complex 37 is at 349 nm, identical to the maximum of the terbium complex 38 before the sublimation process. However, after the sublimation process, the maximum of 38 is at 341 nm where only a shoulder is visible in the spectrum prior the sublimation. This indicates that, implementing the reaction procedure in anhydrous conditions described in Scheme 6.3, probably, two kinds of terbium complexes are formed. One is identical to the product of the reaction in EtOH, whereas the second, which is sublimable, has a different structure.

At last, we have measured the emission spectra of the phenalenyl-based lanthanide complexes illustrated in Figure 6.10. No sensitization of the lanthanide emission by the phenalenyl was observed. The emission is originating by the fluorescence transition localized on the ligands with no contribution or energy transfer to the lanthanide. The temperature dependence of the magnetic susceptibility of [Dy(Op) 2 Cl(HOp)(EtOH)] 32 was measured in an applied magnetic field of 1000 Oe in the temperature range between 1.8 and 300 K. At 300 K, the χT product is 14.11 cm 3 K mol -1 , in a good agreement with the expected value of 14.17 The field dependence of the magnetization at low temperatures has been measured at 2 K, 4 K and 5 K and is illustrated in Figure 6.11. At 2 K and 70 Oe the magnetization grows to ≈5.17 µB. However, due to the incomplete saturation of the magnetization, a residual slope is observed at high fields, indicating a small magnetic anisotropy in the material [254,255]. Moreover, no hysteresis effect is observed under these conditions. As a consequence of the detected magnetic anisotropy, the magnetization relaxation of [Dy(Op) 2 Cl(HOp)(EtOH)] 32 has been probed implementing ac susceptibility measurements as a function of the temperature at different frequencies and, in addition, as a function of frequency at different temperatures. The results are plotted in Figure 6.12. Obviously, [Dy(Op) 2 Cl(HOp)(EtOH)] 32 is characterized by a slow relaxation of its magnetization. At zero dc field, a frequency dependent in-phase and out-of-phase signal is observed below 20 K, suggesting a slow relaxation of the magnetization. At a frequency of 1500 Hz, the out-of-phase component first reaches a maximum at 13 K and afterward steadily increases rather than decline to zero. This indicates a cross-over from a thermally activated to a temperature independent regime in the relaxation process [246,256,257]. The shape and frequency dependence suggests that [Dy(Op) 2 Cl(HOp)(EtOH)] 32 might be a SMM.

In Figure 6.13, the relaxation time was extracted, fitting the frequency sweeping data between 11 and 13 K with an Arrhenius law. As a result, the characteristic energy gap ∆ has been To further study the relaxation process and evaluate the quantum tunneling effect, the frequency dependence of the ac susceptibility at 1.8 K was measured, with the application of a small external dc field, and is illustrated in Figure 6.14. In SMMs with a relaxation partially influenced by quantum effects, the application of a small dc field removes the state degeneracy, and thus, the possibility of quantum tunneling, inducing a slowing down of the magnetization relaxation. The characteristic frequency is 315 Hz at 1.8 K in zero field, whereas with the application of a dc field, the characteristic frequency decreases to 180 Hz at ≈200 Oe. Therefore, a small external dc field is slowing down the relaxation time, as previously observed for some SMMs when the quantum tunneling of the magnetization is suppressed.

Lastly, ac susceptibilities as a function of temperature were measured under a dc field of 200 Oe, to estimate the effective relaxation time. The results are plotted in Figure 6.15. The data was fitted with an Arrhenius law function in the temperature range between 10 and 14 K. The characteristic SMM energy gap ∆ is 49.4 K and the pre-exponential factor is τ 0 is 2.9 × 10 -6 s. Additionally, a quantum relaxation time of 1 × 10 -3 s is observed below 7 K. Compared to the data calculated in zero-field, the energy gap ∆ and its corresponding pre-exponential factor τ 0 are fairly similar, suggesting that the quantum tunneling effect in [Dy(Op) 2 Cl(HOp)(EtOH)] 32 is not pronounced. However, the quantum relaxation time at low temperature under 200 Oe is two time higher than the one under zero dc field. As illustrated in Figure 6.17, at a zero dc field applied, no out-of-phase component was recorded, whereas in the ac susceptibility measurements is detected at 1000 Hz, suggesting the absence of any appreciable barrier to the relaxation of the magnetization, which could be address to a strong quantum tunneling resonance at zero dc field. between a slow magnetic relaxation and a rapid quantum tunneling. The relaxation process immediately slows down to 40 Hz when the applied field is 500 Oe, in contrast, it is faster, ≈10 Hz, at 1500 Oe. This behavior points to the fact that this compound, concerning the dynamic aspect, is characterized by a very fast tunneling process at zero dc field. When the dc field applied increases from 1500 Oe upwards, the relaxation process oscillates to a higher frequency and subsequently slows down again. This observation implies that there is more than one relaxation process in the system. Indeed, considering the presence of two Dy(III) centers with different ion anisotropy in [Dy(Op) 3 (HOp)] 33-[Dy(Op) 3 (EtOH)] 34, this observation is not surprising. Based on the present data, however, it is not possible to discriminate and assign the relaxation processes to their respective structure. At last, as illustrated in Figure 6.19, the frequency sweeping ac susceptibilities measurements were performed at different temperatures under two dc fields: 1500 Oe and 3000 Oe. Under a dc field of 1500 Oe, one set of peaks is observed in the out-of-phase component of the ac susceptibility. Conversely, under a dc field of 3000 Oe, two sets of peaks are clearly visible in the plot of the frequency dependence of the out-of-phase component of the ac susceptibility, indicating the presence of more than one relaxation pathway. Moreover, as a stronger dc field is applied, the smaller peak at lower frequencies increases at the expense of the larger peak beyond the window of the measurements. The relaxation times ∆ and the pre-exponential factors τ 0 of the relaxation pathways are calculated plotting the relaxation time τ versus 1/T (see Figure 6.20). At 1500 Oe, the relaxation time, deduced from the data between 1.8 and 5.1 K, follows an activated behavior with an energy gap ∆ of 14.1 K and a pre-exponential factor τ 0 of 7.1 × 10 -6 s. At 3000 Oe, the relaxation time ∆ of the relaxation pathway located at higher frequencies in the temperature range between 2.6 and 5.5 K is 7.6 K and its preexponential factor τ 0 is 3.0 × 10

Conclusions

In this chapter we have studied the complexes formed by HOp 3 and paramagnetic atoms such as dysprosium and terbium. The complexes were characterized by means of 1 H-NMR, MALDI-TOF and UV-Vis, to determine their structure and properties. Single crystals of [Dy(Op) 2 Cl(HOp)(EtOH)] 32 and single co-crystals of [Dy(Op) 3 (HOp)] 33 and [Dy(Op) 3 (EtOH)] 34, were grown. Thus, their exact molecular structures were determined.

The magnetic properties of [Dy(Op) 2 Cl(HOp)(EtOH)] 32 were measured. The results suggest it might be a SMM with an energy gap ∆ of 43.8 K and a pre-exponential factor τ 0 of 3.3 × 10 -6 s43.8 K, in addition, a quantum relaxation time of ≈5 × 10 -4 s was determined at zero dc field. The measurements have been carried out also under an applied dc field of 200 Oe yielding a energy gap ∆ of 49.4 K and a pre-exponential factor τ 0 of 2.9 × 10 -6 s, moreover, a quantum relaxation time of ≈1 × 10 -3 s was determined. The results indicate that the quantum tunneling effect is not pronounced. Since it was impossible to separate the two complexes, the magnetic characterization was carried out on the co-crystals of [Dy(Op) 3 (HOp)] 33-[Dy(Op) 3 (EtOH)] 34. At zero dc field no out-of-phase component of the susceptibility was detected which could be caused by a strong quantum tunneling resonance. The measurements have been repeated under dc fields of 1500 and 3000 Oe. The relaxation time calculated at 1500 Oe follows an activated behavior with an energy gap ∆ of 14.1 K, whereas at 3000 Oe the energy gap ∆ of the relaxation pathway located at higher frequencies is 7.6 K.

Lastly, further complexes of dysprosium and terbium have been synthesized and characterized. By implementing a synthetic strategy in anhydrous conditions we were able to synthesize sublimable phenalenyl-based dysprosium and terbium complexes. The molecular structure of these complexes could not be determined by single crystal X-ray diffraction. Notheless, the complex formation and thermal stability was confirmed by the analysis prior and after the sublimation process. Although this is a preliminary study, it is opening the possibility to deposit phenalenylbased lanthanide complexes on surfaces for a variety of studies and eventually building devices.

Conclusions and Outlook

In this thesis I have presented a systematic study on aluminum-based OSCs. The main goal was to identify a clear relationship between the chemical structure and the electronic properties of such materials. The work was focused on the low molecular weight class of OSCs, using the well-known Alq 3 as benchmark. In an extended framework of collaborations, we were able to deeply investigate the OSCs implementing several theoretical and experimental techniques.

The rational design, synthesis and characterization of the (novel) OSCs is presented in Chapter 3. Here, the synthesis of a series of (novel) OSCs, listed in Table 3.2, has been presented. The first step was to select and synthesize, when necessary, the ligands listed in Table 3.1, which were then used to form the complexes. Al(Op) 3 4 was the first aluminum complex to be synthesized. A series of halogenated and substituted derivatives of Al(Op) 3 4, namely Al(Op-X) 3 6a-d and Al(Op-R) 3 16a-c, was obtained to study the effect of halogens and substituents on the electronic properties. Al(Oba) 3 19 was investigated as an asymmetric aromatic extension of Al(Op) 3 4. Al(Op-py) 3 23 was chosen because it is structurally similar to Alq 3 . Al(Trop) 3 25 was selected as a consequence of its seven-membered aromatic structure. A series of heteroleptic aluminum complexes was synthesized: Al(q 2 Acac) 28 Al(q 2 Op) 29 and Al(q 2 Trop) 30. At last, the complex Zn(Op) 2 31 was characterized as the first member of a class of phenalenyl-based zinc complexes. Ligands and complexes have been further characterized by means of photophysical and electrochemical methods (findings in Table 3.5, Table 3.6, Table 3.7 and Table 3.8). Al(Op) 3 4 forms excimers in the solid state, most probably due to its flat and extended aromatic system. Excimers were detected also in the thin film emission spectra of Al(Op-p) 3 16a and Al(Oba) 3 19. HOMO and LUMO energy levels of the ligands and complexes were estimated (see Figure 3.45). It can be noted that, clearly, the extension of the aromatic system influences the HOMO and LUMO energy levels. In more detail, molecules with a small aromatic system are characterized by a higher LUMO than those with a bigger aromatic system. On the other hand, the HOMO fluctuates in a narrow range with few eV of difference between the complexes.

In Chapter 4 a theoretical study on the (novel) OSCs is presented. In addition, preliminary results on the experimental charge carrier mobility of Al(Op) 3 are reported. The analysis of the HOMO and LUMO revealed a localization of the orbitals in asymmetric complexes, such as Alq 3 , Al(Op-py) 3 , Al(q 2 Acac), Al(q 2 Op) and Al(q 2 Trop). In contrast, symmetric complexes, such as Al(Op) 3 , Al(Trop) 3 and Al(Acac) 3 , are characterized by an isotropic distribution of the orbitals. This difference gives rise to a wide distribution electrical dipole moments from 6.52 D of Al(q 2 Op) to 0.053 D of Al(Acac) 3 (see Table 4.1). Through the newly developed DEPOSIT method, morphologies of the OSCs were generated "in silico". At last, through the recently published Quantum Patch method, the charge carriers mobility of the OSCs were computed (see Table 4.3). Additionally, preliminary studies on the experimental charge carrier mobility were performed by means of FET, TOF and AS on Al(Op) 3 . So far, only by FET was possible to measure a hole mobility of Al(Op) 3 between 0.6 and 2.1 × 10 -6 cm 2 V -1 s -1 .

An investigation on the Co/Al(Op) 3 hybrid interface is presented in Chapter 5. The occupied manifold of bulk Al(Op) 3 and its interface dipole moment were detected by UPS (see Figure 5.11). By NT-PS two hybrid interface states were unraveled, the SP of HIS1 is 8% higher than that of bare cobalt, whereas the SP of HIS2 is 4% lowered (see Figure 5.12). The LUMO of Al(Op) 3 was observed by 2PPE. Since the LUMO is not a hybrid interface state, the lifetime of the spin-up and spin-down electrons is identical. Preliminary UPS studies on the Co/Al(Op-py) 3 were carried out.

Lastly, the SMM behavior of phenalenyl-based lanthanide complexes was investigated. In this study we have synthesized and structurally characterized phenalenyl-based dysprosium and terbium complexes. The molecular structure of three dysprosium complexes has been resolved. Asymmetric halogenation and substitution might be more effective on the electronic properties of HOp 3, and thus, of Al(Op) 3 4. In addition, this could also hinder the formation of excimers in the solid state. The aromatic system of HOp-py 22 can be easily extended using isoquinoline and/or naphthalen-2-ol as backbone, in addition, by simple reactions it would be possible to insert halogens or aromatic substituents. At last, tropolone 24 can be symmetrically and asymmetrically decorated with a variety of substituents. These changes might be useful to tune the electronic properties of the OSCs. Moreover, these ligands can coordinate a variety of metals giving rise to a wide range of applications. Besides Al(Op) 3 4, the aluminum complexes obtained are currently investigated to measure the mobility and the spin filtering behavior on cobalt substrates. Although a great number of efficient materials is nowadays available for optoelectronic devices, by FET, TOF and AS measurements on the complexes, a deeper understanding on the influence of the chemical structure on the charge carrier mobility can be gained. Nonetheless, these complexes can be implemented in OSPDs to systematically investigate the chemical structure effect on the device performance. These are few studies which can be carried out on these class of materials, however, by exploiting the chemistry of the ligands and complexes, many fields of application can be identified. A clear example is the SMM behavior observed in a phenalenyl-based dysprosium complex. Studies on terbium complexes were preliminary presented, additionally, phenalenyl complexes of holmium and erbium will be investigated. Furthermore, lanthanide complexes can be obtained with the ligands implemented in the synthesis of the aluminum complexes, giving the access to a number of novel molecules. It was also demonstrated that sublimable phenalenyl-based lanthanide complexes can be synthesized, which is most important to probe these materials on surfaces and for application in devices.

Experimental Part

Materials and equipments

All the reactions were carried out under argon inert atmosphere using standard Schlenk techniques. All the purchased chemicals and solvents for the synthesis and column chromatography were used as received without any further purification unless otherwise stated. Elemental analysis of carbon, hydrogen, and nitrogen were carried out in a Vario Micro Cube.1 H-NMR and 13 C-NMR were recorded in a Bruker FT-NMR Avance III 500 MHz with deuterated solvents as internal standards for proton and carbon signals. Matrix-assisted laser desorption/ionizationtime of flight (MALDI-TOF) mass spectrometric data were acquired on a MALDI-TOF Synapt G2-S HDMS with no additional matrix compound other than the sample itself. Electro-spray ionization-time of flight (ESI-TOF) mass spectrometric analytical data were acquired on a Bruker microOTOF-Q II equipped with a nanospray source and on a ESI-TOF Synapt G2-S HDMS. Elemental analyses were carried out on a Vario Micro Cube. Single crystal X-ray diffraction data were collected on a STOE IPDS II diffractometer with graphite monochromated Mo Kα radiation (0.710 73 Å). Structure solution and refinement against F 2 were carried out using shelxs and shelxl software. Refinement was performed with anisotropic temperature factors for all non-hydrogen atoms (disordered atoms were refined isotropically); hydrogen atoms were calculated on idealized positions. 6-Methoxynaphthalen-2-amine 8. In a tube were placed 30 ml of a 2:1 solution of PEG400 and NH 3 (28%). 2-Bromo-6-methoxynaphthalene 7 (1.20 g, 5.1 mmol), CuI (1.00 g, 5.3 mmol) and Na 3 PO 4 (0.80 g, 4.9 mmol) were added and the tube was sealed. The reaction mixture was heated 24 h at 100 • C and allowed to cool to room temperature overnight. The organics were extracted with ether and purified by column chromatography on silica gel with pure DCM yielding the pure product (0.35 g, yield 40%). 2-Fluoro-6-methoxynaphthalene 9. 6-Methoxynaphthalen-2-amine 8 (0.34 g, 2.0 mmol) was dissolved in 1 ml THF and cooled to 0 • C. HBF 4 (5 ml) and NaNO 2 (0.43 g, 6.0 mmol) in 2 ml of H 2 O were added and the solution was stirred 1 h in the cold. BF 4 Na (1.13 g, 10.0 mmol) was added and the mixture was allowed to warm up to room temperature. The solid was filtred, washed with ether, dried in vacuum and suspended in 5 ml of chlorobenzene. The suspension was refluxed 1 h at 140 HOp-F 5a. 2-Fluoro-6-methoxynaphthalene 9 (0.25 g, 1.4 mmol) and cinnamoyl chloride 2 (0.24 g, 1.42 mmol) were dissolved in 30 ml of freshly distilled DCE and cooled down to 0 • C. AlCl 3 (0.19 g, 1.4 mmol) was added and the mixture was stirred 1 h in the cold. After allowing the reaction to warm up to room temperature, another aliquot of AlCl 3 (0.19 g, 1.4 mmol) was added and the mixture was refluxed at 90 • C overnight. The mixture was allowed to cool to room temperature, quenched with HCl 6 N 10 ml and filtered on celite. The solid was repeatedly washed with hot DCM, the organic layer of the filtrate was taken and the solvents evaporated under reduced pressure. The crude product was purified by column chromatography on silica gel with pure DCM (0.19 g ,yield 63%). Al(Op-F) 3 6a. HOp-F 5a (0.16 g, 0.74 mmol) and AlCl 3 (32.0 mg, 0.24 mmol) were dissolved in 15 ml toluene; the solution was refluxed overnight at 110 • C. The yellow precipitate was filtered and washed thoroughly with fresh toluene. The crude product was purified by column chromatography on alumina neutral grade IV with pure DCM (0.13 g, yield 81% 2-Chloro-6-methoxynaphthalene 10. 2-Bromo-6-methoxynaphthalene 7 (3.01 g, 12.7 mmol) was dissolved in 20 ml DMF, CuCl (1.48 g, 15.0 mmol) was added and the mixture was refluxed 24 h at 110 • C. Further CuCl (0.79 g, 7.5 mmol) was added and the mixture was refluxed 24 h more. The solvent was removed in vacuum, the solid was dissolved in ethyl acetate and washed with H 2 O. The pure product was recovered by column chromatography (silica gel, DCM) (2.08 g, yield 85%). HOp-Cl 5b. 2-Chloro-6-methoxynaphthalene 10 (2.17 g, 11.0 mmol) and cinnamoyl chloride 2 (1.89 g, 11.0 mmol) were dissolved in 50 ml of freshly distilled DCE and cooled down to 0 • C. AlCl 3 (1.50 g, 11.0 mmol) was added and the mixture was stirred 1 h in the cold. After allowing the reaction to warm up to room temperature, further AlCl 3 (1.50 g, 11.0 mmol) was added and the mixture was refluxed at 90 • C overnight. The reaction was allowed to cool to room temperature, quenched with HCl 6 N 15 ml and filtered on celite. The solid was repeatedly washed with hot DCM and the organic layer of the filtrate was taken. The solvents were evaporated under reduced pressure and the solid was purified by column chromatography on silica gel with pure DCM yielding the pure product (1.95 g, yield 77%). Al(Op-Cl) 3 6b. HOp-Cl 5b (0.19 g, 0.9 mmol) and AlCl 3 (37.4 mg, 0.28 mmol) were dissolved in 20 ml toluene; the solution was refluxed overnight at 110 • C. The yellow precipitate was filtered and washed thoroughly with fresh toluene. The crude product was purified by column chromatography on alumina neutral grade IV with pure DCM (0.17 g, yield 83%). HOp-Br 5c. 2-Bromo-6-methoxynaphthalene 7 (1.01 g, 4.2 mmol) and cinnamoyl chloride 2 (0.71 g, 4.2 mmol) were dissolved in 20 ml of freshly distilled DCE and cooled down to 0 • C. AlCl 3 (0.56 g, 4.2 mmol) was added, the mixture was stirred 1 h in the cold. After allowing the reaction to warm up to room temperature, further AlCl 3 (0.56 g, 4.2 mmol) was added and the mixture was refluxed at 90 • C overnight. The suspension was allowed to cool to room temperature, quenched with HCl 6 N 10 ml and filtered on celite. The solid was repeatedly washed with hot DCM and the organic layer of the filtrate was taken. The solvents were evaporated under reduced pressure and the solid was purified by column chromatography on silica gel with DCM/hexane (1:1) yielding the pure product (1.01 g, yield 87%). added dropwise and the mixture was refluxed additional 3 h. After allowing the reaction to cool down to room temperature, the suspension was filtered. The clear solution was taken and the solvent was evaporated under reduced pressure (2.6 g, yield 96%). HOp-I 5d. 5-Bromo-9-methoxy-1H-phenalen-1-one 11 (2.50 g, 8.8 mmol) was dissolved in 18 ml DMSO. CuI (10.50 g, 55.0 mmol) and KI (18.30 g, 110.0 mmol) were added and the mixture was refluxed at 160 • C 40 h. The reaction was allowed to cool down to room temperature and quenched with 25 ml HCl 1 N. The mixture was filtred on celite and the filtrate was extracted with DCM. The organic layer was taken and the solvents were evaporated under vacuum. The crude product was purified by recrystallization from a DCM/ethanol solution (2.15 g, yield 76%). Al(Op-I) 3 6d. HOp-I 5d (0.56 g, 1.7 mmol) was dissolved in 40 ml toluene, AlCl 3 (72.0 mg, 0.54 mmol) was added and the solution was refluxed overnight at 110 • C. The yellow precipitate was filtered and washed thoroughly with fresh toluene. The crude product was purified by column chromatography (0.42 g, yield 80%). HOp-p 15a. 5-Bromo-9-methoxy-1H-phenalen-1-one 11 (2.00 g, 6.9 mmol), phenylboronic acid 12 (0.95 g, 7.8 mmol) and CsF (2.24 g, 14.7 mmol) were placed in 50 ml DME and the mixture was bubbled with argon 1 h. Pd(PPh 3 ) 4 (0.55 g, 0.48 mmol) was added and the reaction was refluxed overnight at 90 • C. The mixture was washed with H 2 O after allowing it to cool to room temperature, the organic layer was taken and the solvent evaporated under reduced pressure. The crude product was partially purified by flash column chromatography on silica gel with ethyl acetate/hexane (1:1). 9-Methoxy-5-phenyl-1H-phenalen-1-one 39a (1.30 g, 4.6 mmol) was dissolved in 200 ml DCM, BBr 3 1 M in DCM (9.1 ml, 9.1 mmol) was added dropwise and the mixture was refluxed overnight at 50 • C. The reaction was cooled down to room temperature and quenched with 50 ml NaOH 2 M; the organic layer was separated, the aqueous layer acidified with HCl and extracted with DCM. All the organics were collected, the solvent was evaporated and the crude product was purified by column chromatography on silica gel with pure DCM and recrystallization from a DCM/hexane solution (0.97 g, yield 51%). Al(Op-p) 3 16a. HOp-p 15a (0.97 g, 3.5 mmol) was dissolved in 15 ml toluene, AlCl 3 (0.16 g, 1.1 mmol) was added and the solution was refluxed overnight at 110 • C. The yellow precipitate was filtered and washed thoroughly with fresh toluene. The crude product was purified by column chromatography on alumina neutral grade IV with pure DCM (0.79 g, yield 86%). HOp-n 15b. 5-Bromo-9-methoxy-1H-phenalen-1-one 11 (1.01 g, 3.5 mmol), naphthalen-1ylboronic acid 13 (0.63 g, 3.5 mmol) and CsF (1.11 g, 7.1 mmol) were placed in 40 ml DME and the mixture was bubbled with argon 1 h. Pd(PPh 3 ) 4 (0.16 g, 0.14 mmol) was added and the reaction was refluxed overnight at 90 • C. The reaction was cooled down to room temperature and the mixture was washed with H 2 O, the organic layer was taken and the solvent evaporated under reduced pressure. The crude product was partially purified by flash column chromatography on silica gel with ethyl acetate/hexane (1:1). 9-Methoxy-5-(naphthalen-1-yl)-1H-phenalen-1-one 39b (1.00 g, 3.7 mmol) was dissolved in 50 ml DCM, BBr 3 1 M in DCM (10.0 ml, 10.0 mmol) was added dropwise and the reaction mixture was refluxed overnight at 50 • C. The reaction was cooled down to room temperature and quenched with 50 ml NaOH 2 M; the organic layer was separated, the aqueous layer was acidified with HCl and extracted with DCM. All the organics were collected, the solvent was evaporated under reduced pressure and the crude product was purified by column chromatography on silica gel with pure DCM and sublimation in vacuum (0.60 g, yield 53%). Al(Op-n) 3 16b. HOp-n 15b (0.30 g, 1.0 mmol) and AlCl 3 (40.0 mg, 0.30 mmol) were dissolved in 30 ml toluene; the solution was refluxed overnight at 110 • C. The yellow precipitate was filtered and washed thoroughly with fresh toluene. The crude product was purified by column chromatography on alumina neutral grade IV with pure DCM (0.20 g, yield 67%). HOp-pe 15c. 5-Bromo-9-methoxy-1H-phenalen-1-one 11 (0.41 g, 1.4 mmol) and ethynylbenzene 14 (0.18 ml, 1.6 mmol) were dissolved in 50 ml of a mixture 2:3 THF/Et 3 N. The solution was bubbled 1 h with argon. CuI (20.0 mg, 0.10 mmol), Pd(PPh 3 ) 2 Cl 2 (20.0 mg, 0.03 mmol) and PPh 3 (10.0 mg, 0.04 mmol) were added. The reaction was refluxed over weekend at 75 • C and cooled down to room temperature. DCM was added and the organics were washed with H 2 O. The organic layer was taken and the solvents were evaporated under reduced pressure. The crude product was partially purified by flash column chromatography on silica gel with ethyl acetate/hexane (1:1). 9-Methoxy-5-(phenylethynyl)-1H-phenalen-1-one 39c (0.27 g, 0.9 mmol) was dissolved in 30 ml DCM, boron tribromide 1 M in DCM (2.0 ml, 2.0 mmol) was added dropwise and the reaction mixture was refluxed overnight at 50 • C. The reaction was cooled down to room temperature and quenched with 20 ml NaOH 2 M; the organic layer was separated, the aqueous layer was acidified with HCl and extracted with DCM. All the organics were collected, the solvent was dried and the crude product was purified by column chromatography on silica gel with pure DCM (0.15 g, yield 36%). Suitable crystals for single crystal X-ray diffraction were obtained from slow evaporation at room temperature of a DCM/ethanol solution.

OSCs synthesis

1 H-NMR (500 MHz, CDCl 3 , 25 Al(Trop) 3 25. Tropolone 24 (1.12 g, 9.2 mmol) was dissolved in 50 ml of freshly distilled toluene, AlCl 3 was added (0.40 g, 3.0 mmol) and the resulting solution was refluxed overnight at 110 • C. The white precipitate was filtred and washed thoroughly with fresh toluene. The crude product was purified by column chromatography (0.97 g, yield 83%). Suitable crystals for single crystal X-ray diffraction were obtained from slow evaporation at room temperature of a DCM/ethanol solution. Al(q 2 Acac) 28. Al(CH 3 ) 3 (2 M in toluene, 1.35 ml, 2.7 mmol) was taken in 20 ml of freshly distilled toluene and the resulting solution was cooled to 0 • C. A second solution of Hq 26 (0.78 g, 5.5 mmol) in 10 ml of freshly distilled toluene was added dropwise over 30 min. The solution was warmed up to room temperature and left stirring 3 h. Acac 27 (0.28 ml, 2.7 mmol) in 10 ml of freshly distilled toluene was added dropwise over 30 min; the resulting solution was stirred overnight at room temperature. The yellowish precipitate was filtred and washed thoroughly with fresh toluene. The crude product was purified by column chromatography on alumina neutral grade IV with pure DCM (0.79 g, yield 71%). Suitable crystals for single crystal X-ray diffraction were obtained from slow evaporation at room temperature of a acetone solution. Al(q 2 Op) 29. Al(q 2 Acac) 28 (0.71 g, 1.7 mmol) and HOp 3 (0.30 g, 1.5 mmol) were dissolved in 100 ml on ethanol. The solution was refluxed at 90 • C overnight, cooled down to room temperature and reduced to 20 ml. The precipitate was filtered, washed with cold fresh ethanol and purified by column chromatography on alumina neutral grade IV with pure DCM (0.63 g, yield 73%). Suitable crystals for single crystal X-ray diffraction were obtained from slow evaporation at room temperature of a DCM/ethanol solution. Al(q 2 Trop) 30. Al(q 2 Acac) 28 (0.30 g, 0.7 mmol) and tropolone 24 (85.0 mg, 0.70 mmol) were dissolved in 60 ml of ethanol. The solution was refluxed at 90 • C overnight, cooled down to room temperature and reduced to 10 ml. The precipitate was filtred, washed with cold fresh ethanol and purified by column chromatography on alumina neutral grade IV with pure DCM (0.21 g, yield 68%). Suitable crystals for single crystal X-ray diffraction were obtained from slow evaporation at room temperature of a DCM/ethanol solution.

(C1

ESI-TOF MS (Da

Phenalenyl-based SMMs

[Dy(Op) 2 Cl(HOp)(EtOH)] 32. HOp 3 (117.7 mg, 0.6 mmol) was dissolved in 5 ml of CH 3 Cl. An ethanol solution of NaH (14.4 mg, 0.6 mmol) was added dropwise at room temperature. A second ethanol solution of DyCl 3 • 6 H 2 O (75.4 g, 0.2 mmol) was added dropwise. The final mixture was stirred 2 h at room temperature and refluxed 3 h at 90 • C. After cooling the mixture overnight, the solid was filtered off and single crystals were grown by slow evaporation of the filtrate solution (18.3 mg, yield= 10%).

C. Crystal Refinement Data

Figure 1 :

 1 Figure 1: Liaisons σ et π dans l'éthylène, la plus simple molécule présentant un système conjugué π. Les niveaux d'énergie de la molécule ainsi que son niveau d'excitation électronique le plus faible sont indiqués à droite.

Figure 3 :

 3 Figure 3: Émission de photons observée pour le complexe Alq 3 (jaune) et pour le complexe Al(Op) 3 (bleu) sous illumination UV (en solution). Émission de photons observée pour le complexe Alq 3 (jaune) et pour le complexe Al(Op) 3 (marron) (couche mince). L'émission pour le complexe Al(Op) 3 en couche mince est sensiblement décalée par rapport à celle observée en solution due à la formation d'excimères.

Figure 4 :

 4 Figure 4: (a) Courbe CV cathodique puor Hq et Alq 3 dans une solution de DCM mesurée à température ambiante. Électrolyte: TBAPF 6 . Vitesse de scan: 100 mV s -1 . (b) Courbe CV cathodique pour HOp et Al(Op) 3 dans une solution de DCM mesurée à température ambiante. Électrolyte: TBAPF 6 . Vitesse de scan:100 mV s -1 .

Figure 5 :

 5 Figure 5: Représentation de la surfaces des orbitales moléculaires HOMO (à gauche) et LUMO (à droite) pour les complexes mer-Alq 3 (en haut) et Al(Op) 3 (en bas).

Figure 6 :

 6 Figure 6: (a) Morphologie du complexe mer-Alq 3 . (b) Fonction de corrélation de paire g(r) pour le complexe mer-Alq 3 .

Figure 7 :

 7 Figure 7: Alignement des niveaux d'énergie pour les interfaces Co/[5 nm] Al(Op) 3 et Co/[2.8 nm] Al(Op-py) 3 . Ces données sont extraites des spectres UPS et 2PPE. L'alignement des niveaux d'énergie pour l'interface Co/Alq 3 est indiqué à titre de comparaison.

Figure 8 :

 8 Figure 8: Alignement des niveaux d'énergie pour l'interface Co/[1.5 nm] Al(Op) 3 . Ces données sont extraites des spectres NT-PS et 2PPE. L'alignement des niveaux d'énergie pour l'interface Co/Alq 3 est indiqué à titre de comparaison.

[Figure 9 :

 9 Figure 9: (a) Diagramme d'Arrhenius semi-logarithmique du temps de relaxation τ en fonction de 1/T pour le complexe [Dy(Op) 2 Cl(HOp)(EtOH)]. La susceptibilité magnétique fut mesurée pour un champ magnétique externe nul ainsi que pour un champ statique externe de 200 Oe. La courbe obtenue par régression linéaire pour l'intervalle de température d'activation termique est tracée sur le diagramme.(b) Diagramme d'Arrhenius semi-logarithmique du temps de relaxation τ en fonction de 1/T pour le complexe [Dy(Op) 3 (HOp)]-[Dy(Op) 3 (EtOH)]. La susceptibilité magnétique fut mesurée pour deux valeurs champs magnétiques externes: 1500 Oe et 3000 Oe. La courbe obtenue par régression linéaire pour l'intervalle de température d'activation termique est tracée sur le diagramme.

Figure 1 . 3 :

 13 Figure 1.3: Jablonsky diagram of an organic molecule. Left: singlet manifold. Right: triplet manifold. Blue vertical arrows represent absorption processes, green and red vertical arrows represent emission processes, dashed vertical arrows represent radiationless processes, and black solid vertical arrows represent triplet-triplet annihilation processes. Thick horizontal lines are electronic energy levels, and thin horizontal lines are vibronic sublevels. Γ F,r , Γ F,nr , Γ P,r , and Γ P,nr are radiative and non-radiative rates of fluorescence and phosphorescence, respectively. k and k isc are rates of absorption and intersystem crossing, respectively. Source: [21].

  .1, p = e • r represents the dipole operator and M = | Ψ f | p|Ψ i | is the transition dipole moment between initial and final states of the molecule. When the parity of the two wavefunctions is different, the transition is allowed. The factor | Φ vib,f |Φ vib,i | takes in account the contribution of vibrations to electronic transitions. The Frank-Condon principle statesthat only vertical transitions are allowed, and the intensity of the transition is proportional to the overlap between the vibronic wavefunctions of initial and final states. Additionally, higher vibronic states of the first excited electronic state S 1 and higher excited electronic states are coupled, and thus, a fast relaxation process (internal conversion) occurs to the lowest vibronic state of the first excited state S 1 (Kasha's rule). This leads to the characteristic Stokes shift observed between absorption and emission spectra of a molecule. Figure1.4 illustrates the typical vibronic structure of absorption and emission spectra.

Figure 1 . 4 :

 14 Figure 1.4: Schematic illustration of vibronic transitions (absorption and fluorescence) between S 0 and S 1 in an organic molecule. Source: [21].

Figure 1 . 5 :

 15 Figure 1.5: Illustration of the hopping transport mechanism. The distribution of the density of HOMO and LUMO states is Gaussian with widths σ h and σ e , respectively. Source: [21].In all these four OSCs-based devices, although taking in account the different mechanisms to inject/generate charge carriers, the charge carrier transport process is similar. In molecular crystals, band transport is observed, whereas in the case of amorphous materials hopping transport prevails (see Figure1.5). Since nowadays OSCs-based devices are constituted by thin (often amorphous) layers, and since the molecules studied in this thesis are forming amorphous

1. 2 Figure 1 . 6 :

 216 Figure 1.6: Molecular structures of the meridianal isomer (mer-Alq 3 ) on the left hand side, and of the facial isomer (fac-Alq 3 ) on the right end side. Source: [27].

( 5 )Figure 1 . 7 : 1 :

 5171 Figure 1.7: Molecular structure obtained by single crystal X-ray diffraction of mer-Alq 3 . Hatoms and solvent molecules are omitted for clarity. The crystal refinement data is reported in Table C.1. The molecular packing in the single crystal of mer-Alq 3 is illustrated in (a) yz (b) xz (c) xy perspective.Table: selected bond distances and angles for mer-Alq 3 .

1 Figure 1 . 8 :

 118 Figure 1.8: (a) Simplified illustration of a three-layer OLED. ETL: electron trasport layer, HTL: hole transport layer, and EML: emission layer. To obtain light emission, a voltage must be applied. (b) Schematic energy diagram of a three-layer OLED. The basic processes are illustrated. Electrons are injected from the cathode into the LUMO of the ETL and holes are injected from the anode into the HOMO of the HTL. Subsequently, the charge carriers travel across the organic layers to recombine radiatively in the emission layer. Φ A and Φ C are the work functions of the anode and cathode, respectively. Φ BI is the built-in voltage to be overcome by an external voltage V before current can flow in the device. Source: [18].

Figure 1 . 9 :

 19 Figure 1.9: (a) Configuration of the first two Alq 3 -based OLEDs. In the device on the left, Alq 3 is the electron-transporting and emitting material, on the right, Alq 3 is the electron-transporting and host material. (b) Chemical structure of the hole-transporting material TAPC and of the dopants: Coumarin 540, DMC1 and DCM2. Sources: [9, 10].

Figure 1 . 10 :

 110 Figure 1.10: Chemical structure of Gaq 3 (tris-(8-hydroxyquinoline)gallium) and Inq 3 (tris-(8hydroxyquinoline)indium) on the left hand side and of Znq 2 (bis-(8-hydroxyquinoline)zinc) on the right hand side. Sources: [53-57].

Figure 1 . 11 :

 111 Figure 1.11: Chemical structure of AlOq 3 (tris-(5-hydroxymethyl-8-quinolinato)aluminum) on the left hand side and Alq(Clq) 2 (bis-(5,7-dichloro-8-quinolinato)-(8-quinolinato)aluminum) on the right hand side. Sources: [58, 59].

Figure 1 . 13 :Figure 1 .

 1131 Figure 1.13: Schematic energy band diagram of three types of OPVs. Left: single layer OPV. Center: planar heterojunction OPV. Right: bulk heterojunction OPV (PEDOT: poly(3,4ethylenedioxythiophene)). Source: [60].

Figure 1 .

 1 Figure 1.15: (a) Schematic configuration of OPVs including Alq 3 as buffer layer. Left OPV: CuPc [30 nm]/C60 [40 nm]/Alq 3 [6 nm]. Central OPV: ZnPc [10 nm]/ZnPc:C60 [10 nm]/C60 [10 nm]/Alq 3 [5 nm]. Right tandem-OPV: ZnPc [10 nm]/ZnPc:C60 [10 nm]/C60 [10 nm]/Alq 3 [5 nm]/connecting layer/ZnPc [10 nm]/ZnPc:C60 [10 nm]/C60 [10 nm]/Alq 3 [5 nm]. (b) Chemical structure of the n-type OSC: C60 (electron acceptor), p-type OSCs: MPc (M=Zn,Cu) (electron donor), and connecting layers: SnCl 2 Pc and F 16 CuPc. Sources: [64, 65].

Figure 1 . 16 :

 116 Figure 1.16: Schematic drawing of a spin valve. Ferromagnetic electrodes in parallel configuration on the left hand side, and in antiparallel configuration on the right hand side. Corresponding electrical resistor models illustrated in the bottom. Source: [http://en.wikipedia.org/wiki /Giant_magnetoresistance].

Figure 1 .

 1 Figure 1.17: (a) Schematic representation of a typical vertical Alq 3 -based OSPD. Alq 3 is sandwiched between LSMO, bottom electrode, and cobalt, top electrode. (b) MR loop of a LSMO [100 nm]/Alq 3 [130 nm]/Co [3.5 nm] OSPD measured at 11 K. The magnetization configuration of the electrodes is indicated. Source: [69].

Figure 1 .

 1 Figure 1.18: (a) Schematic representation of the Alq 3 -based OSPD device. A nanoindent is realized in the Alq 3 layer to control the organic tunnel barrier thickness. The nanohole is then filled with cobalt. LSMO is the bottom electrode and cobalt the top electrode. (b) MR curve of a LSMO/Alq 3 [2 nm]/Co OSPD measured at 2 K and -5 mV. In the inset, I(V ) curves recorded at 2 K in the parallel (I P A ) and antiparallel (I AP ) configurations. Source: [74].

Figure 1 .Figure 1 .

 11 Figure 1.19: (a) Molecular structure of ZMP (zinc methyl phenalenyl) in a neutral state and in an anionic radical. Charge transfer processes through hybridization on the ferromagnetic surface can change the chemical state of the phenalenyl from the neutral state to an anionic radical. (b) MR measurements of a device Co [8 nm]/ZMP [40 nm]/Co [12 nm] recorded at 15 mV after cooling the device to 4.2 K in a magnetic field 550 Oe. The magnetization of cobalt is shown with a red arrow. Source: [76].

Figure 1 .

 1 Figure 1.21: (a) Schematic view of the structure of Alq 3 -based ambipolar OFETs. Alq 3 -based OFETs were obtained with Ca source and drain electrodes for the n-channel device and with a bottom contact configuration with Au/Cr electrodes on a HMDS treated substrate for the p-channel device. (b) Chemical structure of PMMA (poly(methyl methacrylate)) and HMDS (hexamethyldisylazane). Source [78].

Figure 1 . 22 :

 122 Figure 1.22: Schematic illustration of the laterally arranged heterojunction fabrication process. A: the substrate is tilted with respect to the horizontal plane and pentacene is evaporated resulting in the layer deposition shown in B. C: the substrate is inclined in the opposite direction and Alq 3 is evaporated resulting in the final configuration shown in D. Source: [79]. Di et al. described LE-OFETs based on laterally arranged heterojunctions formed by pentacene and Alq 3[79]. By implementing the uncommon fabrication strategy illustrated in Figure1.22, the authors could form heterojunctions between pentacene (chemical structure in Table1.1) and Alq 3 . A hole mobility µ between 1.8 × 10 -3 and 2.1 × 10 -3 cm 2 V -1 s -1 , a threshold voltage V T of -10 V, and a on/off current ratio between 10 3 and 10 4 were measured. For electrons, the mobility µ was 1.6 × 10 -6 cm 2 V -1 s -1 , the threshold voltage V T was 20 V, and the on/off current ratio was 10 3 . Additionally, for the device built with gold as source electrode, and lithium fluoride (LiF) as drain electrode, emission of light was detected.

  At last, Capelli et al. built the first triple-layer hetero-structure LE-OFET illustrated in Figure 1.23.

Figure 1 .

 1 Figure 1.23: (a) Schematic representation of the trilayer LE-OFET device. Field-effect charge transport and light -generation processes are illustrated. (b) Optical micrograph of the light emission from the trilayer LE-OFET (V SD = V G = 90 V). (c) Chemical structure of the p-type OSC DH-4T (blue layer) and of the n-type OSC DFH-4T (green layer). Source:[80].

1 / 2

 12 SD,sat versus V G is illustrated in Figure4.14 in Section 4.3.1. Moreover, the performance of OFETs is estimated by two additional parameters: threshold voltage V T and on/off current ratio.Time of flight (TOF).

Figure 1 .

 1 Figure 1.25: (a) Schematic representation of a TOF setup. In the example, the organic material is sandwiched between a semi-transparent Al electrode and a transparent ITO electrode. The carriers are generated near the anode (Al electrode). Under the applied field F , electrons recombine instantaneously at the anode and holes move toward the cathode (ITO electrode). R is representing a resistance (much lower than that of the sample) and CRO is the measuring system (oscilloscope). (b) Typical experimental signal for non-dispersive OSCs on the left. Typical experimental signal for dispersive OSCs on the right, in the inset, double logaritmic plot used to extract the transit time τ . Sources: [61, 106].

Figure 1 .

 1 25) generating a spike 1 Introduction in the photocurrent I, whereas the other type of carriers starts moving through the film (holes in Figure 1.25). When the carriers reach the opposite electrode recombine with a drop of the photocurrent I. Illustrative experimental setup and signal are displayed in Figure 1.25. From the transit time τ , the mobility µ [cm 2 V -1 s -1 ] can be derived from: µ = (d/(τ F ), where d is the thickness of the sample. Admittance spectroscopy (AS).

Figure 1 .

 1 Figure 1.26: (a) Schematic representation of an AS setup. In the example, the organic material is sandwiched between aluminum and ITO electrodes. (b) Typical AS experimental signal. f is the frequency of the applied ac excitation, C is the capacitance, C geo is the geometrical capacitance, -∆B is the negative differential capacitance, and τ r and f r are the characteristic time and frequency, respectively. Source: [106].

  and G, B, and C are the conductance, susceptance and capacitance, respectively. A convenient way to extract the mobility is to measure the frequency-dependent capacitance by an impedance analyzer, and calculating the negative differential susceptance -∆B = -2πf (C -C geo ), where C geo = ǫA/d is the geometrical capacitance (ǫ is the permittivity of the OSC, A and d are the active area and thickness of the sample, respectively) [109]. As illustrated in Figure 1.26, by plotting the negative differential susceptance -∆B versus the frequency f , a maximum at a distinct frequency f r = τ -1 r is obtained. The average transit time is τ dc = 0.56τ r . Finally, the charge carrier mobility µ = d/τ dc F = d/0.56τ r F can be determined (F is the electric field) [106].

Figure 1 .

 1 Figure 1.27: (a) Schematic illustration of UPS and NT-PS. The photon sources are a vacuum ultraviolet lamp for UPS and a Ti:sapphire laser for NT-PS. The emitted photoelectrons are energy and spin selected by a spin detector based on spin polarized low-energy electron diffraction mounted on a commercial cylindrical sector analyzer. (b) Conceptual principle of UPS and NT-PS experiments. Electrons are excited by UV photons (21.2 eV or 5.95 eV) above the vacuum energy and leave the sample. The kinetic energy and spin of the electrons is analyzed by a detector (SPLEED).

Figure 1 . 28 :

 128 Figure 1.28: Schematic illustration of the CSA (cylindrical sector energy analyzer) and the SPLEED (spin polarized low energy electron detector). Polarized electrons are scattered on the W(001) target and detected by channeltrons positioned at the spin dependent LEED spots of the W(001) surface.

Figure 1 . 29 :Figure 1 .

 1291 Figure 1.29: Conceptual principle of 2PPE. An electron is excited by a photon (pump) into an intermediate state . By a second photon (probe) the electron is excited above the vacuum energy and photoemitted. 2PPE belongs to the class of PES techniques, however, in contrast to UPS and NT-PS, the photoemission process is caused by the absorption of two photons, namely, pump and probe photon (for a review [115]). As illustrated in Figure 1.29, the first pump photon excites an electron from an occupied state below the Fermi energy E F to an intermediate state between the Fermi energy E F and the vacuum energy E vac , subsequently, during the survival time in the

Figure 1 .

 1 Figure 1.31: (a) Crystal structure of the first SMM [Mn 12 O 12 (OAc) 16 (H 2 O) 4 ] (Mn 12 Ac). The total spin of the molecule is S= 10 given by 4 Mn 4+ ions, S= 6 (Mn 4+ : S= 3/2) plus 8 Mn 3+ ions, S= 16 (Mn 3+ : S= 2). (b) Plot of the potential energy versus the magnetization for a SMM with S= 10 ground state. The diagram is for zero external magnetic field. Source: [118, 122, 123].

Figure 1 . 32 :

 132 Figure 1.32: Schematic illustration of the relaxation processes of a SMM with a spin ground state S=10. The magnetization reversal can occur via quantum tunneling between energy levels (blue arrow) or by thermal relaxation by climbing up and down all the energy levels (green arrows). Source [120].

Figure 1 . 33 :Figure 1 .

 1331 Figure 1.33: Molecular structure of [LnPc 2 ] -. Hydrogens atoms are omitted. Source: [117]. From the first work of Ishikawa et al., in which SMM behavior was investigated in phthalocya-

Figure 1 .

 1 Figure 1.35: (a) Atomic force micrograph and schematic illustration of the TbPc 2 -based spin valve (hexyl and pyrenyl groups are omitted for clarity). The single-walled carbon nanotube lies on a SiO 2 surface supported by a back gate and is connected to palladium source and drain electrodes. (b) Schematic representation of the mechanism involving two TbPc 2 grafted on a single-walled nanotube. Increasing the magnetic field the molecule A switches leading to an antiparallel configuration of the spin valve with lowest conductance. When molecule B switches, the parallel configuration with high conductance is recovered. Source [125].

Figure 1 . 36 :

 136 Figure 1.36: Idealized square-antiprismatic structure of [Ln(β-diketonate) 3 (L) n ] complexes. Structures of β-diketonates and of neutral ligands (exemplary, 2,2'-bipyridine) are illustrated.

Figure 1 .

 1 Figure1.36 illustrates the structure of [Ln(β-diketonate) 3 (L) n ], the variety of available βdiketonate ligands with R 1 = R 2 , but also with R 1 = R 2 , and the multitude of neutral ligands, open up to countless SMMs which can be obtained. So far a vast number of β-diketonate-based SMMs was synthesized, however, besides the characterization of the magnetic properties, they were not applied in any device. Therefore, in our study, we aim to synthesize phenalenyl-based lanthanide SMMs to investigate their magnetic properties and eventually to be deposited on surfaces by vacuum evaporation. This would be the first step towards the implementation of such molecules in devices.

  fused aromatic rings plus halogen • Symmetric (fast proton transfer)

Scheme 3 . 1 :Figure 3 . 1 : 3 . 4 CompoundFigure 3 . 3 :

 31313433 Scheme 3.1: Synthesis of tris-(1-oxo-1H-phenalen-9-olate)aluminum (Al(Op) 3 ) 4. (a) AlCl 3 , DCE, reflux, 4h, yield: 86% [135]. (b) AlCl 3 , toluene, reflux, overnight, yield: 75%. The numbering is shown in red for HOp 3 and Al(Op) 3 4 (on one ligand).Al(Op) 3 4 is the first molecule to be designed in this study. Its synthesis and implementation in OLEDs was previously reported for commercial applications[136]. The ligand 9-hydroxy-1H-phenalen-1-one (HOp) 3 has been selected for mainly two reasons, which are in contrast to Hq: it is symmetric and it has an extended aromatic system. The symmetry of HOp 3 originates from the characteristic proton tautomerism (or proton transfer) between two degenerate configurations, as illustrated schematically in Figure3.1. The proton transfer, caused by the strong intramolecular hydrogen bond, has been investigated by several experimental techniques [137-142] and theoretical methods[143][144][145][146]. Although HOp 3 is commercially available, an efficient synthesis was described byKoelsch et al. [147] and improved byHaddon et al. [135]. In the latter approach, illustrated in Scheme 3.1, 2-methoxynaphtalene 1 and cinnamoyl chloride 2 are used as precursors. Several metal chelates of HOp 3 were previously studied byDemura et al. [148].

2 .

 2 As demonstrated by the O-Al-O bond angles, which are all close to 90 • or 180 • , the six chelating oxygens are arranged in an almost perfect octahedral geometry around the central aluminum atom. Additionally, the bond lengths Al-O are narrowly distributed between 1.867 and 1.882 Å, indicating that the six oxygens are virtually identical, taking in consideration the deformation caused by solvent molecules in the crystal lattice. Al-O distances in Al(Op) 3 4 are comparable to those in mer-Alq 3 , which are reported in Section 1.2. The molecular packing of Al(Op) 3 4 is clearly driven by the π -π stacking between the flat aromatic ligands. Furthermore, the ligands maintain the aromaticity and flatness after coordinating aluminum. As a result, all the torsion angles of the phenalenyl ligands are close to either 0 • or 180 • . At last, C-C bonds in the phenalenyl moieties of Al(Op) 3 4 and of HOp 3, reported by Svensson et al. [149], are almost identical between ≈1.35 Å and ≈1.45 Å. This indicates that no major deformations are induced on the phenalenyl ligands by the coordination of aluminum.

Figure 3 . 4 .

 34 Figure 3.3 illustrates the 1 H-NMR spectra of HOp 3 and Al(Op) 3 4. HOp 3 presents five resonances. The first, with a chemical shift of ≈16 ppm (out of the range of the figure), is related to the hydrogen H9 involved in the proton tautomerism described in Figure 3.1 [150].The high chemical shift indicates that the hydrogen is between the two oxygens rather than being localized on one oxygen. In other words, the proton transfer at room temperature is faster

Figure 3 . 4 : 3 . 3 .2 5 -Scheme 3 . 2 : 2 .Scheme 3 . 3 :Figure 3 . 5 :

 343353223335 Figure 3.4: MALDI-TOF spectrum of Al(Op) 3 4. The fragment is marked in the figure.

85 Figure 3 . 6 : 24 Figure 3 . 7 :

 85362437 Figure 3.6: 1 H-NMR spectra of the halogenated ligands HOp-X 5a-d in CDCl 3 . The resonances are marked accordingly to the numbering shown in Scheme 3.2.

Figure 3 . 8 :

 38 Figure 3.8: MALDI-TOF spectra of the halogenated complexes Al(Op-X) 3 6a-d. The fragments are marked in the figure.

3

 3 Scheme 3.4: Synthesis of the substituted ligands HOp-R 15a-c and complexes Al(Op-R) 3 16a-c. (a.1) CsF, Pd(PPh 3 ) 4 , DME, reflux, overnight. (a.2) BBr 3 , DCM, reflux, overnight, yield: 51%. (b.1) CsF, Pd(PPh 3 ) 4 , DME, reflux, overnight. (b.2) BBr 3 , DCM, reflux, overnight, yield: 53%. (c.1) CuI, Pd(PPh 3 ) 2 Cl 2 , PPh 3 , THF/Et 3 N (2:3), reflux, 48 h. (c.2) BBr 3 , DCM, reflux, overnight, yield: 36%. (d) AlCl 3 , toluene, reflux, yields: Al(Op-p) 3 16a 86%, Al(Op-n) 3 16b 67%, Al(Op-pe) 3 16c 83%.

Figure 3 . 9 :

 39 Figure 3.9: Molecular structure obtained by single crystal X-ray diffraction on a single crystal of HOp-pe 15c. H-atoms and solvent molecules are omitted for clarity. The crystal refinement data is reported in Table C.4. The molecular packing in the single crystal of HOp-pe 15c is illustrated in (a) yz (b) xz (c) xy perspective.

Figure 3 . 9 . 91 Figure 3 .

 39913 Figure 3.10: 1 H-NMR spectra of the substituted ligands HOp-R 15a-c in CDCl 3 . The resonances are marked accordingly to the numbering shown in Scheme 3.4.

Figure 3 .

 3 Figure 3.11: 1 H-NMR spectra of the substituted complexes Al(Op-R) 3 16a-c in CDCl 3 . The resonances are marked accordingly to the numbering shown in Scheme 3.4.

Figure 3 .

 3 Figure 3.12: MALDI-TOF spectra of Al(Op-R) 3 16a-c. The main fragments are marked in the figure. The substituted complexes Al(Op-R) 3 16a-c have been further characterized by means of elemental analysis and MALDI-TOF spectrometry. The results of the carbon and hydrogen elemental analysis, listed in Table 3.3, are in fairly good agreement with the calculated values considering the adsorption of additional H 2 O molecules. In detail, for Al(Op-p) 3 16a the experimental values are C= 76.58% and H= 4.36% and those calculated are C= 76.49% and H= 4.40%, for Al(Op-n) 3 16b the experimental values are C= 76.54% and H= 4.60% and those calculated are C= 76.65% and H= 4.58% and for Al(Op-pe) 3 16c the experimental values are C= 76.43% and H= 5.79% and those calculated are C= 76.81% and H= 4.20%. In the MALDI-TOF spectra of the complexes Al(Op-R) 3 16a-c, illustrated in Figure 3.12, only peaks corresponding to the fragments [Al(Op-R) 2 ] + are detected. Clearly, to form the cation one ligand is eliminated ([Al(Op-p) 2 ] + m/z= 569, [Al(Op-n) 2 ] + m/z= 669 and [Al(Op-pe) 2 ] +

3. 3 . 4 3 )Scheme 3 . 5 :

 34335 Scheme 3.5: Synthesis of Al(Oba) 3 19. (a) AlCl 3 , DCB, 120 • C, 48 h, yield: 61%. (b) AlCl 3 , toluene, reflux, overnight, yield: 86%. The mer-Al(Oba) 3 and fac-Al(Oba) 3 isomers are schematically depicted.

Scheme 3 . 6 :

 36 Scheme 3.6: Synthesis of Al(Op-py) 3 23. (a) Pd(PPh 3 ) 4 , toluene/ethanol/K 2 CO 3 (2 M) in H 2 O, reflux, overnight, yield: 68%. (b) Al(CH 3 ) 3 , THF, room temperature, 120 h, yield: 73%. The mer-Al(Op-py) 3 and fac-Al(Op-py) 3 are schematically depicted.

Scheme 3 . 7 :

 37 Scheme 3.7: Al(Trop) 3 25. (a) AlCl 3 , toluene, reflux, overnight, yield: 83%.

Figure 3 . 13 :

 313 Figure 3.13: Molecular structure obtained by single crystal X-ray diffraction on a single crystal of Al(Trop) 3 25 [165]. H-atoms and solvent molecules are omitted for clarity. The molecular packing in the single crystal of Al(Trop) 3 25 is illustrated in (a) yz (b) xz (c) xy perspective. Table: selected bond distances and angles for Al(Trop) 3 25.

Figure 3 .

 3 Figure 3.14: 1 H-NMR spectra of tropolone 24 (blue) and Al(Trop) 3 25 in CDCl 3 . The resonances are marked accordingly to the numbering shown in Scheme 3.7.

Figure 3 .

 3 Figure 3.15: MALDI-TOF spectra of Al(Oba) 3 19, Al(Op-py) 3 23 and Al(Trop) 3 25. The main fragments are marked in the figure.

3. 3 . 7 Scheme 3 . 8 :

 3738 Scheme 3.8: Synthesis of Al(q 2 Acac) 28. (a) Al(CH 3 ) 3 , toluene, room temperature, overnight, yield: 71%.

Figure 3 . 16 : 2

 3162 Figure 3.16: Molecular structure obtained by single crystal X-ray diffraction on a single crystal of Al(q 2 Acac) 28 [166]. H-atoms and solvent molecules are omitted for clarity. The molecular packing in the single crystal of Al(q 2 Acac) 28 is illustrated in (a) yz (b) xz (c) xy perspective. Table:selected bond distances and angles for Al(q 2 Acac) 28.

Figure 3 . 17

 317 Figure 3.17: 1 H-NMR spectra of Al(q 2 Acac) 28, Hq 26 and Acac 27 in CD 2 Cl 2 . The resonances are marked accordingly to the numbering shown in Scheme 3.8.

  Figure 3.17: 1 H-NMR spectra of Al(q 2 Acac) 28, Hq 26 and Acac 27 in CD 2 Cl 2 . The resonances are marked accordingly to the numbering shown in Scheme 3.8.

Scheme 3 . 9 :

 39 Scheme 3.9: Synthesis of Al(q 2 Op) 29. (a) Ethanol, reflux, overnight, yield: 73%.

Figure 3 . 18 :

 318 Figure 3.18: Molecular structure obtained by single crystal X-ray diffraction on a single crystal of Al(q 2 Op) 29. H-atoms and solvent molecules are omitted for clarity. The crystal refinement data is reported in Table C.5. The molecular packing in the single crystal of Al(q 2 Op) 29 is illustrated in (a) yz (b) xz (c) xy perspective.Table: selected bond distances and angles for Al(q 2 Op) 29.

Figure 3 .

 3 Figure 3.19: 1 H-NMR spectra of Al(q 2 Op) 29, HOp 3 and Hq 26 in CD 2 Cl 2 (HOp 3 in CDCl 3 ). The resonances are marked accordingly to the numbering shown in Scheme 3.9 and Scheme 3.8 (for Hq 26).

Scheme 3 . 10 :

 310 Scheme 3.10: Synthesis of Al(q 2 Trop) 30. (a) Ethanol, reflux, overnight, yield: 68%.

  Figure B.60, the main peak is corresponding to the fragment [Al(qTrop 2 )H] + (m/z= 414.08), in addition, two peaks relative to the fragments [Al(q 2 Trop)H] + (m/z= 437.09) and [Al(qTrop)] + (m/z= 292.26) are detected. The MALDI-TOF spectrum, shown in Figure 3.21, is characterized by several peaks. The most intense ones correspond to the fragments [Alq 2 ] + (m/z= 315), [Al(qTrop)] + (m/z= 292), and [Al(Trop 2 )] + (m/z= 269). An additional series of peaks, corresponding to dinuclear fragments formed by all the possible combinations of ligands from [Al 2 (qTrop 4 )] + (m/z= 682) to [Al 2 q 5 Trop] + (m/z= 774), was detected. It is clear that, besides the presence of impurities in the samples for ESI-TOF and MALDI-TOF, a recombination of ligands takes place during the ionization process to form unexpected fragments. The content of carbon, hydrogen and nitrogen, C= 69.15% H= 4.37% N= 5.69%, measured by elemental analysis is in fairly good agreement with the expected values, C= 68.80% H= 3.39% N= 6.42%.

Figure 3 .

 3 Figure 3.21: MALDI-TOF spectra of Al(q 2 Acac) 28, Al(q 2 Op) 29 and Al(q 2 Trop) 30. The main fragments are marked in the figure.

3. 3 . 31 Scheme 3 . 11 :

 331311 Scheme 3.11: Synthesis of Bis-(1-oxo-1H-phenalen-9-olate)zinc (Zn(Op) 2 ). (a) Zn(CH 3 COO) 2 , ethanol, reflux, overnight, yield: 84%.

Figure 3 .

 3 Figure 3.23: 1 H-NMR spectra of HOp 3 (blue) and Zn(Op) 2 31 (red) in THF-d 4 . The resonances are marked accordingly to the numbering shown in Scheme 3.11.

Figure 3 .

 3 Figure 3.24: MALDI-TOF spectrum of Zn(Op) 2 31. The fragment is marked in the figure.

  ) 3 solution 454 (4.4 × 10 4 ) 458 0.027 0.7 Al(Op) 3 thin film 463 583 0.014 7.1 a λ abs max = absorption maximum of the first transition band and its extinction coefficient (ǫ).b λ emi max = emission maximum. c Φ = photoluminescence quantum yield. It is determined using rhodamine 6G as a standard. d τ = luminescence lifetime.

Figure 3 .

 3 Figure 3.25 illustrates the absorption and emission spectra in diluted solution of Hq and Alq 3 and in thin film deposited onto a quartz substrate of Alq 3 . There are two bands in the absorption spectrum of Alq 3 , which are at 385 nm and at 250 nm. These bands correspond to π → π * transitions localized on the quinolinate moiety[175, 176]. As a consequence, Hq shows the same bands shifted at lowered wavelength[177]. On the contrary, the band between 300 and 350 nm, which is not visible for the free ligand, is attributed to a charge transfer metal to ligand (MLCT). In addition, since Alq 3 is formed by three quinolinates, its extinction coefficient ǫ is about threefold compared to the extinction coefficient ǫ of Hq. As an example, the extinction coefficient of the first absorption band of Alq 3 is ǫ 385 = 1.1 × 10 4 M -1 cm -1 and that of the first absorption band of Hq is ǫ 314 = 3.1 × 10 3 M -1 cm -1 . The absorption spectrum of Alq 3 in thin film is similar to that in solution, which confirms that the complex was successfully deposited onto the substrate. The slight shift of the peaks is caused by the solvatochromic effect[178, 179]. Furthermore, the emission spectrum of the film is almost identical to that in solution; the emission maximum λ emi max in solution is 517 nm and in thin film is 523 nm, only 6 nm shifted. In solution and in thin film, Alq 3 is characterized by comparable photophysical properties. In

Figure 3 .

 3 Figure 3.25: (a) Absorption (black) and fluorescence (red) spectra at room temperature in diluted DCM solution of Hq and Alq 3 . (b) Absorption (black) and fluorescence (red) spectra at room temperature in solution and in thin film of Alq 3 .

Figure 3 .

 3 Figure 3.26: (a) Absorption (black) and fluorescence (red) spectra at room temperature in diluted DCM solution of Hp 3 and Al(Op) 3 4. (b) Absorption (black) and fluorescence (red) spectra at room temperature in solution and in thin film of Al(Op) 3 4.

Figure 3 .

 3 Figure 3.27: (a) Luminescence decay at room temperature in diluted DCM solution (black) and in thin film (red) of Alq 3 . (b) Luminescence decay at room temperature in diluted DCM solution (black) and in thin film (red) of Al(Op) 3 4.

3 4 .

 4 However, in the spectra illustrated in Figure D.1 and Figure D.2 a long tail, which can be ascribed to the formation of excimers, is observed.

Figure 3 . 28 :

 328 Figure 3.28: Emission in solution of Alq 3 (yellow) and Al(Op) 3 4 (blue). Emission in thin film of Alq 3 (yellow) and Al(Op) 3 4 (brown). The emission in thin film of Al(Op) 3 4 is dramatically shifted compared to the emission in solution due to the formation of excimers.

Figure 3 .

 3 Figure 3.29: (a) Absorption (black) and fluorescence (red) spectra at room temperature in diluted DCM solution of HOp-X 5a-d. (b) Absorption (black) and fluorescence (red) spectra at room temperature in diluted DCM solution of Al(Op-X) 3 6a-d. The absorption and emission spectra in solution of the halogenated ligands HOp-X 5a-d and complexes Al(Op-X) 3 6a-d are illustrated in Figure 3.29. The absorption spectra of the halogenated derivatives are characterized by the same three bands observed in the spectra of HOp 3 and Al(Op) 3 4. Here, these three bands are slightly shifted to higher wavelengths. In the emission spectra of the halogenated ligands HOp-X 5a-d and complexes Al(Op-X) 3 6a-d, the bands are red-shifted compared to those of HOp 3 and Al(Op) 3 4. Moreover, the relative peak intensities exhibit slight variations. A second band at higher wavelength (≈600 nm) is identified in the emission spectra of the iodo derivatives HOp-I 5d and Al(Op-I) 3 6d. This band is assigned to a phosphorescence emission from the triplet state triggered by the intramolecular heavy-atom effect [183]. The presence of three iodine atoms in Al(Op-I) 3 6d results in a partially quenched fluorescence emission in favor of a more intense phosphorescence emission (see Figure 3.37).

Figure 3 .

 3 Figure 3.30 illustrates the absorption and emission spectra in solution of the substituted ligands HOp-R 15a-c and complexes Al(Op-R) 3 16a-c, in addition, the spectra of Al(Op-p) 3 16a in thin film are shown. In solution, the absorption spectra of the substituted ligands HOp-R 15a-c and complexes Al(Op-R) 3 16a-c show considerably different patterns compared to those of HOp 3 and Al(Op) 3 4.In the region between 325 and 475 nm transitions localized on the phenalenyl take place. On the contrary, in the UV region, the absorption spectra of the substituted derivatives present entirely different profiles, due to π → π * transitions localized on the aromatic substituents. In addition, the bulky substituents influence the structure of the peaks in the absorption and emission spectra. As a result, all the bands are less structured and slightly red-shifted. Out of the three substituted complexes, only Al(Op-p) 3 16a was grown onto a quartz substrate to investigate the effect of the bulky phenyl substituent on the excimers formation. The absorption spectrum in thin film resemble the spectrum in solution, confirming that the complex was deposited successfully onto the quartz substrate. In contrast, the emission in thin film is dominated by a band originating from excimers with a maximum

Figure 3 .

 3 Figure 3.30: (a) Absorption (black) and fluorescence (red) spectra at room temperature in diluted DCM solution of HOp-R 15a-c. (b) Absorption (black) and fluorescence (red) spectra at room temperature in diluted DCM solution of Al(Op-R) 3 16a-c. (c) Absorption (black) and fluorescence (red) spectra at room temperature in solution and in thin film of Al(Op-p) 3 16a.

Figure 3 .

 3 Figure 3.31: (a) Absorption (black) and fluorescence (red) spectra at room temperature in diluted DCM solution of HOba 18 and Al(Oba) 3 19. (b) Absorption (black) and fluorescence (red) spectra at room temperature in solution and in thin film of Al(Oba) 3 19.

Figure 3 .

 3 Figure 3.32: (a) Absorption (black) and fluorescence (red) spectra at room temperature in diluted DCM solution of HOp-py 22 .(b) Absorption (black) and fluorescence (red) spectra at room temperature in solid state of Al(Op-py) 3 23.

Figure 3 .Figure 3 .

 33 Figure 3.32 illustrates the absorption and emission spectra in solution of HOp-py 22. Due to the structural analogy between HOp-py 22 and Hq 26, the absorption and emission spectra of the two ligands in solution are similar. Two characteristic bands are observed in the absorption spectrum, corresponding to π → π * transitions. The emission spectrum of HOp-py 22 shows a fluorescence band at ≈475 nm. Al(Op-py) 3 23 is insoluble in all the solvents, therefore, it was impossible to measure the absorption and emission spectra in solution. Nevertheless, Al(Op-py) 3 23 was grown onto a quartz substrate and its spectra, illustrated in Figure 3.32, were recorded. The two bands observed in the absorption spectrum are related to the π → π * transitions localized on the ligands. The maximum of the emission in the thin film of Al(Op-py) 3 23 is 445 nm. The absorption and emission spectra of tropolone 24 and of Al(Trop) 3 25 in solution are illus-

Figure 3 .Figure 3 .Figure 3 . 35 :

 33335 Figure 3.35 illustrates the absorption, emission and excitation spectra of Al(q 2 Trop) 30 in solution. The absorption spectrum of Al(q 2 Trop) 30 is a combination of the absorptions of the quinolinate and tropolonate. As an example, the bands between 350 and 400 nm and between

Figure 3 . 36 :

 336 Figure 3.36: Absorption (black) and fluorescence (red) spectra at room temperature in diluted THF solution of Zn(Op) 2 31.The absorption and emission spectra of Zn(Op) 2 31 in diluted THF solution are illustrated in Figure3.36. The absorption spectrum shows the characteristic bands of the phenalenyl. More in detail, the first band between 380 and 460 nm is assigned to n → π * transitions, and the second band peaked at 350 nm is attributed to π → π * transitions. The emission spectrum of Zn(Op) 2 31 is dominated by an unstructured intense fluorescence emission band at 469 nm characterized by a long tail presumably caused by the emission of excimers which can form in solution due to the flat geometry of Zn(Op) 2 31.

3 4

 3 and Al(Trop) 3 25. As an example, the absorption peak of Al(q 2 Op) 29 at 456 nm has an extinction coefficient ǫ 456 = 1.2 × 10 4 M -1 cm -1 , which is 0.27 times that of the corresponding absorption peak for Al(Op) 3 4 at 454 nm, ǫ 454 = 4.4 × 10 4 M -1 cm -1 . Likewise, for Al(q 2 Trop) 30, the peak at 384 nm has an extinction coefficient, ǫ 384 = 8.3 × 10 3 M -1 cm -1 , which is 0.29 times the extinction coefficient of the corresponding peak at 384 nm for Al(Trop) 3 25, ǫ 384 = 2.9 × 10 4 M -1 cm -1 . At last, the absorption spectrum of Zn(Op) 2 31 was recorded in THF, and thus, it is not possible to compare its extinction coefficient ǫ with that of the corresponding ligand HOp 3 and of Al(Op) 3 4, which were characterized in DCM.

Figure 3 . 37 :

 337 Figure 3.37: Fluorescence emission in solution of the (novel) OSCs studied.

Figure 3 .

 3 Figure 3.38: (a) Cathodic cyclic voltammogram at room temperature in DCM of Hq 26 and Alq 3 . Electrolyte: TBAPF 6 . Scan rate: 100 mV s -1 . (b) Cathodic cyclic voltammogram at room temperature in DCM of HOp 3 and Al(Op) 3 4. Electrolyte: TBAPF 6 . Scan rate: 100 mV s -1 .The cathodic cyclic voltammograms of Hq 26 and Alq 3 , illustrated in Figure3.38, are both characterized by a single irreversible reduction process. The reduction of Hp 26 and Alq 3 takes place at quite negative potentials. In detail, the onset of the reduction of Hp is at -1.87 V and of Alq 3 is at -1.79 V. The small difference between the reduction potential of Hq 26 and Alq 3 clearly indicates that the electro-active species in Alq 3 is the quinolinate. As illustrated in Figure3.38, the cathodic cyclic voltammogram of HOp 3 and Al(Op) 3 4 is characterized by quasi-reversible reduction processes. The reduction potential of HOp 3 is -1.60 V, at a quite positive potential compared to that of Hq 26. Most probably, the reason is the bigger aromatic system of HOp 3, which can delocalize efficiently the additional electron. The cathodic cyclic voltammogram of Al(Op) 3 4 shows three-quasi reversible reduction waves at -1.63, -1.84 and -2.07 V. These waves correspond to the formation of the mono-, di-and trianion, where the electrons are systematically transferred to each phenalenyl. Usually, the same effect is observed in molecules with several electro-active sites in resonance[185][186][187].

Figure 3 .Figure 3 . 4 .Figure 3 .Figure 3 . 4 .

 334334 Figure 3.39 illustrates the cathodic cyclic voltammograms of the halogenated ligands HOp-X 5a-d. As expected, due to the electron-withdrawing character of the halogen atoms, the reduction potentials of the halogenated ligands HOp-X 5a-d, between -1.51 and -1.47 V, are more positive than that of HOp 3. Interestingly, the nature of the halogen atom exhibits a negligible effect on the reduction potentials. As an example, the reduction potentials of HOp-F 5a and HOp-I 5d are -1.51 Vand -1.48 V, respectively. The cathodic cyclic voltammograms of the halogenated complexes Al(Op-X) 3 6a-d are illustrated in Figure3.39. The three reduction

Figure 3 .Figure 3 . 4 .

 334 Figure 3.41: (a) Cathodic cyclic voltammogram at room temperature in DCM of HOba 18 and of Al(Oba) 3 19. Electrolyte: TBAPF 6 . Scan rate: 100 mV s -1 . (b) Cathodic cyclic voltammogram at room temperature in DCM of HOp-py 22. Electrolyte: TBAPF 6 . Scan rate: 100 mV s -1 .Figure 3.41 illustrates the cathodic cyclic voltammograms of HOba 18 and Al(Oba) 3 19. The cyclic voltammogram of HOba 18 is characterized by a single quasi-reversible reduction wave at -1.71 V, which is considerably more negative than the reduction potential of HOp 3. This is unexpected, because, as a consequence of the bigger aromatic system, HOba 18 should be able to delocalize an electron more efficiently than HOp 3. Hence, it should be characterized by a more positive reduction potential. Three quasi-reversible waves at -1.75, -1.93 and -2.15 V are shown in the cathodic cyclic voltammogram of Al(Oba) 3 19. The three consecutive reduction processes are at more negative values than those of Al(Op) 3 4.The cathodic cyclic voltammogram of HOp-py 22 is shown in Figure3.41. Unfortunately, Al(Op-py) 3 23 is insoluble in all the solvents, therefore, it was impossible to record its voltammogram. Nonetheless, from the CV of HOp-py 22 in solution some observation can be drawn. The cathodic cyclic voltammogram is characterized by a single irreversible reduction wave with an onset of -1.94 V. The negative reduction potential, most probably, arises from the separated aromatic backbone of HOp-py 22. In detail, the two separated aromatic rings have a scarce capability to delocalize the additional electron, as a consequence, the reduction potential of HOp-py 22 is more negative compared to the reduction potential of Hq 26.

Figure 3 .

 3 Figure 3.42: (a) Cathodic cyclic voltammogram at room temperature in DCM of tropolone 24 and of Al(Trop) 3 25. Electrolyte: TBAPF 6 . Scan rate: 100 mV s -1 . (b) Cathodic cyclic voltammogram at room temperature in DCM of Al(q 2 Acac) 28. Electrolyte: TBAPF 6 . Scan rate: 100 mV s -1 .

Figure 3 .

 3 Figure 3.43: (a) Cathodic cyclic voltammogram at room temperature in DCM of Al(q 2 Op) 29. Electrolyte: TBAPF 6 . Scan rate: 100 mV s -1 . (b) Cathodic cyclic voltammogram at room temperature in DCM of Al(q 2 Trop) 30. Electrolyte: TBAPF 6 . Scan rate: 100 mV s -1 .

Figure 3 . 44 :

 344 Figure 3.44: Cathodic cyclic voltammogram at room temperature in DMF of Zn(Op) 2 . Electrolyte: TBAPF 6 . Scan rate: 100 mV s -1 .

Figure 3 .

 3 Figure 3.44 illustrates the cathodic cyclic voltammogram of Zn(Op) 2 in DMF. Three reduction waves are shown with potential of -1.50, -1.81 and -2.04 V. The first two reduction, which have potentials similar to the potentials of the first two reduction of Al(Op) 3 4, are assigned to successive reduction processes involving the two phenalenyls. In contrast, the third wave is related to the reduction of Zn 2+ to Zn + . This reduction takes place at much more negative potential than the reduction of the free ion due to the stability of the complex and donor ability of the ligand [177].

Figure 3 . 45 :

 345 Figure 3.45: LUMO-HOMO energy levels calculated from the reduction potentials and the optical band-gaps of the ligands (a) and complexes (b).

3 .

 3 It was found that, in the solid state, Al(Op) 3 4 forms excimers, and thus, the photophysical properties of Al(Op) 3 4 in solution are dramatically different in relation to those in thin film. Absorption and emission spectra of the halogenated and substituted complexes, Al(Op-X) 3 6a-d and Al(Op-R) 3 16a-c, show little variations in comparison to those of the pristine Al(Op) 3 4. Interestingly, phosphorescence emission, triggered by the heavy-atom effect, was observed for Al(Op-I) 3 6d.

Figure 4 . 1 :

 41 Figure 4.1: Chemical structure of Al(Acac) 3 .

Figure 4 . 2 :

 42 Figure 4.2: Molecular orbital surfaces of the HOMO (left) and LUMO (right) and list of the bond lengths of mer-Alq 3 . The labels of the atoms are exemplary shown in green on the atoms in the molecule on the left-hand side (HOMO).

Figure 4 . 3 :

 43 Figure 4.3: Molecular orbital surfaces of the HOMO (left) and LUMO (right) and list of the bond lengths of Al(Op) 3 . The labels of the atoms are exemplary shown in green on the atoms in the molecule on the left-hand side (HOMO).A study on Al(Op) 3 by UPS and DFT-based calculations was recently reported byMüller et al. [203]. As described in Section 3.3.1, in Al(Op) 3 the ligands solely bind to the Al 3+ ion via oxygen donor atoms in the chelating moiety resulting in a symmetrical geometry. Consequently, the HOMO and LUMO of Al(Op) 3 , which are illustrated in Figure4.3, are equally distributed on the three ligands. As a result, the calculated vacuum molecular dipole of Al(Op) 3 turns out to be very small when compared to mer-Alq 3 , namely 0.086 D versus 4.45 D. Calculated HOMO and LUMO of Al(Op) 3 are at lowered energies, -5.71 eV and -2.41 eV, respectively, compared to those of mer-Alq 3 . The equivalent distribution of the molecular orbitals on the three ligands in Al(Op) 3 results, in the first place, from the symmetrical geometry of the ligand HOp (see Table3.1). Consequently, the six oxygen donor atoms arrange in an almost perfect octahedral geometry with identical calculated Al-O bond lengths, 1.896-1.897 Å. This clearly indicates that the three ligands are perfectly identical and the complex is symmetrical. Taking in account the deformation caused by solvent molecules in the crystal lattice, experimental Al-O bond lengths,

Figure 4 . 4 :

 44 Figure 4.4: Molecular orbital surfaces of the HOMO (left) and LUMO (right) and list of the bond lengths of mer-Al(Op-py) 3 . The labels of the atoms are exemplary shown in green on the atoms in the molecule on the left-hand side (HOMO).

Figure 4 . 5 :

 45 Figure 4.5: Molecular orbital surfaces of the HOMO (left) and LUMO (right) and list of the bond lengths of Al(Trop) 3 . The labels of the atoms are exemplary shown in green on the atoms in the molecule on the left-hand side (HOMO).

Figure 4 . 6 :Figure 4 . 7 :

 4647 Figure 4.6: Molecular orbital surfaces of the HOMO (left) and LUMO (right) and list of the bond lengths of Al(Acac) 3 . The labels of the atoms are exemplary shown in green on the atoms in the molecule on the left-hand side (HOMO orbital).

Figure 4 . 8 :

 48 Figure 4.8: Molecular orbital surfaces of the HOMO-2 (a), HOMO-1 (b), HOMO (c), LUMO (d), LUMO+1 (e), LUMO+2 (f) and list of the bond lengths of Al(q 2 Op). The labels of the atoms are exemplary shown in green on the atoms in the molecule on the left-hand side (HOMO orbital).

Figure 4 . 9 :

 49 Figure 4.9: Molecular orbital surfaces of the HOMO-2 (a), HOMO-1 (b), HOMO (c), LUMO (d), LUMO+1 (e) LUMO+2 (f) and list of the bond lengths of Al(q 2 Trop). The labels of the atoms are exemplary shown in green on the atoms in the molecule on the left-hand side (HOMO orbital).

Figure 4 . 10 :

 410 Figure 4.10: Morphologies of mer-Alq 3 (a), mer-Al(Op-py) 3 (c) and pseudofac-Al(q 2 Op) (e). Particular of a single molecule embedded in the morphology for mer-Alq 3 (b), mer-Al(Op-py) 3 (d) and pseudofac-Al(q 2 Op) (f).

Figure 4 . 11 :

 411 Figure 4.11: Pair correlation function g(r) of the generated morphologies for the (novel) OSCs.

Figure 4 .

 4 Figure 4.12: HOMO-LUMO energy levels estimated experimentally (red), theoretically in vacuum (black) and theoretically in environment (morphology) (green).

Figure 4 . 13 :

 413 Figure 4.13: Microscopic parameters computed for holes and electrons of the OSCs in the morphologies. (a) Energy disorder σ(E). (b) Reorganization energy λ. (c) Electronic coupling J 2 r 2 . (d) Charge carriers mobility µ.

Figure 4 . 14 :

 414 Figure 4.14: Holes transfer curve of the Al(Op) 3 -based TFT with a channel length of 100 µm. In this image, I DS and V DS are the source-drain currents. V G refers to the gate voltage. The hole mobility extrapolated by the transfer characteristics range between 0.6 × 10 -6 and 2.1 × 10 -6 cm 2 V -1 s -1

Figure 4 . 15 :

 415 Figure 4.15: Comparison of the source-drain current I DS and the leakage gate current I G from transfer characterization of the Al(Op)3 based TFT with a channel length of 100 µm. The source-drain bias V DS for this measurement is -70 V.

Figure 4 .

 4 Figure 4.16: (a) Scanning electron microscopy images of the patterned source and drain electrodes. The channel length vary from 10 µm (width to length ratio, W/L = 2000) to 100 µm (W/L = 50). (b) Schematic procedure of the TFT fabrication. Step 1: Source and drain electrodes patterning. Step 2: OTS modification. Step 3: OSC deposition. (c) Chemical structure of OTS (trichloro(octadecyl)silane).

Figure 4 .

 4 Figure 4.17: (a) Schematic representation of the ambipolar sample used in our experiments ITO/FI3 [200 nm]/Al-complex [2 µm]/Al [100 nm]. The OSC was sandwiched between a transparent ITO electrode and an aluminum electrode. A charge generation layer (CGL) of FI3 (ter(9,9'-diethylfluorene)) was inserted to increase the absorption at the N 2 laser emission wavelength (337 nm). (b) Chemical structure of FI3.

Figure 4 .

 4 Figure 4.18: (a) Schematic representation of a hole AS setup: Ag [80 nm]/Al-complex [100 nm]/MoO x [5 nm]/Ag [80 nm]. (b) Schematic representation of an electron AS setup: Al [80 nm]/Al-complex [200 nm]/Ca [30 nm]/Al [80 nm].

Figure 4 . 19 :

 419 Figure 4.19: Charge carrier mobility of electrons and holes measured for the sample ITO/FI3 [200 nm]/Alq 3 [2 µm]/Al [100 nm].Applied field F for electron mobility: 4.0 × 10 5 V cm -1 -6.5 × 10 5 V cm -1 ; for hole mobility: 4.0 × 10 5 V cm -1 -6.0 × 10 5 V cm -1 .

Figure 5 . 1 :

 51 Figure 5.1: UPS spectra of the Co/[x nm] Al(Op) 3 system (x= 0 nm, 0.5 nm, 1 nm, 1.5 nm, 2 nm, 3 nm and 5 nm). Right panel: HOMO region; the HOMO (in circle) shifts to lower energies for increasing x. Left panel: normalized low energy cut-off region; the maximal energetic shift of the lower cut-off (∆= -1.5 eV) is marked. Inset: shift of the work function (black) and of the HOMO (red, dashed) versus x; cobalt work function is 5.1 eV, energetic position of the HOMO for x= 5 nm is -3.3 eV.

Figure 5 . 2 :

 52 Figure 5.2: UPS spectrum of the Co/[5 nm] Al(Op) 3 system after subtraction of the inelastic electron background function performed according to [224] (brown). The fitting with an eight-peak function (black) provides the energetic position of the eight occupied states. The eigenvalues calculated with DFT-B3LYP are indicated with purple vertical bars. The purple continuous line represent the density of states (Gaussian broadening 0.22 eV).

3 .

 3 In the spectra, three main features are visible. The first, close to E F , is originated by the excitation of a cobalt bulk state with ∆5 symmetry [114]. As expected, its intensity decreases for increasing Al(Op) 3 coverage and vanishes at x= 2 nm. Up to 3 nm coverage, two additional features are visible. Strictly speaking, with the NT-PS we detect two HISs forming at the Co/Al(Op) 3 interface confirming that NT-PS is highly sensitive to the metal/non-metal interface [112].

Figure 5 . 3 :

 53 Figure 5.3: Normalized NT-PS spectra of the Co/[x nm] Al(Op) 3 system (x= 0 nm, 0.5 nm, 1 nm, 1.5 nm, 2 nm, 3 nm and 5 nm). The energetic positions of the two interface states HIS1 and HIS2, detectable for 1 ≤ x ≤ 3 are marked in the spectra. To extract the energetic position of the two HISs, a multi-peak fit was carried out for the Co/[1.5 nm] Al(Op) 3 system, as illustrated in Figure 5.4. The energetic positions of the two HISs, HIS1 and HIS2, are marked in Figure 5.3 by vertical lines. The energetic position of the two HISs shifts to lower energy with increasing coverage of Al(Op) 3 . As reported for the HOMO of Al(Op) 3 , described in Section 5.3, the shift is due to the interaction of the HISs with the surrounding potential of cobalt, neighboring molecules, and vacuum [223].

Figure 5 . 4 :

 54 Figure 5.4: Multi-peak fit used to extract the energetic position of HIS1 and HIS2 states, shown for the NT-PS spectrum of the Co/[1.5 nm] Al(Op) 3 system. The right y-axis indicates the relative SP of the Co/[x nm] Al(Op) 3 system, calculated as the ratio between the SP of the Co/[x nm] Al(Op) 3 and the SP of caesiated Cobalt (CsCo), measured by spin-resolved NT-PS.

5. 5

 5 Figure 5.5: 2PPE spectra of the Co/[2 nm] Al(Op) 3 system measured for photon energy from 3.02 to 3.30 eV. The secondary electron peaks (SEP) and the LUMO peaks are marked in the spectra. Inset: photo energy dependence of the LUMO energy.

Figure 5 . 6 :

 56 Figure 5.6: 2PPE spectra of the Co/[x nm] Al(Op) 3 systems (x= 0.5 nm, 1 nm, 1.5 nm, 2 nm, 3 nm and 5 nm) measured with a photon energy of 3.1 eV. The LUMO peak is marked in the spectra. Inset: thickness dependence of the spectral intensity of the LUMO.

Figure 5 . 7 :

 57 Figure 5.7: Spin-and time-resolved 2PPE spectrum of the Co/[2 nm] Al(Op) 3 system illustrated for the spin-up (N U P ) and spin-down (N DOW N ) electrons. The time delay varies between -10 000 fs and 10 000 fs. The photon energy is 3.9 eV.

Figure 5 . 8 :

 58 Figure 5.8: Lifetime of the spin-up and spin-down electrons (τ e up and τ e down , respectively) in the LUMO extracted from the spin-and time-resolved measurements of the Co/[2 nm] Al(Op) 3 system in the E * -E F energy range between 0.4 and 2.0 eV.

Figure 5 . 9 :

 59 Figure 5.9: UPS spectra of the Co/[x nm] Al(Op-py) 3 system (x= 0.7 nm, 1.4 nm, 2.1 nm and 2.8 nm). Inset: shift of the work function.

Figure 5 . 10 :

 510 Figure 5.10: Comparison between the UPS spectra of bulk Alq 3 , Al(Op) 3 , and Al(Op-py) 3 on cobalt.

Figure 5 .

 5 11, in comparison with the Co/Alq 3 interface. Eight occupied states and an interface dipole moment of ∆= -1.5 eV were determined for the Co/[5 nm] Al(Op) 3 interface. In addition, the HOMO is -3.3 eV below the Fermi energy E F and the LUMO is 1.2 eV above the Fermi energy E F . For the Co/[2.8 nm] Al(Op-py) 3 interface, a dipole moment of ∆= -1.8 eV and a HOMO -3.5 eV below the Fermi energy E F were detected.

Figure 5 . 11 :

 511 Figure 5.11: Energy level alignment of the Co/[5 nm] Al(Op) 3 and Co/[2.8 nm] Al(Op-py) 3 systems extracted from UPS and 2PPE spectra and compared to the energy level alignment of the Co/Alq 3 interface [218].

Figure 5 . 12 :

 512 Figure 5.12: Energy level alignment of the Co/[1.5 nm] Al(Op) 3 system extracted from NT-PS and 2PPE spectra and compared to the energy level alignment of the Co/Alq 3 interface [218].

Figure 6 . 1 :

 61 Figure 6.1: Chemical structure of β-diketonates and of HOp 3.

6. 3 Scheme 6 . 1 :

 361 Scheme 6.1: Synthesis of [Dy(Op) 2 Cl(HOp)(EtOH)] 32 and of [Dy(Op) 3 (HOp)] 33-[Dy(Op) 3 (EtOH)] 34. (a) NaH, DyCl 3 • 6 H 2 O, EtOH, reflux, 3 h, room temperature, overnight. (b) diisopropylamine, DyCl 3 • 6 H 2 O, EtOH, reflux, 3 h, room temperature, overnight.

Scheme 6 . 2 :Scheme 6 . 3 :

 6263 Scheme 6.2: Synthesis of a phenalenyl-based dysprosium complex 36 in anhydrous conditions. The exact structure of the complex is unknown. (a.1) HN(SiMe 3 ) 2 , n-BuLi, THF, 0 • C, 1 h. (a.2) DyCl 3 , THF, room temperature, overnight. (b) THF, reflux, overnight.

Figure 6 . 2 :

 62 Figure 6.2: (a) Molecular structure obtained by single crystal X-ray diffraction on a single crystal of [Dy(Op) 2 Cl(HOp)(EtOH)] 32. Two molecules are depicted to show the intermolecular hydrogen bond OH-Cl (2.49 Å). Hydrogen atoms non involved in hydrogen bonds are omitted for clarity. Selected bond lengths and angles are listed in Table 6.1. The crystal refinement data is reported in Table C.8. The molecular packing in the single crystal of [Dy(Op) 2 Cl(HOp)(EtOH)] 32 is illustrated in (a) yz (b) xz (c) xy perspective.

Figure 6 . 3 :

 63 Figure 6.3: (a) Molecular structure obtained by single crystal X-ray diffraction on a single crystal of [Dy(Op) 3 (HOp)] 33-[Dy(Op) 3 (EtOH)] 34. Hydrogen atoms non involved in hydrogen bonds are omitted for clarity. Selected bond lengths and angles are listed in Table 6.1. The crystal refinement data is reported in Table C.9. The molecular packing in the single crystal of [Dy(Op) 3 (HOp)] 33-[Dy(Op) 3 (EtOH)] 34 is illustrated in (a) yz (b) xz (c) xy perspective.

Figure 6 . 4 : 34 .

 6434 Figure 6.4: Paramagnetic 1 H-NMR spectra in DMSO-d 6 of the phenalenyl-based dysprosium complexes [Dy(Op) 2 Cl(HOp)(EtOH)], 32 [Dy(Op) 3 (HOp)] 33-[Dy(Op) 3 (EtOH)] 34 and 36.The paramagnetic 1 H-NMR spectra of the dysprosium complexes, obtained by the three reaction procedures described in Section 6.3, are illustrated in Figure6.4. The spectra were

Figure 6 . 5 :

 65 Figure 6.5: Paramagnetic 1 H-NMR spectra in DMSO-d 6 of the phenalenyl-based terbium complexes 37 and 38 before and after the sublimation process.

Figure 6 . 6 :

 66 Figure 6.6: MALDI-TOF spectra of the phenalenyl-based dysprosium complexes [Dy(Op) 2 Cl(HOp)(EtOH)] 32, [Dy(Op) 3 (HOp)] 33-[Dy(Op) 3 (EtOH)] 34 and 36 before and after the sublimation process. The corresponding fragment are reported next to peak. In Table 6.2 are listed the fragments and their relative intensities. The MALDI-TOF spectra (positive mode) of the dysprosium complexes, obtained by the three procedures described in Section 6.3, are illustrated in Figure 6.6. Additionally, the spectrum of 36 after the sublimation process is shown. The most intense peak, in all the spectra, is corresponding to [Dy(Op) 2 ] + (m/z= 554). This is an indication that all the complexes are, at least, including two phenalenyls around the dysprosium. The second peak, observed at m/z= 572, is relative to the fragment [Dy(Op) 2 (H 2 O)] + . The absorption of water during the preparation of the samples is usual. However, in the spectra of the dysprosium complex 36, which was prepared in anhydrous conditions, the relative intensity of the fragment [Dy(Op) 2 (H 2 O)] + , before and after the sublimation process, is considerably lowered. The next two fragments found are formed by a neutral Dy(Op) 3 core plus a metal cation, Li + or Na + ([Dy(Op) 3 Li] + , m/z= 756; [Dy(Op) 3 Na] + , m/z= 772). As a consequence of the MALDI process, these peaks are noticeable also for [Dy(Op) 2 Cl(HOp)(EtOH)]. These two fragments have

Figure 6 . 7 :

 67 Figure 6.7: MALDI-TOF spectra of the phenalenyl-based terbium complexes 37 and 38 before and after the sublimation process. The corresponding fragment are reported next to peak. In Table6.2 are listed the fragments and their relative intensities.

3 (Figure 6 . 8 :

 368 Figure 6.8: (a) Absorption spectra at room temperature of diluted DMSO solutions of [Dy(Op) 3 (HOp)] 33-[Dy(Op) 3 (EtOH)] 34, of 36, before and after the sublimation process, and of HOp 3 (for comparison). (b) Magnification of the absorption spectra in the region between 310 and 380 nm. All the spectra are normalized.To further characterize the phenalenyl-based SMMs, we have measured the absorption spectra at room temperature of diluted DMSO solutions. In detail, we were aiming to investigate the sublimable complexes. The absorption spectra of [Dy(Op) 3 (HOp)] 33-[Dy(Op) 3 (EtOH)] 34 and of 36, before and after the sublimation process, at room temperature are plotted in Figure6.8. The absorption spectra of HOp 3 has been added as a comparison. Clearly all the absorption spectra are shifted in relation to that of HOp 3, and thus, we can conclude that the spectra are not originating from the absorption of the free HOp 3. The absorption bands between 375 and 500 nm, related to n → π * transitions centered on the phenalenyl ligands (see Section 3.4.1),

Figure 6 . 9 :

 69 Figure 6.9: (a) Absorption spectra at room temperature of diluted DMSO solutions of 37, 38, before and after the sublimation process, and HOp 3 (for comparison). (b) Magnification of the absorption spectra in the region between 310 and 380 nm. All the spectra are normalized.

Figure 6 .Figure 6 .

 66 Figure 6.10: (a) Emission spectra at room temperature of diluted DMSO solutions of [Dy(Op) 3 (HOp)] 33-[Dy(Op) 3 (EtOH)] 34 and 36, before and after the sublimation process. (b) Emission spectra at room temperature of diluted DMSO solutions of 37 and 38, before and after the sublimation process.

  cm 3 K mol -1 for one Dy(III) metal ion (S=5/2, L=5, 6 H 15/2 , g=4/3) [121]. Decreasing the temperature, the χT product at 1000 Oe continuously diminishes to 8.78 cm 3 K mol -1 at 1.8 K, as illustrated in Figure 6.11. The gradual depletion of χT versus temperature is indicative of the type of paramagnetic behavior resulting from the thermal depopulation of the Stark sublevels of the 6 H 15/2 ground state or of low-lying excited states of the Dy(III) ion while decreasing the temperature [247-253].

Figure 6

 6 Figure 6.12: ac magnetic susceptibility measurements under zero dc field for [Dy(Op) 2 Cl(HOp)(EtOH)] 32. Temperature dependence of the in-phase χ′ (a) and of the out-of-phase χ′′ (b) ac magnetic susceptibility. Frequency dependence of the in-phase χ′ (c) and of the out-of-phase χ′′ (d) ac magnetic susceptibility.

Figure 6 . 13 :

 613 Figure 6.13: Arrhenius semilogaritmic plots of the relaxation time τ versus 1/T for [Dy(Op) 2 Cl(HOp)(EtOH)] 32 from ac susceptibility measurements under a zero dc field and a dc field of 200 Oe. The solid lines represent a linear fit in the thermally activated range of temperature.

Figure 6 . 14 :

 614 Figure 6.14: Frequency dependence of the in-phase χ′ (a) and of the out-of-phase χ′′ (b) ac magnetic susceptibility at 1.8 K and different dc-field for [Dy(Op) 2 Cl(HOp)(EtOH)] 32.

Figure 6 . 15 :

 615 Figure 6.15: Frequency dependence at 200 Oe of the in-phase χ′ (a) and of the out-of-phase χ′′ (b) ac magnetic susceptibility at different temperatures for [Dy(Op) 2 Cl(HOp)(EtOH)] 32.

6. 9 3 (Figure 6 . 1 6. 9 Figure 6 .

 936196 Figure 6.16: (a) Plot of χT versus T for [Dy(Op) 3 (HOp)] 33-[Dy(Op) 3 (EtOH)] 34 in the range of 1.8-300 K at 1000 Oe. (b) Plot of M versus H for [Dy(Op) 3 (HOp)] 33-[Dy(Op) 3 (EtOH)] 34 at 2 K, 4 K and 5 K The temperature dependence of the magnetic susceptibility of [Dy(Op) 3 (HOp)] 33-[Dy(Op) 3 (EtOH)]34 was measured under an applied magnetic field of 1000 Oe in the temperature range between 1.8 and 300 K. As illustrated in Figure6.16, the χT product at 300 K is 27.11 cm 3 K mol-1

Figure 6 . 18 : 34 .

 61834 Figure 6.18: Frequency dependence of the in-phase χ′ (a) and of the out-of-phase χ′′ (b) ac magnetic susceptibility at 1.8 K and different dc fields for [Dy(Op) 3 (HOp)] 33-[Dy(Op) 3 (EtOH)] 34.

Figure 6 . 19 :

 619 Figure 6.19: Frequency dependence at 1500 Oe of the in-phase χ′ (a) and of the out-ofphase χ′′ (b) ac magnetic susceptibility at different temperatures for [Dy(Op) 3 (HOp)] 33-[Dy(Op) 3 (EtOH)] 34. Frequency dependence at 3000 Oe of the in-phase χ′ (c) and of the out-of-phase χ′′ (d) ac magnetic susceptibility at different temperatures for [Dy(Op) 3 (HOp)] 33-[Dy(Op) 3 (EtOH)] 34.

  -5 s. The parameters obtained under a dc field of 1500 Oe and 3000 Oe are roughly in the same order of magnitude, indicating that the mechanism of the two relaxation processes, corresponding to the two isolated Dy(III) ions in [Dy(Op) 3 (HOp)] 33-[Dy(Op) 3 (EtOH)] 34, is most probably the same.

Figure 6 . 20 :

 620 Figure 6.20: Arrhenius semilogaritmic plots of the relaxation time τ versus 1/T for [Dy(Op) 3 (HOp)] 33-[Dy(Op) 3 (EtOH)] 34 from ac susceptibility measurements under dc fields of 1500 Oe and 3000 Oe. The solid lines represent a linear fit in the thermally activated range of temperature.

[Dy(Op) 2

 2 Cl(HOp)(EtOH)] 32 might be a SMM. [Dy(Op) 3 (HOp)] 33-[Dy(Op) 3 (EtOH)] 34 outlines a strong quantum tunneling.

4 Scheme 8 . 1 :

 481 Scheme 8.1: Al(Op) 3 4. Peaks in 1 H-NMR and 13 C-NMR spectra are labeled according to the numbering shown in the figure.

1

  H-NMR (500 MHz, CD 2 Cl 2 , 25 • C, δ(ppm)): 7.56 (d, 1H, H3), 7.49 (d, 1H, H4), 7.04 (m, 2H, H6,8), 6.93 (m, 2H, H1,9), 3.86 (s, 3H, H11), 1.67 (s, 2H, H12) . 13 C-NMR (125 MHz, CD 2 Cl 2 , 25 • C, δ(ppm)): 155.43 (C10), 142.86 (C5), 130.34 (C7), 128.84 (C2), 127.62 (C3), 127.20 (C8), 118.89 (C4), 118.72 (C9), 108.73 (C6), 106.10 (C1), 55.27 (C11).

8

  Scheme 8.2: 6-Methoxynaphthalen-2-amine 8. Peaks in 1 H-NMR and 13 C-NMR spectra are labeled according to the numbering shown in the figure.

F9

  Scheme 8.3: 2-Fluoro-6-methoxynaphthalene 9. Peaks in 1 H-NMR and 13 C-NMR spectra are labeled according to the numbering shown in the figure.

1Scheme 8 . 4 :

 84 Scheme 8.4: HOp-F 5a. Peaks in 1 H-NMR and 13 C-NMR spectra are labeled according to the numbering shown in the figure.

Scheme 8 . 5 :

 85 Scheme 8.5: Al(Op-F) 3 6a. Peaks in 1 H-NMR spectrum are labeled according to the numbering shown in the figure.

1

  H-NMR (500 MHz, CDCl 3 , 25 • C, δ(ppm)): 7.74 (ds, 1H, H8), 7.66 (m, 2H, H6,3), 7.38 (dd, 1H, H4), 7.17 (dd, 1H, H4), 7.11 (ds, 1H, H1) 3.9 (s, 3H, H11). 13 C-NMR (125 MHz, CDCl 3 , 25 • C, δ(ppm)): 157.96 (C10), 133.00 (C2), 129.64 (C7), 129.24 (C5), 128.68 (C8), 128.38 (C3), 127.31 (C4), 126.54 (C6), 119.95 (C9), 105.91 (C1), 55.50 (C11).

10 Scheme 8 . 6 :

 1086 Scheme 8.6: Synthesis of 2-chloro-6-methoxynaphthalene 10. (a) CuCl, DMF, reflux, 48 h, yield: 85%.

1Scheme 8 . 7 :

 87 Scheme 8.7: HOp-Cl 5b. Peaks in 1 H-NMR and 13 C-NMR spectra are labeled according to the numbering shown in the figure.

1

  H-NMR (500 MHz, CDCl 3 , 25 • C, δ(ppm)): 7.92 (m, 3H, H2,4), 7.14 (d, 2H, H1

Scheme 8 . 8 :

 88 Scheme 8.8: Al(Op-Cl) 3 6b. Peaks in 1 H-NMR spectrum are labeled according to the numbering shown in the figure.

15cScheme 8 . 10 :

 810 Scheme 8.9: HOp-Br 5c. Peaks in 1 H-NMR and 13 C-NMR spectra are labeled according to the numbering shown in the figure.

1

  H-NMR (500 MHz, CDCl 3 , 25 • C, δ(ppm)): 8.13 (m, 2H, H4,8), 7.89 (ds, 1H, H6), 7.64 (d, 1H, H2), 7.52 (d, 1H, H1), 6.81 (d, 1H, H9), 4.20 (s, 3H, H14).

11

  Scheme 8.11: 5-Bromo-9-methoxy-1H-phenalen-1-one 11. Peaks in 1 H-NMR spectrum are labeled according to the numbering shown in the figure.

1Scheme 8 . 12 :

 812 Scheme 8.12: HOp-I 5d. Peaks in 1 H-NMR and 13 C-NMR spectra are labeled according to the numbering shown in the figure.

6d

  Scheme 8.13: Al(Op-I) 3 6d. Peaks in 1 H-NMR spectrum are labeled according to the numbering shown in the figure.

Scheme 8 . 14 :

 814 Scheme 8.14: HOp-p 15a. Peaks in 1 H-NMR and 13 C-NMR spectra are labeled according to the numbering shown in the figure.

1

  H-NMR (500 MHz, CDCl 3 , 25

Scheme 8 . 15 :

 815 Scheme 8.15: Al(Op-p) 3 16a. Peaks in 1 H-NMR and 13 C-NMR spectra are labeled according to the numbering shown in the figure.

Scheme 8 . 16 :

 816 Scheme 8.16: HOp-n 15b. Peaks in 1 H-NMR and 13 C-NMR spectra are labeled according to the numbering shown in the figure.

16b

  Scheme 8.17: Al(Op-n) 3 16b. Peaks in 1 H-NMR and13 C-NMR spectra are labeled according to the numbering shown in the figure.

23 Scheme 8 . 23 :

 23823 Scheme 8.23: Al(Op-py) 3 23.

25 Scheme 8 . 24 :

 25824 Scheme 8.24: Al(Trop) 3 25. Peaks in 1 H-NMR and 13 C-NMR spectra are labeled according to the numbering shown in the figure.

28 Scheme 8 . 25 :

 28825 Scheme 8.25: Al(q 2 Acac) 28. Peaks in 1 H-NMR and13 C-NMR spectra are labeled according to the numbering shown in the figure.

29 Scheme 8 . 26 :

 29826 Scheme 8.26: Al(q 2 Op) 29. Peaks in 1 H-NMR spectrum are labeled according to the numbering shown in the figure.

1

  H-NMR (500 MHz, DMSO-d 6 , 25

3 ) 4 .

 34 on the left hand side, and of the facial isomer (fac-Alq 3 ) on the right end side. Source:[27]. . . . . . . 1.7 Molecular structure obtained by single crystal X-ray diffraction of mer-Alq 3 . Hatoms and solvent molecules are omitted for clarity. The crystal refinement data is reported in Table C.1. The molecular packing in the single crystal of mer-Alq 3 is illustrated in (a) yz (b) xz (c) xy perspective. Table: selected bond distances and angles for mer-Alq 3 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1.8 (a) Simplified illustration of a three-layer OLED. ETL: electron trasport layer, HTL: hole transport layer, and EML: emission layer. To obtain light emission, a voltage must be applied. (b) Schematic energy diagram of a three-layer OLED.The basic processes are illustrated. Electrons are injected from the cathode into the LUMO of the ETL and holes are injected from the anode into the HOMO of the HTL. Subsequently, the charge carriers travel across the organic layers to recombine radiatively in the emission layer. Φ A and Φ C are the work functions of the anode and cathode, respectively. Φ BI is the built-in voltage to be overcome by an external voltage V before current can flow in the device. Source:[START_REF][END_REF]. . . . 1.9 (a) Configuration of the first two Alq 3 -based OLEDs. In the device on the left, Alq 3 is the electron-transporting and emitting material, on the right, Alq 3 is the electron-transporting and host material. (b) Chemical structure of the holetransporting material TAPC and of the dopants: Coumarin 540, DMC1 and DCM2. Sources: [9, 10]. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1.10 Chemical structure of Gaq 3 (tris-(8-hydroxyquinoline)gallium) and Inq 3 (tris-(8hydroxyquinoline)indium) on the left hand side and of Znq 2 (bis-(8-hydroxyquinoline)zinc) on the right hand side. Sources: [53-57]. . . . . . . . . . . . . . . . . . . . . . . . 1.11 Chemical structure of AlOq 3 (tris-(5-hydroxymethyl-8-quinolinato)aluminum) on the left hand side and Alq(Clq) 2 (bis-(5,7-dichloro-8-quinolinato)-(8-quinolinato)aluminum) on the right hand side. Sources: [58, 59]. . . . . . . . . . . . . . . . . . . . . . . . 1.12 Chemical structures of the 5-substituted Alq 3 . In the left hand side complex the electron-rich and -poor substituents are bonded to the quinolinate by an ethynyl bridge. In the right hand side complex the electron-rich and -poor substituents are directly bonded to the quinolinate. Source:[38]. . . . . . . . . . . . . . . . . 13 1.13 Schematic energy band diagram of three types of OPVs. Left: single layer OPV. Center: planar heterojunction OPV. Right: bulk heterojunction OPV (PEDOT: poly(3,4-ethylenedioxythiophene)). Source: [60]. . . . . . . . . . . . . . . . . . . . 14 1.14 (a) Schematic representation of the working principle of a bulk heterojunction OPV. Excitons are formed by the absorption of light. At the pn-heterojunction excitons dissociate generating holes and electrons, which travel toward negative and positive electrodes, respectively. Source: [18]. (b) Typical J-V curve of OPVs: a, in dark, and b, under illumination. J SC is the short-circuit photocurrent density. V OC is the open circuit voltage. Source: [61]. . . . . . . . . . . . . . 15 1.15 (a) Schematic configuration of OPVs including Alq 3 as buffer layer. Left OPV: CuPc [30 nm]/C60 [40 nm]/Alq 3 [6 nm]. Central OPV: ZnPc [10 nm]/ZnPc:C60 [10 nm]/C60 [10 nm]/Alq 3 [5 nm]. Right tandem-OPV: ZnPc [10 nm]/ZnPc:C60 [10 nm]/C60 [10 nm]/Alq 3 [5 nm]/connecting layer/ZnPc [10 nm]/ZnPc:C60 [10 nm]/C60 [10 nm]/Alq 3 [5 nm]. (b) Chemical structure of the n-type OSC: C60 (electron acceptor), p-type OSCs: MPc (M=Zn,Cu) (electron donor), and connecting layers: SnCl 2 Pc and F 16 CuPc. Sources: [64, 65]. . . . . . . . . . . . . . . . . . . . . . . 16 1.16 Schematic drawing of a spin valve. Ferromagnetic electrodes in parallel configuration on the left hand side, and in antiparallel configuration on the right hand side. Corresponding electrical resistor models illustrated in the bottom. Source: [http://en.wikipedia.org/wiki/Giant_magnetoresistance]. . . . . . . . . . 17 1.17(a) Schematic representation of a typical vertical Alq 3 -based OSPD. Alq 3 is sandwiched between LSMO, bottom electrode, and cobalt, top electrode. (b) MR loop of a LSMO [100 nm]/Alq 3 [130 nm]/Co [3.5 nm] OSPD measured at 11 K. The magnetization configuration of the electrodes is indicated. Source: [69]. . . . . . 17 1.18 (a) Schematic representation of the Alq 3 -based OSPD device. A nanoindent is realized in the Alq 3 layer to control the organic tunnel barrier thickness. The nanohole is then filled with cobalt. LSMO is the bottom electrode and cobalt the top electrode. (b) MR curve of a LSMO/Alq 3 [2 nm]/Co OSPD measured at 2 K and -5 mV. In the inset, I(V ) curves recorded at 2 K in the parallel (I P A ) and antiparallel (I AP ) configurations. Source: [74]. . . . . . . . . . . . . . . . . . . . 18 1.19 (a) Molecular structure of ZMP (zinc methyl phenalenyl) in a neutral state and in an anionic radical. Charge transfer processes through hybridization on the ferromagnetic surface can change the chemical state of the phenalenyl from the neutral state to an anionic radical. (b) MR measurements of a device Co [8 nm]/ZMP [40 nm]/Co [12 nm] recorded at 15 mV after cooling the device to 4.2 K in a magnetic field 550 Oe. The magnetization of cobalt is shown with a red arrow. Source: [76]. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 19 1.20 (a) Schematic OFET configurations: top contact configuration (top), and bottom contact configuration (bottom). (b) Schematic representation of the source-drain current I SD in function of the source-drain voltage V SD and the gate voltage V G (a < b < c < d < e). Source: [61]. . . . . . . . . . . . . . . . . . . . . . . . . . . . 19 1.21 (a) Schematic view of the structure of Alq 3 -based ambipolar OFETs. Alq 3 -based OFETs were obtained with Ca source and drain electrodes for the n-channel device and with a bottom contact configuration with Au/Cr electrodes on a HMDS treated substrate for the p-channel device. (b) Chemical structure of PMMA (poly(methyl methacrylate)) and HMDS (hexamethyldisylazane). Source [78]. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1.22 Schematic illustration of the laterally arranged heterojunction fabrication process. A: the substrate is tilted with respect to the horizontal plane and pentacene is evaporated resulting in the layer deposition shown in B. C: the substrate is inclined in the opposite direction and Alq 3 is evaporated resulting in the final configuration shown in D. Source: [79]. . . . . . . . . . . . . . . . . . . . . . . . . 1.23 (a) Schematic representation of the trilayer LE-OFET device. Field-effect charge transport and light -generation processes are illustrated. (b) Optical micrograph of the light emission from the trilayer LE-OFET (V SD = V G = 90 V). (c) Chemical structure of the p-type OSC DH-4T (blue layer) and of the n-type OSC DFH-4T (green layer). Source:[80]. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1.24 Schematic description of the algorithm used for the calculation of energy disorder. In the first step, partial vacuum partial for each molecule are calculated. Afterward, an additional charge is assigned to a certain molecule. Partial charges of this, as well as of the neighboring molecules within a certain cut-off distance, are self-consistently re-evaluated using a cloud of point charges that are iteratively improved until convergence in total energy of the charged molecule is reached. This procedure is repeated for positive and negative additional charges on each molecule in the system. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1.25 (a) Schematic representation of a TOF setup. In the example, the organic material is sandwiched between a semi-transparent Al electrode and a transparent ITO electrode. The carriers are generated near the anode (Al electrode). Under the applied field F , electrons recombine instantaneously at the anode and holes move toward the cathode (ITO electrode). R is representing a resistance (much lower than that of the sample) and CRO is the measuring system (oscilloscope). (b) Typical experimental signal for non-dispersive OSCs on the left. Typical experimental signal for dispersive OSCs on the right, in the inset, double logaritmic plot used to extract the transit time τ . Sources: [61, 106]. . . . . . . . . . . . . . 1.26 (a) Schematic representation of an AS setup. In the example, the organic material is sandwiched between aluminum and ITO electrodes. (b) Typical AS experimental signal. f is the frequency of the applied ac excitation, C is the capacitance, C geo is the geometrical capacitance, -∆B is the negative differential capacitance, and τ r and f r are the characteristic time and frequency, respectively. Source: [106]. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1.27 (a) Schematic illustration of UPS and NT-PS. The photon sources are a vacuum ultraviolet lamp for UPS and a Ti:sapphire laser for NT-PS. The emitted photoelectrons are energy and spin selected by a spin detector based on spin polarized low-energy electron diffraction mounted on a commercial cylindrical sector analyzer. (b) Conceptual principle of UPS and NT-PS experiments. Electrons are excited by UV photons (21.2 eV or 5.95 eV) above the vacuum energy and leave the sample. The kinetic energy and spin of the electrons is analyzed by a detector (SPLEED). . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1.28 Schematic illustration of the CSA (cylindrical sector energy analyzer) and the SPLEED (spin polarized low energy electron detector). Polarized electrons are scattered on the W(001) target and detected by channeltrons positioned at the spin dependent LEED spots of the W(001) surface. . . . . . . . . . . . . . . . . . 1.29 Conceptual principle of 2PPE. An electron is excited by a photon (pump) into an intermediate state . By a second photon (probe) the electron is excited above the vacuum energy and photoemitted. . . . . . . . . . . . . . . . . . . . . . . . . 1.30 (a) Elementary excitation processes in 2PPE. There are two paths leading to the photoemission of the electron above the vacuum energy E vac : a, step-by-step one photon process, and b, and direct two-photon ionization process. (b) Kinetic energy of the photoemittied electrons E kin dependence from the pump and probe photon energy, hν pu and hν pr , respectively. Source: [115]. . . . . . . . . . . . . . 1.31 (a) Crystal structure of the first SMM [Mn 12 O 12 (OAc) 16 (H 2 O) 4 ] (Mn 12 Ac). The total spin of the molecule is S= 10 given by 4 Mn 4+ ions, S= 6 (Mn 4+ : S= 3/2) plus 8 Mn 3+ ions, S= 16 (Mn 3+ : S= 2). (b) Plot of the potential energy versus the magnetization for a SMM with S= 10 ground state. The diagram is for zero external magnetic field. Source: [118, 122, 123]. . . . . . . . . . . . . . . . . . . . 1.32 Schematic illustration of the relaxation processes of a SMM with a spin ground state S=10. The magnetization reversal can occur via quantum tunneling between energy levels (blue arrow) or by thermal relaxation by climbing up and down all the energy levels (green arrows). Source [120]. . . . . . . . . . . . . . . 1.33 Molecular structure of [LnPc 2 ] -. Hydrogens atoms are omitted. Source: [117]. . . 1.34 (a) Artistic illustration of a nuclear spin qubit transistor based on a single TbPc 2 SMM, which is coupled to source, drain, and gate (not shown) electrodes. The four anisotropic nuclear spin states of the Tb 2+ (colored circles) can be manipulated with an electric field. (b) Schematic illustration of the three coupled subsystem of the transistor. The four-level nuclear spin qubit is hyperfine coupled to an Ising-like electronic spin, which in turn is antiferromagnetic exchange coupled to a readout quantum dot. Source: [124]. . . . . . . . . . . . . . . . . . . 1.35 (a) Atomic force micrograph and schematic illustration of the TbPc 2 -based spin valve (hexyl and pyrenyl groups are omitted for clarity). The single-walled carbon nanotube lies on a SiO 2 surface supported by a back gate and is connected to palladium source and drain electrodes. (b) Schematic representation of the mechanism involving two TbPc 2 grafted on a single-walled nanotube. Increasing the magnetic field the molecule A switches leading to an antiparallel configuration of the spin valve with lowest conductance. When molecule B switches, the parallel configuration with high conductance is recovered. Source [125]. . . . . . 1.36 Idealized square-antiprismatic structure of [Ln(β-diketonate) 3 (L) n ] complexes. Structures of β-diketonates and of neutral ligands (exemplary, 2,2'-bipyridine) are illustrated. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3.1 Schematic illustration of the proton transfer in HOp 3. . . . . . . . . . . . . . . .3.2 Molecular structure obtained by single crystal X-ray diffraction on a single crystal of Al(Op) 3 4. H-atoms and solvent molecules are omitted for clarity. The crystal refinement data is reported in Table C.2. The molecular packing in the single crystal of Al(Op) 3 4 is illustrated in (a) yz (b) xz (c) xy perspective. Table: selected bond distances and angles for Al(Op) 3 4. . . . . . . . . . . . . . . . . . . 3.3 1 H-NMR spectra of HOp 3 and Al(Op) 3 4 in CDCl 3 . The resonances are marked accordingly to the numbering shown in Scheme 3.1. . . . . . . . . . . . . . . . . . 3.4 MALDI-TOF spectrum of Al(Op) 3 The fragment is marked in the figure. . . . 3.5 Molecular structure obtained by single crystal X-ray diffraction on a single crystal of HOp-Br 5c. H-atoms and solvent molecules are omitted for clarity. The crystal refinement data is reported in Table C.3. The molecular packing in the single crystal of HOp-Br 5c is illustrated in (a) yz (b) xz (c) xy perspective. . . 3.6 1 H-NMR spectra of the halogenated ligands HOp-X 5a-d in CDCl 3 . The resonances are marked accordingly to the numbering shown in Scheme 3.2. . . . . . . 3.7 1 H-NMR spectra of Al(Op-X) 3 6a-d in CDCl 3 . The resonances are marked accordingly to the numbering shown in Scheme 3.2. . . . . . . . . . . . . . . . . . 3.8 MALDI-TOF spectra of the halogenated complexes Al(Op-X) 3 6a-d. The fragments are marked in the figure. . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3.9 Molecular structure obtained by single crystal X-ray diffraction on a single crystal of HOp-pe 15c. H-atoms and solvent molecules are omitted for clarity. The crystal refinement data is reported in Table C.4. The molecular packing in the single crystal of HOp-pe 15c is illustrated in (a) yz (b) xz (c) xy perspective. .3.10 1 H-NMR spectra of the substituted ligands HOp-R 15a-c in CDCl 3 . The resonances are marked accordingly to the numbering shown in Scheme 3.4. . . . . . . 3.11 1 H-NMR spectra of the substituted complexes Al(Op-R) 3 16a-c in CDCl 3 . The resonances are marked accordingly to the numbering shown in Scheme 3.4. . . . . 3.12 MALDI-TOF spectra of Al(Op-R) 3 16a-c. The main fragments are marked in the figure. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3.13 Molecular structure obtained by single crystal X-ray diffraction on a single crystal of Al(Trop) 3 25 [165]. H-atoms and solvent molecules are omitted for clarity. The molecular packing in the single crystal of Al(Trop) 3 25 is illustrated in (a) yz (b) xz (c) xy perspective. Table: selected bond distances and angles for Al(Trop) 3 25. 3.14 1 H-NMR spectra of tropolone 24 (blue) and Al(Trop) 3 25 in CDCl 3 . The resonances are marked accordingly to the numbering shown in Scheme 3.7. . . . . . . 3.15 MALDI-TOF spectra of Al(Oba) 3 19, Al(Op-py) 3 23 and Al(Trop) 3 25. The main fragments are marked in the figure. . . . . . . . . . . . . . . . . . . . . . . . 3.16 Molecular structure obtained by single crystal X-ray diffraction on a single crystal of Al(q 2 Acac) 28 [166]. H-atoms and solvent molecules are omitted for clarity. The molecular packing in the single crystal of Al(q 2 Acac) 28 is illustrated in (a) yz (b) xz (c) xy perspective.

3.23 1

 1 H-NMR spectra of HOp 3 (blue) and Zn(Op) 2 31 (red) in THF-d 4 . The resonances are marked accordingly to the numbering shown in Scheme 3.11. . . . . . 3.24 MALDI-TOF spectrum of Zn(Op) 2 31. The fragment is marked in the figure. . . 3.25 (a) Absorption (black) and fluorescence (red) spectra at room temperature in diluted DCM solution of Hq and Alq 3 . (b) Absorption (black) and fluorescence (red) spectra at room temperature in solution and in thin film of Alq 3 . . . . . . . 3.26 (a) Absorption (black) and fluorescence (red) spectra at room temperature in diluted DCM solution of Hp 3 and Al(Op) 3 4. (b) Absorption (black) and fluorescence (red) spectra at room temperature in solution and in thin film of Al(Op) 3 4. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3.27 (a) Luminescence decay at room temperature in diluted DCM solution (black) and in thin film (red) of Alq 3 . (b) Luminescence decay at room temperature in diluted DCM solution (black) and in thin film (red) of Al(Op) 3 4. . . . . . . . . 3.28 Emission in solution of Alq 3 (yellow) and Al(Op) 3 4 (blue). Emission in thin film of Alq 3 (yellow) and Al(Op) 3 4 (brown). The emission in thin film of Al(Op) 3 4 is dramatically shifted compared to the emission in solution due to the formation of excimers. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3.29 (a) Absorption (black) and fluorescence (red) spectra at room temperature in diluted DCM solution of HOp-X 5a-d. (b) Absorption (black) and fluorescence (red) spectra at room temperature in diluted DCM solution of Al(Op-X) 3 6a-d. 3.30 (a) Absorption (black) and fluorescence (red) spectra at room temperature in diluted DCM solution of HOp-R 15a-c. (b) Absorption (black) and fluorescence (red) spectra at room temperature in diluted DCM solution of Al(Op-R) 3 16ac. (c) Absorption (black) and fluorescence (red) spectra at room temperature in solution and in thin film of Al(Op-p) 3 16a. . . . . . . . . . . . . . . . . . . . . . 4.14 Holes transfer curve of the Al(Op) 3 -based TFT with a channel length of 100 µm. In this image, I DS and V DS are the source-drain currents. V G refers to the gate voltage. The hole mobility extrapolated by the transfer characteristics range between 0.6 × 10 -6 and 2.1 × 10 -6 cm 2 V -1 s -1 . . . . . . . . . . . . . . . . . . . 118 4.15 Comparison of the source-drain current I DS and the leakage gate current I G from transfer characterization of the Al(Op)3 based TFT with a channel length of 100 µm. The source-drain bias V DS for this measurement is -70 V. . . . . . . . 118 4.16 (a) Scanning electron microscopy images of the patterned source and drain electrodes. The channel length vary from 10 µm (width to length ratio, W/L = 2000) to 100 µm (W/L = 50). (b) Schematic procedure of the TFT fabrication. Step 1: Source and drain electrodes patterning. Step 2: OTS modification. Step 3: OSC deposition. (c) Chemical structure of OTS (trichloro(octadecyl)silane). . . . 120 4.17 (a) Schematic representation of the ambipolar sample used in our experiments ITO/FI3 [200 nm]/Al-complex [2 µm]/Al [100 nm]. The OSC was sandwiched between a transparent ITO electrode and an aluminum electrode. A charge generation layer (CGL) of FI3 (ter(9,9'-diethylfluorene)) was inserted to increase the absorption at the N 2 laser emission wavelength (337 nm). (b) Chemical structure of FI3. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 121 4.18 (a) Schematic representation of a hole AS setup: Ag [80 nm]/Al-complex [100 nm]/MoO x [5 nm]/Ag [80 nm]. (b) Schematic representation of an electron AS setup: Al [80 nm]/Al-complex [200 nm]/Ca [30 nm]/Al [80 nm]. . . . . . . . . . . . . . . . . 121 4.19 Charge carrier mobility of electrons and holes measured for the sample ITO/FI3 [200 nm]/Alq 3 [2 µm]/Al [100 nm]. Applied field F for electron mobility: 4.0 × 10 5 V cm -1 -6.5 × 10 5 V cm -1 ; for hole mobility: 4.0 × 10 5 V cm -1 -6.0 × 10 5 V cm -1 . . . . . . . 122 5.1 UPS spectra of the Co/[x nm] Al(Op) 3 system (x= 0 nm, 0.5 nm, 1 nm, 1.5 nm, 2 nm, 3 nm and 5 nm). Right panel: HOMO region; the HOMO (in circle) shifts to lower energies for increasing x. Left panel: normalized low energy cut-off region; the maximal energetic shift of the lower cut-off (∆= -1.5 eV) is marked. Inset: shift of the work function (black) and of the HOMO (red, dashed) versus x; cobalt work function is 5.1 eV, energetic position of the HOMO for x= 5 nm is -3.3 eV. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 127 5.2 UPS spectrum of the Co/[5 nm] Al(Op) 3 system after subtraction of the inelastic electron background function performed according to [224] (brown). The fitting with an eight-peak function (black) provides the energetic position of the eight occupied states. The eigenvalues calculated with DFT-B3LYP are indicated with purple vertical bars. The purple continuous line represent the density of states (Gaussian broadening 0.22 eV). . . . . . . . . . . . . . . . . . . . . . . . . . . . . 128 5.3 Normalized NT-PS spectra of the Co/[x nm] Al(Op) 3 system (x= 0 nm, 0.5 nm, 1 nm, 1.5 nm, 2 nm, 3 nm and 5 nm). The energetic positions of the two interface states HIS1 and HIS2, detectable for 1 ≤ x ≤ 3 are marked in the spectra. . . . . 129 5.4 Multi-peak fit used to extract the energetic position of HIS1 and HIS2 states, shown for the NT-PS spectrum of the Co/[1.5 nm] Al(Op) 3 system. The right yaxis indicates the relative SP of the Co/[x nm] Al(Op) 3 system, calculated as the ratio between the SP of the Co/[x nm] Al(Op) 3 and the SP of caesiated Cobalt (CsCo), measured by spin-resolved NT-PS. . . . . . . . . . . . . . . . . . . . . . 130 6.19 Frequency dependence at 1500 Oe of the in-phase χ′ (a) and of the out-of-phase χ′′ (b) ac magnetic susceptibility at different temperatures for [Dy(Op) 3 (HOp)] 33-[Dy(Op) 3 (EtOH)] 34. Frequency dependence at 3000 Oe of the in-phase χ′ (c) and of the out-of-phase χ′′ (d) ac magnetic susceptibility at different temperatures for [Dy(Op) 3 (HOp)] 33-[Dy(Op) 3 (EtOH)] 34. . . . . . . . . . . . . . . . . . . . . 6.20 Arrhenius semilogaritmic plots of the relaxation time τ versus 1/T for [Dy(Op) 3 (HOp)] 33-[Dy(Op) 3 (EtOH)] 34 from ac susceptibility measurements under dc fields of 1500 Oe and 3000 Oe. The solid lines represent a linear fit in the thermally activated range of temperature. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . B.1 1 H-NMR of Al(Op) 3 4. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . B.2 13 C-NMR of Al(Op) 3 4. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . B.3 MALDI-TOF of Al(Op) 3 4. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . B.4 1 H-NMR of 8. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . B.5 13 C-NMR of 8. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . B.6 1 H-NMR of 9. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . B.7 13 C-NMR of 9. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . B.8 1 H-NMR of HOp-F 5a. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . B.9 13 C-NMR of HOp-F 5a. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . B.10 1 H-NMR of Al(Op-F) 3 6a. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . B.11 MALDI-TOF of Al(Op-F) 3 6a. . . . . . . . . . . . . . . . . . . . . . . . . . . . B.12 1 H-NMR of 10. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . B.13 13 C-NMR of 10. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . B.14 1 H-NMR of HOp-Cl 5b. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . B.15 13 C-NMR of HOp-Cl 5b. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . B.16 1 H-NMR of Al(Op-Cl) 3 6b. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . B.17 MALDI-TOF of Al(Op-Cl) 3 6b. . . . . . . . . . . . . . . . . . . . . . . . . . . . B.18 ESI-TOF of crude 5c. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . B.19 1 H-NMR of HOp-Br 5c. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . B.20 13 C-NMR of HOp-Br 5c. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . B.21 1 H-NMR of Al(Op-Br) 3 6c. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . B.22 MALDI-TOF of Al(Op-Br) 3 6c. . . . . . . . . . . . . . . . . . . . . . . . . . . . B.23 1 H-NMR of 11. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . B.24 1 H-NMR of HOp-I 5d. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . B.25 13 C-NMR of HOp-I 5d. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . B.26 1 H-NMR of Al(Op-I) 3 6d. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . B.27 MALDI-TOF of Al(Op-I) 3 6d. . . . . . . . . . . . . . . . . . . . . . . . . . . . . B.28 1 H-NMR of HOp-p 15a. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . B.29 13 C-NMR of HOp-p 15a. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

Figure B. 2 :

 2 Figure B.2: 13 C-NMR of Al(Op) 3 4.

Figure B. 3 :

 3 Figure B.3: MALDI-TOF of Al(Op) 3 4.

Figure B. 4 :

 4 Figure B.4: 1 H-NMR of 8.

Figure B. 5 :

 5 Figure B.5: 13 C-NMR of 8.

Figure B. 6 :

 6 Figure B.6: 1 H-NMR of 9.

Figure B. 7 :

 7 Figure B.7: 13 C-NMR of 9.

Figure B. 8 :

 8 Figure B.8: 1 H-NMR of HOp-F 5a.

Figure B. 9 :

 9 Figure B.9: 13 C-NMR of HOp-F 5a.

Figure B. 10 :

 10 Figure B.10: 1 H-NMR of Al(Op-F) 3 6a.

Figure B. 11 :

 11 Figure B.11: MALDI-TOF of Al(Op-F) 3 6a.

Figure B. 12 :

 12 Figure B.12: 1 H-NMR of 10.

Figure B. 13 :

 13 Figure B.13: 13 C-NMR of 10.

Figure B. 14 :

 14 Figure B.14: 1 H-NMR of HOp-Cl 5b.

Figure B. 15 :

 15 Figure B.15: 13 C-NMR of HOp-Cl 5b.

Figure B. 16 :

 16 Figure B.16: 1 H-NMR of Al(Op-Cl) 3 6b.

Figure B. 17 :

 17 Figure B.17: MALDI-TOF of Al(Op-Cl) 3 6b.

Figure B. 18 :

 18 Figure B.18: ESI-TOF of crude 5c.

Figure B. 19 :

 19 Figure B.19: 1 H-NMR of HOp-Br 5c.

Figure B. 20 :

 20 Figure B.20: 13 C-NMR of HOp-Br 5c.

Figure B. 21 :

 21 Figure B.21: 1 H-NMR of Al(Op-Br) 3 6c.

Figure B. 22 :

 22 Figure B.22: MALDI-TOF of Al(Op-Br) 3 6c.

Figure B. 23 :

 23 Figure B.23: 1 H-NMR of 11.

Figure B. 24 :

 24 Figure B.24: 1 H-NMR of HOp-I 5d.

Figure B. 25 :

 25 Figure B.25: 13 C-NMR of HOp-I 5d.

Figure B. 26 :

 26 Figure B.26: 1 H-NMR of Al(Op-I) 3 6d.

Figure B. 27 :

 27 Figure B.27: MALDI-TOF of Al(Op-I) 3 6d.

Figure B. 28 :

 28 Figure B.28: 1 H-NMR of HOp-p 15a.

Figure B. 29 :

 29 Figure B.29: 13 C-NMR of HOp-p 15a.

Figure B. 30 :

 30 Figure B.30: 1 H-NMR of Al(Op-p) 3 16a.

Figure B. 31 :

 31 Figure B.31: 1 H-NMR of Al(Op-p) 3 16a.

Figure B. 32 :

 32 Figure B.32: MALDI-TOF of Al(Op-p) 3 16a.

Figure B. 33 :

 33 Figure B.33: 1 H-NMR of HOp-n 15b.

Figure B. 34 :

 34 Figure B.34: 13 C-NMR of HOp-n 15b.

Figure B. 35 :

 35 Figure B.35: 1 H-NMR of Al(Op-n) 3 16b.

Figure B. 36 :

 36 Figure B.36: 1 H-NMR of Al(Op-n) 3 16b.

Figure B. 37 :

 37 Figure B.37: MALDI-TOF of Al(Op-n) 3 16b.

Figure B. 38 :

 38 Figure B.38: 1 H-NMR of HOp-pe 15c.

Figure B. 39 :

 39 Figure B.39: 13 C-NMR of HOp-pe 15c.

Figure B. 40 :

 40 Figure B.40: 1 H-NMR of Al(Op-pe) 3 16c.

Figure B. 41 :

 41 Figure B.41: 1 H-NMR of Al(Op-pe) 3 16c.

Figure B. 42 :

 42 Figure B.42: MALDI-TOF of Al(Op-pe) 3 16c.

Figure B. 43 :

 43 Figure B.43: 1 H-NMR of HOba 18.

Figure B. 44 :

 44 Figure B.44: 1 H-NMR of HOba 18.

Figure B. 45 :

 45 Figure B.45: MALDI-TOF of Al(Oba) 3 19.

Figure B. 46 :

 46 Figure B.46: 1 H-NMR of HOp-py 22.

Figure B. 47 :

 47 Figure B.47: 1 H-NMR of 22.

Figure B. 48 :

 48 Figure B.48: ESI-TOF of Al(Op-py) 3 23.

Figure B. 49 :

 49 Figure B.49: MALDI-TOF of Al(Op-py) 3 23.

Figure B. 50 :

 50 Figure B.50: 1 H-NMR of Al(Trop) 3 25.

Figure B. 51 :

 51 Figure B.51: 1 H-NMR of Al(Trop) 3 25.

Figure B. 52 :

 52 Figure B.52: MALDI-TOF of Al(Trop) 3 25.

Figure B. 53 :

 53 Figure B.53: 1 H-NMR of Al(q 2 Acac) 28.

Figure B. 54 :

 54 Figure B.54: 1 H-NMR of Al(q 2 Acac) 28.

Figure B. 55 :

 55 Figure B.55: ESI-TOF of Al(q 2 Acac) 28.

Figure B. 56 :

 56 Figure B.56: MALDI-TOF of Al(q 2 Acac) 28.

Figure B. 57 :

 57 Figure B.57: 1 H-NMR of Al(q 2 Op) 29.

Figure B. 58 :

 58 Figure B.58: ESI-TOF of Al(q 2 Op) 29.

Figure B. 59 :

 59 Figure B.59: MALDI-TOF of Al(q 2 Op) 29.

Figure B. 60 :

 60 Figure B.60: ESI-TOF of Al(q 2 Trop) 30.

Figure B. 61 :

 61 Figure B.61: MALDI-TOF of Al(q 2 Trop) 30.

Figure B. 62 :

 62 Figure B.62: 1 H-NMR of Zn(Op) 2 31.

Figure B. 63 :

 63 Figure B.63: MALDI-TOF of Zn(Op) 2 31.

Figure B. 64 :

 64 Figure B.64: 1 H-NMR of Dy(Op) 2 Cl • HOp • EtOH 32.

Figure B. 65 :

 65 Figure B.65: MALDI-TOF of Dy(Op) 2 Cl • HOp • EtOH 32.

Figure B. 66 :

 66 Figure B.66: 1 H-NMR of Dy(Op) 3 • HOp 33-Dy(Op) 3 • EtOH 34.

Figure B. 67 :

 67 Figure B.67: MALDI-TOF of Dy(Op) 3 • HOp 33-Dy(Op) 3 • EtOH 34.

Figure B. 68 :

 68 Figure B.68: 1 H-NMR of 36.

Figure B. 69 :

 69 Figure B.69: MALDI-TOF of 36.

Figure B. 70 :

 70 Figure B.70: 1 H-NMR of 37.

Figure B. 71 :

 71 Figure B.71: MALDI-TOF of 37.

Figure B. 72 :

 72 Figure B.72: 1 H-NMR of 38.

Figure B. 73 :

 73 Figure B.73: MALDI-TOF of 38.

Figure D. 2 :Figure D. 3 :

 23 Figure D.2: Emission in function of the concentration of Al(Op) 3 4.

Table 2 :

 2 Propriétés photo-électroniques des complexes Alq 3 et Al(Op) 3 en solution et en couche mince (substrat: quartz), mesures à température ambiante.

	Composé	λ abs max [nm] ([M -1 cm -1 ]) [nm] a (ǫ) λ emi max	b	Φ c	τ d [ns]
	Alq 3 solution Alq 3 couche mince Al(Op) 3 solution Al(Op) 3 couche mince	385 (1.1 × 10 4 ) 393 362 (9.1 × 10 4 ) 366	517 523 458 0.027 0.7 0.13 16.2 0.17 12.5 583 0.014 7.1

Table 3 :

 3 Potentiels de réduction et niveaux d'énergie HOMO et LUMO pour les OSCs analysés.

	Composé	E red 1/2 [V]	E LU M O [eV]	a E gap [eV]	b E HOM O [eV]
	mer-Alq 3 Al(Op) 3 Al(Op-F) 3 Al(Op-Cl) 3 Al(Op-Br) 3 Al(Op-I) 3 Al(Op-p) 3 Al(Op-n) 3 Al(Op-pe) 3 Al(Oba) 3 Al(Trop) 3 pseudofac-Al(q 2 Acac) pseudofac-Al(q 2 Op) pseudomer-Al(q 2 Trop) Zn(Op) 2	-1.79 c -1.63, -1.84, -2.07 -1.52, -1.70, -1.89 -1.49, -1.68, -1.86 -1.49, -1.68, -1.88 -1.50, -1.66, -1.82, -2.01 -1.62, -1.79, -2.02 -1.57, -1.80, -2.01 -1.55, -1.73, -1.94 -1.75, -1.93, -2.15 -2.10 -1.80 c -1.58, -2.08 c -2.08 -1.50, -1.81, -2.04	-3.01 -3.26 -3.35 -3.37 -3.36 -3.35 -3.28 -3.33 -3.31 -3.12 -2.78 -3.00 -3.31 -2.84 -3.38	2.82 2.67 2.59 2.60 2.60 2.58 2.54 2.56 2.49 2.68 3.14 2.87 2.67 3.11 2.77	-5.83 -5.93 -5.94 -5.97 -5.96 -5.93 -5.82 -5.89 -5.80 -5.80 -5.92 -5.87 -5.98 -5.95 -6.15

a L'énergie LUMO est déterminée à partir du premier pic de réduction mesuré par le méthode CV. b Le gap HOMO-LUMO est determiné par la bande d'absorption de plus basse énergie du spectre.

c Valeur de début de courbe.

  81 V et -2.04 V) ayant lieu sur les deux phenalenyl et, très probablement, sur le zinc. Les niveaux d'énergie des orbitales HOMO et LUMO furent estimés en se basant sur les caractérisations photo-physiques et electrochimiques. Le complexe Al(Op) 3 se caractérise par des niveaux HOMO et LUMO (-5.93 eV et -3.96 eV) plus bas que ceux du complexe Alq 3 (-5.83 eV et -3.01 eV). Les complexes halogenés et substitués Al(Op-X) 3 et Al(Op-R) 3 présentent des niveaux HOMO et LUMO similaires à ceux du complexe Al(Op) 3 (voir Table 3), contrairement au complexe Al(Oba) 3 qui lui présente des niveaux d'énergie supérieurs (-5.80 eV et -3.12 eV). Le complexe Al(Trop) 3 se singularise en ayant le niveau LUMO le plus elevé (-2.78 eV) de tous les OSCs ici etudiés, son niveau HOMO

(-5.92 eV) étant comparable à celui du composé Al(Op) 3 . Les niveaux HOMO et LUMO des complexes à ligands mixtes Al(q 2 Acac) (-5.87 eV et -3.00 eV), Al(q 2 Op) (-5.98 eV et -3.31 eV) et Al(q 2 Trop) (-5.95 eV et -2.84 eV) sont similaires à ceux des complexes Alq 3 , Al(Op) 3 et Al(Trop) 3 respectivement. Malgré sa géométrie différente, le complexe Zn(Op) 2 présente des niveaux HOMO et LUMO (-6.15 eV et -3.38 eV) proches de ceux du complexe Al(Op) 3 .

Table 4 :

 4 Niveaux HOMO and LUMO, gap HOMO-LUMO et moment dipolaire des OSCs étudiés. Ces valeurs ont été calculées pour des systèmes dans le vide ainsi que pour des systèmes déposés en couche mince.

			Vacuum				Environment
	Composé	E HOM O E LU M O E gap [eV] [eV] [eV]	P b [eV] [D] P a E HOM O E LU M O E gap [D] [eV] [eV]
	mer-Alq 3 Al(Op) 3 mer-Al(Op-py) 3 Al(Trop) 3 Al(Acac) 3 pseudofac-Al(q 2 Acac) pseudofac-Al(q 2 Op) pseudomer-Al(q 2 Trop)	-5.14 -5.71 -5.07 -5.72 -5.99 -5.29 -4.99 -5.09	-1.91 -2.41 -1.55 -1.79 -1.19 -1.74 -2.71 -2.07	3.22 4.45 3.30 0.086 3.52 4.79 3.93 0.12 4.80 0.053 3.55 1.47 2.28 6.52 3.02 5.49	-5.07 -5.41 -4.98 -5.30 -5.83 -5.16 -5.02 -4.97	-1.80 -2.22 -1.40 -1.56 -1.09 -1.67 -2.54 -1.79	3.27 5.55 3.19 1.52 3.58 5.88 3.74 1.34 4.74 0.63 3.48 2.04 2.49 7.89 3.18 6.84

a Moment dipolaire électrique dans le vide.

a Moment dipolaire électrique lorsque déposé en couche mince.

Table 1 .

 1

	Molecule	Structure	Abs. Max. [nm]
	Ethene		185
	Butadiene		215
	Octatetraene		400
	Benzene		255
	Naphthalene		315
	Anthracene		380
	Tetracene		480
	Pentacene		580

1: Molecular structure of the first three polyenes and first five polyacenes, together with the wavelength of the main absorption peak. Sources: http://photonicswiki.org,

[START_REF] Pope | Electronic processes in organic crystals and polymers[END_REF]

.

  • -96.35 • and 167.98 • -173.71 • .

1

  Introductiona brightness >1000 cd m -2 were reported at a driving voltage below 10 V. In a second experiment, Tang and VanSlyke used Alq 3 as electron-transporting and host material for fluorescent molecules (Coumarin 540, DMC1 and DCM2) resulting in a two times higher external quantum yield η EQE at an operating voltage below 10 V[10]. Acting solely as electrontransporting material in an experiment ofKim et al., Alq 3 improved the external quantum efficiency η EQE of a bilayer OLED device based on MEH-PPV (poly[2-(2-ethylhexyloxy)-5methoxy-1,4-phenylenevinylene]

  Bu 4 N][LnPc 2 ] (Ln= Dy, Tb)[126], phthalocyanine-based SMMs are the most widely studied mononuclear lanthanide SMMs. Furthermore, they are seemingly the SMMs with the most potential to be developed for surface deposition, and thus, device applications. The most common molecular structural motif is the double-decker structure, where two phthalocyanine rings sandwich a lanthanide ion with a D 4d symmetry and a square-antiprismatic coordination geometry, as illustrated in Figure1.33. The complex can be a cation, an anion, or uncharged. Phthalocyanine can be substituted using conventional organic chemistry giving rise to a number of derivatives. Phthalocyanine-based SMMs were deposited onto graphene [127], carbon nanotubes [128], copper(111) [129], and more. Among the most interesting results, pristine as well substituted TbPc 2 were used in molecular-based transistor to read single-nuclear spin [130], and, in addition, the nuclear spin could be controlled electrically[124] (seeFigure 1.34). In an another experiment, spintronic devices with carbon nanotubes as a supramolecular spin valve were built implementing TbPc 2 [125] (see Figure1.35).Besides phthalocyanines, many ligands have been employed in the synthesis of mononuclear lanthanide SMMs[117]. In the synthesis of SMMs described in Chapter 6, we have implemented

	1 Introduction
	nine complexes [

a molecule belonging to the class of the β-diketonate ligands, which are widely utilized to form SMMs. The most simple β-diketonate is 4-hydroxypent-3-en-2-one (acac), which is illustrated in Table

3

.1. Generally, β-diketonate-based SMMs are of the type [Ln(β-diketonate) 3 (L) n ],

where, uncharged ligands L (monodentate or bidentate) complete the coordination sphere of the lanthanide. This results in a neutral complex where the eight coordinating atoms are arranged in a square-antiprismatic geometry.

Table 3 .

 3 1: List of ligands used in the synthesis of the (novel) OSCs. Their respective structures and characteristics are described, Hq is added as reference (in the thicker box). X: F, Cl, Br, I. R: phenyl, naphthalenyl, phenylethynynl.

	Name	Structure	Characteristics
	Hq	N
		OH

Table 3 .

 3

	Name	Structure	Characteristics
	Alq 3	O N	N O Al	O N

2: List of (novel) OSCs synthesized. Their respective structures and characteristics are described, Alq 3 is added as reference (in the thicker box). X: F, Cl, Br, I. R: phenyl, naphthalenyl, phenylethynynl.

  Oba) 3 , which are schematically illustrated in Scheme 3.5. The purification of one isomer by separation methods was impossible, and thus, we were unable to grow high quality single crystals for single crystal X-ray diffraction. Moreover, was impossible to record clear NMR spectra of Al(Oba) 3 19. However, the carbon and proton content measured by elemental analysis, C= 76.48% and H= 5.05%, is in a fairly good agreement with the calculated values, C= 76.68% and H= 3.92% (see Table3.3). In

1

H-NMR spectrum (see Figure

B.43

) is at 15.87 ppm, which is similar to that of H9 in HOp 3 (see Section 3.3.1). This indicates that H18 is involved in a fast proton transfer between the two oxygens at room temperature. In the spectrum, resonances relative to the aromatic hydrogens are between 7.37 and 8.37 ppm. Due to the asymmetric nature of HOba 18, Al(Oba) 3 19 can form two different geometrical configurations, mer-Al(Oba) 3 and fac-Al(addition, the MALDI-TOF spectrum, illustrated in Figure

3

.15, is characterized by a single peak corresponding to the fragment [Al(Oba) 2 ] + . We can assume the formation of Al(Oba) 3 19 is unambiguously proved.

  Al(Op-py) 3 in all the common solvents is too low to run solution-based characterization methods. Nonetheless, by both ESI-TOF measurements on the crude reaction (see FigureB.48) and MALDI-TOF measurements on the precipitate (see Figure3.15), the fragment corresponding to the cation [Al(Op-py) 2 ] + was detected, and thus, we can assume the formation of Al(Op-py) 3 23. Furthermore, the carbon, hydrogen and nitrogen content measured by elemental analysis, C= 67.48%, H= 4.59% and N= 7.13%, is in a good agreement with the expected values for Al(Op-py) 3 23, C= 67.00%, H= 5.12% and N= 7.10% (see Table3.3).

al.

[157]

. Moreover, in an earlier work, the ligand HOp-py 22 was used to form lithium derivatives to be implemented as electron injection layers in OLEDs

[158]

. HOp-py 22 is obtained by a coupling reaction between 2-hydroxybenzenboronic acid 20 and 2-bromopyridine 21 with a yield of ≈68%. To form the aluminum complex, we reacted HOp-py 22 with Al(CH 3 ) 3 , which was formerly used to obtain complexes with similar ligands

[159, 160]

. The overall yield of the synthesis of Al(Op-py) 3 23 is ≈50%.

HOp-py 22 is characterized by a strong intramolecular hydrogen bond involving H12 (according to Scheme 3.6), and thus, in 1 H-NMR, its resonance is at 14.36 ppm (see

Figure B.46)

. Additionally, resonances of aromatic hydrogens are between 6.90 and 8.42 ppm. Since HOp-py 22 is asymmetric, as Alq 3 (see Section 1.2), Al(Op-py) 3 23 can occur in two geometrical isomers, mer-Al(Op-py) 3 and fac-Al(Op-py) 3 . However, as described for Alq 3 , and reported for HOppy 22 complexes with trivalent metals [161-163], the mer-isomer is normally formed. Hence, we have assumed that mer-Al(Op-py) 3 is the predominant species. The solubility of mer-

  Acac) 28 is formed with a yield of ≈71% by the reaction between one equivalent of Al(CH 3 ) 3 and two equivalents of Hq 26. Subsequently, the coordination sphere was completed by adding one equivalent of Acac 27. Suitable single crystals were grown for single crystal X-ray diffraction measurements. The cell parameters were compared with those reported by Montes et al. to confirm the structure[166]. The molecular structure obtained single crystal X-ray diffraction is illustrated in Figure3.16. Despite the introduction of a symmetric moiety such as Acac 27, Al(q

	(a)	(b)	(c)
	Bond	Length [Å] Bond angle Angle [ • ] Bond angle Angle [ • ]
	Al(q 2 Acac) 28 Al1-O1 1.8549(14) O1-Al1-O2 169.80(7) O2-Al1-N2 82.32(6)
	Al1-O2 1.8530(14) O1-Al1-O3 90.36(6)

28,

was previously synthesized and studied for application in OLEDs

[167, 168]

. Furthermore, several quinoline-based mixed-ligands aluminum complexes have been synthesized and studied in former works

[START_REF] Li | Organic Light-Emitting Materials and Devices[END_REF][169][170][171]

]. To synthesize the coordination complex Al(q 2 Acac) 28, we have implemented a modified version of the procedure described by Yamaguchi et al.

[172]

. As illustrated in Scheme 3.8, Al(q 2 2 Acac) 28 can form two geometrical isomers. In the pseudomer-isomer the two axial nitrogens are facing each other. Conversely, in the pseudofacisomer the two neighboring nitrogens are facing two oxygens. As illustrated in Figure

3

.16, pseudofac-Al(q 2 Acac) 28 is obtained by the synthetic procedure implemented. Since Hq 26

  Op) 29 7.06 7.50 7.06 8.23 7.34 8.68 6.96 8.09 8.04 7.58

							[ppm]
		H1	H2	H3	H5	H6	H7	H1	H2	H4	H5
	Hq 26	7.36 7.47 7.16 8.20 7.47 8.79	-	-	-	-
	HOp 3	-	-	-	-	-	-	7.19 8.11 8.03 7.61
	Al(q 2

  30 the six chelating atoms are arranged in a distorted octahedral geometry with bond angles of 81.19-98.51 • and 170.60-172.81 • . However, the geometry has a plane of symmetry, which lies on the N-O-N angle and cuts in half the tropolonate. Trop) 30. H-atoms and solvent molecules are omitted for clarity. The crystal refinement data is reported in Table C.6. The molecular packing in the single crystal of Al(q 2 Trop) 30 is illustrated in (a) yz (b) xz (c) xy perspective. Table: selected bond distances and angles for Al(q 2 Trop) 30.

	As a consequence, the angles O1-Al-O2 and O1a-Al-O2a (170.60 • ) are identical as well as the angles O1-Al-N1 and O1a-Al-N1a (92.98 • ), O1-Al-O2a and O1a-Al-O2 (90.27 • ), O1-Al-N1a and O1a-Al-N1 (92.48 • ), O2-Al-N1 and O2a-Al-N1a (83.44 • ), and O2-Al-N1a and O2a-Al-N1 (91.85 • ). Similarly, the bond lengths Al-O1 and Al-O1a (1.909 Å) are equivalent as the bond lengths Al-O2 and Al-O2a (1.863 Å) and Al-N1 and Al-N1a (1.993 Å). Since in pseudomer-Al(q 2 Trop) 30 the two nitro-(b) (c) Bond Length [Å] Bond angle Angle [ • ] Bond angle Angle [ • ] Al(q 2 Trop) 30 Al1-O1 1.909(3) O1-Al1-O1a 81.19(13) O1a-Al1-N1a 92.98(13) Al1-O1a 1.909(3) O1-Al1-O2 170.60(14) O2-Al1-O2a 98.51(14) Al1-O2 1.863(3) O1-Al1-O2a 90.27(12) O2-Al1-N1 83.44(12) Al1-O2a 1.863(3) O1-Al1-N1 92.98(13) O2-Al1-N1a 91.85(12) Al1-N1 1.993(3) O1-Al1-N1a 92.48(13) O2a-Al1-N1 91.85(12) Al1-N1a 1.993(3) O1a-Al1-O2 90.27(12) O2a-Al1-N1a 83.44(12) O1a-Al1-O2a 170.60(14) N1-Al1-N1a 172.81(16) O1a-Al1-N1 92.48(13) Figure 3.20: Molecular structure obtained by single crystal X-ray diffraction on a single crystal gens are facing each other, the bond lengths Al-N result shorter than those of mer-Alq (a) of Al(q 2

3

(see Section 1.2). Furthermore, the bond lengths Al-N in pseudomer-Al(q 2 Trop) 30 are shorter than those of pseudofac-Al(q 2 Acac) 28 and those of pseudofac-Al(q 2 Op) 29. On the contrary, the Al-O bond lengths in pseudomer-Al(q 2 Trop) 30, 1.863-1.909 Å, are slightly longer than those of

  Molecular structure obtained by single crystal X-ray diffraction on a single crystal of Zn(Op) 2 31. H-atoms and solvent molecules are omitted for clarity. The crystal refinement data is reported in Table C.7. The molecular packing in the single crystal of Zn(Op) 2 31 is illustrated in (a) yz (b) xz (c) xy perspective. Table: selected bond distances and angles for Zn(Op) 2 31.

	31 180.00 88.49(10) O2-Zn1-O2a O1a-Zn1-O3a 91.81(11) 180.00 91.51(10) O2-Zn1-O3 89.64(11) 91.81(11) O2-Zn1-O3a 90.36(11) 88.19(11) O2a-Zn1-O3 90.36(11) 91.51(10) O2a-Zn1-O3a 89.64(11) O1a-Zn1-O2a 88.49(10) O3-Zn1-O3a O1-Zn1-O1a O1-Zn1-O2 O1-Zn1-O2a O1-Zn1-O3 O1-Zn1-O3a O1a-Zn1-O2 180.00(16) O1a-Zn1-O3 88.19(11) Resonances [ppm] H1 H2 H4 H5 H9 Figure 3.22: Compound Zn1-O1 2.012(2) Zn1-O1a 2.012(2) Zn1-O2 2.016(3) Zn1-O2a 2.016(3) Zn1-O3 2.186(3) Zn1-O3a 2.186(3) HOp 3

7.19 8.11 8.03 7.61 16.05 Zn(Op) 2 31 7.14 8.01 7.96 7.51 -

Table 3 .

 3 3: Carbon, hydrogen and nitrogen content of the synthesized complexes measured by elemental analysis. The calculated values are listed for comparison.

	Compound	Experimental		Calculated
		C [%] H [%] N [%] C [%] H [%] N [%]
	Al(Op) 3 Al(Op-F) 3 + 2H 2 O 4 + 4H 2 O 6a Al(Op-Cl) 3 + 2H 2 O 6b Al(Op-Br) 3 + H 2 O 6c Al(Op-I) 3 + H 2 O 6d Al(Op-p) 3 + 3H 2 O 16a Al(Op-n) 3 + 5H 2 O 16b Al(Op-pe) 3 + 4H 2 O 16c 76.43 72.29 63.97 62.65 54.53 46.81 76.58 76.54 Al(Oba) 3 76.84 + 2H 2 O 19 Al(Op-py) 3 67.48 + 3H 2 O 23 64.57 Al(Trop) 3 25 65.98 Al(q 2 Acac) 28 72.17 Al(q 2 Op) 29 69.15 Al(q 2 Trop) 30 Zn(Op) 2 • 2 H 2 O 31 63.53	4.01 3.53 3.18 2.57 2.41 4.36 4.60 5.79 5.05 4.59 3.83 4.38 3.97 4.37 4.12	---------7.13 -6.55 5.31 5.69 -	72.00 63.41 62.29 54.01 46.46 76.49 76.65 76.81 76.68 67.00 64.61 66.66 72.93 68.80 63.49	4.19 3.56 2.96 2.33 2.00 4.40 4.58 4.20 3.92 5.12 3.88 4.63 3.76 3.39 3.70	---------7.10 -6.76 5.49 6.42 -

Table 3 .

 3

4: Photophysical properties recorded at room temperature for Alq 3 and Al(Op) 3 4 in solution and in thin film deposited on quartz. Compound λ abs max a

  Solution 295 (2.1 × 10 4 ), 356 (2.1 × 10 4 ), 424 (7.5 × 10 3 ), 448 (7.9 × 10 3 ) 491 HOp-pe, 15c Solution 298 (7.8 × 10 4 ), 356 (2.1 × 10 4 ), 424 (7.5 × 10 3 ), 448 (7.9 × 10 3 )

			]
	Hq, 26 HOp, 3	Solution Solution 235 (2.6 × 10 3 ) 243 (4.7 × 10 4 ), 314 (3.1 × 10 3 )	468 484
	HOp-Br, 5c Hp-I, 5d HOp-p, 15a HOp-n, 15b 491 461, 483 Solution 248 (4.0 × 10 4 ), 350 (2.6 × 10 4 ), 425 (9.7 × 10 3 ), 450 (1.0 × 10 4 ) Solution 251 (3.4 × 10 4 ), 352 (2.3 × 10 4 ), 426 (8.0 × 10 3 ), 452 (8.9 × 10 3 ) 465, 485, 600 480 Solution 277 (4.8 × 10 4 ), 356 (2.1 × 10 4 ), 429 (7.0 × 10 3 ), 454 (7.6 × 10 3 )
	HOba, 18 HOp-py, 22 Tropolone, 24 Solution Solution 235 (4.9 × 10 4 ), 358 (2.2 × 10 4 ), 434 (8.2 × 10 3 ), 459 (9.1 × 10 3 ) Solution 257 (3.7 × 10 3 ), 320 (2.7 × 10 3 ) 320 (9.5 × 10	486 470

4

), 351 (1.8 × 10 4 ), 415 (7.9 × 10 3 ), 439 (9.0 × 10 3 ) 446, 470 HOp-F, 5a Solution 236 (1.8 × 10 4 ), 347 (1.6 × 10 4 ), 426 (6.7 × 10 3 ), 451 (6.9 × 10 3 ) 460, 483 HOp-Cl, 5b Solution 245 (3.1 × 10 4 ), 349 (2.0 × 10 4 ), 425 (7.7 × 10 3 ), 451 (8.2 × 10 3 ), 353 (5.6 × 10 3 ), 370 (5.3 × 10 3 ) 462

  × 10 4 ), 256 (5.4 × 10 4 ), 361 (2.2 × 10 4 ), 429 (8.7 × 10 3 ), 456 (1.2 × 10 4 ) 463, 486 a Al(q 2 Trop), 30 Solution 246 (4.7 × 10 4 ), 320 (1.3 × 10 4 ), 376 (9.0 × 10 3 ), 384 (8.3 × ) 489 a Zn(Op) 2 , 31 Solution 351 (2.4 × 10 4 ), 414 (9.4 × 10 3 ), 439 (1.1 × 10 4 ) 469

		]
	Alq 3 Alq 3 Al(Op) 3 , 4 Al(Op) 3 , 4 Al(Op-F) 3 , 6a Al(Op-Cl) 0 × ) Solution 244 (9.7 × 10 4 ), 259 (1.4 × 10 5 ), 385 (1.1 × 10 4 ) Thin film 266, 393 Solution 244 (9.3 × 10 4 ), 362 (9.1 × 10 4 ), 427 (3.5 × 10 4 ), 454 (4.4 × ) Thin film 244, 366, 435, 463 Solution 244 (9.4 × 10 4 ), 358 (9.0 × 10 4 ), 440 (4.1 × 10 4 ), 469 (5.1 × ) Thin film 287, 368, 452, 470 Al(Op-p) 3 , 16a Al(Op-n) 3 , 16b Solution 297 (9.3 × 10 4 ), 366 (9.9 × 10 4 ), 438 (2.4 × 10 4 ), 464 (2.9 × ) Al(Op-pe) 3 , 16c Solution 308 (2.0 × 10 5 ), 363 (1.2 × 10 5 ), 448 (2.9 × 10 4 ), 475 (3.6 × ) Al(Oba) 3 , 19 Solution 236 (1.5 × 10 5 ), 372 (4.9 × 10 4 ), 426 (4.7 × 10 4 ), 452 (5.1 × ) Thin Film 240, 378, 432, 481 Al(Oba) 3 , 19 Thin Film 274, 358 Al(Op-py) 3 , 23 Al(Trop) 3 , 25 Solution 242 (1.1 × 10 5 ), 327 (4.8 × 10 4 ), 375 (3.0 × 10 4 ), 384 (2.9 × ) Al(q 2 Acac), 28 Solution 257 (1.3 × 10 5 ), 296 (3.4 × 10 4 ), 374 (8.0 × 10 3 ) Al(q 2 Op), 29 Solution 246 (5.2	517 523 458, 486 583 473, 504 486 537 492 493 461, 486 591 445 456 512

3 , 6b Solution 253 (1.2 × 10 5 ), 359 (1.0 × 10 5 ), 439 (4.0 × 10 4 ), 467 (4.8 × ) 472, 502 Al(Op-Br) 3 , 6c Solution 255 (1.4 × 10 5 ), 359 (1.0 × 10 5 ), 439 (3.9 × 10 4 ), 467 (4.6 × ) 474, 502 Al(Op-I) 3 , 6d Solution 259 (1.5 × 10 5 ), 361 (1.2 × 10 5 ), 440 (3.8 × 10 4 ), 468 (4.8 × ) 478, 504, 571 Al(Op-p) 3 , 16a Solution 284 (1.7 × 10 5 ), 364 (1.0 × 10 4 ), 443 (2.6 × 10 4 ), 470 (3.

Table 3 .

 3 7: Reduction potentials and HOMO and LUMO energy levels determined experimentally and HOMO and LUMO energy levels calculated with a B3-LYP[83]/def2-TZVPP [90] level of theory.

			Experimental		Calculated
	Compound	E red 1/2 [V]	E LU M O [eV]	a E gap [eV]	b E HOM O E LU M O E gap E HOM O [eV] [eV] [eV] [eV]
	Hq, 26	-1.87 c -2.93	3.49	-6.42	-1.72	4.25	-5.97
	HOp, 3	-1.60	-3.25	2.76	-6.01	-2.71	3.57	-6.28
	HOp-F, 5a	-1.51	-3.38	2.68	-6.06	-2.91	3.42	-6.34
	HOp-Cl, 5b	-1.48	-3.39	2.67	-6.06	-2.93	3.43	-6.36
	HOp-Br, 5c	-1.47	-3.40	2.68	-6.08	-2.94	3.43	-6.37
	Hp-I, 5d	-1.48	-3.40	2.65	-6.05	-2.93	3.39	-6.32
	HOp-p, 15a	-1.57	-3.30	2.61	-5.91	-2.71	3.37	-6.09
	HOp-n, 15b -1.55	-3.32	2.64	-5.96	-2.72	3.27	-5.99
	HOp-pe, 15c -1.54	-3.34	2.56	-5.90	-2.79	3.13	-5.92
	HOba, 18	-1.71	-3.16	2.77	-5.93	-2.53	3.55	-6.08
	HOp-py, 22	-1.94 c -2.86	3.49	-6.35	-1.57	4.31	-5.88
	Tropolone, 24 -2.06 c -2.74	3.10	-5.84	-2.21	4.16	-6.37

a LUMO energy is determined by the onset of the first reduction wave recorded in the CV measurements.

b HOMO-LUMO gap is determined by the onset of the lowest visible absorption band. c Onset value.

Table 3 .

 3 8: Reduction potentials and HOMO and LUMO energy levels of the (novel) OSCs.

	Compound	E red 1/2 [V]	E LU M O [eV]	a E gap [eV]	b E HOM O [eV]
	Alq 3 Al(Op) 3 , 4 Al(Op-F) 3 , 6a Al(Op-Cl) 3 , 6b Al(Op-Br) 3 , 6c Al(Op-I) 3 , 6d Al(Op-p) 3 , 16a Al(Op-n) 3 , 16b Al(Op-pe) 3 , 16c Al(Oba) 3 , 19 Al(Trop) 3 , 25 Al(q 2 Acac), 28 Al(q 2 Op), 29 Al(q 2 Trop), 30 Zn(Op) 2 , 31	-1.79 c -1.63, -1.84, -2.07 -1.52, -1.70, -1.89 -1.49, -1.68, -1.86 -1.49, -1.68, -1.88 -1.50, -1.66, -1.82, -2.01 -1.62, -1.79, -2.02 -1.57, -1.80, -2.01 -1.55, -1.73, -1.94 -1.75, -1.93, -2.15 -2.10 -1.80 c -1.58, -2.08 c -2.08 -1.50, -1.81, -2.04	-3.01 -3.26 -3.35 -3.37 -3.36 -3.35 -3.28 -3.33 -3.31 -3.12 -2.78 -3.00 -3.31 -2.84 -3.38	2.82 2.67 2.59 2.60 2.60 2.58 2.54 2.56 2.49 2.68 3.14 2.87 2.67 3.11 2.77	-5.83 -5.93 -5.94 -5.97 -5.96 -5.93 -5.82 -5.89 -5.80 -5.80 -5.92 -5.87 -5.98 -5.95 -6.15

a LUMO energy is determined by the onset of the first reduction wave recorded in the CV measurements. b HOMO-LUMO gap is determined by the onset of the lowest visible absorption band.

c Onset value.

  Trop) 30 are similar to those of Alq 3 , Al(Op) 3 4 and Al(Trop) 3 25, respectively. Despite the different geometry, the HOMO and LUMO of Zn(Op) 2 31 are close to those of Al(Op) 3 ALOP 3 .

(Op) 3 4 is characterized by both lowered HOMO and LUMO compared to Alq 3 . The halogenated and substituted complexes Al(Op-X) 3 6a-d and Al(Op-R) 3 16a-c show similar HOMO and LUMO energy levels to those of Al(Op) 3 4. On the contrary, Al(Oba) 3 19 presents higher HOMO and LUMO. Al(Trop) 3 25 is characterized by the highest LUMO (among the studied OSCs) and a LUMO comparable to that of Al(Op) 3 4. The HOMO and LUMO of the mixed-ligands complexes Al(q 2 Acac) 28, Al(q 2 Op) 29, and Al(q 2

Table 4 .

 4 1 lists all the findings.

	Bond Length [Å] Bond Length [Å]
	Al-N1	2.084	Al-O1	1.857
	Al-N2	2.065	Al-O2	1.883
	Al-N3	2.127	Al-O3	1.881

Table 3 .

 3

	Bond Length [Å] Bond Length [Å]
	Al-N1	2.102	Al-O1	1.831
	Al-N2	2.114	Al-O2	1.813
	Al-N3	2.291	Al-O3	1.819

1)

. Consequently, the six oxygen donor atoms arrange in an almost perfect octahedral geometry with identical calculated Al-O bond lengths, 1.896-1.897 Å. This clearly indicates that the three ligands are perfectly identical and the complex is symmetrical. Taking in account the deformation caused by solvent molecules in the crystal lattice, experimental Al-O bond lengths, determined by single crystal X-ray diffraction between 1.867 and 1.882 Å (see Section 3.3.1), are in good agreement with those calculated.

  Å, respectively, are longer than Al-O3 and Al-O4, 1.878 and 1.879 Å, respectively. This, together with the electrostatic repulsion between the chelating atoms, results in a slightly distorted octahedral geometry. Experimentally, the O(acac)-Al bond lengths are 1.8765 and 1.8816 Å, the O(quinolinate)-Al bond lengths are 1.8549 and 1.8530 Å, the nitrogen-aluminum bond lengths are 2.0464 and 2.0738 Å, and the six chelating atoms are arranged in a distorted octahedral geometry [166] (see3.3.7). Experimental and theoretical results are in fairly good agreement, considering the deformation effect caused by solvent molecules in the crystal lattice.

Table 4 .

 4 1: HOMO and LUMO energy levels, HOMO-LUMO gaps and dipole moments of the OSCs calculated in vacuum and in the generated morphologies.

			Vacuum				Environment
	Compound	E HOM O E LU M O E gap [eV] [eV] [eV]	P a [eV] [D] P a E HOM O E LU M O E gap [D] [eV] [eV]
	mer-Alq 3 Al(Op) 3 mer-Al(Op-py) 3 Al(Trop) 3 Al(Acac) 3 pseudofac-Al(q 2 Acac) pseudofac-Al(q 2 Op) pseudomer-Al(q 2 Trop)	-5.14 -5.71 -5.07 -5.72 -5.99 -5.29 -4.99 -5.09	-1.91 -2.41 -1.55 -1.79 -1.19 -1.74 -2.71 -2.07	3.22 4.45 3.30 0.086 3.52 4.79 3.93 0.12 4.80 0.053 3.55 1.47 2.28 6.52 3.02 5.49	-5.07 -5.41 -4.98 -5.30 -5.83 -5.16 -5.02 -4.97	-1.80 -2.22 -1.40 -1.56 -1.09 -1.67 -2.54 -1.79	3.27 5.55 3.19 1.52 3.58 5.88 3.74 1.34 4.74 0.63 3.48 2.04 2.49 7.89 3.18 6.84

a Electrical dipole moment.

Table 4 .

 4 2: Microscopic parameters calculated for holes and electrons in the morphologies of the studied OSCs. Acac) 0.15 8.85 × 10 -3 0.19 0.16 1.21 × 10 -2 0.29 pseudofac-Al(q 2 Op) 0.24 1.22 × 10 -2 0.27 0.24 6.05 × 10 -3 0.49 pseudomer-Al(q 2 Trop) 0.23 1.10 × 10 -2 0.26 0.21 1.77 × 10 -2 0.42

			Holes			Electrons
	Compound	σ a	J 2 r 2 b	λ c	σ a	J 2 r 2 b	λ c
		[eV]	[eV 2 Å 2 ]	[eV] [eV]	[eV 2 Å 2 ]	[eV]
	mer-Alq 3 Al(Op) 3 mer-Al(Op-py) 3 Al(Trop) 3 Al(Acac) 3 pseudofac-Al(q 2	0.19 1.10 × 10 -2 0.33 0.18 1.34 × 10 -2 0.28 0.14 4.42 × 10 -3 0.055 0.17 7.05 × 10 -3 0.060 0.16 6.06 × 10 -3 0.39 0.19 9.51 × 10 -3 0.25 0.21 8.32 × 10 -3 0.23 0.20 1.08 × 10 -2 0.11 0.10 1.52 × 10 -2 0.12 0.12 5.87 × 10 -3 0.12

a Energetic disorder σ.

b Electronic coupling J 2 r 2 . c Reorganization energy λ.

Table 4 . 3

 43 Op) 8.32 × 10 -12 2.43 × 10 -13 pseudomer-Al(q 2 Trop) 2.64 × 10 -11 3.27 × 10 -10

	Compound	Mobility µ
		[cm 2 V -1 s -1 ]
		Holes	Electrons
	mer-Alq 3 Al(Op) 3 mer-Al(Op-py) 3 Al(Trop) 3 Al(Acac) 3 pseudofac-Al(q 2 Acac) pseudofac-Al(q 2	3.26 × 10 -8 1.42 × 10 -4 5.67 × 10 -7 4.70 × 10 -10 2.62 × 10 -8 9.23 × 10 -8 9.49 × 10 -6 6.64 × 10 -8 8.57 × 10 -3 6.31 × 10 -4 1.59 × 10 -5 4.68 × 10 -6

: Calculated charge carrier mobilities µ of the (novel) OSCs.

Table 6 . 2 :

 62 List of the fragments detected in the MALDI-TOF experiments for the phenalenyl-based dysprosium complexes [Dy(Op) 2 Cl(HOp)(EtOH)], 32, [Dy(Op) 3 (HOp)] 33-[Dy(Op) 3 (EtOH)] 34 and 36 before and after the sublimation process and for the phenalenylbased terbium complexes 37 and 38 before and after the sublimation process.

		Fragment					m/z		Rel. Intensity [%]
										32	33-34	36 (Aft. Sub.)
		554 100.0 572 14.9 756 2.5 772 5.0 945 7.1 1301 7.8 5.0 [Dy 2 (Op) 6 (H 2 Op)] + 1693 [Dy(Op) 2 ] + [Dy(Op) 2 (H 2 O)] + [Dy(Op) 3 Li] + [Dy(Op) 3 Na] + [Dy(Op) 3 (H 2 Op)] + [Dy 2 (Op) 5 ] + 37	100.0 18.2 <2.0 <2.0 20.2 5.1 10.1 38 (Aft. Sub.)	100.0 (100.0) 2.2 (3.8) 3.8 (14.4) 2.0 (5.5) 4.0 (4.4) 3.9 (4.1) <2.0 (2.0)
		[Tb(Op) 2 ] + [Tb(Op) 2 (H 2 O)] + [Tb(Op) 3 Li] + [Tb 2 (Op) 5 ] +		549 100.0 100.0 (100.0) 567 2.3 5.8 (4.0) 751 <2.0 4.9 (31.4) 1293 <2.0 12.1 (3.0)
	6.7 Photophysical studies
		[Dy(Op)
				38 Sublimed			HOp
	1,0
	0,8
	0,6
	0,4
	0,2
	0,0
	275	300	325	350	375	400	425	450	475	500

Al(Op) 3 4.

  HOp 3 (1.02 g, 5.2 mmol) was dissolved in 50 ml of freshly distilled toluene, AlCl 3 (0.21 g, 1.6 mmol) was added and the solution was refluxed overnight at 110 • C. The yellow precipitate was filtered and washed thoroughly with fresh toluene. The crude product was purified by column chromatography on alumina neutral grade IV with pure DCM and recrystallization from slow evaporation of a DCM/Ethanol solution (0.77 g, yield 75%). Suitable crystals for single crystal X-ray diffraction were obtained from slow evaporation at room temperature of a chloroform solution.

  • C, cooled to room temperature and 50 ml of H 2 O were added. The organics were extracted with DCM and purified by column chromatography on silica gel with pure DCM (0.20 g, yield 58%). (C5), 158.52 (C10), 157.23 (d, C7) , 131.57 (C2), 128.90 (d, C3), 128.75 (d, C4), 119.93 (C9), 116.65 (d, C6), 111.00 (d, C8), 106.08 (C1), 55.48 (C11).

  ). calc. = 453.36) Elemental analysis found (calc.): C 39 H 26 O 10 F 3 Al (Al(C 39 H 18 O 6 F 3 ) • 4 H 2 O, 738.63 g mol -1 ): C 63.97 (63.41)%, H 3.53 (3.56)%.

  ). MALDI-TOF MS (Da) m/z (rel. intensity, assigned structure): 486 (100%, C 26 H 12 O 4 Cl 2 Al calc. = 486.26), 452 (10%, C 26 H 13 O 4 ClAl calc. = 451.82). Elemental analysis found (calc.): C 39 H 22 O 8 Cl 3 Al (Al(C 39 H 18 O 6 Cl 3 ) • 2 H 2 O, 743.94 g mol -1 ): C 62.65 (62.29)%, H 3.18 (2.96)%.

1

  H-NMR (500 MHz, CDCl 3 , 25 • C, δ(ppm)): 8.24 (s, 2H, H4), 7.91 (d, 2H, H2), 7.11 (d, 2H, H1). MALDI-TOF MS (Da) m/z (rel. intensity, assigned structure): 669 (100%, C 26 H 12 O 4 I 2 Al calc. = 669.16), 542 (60%, C 26 H 12 O 4 IAl calc. = 542.26), 415 (10%, C 26 H 12 O 4 Al calc. = 415.36). Elemental analysis found (calc.): C 39 H 20 O 7 I 3 Al (Al(C 39 H 18 O 6 I 3 ) • H 2 O, 1008.27 g mol -1 ): C 46.81 (46.46)%, H 2.41 (2.00)%.

  • C, δ(ppm)): 8.17 (s, 1H, H4), 8.08 (d, 2H, H2), 7.72 (t, 2H, H11), 7.51 (d, 2H, H10), 7.40 (t, 1H, H12), 7.18 (d, 2H, H1). 13 C-NMR (125 MHz, CDCl 3 , 25 • C, δ(ppm)): 179.14 (C8), 141.51 (C4), 140.34 (C9), 136.21 (C2), 131.38 (C5), 129.17 (C11), 128.23 (C10), 127.62 (C12), 127.36 (C3), 125.72 (C6), 113.31 (C7). MALDI-TOF MS (Da) m/z (rel. intensity, assigned structure): 569 (100%, C 38 H 22 O 4 Al calc. = 569.58). Elemental analysis found (calc.): C 57 H 39 O 9 Al (Al(C 57 H 33 O 6 ) • 3 H 2 O, 894.94 g mol -1 ): C 76.58 (76.49)%, H 4.36 (4.40)%.

) 3 19.

  HOp-pe 15c (0.10 g, 0.3 mmol) was dissolved in 10 ml toluene, AlCl 3 (14.0 mg, 0.1 mmol) was added and the solution was refluxed overnight at 110 • C. The yellow precipitate was filtered and washed thoroughly with fresh toluene. The crude product was purified by column chromatography on alumina neutral grade IV with pure DCM(76 mg, yield 83%). 42 H 22 O 4 Al calc. = 617.62). Elemental analysis found (calc.): C 63 H 41 O 10 Al (Al(C 63 H 33 O 6 ) • 4 H 2 O, 985.02 g mol -1 ): C 76.43 (76.81)%, H 5.79 (4.20)%.(5.00 g, 32.0 mmol) and benzoyl chloride 17 (3.7 ml, 32.0 mmol) were dissolved in 60 ml DCB. The mixture was cooled to 0 • C and AlCl 3 (4.30 g, 32.0 mmol) was slowly added. The reaction was warmed up to room temperature and stirred 1 h. Another aliquote of AlCl 3 (4.30 g, 32.0 mmol) was added and the mixture was refluxed at 120 • C over 48 h. The mixture was cooled to room temperature and quenched with HCl 6 N 40 ml. The solid was filtered off on celite and washed with hot DCM; the organic layer was taken and the solvents were evaporated under vacuum. The crude product was purified by chromatography on silica gel with DCM/hexane (1:1) (4.79 g, yield 61%). Peaks in 1 H-NMR and13 C-NMR spectra are labeled according to the numbering shown in the figure. HOba 18 (0.41 g, 1.7 mmol) and AlCl 3 (66.7 mg, 0.5 mmol) were dissolved in 20 ml of toluene. The mixture was refluxed at 110 • C overnight, the crude precipitate was purified by column chromatography on alumina neutral grade IV with pure DCM (0.33 g, yield 86%).MALDI-TOF MS (Da) m/z (rel. intensity, assigned structure): 517 (100%, C 35 H 18 O 4 Al calc. = 517.50). Elemental analysis found (calc.): C 51 H 31 O 8 Al (Al(C 51 H 27 O 6 ) • 2 H 2 O, 798.08 g mol -1 ): C 76.84 (76.68)%, H 5.05 (3.92)%. Peaks in 1 H-NMR and 13 C-NMR spectra are labeled according to the numbering shown in the figure.

	(C10), 137.66 (C8), 131.38 (C4), 126.10(C2), 121.42 (C5), 118.92 (C9), 118.72 (C3), 118.70 HOba (C7), 118.47 (C1).
		5
	2	3 4 HOp-py 6 7 8 9 17	10
	1 H-NMR (500 MHz, CD 2 Cl 2 , 25 • C, δ(ppm)): 8.18 (s, 2H, H4), 8.08 (d, 2H, H2), 7.59 (m, 2H, H12), 7.41 (m, 3H, H13,14), 7.09 (d, 2H, H1). 13 C-NMR (125 MHz, CD 2 Cl 2 , 25 • C, δ(ppm)): 179.42 (C8), 141.87 (C2), 135.87 (C4), 131.99 (C12), 128.91 (C13), 128.17 (C14), 125.52 (C3), 123.42 (C1), 113.47 (C7), 89.81(C9), 88.82 (C10). MALDI-TOF MS (Da) m/z (rel. intensity, assigned structure): 617 (100%, C O O Al Al(Op-pe) 3 1 2 3 4 5 6 7 8 9 10 11 12 13 14 3 16c O 1 11 12 13 15 3 4 8 7 14 16 2 5 6 9 18 H 18 N OH 1 10 11 12 22 Scheme 8.19: Al(Op-pe) O O Al(Oba) 3 3 Scheme 8.20: HOba 18. Al(ObaO Scheme 8.22: HOp-py 22. Al
	• C, δ(ppm)): 15.91 (s, 1H, H15), 8.15 (s, 2H, H4), 8.06 (d, 2H, Al
	H2), 7.55 (m, 2H, H12), 7.36 (m, 3H, H13,14), 7.17 (d, 2H, H1). 13 C-NMR (125 MHz, CDCl 3 , 25 • C, δ(ppm)): 179.49 (C8), 140.83 (C2), 135.42 (C4), 131.83 (C12), 128.81 (C13), 128.65 19
	(C14), 125.73 (C3), 124.63 (C6), 122.96 (C1), 88.37 (C9,10). Scheme 8.21: Al(Oba) 3 19.
	HOp-pe 2 HOp-py 22. 210 ml of a mixture 4:2:1 toluene/ethanol/K 2 CO 3 (2 M in H 2 O) was prepared 1 and 2-bromopyridine 21 (3.0 ml, 31.0 mmol) and 2-hydroxybenzenboronic acid (20) (4.14 g,
	15 O 30.0 mmol) were dissolved in it. The mixture was bubbled with Ar 1 h and Pd(PPh 3 ) 4 (0.71 g, H 3 4 5 6 7 8 9 10 11 12 13 0.63 mmol) was added. The reaction was refluxed overnight at 80 • C. The resulting solution was 14 cooled down and extracted with ethylacetate; the organics were collected and the solvents were O evaporated under reduced pressure. The crude product was purified to column chromatography
	on silica gel with pure DCM (3.48 g, yield 68%).

15c Scheme 8.18: HOp-pe 15c. Peaks in 1 H-NMR and 13 C-NMR spectra are labeled according to the numbering shown in the figure. Al(Op-pe) 3 16c. 3 16c. Peaks in 1 H-NMR and 13 C-NMR spectra are labeled according to the numbering shown in the figure. HOba 18. 2-Methoxynaphthalene 1

(Op-py) 3 23.

  HOp-py 22 (3.48 g, 4.0 mmol) was dissolved in 50 ml of freshly distilled THF; the solution was cooled to -78 • C and Al(CH 3 ) 3 (2 M in toluene) was slowly added (0.61 ml, 1.2 mmol). The reaction mixture was warmed up to room temperature and left stirring over five days. The white precipitate was filtered, washed thoroughly with fresh THF and dried under vacuum (0.47 g, yield 73%). ESI-TOF MS (Da) m/z (rel. intensity, assigned structure): 367.08 (100%, C 22 H 16 O 2 N 2 Al calc. = 367.36). MALDI-TOF MS (Da) m/z (rel. intensity, assigned structure): 367 (100%, C 22 H 16 O 2 N 2 Al calc. = 367.36). Elemental analysis found (calc.): C 33 H 30 O 6 N 3 Al (Al(C 33 H 24 O 3 N 3 )• 3 H 2 O, 591.19 g mol -1 ): C 67.48 (67.00)%, H 4.59 (5.12)%, N 7.13 (7.10)%.

  ). MALDI-TOF MS (Da) m/z (rel. intensity, assigned structure)269 (100%, C 14 H 10 O 4 Al calc. = 269.22), 659 (41%, C 35 H 25 O 10 Al 2 calc. = 659.56). Elemental analysis found (calc.): C 21 H 15 O 6 Al (Al(C 21 H 15 O 6 ), 650.64 g mol -1 ): C 64.57 (64.61)%, H 3.83 (3.88)%.

  23 H 20 O 4 N 2 Al calc. = 415.43), 370.12 (12%, C 19 H 21 O 5 NAl calc. = 370.39), 315.07 (12%, C 18 H 12 O 2 N 2 Al calc. = 315.28), 270.07 (5%, C 14 H 13 O 3 NAl calc. = 270.25). MALDI-TOF MS (Da) m/z (rel. intensity, assigned structure): 315 (100%, C 18 H 12 O 2 N 2 Al calc. = 315.28), 270 (22%, C 14 H 13 O 3 NAl calc. = 270.25), 729 (20%, C 41 H 31 O 6 N 4 Al 2 calc. = 729.68), 684 (18%, C 37 H 32 O 7 N 3 Al 2 calc. = 684.65). Elemental analysis found (calc.): C 23 H 19 O 4 N 2 Al (Al(C 23 H 19 O 4 N

	1 H-NMR (500 MHz, CD 2 Cl 2 , 25 • C, δ(ppm)): 8.52 (dd, 2H, H7), 8.17 (dd, 2H, H5), 7.51 (t, 2H, H2), 7.29-7.25 (m, 2H, H6), 7.10-7.00 (m, 4H, H1,3), 5.64 (s, 1H, H12), 1.94 (s, 6H,
	H10). 13 C-NMR (125 MHz, CDCl 3 , 25 • C, δ(ppm)): 192.79 (C11), 191.76 (C9), 159.17 (C1), 144.27 (C8), 139.43 (C3), 139.11 (C4), 131.04 (C6), 129.58 (C2), 121.95 (C5), 112.01 (C7),
	101.83 (C12), 27.02 (C10). ESI-TOF MS (Da) m/z (rel. intensity, assigned structure): 415.12
	(100%, C

2 ), 414.12 g mol -1 ): C 65.98 (66.66)%, H 4.38 (4.63)%, N 6.55 (6.76)%.

  ) m/z (rel. intensity, assigned structure): 414.08 (100%, C 23 H 17 O 5 NAl calc. = 414.38), 437.09 (60%, C 25 H 18 O 4 N 2 Al calc. = 437.41), 292 (15%, C 16 H 11 O 3 NAl calc. = 292.26). MALDI-TOF MS (Da) m/z (rel. intensity, assigned structure): 315 (100%, C 18 H 12 O 2 N 2 Al calc. = 315.30), 292 (80%, C 16 H 11 O 3 NAl calc. = 292.26), 269 (62%, C 14 H 10 O 4 Al calc. = 269.22), 728 (41%, C 41 H 28 O 7 N 3 Al 2 calc. = 728.68), 751 (38%, C 43 H 29 O 6 N 4 Al 2 calc. = 751.72), 705 (21%, C 39 H 27 O 8 N 2 Al 2 calc. = 705.64), 774 (15%, C 45 H 30 O 5 N 5 Al 2 calc. = 774.76), 682 (10%, C 37 H 26 O 9 NAl 2 calc. = 682.60). Elemental analysis found (calc.): C 25 H 17 O 4 N 2 Al (Al(C 25 H 17 O 4 N 2 ), 436.40 g mol -1 ): C 69.15 (68.80)%, H 4.37 (3.39)%, N 5.69 (6.42)%. Scheme 8.28: Zn(Op) 2 31. Peaks in 1 H-NMR and 13 C-NMR spectra are labeled according to the numbering shown in the figure.

		Al(q 2 Trop)
			N		O
				Al
	2		O		O
				30
	Scheme 8.27: Al(q 2 Trop) 30.
		Zn(Op) 2
			1	2
	Zn	O	8	7	6 3 4	5
		O
						2
			31

Zn(Op) 2 31. HOp 3 (0.50 g, 2.5 mmol) was dissolved in 60 ml of ethanol, zinc acetate (0.23 g, 1.2 mmol) was added and the mixture was refluxed overnight at 90 • C. The reaction was cooled down to room temperature; the precipitate was filtred, washed thoroughly with fresh ethanol (0.46 g, yield 84%). Suitable crystals for single crystal X-ray diffraction were obtained from slow evaporation at room temperature of a DCM/ethanol solution.

32. [Dy(Op) 3 (HOp)] 33-[Dy(Op) 3 (EtOH)] 34.

  • C, δ(ppm)): 49.23, 40.63, 36.40, 33.58, 28.49, 16.27 (s, 1H), 8.33 (dd, 2H), 7.77 (t, 1H), 7.28 (d,2H). MALDI-TOF MS (Da) m/z (rel. intensity, assigned structure): 554 (100%, C 26 H 14 O 4 Dy calc. = 552.90), 572 (15%, C 26 H 16 O 5 dy calc. = 570.92), 1301 (8%, C 65 H 35 O 10 Dy calc. = 1301.0), 945 (7%, C 52 H 29 O 8 Dy calc. = 944.31), 772 (5%, C 39 H 21 O 6 DyNa calc. = 771.09), 1693 (5%, C 91 H 50 O 14 Dy 2 calc. = 1692.41), 756 (2%, C 39 H 21 O 6 DyLi calc. = 755.04). Elemental analysis found (calc.): C 41 H 28 O 7 DyCl (Dy(C 26 H 14 O 4 )Cl• C 13 H 8 O 2 • C 2 H 6 O, 830.58 g mol -1 ): C 59.87 (59.29)%, H 3.67 (3.40)%. HOp 3 (117.7 mg, 0.6 mmol) was suspended in 5 ml of ethanol. Diisopropylamine (60.6 mg, 0.6 mmol) was added dropwise at room temperature. An ethanol solution of DyCl 3 • 6 H 2 O (75.4 g, 0.2 mmol) was added dropwise. The final mixture was stirred 2 h at room temperature and refluxed 3 h at 90 • C. After cooling the mixture overnight, the solid was filtered off and single crystals were grown by slow evaporation of the filtrate solution (20.8 mg, yield= 13%). The precipitate was filtered and washed thoroughly with fresh ethanol (0.15 g). 52 H 29 O 8 Dy calc. = 944.31), 572 (18%, C 26 H 16 O 5 dy calc. = 570.92), 1693 (10%, C 91 H 50 O 14 Dy 2 calc. = 1692.41), 1301 (5%, C 65 H 35 O 10 Dy calc. = 1301.0). Elemental analysis found (calc.): C 97 H 68 O 17 Dy 2 ([Dy(C 39 H 21 O 6 ) • C 13 H 8 O 2 -Dy(C 39 H 21 O 6 )• C Hexamethyldisilazide (16.5 ml, 78.0 mmol) was taken in 40 ml of freshly distilled THF and the solution was cooled to 0 • C. n-Butyllithium (1.6 M in hexane, 50.0 ml, 80.0 mmol) was slowly added and the reaction was stirred 1 h. DyCl 3 (6.45 g, 24.0 mmol) was carefully added and the solution was stirred and allowed to warm up to room temperature overnight. The resulting product was purified by sublimation in high vacuum (2 × 10 -6 mbar, 90 • C) and added (0.50 g, 0.8 mmol) to a solution of HOp 3 (0.46 g, 2.4 mmol) in 20 ml in freshly distilled THF. The mixture was refluxed at 65 • C overnight. The yellow precipitate was filtered and washed with fresh THF (0.29 g). 36.28, 33.41, 28.43, 21.51, 19.26, 17.61, 7.86, 7.31, 6.79. MALDI-TOF MS (Da) m/z (rel. intensity, assigned structure): 554 (100%, C 26 H 14 O 4 Dy calc. = 552.90), 945 (4%, C 52 H 29 O 8 Dy calc. = 944.31), 1301 (4%, C 65 H 35 O 10 Dy calc. = 1301.0), 756 (4%, C 39 H 21 O 6 DyLi calc. = 755.04), 572 (2%, C 26 H 16 O 5 dy calc. = 570.92), 772 (2%, C 39 H 21 O 6 DyNa calc. = 771.09). Absorption peaks (nm), DMSO solution, 25 • C: 341, 434, 460. 32.62, 30.42, 29.20, 25.26, 22.33, 7.97, 7.43, 6.91. MALDI-TOF MS (Da) m/z (rel. intensity, assigned structure): 549 (100%, C 26 H 14 O 4 Tb calc. = 549.33), 567 (100%, C 39 H 23 O 7 Tb calc. = 567.35). Elemental analysis found (calc.): C 39 H 27 O 9 Tb (Tb(C 39 H 21 O 6 ) • 3 H 2 O, 798.59 g mol -1 ): C 58.78 (58.65)%, H 3.08 (3.41)%. Absorption peaks (nm), DMSO solution, 25 • C: 349, 434, 460. 12%, C 65 H 35 O 10 Tb 2 calc. = 1293.86), 567 (6%, C 39 H 23 O 7 Tb calc. = 567.35), 751 (5%, C 39 H 21 O 6 TbLi calc. = 751.47). Elemental analysis found (calc.): C 39 H 25 O 8 Tb (Tb(C 39 H 21 O 6 ) • 2 H 2 O, 798.59 g mol -1 ): C 60.06 (60.01)%, H 3.18 (3.26)%. Absorption peaks (nm), DMSO solution, 25 • C: 349, 434, 460. Liaisons σ et π dans l'éthylène, la plus simple molécule présentant un système conjugué π. Les niveaux d'énergie de la molécule ainsi que son niveau d'excitation électronique le plus faible sont indiqués à droite. . . . . . . . . . . . . . . . . . . v Représentation de la structure moléculaire de l'isomère méridional (mer-Alq 3 ) (à gauche) et de celle de l'isomère facial (fac-Alq 3 ) (à droite). . . . . . . . . . . . . . vi Émission de photons observée pour le complexe Alq 3 (jaune) et pour le complexe Al(Op) 3 (bleu) sous illumination UV (en solution). Émission de photons observée pour le complexe Alq 3 (jaune) et pour le complexe Al(Op) 3 (marron) (couche mince). L'émission pour le complexe Al(Op) 3 en couche mince est sensiblement décalée par rapport à celle observée en solution due à la formation d'excimères. . viii (a) Courbe CV cathodique puor Hq et Alq 3 dans une solution de DCM mesurée à température ambiante. Électrolyte: TBAPF Op) 3 . Ces données sont extraites des spectres NT-PS et 2PPE. L'alignement des niveaux d'énergie pour l'interface Co/Alq 3 est indiqué à titre de comparaison. . . . . . Polyacetylene polymers studied in reference [8]. Left: trans-polyacetylene. Right: cis-polyacetylene. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1.2 σ-and π-bonds in ethene as an example for the simplest conjugated π-electron system. On the right-hand side are depicted energy levels and lowest electronic excitation of ethene. Source: [17]. . . . . . . . . . . . . . . . . . . . . . . . . . . . 1.3 Jablonsky diagram of an organic molecule. Left: singlet manifold. Right: triplet manifold. Blue vertical arrows represent absorption processes, green and red vertical arrows represent emission processes, dashed vertical arrows represent radiationless processes, and black solid vertical arrows represent triplet-triplet annihilation processes. Thick horizontal lines are electronic energy levels, and thin horizontal lines are vibronic sublevels. Γ F,r , Γ F,nr , Γ P,r , and Γ P,nr are radiative and non-radiative rates of fluorescence and phosphorescence, respectively. k and k isc are rates of absorption and intersystem crossing, respectively. Source: [21]. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1.4 Schematic illustration of vibronic transitions (absorption and fluorescence) between S 0 and S 1 in an organic molecule. Source: [21]. . . . . . . . . . . . . . . . 1.5 Illustration of the hopping transport mechanism. The distribution of the density of HOMO and LUMO states is Gaussian with widths σ h and σ e , respectively. Source: [21]. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

	Dy O Cl [Dy(Op) 2 Cl(HOp)(EtOH)] O O OH O H 1 H-NMR (500 MHz, DMSO-d 6 , 25 • C, δ(ppm)): 49.21, 40.67, 36.47, 33.55, 28.55, 21.63, 19.36, 2 17.73. MALDI-TOF MS (Da) m/z (rel. intensity, assigned structure): 554 (100%, C 26 H 14 O 4 Dy Dy O O OH O O Dy O O H 3 3 33 34 Scheme 8.30: [Dy(Op) 3 (HOp)] 33-[Dy(Op) 3 (EtOH)] 34. Sublimable phenalenyl-based dysprosium complex 36. Phenalenyl-based terbium complex 37. HOp 3 (0.51 g, 2.6 mmol) was dissolved in 60 ml of ethanol, TbCl 3 • 6 H 2 O (0.32 g, 0.8 mmol) was added and the solution was refluxed overnight at 90 Sublimable phenalenyl-based terbium complex 38. Hexamethyldisilazide (5.2 ml, 25.0 mmol) calc. = 549.33), 1293 (List of Figures . xiv calc. = 552.90), 945 (20%, C 8.3 Phenalenyl-based SMMs was taken in 20 ml of freshly distilled THF and the solution was cooled to 0 • C. n-Butyllithium (a) Diagramme d'Arrhenius semi-logarithmique du temps de relaxation τ en fonc-(1.6 M in hexane, 17.0 ml, 27.2 mmol) was slowly added and the reaction was stirred 1 h. TbCl 3 (2.00 g, 7.5 mmol) was carefully added and the solution was stirred and allowed to warm up to tion de 1/T pour le complexe [Dy(Op) 2 Cl(HOp)(EtOH)]. La susceptibilité mag-nétique fut mesurée pour un champ magnétique externe nul ainsi que pour un room temperature overnight. The resulting product was purified by sublimation in high vacuum champ statique externe de 200 Oe. La courbe obtenue par régression linéaire pour (2 × 10 -6 mbar, 90 • C) and added (0.50 g, 0.8 mmol) to a solution of HOp 3 (0.46 g, 2.4 mmol) l'intervalle de température d'activation termique est tracée sur le diagramme.(b) in 20 ml of freshly distilled THF. The mixture was refluxed at 65 • C overnight. The yellow Diagramme d'Arrhenius semi-logarithmique du temps de relaxation τ en fonc-precipitate was filtered and washed with fresh THF (0.33 g). tion de 1/T pour le complexe [Dy(Op) 3 (HOp)]-[Dy(Op)

32 Scheme 8.29: [Dy(Op) 2 Cl(HOp)(EtOH)] 2 H 6 O]•2 C 2 H 6 O, 1830.51 g mol -1 ): C 63.51 (63.64)%, H 3.66 (3.74)%. Absorption peaks (nm), DMSO solution,

25

• C: 349, 432, 458.

1 H-NMR (500 MHz, DMSO-d 6 , 25 • C, δ(ppm)): • C. The precipitate was filtered and washed thoroughly with fresh ethanol (0.44 g).

1 H-NMR (500 MHz, DMSO-d 6 , 25 • C, δ(ppm)): 6 . Vitesse de scan: 100 mV s -1 . (b) Courbe CV cathodique pour HOp et Al(Op) 3 dans une solution de DCM mesurée à température ambiante. Électrolyte: TBAPF 6 . Vitesse de scan:100 mV s -1 . . . . ix Représentation de la surfaces des orbitales moléculaires HOMO (à gauche) et LUMO (à droite) pour les complexes mer-Alq 3 (en haut) et Al(Op) 3 (en bas). . . xi (a) Morphologie du complexe mer-Alq 3 . (b) Fonction de corrélation de paire g(r) pour le complexe mer-Alq 3 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . xi Alignement des niveaux d'énergie pour les interfaces Co/[5 nm] Al(Op) 3 et Co/[2.8 nm] Al(Op-py) 3 . Ces données sont extraites des spectres UPS et 2PPE. L'alignement des niveaux d'énergie pour l'interface Co/Alq 3 est indiqué à titre de comparaison. xiii Alignement des niveaux d'énergie pour l'interface Co/[1.5 nm] Al(3 (EtOH)]. La susceptibilité magnétique fut mesurée pour deux valeurs champs magnétiques externes: 1500 Oe et 3000 Oe. La courbe obtenue par régression linéaire pour l'intervalle de température d'activation termique est tracée sur le diagramme. . . . . . . . . xv 1.1 1.6 Molecular structures of the meridianal isomer (mer-Alq

  Table: selected bond distances and angles for Al(q 2 Acac) 28. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3.17 1 H-NMR spectra of Al(q 2 Acac) 28, Hq 26 and Acac 27 in CD 2 Cl 2 . The resonances are marked accordingly to the numbering shown in Scheme 3.8. . . . . . . 3.18 Molecular structure obtained by single crystal X-ray diffraction on a single crystal of Al(q 2 Op) 29. H-atoms and solvent molecules are omitted for clarity. The crystal refinement data is reported in Table C.5. The molecular packing in the single crystal of Al(q 2 Op) 29 is illustrated in (a) yz (b) xz (c) xy perspective. Table: selected bond distances and angles for Al(q 2 Op) 29. . . . . . . . . . . . . 3.19 1 H-NMR spectra of Al(q 2 Op) 29, HOp 3 and Hq 26 in CD 2 Cl 2 (HOp 3 in CDCl 3 ). The resonances are marked accordingly to the numbering shown in Scheme 3.9 and Scheme 3.8 (for Hq 26). . . . . . . . . . . . . . . . . . . . . . . . 3.20 Molecular structure obtained by single crystal X-ray diffraction on a single crystal of Al(q 2 Trop) 30. H-atoms and solvent molecules are omitted for clarity. The crystal refinement data is reported in Table C.6. The molecular packing in the single crystal of Al(q 2 Trop) 30 is illustrated in (a) yz (b) xz (c) xy perspective. Table: selected bond distances and angles for Al(q 2 Trop) 30. . . . . . . . . . . . 3.21 MALDI-TOF spectra of Al(q 2 Acac) 28, Al(q 2 Op) 29 and Al(q 2 Trop) 30. The main fragments are marked in the figure. . . . . . . . . . . . . . . . . . . . . . . . 3.22 Molecular structure obtained by single crystal X-ray diffraction on a single crystal of Zn(Op) 2 31. H-atoms and solvent molecules are omitted for clarity. The crystal refinement data is reported in Table C.7. The molecular packing in the single crystal of Zn(Op) 2 31 is illustrated in (a) yz (b) xz (c) xy perspective. Table: selected bond distances and angles for Zn(Op) 2 31. . . . . . . . . . . . . .

  Table C.1: Crystallographic and refinement data of mer-Alq 3 . range for data collection [ • ] 2.140 -25.698 Final R indices [I2> σ(I)] R 1 = 0.0330, wR 2 = 0.0862 R indices (all data) R 1 = 0.0394, wR 2 = 0.0892 GoF on F 2 1.027 Table C.2: Crystallographic and refinement data of Al(Op) 3 4. Compound Al(Op) 3 • 3.5 CHCl 3 Empirical formula C 42.5 H 24.5 Cl 10.5 O 6 Al M [g mol -1 ] range for data collection [ • ] 2.13 -26.81 Final R indices [I2> σ(I)] R 1 = 0.0609, wR 2 = 0.1589 R indices (all data) R 1 = 0.0862, wR 2 = 0.1757 GoF on F 2 1.054 Table C.3: Crystallographic and refinement data of HOp-Br 5c. range for data collection [ • ] 2.43 -25.61 Final R indices [I2> σ(I)] R 1 = 0.0198, wR 2 = 0.0540 R indices (all data) R 1 = 0.0217, wR 2 = 0.0549 GoF on F 2 1.077 Table C.4: Crystallographic and refinement data of HOp-pe 15c. range for data collection [ • ] 2.169 -25.271 Final R indices [I2> σ(I)] R 1 = 0.0463, wR 2 = 0.1097 R indices (all data) R 1 = 0.0774, wR 2 = 0.1227 GoF on F 2 0.930 Table C.5: Crystallographic and refinement data of Al(q 2 Op) 29. range for data collection [ • ] 3.05 -51.996 Final R indices [I2> σ(I)] R 1 = 0.0496, wR 2 = 0.0618 R indices (all data) R 1 = 0.3187, wR 2 = 0.1180 GoF on F 2 0.476 Table C.6: Crystallographic and refinement data of Al(q 2 Trop) 30. range for data collection [ • ] 4.76 -51.3 Final R indices [I2> σ(I)] R 1 = 0.0727, wR 2 = 0.1896 R indices (all data) R 1 = 0.1197, wR 2 = 0.2192 GoF on F 2 1.041 Table C.7: Crystallographic and refinement data of Zn(Op) 2 31. range for data collection [ • ] 4.68 -51.34 Final R indices [I2> σ(I)] R 1 = 0.0433, wR 2 = 0.0875 R indices (all data) R 1 = 0.0796, wR 2 = 0.0990 GoF on F 2 1.029 Table C.8: Crystallographic and refinement data of [Dy(Op) 2 Cl(HOp)(EtOH)] 32. range for data collection [ • ] 4.28 -51.20 Final R indices [I2> σ(I)] R 1 = 0.0172, wR 2 = 0.0441 R indices (all data) R 1 = 0.0194, wR 2 = 0.0447 GoF on F 2 1.047 Table C.9: Crystallographic and refinement data of [Dy(Op) 3 (HOp)] 33-[Dy(Op) 3 (EtOH)] 34.

	Compound Empirical formula M [g mol -1 ] Crystal colour T [K] λ [Å] Crystal system Space group a [pm] b [pm] c [pm] α [ • ] β [ • ] γ [ • ] Volume [Å 3 ] Z ρ calcd. [g cm -3 ] µ(Mo-Kα) [mm -1 ] F(000) Crystal size [mm] θ 1030.33 Alq 3 • EtOH C 29 H 24 O 4 N 3 Al 505.49 Yellow/gree 180.00(2) 0.71073 Monoclinic P21/n 1109.86(5) 1313.34(5) 1657.59(7) 90.00 94.068(3) 90.00 2410.05(18) 4 1.393 0.127 1056 0.45 x 0.28 x 0.27 Crystal colour Yellow T [K] 180.00(2) λ [Å] 0.71073 Crystal system Monoclinic Space group P2(1)/n a [pm] 934.61(4) b [pm] 2177.32(6) c [pm] 2133.06(9) α [ • ] 90.00 β [ • ] 90.797(3) γ [ • ] 90.00 Volume [Å 3 ] 4340.2(3) Z 4 ρ calcd. [g cm -3 ] 1.577 µ(Mo-Kα) [mm -1 ] 0.742 F(000) 2076 Crystal size [mm] 0.34 x 0.31 x 0.30 θ Compound HOp-Br Empirical formula C 13 H 7 O 2 Br M [g mol -1 ] 275.10 Crystal colour Yellow T [K] 180.00(2) λ [Å] 0.71073 Crystal system Monoclinic Space group C2/c a [pm] 1212.60(14) b [pm] 1170.76(11) c [pm] 703.64(8) α [ • ] 90.00 β [ • ] 98.682(9) γ [ • ] 90.00 Volume [Å 3 ] 987.49(18) Z 4 ρ calcd. [g cm -3 ] 1.850 µ(Mo-Kα) [mm -1 ] 4.139 F(000) 544 Crystal size [mm] 0.39 x 0.17 x 0.16 θ Compound HOp-pe Empirical formula C 21 H 12 O 2 M [g mol -1 ] 296.31 Crystal colour Yellow T [K] 180.00(2) λ [Å] 0.71073 Crystal system Monoclinic Space group P2(1)/n a [pm] 805.94(5) b [pm] 2933.95(12) c [pm] 1280.33(7) α [ • ] 90.00 β [ • ] 107.309(5) γ [ • ] 90.00 Volume [Å 3 ] 2890.4(3) Z 8 ρ calcd. [g cm -3 ] 1.362 µ(Mo-Kα) [mm -1 ] 0.087 F(000) 1232 Crystal size [mm] 0.36 x 0.24 x 0.02 θ Compound Al(q 2 Op) Empirical formula C 31 H 19 N 2 O 4 Al M [g mol -1 ] 510.46 Crystal colour Yellow T [K] 150.00 λ [Å] 0.71073 Crystal system Triclinic Space group P-1 a [Å] 8.1895(17) b [Å] 10.8580(17) c [Å] 14.312(3) α [ • ] 68.926(13) β [ • ] 85.576(16) γ [ • ] 74.327(14) Volume [Å 3 ] 1143.1(4) Z 2 ρ calcd. [g cm -3 ] 1.483 µ(Mo-Kα) [mm -1 ] 0.134 F(000) 528.0 Crystal size [mm] 0.07 x 0.05 x 0.01 θ Compound Al(q 2 Trop) Empirical formula C 25 H 17 N 2 O 4 Al M [g mol -1 ] 436.39 Crystal colour Yellow T [K] 180.15 λ [Å] 0.71073 Crystal system Monoclinic Space group C2/c a [Å] 16.3233(17) b [Å] 10.0992(10) c [Å] 11.9293(15) α [ • ] 90.00 β [ • ] 99.621(9) γ [ • ] 90.00 Volume [Å 3 ] 1938.9(4) Z 4 ρ calcd. [g cm -3 ] 1.495 µ(Mo-Kα) [mm -1 ] 0.144 F(000) 904.0 Crystal size [mm] 0.18 x 0.13 x 0.10 θ Compound Zn(Op) 2 • 2 H 2 O Empirical formula C 26 H 18 O 6 Zn M [g mol -1 ] 491.77 Crystal colour Orange T [K] 180.15 λ [Å] 0.71073 Crystal system Monoclinic Space group C2/c a [Å] 35.005(2) b [Å] 5.2112(2) c [Å] 11.0530(7) α [ • ] 90.00 β [ • ] 95.542(5) γ [ • ] 90.00 Volume [Å 3 ] 2006.9(2) Z 4 ρ calcd. [g cm -3 ] 1.628 µ(Mo-Kα) [mm -1 ] 1.269 F(000) 1008.0 Crystal size [mm] 0.31 x 0.10 x 0.01 θ Compound [Dy(Op) 2 Cl(HOp)(EtOH)] Empirical formula C 41 H 28 O 7 DyCl M [g mol -1 ] 830.58 Crystal colour Orange T [K] 180.15 λ [Å] 0.71073 Crystal system Triclinic Space group P-1 a [Å] 10.4482(7) b [Å] 12.5823(8) c [Å] 13.2433(8) α [ • ] 93.446(5) β [ • ] 112.211(5) γ [ • ] 95.762 Volume [Å 3 ] 1594.55(18) Z 2 ρ calcd. [g cm -3 ] 1.730 µ(Mo-Kα) [mm -1 ] 2.483 F(000) 826.0 Crystal size [mm] 0.18 x 0.15 x 0.14 [Dy(Op) 3 (HOp)]-[Dy(Op) 3 (EtOH)] • 2 EtOH Empirical formula C 194 H 136 O 34 Dy 4 M [g mol -1 ] 3661.03 Crystal colour Orange T [K] 180.15 λ [Å] 0.71073 Crystal system Monoclinic Space group C2/c a [Å] 11.0591(8) b [Å] 17.2521(8) c [Å] 19.8266(10) α [ • ] 92.328(4) β [ • ] 104.285(5) γ [ • ] 95.206(5) Volume [Å 3 ] 3642.9(4) Z 1 ρ calcd. [g cm -3 ] 1.669 µ(Mo-Kα) [mm -1 ] 2.114 F(000) 1836.0 Crystal size [mm] 0.24 x 0.15 x 0.11 θ Compound θ range for data collection [ •

2-Hydroxycyclohepta-2,4,6-trien-1-one (tropolone) 24 was selected due to its structural analogy with HOp 3. Similarly to HOp 3, the chelating atoms of tropolone 24 are two oxygen atoms. On the contrary, the backbone of tropolone 24 is formed by a single seven-membered aromatic

Theoretical and preliminary experimental studies on the (novel) OSCs

H-NMR (500 MHz, CDCl 3 ,

• C, δ(ppm)): 8.01 (d, 2H, H2), 7.96 (d, 2H, H4), 7.51 (t, 1H, H5), 7.14 (d, 2H, H1). 13 C-NMR (125 MHz, CDCl 3 , 25 • C, δ(ppm)): 179.09 (C8), 141.34 (C2), 132.86 (C4), 127.94 (C1), 127.87 (C5), 125.29 (C3), 122.91 (C6), 113.40 (C7). MALDI-TOF MS (Da) m/z (rel. intensity, assigned structure): 417 (100%, C

H 14 O 4 Al calc. = 417.07). Elemental analysis found (calc.): C 39 H

O 8 Al (Al(C 39 H 21 O 6 ) • 2 H 2 O, 650.64 g mol -1 ): C 72.29 (72.00)%, H 4.01 (4.19)%.

H-NMR (500 MHz, CDCl 3 ,

• C, δ(ppm)): 7.72-7.67 (m, 2H, H3,8), 7.39 (dd, 1H, H6), 7.25-7.13 (m, 3H, H1,4,9), 3.91 (s, 3H, H11) .13 C-NMR (125 MHz, CDCl 3 , 25 • C, δ(ppm)): 160.44

H-NMR (500 MHz, CDCl 3 ,

• C, δ(ppm)): 7.96 (d, 2H, H2), 7.68 (d, 2H, H4), 7.17 (d, 2H, H1). MALDI-TOF MS (Da) m/z (rel. intensity, assigned structure): 453 (100%, C

H 12 O 4 F 2 Al

H-NMR (500 MHz, CDCl 3 ,

• C, δ(ppm)): 8.06 (s, 2H, H4), 7.93 (d, 2H, H2), 7.13 (d, 2H, H1) . MALDI-TOF MS (Da) m/z (rel. intensity, assigned structure): 575 (100%, C

H 12 O 4 Br 2 Al calc. = 575.16), 495 (20%, C 26 H 12 O 4 ClAl calc. = 495.26), 415 (10%, C 26 H 12 O 4 Al calc. = 415.36). Elemental analysis found (calc.): C 39 H 20 O 7 Br 3 Al (Al(C 39 H 18 O 6 Br 3 )•H 2 O, 867.27 g mol -1 ): C 54.53 (54.01)%, H 2.57 (2.33)%.

H-NMR (500 MHz, CDCl 3 ,

• C, δ(ppm)): 15.98 (s, 1H, H13), 8.25 (s, 2H, H4), 8.17 (d, 2H, H2), 7.74 (dt, 2H, H11), 7.53 (d, 2H, H10), 7.44 (dt, 1H, H12), 7.22 (d, 2H, H1). 13 C-NMR (125 MHz, CDCl 3 , 25 • C, δ(ppm)): 141.52 (C8), 140.28 (C2), 137.82 (C4), 131.79 (C5), 129.50 (C11), 128.19 (C3), 127.70 (C10), 126.43 (C12), 124.53 (C1).

H-NMR (500 MHz, CDCl 3 ,

• C, δ(ppm)): 15.87 (s, 1H, H18), 8.67 (d, 2H, H4,6), 8.53 (d, 1H, H9), 8.20 (d, 1H, H12), 8.02 (d, 1H, H2), 7.86 (s, 1H, H5), 7.67 (t, 2H, H10,11), 7.37 (d, 1H, H1). 13 C-NMR (125 MHz, CDCl 3 , 25 • C, δ(ppm)): 186.40 (C14,16), 140.07 (C2), 133.51 (C8), 130.97 (C10), 129.84 (C17), 128.01 (C4), 127.29 (C3), 126.74 (C11), 125.61 (C12), 124.25 (C7), 123.25 (C6), 120.58 (C5).

H-NMR (500 MHz, CDCl 3 ,

• C, δ(ppm)): 14.36 (s, 1H, H12), 8.42 (dd, 1H, H4), 7.81 (d, 1H, H10), 7.76-7.70 (m, 2H, H1,8), 7.32 (dt, 1H, H2), 7.14 (dt, 1H, H3), 7.10 (dd, 1H, H7), 6.90 (dt, 1H, H9). 13 C-NMR (125 MHz, CDCl 3 , 25 • C, δ(ppm)): 159.96 (C11), 157.63 (C6), 145.61

H-NMR (500 MHz, CDCl 3 ,

• C, δ(ppm)): 7.55 (t, 2H, H2), 7.49 (d, 2H, H1), 7.11 (t, 1H, H3). 13 C-NMR (125 MHz, CDCl 3 , 25 • C, δ(ppm)): 178.09 (C4), 140.28 (C2), 127.59 (C3), 125.84

H-NMR (500 MHz, CD

Cl 2 , 25 • C, δ(ppm)): 8.68 (d, 2H, H7), 8.23 (d, 2H, H5), 8.09 (d, 2H, H11), 8.04 (d, 2H, H13), 7.58 (t, 1H, H14), 7.50 (t, 2H, H2), 7.34 (m, 2H, H6), 7.06 (m, 4H, H1,3), 6.96 (d, 2H, H10). ESI-TOF MS (Da) m/z (rel. intensity, assigned structure): 511.11 (100%, C

H 20 O 4 N 2 Al calc. = 511.51), 366.06 (95%, C 22 H 13 O 3 NAl calc. = 366.34). MALDI-TOF MS (Da) m/z (rel. intensity, assigned structure): 417 (100%, C 26 H 14 O 4 Al calc. = 417.38), 366 (40%, C 22 H 13 O 3 NAl calc. = 366.34). Elemental analysis found (calc.): C 31 H 19 O 4 N 2 Al (Al(C 31 H 19 O 4 N 2 ), 510.48 g mol -1 ): C 72.17 (72.93)%, H 3.97 (3.76)%, N 5.31 (5.49)%.

H-NMR (500 MHz, THF-d 8 ,

• C, δ(ppm)): 7.99 (d, 2H, H2), 7.89 (d, 2H, H4), 7.40 (t, 1H, H5), 7.03 (d, 2H, H1). MALDI-TOF MS (Da) m/z (rel. intensity, assigned structure):

(100%, C 13 H 7 O 2 NZn calc. = 260.59). Elemental analysis found (calc.): C 26 H 18 O 6 Zn (Zn(C 26 H 14 O 4 ) • 2 H 2 O, 491.83 g mol -1 ): C 63.53 (63.49)%, H 4.12 (3.70)%.

H-NMR (500 MHz, DMSO-d 6 ,

• C, δ(ppm)): 32.58, 30.36, 29.16, 25.23, 22.32, 7.84, 7.30, 6.78. MALDI-TOF MS (Da) m/z (rel. intensity, assigned structure): 549 (100%, C

H 14 O 4 Tb

Studies on Co/OSCs Hybrid Interfaces

In collaboration with: Dr. Mirko Cinchetti and Nicolas Großmann Prof. Martin Aeschlimann group Department of Physics and Research center OPTIMAS University of Kaiserslautern, Kaiserslautern, Germany

Introduction

The performance of organic spintronic devices is strongly determined by the peculiar spindependent properties of the hybrid interface, or spinterface [216], formed between the organic semiconductor and the ferromagnetic electrodes [74,217]. As described in 1.2.3, the prototypical spinterface is Co/Alq 3 , since it constitutes the basic building block of a large number of organic spintronic devices [15]. The existence of spin polarized hybrid interface states (HISs) has been revealed by spin-and time-resolved spectroscopy experiments. In addition, it has been suggested that Alq 3 -based spinterfaces can be easily tuned to control the spintronic performance of organic spin valves [75,218]. Additionally, to tailor the spin-dependent properties of the Co/Alq 3 interface, and thus, the performance of the related devices, a systematic chemical substitution is a possible approach.

In this work, we have studied Al(Op) 3 as an alternative OSC to form hybrid interfaces, exploiting the mutability of organic semiconductors [219]. As a result of the bigger ligands, compared to those of Alq 3 (see Table 3.1), we expect a modification of the chemisorption on cobalt, and thus, different spin-dependent properties of the Co/Al(Op) 3 hybrid interface with respect to those of Co/Alq 3 . Different electronic properties of the OSCs deposited on cobalt will inevitably lead to a modified interaction, in character and strength, between the molecule and the ferromagnetic substrate, resulting in modified spin-filtering properties. The hybrid interface Co/Al(Op) 3 has been systematically investigated by spin-dependent spectroscopy to determine its spin-dependent properties [203]. In detail, we have made use of the photoemission spectroscopy techniques (PES) described in 1.3.3: ultraviolet photoemission spectroscopy (UPS), near threshold photoemission spectroscopy (NT-PS), and two-photon photoemission (2PPE). In addition, preliminary UPS studies on the Co/Al(Op-py) 3 hybrid interface are reported. • Yanhua Lan, Andrea Magri, and Mario Ruben. "Magnetic properties of phenalenyl-based dysprosium SMMs". In preparation.

List of Tables

E. Publications