Résumé : La luminescence polarisée circulairement (CPL) est prometteuse pour le développement des futurs dispositifs émissifs. Le défi est maintenant de concevoir et de synthétiser une petite molécule organique active en CPL avec des valeurs gCPL élevées afin qu'elle soit adaptée à la fabrication de dispositifs. Nous nous sommes récemment concentrés sur les complexes de difluorure de bore à ligand dicétone (DFB) en raison de leur rendement quantique élevé à l'état solide et en solution, de leur déplacement de Stokes élevé et de leur sensibilité aux stimuli mécaniques (mécanofluorochromisme). Il a été montré précédemment que le complexe DFB portant un groupe amide chiral présente un bon signal CPL et une bonne réponse à la contrainte mécanique à l'état solide. Cependant, les agrégats supramoléculaires à longue portée basés sur ce chromophore restent à étudier. Dans cette étude, des unités DFB bichromophore avec une connectivité variable ont été synthétisées et ont présenté une inversion de chiralité basée sur l'arrangement spatial des chromophores. Une propriété chiroptique améliorée a été observée dans le nanofil auto-assemblé avec une valeur gCPL de 0,015. Dans la deuxième partie de l'étude, le transfert d'énergie a été étudié en utilisant des mesures d'anisotropie. Cela a montré un transfert d'énergie très efficace dans l'assemblage supramoléculaire par rapport à la forme monomère du DFB mono et di-substitué. De plus, les nanofils autoassemblés présentent une sensibilité à l'exposition aux UV. Enfin, des mesures spectroscopiques à l'état solide ont été réalisées pour comprendre les propriétés mécanofluorochromes du DFB mono et di-substitué. Grâce à des mesures de spectroscopie résolues en temps et à la diffraction des rayons X, il a été constaté que les petits changements dans les espaceurs tels que l'amide et l'ester influencent fortement les propriétés mécanofluorochromes du DFB bichromophore.

Title: Design and Characterization of Supramolecular Materials Displaying Enhanced Circularly Polarized Luminescence and Mechanoflurochromism

Keywords: supramolecular chemistry, CPL, fluorescence, mechanofluorochromism Abstract: Circularly polarized light (CPL) has promising application in the development of future emissive displays. The challenge now is to design and synthesize a small organic CPL active molecule that has high gCPL values to make it suitable for device fabrications. We have been recently focusing on difluoroboron-β-diketonate (DFB) complexes because of the high quantum yield in both solid and solution states, high Stokes shift and sensitivity to stimuli such as mechanical stress (mechanofluorochromism). It has been previously reported that DFB complex bearing chiral amido group displays a good CPL signal and response to mechanical stress in solid state. However, long range supramolecular aggregates based on this chromophore remain to be investigated. In this study, bichromophore DFB units with varying connectivity were synthesized and displayed an inversion of chirality based on spatial arrangement of chromophores. Enhanced chiroptical property was observed in selfassembled nanowire with gCPL value of 0.015. In the second part of the study, energy transfer was investigated using anisotropy measurements. This showed a highly efficient energy transfer in supramolecular assembly as compared to monomeric form of both mono and di-substituted DFB. Moreover, self-assembled nanowires exhibit sensitivity to UV irradiation.

Finally, solid-state spectroscopic measurements were conducted to understand the mechanofluorochromic properties of mono and disubstituted DFB. Using time-resolved spectroscopy measurements and single crystal XRD analysis, it was found that changes in spacers such as the amide and ester highly influenced the mechanofluorochromic properties of bichromophore DFB through the strength of intermolecular interactions and molecular packing.

CHAPTER 1

Introduction: Circularly Polarized Luminescence and Mechanofluorochromism Chiral active materials are widely existing in nature such as our DNA, and biomolecular components from living organism. [1][2][3] Such chirality of molecules is due to the non-superimposable and mirror image structures of molecules which behaves differently from its enantiomer. Early study of stereochemistry was rooted in first half of 19 th century with the discovery of Hemidrism of crystals, and series of exploration such as circularly polarized light, the response of natural compound with circularly polarized light and Pasteur's efforts in deducing structure of enantiomers of paratartaric acid 4,5 (see Figure 1). This has initiated the growth of study and interest in molecular chirality on traditional medicine and natural products. 4 Fundamental and in-depth understanding of molecular chirality and its interaction with light was the foundation of chiral optics or chiroptics and this field of study has taken important parts in biology, toxicology, and medicine especially drug discovery and synthesis. Chiroptical properties of molecules can be measured through circular dichroism or the difference in the absorption of left and right circularly polarized light 6 and through the circularly polarized luminescence (CPL) or difference in the emission of left and right circularly polarized light. [7][8][9] CPL active materials has become appealing as it provides more application in state-of-the-art fabrication of light harvesting devices, 3D-displays, information storage and optical sensors. 10 This can be quantified with luminescence dissymmetry factors (glum) which can be calculated using the equation:

𝑔 lum = 2(𝐼 𝐿 -𝐼 𝑅 ) (𝐼 𝐿 +𝐼 𝑅 )
where IL and IR are the intensities of left and right CPL. Theoretically, it can also be calculated with the following equation: 2 where |µ|and |𝑚| are the electric and magnetic dipole transition moment, θ is the angle between them and the highest theoretical value for glum is 2. Meanwhile, the difference in absorbance of the left and right circularly polarized light in ground state was defined as circular dichroism (CD= A L -A R ) where A L and A R are the absorbances from left and right circularly polarized light. Useful quantity called dissymmetry factor (gabs) can be derived from this equation and can be calculated as follows:

𝑔 lum = 4 x 𝑐𝑜𝑠𝜃 |𝑚||µ| |𝑚| 2 + |µ|
gabs = Δε ε = 𝐴 𝐿 -𝐴 𝑅 𝐴
where Δε= ε L -ε R is difference in molar quantity; A L and A R are the absorbances from left and right circularly polarized light and A is absorbance in non-polarized light.

From the equation, it was clear that the luminescence dissymmetry factors are highly dependent on molecular structure with magnetic allowed transition and electronic dipole forbidden transitions. [11][12][13] Several early studies on lanthanide complexes have been reported to exhibit high glum values because of favorable f-f transitions. 14,15 On the other hand, studies on CPL active small organic molecules (SOMs) have gained interest because of advantages over lanthanide complexes such as tunability, wider emission range and processibility in some device manufacturing processes. 14 However, obtaining high glum values with high quantum yield for organic compounds is still a challenge.

Another

interesting property of luminescent compounds is mechanofluorochromism or the changes of emission after application of mechanical stress such as smearing, shearing, and grinding. The first induced emission through mechanical force was reported in 1904 when Francis Bacon showed that lumps of sugars emitted light after crushing. 16,17 However, because of complexity of studies with the molecular structures it was not sustained until in 2000s where the advances in mechanofluorochromic materials were explored. 18 Molecular re-arrangement, intermolecular interactions, chemical reactions and formation of excimers or combination of those upon application of mechanical stress are the main reasons for mechanofluorochromism. [19][20][21][22][23] The mechanofluorochromic compounds are gaining interest for applications in optoelectronics, security ink and papers and mechanosensors. 24-26 Several mechanofluorochromic compounds were published in the last 10 years such as oligophenylenevinylenes 27,28 pyrene [29][30][31] metal complexes 32-34 tetrathiazolylthiophene, [START_REF] Nagura | Distinct Responses to Mechanical Grinding and Hydrostatic Pressure in Luminescent Chromism of Tetrathiazolylthiophene[END_REF][START_REF] Mosca | Mechanochromic Luminescent Tetrathiazolylthiophenes: Evaluating the Role of Intermolecular Interactions through Pressure and Temperature-Dependent Raman Spectroscopy[END_REF] and organoboron. [START_REF] Zhou | Triphenylamine Functionalized β-Ketoiminate Boron Complex Exhibiting Aggregation-Induced Emission and Mechanofluorochromism[END_REF][START_REF] Zhao | Mechanofluorochromism of Difluoroboron β-Ketoiminate Boron Complexes Functionalized with Benzoxazole and Benzothiazole[END_REF][START_REF] Tanaka | Recent Progress of Optical Functional Nanomaterials Based on Organoboron Complexes with β-Diketonate, Ketoiminate and Diiminate[END_REF][START_REF] Yoshii | Mechanofluorochromic Materials Based on Aggregation-Induced Emission-Active Boron Ketoiminates: Regulation of the Direction of the Emission Color Changes[END_REF] Of all the organoboron-based mechanofluorochromic compounds, we mainly focused with difluoroboron β-diketonate (DFB) because of high quantum yield in solution and solid state as well as its promising mechanofluorochromic properties. 22,[START_REF] Tanaka | Recent Progress of Optical Functional Nanomaterials Based on Organoboron Complexes with β-Diketonate, Ketoiminate and Diiminate[END_REF][START_REF] Zhang | A Difluoroboron B-Diketonate-Based Luminescent Material with Tunable Solid-State Emission and Thermally Activated Delayed Fluorescence[END_REF][START_REF] Xu | Aromatic Difluoroboron β-Diketonate Complexes: Effects of π-Conjugation and Media on Optical Properties[END_REF][START_REF] Qi | High-Contrast Mechanochromism and Polymorphism-Dependent Fluorescence of Difluoroboron β-Diketonate Complexes Based on the Effects of AIEE and Halogen[END_REF] As we have realized the importance of molecular design in improving CPL and mechanofluorochromism, this thesis therefore explores the techniques in improving the properties from molecular design and synthesis to formation of supramolecular assembly and finally its responsiveness. The design and synthesis of organic compounds with multiple functionalities are of great interest as it expands the use of the material in different applications. It goes beyond the borderline of specific application limited only with either CPL or mechanofluorochromism thus, unique design of compounds can be revolutionary and may contribute to expansion of perspectives for single molecules design with multiple functionalities. This introductory chapter discuss early studies with isolated CPL active SOMs with a special focus on organoboron compounds. Molecular design approaches in improving chiroptical properties such supramolecular assemblies and aggregates are then discussed. Moreover, this also covers the mechanofluorochromism of organic molecules and the recent studies divulging the factors affecting the sensitivity and its reversibility. We also stated the objectives and scope of the study to impart our efforts in contributing for the future direction in the field of CPL and mechanofluorochromism.

Circularly Polarized Luminescence of Small Organic Molecules

Discovery of CPL active compounds has been instrumental for advances in the field of study in biomolecules, drug development and modern opto-electronics. So far, circularly polarized luminescence (CPL) active compounds with highest luminescence (glum) dissymmetry were reported for lanthanide complexes because of favorable transition satisfying the magnetic dipole selection rule. This was owed with the f-f transitions for lanthanide complexes and d-d transition for transition metals which satisfied the magnetic (𝑚) allowed and electric (𝜇) forbidden transition. [START_REF] Gong | Coordination-Based Circularly Polarized Luminescence Emitters: Design Strategy and Application in Sensing[END_REF] The highest glum reported was Eu (III) complex with glum value of 1.38 from transition of 5 D0→ 7 F1, however low φF is limiting its applications. 15,[START_REF] Greenfield | Pathways to Increase the Dissymmetry in the Interaction of Chiral Light and Chiral Molecules[END_REF] On the other hand, organic molecules have low glum values because of overwhelming electronic allowed transition (𝜇) and usually displays glum values in the range of 10 -5 to 10 -3 for isolated organic molecules. 9,14,[START_REF] Greenfield | Pathways to Increase the Dissymmetry in the Interaction of Chiral Light and Chiral Molecules[END_REF] Despite low glum values compared with lanthanide complexes, the quest for CPL active SOMs was boosted by advantages in terms of tunability of the emission wavelength, responsiveness to stimuli, biocompatibility, and processability in device fabrication. 10,[START_REF] Liao | Generating Circularly Polarized Luminescence from Clusterization-triggered Emission Using Solid Phase Molecular Self-Assembly[END_REF] The early study of CPL active organic compound was reported in 1967 where Emeis and Oosterhof presented the chirality of trans β-hydrindanone, which displayed intrinsically chiral ketones. [START_REF] Emeis | Emission of circularly polarized radiation by optically active compounds[END_REF] During this time, most of the studies with CPL active compounds was focused on chiral ketones displaying glum values in the range of 10 -3 to 10 -2 owing to the n-π* and satisfying the electronic forbidden and magnetic allowed transitions. Some of the cyclic ketones displaying CPL activity that were explored during 1960s are listed in Figure 1 Since most of the chiral carbonyl compounds based on ketones have low φF, the research has shifted to molecular compounds with extended aromatic groups. SOMs with extended aromatic groups may display higher φF and glum values that will make them suitable for different applications in opto-electronics. One of the earliest conjugated aromatic CPL active compounds was reported by Drake et al, in 1979 displaying glum values of glum = +8x10 -3 for C2-symmetric calycanthine. 14 From CPL-active SOMs emitting in UV region, the interest in the development of molecules has shifted to emissive compounds in visible region. One of the interesting dyes are organoboron because of simpler synthetic pathways, high fluorescence emission quantum yield, high molar absorptivity and photostability. Moreover, most emission and absorption of organoboron are within near IR and visible region making it a promising compound for various applications. [START_REF] Sánchez-Carnerero | Circularly Polarized Luminescence by Visible-Light Absorption in a Chiral O-BODIPY Dye: Unprecedented Design of CPL Organic Molecules from Achiral Chromophores[END_REF][START_REF] Beer | Redox Switches with Chiroptical Signal Expression Based on Binaphthyl Boron Dipyrromethene Conjugates[END_REF] However, most of these organoboron compounds such as BODIPY are achiral thus, the inclusion or embedding of dyes to chiral molecules has been the primary techniques to gain significant chirality. [START_REF] Lu | Optically active BODIPYs[END_REF] There are many reported studies on CPL active small organic fluorescent dyes but in the next section, we focused the discussion on organoboron based CPL active molecules.

Circularly Polarized Luminescence based on Organoborons

The early molecular designs of chiral BODIPY was the covalently bonded asymmetric phenyls including the urobilin derivatives shown in Figure 1.2-a and 1.2-b. [START_REF] Beer | Redox Switches with Chiroptical Signal Expression Based on Binaphthyl Boron Dipyrromethene Conjugates[END_REF][START_REF] Gossauer | Synthesis and Conformational Studies of Urobilin Difluoroboron Complexes. Unprecedented Solvent-Dependent Chiroptical Properties of the BF2 Chelate of an Urobilinoid Analogue[END_REF] Most of these molecular design of mono-BODIPY displayed low glum values (~10 -3 ) hence, to improve the chiroptical properties axial chiral compounds were introduced. Binaphthyls are one of the most used axial chiral inducers in the early study of CPL-active BODIPY. The perturbation of achiral BODIPY was demonstrated in the study of Beer et al., (2000) where they synthesized mono and bis-BODIPY shown in Figure 1.2-c and 1.2-d. [START_REF] Beer | Redox Switches with Chiroptical Signal Expression Based on Binaphthyl Boron Dipyrromethene Conjugates[END_REF] Although axial chiral binaphthyl was introduced in BODIPY, glum value remains weak (10 - 3 ). An attempt to increase the CPL signal by changing the fluorophores from BODIPY to dimesytilboron was performed however, no significant improvement in the glum values was observed. This indicated that the chirality of compounds is mainly dependent on the nature of chiral source and not in the fluorophores attached. [START_REF] Gong | Coordination-Based Circularly Polarized Luminescence Emitters: Design Strategy and Application in Sensing[END_REF][START_REF] Jiang | Easily Accessible Axial Chiral Binaphthalene-Triarylborane Dyes Displaying Intense Circularly Polarized Luminescence Both in Solution and in Solid-State[END_REF] Efforts in improving chiroptical properties through molecular design continues and another simple functionalization of BODIPY was demonstrated by the group of de la Moya when they synthesized chiral O-BODIPY dyes. It was the first demonstration of structural design to obtain spiranic structures of O-BODIPYs where the BODIPY and 1'1binaphthyl derivative is orthogonally arranged. This study showed that the simple complexation with chiral binaphthyl can cause perturbation of achiral fluorophores. The chiral perturbation of inherently achiral BODIPY was shown to enable CPL activity through absorption visible light. While the CPL of O-BODIPY dyes exhibited the usual glum values in the range of 10 -5 -10 -3 , they showed that the simple and straight forward functionalization of BODIPY moiety can easily induces chirality to achiral fluorophores. [START_REF] Sánchez-Carnerero | Circularly Polarized Luminescence by Visible-Light Absorption in a Chiral O-BODIPY Dye: Unprecedented Design of CPL Organic Molecules from Achiral Chromophores[END_REF] With continuous search for chiral active organic compounds displaying high glum and φF, researchers gained interest with helicenes as potential CPL active compounds because of their promising glum values and high quantum yield. [START_REF] Gong | Coordination-Based Circularly Polarized Luminescence Emitters: Design Strategy and Application in Sensing[END_REF][START_REF] Norel | Metallahelicenes: Easily Accessible Helicene Derivatives with Large and Tunable Chiroptical Properties[END_REF] In 2001, aggregating heterocyclic helicenes were reported by Phillips et al., unfortunately the glum values reported are limited for the aggregated form with glum value of 0.01. [START_REF] Phillips | Synthesis and Properties of an Aggregating Heterocyclic Helicene[END_REF] Two years later, Venkataraman et al, (2003) reported the first triarylamine based with glum value of 0.01 for aggregating helicenes. In that same paper, they compared shorter helicene (M-1) with longer conjugated helicene (P-2) in isolated form shown in Figure 1.3. The shorter helicene showed glum value of |0.001| while the longer conjugated helicene displayed glum value of |0.0008| indicating that the increase in helicity of molecular geometry is not the only function to consider in obtaining high glum values. [START_REF] Field | Circularly Polarized Luminescence from Bridged Triarylamine Helicenes[END_REF] Helicenes as promising CPL-active compound was utilized as chiral platform for organoboron compounds to impart the chirality in fluorophores. Azahelicenes with BODIPY was demonstrated by the group of Maeda forming a unique molecular design of carbazole based-helicenes. [START_REF] Maeda | Azahelicene -Fused BODIPY Analogues Showing Circularly Polarized Luminescence[END_REF] Series of carbazole-helicenes were synthesized with tunable emission targeting NIR-responsive CPL dyes, and through structure analysis it was revealed that the chirality of helicenes were imparted to the organoboron moieties. These series of isolated carbazole based-helicenes displayed glum values in the range of |7.0x10 -4 | to |1.9x10 -3 |. The group of Crassous demonstrated the influence of helicene sizes and the number of boron atoms in azabora[n]helicenes as well as with corresponding platina[n]helicenes analogues (see Figure 1.4). 57 The glum for platina [n]helicences displayed values in the order of 10 -3 to 10 -4 which is typical with SOMs, but these complexes exhibit higher quantum yields. Interestingly, the glum values for azabora[n]helicences displayed glum values as high as 10 -2 with red phosphorescence showing that these compounds are potential materials for CPL-OLEDs. Moreover, sign of CPL signals for M and P for the compounds 1a-1c are opposite of what was obtained with the bis azabora [10] helicene (structure 1d). Meanwhile, the corresponding platina complex (structure 1d 1 ) showed no CPL signal due to planarity of geometry of platinum, hence it clearly shows that the Boron influenced the geometry hence optical chirality in helicenes. [START_REF] Shen | Synthesis and Chiroptical Properties of Hexa-, Octa-, and Deca-Azaborahelicenes: Influence of Helicene Size and of the Number of Boron Atoms[END_REF] The direction of the studies and perspectives was then focused on the perturbation of achiral organoboron complex to induce chirality through molecular designs. One example is the unique boron fused double-helicenes synthesized by Hatakeyama et al, (2016). [START_REF] Katayama | Two-Step Synthesis of Boron-Fused Double Helicenes[END_REF] They demonstrated boron complexation and introduction of bulky alkyl group such as tert-butyl caused distorted racemic structure. The structure of the compound and stacked arrangement was shown in Figure 1.4-B. This has formed chiral helicenes which exhibited glum value of 1.7 x 10 -3 (see Figure 1.5). Another example of molecular structure manipulation in inducing chirality was the synthesis of figure-of-eight helicity. The group of Nabeshima designed synthesized macrocyclic bis-BODIPY (bis(boron-dipyrromethene)) complex [1B2] shown in Figure 1.6. [START_REF] Saikawa | Synthesis of Figure-of-Eight Helical BisBODIPY Macrocycles and Their Chiroptical Properties[END_REF] In their work, they introduced BODIPY units into a macrocyclic ring framework that has induced the chirality of macromolecule. This compound exhibits glum value of 9 x10 -3 and φF = 0.58. Moreover, the emission of this figure-of-eight macromolecule was far red shifted which is very useful in bioimaging applications. So far, this figure-of-eight macromolecule bis-BODIPY boron complex is one of the isolated organic molecules that exhibits high glum values (~10 -2 ) in red region (663nm). The comparison of chiroptical property with reference monomer revealed that bis-BODIPY boron has glum values more than three times of reference monomer. This is an

A B
indication of synergistic effect of multichromophoric groups which is responsible for enhanced CPL in figure-of-eight conformation. [START_REF] Saikawa | Synthesis of Figure-of-Eight Helical BisBODIPY Macrocycles and Their Chiroptical Properties[END_REF] 1.1.2. Enhancing Chiroptical Properties: Supramolecular Assembly From the early studies on molecular manipulation of the isolated small organic molecules, it is still noticeable that CPL signals are far lower than the lanthanide complexes and obtaining higher glum values for SOMs remains a challenge for researchers. In the previous section, it was discussed that the perturbation of achiral molecules can be achieved through manipulation of molecular structure and inducing chirality to fluorophore. The synergy between fluorophores in multichromophoric isolated organic molecule has also enhanced the glum values. Another way of modulating the electronic states of organic molecules in through supramolecular assembly. The first observed enhancement of chiroptical properties through aggregation was in 2001. The helicenes synthesized by the group of Turro showed that the monomeric form (2x10 -6 M) did not display any CPL signals, while increase in concentration to 1x10 -3 M caused appearance of emission at 600nm and 700nm accompanied by enhanced CPL signals (glum = 0.01). The group of Takeuchi developed a helicene containing phthalhydrazide forming trimeric disk through hydrogen bonding that eventually forms 1D nanofibers as shown in Figure 1.7. The 1D fibrous self-assembled trimeric disk was found to form in non-polar solvents and the self-assembly is highly dependent on the purity of the enantiomer. This system exhibits promising CPL with glum value =0.035, which is one of the highest values obtain for compounds without any chiral platforms. [START_REF] Kaseyama | Hierarchical Assembly of a Phthalhydrazide-Functionalized Helicene[END_REF] On the other hand, the group of Haino studied supramolecular assembly of tris(phenylisoxazolyl)benzenes. They revealed that supramolecular assembly of this compound is driven by π-π, and dipole-dipole interaction while the alkyl side chains highly affect its stability. Moreover, this compound formed both achiral and chiral supramolecular assembly, the helical assemblies being responsible for the chiroptical properties in both solution and gel forms. [START_REF] Tanaka | Self-Assembly and Gelation Behavior of Tris(Phenylisoxazolyl)Benzenes[END_REF] This was followed with another study of tris(phenylisoxazolyl)benzenes bearing perylenebisimide moiety. Herein, they showed the helical stacking of both S and R enantiomers is favorable in decalin and was not formed in chloroform. The helical structure of tris(phenylisoxazolyl)benzenes bearing perylenebisimide displayed glum value of 0.007. They also showed in this study that the chiroptical properties can be controlled with temperature, wherein they demonstrated the increase in CD of S enantiomer at low temperature 293k (gabs value of 0.0014). [START_REF] Ikeda | Circular Dichroism and Circularly Polarized Luminescence Triggered by Self-Assembly of Tris(Phenylisoxazolyl)Benzenes Possessing a Perylenebisimide Moiety[END_REF] Axial chiral platform is also commonly used to induce chirality in achiral fluorophore and in 2013, the group of Kawai demonstrated the first study on enhanced chirality of supramolecular assembled bichromophore system. They covalently attached achiral fluorophore perylene bisimides in enantiopure cyclohexane diamine and formed nanowires which enhance glum value of monomers (8x10 -3 at 630 nm) to glum value of 2.5x10 -2 (at 650 nm) in nanowires formed in methylcyclohexane. 11 Kawai's group continues to evaluate the effect of supramolecular assemblies by comparing the CPL signals from spherical and nanowires of bichromophore perylene bisimides using binaphthyl as chiral bridge (see Figure 1.8). They revealed that the glum values are highly dependent on the morphologies of supramolecular assembly wherein spherical aggregates display glum values 0.01 while the 1D nanowires has glum values 0.02 and lastly, the monomer has glum values of 3.0x10 -3 . This only shows that the chiroptical properties of SOMs can be modulated with the morphology. [START_REF] Kumar | Circularly Polarized Luminescence in Chiral Aggregates: Dependence of Morphology on Luminescence Dissymmetry[END_REF] Another example of helical aggregates exhibiting enhanced glum values upon formation of supramolecular assembly is chiral pyrene derivatives shown in Figure 1.9. In the study conducted by the group of Akutagawa, chiral alkylamide pyrene derivatives formed 1D nano helical π-stacked formed in different solvents such as methylcyclohexane (MCH) and toluene. [START_REF] Anetai | Circular Polarized Luminescence of Hydrogen-Bonded Molecular Assemblies of Chiral Pyrene Derivatives[END_REF] The formation of supramolecular assembly was governed not only with π-π stacking but also with the formation of H-bond which was highly affected by the solvent polarity. Using THF and chloroform as solvents, the organogels formation was not observed owing to the destabilized hydrogen bonding, while the supramolecular assembly formed in MCH displayed the most stable and largest excitonic coupling. This has resulted to high glum value of 0.003. Moreover, the CPL signals of 1D nanowires formed in chloroform and THF was inverted compared to the supramolecular assembly formed in MCH and toluene because of hydrogen bonding modification in self-assembly through solvent polarity.

Figure 1.9. Structures of chiral alkylamide pyrene derivatives (R-1 and S-1). [START_REF] Anetai | Circular Polarized Luminescence of Hydrogen-Bonded Molecular Assemblies of Chiral Pyrene Derivatives[END_REF] Reprinted with permission form American Chemical Society.

Although the formation of supramolecular assembly has evidently enhanced the chiroptical properties, most of these compounds showed decrease in quantum yield upon aggregation. This was mainly caused by the increasing non-radiative pathways that was promoted within the aggregated chromophores. Compounds exhibiting aggregation induced emissions (AIE) were shown to counter the challenges in fluorescence quenching upon self-assembly. In 2001, the group of Tang ed the aggregation induced emission (AIE) in 1-methyl-1,2,3,4,5-pentaphenylsilole which exhibits an increase in emission by more than two orders of magnitude. [START_REF] Luo | Aggregation-induced emission of 1-methyl-1,2,3,4,5pentaphenylsilole[END_REF] They extended the studies in combing AIE compound with chiral pendants to develop CPL active compound with high fluorescence and glum values in condensed phase. They designed and synthesized the AIE chromophore (silole) attached to chiral sugars which was shown in Figure 1.10a. Initially, this compound did not exhibit CD signals in monomeric form (low φF =0.6%). Upon formation of aggregates, silole compound self-assembled into right-handed nano helical wires with high quantum yield (φF =81.3%) and high glum values ranging from 0.08-0.32 in cast film, suspension, in PMMA and microfluidic channel (see Figure 1.10b).

Responsive CPL-active Organic Molecules

As discussed in the previous section, self-assembled SOMs were shown to enhance the CPL signals as compared with isolated molecules and interestingly, some of these are found to be responsive with different stimuli. Organic molecules which are both CPL-active and responsive with different stimuli are gaining interest for multiple applications. In the past few years, several responsive CPL-active molecules have been developed. This responsivity is based on the fact that the formation of stacked molecules is driven by different intermolecular interactions (π-π stacking, hydrogen bonding formation, and dipole-dipole interactions) which are often sensitive to different stimuli. One example is the dependence of the morphology of the supramolecular assembly with the polarity of solvent which was previously discussed in the study of Kawai's group. [START_REF] Kumar | Circularly Polarized Luminescence in Chiral Aggregates: Dependence of Morphology on Luminescence Dissymmetry[END_REF] Another example is the formation of 0D nanospheres, 2D flake, 3D nanoflakes of R and S SPAn 9 (see Figure 1.11) at different solvent compositions. By varying the water fraction of the solvent system various aggregates with different morphologies and glum values were observed, wherein highest glum values were obtained from 3D nanoflakes (~10 -2 ).

A B

Wavelength

The enhanced glum values at 3D nanoflakes were attributed to formation of excimers through the molecular packing in this arrangement. CPL inversion was also reported as an effect of variation in pH of the environment. In the study of Liu's group, they showed that the proton-deprotonation has highly affected the molecular orientation and packing of CPL active compounds through suppression of hydrogen bonding. This was the main reason for the inversion of chirality of the histidine π-gel (PyC3H). [START_REF] Niu | Histidine Proton Shuttle-Initiated Switchable Inversion of Circularly Polarized Luminescence[END_REF] The cycle of protonation-deprotonation is highly efficient for at least five cycles and this system was the first reported bio-inspired histidine proton shuttle. The structure and CPL signals including the reversibility was shown in Figure 1.12. Aside from the pH, light is also a good stimulus in modulating the CPL signals from organic chromophores. While the previous examples of CPL-active organic compounds sensitive to pH and solvent polarity are mostly from supramolecular assembly, light sensitive CPL active SOMs are reported from isolated molecules. Most common examples of light sensitive isolated CPL-active molecules are based on photochromic materials. In one of the studies of Kawai's group, a CPL switch (CPL signals can be turn on or off) was developed based on pyrene-bearing helical tetrathiazole. [START_REF] Niu | Histidine Proton Shuttle-Initiated Switchable Inversion of Circularly Polarized Luminescence[END_REF] Reprinted with permission from American Chemical Society.

The switching of the CPL signals is owed to geometrical changes upon photoisomerization (see Figure 1.13). The open and closed form of tetrathiazole moiety causes large structural changes which induce or prevent the excimers formation from intermolecular interaction of two pyrenes. Formation of hydrogen bonding and π-π stacking between interacting pyrenes were evident in the NMR structures. Moreover, the chirality of the pyrene derivatives was also influenced by the conformation of pyrenes of 1D-o. This has induced excimer formation with enhanced CPL signals and was found to have sign as with the cotton effect observed in CD spectra. [START_REF] Hashimoto | Photoswitching of an Intramolecular Chiral Stack in a Helical Tetrathiazole[END_REF] CPL switches was also reported for supramolecular assembly. In the study from the group of Liu, enantiomeric glutamate spiropyran moiety gels were found to display reversible changes in morphology of the supramolecular assembly from fibers to helical structures after exposure to UV and visible light. [START_REF] Miao | Reversible Quadruple Switching with Optical, Chiroptical, Helicity, and Macropattern in Self-Assembled Spiropyran Gels[END_REF] The structural changes are responsible for the CPL-switching characteristic of the glutamate spiropyran gels. Packing of gels were investigated to understand the structural changes of supramolecular assembly. They found that the interchangeable zwitterion merocyanine and ring closed state of spiropyran influencing the distortion of aromatic rings out of plane was the reason for chiral arrangement (see Figure 1.14). Isolated molecules in solution did not exhibit chiroptical properties, however upon formation of gels the compound display both CD and CPL signals. The glutamic gelator has chiral center while the fluorophores are achiral, hence chiroptical properties obtained after the formation of supramolecular assembly only proves that the chirality was transferred from gelator to the spiropyran. [START_REF] Miao | Reversible Quadruple Switching with Optical, Chiroptical, Helicity, and Macropattern in Self-Assembled Spiropyran Gels[END_REF] From the discussed studies on responsive CPL active compounds, it was shown that most of the changes in chiroptical properties are rooted from the structure changes with stimuli. Hence, application of mechanical force which highly affect the molecular packing of compounds was also reported to cause CPL signal changes. Several studies on CPL sensitivity after applying mechanical stress were reported on metal-organic frameworks. 10 On the other hand, only few studies on solid state SOMs and the sensitivity of its CPL signal to mechanical stress have been reported. In 2019, the group of Allain and Métivier revealed the mechano-CPL (changes in CPL signal upon application of mechanical stress) of difluoro-boron β-diketonate (DFB) complexes attached to chiral amido groups shown in Figure 1.15. [START_REF] Louis | Mechano-Responsive Circularly Polarized Luminescence of Organic Solid-State Chiral Emitters[END_REF] These chiral difluoro-boron β-diketonate (DFB) complexes display low glum values (<10 -3 ) in monomeric form. Solutions DFB-Hex-amide and DFB-Phet-amide were deposited in paper which also exhibited low CPL signals however, after thermal annealing the deposited samples the CPL signals increased with glum values in the range of 10 -2 . The thermal annealed samples were smeared displaying CPL signal inversion in DFB-Hexamide accompanied with appearance of emission at longer wavelength. The red shifted emission and CPL signals including its inversion was mainly due to the exciton-coupling induced after smearing. On the other hand, the DFB-Phet-amide did not show inversion of CPL signals and promotes the formation of amorphous form. The differences in the B A behavior of these two chiral DFB compounds lies behind the conformational freedom brought by their structures in crystalline form. It is also the first reported signal inversion of CPL in solid state after application of mechanical stress. [START_REF] Louis | Mechano-Responsive Circularly Polarized Luminescence of Organic Solid-State Chiral Emitters[END_REF] 1.2. Mechanofluorochromism of Small Organic Molecules

The last example of CPL active compounds based on DFB was displaying CPL signals sensitive to mechanical stress. Moreover, these compounds display mechanofluorochromism or the shift in emission brought by application of mechanical force. Mechanofluorochromic compounds have been capturing the interest of researchers for the past 10years because of their potential use in development of advanced smart materials and sensors. Mechanofluorochromism exhibited by organic molecules has some advantages such as tunability of its emission through molecular structure manipulation. One of the early studies in mechanofluorochromism of organic dyes was in 2002 when Weder demonstrated the mechanofluorochromism of oligo (pphenylene vinylene) (OPVs) derivatives deposited in LLDPE blend films (see Figure 1.16a). 27 Reprinted with permission from John Wiley and Sons.

Years before Weder's experiment, cyano-OPVs were already known to display emission from induced excimer formation in compounds owing on different crystallinity and pronounced π-π stacking of OVPs. It was shown in Weder's work that the emission of OPVs derivatives deposited in host polymer can be controlled through the extent of aggregation with varying concentrations. Most importantly, changes in emission were observed after uniaxial tensile stretching mainly caused by suppressed excimer formation and dominant contribution from monomers in stretched films. The images of dyed polymer films before and after stretching were shown in Figure 1.16b. 27 This study was

A B
believed to be the first demonstration of mechanofluorochromism of organic molecules deposited in polymer hosts. To further intensify the emission shift, organic dyes are then covalently attached in polymer. Herein, they showed the more intense mechanofluorochromic effect caused by the higher forces directly experienced by OPVs after applying mechanical stress. This method induced smaller aggregate of dyes which was seldom observed in physical blending. The application of mechanical stress caused the destruction of molecular arrangement of these small aggregates triggering more pronounced changes in emission. [START_REF] Kunzelman | Pressure-Sensitive Chromogenic Polyesters[END_REF] In a similar study by the group Pucci, they used bis(benzoxazolyl)stilbene in poly(propylene) film and similar emission shifts due to suppressed excimer formation were obtained after stretching the film. [START_REF] Pucci | Luminescent Bis(Benzoxazolyl)Stilbene as a Molecular Probe for Poly(Propylene) Film Deformation[END_REF] From these series of studies, it was then suggested that the mechanoflurochromism was highly dependent on molecular packings and aggregation of dye in the polymer platforms. These can be modulated with varying concentrations as well as the molecular structure of dyes.

From the embedded or covalently bonded organic dyes in polymers platforms, studies were shifted to pure solid-state materials displaying mechanofluorochromism. Several factors affecting the mechanofluorochromic properties in organic compounds such as intermolecular interactions, molecular structures, crystal packing and aggregation was explored in later years after discovering mechanofluorochromism. The group of Akari showed the importance of hydrogen bonding sites specifically of amide group (C6TPPy) in mechanofluorochomism of pyrenes. [START_REF] Sagara | Material Design for Piezochromic Luminescence: Hydrogen-Bond-Directed Assemblies of a Pyrene Derivative[END_REF] They demonstrated that the presence of amide helped to stabilize the columnar stacking of these pyrene units exhibiting blue emissive powder (B-form) shown in Figure 1.17b. [START_REF] Sagara | Material Design for Piezochromic Luminescence: Hydrogen-Bond-Directed Assemblies of a Pyrene Derivative[END_REF] Reprinted with permission from American Chemical Society.

On the other hand, smearing B-form pyrenes lead to distortion of molecular stacking causing emission shift with green emissions (G-form) shown in Figure 1.17c. The structural investigation through XRD and IR revealed that the green emissive powder has weaker hydrogen bonding, hence proves the impact of intermolecular interaction in mechanofluorochromic properties. This is also the first reported study of mechanofluorochromism of organic compound in pure solid-state form. The continuation of study with pyrene derivatives by Akari's group evaluated the effect hydrogen bonding in mechanofluorochromism through replacement of the amide groups with esters. The strength of hydrogen bonding in pyrenes with four amide groups are responsible for the formation of molecular stacking with blue emission, while the ester derivative was shown to form slip stacking causing the red shifted emission. It was also discovered that these compounds are displaying reversible emission. The recovery of the initial state for pyrene with amide groups is achievable when lower pressure was exerted in smearing the compound. High-pressured smearing displayed irreversible mechanofluorochromic effect caused by complete destruction of hydrogen bonds. On the other hand, ester derivative requires higher pressure to observe mechanofluorochromic effect. This demonstrates that intermolecular interactions are not only crucial with emission shift after smearing, but also playing significant role in recovery of emissions.

Recovery of emission from smeared to initial state was attained with series of thermal annealing-smearing cycles. The effect of bulkiness of side chains was revealed to affect the reversibility of the emission. In the same study of Akari's group, shortest alkyl chains did not show any reversibility, while the intermediated length of alkyls (C6-C14) showed reversibility. This is indicating that side chains support the rearrangement of molecules. Finally, the bulkiest side chain 2-ethylhexyl prevented the molecular arrangement resulting to partially reversed emission. [START_REF] Sase | Piezochromic Luminescence of Amide and Ester Derivatives of Tetraphenylpyrene-Role of Amide Hydrogen Bonds in Sensitive Piezochromic Response[END_REF] Another study of mechanofluorochromism in pyrene derivatives bearing bulky sidechains was reported by the group of Métivier and Allain (see Figure 1.18). 29 Similar observations from Akari's group were observed wherein the pyrene derivative with bulky sidechain (3) displayed partial emission recovery indicating hindered re-arrangement while the less bulky side chain (2) exhibits recovery after thermal annealing. Lastly, the structure of (1) promotes formation of polymorphs exhibiting hypsochromic and bathochromic shift with monomer-like and dynamic excimer behaviors. For both polymorphs, only partial recovery was observed owing to the formation of meta-stable state after thermal annealing.

Figure 1.17. Structures of pyrene derived acrylates (1-3). 29 Reprinted with permission from Elsevier.

One of the fastest emission recoveries after smearing the crystals has been observed in difluoro-boron β-diketonate (DFB) derivatives. The group of Fraser demonstrated that the dendritic blue emissive crystals of DFB Avobenzone (BF2AVB) turned to yellow emissive powder after smearing. It recovers its blue emission after few seconds of annealing. The possibility of multiple interactions such as hydrogen bonding, arene stacking, and fluorine interactions was the suggested cause of such reversibility in emission. [START_REF] Zhang | Polymorphism and Reversible Mechanochromic Luminescence for Solid-State Difluoroboron Avobenzone[END_REF] Moreover, they also demonstrated in this work that emissions are tunable through different solid-state morphologies. Herein, they exhibited green crystals, blue crystals, and dendritic crystals arranged in different molecular packings (see Figure 1.18). [START_REF] Zhang | Polymorphism and Reversible Mechanochromic Luminescence for Solid-State Difluoroboron Avobenzone[END_REF] Reprinted with permission from American Chemical Society.

Although several studies prior to the paper of Fraser were published explaining the emission shift through excimer formation, the reversibility of the emission after smearing are not well understood. Two years later, Fraser together with the group Reddy explained the mechanofluorochromic property of two polymorphs BF2AVB (cyan and green emitting crystals) through molecular structure and properties of crystals. In depth crystal analysis and nanoindentation measurements revealed that the cyan emitting crystals contains weak slip planes which tends to recover after thermal annealing and was easily deformed as compared to green emitting crystal which is harder (see Figure 1.19). [START_REF] Krishna | The Relationship of Solid-State Plasticity to Mechanochromic Luminescence in Difluoroboron Avobenzone Polymorphs[END_REF] [START_REF] Krishna | The Relationship of Solid-State Plasticity to Mechanochromic Luminescence in Difluoroboron Avobenzone Polymorphs[END_REF] Reprinted with permission from John Wiley and Sons.

The findings in the study of Reddy's group hence recommends designing of mechanofluorochromic compounds where the crystal structures contain many slip planes for it was expected to display promising emission shift and recovery.

To further understand the mechanofluorochromism in difluoro-boron βdiketonate (DFB) compounds, the group of Allain and Métivier conducted an in-depth study on the polymorphism and thermal back reaction of DFB-Ester through combination of spectroscopic and photophysico-chemical measurements. They revealed in this study that DFB-Ester formed green crystals and yellows emissive crystals which mainly differs in the degree of overlap and π-π stacking among its aromatic groups. Smearing or depositing the solution forms amorphous state with yellow orange emission. The thermal back reactions from yellow orange to green was explained through residual crystals that re-grow after thermal annealing. However, since two crystals may co-exist, the process of thermal annealing causes competitive formation of yellow crystals (meta-stable) and green crystals (thermal stable). Increasing the annealing temperature favors formation of more thermally stable crystals (green crystals). [START_REF] Louis | Polymorphism, Mechanofluorochromism, and Photophysical Characterization of a Carbonyl Substituted Difluoroboron-β-Diketone Derivative[END_REF] A scheme summarizing the different processes is shown in Figure 1.20. [START_REF] Louis | Polymorphism, Mechanofluorochromism, and Photophysical Characterization of a Carbonyl Substituted Difluoroboron-β-Diketone Derivative[END_REF] Reprinted with permission from publisher American Chemical Society.

Although studies on in-depth studies on mechanofluorochromism and its emission recovery were reported, efforts were still exerted by different groups to unveil the effects of molecular structures on solid state properties of DFB derivatives. Some of these are the variation in alkoxy length of side chain in DFB revealing the threshold length of n=6 in reversibility of ordered structure. 22 Also, the effect of chelating group in βdiketonates such as phenyl group instead of fluorine were explored. This revealed the fluorescence quenching, and poor mechanofluorochromism with phenyl owing to the non-radiative relaxation pathway and bulky groups. [START_REF] Louis | β-Diketone Derivatives: Influence of the Chelating Group on the Photophysical and Mechanofluorochromic Properties[END_REF]

Objective and Scope of the Studies

In this chapter, the early studies and discovery of CPL-active materials of small organic molecules were discussed. The different molecular designs from monochromophore, helicenes, spiranic fluorophores, to synergistic multi-chromophores twisted macromolecules in isolated form have given its contribution in enhancing the chiroptical properties of organic molecules. Moreover, supramolecular assembly introduced an elevated strategy to enhance the glum values of small organic molecules while avoiding the challenges in synthesizing large molecules. It was also introduced some of the CPL-responsive compounds to different stimuli like mechanical stress. Development of such materials has become more appealing for continuous study of single molecules with multiple functionalities; therefore, this thesis aims to contribute to design and synthesis of a unique small organic displays which displays both CPL-activity and mechanofluorochromism. Specifically, we aim: (1) to synthesize a bichromophore DFB compound and explore its chiroptical properties in solution and supramolecular assembly; (2) to study the photophysical properties of supramolecular assembly and its sensitivity to stimuli; and finally (3) to study the mechanofluorochromism of bichromophore DFBs.

The synthesis of bichromophoric DFB was discussed in the first part of the study and, we extended the investigation on the effect of connectivity in meta and para position of β-diketonate. Photophysical properties as well as the theoretical calculations using DFT and TD-DFT were executed to further understand the nature of the bichromophores bearing two DFB in para and meta positions. Supramolecular assembly was attempted for both compounds using different solvent system followed by CD and CPL spectroscopy measurements to investigate the effect of aggregation to the chiroptical properties. Structural analysis using XRD, and molecular modelling were carried out to understand the molecular packing in supramolecular assembly.

In second part, the research focused on the comparison of photophysical properties of mono and bichromophoric DFB as well as its ability to form supramolecular assembly. We then proceeded in the energy migration property of mono-substituted compared to di-substituted DFB and finally the supramolecular assembly. In the later part of the chapter 3, we discussed the responsiveness of the supramolecular self-assembled nanowires to UV light, and we investigated the primary reasons for such responsiveness through combination of photophysical measurements and microscopy.

The last part of the research was focused on the solid-state measurements wherein the mechanofluorochromic properties of mono-DFB and bichromophore DFB was compared. Moreover, we studied the mechanofluorochromism of bichromophore bearing amide and ester bridges to determine the impact of intermolecular interactions such as hydrogen bonding. To gain insights and understanding to the mechanofluorochromic properties of these compounds, we did single crystal analysis and time-resolved fluorescence spectroscopy. The reversibility of the emission was also investigated, and some calculations were performed to understand the intermolecular interactions within the crystal system. In the last chapter, the conclusions and perspectives for the study was discussed.

CHAPTER 2

Circularly Polarized Luminescence and Circular Dichroism of Bichromophoric Difluoroboron-β-diketonates CPL nature of organic molecules and coordination substances in self-organized supramolecular aggregates have been extensively studied, in which long-range exciton coupling is expected to enhance chiroptical activity. [1][2][3] Aggregation induced emission (AIE) of some chiral organic molecules has also been reported for enhanced CPL capability. 4,5 As one of the most promising fluorophores for the supramolecular approaches, we have been recently focusing on difluoroboron-β-diketonate (DFB) complexes because of the high quantum yield in both solid and solution states, 6 high Stokes shift and sensitivity to stimuli such as mechanical stress [7][8][9][10] and presence of organic vapors. 10 Typical BF2 units may promote specific inter-molecular association. It has been previously reported that DFB complex bearing chiral amido group displays a good CPL signal and response to mechanical stress in solid state but showed weak CPL signals in monomeric state. 11 However, supramolecular aggregates of long range selfassembly based on this chromophore remain to be investigated.

In this chapter, we report two new bichromophoric DFB compounds with chiral cyclohexane diamine bridge (Figure 2.1). Different solvents systems lead to different aggregated forms and photophysical and chiroptical properties. We show that both the geometry of the bichromophore (relative orientations of the DFB units toward the chiral diamine, see figure 1) and the solvent systems strongly influence the chiroptical properties. The results of this chapter were already submitted for publication:

Circularly Polarized Luminescence and Circular Dichroism of Bichromophoric Difluoroboron-β-diketonates: Inversion and Enhanced Chirality based on Spatial Arrangements and Self-assembly

Synthesis

The target compound para (R/S)-CyDFB was synthesized by Claisen condensation reaction of 4-methoxy acetophenone and dimethyl terephthalate forming β-keto enol. Herein, para and meta (R/S) were referring to 1R,2R and 1S,2S(-)-1,2-cyclohexanediamine enantiopure compounds. Saponification with LiOH converts ester to carboxylic group, 12 and this step was followed by peptidic coupling of para (R/S) cyclohexane diamine forming the bichromophoric ligand 13 . Finally, complexation of the bichromophore ligand using BF3(OEt)2 yields a yellow powder of para (R/S)-CyDFB after purification. Characterizations with 1 H, 13 C NMR, and Spiral TOF mass spectrometry confirms the target compound. The same steps were used to synthesize the meta (R/S)-CyDFB but using dimethyl isophthalate in Claisen condensation reaction instead of dimethyl terephthalate as shown in Scheme 2.1 and Scheme 2.2. The complete synthesis procedures are written in Chapter 6. We first measure the photophysical properties of para and meta (S)-CyDFB in dichloromethane (DCM) wherein the compounds displayed a good solubility. Both compounds display a broad and intense absorption band centered at 390nm. The molar absorption coefficient (ԑ) of para (S)-CyDFB was higher (105,000 M cm -1 ) than meta (S)-CyDFB (72,000 M cm -1 ) indicating a higher energy harvesting property. The fluorescence quantum yield of para and meta (S)-CyDFB in DCM are 0.67 and 0.64 respectively.

Photophysical Properties in Solution and Time-Correlated Single Photon Counting

The absorption and emission spectra of para and meta (S)-CyDFB were measured with different solvent polarities as shown in Figure 2.2 and Figure 2.3. Absorption spectra for both compounds do not significantly shift ranging from 389nm to 398nm for para (S)-CyDFB and 385nm to 393nm for meta (S)-CyDFB indicating less interactions of their ground state to solvent molecules. 14 Emissions for para (S)-CyDFB displayed maximum wavelength at 440nm, 446nm 443nm and 444nm in chloroform, DCM, THF and toluene while meta (S)-CyDFB displayed at 436nm, 442nm, 436nm and 440nm respectively. However, there are noticeable shifts of emissions in polar solvents such as DMF and acetonitrile indicating a weak intramolecular charge transfer nature in the excited state with the presence of methoxy as electron donating group. 15 Lippert-Mataga plot (see Tables 2.1-2.2 and Figure 2.4) showed a linear correlation between the solvent orientation polarizability and the Stokes shift, excluding toluene for which specific aromatic solute to solvent interactions may occur. 16 Lippert-Mataga equation is as follows:

where νA -νF are the wavenumbers (cm -1 ) of the absorption and emission ℎ is Planck's constant (=6.6256 x 10 -27 ergs) 𝑐 is speed of light (3.0 x 10 10 /cm) 𝜀 is dielectric constant of solvent 𝑛 is refractive index of solvent 𝜇 𝐺 is dipole moment in ground state 𝜇 𝐸 is dipole moment in excited state 𝑎 is cavity radius Time-resolved spectroscopy measurements were conducted to gain insights to the emitting species in para and meta (S)-CyDFB in DCM solution. The decays were fitted with required satisfactory value of X 2 < 1.2 and the summary of decays are listed in Table 2.3 (see Chapter 6 for complete TCPSC plots). Para (S)-CyDFB exhibits a bi-exponential decay with decay time values τ1= 12ns (a1=0.01) and τ2=2.0ns (a2=0.99) while meta (S/R)-CyDFB exhibited tri-exponential decay with decay time values τ1=7ns (a1=0.02) and τ2=2ns (a2=0.70) and τ3=0.7ns (a3=0.27) measured at emission wavelength of 463nm (Table 2.2). For both compounds, the main contributions are from emitting species with decays around 2ns which may be attributed to the individual DFB unit by comparison with related monomeric compounds. 11 Long decay times 12ns for para (S)-CyDFB and 7ns for meta (S)-CyDFB) may be attributed to intramolecular exciton coupling between the two DFB units bridged by the cyclohexane diamine. (a) and fraction of intensity (f) of monomers in DCM of para and meta (S)-CyDFB (λexc = 390nm, λem = 463nm).

Fraction of intensity was calculated from decay time constant (τ), pre-exponential factor (a) according to equation Iαiτi/∑ αiτi.

Density Functional Theory (DFT) and Time-dependent DFT (TD-DFT) Calculations

To understand the molecular electronic properties of the compounds, density functional theory (DFT) and time-dependent DFT (TDDFT) calculations were performed in Gauss view 16 using the functional CAM-B3LYP and basis set (6-31+) G(d,p) with IEFPCM (DCM) solvation method. Optimized ground state geometry revealed that para (S)-CyDFB in DCM have two non-equivalents DFB units (Figure 2 In the first DFB, dihedral angle of phenyl group connected through amide bond has dihedral angle of 27.4° with respect to amide plane which is more twisted than the second DFB moiety with an angle -4.8°. Phenyl rings of the first DFB moiety has dihedral angle of 13.3° and -1.19° with respect to the difluoroboron β-diketonate plane while the phenyl rings of second DFB unit have dihedral angles of 24.9° and 6.97° respectively. The two DFB groups in para (S)-CyDFB were in proximity and overlapped their phenyl group attached in amide bonds. Single crystal analysis of para (S)-CyDFB showed a slight variation in arrangement of DFB moeities mainly because of presence of intermolecular interactions in crystals while the DFT was calculated in monomeric form (see Figure 2.6a).

On the other hand, optimized geometry of meta (S)-CyDFB showed that the DFB groups are in equatorial position where both are headed to the opposite sides. The phenyl rings connected to amide group has dihedral angle of -18.4° and -18.9° with respect to amide plane. In the first DFB moiety, phenyl rings have dihedral angle of -13.5° and -7.6° with respect to difluoro boron β-diketonate plane while in the second DFB moiety, phenyl rings have dihedral angle of -9.9° and 8.2° with respect to difluoro boron β-diketonate plane (see Figure 2.6b). The electronic transitions and corresponding involved molecular orbitals of para and meta (S)-CyDFB were calculated by time-dependent DFT (TD-DFT). The results showed that there are multiple molecular orbitals involved in each transition. Natural transition orbitals (NTO) were also calculated to clearly demonstrate the electronic

Chiroptical Properties of Monomeric and Aggregated Bichromophores

Chirality of monomeric compounds in the ground state were studied by circular dichroism (CD) measurement of both para and meta (S/R)-CyDFB compounds dissolved in DCM. CD spectra of para (S/R)-CyDFB enantiomers show mirror images with positive Cotton effect for S enantiomer while negative cotton effect for R enantiomer. Interestingly, meta (S/R) CyDFB display an opposite Cotton effect measured at the same wavelength as para (S/R)-CyDFB (see Figure 2.9). The observed Cotton effect signs for both para and meta-CyDFB are in good agreement with the theoretical CD spectra from TD-DFT (see Chapter 6 for ECD plots).

As shown in the DFT optimized geometry, variation in connectivity of para and meta leads to different spatial arrangement of DFB units. Para (S/R)-CyDFB units are in axial position and the DFB groups are more aligned and overlapped with one aromatic ring. In contrast, the meta derivative favors the equatorial position and rearranged the DFB groups towards the opposite sides preventing interactions of two DFB units. Notably, CD spectra of bichromophoric DFB in para position showed more intense CD response and displayed twice the dissymmetry factor with |gabs| value of 4x10 -4 as compared with DFB in meta position with |gabs| value of 2x10 -4 (Figure 2.9). Higher |gabs| value may be due to shorter distance of DFB units in para position causing excitonic coupling between the DFB units. Moreover, degree of overlap between the chromophores and the configurations of DFB units in DCM have directed the inversion of chirality. 17 The measurements of photophysical properties were extended to self-assembled aggregates of para and meta (S/R)-CyDFB in a mixture of chloroform and methylcyclohexane (MCH) (29:1) at concentration 3.5x10 -5 M. The solution turns from bright blue emission in monomeric form (DCM) to yellow emission (insert image in Figure 2.10a) in mixture of MCH and chloroform (29:1) under UV light. This is accompanied by broadening of absorbance as compared with the monomeric form. SEM images showed a randomly connected spherical aggregates both in para and meta derivatives (Figure. to the intermolecular excitonic coupling between DFB units in chiral aggregates, which should operate over 4 or more DFB units. 17,18 In contrast, the meta-isomer displayed no significant CPL activity in both monomeric and the aggregated forms, which is attributable to less CPL activity to be detected in our system. These results clearly demonstrate significant difference in the intramolecular and intermolecular excitonic coupling between DFB units of two these isomers. To further understand the changes in dissymmetry factors in MCH rich solution, fluorescence decays were measured by TCSPC at λem = 550nm for both para and meta (S)-CyDFB. Para (S)-CyDFB aggregates exhibited tri-exponential decay with decay times at τ1=40.5ns (a1=0.72), τ2=14.7ns (a2=0.21) and τ3=1.6ns (a3=0.07). Likewise, meta (S)-CyDFB aggregates also displayed a tri-exponential decays with decay times at τ1=40.8ns (a1=0.33), τ2=16.9ns (a2=0.27) and τ3=2.7ns (a3=0.40) (Table 2.4).

Table 2.4 Emission decay time constant (τ), pre-exponential factor (a) and fraction of intensity (f) aggregates in MCH/CHCl3 of para and meta (S)-CyDFB (λexc = 390nm, λem = 550nm).

Noticeably, the pre-exponential factor of decays at 40ns in para-CyDFB is more than twice the pre-exponential in the meta isomer. This is in contrast with the short-lived species at around 2ns which has higher pre-exponential factors in meta-aggregates (40%) but has low pre-exponential factor in para (7%). The predominant decays of long-lived emitting species with decays at around 40ns and 15-17ns formed through intermolecular and intramolecular excitonic coupling may explain the enhanced chiroptical properties of para as compared with meta. These results also suggest rather minor and random biand multi-chromophoric coupling in the aggregated meta-isomers.

Supramolecular Assembly

Formation of para (R/S)-CyDFB organogels were observed in mixture of DCM and toluene (50:50) stimulated by ultrasonication followed by heating at 40°C for 10mins. The organogels were formed after 144 hours of slow evaporation of DCM at room temperature. Pure toluene assisted with ultra-sonication and heating formed a mixture of opaque aggregates and gels due to poor solubility of compounds in pure toluene. The presence of DCM in the solvent system balanced the solubility-precipitation of compounds and assisted the formation of thermodynamically stable organogels driven by π-π and hydrogen bonding 19 . The formation of gels is confirmed by stable inversion of test tube method and the emission while forming the gels were monitored as shown in Figure 2 which is attributed to the monomeric form shown in Figure 2.12b. After 144 hours, majority of the bichromophoric units were self-assembled into nanowires. Morphology of nanowires were observed after deposition and drying of organogels under vacuum (xerogels). SEM images of xerogels (Figure 2.13) shows the formation of extended nanofibers with thickness ranging from 5nm-15nm. The single para (S)-CyDFB unit has molecular length around 1.8nm as measured from the optimized structure calculated with DFT, hence it indicates that fibers formed are not onedimensional but rather composed of multiple intertwined fibers which is evident in the images. To gain more insights in the molecular arrangement, single crystal structure of para (S)-CyDFB complex was determined from a crystal obtained by slow solvent evaporation using DCM as solvent. Crystal structure revealed that the bichromophoric units has various side-to-side interactions involving fluorine atoms to the methoxy as well as H-atom of the adjacent DFB units via CH/F hydrogen bonding as shown in Hirshfeld surface analysis (Figure 2.14b). 20 Moreover, extending the structures from top to bottom shows the π-π stacking between the extended fibers owing to H-bonding (Figure 2 Simulated packing structures of bichromophoric units were obtained through Materials Studio 7.0 program using COMPASSII force field. 21 The hydrogen bonding observed in crystal structure through amide group is also present in simulated packing but differs mainly in twisting of DFB group (Figure 2.14c). Notably, the proposed calculated structures of nanowires displayed a periodical single and double hydrogen bonding every four bichromophoric units leading to twisting of one-dimension wires. DFB units were also bent downward as seen in the top DFB units and slightly reversing the bending towards the upward direction as seen in the last DFB unit located at the bottom part of the model. This possibility of one-dimensional twisting based on the proposed packing may explain the intertwining of fibers as observed in SEM images. Moreover, formation of nanowires through amides and carbonyl hydrogen bonding is in good agreement with the previous studies of self-assembled nano-helical wires involving cyclohexane diamine as the chiral backbone moiety. 17,18,21,22 The same method for the formation of organogels were tested for meta (R/S)-CyDFB using different solvents such as cyclohexane, hexane, toluene, acetonitrile, DCM, chloroform, and mixtures of polar and non-polar solvents. Unlike with the para-isomer, the meta isomer showed no organogels in any of these solvents but rather precipitations occurred in both non-polar and mixtures of solvents.

Molecular packing arrangements of nanowires in para-CyDFB compounds revealed that hydrogen bonding involving amide groups is crucial in the formation of chiral backbone in stacked bichromophoric units. Comparison of the orientation of meta and para in DFT optimized geometry showed that the orientation of DFB units of meta are causing hindrance or blocking to the amide group hence suppressing the formation hydrogen bonding between the adjacent DFB bichromophoric units. Introduction of long alkyl chain may help to form molecular wires and liquid crystalline states in future molecules. 23

Photophysical Properties and Chiroptical Properties of Supramolecular Assembly

In section 2.4, it was shown the emission spectra of gels were initially displayed two emission bands at around 450nm and 550nm. The emission around 450nm was attributed to the monomeric form while the emission at 550nm is from the self-assembly which immediately formed after cooling down the solution at room temperature. Disappearance of emission at 430nm after 144 hours indicated that most of bichromophoric units were assembled into the helical nanowires (see Figure 2.12b).

TCSPC measurements of organogels provided more insights to the nature of emitters in nanowires. Table 2.5 shows that the long-live emitting species with decaytimes τ1=35ns (a1=0.42) and τ2=12.3ns (a2=0.04) were prominent at longer wavelength but almost did not exist at 450nm. These decays along with the shift in emission to higher wavelength suggests the formation of new emitting species through intramolecular and intermolecular coupling of DFB units. Shorter decay was observed at 550nm (τ3=2.3ns, a3=0.35) but more prominent at 450nm (τ2=2.1ns, a2=0.72) which is attributed to the residual monomers in the toluene solution (see Chapter 6 for decay plots). CPL measurements of para (R/S)-CyDFB organogels exhibited |glum| value of about 0.015 which is not fully reproducible due to stability of gels with long exposure to UV source during CPL measurements but relatively high values for organic molecules that usually ranges from 10 -2 to 10 -5 . 13 High gCPL values were observed at the range 530nm-550nm, which suggests that these CPL signals correspond to the newly formed emitting species in the self-assembled nanowires. This value has two orders of magnitude higher than its monomeric form and an order of magnitude higher than the random aggregates in MCH:CHCl3 solution. Similarities in lifetimes and CPL signals observed at λem 500nm-550nm for aggregated form and organogels may indicate that emitting species with longer lifetimes are present for both assemblies formed through intermolecular interactions. Significantly intense CPL signal observed in the nanowires is probably due to the highly ordered arrangement of bichromophoric DFB units forming helical and intertwined fibers. Such arrangement promotes the long range cooperative excitonic coupling between the chromophores causing enhanced CPL signals. 3,17,18

Conclusion

In this chapter we have synthesized two bichromophoric DFB complexes connected in para and meta position using cyclohexane diamine as chiral bridge moiety. We have shown that the difference in connectivity of para and meta has led to variation in spatial arrangement of DFB units, hence exhibited inversed sign of Cotton effect. DFB complex in para position appeared to have stronger CD and CPL signals owing to the overlap and shorter distance of DFB units which favored the intramolecular coupling.

CD and CPL signals in aggregated forms has increased as compared to the monomeric form accompanied by the existence of long-lived emitting species. This indicates prominent intermolecular and intramolecular excitonic coupling in the random aggregates. Moreover, para isomer formed nanowires in mixture of toluene and DCM solvent while the meta isomer failed to form nanowires showing that the spatial arrangements highly influenced the formation of π-π stacking and hydrogen bonding. Notably, the organogels displayed a |glum| value of about 0.015. The results in this study may contribute to the future design of supramolecular assembled nanowires considering the influence of spatial arrangement of the supramolecular assembly formation and the tunability of the bichromophore units that induces the inversion of chirality.

CHAPTER 3 Energy Transfer and Sensitivity to UV Light of Supramolecular Nanowires based on

Bichromophoric DFB compound Synthetic light harvesting materials based on metal organic frameworks, dendrimers, polymers and supramolecular assemblies through arrays of chromophores have been utilized for device fabrications such as organic light emitting diodes, sensors and photovoltaic cells. [1][2][3] Supramolecular assembled compounds have advantages in device fabrication due to simplicity of each molecular units and less complicated synthesis as these supramolecular architectures are driven by spontaneous weak intermolecular interactions 4 . The efficiency of light harvesting properties originates from the intermolecular electronic interactions within the chromophores units that induce exciton migration. 1,[5][6][7] Thus, it is equally important to evaluate the energy transfer in supramolecular assembly and its electronic communications in coupled chromophore with respect to its monomeric form for effective supramolecular molecular design for device fabrication.

The formation of supramolecular assembled nanowires in bichromophore DFB as well as its molecular stackings, electronic transitions, and enhanced chiroptical properties were discussed in the previous chapter. This chapter provides insights on the comparison of mono-substituted and di-substituted DFB (Figure 3.1) in terms of formation of supramolecular assembly and photophysical properties in monomeric form (Sections 3.2-3.4). The efficiency of energy transfer was evaluated with anisotropy measurements for mono and di-substituted DFB diluted in frozen matrices as well as in supramolecular assembly (Section 3.5). Lastly the sensitivity of the supramolecular assembly to exposure in high photon flux was evaluated (section 3.6).

Synthesis

In this study we synthesized two compounds bearing one DFB unit (cydiamine mono-DFB) and two DFB units (cydiamine di-DFB) with pure (S) enantiomers (S is referring to 1S,2S). The target compounds cydiamine mono-DFB and cydiamine di-DFB were obtained by synthesizing first the intermediate P-1. This was already discussed in the previous chapter: P-1 was synthesized through Claisen condensation reaction of 4methoxy acetophenone and dimethyl terephthalate at 70°C for 12hours. 8 This was followed with reaction of LiOH to convert P-1 to β-keto enol acid (P-2). 8,9 First step in synthesizing cydiamine mono-DFB is through protecting one amine group in 1S,2S cyclohexane diamine using tert-butoxycarbonyl (t-BOC) to obtain Cydiamine-BOC compound (scheme 3.1). 10 This was followed by peptidic coupling of P-2 with Cydiamine-BOC using diethyl cyanophosphate (DECP) and triethylamine. After peptidic coupling, BOC protecting group was then removed using a mixture of trifluoroacetic acid (TFA) and dichloromethane (DCM) (2:1) to form the cyclohexane diamine mono-β-keto enol ligand. 11 Complexation with BF2 was completed using BF3(OEt)2 and the target compound cydiamine mono-DFB was isolated through automatic column chromatography. Cyclohexane diamine difluoroboron-β-diketonate (cydiamine di-DFB) was synthesized using the previously reported scheme as discussed in Chapter 2. The reaction scheme is shown in 3.1 (see Chapter 6 for detailed synthesis).

Photophysical Properties in Solution

The comparison of the photophysical properties of the two compounds in solution was done by measuring absorbance and emission of cydiamine mono-DFB and cydiamine di-DFB in different solvents as summarized in Table 3.1. As shown in Figure 3.2, both compounds display similar range of absorbance (387nm to 391nm for cydiamine mono-DFB and 390nm-394nm for cydiamine di-DFB) at different solvent polarity. The emission of di-substituted DFB are expected to display at longer wavelengths due to the intramolecular coupling of two chromophore units within one molecular unit. 12,13 However, emission spectra of cydiamine mono-DFB at different solvents polarity showed similar emission and solvatochromism as cydiamine di-DFB.

A B

Time-resolved fluorescence spectroscopy measurements were conducted to gain insights on the lifetimes in solution. The decays were fitted required satisfactory value of X 2 < 1.2 in global analysis and the summary of decays are listed in Table 3.2. Both compounds exhibit bi-exponential decay where cydiamine mono-DFB has decay time values τ1= 0.99ns (a1=0.08) and τ2=0.6ns (a2=0.92) while cydiamine di-DFB has τ1= 12.18 ns (a1=0.01) and τ2=2.06ns (a2=0.92). Although two decay times were observed, it is noticeable that one of them are with traceable contribution (τ1= 0.99ns for cydiamine mono-DFB and τ1= 12.18 ns for cydiamine di-DFB).

Similar with cydiamine di-DFB, quantum yield was calculated using quinine sulfate standard. The cydiamine mono-DFB in DCM has QY 0.31 while in the previous chapter, it was shown that cydiamine di-DFB in DCM has QY = 0.69. The red shift in emission spectra accompanied by positive solvatochromism and lower quantum yield was previously explained with the presence of electron donating group to the DFB molecules and intramolecular charge transfer (ICT) character. 14,15 where τn is decay time, an is pre-exponential factor and fn is fraction of intensity, QY is fluorescence quantum yield Knr and Kr are non-radiative and radiative rate constants.

Density Functional Theory (DFT) and Time-dependent DFT Calculations

To gain insights into the photophysical behavior of the two compounds and to determine the molecular orbitals involved as well as the electronic transitions, density functional theory (DFT) and time dependent DFT calculations were performed. In this calculation, functional CAMB3LYP, basis set 6-31+G (d,p), and IEFPCM solvation method using DCM were used. The optimized geometry of cydiamine di-DFB was previously discussed in Chapter 2, while the optimized geometry of cydiamine mono-DFB is included in supplementary documents (Chapter 6). 6.6) (a) and cydiamine di-DFB (refer to chapter 6 table 6.4) (b) and their energies (Hartree), calculated using TDDFT with functional CAMB3LYP, basis set 6-31+G (d,p), and IEFPCM solvation method.

The TD-DFT calculations of cydiamine mono-DFB revealed that the electronic transitions from the lowest energy involve multiple molecular orbitals as shown in Figure 3.3. (See chapter 6 for tables of molecular orbitals and their contributions). Transitions from HOMO-2 to LUMO involves primary amine group which has contributed to the intramolecular charge transfer (ICT) from NH2 to the electron withdrawing group DFB. In contrast, for cydiamine di-DFB, the molecular orbitals involved in the transitions show that the electrons are mainly delocalized to each β-diketonate moiety (see Figure 3.2b). Cydiamine di-DFB have the following transition: HOMO-1 to LUMO, HOMO to LUMO, and HOMO to LUMO+1. It was also noticeable that there is electron delocalization on the diketonate rings of opposite DFB unit shown in Figure 3.3b, indicating intramolecular coupling between the two DFB units of bichromophore.

Self-Assembled Nanowires

In the previous chapter, we have shown the formation of self-assembled nanowires of cydiamine di-DFB with mixture of toluene and DCM showing intertwined wires. Self-assembled nanowires formation was also attempted with cydiamine mono-DFB using different solvent systems and combinations of polar and non-polar solvents initiated with ultrasonication and heating. However, the compounds are either fully dissolved or precipitated in all the experimental conditions. First, failure to form a supramolecular assembly may result from the presence of a primary amine which may tend to form stronger hydrogen bonds causing precipitation of the compound. Secondly, it was clear from the calculated structures of nanowires from Materials Studio COMPASS II from the previous chapter that the presence of two amide groups is playing crucial part in supramolecular assembly. It is through the formation of H-bonds between the carbonyl and amide groups of the adjacent bichromophoric DFB units that the supramolecular backbone is formed. From these observations, it was suggested that single carbonyl and amide groups alongside with the presence of primary amine located at the cyclohexane moiety are not enough to form a stabilize the supramolecular backbone of nanowires.

Energy Transfer in Supramolecular Assembly

We then studied the comparison of energy transfer within mono substituted DFB to di-substituted DFB and its supramolecular assembly. The efficiency of energy migration was evaluated based on its anisotropy values. The steady-state fluorescence anisotropy measurements are based on the principle photo selective excitation of fluorophores wherein the absorbance of photons takes places if the fluorophores have parallel transition moments with the electric vectors of photons. 16,17 The anisotropy was calculated with the following equation:

𝑟 = (𝐼 𝑉𝑉 -𝐺𝐼 𝑉𝐻 ) (𝐼 𝑉𝑉 + 2𝐺𝐼 𝑉𝐻 ) 𝐺 = 𝐼 𝐻𝑉 𝐼 𝐻𝐻
where:

r is anisotropy value IVV and IVH are emission intensity measured at vertical and horizontal position when the polarizer is vertically oriented.

IHV and IHH are emission intensity measured at vertical and horizontal position when the polarizer is horizontally oriented.

G is gain factor

The measurements for monomeric forms of cydiamine mono-DFB and cydiamine di-DFB are done at -50°C with cryostat system using polypropylene glycol as solvent. The anisotropy values of cydiamine mono-DFB as a function of excitation and emission have similar average anisotropy values of r = 0.36 measured at range 390nm -410nm and 440nm -460nm respectively. On the other hand, cydiamine di-DFB exhibits anisotropy values of r = 0.18 as a function of excitation (390nm -410nm) and r = 0.14 as function of emission (450nm -470nm) as shown in Figures 3.4 and 3.5. High anisotropy values in cydiamine mono-DFB clearly shows that there is no exciton migration within the neighboring chromophore while the decrease in anisotropy values in cydiamine di-DFB clearly exhibits intra-molecular exciton migration between the two DFB units. This result is also parallel with the molecular orbitals calculated with TDDFT showing intramolecular interactions between the two DFB units of a bichromophore. The measurements were extended to the supramolecular assembly which displayed a dramatic decrease in anisotropy values to r = 2x10 -3 and a function of excitation (average at 410nm to 430nm) and r = 5x10 -3 as a function of emission (530nm-550nm). The depolarization is clear evidence of exciton migration in supramolecular assembly (see Figure 3.6). Small amount of cydiamine di-DFB nanowires was deposited in a clean glass by sliding off a portion of organogels to the glass leaving a thin layer of nanowires on the surface. The glass was then placed under vacuum for at least 6 hours to remove the solvents. Isolated nanowires were subjected for emission measurements before and after exposure to UV. The UV source was set to excitation wavelength of 400nm with I=2% and total exposure time of 2 seconds. The measurement slit was set to 200 µm and the emission before and after exposure was measured in several areas along the measurement slit (see Figure 3.8a). It was observed that the emission has shifted to lower wavelength from 545nm to 480nm accompanied by a decrease in emission intensity as shown in Figure 3.8b. Photobleaching in nanowires was further investigated by monitoring the fluorescence intensity with exposure time. The same AFM coupled with fluorescence microscope was used but the exposure time was extended to 10mins while capturing the emission in 1 frame per second using the CCD camera. The decrease in emission intensity was monitored in several areas within the frame as shown in Figure 3.9a. The intensity vs time plotted for different areas under observation showed that there is ~75% decrease of intensity after 10minutes of exposure (see Figure 3.9b).

A B

To further understand the emission shift and decrease in the fluorescence intensity, the measurements were extended to macro-scale analysis. Organogel was exposed in UV source equipped with filters to select the wavelength around 380nm and was set to I=100%. The set-up was kept at 25°C to reduce the errors caused by accumulating heat from the source. The steady-state fluorescence emission was measured after exposure at different times while simultaneously measuring the timeresolved fluorescence emission to understand the nature of emitting species at both wavelengths shown in Figure 3.10a. The steady state fluorescence spectra showed that the overall emission intensity is decreasing which agreed with the photobleaching effect observed at microscale analysis. Apparently, emission peak at 450nm has gradually increased with respect to the emission peak at 550nm as shown in intensity ratio plot vs time (see Figure 3.10b). This is in contrast with the dramatic decrease in intensity at 550 nm after 15minutes of exposure time. 1. The emitting species with decay time 21.6ns has very low pre-exponential factors which may be attributed to the residual aggregates from the long-lived emissive species. Meanwhile, the pre-exponential factors from the emitting species with decays τ3 = 0.54 ns and τ4 = 0.05ns are showing mirror images indicating that these are coming from one component (0.54ns) which eventually was converted to fast decays (0.05ns) after exposure to UV. The emitting species with decay at τ2 = 2.13ns was gradually decreasing with exposure time which may be attributed to the monomeric form. Similarly, time-resolved spectroscopic measurement data for wavelength peak 550nm was fitted with global analysis (see Figure 2.12 and Table 2). The decay times were found τ1 = 38.4ns, τ2 = 25.7ns, τ3 = 5.74ns, and τ4 = 0.71ns. The emitting species at longer decay times τ1 = 38.4ns, τ2 = 25.7ns, τ3 = 5.74ns were from multimers formed through intermolecular interactions in the supramolecular assembly of nanowires and exhibit decay times which are far longer than the decay time of monomeric form (<2ns as discussed in chapter 2). The emission from long decay (38.4ns) exhibits the same mirror image as with short decay time (0.7ns), which also indicates these are emissions are from the same species. Noticeably there are emissive species with intermediate decays (25.7ns and 5.7ns) which further emerged after exposing the organogels to UV source. The shortest decay time are predominant for both emissions in 450nm and 550nm after exposure to UV. This may be attributed to the emission from bichromophore units without BF2 which agree with the TCSPC analysis of this compound in solution showing a very short lifetime (< 0.01ns) (see Chapter 6 for supporting details).

The results obtained from the combination of time-resolved and steady state fluorescence spectroscopy, it was evident that the emissive components with long decays formed in 550nm wavelength was reduced in contribution after exposure of organogels in UV light. On the other hand, emissive species with intermediate and shorter decays gradually increase with UV exposure suggesting that there are possible distortion of long range multimers formed in supramolecular assembly.

AFM Image Analysis

The morphologies of the nanowires were compared before and after exposure to UV. The exposed nanowires were carefully collected and deposited in cleaned glass slides and dried under vacuum to remove the solvents prior to AFM analysis. AFM images showed fragments of nanowires and surprisingly radial aggregates were also found in the images in Figure 3.13. The fragmented fibers as well as the radial aggregates were not observed in morphological analysis of isolated unexposed nanowires. This may indicate that high energy photons from the UV source may not only caused destructed BF2 to carbonyl interactions, but also disruption of H-bonding of molecular backbone of nanowires. On the other hand, the radial deposits may be due to re-agglomeration of monomeric bichromophore units after dislodging from supramolecular assembly. It should also be noted that the solvent in organogels is toluene which is a poor solvent for cydiamine di-DFB which rationalizes the re-agglomeration into radial arrangement. Image analyses were conducted to determine the average length of fragments and the diameters of aggregates which gives the range of 200nm -500nm for fragments (see Figure 3 The time-resolved spectroscopic measurements for both 450nm and 550nm may then suggest that influx of photons to the organogels caused degradation of supramolecular assembly as evident with emerging decays with long exposure to UV.

200nm-500nm

Finally, to demonstrate the emission shift after exposure to 380nm UV light source, we printed pattern in the surface of the organogels. It was shown that the exposed part has blue emission while the unexposed organogels emits yellow under visualized 365nm UV source shown in Figure 3.16.

Conclusion

In this chapter, we discussed the photophysical properties of mono-substituted DFB (cydiamine-monoDFB) and di-substituted DFB (cydiamine-diDFB). Moreover, the DFT and TD-DFT calculations give an insight into the electronic transitions and electron delocalization within the DFB moiety of mono and di-substituted DFB. The supramolecular assembly formation was attempted for cydiamine-monoDFB and its failure justified the importance of two groups of carbonyls to amide H-bonding in stabilizing the molecular backbone as exhibited by cydiamine-diDFB in the previous chapter.

Energy transfer in monomeric form was evaluated through anisotropy measurements showing an efficient energy transfer within the two DFB units of isolated di-DFB, while the mono-DFB did not demonstrate such energy transfer. Meanwhile, the supramolecular assembly exhibits effective depolarization which proves the efficient exciton migration within the chromophores. This exhibits the potential applications in fabrication of light harvesting devices. Finally, the responsiveness of the nanowires to the UV exposure were explained by following the nature of emitting species in organogels at different exposure time. In accordance with the emerged short and intermediate lifetime emission, AFM image analysis provided evidence of disrupted H-bonding and reagglomeration of monomeric forms which shifted the emission to lower wavelength. The responsiveness of the organogels with UV may suggest the potential use in sensors.

CHAPTER 4 Mechanofluorochromic Properties of Bichromophoric difluoroboron β-Diketonate

Several organic compounds display emission shift upon external stimuli such as force application, grinding and smearing which is known as mechanofluorochromism (MFC) or mechanochromic luminescence (MCL). 1 Highly mechano-responsive and emissive solid state organic materials are gaining interest for device fabrication such as OLEDs, 1,2 security tags 3,4 , memory data storage 5 and microsensors. [6][7][8] Such responsiveness was explained through the molecular arrangements, formation of dimers and modulation of non-covalent intermolecular interactions such as H-bonding and π-π stacking after application of mechanical stress. [9][10][11][12] One of the most promising MFC organic compounds are difluoroboron β-diketonates (DFB) which display high quantum yield in both solution and solid state, high molar absorptivity, tunable and reversible MFC. [1][2][3]5,7,13 The mechanofluorochromic properties of difluoroboron β-diketonates and its reversibility have been intensively studied through variation of side chains 13,14 monitoring the dynamics of molecular arrangements 9,15 and in depth physico-chemical investigation with theoretical approach. 4,12 Molecular interactions not only direct the mechanofluorochromic properties but also enhance optical properties in solutions and supramolecular assemblies. For example in the study of Kawai group, they synthesized bichromophore perylene-BINAP units which displayed enhanced chiroptical properties caused by intense intramolecular coupling as compared to mono-chromophore 16 and dramatically increase in supramolecular assembly. 17,18 Such molecular design which promotes excitonic coupling within molecular units has broaden the perspectives in future design and fabrication of small organic molecules.

In this chapter, we present the mechanofluorochromic properties of a small series of bichromophore DFB.We compare solid state photophysical properties of mono-and bi-chromophore units of difluoroboron β-diketonates (DFB) using cyclohexane diamine bridge. To better understand the different photophysical properties of the three compounds before and after mechanical stimulus, we analyze their structures obtained with X-Ray diffraction on single crystal, including the surface interaction using Hirschfeld surface analysis and net interaction energy in the crystal system using energy framework. Time-resolved fluorescence spectroscopy measurements allowed us to understand the mechanofluorochromic properties and the behavior of emitting species including their intermolecular interactions in crystal form, smeared, and thermal annealed samples. Finally, the impact of variation in spacers such as amide and ester to the molecular packing of bichromophoric DFB and their mechanofluorochromic behavior was studied.

Synthesis

The target compounds with pure (R/S) enantiomers (referring to 1S,2S and 1R,2R) of cydiamine mono-DFB, cydiamine di-DFB are synthesized using the scheme discussed in Chapters 2 and 3. Racemic cyclohexane diester difluoroboron-β-diketonate (cydiester di-DFB) was synthesized by coupling the intermediate P-2 (see Chapter 6) to cyclohexane diol using NN'-Diisopropylcarbodiimide (DCC), and 4-Dimethylaminopyridine (DMAP) at 40°C for 12hours then purified with column chromatography using EtOAc:hexane (30:70) as eluent. 19 The cyclohexane β-diketo enol ligand was reacted with BF3 • O(C2H5)2 to form the target compound cydiester di-DFB. Scheme 4.1 shows the synthetic route used in for synthesis (the detailed synthesis is discussed in Chapter 6). The optimized geometry was shown in Figure 4.1a wherein the DFB moiety of cydiamine mono-DFB was slightly twisted with dihedral angles of phenyl rings 14.8° and -6.13° with respect with the diketonate plane. Both NH2 and DFB moiety are in equatorial Steady state fluorescence and absorbance of the compounds were measured in DCM, and it was shown that cydiamine mono-DFB, cydiamine di-DFB and cydiester di-DFB display similar absorption and emission wavelengths (see Figure 4.4). Time-resolved fluorescence spectroscopy measurements were conducted to determine the decay time of emissive species in solutions. The decays were fitted with global analysis and all the compounds under observation displayed bi-exponential decays showed in Table 4.1. Higher concentrations of cydiamine mono-DFB in DCM formed aggregation, hence acetonitrile was used in decay measurements because of high solubility in acetonitrile.

Hole Electron

Single Crystal Structures and Hirshfeld Surface Analysis

Needle-like crystals of cydiamine mono-DFB were formed in a mixture of ethyl acetate and hexane (30:70) at room temperature. These crystals emit yellow green fluorescence under UV excitation (365nm). Single crystal structure revealed that there are two distinct arrangements of cydiamine mono-DFB units that mainly differ in the twisted DFB around cyclohexane moiety. The single crystal structure is comparable to the calculated optimized geometry where both DFB and NH2 are in equatorial position, but the DFB moiety is slightly twisted due to presence of intermolecular interactions. These units are alternately stacked with overlapping diketonate rings and distance of 3.8 Å which makes up the molecular column (see Figure 4.5a).

To gain insights on the intermolecular interactions in the crystal system, Hirshfeld surface was calculated. Hirshfeld surface analysis is a theoretical calculation based on F.L. Hirshfeld's stockholder partitioning which calculates the electron density of each atom to define the shape and occupied space in a molecular fragment as well as its interaction with neighboring atoms. 20,21 Crystal Explorer21 software was used for calculations which provides visual illustration of intermolecular interactions and two-dimensional fingerprint plots of Hirshfeld surfaces.

Hirshfeld surface analysis and the finger print plots provides more extensive visual information on the interaction on molecular surfaces in a crystal. 20,22 Figure 4.5b shows that there is a strong interaction between the primary amine to the C=O of neighboring cydiamine mono-DFB and a solvent molecule. This was indicated by the red surface through H-bonds which made up the stacked molecular column. Moreover, a strong amide to BF2 surface interactions also exists on the other side of cydiamine mono-DFB inducing the inter-columnar interactions. Fingerprint plots of Hirshfeld surface showed a C•••C surface interactions consists of 6% (di-de at 1.8 Å ) pertaining to the typical π-π stacking 11 while other atomic interactions such as C•••H (13%), F•••H (14%), and H•••H (48%) comprised most of the molecular surface interaction in the cydiamine mono-DFB crystal. The fingerprint plots of all the atom-atom interactions were summarized in supporting details in Chapter 6. Crystal packing structures viewed along a-axis and its top view showing overlap of the diketonate rings were shown in Figure 4.6a. View along aaxis of extended structures of crystals revealed a columnar stacking corresponding to crystal packing motif γ which is characterized with angled face-to-face stacking (see Figure 4.6b). 23,24 Bichromophore units cydiamine di-DFB formed blue green emissive crystals by slow solvent evaporation using DCM at room temperature. Single crystal structures of cydiamine di-DFB revealed a uniform co-facial stacking with centroid distance of ca. 5.0 Å as shown in Figure 4.7. Hirshfeld surface analysis showed that C=O and amide group formed the stacked cydiamine di-DFB units through H-bonds. These are the main interactions responsible for the formation of columnar stacked cydiamine di-DFB units. On the other hand, BF2•••CH from diketonate of neighboring unit induced the inter- Another bichromophoric compound bearing ester group as spacer instead of amide (cydiester di-DFB) formed blue emissive crystals in mixture of chloroform and hexane (50:50) at room temperature. Single crystal analysis showed that the cydiester di-DFB crystals units were stacked in a brick-layer arrangement (see Figure 4.9a). Comparing the interlayer stacking in cydiamine di-DFB which was driven by close surface interaction of amide to C=O, cydiester di-DFB was driven by the C=O group interacting with BF2 group of the adjacent unit forming a row of cydiester di-DFB with interlayer distance of ca. 5.7 Å (see Figure 4.9b).

Mechanofluorochromic Property

The emissions of crystals of cydiamine mono-DFB, cydiamine di-DFB and cydiester di-DFB are shown in Figure 4.12a using excitation wavelength of 350nm. These crystals are grinded using mortar and pestle and the powdered samples are collected on a quartz plate then measured for emission (see Figure 4.12b). The emissions of all the compounds shifted to higher wavelength after smearing and are also evident in the images of crystals and smeared samples shown in Figure 4.13.

Mechanofluorochromism of Cydiamine mono-DFB

The needle-like crystals of cydiamine mono-DFB display a maximum fluorescence emission at λem = 543nm. The comparison of emissions of the three compounds under study revealed that cydiamine mono-DFB crystals emission is the most red-shifted (Figure 4.12a). After smearing using mortar and pestle, it further shifts to higher wavelength λem at 552nm as shown in Figure 4.12b. To understand the mechanofluorochromic behavior as well as the molecular interactions in crystal, time-resolved spectroscopy measurements at different wavelengths were conducted to the samples. The decays of emitting species in crystalline, smeared, and thermal annealed samples were measured at different emission wavelengths using excitation wavelength of 350nm. The results were fitted using global analysis and the decay times (τi), pre-exponential factors (ai) and fraction of intensites (fi) obtained after fitting are summarized in Chapter 6. The plots of fraction of intensities of crystals, smeared, thermal annealed and pristine powders (as collected powder after synthesis) are shown in Figure 4.14. The tables decays, fraction of intensity and pre-exponentials factors are listed in supporting documents (Chapter 6).

Cydiamine mono-DFB crystals exhibit exponential decays with decay time τ1= 15.6ns, τ2= 7.5ns, τ3= 1.5ns, and τ4= 0.5ns at different wavelengths (see Figure . 4.14a). Shorter decay times (<2ns) are attributed to the residual emission from monomeric species as these decay times are similar to the decays observed in monomeric form in solution (see Table 4.1) while the longer decays at τ1= 15.6ns and τ2= 7.5ns may be attributed to preformed excimers within the crystals. This also agree with the crystal structure showing a π-π interactions and close distance stacking of cydiamine mono-DFB units ca. 3.5 Å which favors intermolecular interactions thus red-shifted emission (λem = 543nm) was observed as shown in Figure 4.12a. After smearing the cydiamine mono-DFB crystals, a new emissive species with longer decay time τ1= 22ns was observed (see Figure 4.14b). Smearing induced a shift in longer wavelength (λem = 552nm) caused by the destruction of intra-columnar molecular stacking leading to a closer π-π interaction as characterized by broader and bathochromic shift in emission. 3,10,25 The emerged emitting species with longer decays time in smeared samples may indicate the formation of new dimers or aggregates formed through intermolecular interaction induced after smearing. 4,11 This was evident with the time-resolved spectroscopy showing a higher fraction of intensity from longest decays τ1= 22ns (f1=0.41) and τ2= 8.6ns (f2=0.48) measured at 550nm shown in Figure 4.14b.

Thermal annealing did not show any significant changes in emission wavelength at 80°C for 3hours, however time-resolved fluorescence spectroscopy measured at 550nm showed that the contribution from longer emissive species τ1= 22ns (f1=0.58) gradually increased indicating that thermal annealing favors the formation of closed packed arrangement of cydiamine mono-DFB units (see Figure 4.14c). Powder XRD also showed that after smearing, few XRD peaks are still visible suggesting that there are residual crystals even after applying of mechanical stress (see Figure 4.15). After thermal annealing at 80°C for 2 hours, the XRD patterns remains the same as with smeared samples shown (Figure 4.15). Single visible peak at 2θ = 5.2° and several broad peaks beyond 2θ= 5.5° suggest low crystallinity even after thermal annealing. 26 C D Increasing the annealing temperature higher than 80°C decreased the fluorescence intensity of smeared powder showing thermal instability and degradation at higher temperature. The decays profile of thermal annealed and as-collected powder after synthesis (pristine powders) shown in Figures 4.14c and 4.14d is almost identical which implies that thermal annealing induced molecular packing similar with pristine powder. This may indicate a meta-stable state since the compounds did not display any further changes in emission even after prolonged heating.

Mechanofluorochromism of Cydiamine di-DFB

Blue green emissive crystals of cydiamine di-DFB formed by slow solvent evaporation using DCM displayed a maximum emission (λem) at 529nm (see Figure 4.11b). Surprisingly, the emission of crystals is blue shifted as compared to the emission observed in cydiamine mono-DFB crystals. Since cydiamine di-DFB was covalently bridge by cyclohexane moiety, it was expected to form emissive species with longer emission wavelength as compared to mono substituted DFB due to intra-molecular coupling as what was previously observed in bichromophores. 16,27,28 The crystals were smeared with mortar and pestle and the fully grinded powder were deposited on a quartz plate. Upon smearing, yellow green emissive powder with λem=540nm was observed (see Figure 4.11b). Time-resolved fluorescence spectroscopy measurements were conducted to follow the behavior of emitting species in crystal and smeared form. Cydiamine di-DFB crystals display exponential decays with decay times τ1= 23ns, τ2= 7ns, τ3= 2ns and τ3= 0.2ns (see Figure 4.16a). Similar with cydiamine mono-DFB crystals, the shorter lifetimes <2ns were attributed to the monomeric components while intermediate (τ2= 7ns) and longer lifetime (τ1= 23ns) are due to formation of dimers. Pre-exponential factor from short-lived (2ns) and intermediate components (7ns) have the largest values at 550nm while highest fraction of intensity was observed from intermediate component τ2= 7ns (f2=0.57). Moreover, emissive species with longer decay (τ1= 23ns) was initially observed in crystals but with low fraction of intensity (<0.2) as shown in interactions while minimal π-π interaction resulted to columnar stacking distance of ca. 5.0 Å as previously discussed in crystal structures (see Figure 4.7). The observed stacking distance is longer than the distance in cydiamine mono-DFB units (ca. 3.8 Å) which have resulted in low intermolecular interactions. This is parallel with the time-resolved fluorescence spectroscopy measurements displaying low fraction of intensity from long decay components (23ns) and blue shifted emission of cydiamine di-DFB crystals (λem=529nm) as compared with cydiamine mono-DFB crystals (λem=543nm). It is also noticeable that despite the larger interlayer distance and low C•••C interactions, the cydiamine di-DFB crystal emits at longer emission wavelength (λem=529nm) as compared to its monomeric form in solution (λem=453nm). The red-shift emission may indicate that long-range coupling among identical DFB chromophores in cydiamine di-DFB still occur with its neighboring DFB within the molecular column. 29,30 This is evident by prominent intermediate decay time (7ns) which is longer than the decays for monomeric form with decay time 2ns. Smeared crystals exhibited bathochromic shift and broadened emission peaks caused by the destructed columnar packing. The bathochromic shift in smeared samples may be caused by favored formation of long-lived dimers or aggregates. 4,11,25 This was evident by the prominent fraction of intensity of long emissive components τ1= 23ns (f1=0.41) measured at 550nm in smeared samples while the intermediate decays (τ2= 7ns) remarkably decreased (Figure 4.16b).

On the other hand, Figure 4.16c shows that thermal annealing at 80°C for 2hours further increase the fraction of intensity of long emissive components (τ1= 23ns) suggesting that annealing induces the close distance stacking of cydiamine di-DFB, however XRD patterns did not significantly change showing low crystallinity (see Figure 4.17). The maximum emission peak of cydiamine di-DFB remains constant after thermal annealing at 80°C and even at higher annealing temperature (130°C) (see Figure 4.18). Smeared and thermal annealed samples shown in Figures 4.16b and 4.16c have similar decay profiles indicating that the compound reached a meta-stable state even before annealing.

The decay profiles of smeared and thermal annealed are also similar with pristine powders measured at 550nm-600nm, however higher fraction of intensity in intermediate decays τ2= 11ns (f1=0.31) was observed at shorter wavelength (500nm). The dominating emission from intermediate decay component (τ2= 11ns) at 500nm and broader emission peaks of pristine powders (Figure 4.16d). Thermal annealing at 80°C for 2 hours shows partial recovery of emission as shown in the increased intensity in 500nm (see Figure 4.21) accompanied by increase in components with short decay time (τ3= 1.8ns) as shown in Figure 4.19c. Higher annealing temperature (130°C) has caused further increase in the shouldering peak at 500nm as shown in Figure 4.21, moreover powder XRD displayed an increased intensity in 2θ=9.2° indicating higher crystallinity due to recovery of the molecular packing. Annealing at higher temperature (130°C) did not induce degradation as shown in thermogravimetric analysis (see Chapter 6). Steric hindrance and bulkiness of some organic molecules affect the thermal back reaction by hindered reversion to the initial molecular stacking. 10 Interestingly, partial emission recovery was only observed in cydiester di-DFB crystals and did not occur in cydiamine mono-DFB and cydiamine di-DFB. To understand this, we compare the intermolecular interaction energies of the crystals through calculations.

Intermolecular Interaction Energy in Crystals: Energy Framework

Energy framework was calculated to gain more insights not only to the close surface contact but also to the overall intermolecular interaction energy within the crystal. This computational approach was previously used by Spackman et al. to study the intermolecular energy and explain the mechanical properties of crystals at molecular level. 31,32 In this calculation, total energy was reported as the summation of all the intermolecular interactions such as polarization, dispersion, repulsion, and dispersion energies (kJ). The calculation was performed for the interaction of all molecules within the 3.8Å distance from the central molecule. The calculations were performed using CE HF/3-21G electron densities model. The It was shown that in cydiamine mono-DFB, the highest energies (largest cylinder diameter) were observed within the molecular column (-105.1kJ) and weaker intercolumnar energies (-50.2kJ, and -32.3kJ). Moreover, there are noticeable smaller radius cylinders indicating weaker but significant long distance inter-columnar interaction energies (-23 kJ).

A B

Similar with the mono-DFB, there are strong intermolecular energies with the top to bottom stacking of bichromophore units (-154kJ) as well as interactions within the adjacent columns (-117.3kJ, -96.5kJ and -39.5kJ). It is also noticeable that there is smaller radius cylinder from long distance inter-columnar interaction (-12.8kJ) which are weaker than what was observed in cydiamine mono-DFB.

Lastly, the total energy framework for cydiester di-DFB showed that most of the thick cylinders are concentrated within the column (-101.9 kJ, -52.8 kJ and -25.7 kJ) while very weak long distance inter-columnar interaction was demonstrated with small radius cylinder (-3.9 kJ) shown in Figures 4.24a It is noticeable that there is a large yellow cylinder which corresponds to positive Coulomb energy (repulsive) and red cylinder inter-columnar indicating negative coulomb energy (attractive) shown in Figure 4.25c. Although the repulsive energy is significantly large in crystal unit of cydiester di-DFB, dispersive forces counteract the Coulomb energy which is enough to stabilize the structure in crystal as shown in small blue cylinders in total energy framework.

Comparison of the Coulomb energies within the crystal system of cydiester di-DFB to the cydiamine mono-DFB and cydiamine di-DFB revealed that there are no significant inter-columnar repulsive forces (see Figures 4.25and 4.25b). The combined total interaction energy, strong atom-atom, and surface interactions of cydiamine mono-DFB and cydiamine di-DFB may explain the favored formation of close packing structures after smearing. These energies may stabilize the new conformations preventing the back reaction even after thermal annealing. These observations agreed with time-resolved spectroscopy measurements showing similar decay profiles in smeared and thermal annealed samples. In contrast with cydiester di-DFB, total energy framework shows a weak long-range distance interaction because of repulsive forces, however strong intracolumnar interactions energy forces have stabilized the structure. Smearing the crystals did not fully destruct the initial stacking of the molecules which may be brought by strong intra-columnar stacking. This is evidenced by the emission spectra of smeared samples showing shouldering peaks at emission wavelength 500nm and retained diffraction peaks in powder XRD of smeared powder. Thermal annealing induced the back reaction which may be due to combination of repulsive forces and weaker atom-atom interaction that made it easier to recover the initial state of the cydiester di-DFB crystal. This agrees with time-resolved spectroscopy measurements of thermal annealed samples showing a significant increase in fractions of intensity from short decay times accompanied by the decrease in fraction of intensity from dimers with long decay times. The comparison of these three compounds showed that cydiester di-DFB has the most promising mechanofluorochromic property as well as the partial reversibility. The observed weak intercolumnar and atom-atom interactions by cydiester di-DFB as compared with cydiamine mono-DFB and cydiamine di-DFB played a significant role in the mechanofluorochromic property. This result is in good agreement with the previous study of Krishna et al. showing that easy-to-deform crystals displayed better mechanofluorochromic property due to presence of slip planes formed by weak interactions of functional groups. 33,34

Conclusion

The mechanofluorochromic properties of three compounds, consisting of monochromophore DFB (cydiamine mono-DFB), bichromophore with amide spacer (cydiamine di-DFB) and bichromophore with ester spacer (cydiester di-DFB), were studied. It was revealed that cydiamine mono-DFB crystals displayed the longest emission wavelength while the bichromophore with ester spacer cydiester di-DFB crystals emit at the shortest wavelength. The presence of amine (NH2) in cydiamine mono-DFB and amide (-NH) cydiamine di-DFB favors the atom-atom interactions with carbonyl group of neighboring bichromophore unit with closer interlayer distances indicating stronger intermolecular interactions. On the other hand, cydiester di-DFB favors the carbonyl to BF2 interactions displaying brick-layering and longer intermolecular stacking distance leading to a blue shifted emission comparing to bichromophore with -NH and -NH2 spacers. Bathochromic shifts were observed for the three compounds after smearing while cydiester di-DFB displayed the largest emission shift with increased intermolecular interaction as confirmed by time-resolved spectroscopy measurements. This proves that the spacers amine and ester highly influenced the mechanofluorochromic properties of bichromophore DFB crystals through its atom-atom interactions and molecular stacking. Finally, only cydiester di-DFB displayed back reaction after thermal annealing and showed large positive coulomb energy (repulsive) as observed in the energy framework. The thermal back reaction as well as the significant positive coulomb energy was not observed in cydiamine mono-DFB and cydamine di-DFB which suggested that weaker atom-atom interactions and net repulsive forces favors back reaction cydiester di-DFB crystals. As demonstrated in this study, the small differences in the functional groups (amides and esters) with different interaction strengths highly influence the mechanofluorochromic properties as well as the thermal back reaction. The understanding of the molecular behavior of both mono and bichromophore DFB crystals will broaden the perspective in molecular design of reversible MFC materials for application in security and sensing devices.

the study we investigated the energy transfer between the two DFB units within the isolated bichromophore as compared to mono-DFB and supramolecular self-assembled nanowires. In this study we have shown that in mono-DFB, isolated molecules do not have any interactions with neighboring mono-DFB units. On the contrary with bichromophore DFB, we have proven that the two DFB units bridged with cyclohexane diamine have intramolecular coupling as evident by low anisotropy values. Lastly, supramolecular assembly has very efficient energy transfer which agree with the work of Spano et al. (2011) showing that long range excitonic coupling exist between the chromophore units in supramolecular assembly. 4,5 We have also investigated the response of the nanowires to UV irradiation, wherein the exposure has caused emission shift to lower wavelength accompanied by decreased in emission intensity. Through the combination of atomic force microscopy analysis and time-resolved fluorescence measurements, we have proved that the UV exposure destruct the BF2 to oxygen bonding in DFB moieties, also the H-bonding in supramolecular assembly which has caused the fragmentations of nanowires thus, emission shift was observed. The sensitivity of the supramolecular assembly to UV was demonstrated by printing patterns on the surface of gels.

In the previous parts of the study, we have discussed the intermolecular coupling of DFB in bichromophore units and how it has influenced the properties in solution and gel states. In the last part of the study, we therefore extend the measurements of bichromophore units in solid state wherein we compared the mechanofluorochromic property of cydiamine mono-DFB to cydiamine di-DFB. We uncover the effect of amine and DFB units to the molecular packing distance and strength of atom-to-atom interactions through single crystal analysis and Hirshfeld surface analysis. 6,7 We showed that the cydiamine mono-DFB has shorter molecular stacking distance as compared to the cydiamine di-DFB which is mainly due to stronger H-bonding attributed to the presence of amine. Meanwhile, cydiamine di-DFB has longer molecular packing distance in crystals resulting to low π-π interactions. These explains the red-shifted emission of mono-DFB as compared with di-DFB. Moreover, we also show that the variation in spacer from amide to ester highly influenced the molecular stacking in crystal. The weaker Hbonding in cydiester di-DFB leads to longer interlayer brick arrangement hence, displayed the shortest wavelength emission among the three compounds. Through the combination of time-resolved fluorescence measurements, Hirshfeld surface analysis and energy frameworks, [7][8][9] we reveal the role of atom-to-atom interactions, stacking of molecules as well as repulsive forces to mechanofluorochromism and its thermal reversibility.

Recent research for CPL active small organic compounds based on axial chirality involved chiral bridges such as BINOL, BINAP and cyclohexane. 5,10,11 While some of these compounds exhibits tunable CPL through external stimulation, solvent effect or presence of guest molecules, [12][13][14][15] our study divulged the significance of molecular design in inversion of chirality in monomeric form. We also highlighted the effect of the orientation of chromophores in hindered formation of supramolecular assembly. These findings may be supplemental for future molecular design of CPL active supramolecular assembly. One of the emerging applications of supramolecular assembled SOMs are the CPL switches wherein CPL signals can be turned "on" and "off" as a response to stimuli such as light. Incorporation of chromic molecules to a chiral compound or supramolecular assembly has made this CPL switching possible. We have shown in this study that supramolecular assembled DFB display gCPL values comparable to other SOMs and has efficient energy transfer thus, a potential chiral molecular backbone for CPL switches. Design of chromic molecules which can directly interact with supramolecular assembled DFB can be a subject for further studies in such a way that energy transfer (FRET) may induce the turning "on" or "off" the CPL signals.

Through molecular modification of spacers, we also revealed the role of intermolecular stacking and strength of atom-to-atom interactions to solid state photophysical properties of bichromophore DFB. From these, we revealed that ester has the most promising emission shift after smearing as well as thermal back reaction. However, these are limited to methoxy as side chain in DFB moiety. Variation of side chains such as longer alkyl or bulky groups may be subjected for study as these has previously reported in some chromophore. To the best of our knowledge these are not explored yet for bichromophoric DFB. These findings may direct the molecular design of mechanofluorochromic compounds for mechano-sensing device fabrication.

The discussed results and conclusions from these three-part studies may contribute to the field of photochemistry specifically in supramolecular assembly, chirality and mechanofluorochromism. Combined efforts in study of molecular design, theoretical calculations, and utilization of specialized photophysical measuring instruments have made it feasible to understand the connection between macroscopic photophysical properties to molecular-level arrangements and behavior of the compounds. These are the fundamental building block for efficient molecular design for future fabrication of sensing and opto-electronic devices. CHAPTER 6 Methods and Supplementary Information 6.1

General Synthesis and Characterizations Analytical reagents were purchased from Tokyo Chemical Industry Co., Ltd (TCI) and Sigma Aldrich and were used without further purification. The reactions were monitored using Merck TLC silica gel 60 F254 and visualized using UV lamp with wavelength 254nm and 365nm. 1 H, 13 C, 19 F and 11 B NMR analyses were recorded using 400MHz, 500MHz NMR JEOL JNM-ECX-500 and 600MHz NMR JEOL JNM-ECA600. The reference used for the 19 F and 11 B NMR analyses is BF3 O(C2H5)2 in CDCl3. Mass was analyzed using high Bruker Autoflex II MALDI-TOF and JEOL MALDI Spiral-TOF high resolution mass spectrometer.

Synthesis of Compounds in Chapter 2

Synthesis of P-1 methyl (Z)-4-(1-hydroxy-3-(4-methoxyphenyl)-3-oxoprop-1-en-1-yl)benzoate Synthesis of P-1 and P-2 were already reported from the previous manuscript of Wilbraham, Louis et al. 1 Sodium hydride (1.04 g, 1.3eq) was loaded in flamed dried flask and dissolved in 100mL of dry THF under nitrogen atmosphere. In separate flask, 4methoxyacetophenone (5 g, 1.0 eq) was dissolved in dry 30mL THF under nitrogen atmosphere then loaded dropwise to the sodium hydride suspension. The solution was heated to 45°C with continuous stirring for 30 mins. In another flask, dimethyl terephthalate (7.98 g, 1.23 eq) was dissolved in 50 mL THF and slowly loaded to the reaction medium. The reaction was put under reflux for 12 hours. Reaction was cooled down to 30°C and quenched by adding 1.35mL concentrated HCl. Excess THF solvent was removed in vacuum, and the compound was extracted with 200mL DCM then washed with water (100mL) for three times. The organic moiety was washed with brine (50mL) two times then dried with MgSO4. The crude product was purified by silica gel column chromatography using EtOAc/Hexane (30/70) as eluent. The target compound was obtained with 67% yield. The protecting group (BOC) in intermediate was removed by dissolving the cydiamine-BOC βdiketonate (400mg) in 8mL of trifluoroacetic acid:DCM solution (1:2) and stirring at room temperature for 2hours. 5 The solution was neutralized with ammonium hydroxide solution until pH reached 9-10. The compound was extracted with DCM (50mL) and washed with deionized water (100mL) for three times then dried over magnesium sulfate. The excess solvent was removed under vacuum with 81% yield. Racemic cydiester di β-keto enol was synthesized by esterification of P-1 intermediate with 1,2cyclohexane diol. 7 1,2-cyclohexane diol (51.9 mg, 1 eq.) and β-keto enol acid (400mg, 3 eq.) was loaded in pre-dried flask under atmospheric condition and dissolve in dry THF (10ml). After dissolving the cyclohexane diol, 4-dimethylaminopyridine (DMAP) (70mg, 1.2eq) and N, N-Dicyclohexylcarbodiimide (DCC) (0.21 mL, 3 eq.) was added to the flask and heat the solution to 40°C for 12hours with stirring. 7 The solution was cooled down to room temperature and the compound was extracted with DCM and washed with DI water for three times. The organic phase was collected and dried over magnesium sulfate. The compound was purified by column chromatography using hexane and ethyl acetate as eluent (30:70). Yellowish powder was collected with 32% yield. δ (ppm)

Fluorescence Measurements

Steady-State Photophysical Measurements

All absorbance and emission measurements were conducted using spectroscopy grade solvent purchased from Fujifilm Wako Pure Chemicals Industries Ltd. without any purification. The absorbances were obtained using double beam UV-Vis Jasco V-760 and double beam spectrometers Cary 100. The emissions were measured using Jasco FP-8500, Horiba Jobin-Yvon spectrofluorometers Fluoromax FM3 and Fluorolog FL3-221 while the PLQY of aggregates were measured using integrating sphere made by Hamamatsu and calculated using system software U6039-05 ver.3.2.1.

Time-Resolved Fluorescence Measurements

Fluorescence decay curves were obtained by the time-correlated single-photon counting (TCSPC) method. The setup is composed of a titanium sapphire Ti:Sa oscillator (Spectra Physics, Maï Taï HP) emitting pulses of 100 fs duration at 780nm, 80MHz frequency. The laser pulses then pass through a pulse picker which implements acoustooptic modulator to pick up specific pulse to reduce the repetition rate at 4MHz. Then the signal was doubled at 390nm (solutions) and 350nm (solids/crystals) by focalizing the laser in a non-linear SHG crystal (GWU Lasertechnik, UHG-23-PSK). Then the beam passes through the sample solution after adjusting the excitation power with an intensity attenuator filter wheel. Fluorescence photons were detected at 90° through a monochromator and slit of 0.3mm (CVI Laser Corporation, Digikröm CM110) and a polarizer at magic angle by means of a micro channel plate photomultiplier (Hamamatsu, MCP-PMT R3809U-50), connected to a TCSPC module (Becker & Hickl, SPC-130-EMN). The instrumental response function was recorded before each decay measurement with a fwhm (full width at half-maximum) of ~25 ps. Time-correlated fluorescence decay data is finally processed and analyzed with the help of a software which implements the nonlinear square method (Globals, Laboratory for Fluorescence Dynamics at the University of Illinois at Urbana-Champaign). Output for decays (τi) and pre-exponential factor (αi) were obtained after Global analysis, while the fraction of intensity (fi) was calculated based on the equation: Iαiτi/∑ αiτi. A B

TCSPC Plots of Compounds in Chapter 2

Crystal Analysis

The powder XRD patterns were recorded using Rigaku Smartlab9kW using CuKα1 monochormatization Ge220crystals. Suitable single crystal was isolated and mounted in sample holder. X-ray diffractions were recorded using Rigaku Varimax Rapid RA Micro7 equipped with imaging plate detector monochromated Mo Kα radiation at 103.15K. The crystal structure and calculations were done using the system software Rigaku Crystal structure 3.8.1.

Crystal Analysis of Cydiamine mono-DFB

Thermogravimetric Analysis

Thermogravimetric analyses were conducted using Shimadzu DTG-60 (DTA-TGA apparatus) using aluminum crimp pan (max. 600°C). Analyses were performed from 45°C to 300°C with constant rate temperature of 10°C/min. under atmospheric condition. The CPL were measured using the lab-designed CPL system consisting of excitation laser at 375nm, Hinds PEM-90 photoelastic modulator with frequency of 50KHz, Hamamatsu H7732 photomultiplier tube with signal amplifier, polarizing prism, and Shimadzu monochromator (10cm, single grating). 10

Synthèse en français du travail de thèse

Les complexes de difluorure de bore à ligand β-dicétone (DFB) sont l'un des matériaux fluorescents potentiels pour des applications dans le domaine de l'opto-électronique, des dispositifs de biodétection et des étiquettes de sécurité, en raison de leur rendement quantique élevé en solution et à l'état solide. Ces dernières années, leurs propriétés mécanofluorochromes ainsi que la mécano-CPL (changements dans les signaux de luminescence polarisés circulairement lors de l'application d'une contrainte mécanique) ont été étudiées. Les composés actifs chiraux à base de DFB qui présentent à la fois la CPL et le mécanofluorochromisme vont étendre leur utilisation aux CPL-OLED et aux microcapteurs, cependant les faibles valeurs du facteur de dissymétrie restent un défi. Dans cette étude, nous avons synthétisé des DFB bichromophores. Le travail a été principalement divisé en trois parties : (1) chiralité des bichromophores en solution et assemblage supramoléculaire ; (2) transfert d'énergie et sensibilité des nano-fils aux UV et (3) mécanofluorochromisme du DFB bichromophore.

Dans la première partie de l'étude, nous avons synthétisé deux complexes de difluorure de bore à ligand dicétone (DFB) bichromophores connectés en positions para et méta en utilisant la cyclohexane diamine comme pont chiral (para et méta (R/S)-CyDFB). Les calculs TD-DFT ont révélé que la variation de la connectivité des unités DFB conduit à différents arrangements spatiaux et à une inversion de chiralité du DFB bichromophore. Des valeurs de facteur de dissymétrie en absorption gabs plus élevées ont été obtenues dans le (R/S)-CyDFB connecté en position para par rapport à la position méta. L'agrégation du (R/S)-CyDFB en para dans un mélange de solvants augmente les valeurs de g_abs par rapport à sa forme monomère. L'ultrasonication et le chauffage ont induit la formation de nano-fils hélicoïdaux hautement ordonnés de para (R/S)-CyDFB qui ont augmenté les valeurs de g_lum à 0,015. D'autre part, le méta (R/S)-CyDFB n'a pas réussi à former des fils auto-assemblés hautement ordonnés en raison de sites de liaisons hydrogène entravés. Ces observations indiquent que les propriétés chiroptiques du système bi-chromophore DFB peuvent être fortement modulées par l'autoassemblage et la disposition spatiale des chromophores. La deuxième partie de l'étude s'est concentrée sur le transfert d'énergie. La formation d'un assemblage supramoléculaire piloté par formation de liaisons H a été comparée entre le complexe de difluorure de bore à ligand dicétone (DFB) mono-substitué et di-substitué. Le transfert d'énergie a été évalué avec des mesures d'anisotropie de fluorescence révélant que le transfert d'énergie intramoléculaire se produit entre les deux unités de complexe de difluorure de bore à ligand dicétone dans le système isolé en solution. L'assemblage supramoléculaire a montré un transfert d'énergie efficace avec une valeur d'anisotropie <r> =5.10 -3 . De plus, la photosensibilité du matériau moléculaire a été démontrée avec un décalage hypsochrome de l'émission après exposition aux UV. La combinaison de mesures de fluorescence résolues dans le temps et d'analyses d'images de microscopie a révélé la rupture des liaisons H et le réarrangement des molécules en agrégats radiaux à l'origine du changement d'émission.

La troisième partie de l'étude s'est concentrée sur les mesures à l'état solide. La comparaison des propriétés mécanofluorochromes du DFB mono-substitué (cydiamine mono-DFB) et du DFB disubstitué (cydiamine di-DFB) a révélé que les deux composés présentent un léger déplacement bathochrome après frottement, le compose cydiamine di-DFB émettant à des longueurs d'onde plus courtes. Le remplacement de la diamine par un espaceur diester dans le bichromophore DFB (cydiester di-DFB) entraîne un mécanofluorochromisme et un retour à la fluorescence initiale après chauffage plus importants. L'analyse des cristaux et la spectroscopie de fluorescence résolue en temps révèlent les interactions intermoléculaires à l'origine de la formation des excimères. De plus, les calculs des énergies intervenant pour la cohésion du réseau cristallin ont fourni une approche quantitative pour déterminer les plans de glissement actifs dans les cristaux, ce qui est d'une importance capitale pour les propriétés mécanofluorochromes des cristaux.

Titre:

  Conception, synthèse et caractérisation de matériaux supramoléculaires pour la luminescence polarisée circulairement et le mécanofluorochromisme Mots clés : chimie supramoléculaire, CPL, fluorescence, mécanofluorochromisme

Figure 1 . 1 .

 11 Figure 1.1. Tartaric acid (+), (-) and meso. Reprinted from ref. 4 with permission from Springer Nature.

  .1.

Figure 1 .

 1 Figure 1.1. (++)-(S,S)-trans-b-hydrindanone ((S,S)-1), (1R)-camphor ((1 R)-2), (1R)fenchone ((1 R)-3), (1R)-camphenilone ((1 R)-4), or (1R)-camphorquinone ((1 R)-5). Reprinted from ref. 14 with permission from John Wiley and Sons.

Figure 1 . 2 .

 12 Figure 1.2. Mono chiral BODIPY attached with chiral phenyl (a), BODIPY with urobilin derivative (b) 51 , mono-BODIPY in binaphthyl (c) and bis-BODIPY in binaphthyl (d). 49 Reprinted from ref. 49 and 51 with permission from John Wiley and Sons and American Chemical Society.

Figure 1 . 3 .

 13 Figure 1.3. Hetero-helicenes based on triarylamines. Reprinted from ref. 55 with permission from American Chemical Society.

Figure 1 . 4 .

 14 Figure 1.4. Structures of azabora[n]helicenes (1a to 1d) and the corresponding platina[n]helicenes (1a 1 to 1d 1 ). Reprinted from ref. 57 with permission from John Wiley and Sons.

Figure 1 . 5 .

 15 Figure 1.5. Boron fused double-helicenes structure (a) and packing (b). Reprinted from ref. 58 with permission from American Chemical Society.

Figure 1 . 6 .

 16 Figure 1.6. Figure-of-eight helicity of N2O2 dipyrrins boron complex. Reprinted from ref. 59 as permitted by Royal Society of Chemistry.

60

 60

Figure 1 . 7 .

 17 Figure 1.7. Structure of M-1 and self-assembly of helicene containing phthalhydrazide. Reprinted from ref. 60 with permission from John Wiley and Sons.

Figure 1 . 8 .

 18 Figure 1.8. Structures of bichromophore perylene bisimides using binaphthyl as chiral bridge where R = CH(C6H13)2. Reprinted from ref. 63 with permission from American Chemical Society.

Figure 1 .

 1 Figure 1.10. Structures AIE silole attached to chiral sugars (a) and the CPL signals at different experimental conditions (b). Image from ref. 6 as permitted by Royal Chemical Society.

Figure 1 . 11 .

 111 Figure 1.11. Structures of S and R SPAn and the different morphologies with corresponding glum values obtained at different THF/water ratio. Image from ref. 9 as permitted by Royal Society of Chemistry.

Figure 1 .

 1 Figure 1.12. Structures of histidine π-gel (PyC3H) protonated-deprotonated (a) CPL signals at different proton ratios (b) and the cycles of CPL inversion (c).[START_REF] Niu | Histidine Proton Shuttle-Initiated Switchable Inversion of Circularly Polarized Luminescence[END_REF] Reprinted with permission from American Chemical Society.

Figure 1 .

 1 Figure 1.13. Photoswitching (open and close form) of chiral pyrene stack with tetrathiazole D-1. Reprinted from ref. 68 with permission from Royal Society of Chemistry.

Figure 1 . 14 .

 114 Figure 1.14. Structures of enantiomeric glutamate spiropyran moiety in zwitterionic merocyanine (MC) and closed ring form including the SEM images (a) and schematic diagram of structural changes after exposure to UV and visible light.69

Figure 1 . 15 .

 115 Figure 1.15. Structures of DFB-Hex-amide and DFB-Phet-amide (a) and the CPL signals of thermal annealed and smeared samples (b).[START_REF] Louis | Mechano-Responsive Circularly Polarized Luminescence of Organic Solid-State Chiral Emitters[END_REF]

Figure 1 . 16 .

 116 Figure 1.16. Structures of oligo (p-phenylene vinylene) (OPVs) derivatives (a) and the emissions of LDDPE dyed with (OPVs) derivatives before and after stretching (b).27 Reprinted with permission from John Wiley and Sons.

Figure 1 . 17 .

 117 Figure 1.17. Structures of pyrene derivative with C6TPPy (a) the B-form (b) and G-form (c) under ambient light (left) and UV (right).[START_REF] Sagara | Material Design for Piezochromic Luminescence: Hydrogen-Bond-Directed Assemblies of a Pyrene Derivative[END_REF] Reprinted with permission from American Chemical Society.

Figure 1 .

 1 Figure 1.18. Structures BF2AVB (a) and the images of green crystals (b), blue crystal (c) and dendritic crystals(d).[START_REF] Zhang | Polymorphism and Reversible Mechanochromic Luminescence for Solid-State Difluoroboron Avobenzone[END_REF] Reprinted with permission from American Chemical Society.

Figure 1 . 19 .

 119 Figure 1.19. Powder film from crushed cyan BF2AVB (a) after smearing showing yellow emission (b), recovery after few minutes of exposure in heating gun (c).[START_REF] Krishna | The Relationship of Solid-State Plasticity to Mechanochromic Luminescence in Difluoroboron Avobenzone Polymorphs[END_REF] Reprinted with permission from John Wiley and Sons.

Figure 1 . 20 .

 120 Figure 1.20. The schematic diagram showing the morphologies, photophysical processes of the emitting species including the decay times.[START_REF] Louis | Polymorphism, Mechanofluorochromism, and Photophysical Characterization of a Carbonyl Substituted Difluoroboron-β-Diketone Derivative[END_REF] Reprinted with permission from publisher American Chemical Society.

JFigure 2 . 1 .

 21 Figure 2.1. Chemical Structures of DFB derivatives studied here.

3 Scheme 2 . 2 . 2

 3222 Scheme 2.1. Synthetic route for synthesis of Para (S/R)-CyDFB.

Figure 2 . 2

 22 Figure 2.2 Absorbance (a) and emission (b) (λexc=390nm) of para-Cy DFB in acetonitrile, DMF, THF, DCM, chloroform, and toluene.

Figure 2 . 3

 23 Figure 2.3 Absorbance (a) and emission (b) (λexc=390nm) of meta-Cy DFB in acetonitrile, DMF, THF, DCM, chloroform, and toluene.

Figure 2 . 4

 24 Figure 2.4 Lippert-Mataga plot of para-Cy DFB (a) and meta-Cy DFB (b) in different solvent.

Figure 2 . 5

 25 Figure 2.5 Optimized geometry of para-Cy DFB (a) and meta-Cy DFB (b) calculated with Gaussview 16 DFT calculation using CAM-B3LYP and basis set (6-31+) G(d,p) with IEFPCM (DCM) solvation method

Figure 2 . 6 .

 26 Figure 2.6. Optimized geometry showing dihedral angles of DFB moieties of para-Cy DFB (a) and meta-Cy DFB (b) calculated with Gaussview 16 DFT calculation using CAM-B3LYP and basis set (6-31+) G(d,p) with IEFPCM (DCM) solvation method.

  multiple molecular orbitals. Both transitions showed a π-π* character with a slight shift of electron density from methoxy towards the β-diketonate group (see Figures 2.7 and Figure 2.8). This explains the weak solvatochromism property of both para and meta (S/R)-CyDFB (see Chapter 6 for list of molecular orbitals and oscillation strengths). Excited State 1 (f=0.4590)

Figure 2 . 7 .Figure 2 . 8 .

 2728 Figure 2.7. Molecular orbitals and electronic transitions of para (S)-CyDFB as calculated by TD-DFT using CAMB3LYP, 613+G (d,p), IEFPCM solvent DCM (a). Generated natural transition orbitals (NTOs) (b).

Figure 2 . 9 .

 29 Figure 2.9. CD spectra and normalized absorbance of para CyDFB and meta CyDFB in DCM (3.5 x10 -5 M) and insert image of the solution in DCM under 365nm UV source (a) and theoretical CD spectra from TD-DFT (b).

  2.10b). Like the monomeric form, CD spectra of para (S/R)-CyDFB aggregates displayed mirror images for (R) and (S) enantiomers with formation of new band at 430nm displaying an opposite sign of more intense band at 385nm (Figure 2.10a). These new bands correspond to the CD signals of newly formed absorbing species in aggregated form. (PARA) S-CyDFB (META) S-CyDFB A B

Figure 2 .

 2 Figure 2.11. CPL spectra of para CyDFB and meta CyDFB in (29:1) MCH:Chloroform (3.5 x10 -5 M) λexc 375nm.

Figure 2 . 12 .

 212 Figure 2.12. The gels formed in mixture of toluene and DCM (a) and the emissions of the solution while forming the gels (b).

Figure 2 .

 2 Figure 2.13. SEM images of nanowires para (S)-(left) and (R)-(right) CyDFB obtained from gels (D).

  .14a). It was clearly shown that C=O and NH from amide were mainly involved in hydrogen bonding. Diffraction patterns of xerogels obtained from powder XRD coincided with the simulated patterns from CIF file, suggesting that the nanowires have similar stacking with the crystal structures as shown in Figure 2.15.

Figure 2 . 14 .Figure 2 .

 2142 Figure 2.14. Top and side view of crystal packing induced by π-π stacking and hydrogen bonding of amide groups (A), Hirshfeld surface analysis showing intermolecular interactions (B). Simulated packing structures of using Materials Studio 7.0 (C).

Table 2 . 5 .

 25 Emission decay time constant (τ), pre-exponential factor (a) and fraction of intensity (f) of gels in toluene of para (S)-CyDFB measured (λexc = 390nm, λem = 450nm and 550nm).

Figure 2 .

 2 Figure 2.16. CPL Spectra of para (R/S) CyDFB gels formed in toluene (solid and broken dark red lines) and aggregates formed in MCH/CHCl3 (solid and broken red lines) (A). Normalized emission of para (R/S)-CyDFB gels (solid dark red line) and aggregates in (29:1) MCH/CHCl3 (solid red line) (B).

Figure 3 . 1 :

 31 Figure 3.1: Chemical structures of cydiamine mono-DFB and cydiamine di-DFB. (S) Cydiamine mono-DFB (S) Cydiamine di-DFB

  Scheme 3.1: Reaction scheme for synthesis of cydiamine mono-DFB

  β-keto enol Cydiamine mono β-keto enol (S) Cydiamine mono-DFB Cydiamine-BOC β-keto enol

Figure 3 . 2 .

 32 Figure 3.2. Absorbance and emissions of cydiamine mono-DFB (a) and cydiamine di-DFB (b) in chloroform, DCM, THF and acetonitrile (λexc 390nm).

Figure 3 . 3 .

 33 Figure 3.3. Molecular orbital surfaces involved in electronic transitions of cydiamine mono-DFB (refer to chapter 6 Table6.6) (a) and cydiamine di-DFB (refer to chapter 6 table 6.4) (b) and their energies (Hartree), calculated using TDDFT with functional CAMB3LYP, basis set 6-31+G (d,p), and IEFPCM solvation method.

BA

  Other transitions such as HOMO to LUMO and HOMO to LUMO+1 display the typical ππ* and delocalized electrons within the DFB moiety (see Figure3.2a).

Figure 3 . 4 .

 34 Figure 3.4. Anisotropy as a function of excitation (λem=480nm) and as a function of emission (λexc=380nm) of cydiamine mono-DFB in propylene glycol measured at -50°C.

Figure 3 . 5 .

 35 Figure 3.5. Anisotropy as a function of excitation (λem=480nm) and as a function of emission (λexc=380nm) of cydiamine di-DFB in propylene glycol measured at -50°C.

Figure 3 . 6 .

 36 Figure 3.6. Anisotropy as a function of excitation (λem=550nm) and as a function of emission (λexc=450nm) of supramolecular assembly of cydiamine di-DFB measured at room temperature.

3. 5

 5 Responsiveness to UV Light3.5.1 Photobleaching and Emission shiftThe sensitivity of the nanowires to the UV light was first observed serendipitously using the specialized spectroscopic method wherein the atomic force microscope (AFM) was coupled with fluorescence microscopy equipped with EM-CCD camera and CCD spectrograph as shown in Figure3.7.

Figure 3 . 7 :

 37 Figure 3.7: Experimental set-up of AFM coupled with fluorescence microscopy

Figure 3 . 8 .

 38 Figure 3.8. The fluorescence image of nanowires using CCD camera including the slit measurement area (a) and the emission before and after exposure 400 nm wavelength source (b).

Figure 3 . 9 .

 39 Figure 3.9. The fluorescence image of nanowires using CCD camera including the slit measurement area (a) and the emission before and after exposure 400 nm wavelength source (b).

Figure 3 .

 3 Figure 3.10: Steady-state fluorescence emission of organogels after exposure to UV (380nm) at different time (a) and the ratio of intensity at 450nm and 550nm at different exposure time (b).

Figure 3 .

 3 Figure 3.11: Time-resolved spectroscopic measurements of organogels exposed in UV (380nm) at different exposure time measured at 450nm.

Figure 3 .

 3 Figure 3.12: Time-resolved spectroscopic measurements of organogels exposed in UV (380nm) at different exposure time measured at 550nm.

Figure 3 .

 3 Figure 3.13. AFM images of nanowires after exposure to UV

  .

  14) and 150nm-200nm for diameters of radial aggregates as shown in Figure 3.15.

Figure 3 . 14 :

 314 Figure 3.14: Histogram of the lengths of fragmented nanowires after exposure to UV analyzed using Gwyddion software.

Figure 3 . 15 :

 315 Figure 3.15: Distribution of diameter sizes of radial aggregate found in AFM image analyzed using Gwyddion software.

Figure 3 . 16 :

 316 Figure 3.16: Image of printed pattern in organogels through UV light exposure at 380nm (blue emissive pattern) while the yellow emissive background are the non-exposed organogels visualized under 365nm light.

2

 2 Scheme 4.1: Synthesis of cydiester di-DFB.

Figure 4 . 1 .

 41 Figure 4.1. Chemical structure (top) and optimized geometry (bottom) of (S)-cydiamine mono-DFB (a) (S)-cydiamine di-DFB (b) and (R/S)-cydiester di-DFB (c) calculated with DFT using the functional CAM-B3LYP and basis set 6-31G+(d,p) with IEFPCM (DCM) solvation method.

  dihedral angles inChapter 6). Optimized geometry of cydiamine di-DFB showed a similar arrangement but both DFB moieties are in axial position. The optimized geometry showed two unequal DFB moieties which are situated parallel to the cyclohexane ring and the corresponding dihedral angles are previously discussed in Chapter 2 (see Figure4.1b). On the other hand, the optimized geometry of cydiester di-DFB showed that the two DFB units were situated at opposite direction and at equatorial position of cyclohexane ring (see Figure4.1c). Corresponding dihedral angles for each DFB moiety with respect to β-diketonate plane are shown in Figure4.2. The variation of spacer from amide to ester drastically changed the orientation of DFB moieties in cydiamine di-DFB and cydiester di-DFB.

Figure 4 . 2 .

 42 Figure 4.2. Optimized geometry of cydiester di-DFB with corresponding dihedral angles of DFB moieties.

Figure 4 . 3 .

 43 Figure 4.3. NTO of cydiamine mono-DFB (a) and cydiester di-DFB (b) from lowest energy transition calculated using the functional CAM-B3LYP and basis set 6-31G+(d,p) with IEFPCM (DCM) solvation methods (see chapter 6 for list of the transitions).

Figure 4 . 4 .

 44 Figure 4.4. Absorbance and steady-state fluorescence spectra of cydiamine mono-DFB, cydiamine di-DFB and cydiester di-DFB (excitation at 390nm). Refer to chapter 6 for table of TDDFT vs experimental values.

Figure 4 . 5 .

 45 Figure 4.5. Crystal structure of cydiamine mono-DFB showing distinct arrangement of two units twisted in cyclohexane diamine moiety (a) and Hirshfeld surface analysis showing surface interactions to neighboring cydiamine mono-DFB units (b).

Figure 4 . 6 .

 46 Figure 4.6. Crystal packing of cydiamine mono-DFB including top and side view (a) and the extended view along a-axis showing crystal packing motif γ (b).

  cydiamine di-DFB crystal (see Figure4.8a). Extending the crystal structures revealed the herringbone crystal packing motif characterized by edge-to-face packing which tends to reduce steric hindrances between DFB moieties as illustrated in Figure 4.8b. Fingerprint plots showed that C•••C surface interactions in cydiamine di-DFB crystal consists of 1.1% (di-de at 1.8 Å) which is lower as compared with cydiamine mono-DFB. Other surface interactions involving C•••H (19.5%), H•••F (17.2%), H•••H (36.8%) and O•••H (14.2%) comprised most interactions within the surface of cydiamine di-DFB (see Chapter 6).

Figure 4 . 7 .

 47 Figure 4.7. Crystal structure of cydiamine di-DFB showing inter-layer distance of ca. 4.9Å and columnar stacking showing amide to carbonyl H-bonding.

Figure 4 . 8 .

 48 Figure 4.8. Hirshfeld surface analysis (a) and extended structures showing herringbone crystal packing motif (b).

Figure 4 . 9 .B

 49 Figure 4.9. Extended crystal packing of cydiester di-DFB view along b-axis showing brick-layered arrangement (a) layers of cydiester di-DFB as viewed from top showing interlayer distance of 5.7 Å (b).

Figure 4 . 10 .B

 410 Figure 4.10. Hirshfeld surface analysis showing surface interactions to neighbor cydiester di-DFB units (a) and top to bottom interactions cydiester di-DFB as viewed from right (non-overlapping DFB moiety) and left (overlapping DFB moiety) (b).

Figure 4 . 11 .

 411 Figure 4.11. Summary of the atom-atom interaction in fingerprint plot of Hirshfeld surface analysis of cydiamine mono-DFB (orange), cydiamine di-DFB (green) and cydiester di-DFB (blue).

Figure 4 . 12 .

 412 Figure 4.12. Fluorescence emissions of cydiamine mono-DFB, cydiamine di-DFB and cydiester di-DFB crystals (a) and smeared (b) (excitation at 350nm).

Figure 4 . 13 .

 413 Figure 4.13. Crystals and smeared samples of cydiamine mono-DFB (a), cydiamine di-DFB (b) and cydiester di-DFB (c).

Figure 4 . 14 .

 414 Figure 4.14. Plots of fraction of intensity obtained from time-resolved spectroscopy measurements of cydiamine mono-DFB crystals (a), smeared (b), thermal annealed (c), and pristine powders (d) measured at difference wavelengths (500nm to 600nm) using excitation at 350nm.

Figure 4 . 15 .

 415 Figure 4.15. Simulated powder XRD of crystal from CIF file, powder XRD of smeared, thermal annealed samples of cydiamine mono-DFB annealed at 80°C.

Figure 4 Figure 4 . 16 .

 4416 Figure 4.16. Plots of fraction of intensity obtained from time-resolved spectroscopy measurements of cydiamine di-DFB crystals (a), smeared (b), thermal annealed (c), and pristine powders (d) measured at difference wavelengths (500nm to 600nm) using excitation at 350nm. Single crystal structure of cydiamine di-DFB has a good overlap between each bichromophoric units, but the amide group (NH•••C=O) provides the shortest surface

Figure 4 .

 4 Figure 4.17. Simulated powder XRD of crystal from CIF file, powder XRD of smeared, thermal annealed samples of cydiamine di-DFB annealed at 130°C.

Figure 4 . 18 .

 418 Figure 4.18. Emission spectra of smeared and thermal annealed samples of cydiamine di-DFB.

4. 4 . 3 Figure 4 . 19 .

 43419 Figure 4.19. Plots of fraction of intensity obtained from time-resolved spectroscopy measurements of cydiester di-DFB crystals (a), smeared (b), thermal annealed (c) and pristine powders (d) measured at difference wavelengths (500nm to 600nm) using excitation at 350nm.

Figure 4 . 20 .

 420 Figure 4.20. Simulated powder XRD of crystal from CIF file, powder XRD of smeared, thermal annealed samples of cydiester di-DFB annealed at 130°C. Smearing shifted the maximum emission to higher wavelength induced by closer π-π stacking bought by destructed crystal structure and this was evident by broader emission and existence of longer decay time (τ1= 25ns) as shown in the fraction of intensity plot in Figure 4.19b. Pristine powders showed similar decay profile with smeared samples except for shouldering peak at 500nm, which may also indicate a metastable state after smearing (see Figure 4.19d).

Figure 4 . 21 .

 421 Figure 4.21. Emission spectra of smeared and thermal annealed samples of cydiester di-DFB.

Figure 4 .

 4 22a shows the total interaction energy framework viewed along a-axis of cydiamine mono-DFB represented by interconnected blue cylinders which are proportional to the intermolecular interaction energy. The calculated intermolecular energy values in kJ were indicated in annotated energy diagrams shown in Figure 4.22b.

Figure 4 . 22 .

 422 Figure 4.22. Total energy framework of cydiamine mono-DFB (a) and annotated energy diagram viewed along a-axis (b).

  and 4.24b.

Figure 4 .

 4 Figure 4.24. Total energy framework of cydiamine di-DFB (a) and annotated energy diagram viewed along a-axis (b).

Figure 4 .

 4 Figure 4.25. Electrostatic (red and yellow) and dispersive (green) components of cydiamine mono-DFB (a) cydiamine di-DFB (b) and cydiester di-DFB (c) viewed along a-axis.

  1 H-NMR (500MHz, CDCl3): δ (ppm) 17.10 (s, 1H), 8.13 (d, J=8.Hz, 2H), 8.01 (dd, J=8.5Hz, 4H),6.99 (d, J=8.5Hz, 2H), 6.83 (s,1H) 3.96(s, 3H) and 3.89 (s,3H). MALDI-TOF mass spectrometry C18H16O5 [M + H] + : m/z =313.134 (calculated: 313.100). Synthesis of P-2 (Z)-4-(1-hydroxy-3-(4-methoxyphenyl)-3-oxoprop-1-en-1-yl)benzoic acid P-2 was synthesized using the same method used by Wilbraham, Louis et al. Compound P-1 (0.5 g, 1.0 eq.) was dissolved in 8 mL of THF. The medium was cooled down to 0°C. In separated flask, LiOH (0.34 g, 9.0 eq.) was pre-dissolved in 7.5 mL distilled water then slowly added to compound P-1. The medium was stirred for 24 hours at room temperature. Afterwards, the solution was poured in distilled water and washed with DCM (50mL) thrice. The aqueous phase was collected, the compound was precipitated by adding 1M HCl and isolated by filtration. No further purification was needed1. 1 H-NMR (500MHz, DMSO): δ (ppm) 17.19 (s, 1H), 13.29 (s, 1H), 8.22 (d, J=6.4 Hz, 2H), 8.17(d, J=7.2 Hz, 2H), 8.04 (d, J=6.8 Hz, 2H), 7.34 (s, 1H), 7.08 (d, J=6.0 Hz, 2H), 3.85 (s, 3H). MALDI-TOF mass spectrometry C17H14O5 [M + H] + : m/z =299.138 (calculated: 299.084).

  Synthesis of meta (S/R)-Cy DFB methyl (Z)-3-(1-hydroxy-3-(4-methoxyphenyl)-3-oxoprop-1-en-1-yl)benzoateThe synthesis of (R/S) meta-cyclohexane diamine 2-DFB was synthesized using the same steps as for (R/S) para cyclohexane diamine 2-DFB. Dimethyl isophthalate was used instead of dimethyl terephthalate to synthesize pre-cursor M1 with the yield of 78%. 1 H-NMR (500MHz, CDCl3): 16.98 (s,1H), 8.60 (s,1H), 8.19 (t, J=8.0, 2H), 8.00 (d, J=8.0, 2H), 7.58 (t, J=8.0, 1H), 7.00 (d, J=8.0, 2H), 6.84 (s, 1H), 3.97 (s, 3H), 3.90 (s, 3H). 13 C-NMR (150MHz, CDCl3/TMS): 186.66, 182.81, 166.55, 163.53, 136.05, 133.00, 131.37, 130.75, 129.57, 129.01, 128.14, 128.03, 114.13, 92.65, 55.62, 55.52. MALDI-TOF mass spectrometry C18H16O5 [M+H] + : m/z =313.124 (calculated: 313.100). δ (ppm) Synthesis of Cydiamine mono β-keto enol (BOC de-protection): N-((1S,2S)-2-aminocyclohexyl)-4-((Z)-1-hydroxy-3-(4-methoxyphenyl)-3-oxoprop-1-en-1yl)benzamide

  1 H-NMR (500MHz, Acetonitrile-D3/TMS): δ(ppm) 1.25 (m, 4H), 1.39 (m, 1H), 1.78 (m, 2H), 2.02 (m, 1H), 2.17 (m, 1H), 2.56 (m, 1H), 3.74 (m, 2H), 3.88 (m, 3H), 6.26 (s, 1H), 6.83 (s, 1H), 6.98 (d, J=9, 2H), 7.87 (d, J=9, 2H), 7.99 (dd, J=9, 2H), 13 C-NMR (150MHz, Acetonitrile-D3/TMS) : δ(ppm) 187.12, 182.15, 166.99, 163.57, 138.22, 137.74, 129.59, 128.12, 127.36, 127.23, 114.14, 93.01, 56.69, 55.62, 35.93, 32.57, 25.08. MALDI-TOF mass spectrometry C23H26N2O4[M+Na] + : m/z = 417.176 (calculated: 417.179). δ (ppm) 6.1.3 Synthesis of Compounds in Chapter 4 Synthesis of Cydiester β-keto enol: cyclohexane-1,2-diyl bis(4-((Z)-1-hydroxy-3-(4-methoxyphenyl)-3-oxoprop-1-en-1yl)benzoate)

  1 H-NMR (500MHz, CDCl3/TMS): δ (ppm) 1.25 (m, 2H), 1.69 (m, 2H), 1.86 (m, 2H), 2.27 (d, J=13, 2H), 3.89 (s, 6H), 5.28 (m, 2H), 6.77 (s, 2H), 6.96 (d, J=9, 2H), 7.93 (d, J=9, 2H), 7.97 (d, J=9, 2H), 8.02 (d, J=9, 2H), 16.86 (s, 2H). 13 C-NMR (150MHz, CDCl3/TMS): 187.42, 181.74, 165.41, 163.59, 139.48, 132.98, 129.90, 129.62, 128.14, 126.92, 114.13, 93.27, 74.92, 55.61, 30.37, 23.64. MALDI-TOF mass spectrometry C40H36O10 [M + Na] + : m/z =699.208 (calculated: 699.211).

Figure 6 . 1 .Figure 6 . 2 .AFigure 6 . 3

 616263 Figure 6.1. Time-resolved flurorescence decay of para and meta (S)-Cy DFB monomers measured with λexc=390nm/ λem=463nm (A) and para and meta (S)-Cy DFB aggregates measured with λexc=390nm/λem=550nm including the residuals (upper panel). The decays were fitted with satisfactory X 2 < 1.2.

Figure 6 . 4 .Figure 6 . 6 .

 6466 Figure 6.4. Time-resolved flurorescence decay of para (S)-Cydiamine β-diketonate measured at λem=480nm; λexc=390nm) with X 2 = 1.24 with residuals shown in upper panel.

Figure 6 . 7 .

 67 Figure 6.7. Time-resolved spectroscopy measurement plots of cydiamine di-DFB crystals, smeared, thermal annealed and pristine powder measured at 550nm and 600nm (excitation at 350nm).

Figure 6 . 8 .

 68 Figure 6.8. Time-resolved spectroscopy measurement plots of cydiester di-DFB crystals, smeared, thermal annealed and pristine powder measured at 550nm and 600nm (excitation at 350nm).

Figure 6 . 9 .

 69 Figure 6.9. Simulated UV-Vis and ECD spectra of para S-cyclohexane diamine DFB (A) meta Scyclohexane diamine DFB (B) as calculated by TD-DFT with CAMB3LYP, 613+G (d,p) basis set and IEFPCM using DCM as solvent.

Figure 6 . 11 . 2 Figure 6 . 12 . 3 Figure 6 . 13 .

 61126123613 Figure 6.11. Single Crystal structure of Cydiamine mono-DFB

Figure 6 . 14 .

 614 Figure 6.14. Thermogravimetric analysis of cydiamine di-DFB and cydiester di-DFB.

Figure 6 .

 6 Figure 6.17. Fingerprint plots of cydiester di-DFB calculated from Hirshfeld surface analysis.

Figure 6 .

 6 Figure 6.18. CPL spectra of para and meta (R/S)-CyDFB monomeric form in chloroform (A) and meta (S)-CyDFB aggregates in MCH: CHCl3 (29:1) (B). The concentration was kept at 3.0 x10-5M. A Fi g u r e S 7. C P L s p e ct r a o f p a r a a n d m e t a ( R / S) -C y D F B m o n B Fi g u r e S 7. C P L s p e ct r a o f p a r a a n d

  18

	A	B	C
	Fi	F	Fi
	g	i	g
	u	g	u
	r	u	r
	e	r	e
	1.	e	1.
	1	1	1
	6.	.	6.
	St	1	St
	r	6	r
	u	.	u
	ct	S	ct
	u	t	u
	r	r	r
	e	u	e
	s	c	s
	o	t	o
	f	u	f
	ol	r	ol
	ig	e	ig
	o	s	o
	(	o	(

Table 2 .

 2 1 Characteristics of para-CyDFB at different solvent polarity Table 2.2 Characteristics of meta-CyDFB at different solvent polarity

Table 2 . 3

 23 Emission decay time constant (τ), pre-exponential factor

  .5).

	Sample	τ1 (ns), (a1, f1)	τ2 (ns), (a2, f2)	τ3 (ns), (a3, f3)
	para (S)-CyDFB (Monomers in DCM) (λem = 463nm)	12.2ns, (0.01, 0.03)	2.06ns, (0.99, 0.97)	-
	meta (S)-CyDFB (Monomers in DCM) (λem = 463nm)	7.0ns, (0.02, 0.06)	2.4ns, (0.71, 0.84)	0.7ns, (0.27, 0.10)

  .12a. It was clearly shown that peak around 460nm was slowly decreasing

	Sample	τ1 (ns), (a1, f1)	τ2 (ns), (a2, f2)	τ3 (ns), (a3, f3)
		40.5ns,	14.7ns,	1.6ns,
	para (S)-CyDFB (Aggregates MCH/CHCl3)
		(0.72, 0.90)	(0.21, 0.10)	(0.07, <0.01)
	(λem = 550nm)
	meta (S)-CyDFB (Aggregates MCH/CHCl3)	40.9ns,	17.0ns,	2.7ns,
	(λem = 550nm)	(0.33, 0.70)	(0.27, 0.24)	(0.40, 0.06)

Table 3 .

 3 1. Maximum absorbance (λabs) and emission (λem) of cydiamine mono-DFB and cydiamine di-DFB in different solvent (λexc 390nm).

	Solvent	ε (static dielectric constant)	Cydiamine mono-DFB λabs λem	Cydiamine di-DFB λabs λem
	Chloroform	4.81	388 nm	438 nm	393 nm	440 nm
	THF	7.58	388 nm	444 nm	390 nm	443 nm
	DCM	8.93	391 nm	455nm	394 nm	446 nm
	Acetonitrile	37.5	387 nm	461 nm	394 nm	465 nm

Table 3 .

 3

	2. Decay times of cydiamine mono-DFB (in acetonitrile) and cydiamine di-DFB (in DCM)
	using excitation wavelength of 390nm
		τ1 (a1, f1)	τ2(a2, f2)	<τave>	Φf	Knr, s -1	Kr, s -1
		ns	ns	ns
	cydiamine	0.99	0.60	0.65	0.31	1.06x10 9	4.77x10 8
	mono-DFB	(0.08, 0.13)	(0.92, 0.87)
	cydiamine di-	12.18	2.06	2.41	0.69	1.29x10 8	2.86x10 8
	DFB	(0.01, 0.02)	(0.99, 0.97)

Table 1 .

 1 Pre-exponential factors (an) and fraction of intensity (fn) of cydiamine di-DFB organogels at emission wavelength 450nm measured at different exposure time (excitation at 360nm).

		τ1 (a, ƒ1)	τ2 (a2, ƒ2)	τ3 (a3, ƒ3)	τ4 (a4, ƒ4)
	Before irradiation	21.5	2.13	0.54	0.06
		(0.01, 0.11)	(0.43,0.73)	(0.35, 0.15)	(0.21, 0.01)
	15mins	21.5	2.13	0.54	0.06
		(<0.01 0.11)	(0.32,0.74)	(0.22, 0.13)	(0.45, 0.03)
	30mins	21.5	2.13	0.54	0.06
		(<0.01, 0.12)	(0.25,0.70)	(0.19, 0.14)	(0.55, 0.04)
	45mins	21.5	2.13	0.54	0.06
		(<0.01, 0.13)	(0.24,0.67)	(0.22, 0.16)	(0.53, 0.04)
	60mins	21.5	2.13	0.54	0.06
		(<0.01, 0.14)	(0.19,0.64)	(0.18, 0.16)	(0.63, 0.06)

Table 2 .

 2 Pre-exponential factors (an) and fraction of intensity (fn) of cydiamine di-DFB organogels at emission wavelength 550nm measured at different exposure time (excitation 360 nm).

		τ1 (a, ƒ1)	τ2 (a2, ƒ2)	τ3 (a3, ƒ3)	τ4 (a4, ƒ4)
	Before	38.40	25.71	5.74	0.71
	irradiation	(0.57, 0.84)	(0.14, 0.14)	(0.10, 0.02)	(0.19, 0.01)
	15mins	38.40	25.71	5.74	0.71
		(0.13, 0.39)	(0.23,0.48)	(0.25, 0.12)	(0.39, 0.02)
	30mins	38.40	25.71	5.74	0.71
		(0.09, 0.32)	(0.21,0.51)	(0.26, 0.14)	(0.45, 0.03)
	45mins	38.40	25.71	5.74	0.71
		(0.07, 0.29)	(0.20,0.53)	(0.25, 0.15)	(0.47, 0.03)
	60mins	38.40	25.71	5.74	0.71
		(0.06, 0.26)	(0.19,0.53)	(0.27, 0.17)	(0.48, 0.04)

Table 4 .

 4 1. Decay time (τi), pre-exponential factors (ai) and fraction of intensity (fi) of cydiamine mono-DFB solution (in acetonitrile), cydiamine di-DFB solution (in DCM) and cydiester di-DFB (in DCM).

		τ1 (a1, f1)	τ2 (a2, f2)
	Cydiamine mono-DFB	0.6ns (0.92, 0.87)	1ns (0.08, 0.13)
	Cydiamine di-DFB	2ns (0.99, 0.96)	12ns (0.01, 0.03)
	Cydiester di-DFB	1.8ns (0.78, 0.68)	3ns (0.22, 0.32)
	*Cydiamine mono-DFB exc. = 390nm, em. =480nm, X 2 = 1.05
	Cydiamine di-DFB exc. = 390nm, em. =463nm; X 2 = 1.09
	Cydiester di-DFB exc. = 390nm, em. =480nm; X 2 = 1.13

Table 6 .

 6

	a. Crystals
	Wavelength	τ1(a1, f1)	τ2 (a2, f2)	τ3 (a3, f3)	τ4 (a4, f4)
	500	9.2(<0.01, 0.03) 3.0 (0.25, 0.60) 0.95(0.40, 0.30) 0.3 (0.34, 0.07)
	550	9.2 (0.01, 0.06)	3.0 (0.43, 0.59) 0.95 (0.06, 0.03) 0.3 (0.20, 0.02)
	580	9.2 (0.01, 0.05)	3.0 (0.26, 0.36) 0.95 (0.01, 0.00) 0.3 (0.15, 0.02)
	600	9.2 (0.01, 0.04)	3.0 (0.18, 0.25) 0.95 (0.03, 0.01) 0.3 (0.10, 0.01)
	τn decay time
	an pre-exponential factor
	fn fraction of intensity
	Excitation: 350nm; χ 2 R = 1.17
	b. Smeared
	Wavelength	τ1 (a1, f1)	τ2 (a2, f2)	τ3 (a3, f3)	τ4 (a4, f4)
	500	25 (0.01, 0.16)	7.3 (0.04, 0.28)	1.6 (0.16, 0.27)	0.2 (0.61, 0.11)
	550	25 (0.06, 0.39)	7.3 (0.18, 0.35)	1.6 (0.41, 0.18)	0.2 (0.29, 0.01)
	580	25 (0.09, 0.36)	7.3 (0.20, 0.23)	1.6 (0.39, 0.10) 0.2 (0.01, <0.01)
	600	25 (0.07, 0.30)	7.3 (0.14, 0.26)	1.6 (0.25, 0.06) 0.2 (0.06, <0.01)
	τn decay time
	an pre-exponential factor
	fn fraction of intensity
	Excitation: 350nm; χ 2 R = 1.39

3. Normalized pre-exponential factors (an) and fraction of intensity (fn) of cydiester di-DFB measured at different wavelength.

Table 6 .

 6 11 Crystallographic parameters of Cydiester-DFB single crystals.

	Properties of Cydiester di-DFB
	Formula weight	772.32
	Crystal system	monoclinic
	calculated density	1.432
	a (Å)	10.479 (3)
	b (Å)	8.980 (2)
	C (Å)	19.289 (6)
	α (deg)	90.000
	β (deg)	99.312 (7)
	γ(deg)	90.000
	Z value	2

A B

Acknowledgements

I would like to acknowledge my supervisors Prof. Tsuyoshi Kawai (NAIST) and Dr. Clémence Allain (ENS-Paris Saclay) for their support and guidance throughout my PhD journey. To NAIST and ENS-Paris Saclay for the financial support as well and the scholarship grants. I am also very thankful to Dr. Rémi Métivier and Assistant Prof. Marine Louis for their guidance and for sharing their expertise to help me with the experimental set-up and made the necessary measurements possible. Their directions and guidance shaped me to become a better student and future researcher. I also would like to express my sincerest gratitude to the jury members: Prof. Gwénaël Rappene, Prof. Jeanne Crassous, Prof. Michel Sliwa, Prof. Shun Hirota and Prof. Takuya Nakashima for giving part of their time to read, suggest and help me improve my manuscript and research.

I am very thankful to the new and previous members of Photonics and Reactive Molecular Science Laboratory especially to my senpai and tutors Dr. Yoshida, Dr. Mizutsu, Dr. Kuno, and Dr. Asato who helped me a lot during my first year of stay in NAIST. Also, to all the members under Marine sensei's team for all the fun memories especially to Katsumi-san. To Dr. Pablo Reiné for sharing his expertise and time, also to my colleagues in PPSM especially Dr. Poggi, Dr. Sethy, and Dr. Hirai who imparted their knowledge in solid state chemistry and became my support group while I was in France. To Dr. Calupitan for his support and encouragement to apply for double-degree Doctoral Program of NAIST and ENS-Paris Saclay, I am not here without his advice. Also, to all the technical staffs in NAIST and ENS-Paris Saclay especially to Arnaud Brosseau who I spent most of my time doing solid-state measurements; to Katao-san, Asanoma-san and Nishikawa-san for patiently analyzing and characterizing my samples.

To the Filipino community in NAIST especially Candell, James, Virgil, Mark, Nicko, JC, Dianne, Paul, Ken, Chi, Peki, Enzo, Magin and Josh for being my support group and making my PhD life fun and memorable. Also, I am expressing gratitude to all the friendly international students of NAIST and ENS-Paris Saclay.

To my mentor Dr. Diaz and all my professors in Ateneo de Manila University and Polytechnic University of the Philippines, and Department of Science and Technology thank you so much. I will not acquire all the basic skills and knowledge needed to pursue my doctoral studies without the scholarship, guidance, and teachings from you.

To my family and extended family, Mama, Papa, Ate, Cherry, Jay, Joseph, Jheel and Mairene thank you so much for taking care of things while I was away, also for the for the support and encouragement.

Interestingly, random aggregates formed by interacting units of para (S/R)-CyDFB showed an enhanced |gabs| values as compared to its monomeric form. Further increase in concentration from 3.5x10 -5 M to 1.0x10 -4 M displayed a decrease in dissymmetry factor from |gabs| value of 1.0x10 -3 to |gabs| value of 3.0x10 -4 . This is due to formation of bigger aggregates forming precipitation in higher concentration, which suggests low reliability in the latter value. As compared with the aggregates formed with para (R/S)-CyDFB, CD spectra of meta (R/S)-CyDFB have broader but weaker bands between 360nm-460nm. Newly formed bands in aggregated form of para and meta displayed an opposite sign of Cotton effect to its corresponding monomeric form. In contrast to enhancement of |gabs| values of para, meta (R/S)-CyDFB did not show any significant enhancement in dissymmetry factor upon formation of aggregates which remains |gabs| value of ca. 2.0x10 -4 at concentration of 3.5x10 -5 M. Circularly polarized luminescence (CPL) measurements provided more evidence in chiroptical properties of meta and para (R/S)-CyDFB in their excited states. The |glum| values of both para and meta isomers in monomeric form are too low to be reliably analyzed by the instrument (see Chapter 6). This seems reasonable as the lowest |glum| of our lab-designed machine is about 1x10 -3 , which is not sufficient to characterize those as low as 2.0x10 -4 . Meanwhile, the aggregated form of para (R/S)-CyDFB compounds notably showed a mirror image of R and S enantiomers and has |glum| value of around 4.0x10 -3 measured at 530nm which corresponds to the emission from aggregates shown in Figure 2.11. This clearly showed that the significant increase in |glum| was attributed

Same parameters were used to calculate the total interaction energy cydiamine di-DFB and Figure 4.23 shows the total energy framework and the annotated energy diagram for the crystal structure.

Conclusion and Prospects

This work was divided into three main parts: chiroptical properties of bichromophore difluoroboron β-diketonate (DFB), energy transfer and responsiveness to UV and mechanofluorochromic properties of bichromophore DFB. The discussion in each chapter mainly covers the combination of theoretical calculations and photophysical properties to understand the fundamental reasons for the behavior and responses of the molecules with light and mechanical stress.

We first introduce the concept of circularly polarized luminescence (CPL) and the overview of instrument as well as the early studies of CPL active compounds such as lanthanide complexes and small organic compounds (SOMs). We discussed the advantages of SOMs such as their tunability, simple synthetic route and biocompatibility. One of the challenges with CPL active SOMs is the low gCPL values hence, recent studies were focusing on enhancement of CPL of SOMs using self-assembly. In this study, we used difluoroboron β-diketonate (DFB) as our chromophore because of high QY both in solution and solid state. This compound is known to display mechanofluorochromic property. In the recent paper of Louis et al. they designed DFB linked with chiral amide group which exhibits both CPL and mechanofluorochromic properties. However, enhancement through self-assembly was not yet explored. We aimed to synthesize similar DFB based CPL active and mechanofluorochromic SOMs with enhance the chiroptical properties. Bichromophoric compound was already reported to enhance CPL through intramolecular coupling. Moreover, the chiral bridge and chromophore surface interaction may induce formation of supramolecular assembly.

In the first part of this study, we synthesized a series of bichromophoric DFB using cyclohexane diamine as chiral bridge (R/S para and meta cydiamine DFB). The effect of connectivity in para and meta positions in DFB moieties to the orientation of chromophores as well as to the chiroptical properties of the bichromophore DFB was explored. Through theoretical calculations (DFT and TD-DFT) we show that the variation in connectivity from para to meta position of DFB displayed a totally different direction of chromophores. This has led to inversion of chirality in monomeric form. Moreover, the orientation of DFB influenced the intramolecular coupling of chromophore leading to higher gCPL values for para as compared to meta. The formation of supramolecular assembly of para cydiamine di-DFB was confirmed to enhance the gCPL values wherein we obtained 0.015. We also divulged the effect of chromophore orientation on the formation or hindrance of H-bonding among the carbonyl and amides functional group leading to long range supramolecular assembly. Supramolecular assemblies of organic compounds can be utilized in device fabrications and artificial light harvesting materials. [1][2][3] Therefore, in the second part of

Compound P-2 (600mg, 2.2 eq.) was loaded in flame dried flask and dissolved in 5ml of dry THF under nitrogen atmosphere. Diethylcyanophosphate (DECP) (300 µL, 2.2 eq.) and Et3N (297µL, 2.2 eq.) were added dropwise, and the solution was stirred for 15mins 2 . In a separate flask, (R/S) Cyclohexane diamine (104.5mg, 1eq) was dissolved in 3mL of dry THF and added dropwise to reaction vessel. The medium was stirred for 48 hours at room temperature. Excess solvent was removed in vacuo and the crude was extracted with DCM (100mL). The compound was washed with distilled water (100mL, twice) and dried with MgSO4. Crude solution was purified with silica gel column chromatography using EtOAc/Hexane (40/60) as eluent. The desired compound was obtained with 47% yield (S) and 21% yield (R). The intermediate cydiamine-BOC (2.15g, 1.1 eq.) was loaded in flame dried flask and dissolved in 8mL of dry THF under nitrogen atmosphere. Diethylcyanophosphate (DECP) (1.6mL, 1.3 eq.) and Et3N (1.7mL, 1.3 eq.) were added dropwise, and the solution was stirred for 15minutes at room temperature. In another flask, P-1 intermediate was dissolved (2.72g, 1 eq.) in 8mL dry THF and added dropwise to the cydiamine-BOC medium. 4 The medium was stirred for 48 hours at room temperature. Excess solvent was removed in vacuum and the crude was extracted with DCM (100mL). The compound was washed with distilled water (100mL, twice) and dried over MgSO4. Crude solution was purified with silica gel column chromatography using EtOAc/Hexane (40/60) as eluent. The solvent was dried under vacuum with 32% yield. Cydiamine mono β-diketonate (250mg, 1 eq.) and DIEA (0.22 mL, 2 eq.) were dissolved in dry DCM (8mL) in a flame dried flask and under nitrogen atmosphere. BF3 • O(C2H5)2 in DCM (0.31 mL, 4 eq.) was added dropwise to the flask and the reaction and was stirred at room temperature for 12 hours. Excess DCM was removed in vacuo and the crude sample was purified with silica gel flash column chromatography using EtOAc/petroleum ether (50/50) as eluent. The solvent was dried under vacuum and the target compound was collected with 44% yield. Racemic cydiester di β-diketonate (50mg, 1 eq.) and DIEA (51.6 µL, 4 eq.) were dissolved in dry DCM (5ml) in a flame dried flask and under nitrogen atmosphere. BF3 • O(C2H5)2 in DCM (55µL, 6 eq.) was added dropwise to the flask and the reaction and was stirred at room temperature for 12 hours. Excess DCM was removed in vacuo and the crude sample was purified with silica gel column chromatography using EtOAc/Hexane (50/50) as eluent. The target compound was obtained with 74% yield.