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L’amélioration des performances des dispositifs photovoltaïques organiques passe par le contrôle de la morphologie de leurs couches actives. Nous cherchons à préparer une hétérojonction volumique donneur-accepteur nanostructurée en utilisant la nucléation hétérogène des poly(3-alkylthiophène)s (P3AT) donneurs sur des fibres d'organogélateurs accepteurs à base de pérylène bisimide (PBI).La première partie de ce travail présente la synthèse de trois dérivés PBI symétriquement N-substitués par des dendrons portant des groupes amides avec des chaînes latérales linéaires (PBI-C8) et ramifiées (PBI-C10) ou par une chaîne alkyle linéaire (PBI-L18). Leur étude physicochimique comparée met en évidence le rôle des liaisons H et de la substitution des chaînes latérales dans l’auto-assemblage.La seconde partie détaille les conditions d’obtention, la structure et les propriétés de deux polymorphes du PBI-C10 générés par la réorganisation des liaisons H.Finalement nous donnons une preuve de concept de l’obtention d’une hétérojonction donneur-accepteur par la nucléation des fibrilles de P3BT sur des rubans de PBI-C8 auto-assemblés. / Improving the performances of organic photovoltaic devices requires morphology control of the active layers. We seek to prepare highly nanostructured donor-acceptor bulk heterojunctions using the nucleation of semi-conducting donor polymers e.g. poly(3-alkylthiophene)s (P3AT) on self-assembled ribbons of perylene bisimide organogelators.The first part of this work concerns the synthesis of three PBI compounds symmetrically N-substituted by dendrons bearing amide groups and having linear (PBI-C8) and branched (PBI-C10) side-chains or a linear alkyl chain (PBI-L18). Their compared physicochemical study points to the role of H bonds and of side-chains substitution in the self-assembly process.The second part develops to a large extent the structure and the properties of two polymorphs of PBI-C10 generated by H bond reorganization.Finally, a proof of concept is given for the elaboration of donor-acceptor heterojunctions in solution by nucleating P3BT fibrils on self-assembled ribbons of PBI-C8.

Chapter 1. An Overview of Bile Acid Science This chapter deals with an overview of bile acid science (cholanology) compiling elevant literature review, covering bile acid chemistry, biosynthesis, bile salt evolution, physiology and medicinal values. Figure 1. (a) Digestive system; (b) enterohepatic circulation and (c) cholic acid Bile acids are the end products of cholesterol metabolism, secreted in the liver and stored in the gall bladder (Figure 1). They are normally conjugated with glycine (75%) or taurine (25%). Because of their facially amphiphilic nature, bile salts tend to form micellar aggregates in aqueous solution. They have remarkable ability to transform lamellar array of lipids into mixed micelles. All primary bile acids seem to have three features in common: (1) They are major products of cholesterol metabolism; (ii) they are secreted into the bile largely in a conjugated form and (iii) the conjugates are membrane impermeable, water soluble, amphiphilic molecules. Recent advances in molecular biology have greatly accelerated the knowledge relating to the significance of bile salts in a number of physiological functions. The new role of bile salts as pheromones and ligands for nuclear hormone receptors has been discussed. Chapter 2. Pythocholic Acid: A Major Constituent of Python’s Bile and 16α-Hydroxycholic Acid: A Minor Constituent of Avian’s Bile The first chemical synthesis of pythocholic acid (major constituent of python’s bile) and 16α-Hydroxycholic acid (a minor constituent of avian’s bile) were accomplished starting from cholic acid with overall yields of 5.0% and 5.5%, respectively. A biomimetic remote functionalization strategy was utilized as a key step to achieve the selective chlorination at C-17. Dehydrochlorination of 17-chlorosteroid resulted in the Δ16 olefin. Hydroboration-oxidation of the Δ16 olefin followed by the selective oxidation of the pentol under TEMPO mediated oxidation resulted in an ε-lactone. Hydrolysis of the lactone using 5% KOH in MeOH furnished the 16α-Hydroxycholic acid. On the other hand, selective oxidation of 7-OH of the lactone was achieved using N-bromosuccinimide in acetone/H2O to yield the 7-keto lactone. The ketolactone when subjected to the Huang-Minlon modification of the Wolf-Kishner reduction furnished pythocholic acid. Pythocholic acid showed unusual aggregation behavior and high cholesterol solubilization ability, compared to other trihydroxy bile acids. Chapter 3. 16-Epi-pythocholic acid: An Unnatural Analogue of Pythocholic Acid The synthesis of 16-epi-pythocholic acid, an unnatural analogue of pythocholic acid, was accomplished starting from cholic acid. Cholic acid was converted to Δ8-14) olefin using ZnCl2 in refluxing acetone. Methylation followed by isomerization in CHCl3 by passing dry. HCl at -78 oC resulted in the Δ14 olefin. Allylic oxidation using Na2Cr2O7.2H2O in the presence of N-hydroxysuccinimide in acetone furnished the enone. Selective reduction of the olefin using Pd/C-H2 resulted in 16-Epi-pythocholic acid the 16-keto steroid. NaBH4 reduction of this ketone in MeOH/THF (2:1 v/v) followed by hydrolysis produced the 16-OH bile acid. Analysis of spectral data confirmed that it is a 16β-epimer of pythocholic acid (3α,12α,16β-trihydroxy-5β-cholan-24-oic acid). Critical micellar concentration and cholesterol solubilization properties were studied. Chapter 4. Low Molecular Mass Organogelators Derived from Simple Esters of Cholic Acid This chapter begins with an introduction to low molecular mass organogelators and highlights their applications. Serendipitous gelation of a number of organic solvents by allyl cholate and the design of related simple esters of cholic acid are discussed. A series of simple and easily accessible esters of bile acids were prepared. Ethyl cholate and propyl cholate were found to immobilize a variety of organic solvents like benzene, toluene, xylene, mesitylene, 1,2-dichlorbenzene (DCB) and chlorobenzene (Figure 2). The morphology of the xerogels was well characterized using SEM, AFM and polarizing optical microscopy (POM) techniques, Which revealed the presence of highly entangled self-assembled 3D-fibrillar network (SAFINs). The fiber diameter was found to vary between 300-500 nm. Direct imaging of the collapse of this fibrillar network and direct observation of the evolution of nanofibers was achieved for the first time using variable temperature POM techniques. FT-IR studies, X-ray powder diffraction and variable temperature POM studies revealed the resemblance of SAFINs to the bulk solid. Formation of helical fibrillar network was observed in SEM images and the existence of chiral aggregates was confirmed by induced circular dichroism experiment using achiral Reichardt’s dye as the chromophore. Chapter 5. Ambidextrous Gelators Derived from Spacer Linked Bile Acid Derivatives Based on our observation of simple esters of cholic acid as organogelators a rational design of a series of spacer linked dimers and tripodal derivatives were carried out. Some of these molecules formed highly transparent gels in solvents like haloarenes, anisole, xylene and dibromoalkanes. These molecules also showed rapid gelation in DMF/H2O and DMSO/H2O mixtures in varying proportions of water and the co-solvent. These types of gelators are known as ambidextrous gelators. The xerogels were characterized using SEM, TEM and POM techniques and the presence of highly entangled 3D-fibrillar network (Figure 3) was observed. XRPD showed crystalline nature of bulk solid, whereas the xerogels were shown to lose their crystalline nature. (For figures and structural formula pl see the pdf file.)

L’amélioration des performances des dispositifs photovoltaïques organiques passe par le contrôle de la morphologie de leurs couches actives. Nous avons cherché à préparer une hétérojonction volumique donneur-accepteur nanostructurée en utilisant la nucléation hétérogène du poly (3-hexylthiophène) (P3HT, donneur) par des fibres d’organogélateurs à base de naphthalène diimide (NDI, accepteur). La première partie de ce travail présente l’étude des propriétés d’auto-assemblage d’organogélateurs à cœur NDI substitué par des groupements amides et des dendrons trialkoxyphényles. Nous avons évalué l’influence de la longueur de la chaîne flexible entre le cœur naphthalène et les groupements amides (2 liaisons C-C pour NDI2 et 4 pour NDI4) sur les propriétés physico-chimiques des organogélateurs. La seconde partie de ce travail met en évidence le polymorphisme du composé NDI2 en identifiant 4 polymorphes ainsi que leurs signatures optiques, spectroscopiques et structurales. Un diagramme de phase de l’état solide du NDI2 est proposé. La dernière partie de la thèse concerne l’élaboration de nano-composites donneur-accepteur entre les organogélateurs à cœur NDI et le P3HT. Le processus de formation en solution de ces nano-composites est analysé en suivant les cinétiques de cristallisation du P3HT par spectroscopie d’absorption UV-Visible et les morphologies obtenues (structures shish-kebab) par microscopie électronique en transmission. L’effet nucléant des organogélateurs sur le P3HT a été montré. Les études en cellules solaires des composés P3HT:PCBM : organogélateur ont prouvé que le rendement de conversion énergétique peut être augmenté en présence d’organogélateurs. / Improving the performances of organic photovoltaic devices requires morphology control of the active layers. Highly nanostructured donor-acceptor bulk heterojunctions were prepared by heterogeneous nucleation of poly (3-hexylthiophene) (P3HT, donor) on naphthalene diimide organogelators fibers (NDI, acceptor). The first part of this work was dedicated to the self-assembly of NDI-core organogelators substituted by amide groups and trialkoxyphenyls dendrons. We evaluated the influence of the flexible chain between the naphthalene core and the amide groups (2 C-C bonds for NDI2 and 4 for NDI4) on the physico-chemical properties of the organogelators.The second part of this work focused on the polymorphism of NDI2 with identification of four different polymorphs with their optical, spectroscopic and structural signatures. A phase diagram of NDI2 in the solid state was determined. The last part of this manuscript concerns the fabrication of donor-acceptor nano-composites between NDI organogelators and P3HT. The formation process in solution of these nano-composites was analyzed by following the crystallization kinetics of P3HT by UV-Vis absorption spectroscopy and the thin film morphology (shish-kebab structures) by transmission electron microscopy. The nucleating effect of various organogelators on P3HT was demonstrated. Solar cells were made from the composites P3HT:PCBM : organogelator and their energetic conversion yield was shown to be increased in the presence of organogelators.

Chapter 1. General Introduction This chapter gives an introduction to supramolecular organo/hydrogels and the related bile acid chemistry touching upon the gelation properties of the bile acid derivatives. Diverse applications of the supramolecular gels are illustrated with several examples. In the concluding section of this chapter, a brief introduction on the semiconductor nanocrystals is provided. Finally, the content of the thesis is outlined. Chapter 2. Bile Acid Derived Novel Organo/hydrogelators Part 1. Bile Acid Derived Organo/hydrogelators With a Basic Side Chain Cationic analogues of bile acids which showed remarkable gelation properties in water were reported from our laboratory. This led us to investigate the aggregation behaviour of some of the lithocholic and deoxycholic acid derivatives having a basic side-chain. Figure 1. Bile acid based organo/hydrogelators containing a basic side-chain. In this part, an organogelator 1 and a hydrogelator 2 derived from parent bile acids have been described with respect to their gelation properties, morphology, thermal and mechanical stability of the gels. The organo/hydrogels were shown to be responsive to acid-base stimuli as the organogel formed only in the protonated state and the hydrogel formed in the neutral form of the tertiary amines. The xerogel fibres obtained from the organogel were found to be solid-like and stable up to 200 oC as confirmed by variable temperature polarizing optical microscopy. The non-fluorescent organogel was doped with a fluorescent dye (coumarin 153) to design a novel dye-organogel composite material which was investigated with laser scanning confocal fluorescence microscopy showing the dye molecules were uniformly deposited on the organogel fibres. Part 2. Serendipitous Organogelation by Dimeric Bile Acid Esters This section highlights our work on the organogelators based on a number of dimeric esters consisting of different bile acid units. Figure 2. The three different dimeric bile acid esters as organogelators. In this part, three bile acid derived dimeric esters (1, 2 and 3) were shown to possess organogelation properties in aromatic and halogenated aromatic solvents. We studied the morphological features and rheological properties of these organogels. Next, the organogel matrix was exploited to generate and stabilize gold nanoparticles and prepare AuNP/gel hybrid material. Chapter 3. Cholate Hydrogels and Soft Gel-nanoparticle Hybrid Materials Sodium cholate does not form gel in water under any condition as compared to other sodium salts of other bile acids such as sodium deoxycholate and lithocholate which show pH-dependent gelation behaviour. Figure 3. Metal cholate hydrogels derived from sodium cholate and a variety of metal ions. In this chapter, super hydrogelation of sodium cholate induced by a variety of metal ions (Ca2+, Cu2+, Co2+, Zn2+, Cd2+, Hg2+ and Ag+) is highlighted with respect to their morphology and mechanical strength/stability. The calcium cholate supramolecular system showed the presence of helically twisted nanofibres which were utilised in the synthesis of soft hybrid materials containing metal (Au and Ag) and metal sulphide (CdS, ZnS, HgS, etc.) nanoparticles. Chapter 4. Cadmium Deoxycholate and Highly Luminescent CdSe Nanocrystals Bile acid derivatives have very high chemical and thermal stability owing to the presence of a rigid steroidal nucleus. We explored the possibility of utilizing the bile salt derived from Cd as a metal complexes as precursor to high quality nanocrystals (NCs) which can only be accessed at high temperatures (>200 oC). Figure 4. Synthesis of high quality CdSe NCs from cadmium deoxycholate. In this chapter, the synthesis of high quality CdSe nanocrystals is discussed using a novel bile acid based precursor: cadmium salt of 7-deoxycholic acid, which has high thermal stability and can be conveniently used at very high temperatures (>300 oC) required for the synthesis of high quality nanocrystals. Syntheses were done both by ‘injection’ and ‘non-injection’ modes. The as-prepared nanocrystals have high photoluminescence quantum yield, multiple excitons, narrow size-distributions and zinc blende/wurtzite crystalline cores. Appendix. Steroidal Thiols in Design of Novel Quantum dot (QD)/Gel Hybrid Materials Bile acid derived steroidal thiols were reported to be efficient capping agents for silver and gold nanoparticles from our laboratory. So, we wanted to check whether they could stabilize the semiconductor nanocrystals as well. Figure 5. Steroidal thiols as stabilizers of semiconductor quantum dots. In this short report, we describe the efficient capping by bile acid derived thiols of group II-VI semiconductor nanocrystals/quantum dots (QDs) (CdS, CdSe). After synthesizing the thiol capped QDs, we tried to disperse the capped nanoparticles into the gel fibres. The hybrid gels showed the presence of nanoparticles inside the fibres as observed by transmission electron microscopy, although the photoluminescence of the QDs was very low in the gel matrix, which might be due to the inefficient surface passivation of the nanoparticles in the gel.