Halorhodospira halophila photoactive yellow protein (PYP) is a promising candidate to act as a photoswitching domain in engineered proteins due to the structural changes that occur during its photocycle. Absorption of a photon of wavelength 446 nm triggers trans to cis isomerization of its 4-hydroxycinnamic acid chromophore leading to large structural perturbations in the protein, particularly in the N-terminus. In the dark, a slower cis to trans reisomerization of the chromophore restores the protein’s native fold. The fusion of proteins to PYP’s N-terminus may therefore enable photomodulation of the activity of the attached protein. To test this hypothesis, this thesis descibes genetically encoded photoswitchable DNA-binding proteins that were developed by fusing the prototypical leucine-zipper type DNA-binding protein GCN4 bZIP to the N-terminus of PYP. Five different fusion constructs of full length or truncated GCN4 bZIP and full length PYP as well as fusion constructs of full length GCN4 bZIP and N-terminally truncated PYP mutants were designed in a structure-based approach to determine if the dimerization and DNA binding activities could be controlled by the PYP photocycle. Extensive biophysical characterization of the fusion constructs in the dark and under blue light irradiation using electronic absorption, circular dichroism and fluorescence spectroscopic techniques were performed. As all the fusion proteins could complete photocycles, the DNA binding abilities of the dark and light-adapted states of the proteins were characterized using spectroscopic techniques as well as by the electrophoretic mobility shift assay. All the fusion constructs maintained DNA-binding abilities, however they each differed in their affinities and the extent to which they were activated by blue light irradiation. The reasons for these differences in DNA-binding abilities and photoactivation are explored. Using the results from the characterization of these constructs, proposals are also made to develop more robust genetically encoded photoactivatable DNA-binding proteins of the same type.

Harvesting solar energy can potentially be a promising solution to the energy crisis now and in the future. However, material and processing costs continue to be the most important limitations for the commercial devices. A key solution to these problems might lie within the development of bio-hybrid solar cells that seeks to mimic photosynthesis to harvest solar energy and to take advantage of the low material costs, negative carbon footprint, and material abundance. The bio-photoelectrochemical cell technologies exploit biomimetic means of energy conversion by utilizing plant-derived photosystems which can be inexpensive and ultimately the most sustainable alternative. Plants and photosynthetic bacteria harvest light, through special proteins called reaction centers (RCs), with high efficiency and convert it into electrochemical energy. In theory, photosynthetic RCs can be used in a device to harvest solar energy and generate 1.1 V open circuit voltage and ~1 mA cm-2 short circuit photocurrent. Considering the nearly perfect quantum yield of photo-induced charge separation, efficiency of a protein-based solar cell might exceed 20%. In practice, the efficiency of fabricated devices has been limited mainly due to the challenges in the electron transfer between the protein complex and the device electrodes as well as limited light absorption. The overarching goal of this work is to increase the power conversion efficiency in protein-based solar cells by addressing those issues (i.e. electron transfer and light absorption). This work presents several approaches to increase the charge transfer rate between the photosynthetic RC and underlying electrode as well as increasing the light absorption to eventually enhance the external quantum efficiency (EQE) of bio-hybrid solar cells. The first approach is to decrease the electron transfer distance between one of the redox active sites in the RC and the underlying electrode by direct attachment of the of protein complex onto Au electrodes via surface exposed cysteine residues. This resulted in photocurrent densities as large as ~600 nA cm-2 while still the incident photon to generated electron quantum efficiency was as low as %3 × 10-4. 2- The second approach is to immobilize wild type RCs of Rhodobacter sphaeroides on the surface of a Au underlying electrode using self-assembled monolayers of carboxylic acid terminated oligomers and cytochrome c charge mediating layers, with a preferential orientation from the primary electron donor site. This approach resulted in EQE of up to 0.06%, which showed 200 times efficiency improvement comparing to the first approach. In the third approach, instead of isolated protein complexes, RCs plus light harvesting (LH) complexes were employed for a better photon absorption. Direct attachment of RC-LH1 complexes on Au working electrodes, resulted in 0.21% EQE which showed 3.5 times efficiency improvement over the second approach (700 times higher than the first approach). The main impact of this work is the harnessing of biological RCs for efficient energy harvesting in man-made structures. Specifically, the results in this work will advance the application of RCs in devices for energy harvesting and will enable a better understanding of bio and nanomaterial interfaces, thereby advancing the application of biological materials in electronic devices. At the end, this work offers general guidelines that can serve to improve the performance of bio-hybrid solar cells.

"An apparatus for the delivery of radiation to the tip-sample interface of an Atomic Force Microscope (AFM) is demonstrated. The Pulsed Light Delivery System (PLDS) was fabricated to probe photoinduced conformational changes of molecules using an AFM. The PLDS is 67 mm long, 59 mm wide, and 21 mm high, leaving clearance to mount the PLDS and a microscope slide coated with a thin film of photoactive molecules beneath the cantilever tip of a stand-alone AFM. The PLDS is coupled into a fiber pigtailed Nd:Yag frequency doubled laser, operating at a wavelength of 532 nm. The radiation delivered to a sample through the PLDS can be configured for continuous or pulsed mode. The maximum continuous wave (CW) power delivered was 0.903 mW and the minimum pulse width was 12.3 ms (maximal 401 ms), corresponding to a minimal energy of 0.150 nJ (maximal 362 nJ), and had a cycle duration of 10.0 ms. The PLDS consists of micro-optical components 3.0 mm and smaller in diameter. The optical design was inspired by the three-beam pick-up method used in CD players, which could provide a method to focus the pulse of light onto the sample layer. In addition, the system can be easily modified for different operational parameters (pulse width, wavelength, and power). As proof that the prototype design works, we observed a photoinduced ‘bimetallic’ bending of the cantilever, as evidenced by observing no photoinduced bending when a reflective-coated cantilever was replaced by an uncoated cantilever. Using the apparatus will allow investigation of many different types of molecules exhibiting photoinduced isomerization."

Morphological architecturing is one of the smart and efficient ways to maximize the number of excitons harvested from the known photoactive materials and existing fabrication technologies. Surfaces and interfaces play a vital role in absorbing light and therefore when patterned regularly, aid in the improvement of light absorption. This thesis deals with the study of light management by morphologically architecturing the organic electroactive materials. Here, morphological architecturing is carried out using electrospinning technique by optimizing various parameters. In the first part, organic photovoltaic system is tailored by morphologically modifying the conjugated polymer active layer and analyzing the enhancement in light collection and hence performance of photovoltaic devices. In the second part, the prospects of using free standing buffer layer instead of thin film buffer layer in a solar cell is evaluated. Furthermore, the study on morphological engineering of conjugated small molecule is carried out, by varying the solvents and derivatives, in order to control morphologies by understanding the underlying mechanism. Overall this thesis attempts to understand the fundamentals in morphological architecturing, by physical architecturing of the small molecules in a device for light management applications as well as demonstrating improvement in light absorption in existing organic photovoltaic systems. In the introduction chapter, a brief description of organic photovoltaics is given followed by highlighting the importance of processing methods in light management and in organic photovoltaics. The significance of structured architecture in improving the device characteristics is presented. The issues and challenges in existing architecturing techniques available in literature are discussed. Electrospinning as a tool for morphological modification for organic photovoltaics is demonstrated. This is followed by an outline of the thesis. In Chapter 2, brief description of procedures carried out for fabrication, characterization and optimization of electrospinning process parameters are discussed. The description of fabrication procedures including electrospinning, spincoating and thermal evaporation are given. Characterization techniques used in this thesis for surface and feature analysis, structural, compositional, optical and opto-electrical analyses are described. Optimization of electrospinning process parameters in obtaining various morphologies are evaluated. In Chapter 3, enhancement of device characteristics of poly (3-hexylthiophene): phenyl C61-butyric acid methyl ester (P3HT: PCBM) by changing active layer film morphology into network structure is elucidated. Network structure is provided by electrospraying assisted hierarchical assembly of short fibrils. Effect of electrospraying parameters such as solvent, polymer blend concentration, applied voltage, tip to collector distance, flow rate and deposition time are analyzed. Solvent and applied voltage are observed to be the major parameters governing the formation of network structure. The optimized conditions are used to investigate the optical and structural properties. Percent reflectance studies showed improvement in light absorption due to increase in surface area. Structural characterization studies indicate an increase in orientation of crystallites and crystallinity as compared to spincoated samples. The optimized conditions along with additional spincoated layer of P3HT:PCBM are used to fabricate bulk heterojunction device. Device characteristics exhibited an increase in short circuit current and thus increase in efficiency from 2.18% to 3.66%. There is a enhancement of 37.5% going from maximum external quantum efficiency of 40%-55% for electrosprayed and spincoated devices. It is anticipated that network morphology could be the next possible structure to be explored in organic photovoltaic materials. In Chapter 4, photonic structure is analyzed and compared. A photonics device requires uniform periodic structural arrangement. Various techniques are used to fabricate these types of structures, employing several steps of fabrication. This work proposes single step hierarchical array of equal submicron size porous structure fabricated by tuning electrospinning processing parameters. The dictating process parameters on evolving structure are high voltage, tip to collector distance and solvent. Morphological and optical investigations suggest that uniform periodic topography helps in light scattering leading to multi reflection and thus enhancement in light absorption. This structure is evaluated as active layer in organic photovoltaic devices using poly (3 hexyl thiophene) (P3HT) and phenyl-C61-butyric acid methyl ester (PCBM) blend and its device characteristics are analyzed. Consistent and reliable device characteristics obtained through photonic structure is demonstrated. Finally, comparison is drawn to network structure to assess the advantages and limitations of both morphologies as active layer in organic photovoltaics. In Chapter 5, instead of architecturing active layer the next polymer film layer in the organic solar cells, that is the hole transport layer is transformed into free standing nanofiber mats. Morphological, structural and surface wetting properties are assessed for these nanofiber mats followed by fabrication of inverted organic solar cell. The free standing nanofibers mats are obtained by electrospinning the blend of Poly(3,4-ethylenedioxythiophene) Polystyrene sulfonate (PEDOT:PSS) a conducting water soluble polymer with other water soluble polymers such as poly vinyl alcohol (PVA) and poly ethylene oxide (PEO). The study is further extended by employing two batches of PEDOT:PSS of varying conductivity that are analyzed side by side for six ternary and two binary blends each. Electrospinning parameters such as applied voltage and flow rate are optimized and fibers of diameter 150-200 nm are obtained. Maximum content of PEDOT:PSS with which free standing fiber mats could be achieved are 98 and 99%. Subsequent increase in PEDOT:PSS results in formation of beads. Surface wetting behavior showed that hydrophillicity increases with increase in PEDOT:PSS content. Devices are fabricated and the variation in characteristics and charge collection with respect to addition of PEO and PVA are discussed. In Chapter 6, a conjugated small molecule is taken as case study unlike the use of the conjugated polymer studies in previous chapters. A mechanism is proposed for tuning the sphere-spike morphology and also to control the crystallite size through solvent management using a conjugated small molecule. Electrospraying of an organic molecule is carried out using various solvents, obtaining fibril structures along with a range of distinct morphologies. Solvent characteristics play a major role in achieving the morphology of the organic material. A thiophene derivative (7, 9-di (thiophen-2-yl)-8H-cyclopenta [a]acenaphthylen-8-one) (DTCPA) of donor-acceptor-donor (DAD) architecture is used to study this solvent effect. Seven solvents with decreasing vapor pressure are selected for experiments. Electrospraying is conducted at a solution concentration of 1.5 wt % and a constant applied voltage of 15 kV. Gradual transformation in morphology of the electrospun product from spikes-sphere to only spikes is observed. A mechanism describing this transformation is proposed based on the electron micrograph analysis and XRD analysis. These data indicate that the morphological change is due to the synergistic effect of both vapor pressure and dielectric constant of the solvents. Through a reasonable control over the crystallites size and morphology along with supporting transformation mechanism theory, the work in this chapter elucidates electrospraying as a prospective method for designing the architectures in organic electronics. In Chapter 7, light management studies are carried out by morphologically architecturing the carbazole derivatives through electrospraying. The effect of derivatives on morphology is analyzed. The two carbazole derivatives; carbazole-benzothiadiazole (Cz-Bz) resulted in 2D structures and carbazole-benzothiadiazole-bithiophene (Cz-Bz-Bt) resulted in 3D structures after electrospraying. These structures are further analyzed to study the effect of vapor pressure of solvents and solution concentration. Structural characteristics indicate that electrospraying imparts change in molecular structure orientation. Optical studies showed 19 – 31% enhancement in light absorption. Further, three types of organic photovoltaic devices are fabricated and the opto-electrical properties are evaluated. Also, the effect of substrate on morphological formation is assessed. In Chapter 8, the major contributions and conclusions drawn from the morphological architecturing of both conjugated polymers and small molecules are summarized, along with few recommendations for future research.

Water pollution has become an environmental catastrophe due to the rapid urbanization. The treatment of dumping of waste chemicals in water bodies has contributed to the increase in pollution. In addition to the pollution caused by waste chemicals, faecal bacteria such as Escherichia, Staphylococcus, Pseudomonas etc., can cause serious health issues. Techniques such as filtration and chlorination provide clean water but are associated with disadvantages such as toxic by-products. Although clean water can be still obtained by these techniques, the development of resistance by microorganisms with such conventional treatments of antibiotics is inevitable and poses a new threat. Various researches have taken place in the past few decades to provide clean drinking water. Photocatalysis is considered to be a promising viable alternative for the existing methods to solve the menace of water pollution. It is an advanced oxidation process where the reactive oxygen species are generated by using nanomaterials that can cause degradation of chemicals and pathogens. Particularly, photocatalysis using semiconductors and their composites have been tested for their use in the destruction of contaminants. Several methods have been used in the synthesis of nanomaterials and the variations in their morphologies have resulted in different applications such as photocatalysis and electrocatalysis. Among all semiconductors, TiO2 has been widely used in this application owing to their non-toxicity and abundance in availability. However, TiO2 can be activated only in the presence of UV light. Therefore, the formation of heterojunctions, doping of metals/no- metals in TiO2 has enabled the activation of TiO2 in the visible region. The former approach has also been studied with ceria and silver salts combination. Besides conventional metal oxides, other transitional metal oxides such as copper oxide and bismuth oxide have also been studied owing to its conducting property and facile growth on substrates respectively for enhanced photocatalysis. All the above tweaking has enabled efficient charge separation, band gap reduction, and prevention of recombination. In this thesis, all the nanomaterials and their composites have been synthesized using simple methods such as solution combustion, hydrothermal, solution co-precipitation, and chemical deposition. The primary aim of this thesis is to synthesize various effective nanomaterials with different morphologies, bandgap engineered nanocomposites, metal or non-metal doped metal oxides for efficient waste water treatment of dyes, antibiotics, phenols, and bacteria. Besides, relying on photocatalytic ability, the photoconductivity and intrinsic conducting properties of nanomaterials were exploited to perform photoelectrocatalysis that enhances the rate of decontamination to several orders than photocatalysis. In addition to focusing on increasing the rate of degradation, the main drawback of photocatalysis which is catalyst retrieval has been overcome using conducting substrates and nanomaterial coated substrates for efficient photocatalytic and photoelectrocatalytic decontamination of waste water. All the structural, morphological, chemical and optical properties were thoroughly studied using various characterization techniques such as XRD, SEM, TEM, XPS, UV-DRS, PL respectively. The rate kinetics of dye, antibiotic and phenol degradation was examined. Experimental data was tested with the proposed model in the case of photoelectrocatalytic degradation. The photocatalysts were also studied for its reusability for many cycles. All the proposed works have analyzed the reason for the enhanced activity by performing scavenger reactions to determine the responsible reactive oxygen species. Thus, this thesis exhibits a thorough understanding of how to design and engineer nanomaterials for photocatalytic and photoelectrocatalytic water remediation. The following are the chapters discussed in this thesis. Chapter 1 discusses the drawbacks associated with the current waste water treatment methods and the possibilities of photocatalysis to replace the existing treatments. The advantages of certain transition metals, conventional methods of synthesis and various other properties of the nanomaterials have been discussed. Chapter 2 explains the synthesis of TiO2 nanobelts using combustion synthesized TiO2 under UV and solar irradiation. The catalyst has been characterized for its structural, morphological, chemical and optical properties. The degradation of anionic and cationic dyes and their activity against E.coli bacteria have been evaluated. The efficiency of this catalyst has been compared with commercial Degussa P25. This study shows the morphological influence of nanomaterials on photocatalytic activity. Chapter 3 describes the synthesis of Ag3PO4 impregnated combustion synthesized TiO2 nanobelts using co-precipitation technique. The activity of this material has been studied under solar light. The catalyst has been characterized for its structural, morphological, chemical and optical properties. Similar to the previous chapter, the degradation of dyes and the antibacterial activity of this catalyst has been compared with commercial Degussa P25. This study explains the importance of morphology and charge carrier facilitation in the case of heterojunction formation. Chapter 4 explains the synthesis of ceria nanoflakes by solution combustion method using ascorbic acid as fuel and PEG assisted sonochemical method. The catalyst has been characterized for its structural, morphological, chemical and optical properties. The effect of silver salts such as AgBr on ceria/Ag3PO4 under visible region for degradation of dyes and antibacterial activity has been evaluated. This work elucidates the effect of band engineering in the charge carrier dynamics between interfaces of components within the catalysts. Chapter 5 elucidates the synthesis of vanadium, nitrogen co doped TiO2 catalysts for the simultaneous degradation of microbes and antibiotics. The primary aim of this work is to understand whether interstitial or substituted doped nitrogen will be effective in the presence of vanadium. The photoactivity of this novel catalyst was studied for its synergistic degradation of antibiotics and bacteria simultaneously towards the prevention of microbial resistance towards antibiotics. Chloramphenicol and E.coli were subjected to photodegradation under visible light. Chapter 6 explains the synthesis of copper oxide based nanomaterial for antibiotic and bacterial degradation by photoelectrocatalysis. In order to enhance the rate of photodegradation, photocatalysis has been upgraded with the application of a potential to photocatalytic systems that possess better charge conducting capability. Highly network like copper oxide has been synthesized using conventional combustion synthesis method and compared with copper oxide nanorods synthesized by hydrothermal method. The rate kinetics of photocatalytic and photoelectrocatalytic degradation of antibiotics has been examined thoroughly and validated based on a cyclic network model. This work demonstrates the synergistic rate enhancing capacity upon combining photocatalysis and electrocatalysis. Chapter 7 discusses the fabrication of Cu/CuO/FTO (fluorine doped tin oxide) based substrates for bacterial degradation. Considering the difficulties in photocatalyst retrieval processes and realizing the importance of electrocatalysis, conducting substrates such as Cu strip, FTO were subjected to antibacterial treatment. Formation of copper oxide onto copper strip during the course of reaction forced us to develop CuO/Cu and CuO/FTO interfaces to examine the photocatalytic and photoelectrocatalytic killing of E.coli. Chapter 8 investigates the fabrication of Bi2O3/Ag based material for photocatalytic and photoelectrocatalytic degradation for phenols and substituted phenols. This work starts with fabrication of Bi2O3 working electrodes by chemical deposition. Photodegradation experiments were conducted under UV irradiation and enhancement of the rate of degradation was observed when the working electrode was deposited with silver nanoparticles via chemical reduction method. Formation of the intermediate Bi(OH)x on Bi2O3 or Bi2O3/Ag has resulted in better hydroxyl radical generation upon excitation. Similarly, surface plasmon resonance due to silver nanoparticles was found to be responsible for augmentation in degradation efficiency of phenol. Chapter 9 briefly summarizes the work and provides future directions. The research work thus attempts to design and engineer photocatalytic nanomaterials that are better than the existing materials and emphasizes the importance towards water remediation.

Les matériaux poreux silicatés ont été mis à profit pour encapsuler différents types de molécules, clusters ou nano-objets fonctionnels, donnant lieu à des nanocomposites hybrides organiques-inorganiques à propriétés physiques, chimiques ou biologiques remarquables. Élucider l'organisation structurale à l'échelle moléculaire de tels nanocomposites est indispensable pour l'analyse et la compréhension des propriétés macroscopiques qui en découlent. Ainsi, les techniques de diffusion totale associées à la fois à l'analyse Debye et la Fonction de Distribution de Paires (PDF) sont des méthodes de choix pour la caractérisation des propriétés structurales de matériaux hybrides nano-structurés. Le principal objectif de ce travail consiste à l'utilisation des approches basées sur la diffusion totale de rayons X pour l'analyse structurale complète de molécules photoactives confinées dans des matrices silicatées amorphes avec différentes tailles de pores, afin d'étudier l'influence de l'organisation structurale sur les propriétés optiques et d'explorer également les limites de ces approches d'analyse. Nous avons étudié deux systèmes photoactifs. L'analyse structurale du premier complexe confiné, Na2[Fe(CN)5NO].2H2O (SNP), a été entreprise par une approche multi-échelle combinant la RMN du solide et l'analyse PDF. Cette approche a permis l'identification de la nature des espèces incorporées, l'arrangement des cations et des anions ainsi que la distinction des différentes phases existantes : molécules isolées et nanoparticules. Les analyses Debye et PDF sur le deuxième composé étudié, [NdCl2(H2O)6]Cl, montrent que l'organisation structurale du complexe confiné est différente de celle du matériau massif cristallin. De plus, les cations Nd3+ changent de coordination de 8 à 9 durant le processus d'imprégnation et adoptent ainsi un arrangement structural très similaire à celui en solution aqueuse. Cette modification structurale est en accord avec le changement des propriétés luminescentes de ce complexe / Silica xerogels are versatile host materials for the inclusion of molecules, clusters, or nano-objects yielding host-guest compounds with unique physical, chemical or biological properties. The knowledge of the structural organization of the guest within the host is crucial for the understanding of its properties. Total scattering methods, based on Debye function analysis (DFA) and Pair Distribution Function (PDF), have become powerful tools for structural characterization of nanostructured hybrid materials. The aim of this work is to use the X-ray total scattering method to obtain structural information on photoactive molecules embedded into amorphous silica hosts with different pore sizes, to correlate their structure with the optical properties, and to explore the limitations of the chosen method. Two different photoactive complexes have been investigated. In the first example, the combined PDF and NMR study on Na2[Fe(CN)5NO].2H2O (SNP) embedded into silica matrices allows to extract the nature of the inserted species: quasi-free isolated molecules can be distinguished from nanoparticles and in the former case a model for the arrangement of cation-anion can be proposed from the PDF analysis. In the second example, a luminescent Nd3+ complex, the PDF and DFA analysis reveal that the structural organization of the embedded Nd3+ complexes is different from that of the crystalline material. Furthermore, the Nd3+ cations change the coordination from 8 to 9 during the wet-impregnation doping and adopt very similar structural arrangement as in aqueous solution, which is in agreement with the observed change in the luminescence properties

No description available.

Im Rahmen der vorliegenden Arbeit werden die Synthese und Charakterisierung eines thermisch-kontrollierten und eines photochemisch-kontrollierten reversiblen Polymersystems vorgestellt. Weiterhin werden Poly(dimethyl)siloxan-Oberflächen mit Amino-, Isocyanat-, Furan-, Maleimid- und Cumarin-Gruppen funktionalisiert. Hierbei werden sowohl bekannte als auch neuartige Wege der Oberflächenmodifizierung vergleichend untersucht und bewertet. Ausgehend von den hergestellten Cumarin-funktionalisierten Poly(dimethyl)siloxan-Oberflächen wird eine Anbindung des synthetisierten photochemisch-kontrollierten reversiblen Polymersystems an diese Oberflächen untersucht. Des Weiteren wird die Anbindung des synthetisierten thermisch kontrollierten reversiblen Polymersystems sowohl an den hergestellten Maleimid- als auch an den Furan-funktionalisierten Poly(dimethyl)siloxan-Oberflächen analysiert. Basierend auf den vorgestellten Cumarin-Funktionalisierungen werden photoaktive Oberflächen beschrieben und mittels ATR-IR-spektroskopischer und UV/Vis-spektroskopischer Methoden analysiert.

La présente thèse décrit la synthèse de briques de base de fullerènes pour la préparation de dispositifs moléculaires photoactifs combinant C60 et porphyrines. La cycloaddition alcyne-azoture catalysée au cuivre (I) a été utilisée comme outil de synthèse pour la préparation des dérivés C60 complexes.L’utilité synthétique de synthons C60 a été montrée avec la préparation d’édifices moléculaires complexes présentant des propriétés spécifiques pour diverses applications. Ainsi, un système photoactif flexible combinant C60 et porphyrine a été synthétisé. Cependant la flexibilité de l’espaceur liant les sous-unités de ce composé conduit à des variations de structurales importantes et complique ainsi l’analyse des études photophysiques.Dans ce contexte, nous nous sommes proposé dans une première partie de la présente thèse de parfaitement contrôler l’orientation et la distance des différentes sous-unités au sein de systèmes C60-donneurs. Afin de répondre à ce besoin, nous avons construit une brique de base de C60 rigide ayant un groupe azoture aromatique. Ainsi, la réaction « click » avec un phénylacétylène conjugué au groupement donneur conduit à un espaceur rigide entre les deux sous-unités.La deuxième partie de ce travail a été consacrée à la synthèse d’hexa-adduits du C60 portant différents groupements fonctionnels. Une méthode de synthèse permettant de préparer des hexa-adduits du C60 fonctionnalisés a été mise au point au laboratoire.Cette stratégie a été modifiée et des composés de C60 comportant dix fonctions azotures et une fonction alcyne protégée ont été synthétisés; dans ce cas il est possible d’introduire dans un premier temps par une réaction click dix groupes fonctionnels. Et dans un second temps; après déprotection de la fonction alcyne, une seconde réaction de click permet alors de greffer un fonctionnel différent. / The present PhD thesis manuscript is focused on the use of fullerene building blocks for the preparation of photoactive molecular devices combining C60 and porphyrins. Cu(I) Catalyzed alkyne-azide cycloaddition was used as a synthetic tool for the preparation of complex C60 derivatives. Specifically, in the first part (Chapter II-B), a flexible fullerene-porphyrin triad has been developed and the photophysical studies were performed. The flexible linker between the fullerene core and the azide groups prevented any conformational control on the relative orientation and distance between the two photoactive subunits connected together. This prompted the development of an analogous building block in which the azide unit is directly connected to the bridging phenyl ring (Chapter II-C). In this way, the click reaction with porphyrin-alkyne derivatives give access to hybrid systems with a controlled relative orientation of the two moieties. This is of fundamental importance for a better understanding of the structural parameters affecting the electron and/or energy transfer kinetic in such dyads.In the second part (Chapter III), a fullerene hexaadduct scaffold is used to build up sophisticated multiporphyrin systems for various applications. The preparation of these multi-chromophoric ensembles relies on the click-click approach developed in our group.

Photosensitizing effects of xenobiotics are of increasing concern in public health since modern lifestyle often associates sunlight exposure with the presence of chemical substances in the skin. An important number of chemicals like perfumes, sunscreen components, or therapeutic agents have been reported as photosensitizers. In this context, a considerable effort has been made to design a model system for photosafety assessment. Indeed, screening for phototoxicity is necessary at the early phase of drug discovery process, even before introducing drugs and chemicals into clinical therapy, to prevent undesired photoreactions in humans. In the case of new pharmaceuticals, their phototoxic potential has to be tested when they absorb in the regions corresponding to the solar spectrum, that is, for wavelengths >290 nm. So, there is an obvious need for a screening strategy based on in vitro experiments. The goal of the present thesis was the photochemical study of different photoactive drugs to investigate the key molecular aspects responsible for their photosensitivity side effects. In a first stage, rosuvastatin was considered in chapter 3 as representative compound of the statin family. This lipid-lowering drug, also known as “superstatin”, contains a 2-vinylbiphenyl-like moiety and has been previously described to decompose under solar irradiation, yielding stable dihydrophenanthrene analogues. During photophysical characterization of rosuvastatin, only a long-lived transient at ca. 550 nm was observed and assigned to the primary photocyclization intermediate. Thus, the absence of detectable triplet-triplet absorption and the low yield of fluorescence ruled out the role of the parent drug as an efficient sensitizer. In this context, the attention was placed on the rosuvastatin main photoproduct (ppRSV). Indeed, the photobehavior of this dihydrophenanthrene-like compound presented the essential components needed for an efficient biomolecule photosensitizer i.e. (i) a high intersystem crossing quantum yield (ΦISC =0.8), (ii) a triplet excited state energy of ca. 67 kcal mol−1 , and (iii) a quantum yield of singlet oxygen formation (Φ∆) of 0.3. Furthermore, laser flash photolysis studies revealed a triplet-triplet energy transfer from the triplet excited state of ppRSV to thymidine, leading to the formation of cyclobutane thymidine dimers, an important type of DNA lesion. Finally, tryptophan was used as a probe to investigate the Type I and/or Type II character of ppRSV-mediated oxidation. In this way, both an electron transfer process giving rise to the tryptophanyl radical and a singlet oxygen mediated oxidation were observed. On the basis of the obtained results, rosuvastatin, through its major photoproduct ppRSV, should be considered as a potential sensitizer. Then, itraconazole (ITZ), a broad-spectrum antifungal agent, was chosen as main character of chapter 4. Its photochemical properties were investigated in connection with its reported skin photosensitivity disorders. Steady state photolysis, fluorescence and phosphorescence experiments were performed to understand ITZ photoreactivity in biological media. The drug is unstable under UVB irradiation, suffering a primary dehalogenation of the 2,4-dichlorophenyl moiety that occurs mainly at the ortho-position. In poorly H-donating solvents, as acetonitrile, the major photoproduct arises from intramolecular attack of the initially generated aryl radical to the triazole ring. In addition, reduced compounds resulting from homolytic cleavage of the C-Cl bond in ortho or para positions and subsequent Habstraction from the medium are obtained to a lesser extent. In good H-donating solvents, such as ethanol, the main photoproducts are formed by reductive dehalogenation. Furthermore, irradiation of a model dyad containing a tryptophan unit and the reactive 2,4-dichlorophenyl moiety of itraconazole leads to formation of a new covalent link between these two substructures revealing that homolysis of the C-Cl bond of ITZ can result in alkylation of reactive amino acid residues of proteins, leading to formation of covalent photoadducts. Therefore, it has been established that the key process in the photosensitization by itraconazole is cleavage of the carbon-halogen bond, which leads to aryl radicals and chlorine atoms. These highly reactive species might be responsible for extensive free radical-mediated biological damage, including lipid peroxidation or photobinding to proteins. In chapter 5, photobehavior of imatinib (IMT) was addressed. This is a promising tyrosine kinase inhibitor used in the treatment of some types of human cancer, which constitutes a successful example of rational drug design based on the optimization of the chemical structure to reach an improved pharmacological activity. Cutaneous reactions, such as increased photosensitivity or pseudoporphyria, are among the most common nonhematological IMT side effects; however, the molecular bases of these clinical observations have not been unveiled yet. Thus, to gain insight into the IMT photosensitizing properties, its photobehavior was studied together with that of its potentially photoactive anilino-pyrimidine and pyridyl-pyrimidine fragments. In this context, steady-state and time resolved fluorescence, as well as laser flash photolysis experiments were run, and the DNA photosensitization potential was investigated by means of single strand breaks detection using agarose gel electrophoresis. The obtained results revealed that the drug itself and its anilino-pyrimidine fragment are not DNA-photosensitizers. By contrast, the pyridyl-pyrimidine substructure displayed a marked photogenotoxic potential, which was associated with the generation of a long-lived triplet excited state. Interestingly, this reactive species was efficiently quenched by benzanilide, another molecular fragment of IMT. Clearly, integration of the photoactive pyridyl-pyrimidine moiety in a more complex structure strongly modifies its photobehavior, which in this case is fortunate as it leads to an improved toxicological profile. Thus, on the bases of the experimental results, direct in vivo photosensitization by IMT seems unlikely. Instead, the reported photosensitivity disorders could be related to indirect processes, such as the previously suggested impairment of melanogenesis or the accumulation of endogenous porphyrins. Finally, a possible source of errors in the TEMPO/EPR method for singlet oxygen detection was analyzed. For many biological and biomedical studies, it is essential to detect the production of 1O2 and to quantify its production yield. Among the available methods, detection of the characteristic 1270 nm phosphorescence of singlet oxygen by time-resolved near infrared (TRNIR) emission constitutes the most direct and unambiguous approach. An alternative indirect method is electron paramagnetic resonance (EPR) in combination with trapping. This is based on the detection of the TEMPO free radical formed after oxidation of TEMP (2,2,6,6- tetramethylpiperidine) by singlet oxygen. Although the TEMPO/EPR method has been largely employed, it can produce misleading data. This was demonstrated by the present study, where the quantum yields of singlet oxygen formation obtained by TRNIR emission and by the TEMPO/EPR method were compared for a set of well-known photosensitizers. The results revealed that the TEMPO/EPR method leads to significant overestimation of singlet oxygen yield when the singlet or triplet excited state of the photosensitizers were efficiently quenched by TEMP, acting as electron donor. In such case, generation of the TEMP+• radical cation, followed by deprotonation and reaction with molecular oxygen gives rise to a EPR detectable TEMPO signal that is not associated with singlet oxygen production. This knowledge is essential for an appropriate and error-free application of the TEMPO/EPR method in chemical, biological and medical studies. / Nardi, G. (2014). MECHANISTIC STUDIES ON THE PHOTOTOXICITY OF ROSUVASTATIN, ITRACONAZOLE AND IMATINIB [Tesis doctoral no publicada]. Universitat Politècnica de València. https://doi.org/10.4995/Thesis/10251/48535 / TESIS