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Bile acid-based cation sensors involving through space photo-induced electron transfer (PET) processes have been synthesized. In this approach, appropriate known fluorophores and aza crown ether receptor units were attached on a suitable bile acid scaffold. A through space photo induced electron transfer from N-atom of the aza 18-crown-6 to the excited pyrene was responsible for quenching of the pyrene fluorescence. A fluorescence enhancement was observed with the addition of K+ due to the inhibition of fluorescence quenching by PET mechanism. In order check the relationship between the sensitivity and the molecular structure of the sensors, four different molecules with different geometries were synthesized. The changes in the fluorescence spectra for different sensors were recorded in MeOH. The binding constants calculated by curve fitting showed that while the binding constants did not significantly vary, the sensitivities were different depending on the structure of the sensors. The modular nature of the sensor design was verified by changing the receptor module from aza-18-crown-6 to aza-15-crown-5, keeping other parts of the sensor same, to prepare a sodium selective sensor using the same principle. Fluorescence titration in MeOH confirmed the Na+ selective sensing in the presence of K+. The modular design concept was further extended by replacing the fluorophore pyrene to a coumarin derivative. Coumarin sensors showed a behavior similar to that of the pyrene sensors. In order to check the possibility of sensing metal ions in water, non ionic surfactant, Triton X-100 was chosen to dissolve the sensor in water. Fluorescence titration of the sensors showed a desired selective fluorescence enhancement with the particular metal ions. Merrifield resin and water swellable Tentagel® was used to immobilize the sensor to fabricate reusable sensor beads for detecting the metal ions in non polar solvent and water respectively. Fluorescence enhancements of the sensor beads with the metal ions confirmed the process in the immobilized solid state. K+ and Na+ selective sensor beads successfully demonstrated the fluorescence enhancement with the respective cations. This general strategy can be extended to fabricate other sensors for practical uses.

Le développement de sources d’énergie renouvelables telles que les combustibles solaires est une question cruciale dans le contexte actuel du réchauffement de la planète. L'eau est une source abondante, respectueuse de l'environnement, bon marché et abondante en électrons et en protons nécessaires à la production de combustible. Par conséquent, l'oxydation de l'eau activée par la lumière est une étape clé de la photosynthèse artificielle et le développement de catalyseurs efficaces, robustes et durables constitue un objectif important pour les chimistes. Dans la première partie de cette étude, nous nous concentrons sur le développement de tels catalyseurs basés sur des complexes métalliques à base de métaux de la première série des éléments de transition tel que le cuivre pour cette étude. L'électrocatalyse et la photocatalyse par oxydation de l'eau ont été étudiées. La deuxième partie du travail concerne la formation de paires d'ions entre les espèces à double charge opposée du catalyseur complexe et de l'accepteur d'électrons et du photosensibilisant et du catalyseur complexe. Cette étude devrait apporter des preuves solides de l'influence de chaque composant du photosystème par l'association et la dissociation de paires d'ions.Dans la troisième partie, nous étudions un système synthétique sensibilisant-catalyseur capable de photoactiver une molécule d’eau liée à l’unité catalytique par le biais d’une oxydation à deux électrons et à deux protons, réalisant toute la caractérisation photophysique de la dyade. Par conséquent, l’étude des complexes moléculaires pour la photosynthèse artificielle fournit diverses orientations pour développer le rendement d’utilisation de l’énergie solaire. / Development of renewable energy sources like solar fuels is a crucial issue in the actual context of global warming. Water is an environmentally friendly, cheap and abundant source of the electrons and protons needed for fuel production. Therefore, light-activated water oxidation is a key step in artificial photosynthesis and the development of efficient, robust and sustainable catalysts is an important goal for chemists. In the first part of this study, we focus on the development of such catalysts based on earth abundant copper complexes. The water oxidation electrocatalysis and photocatalysis were investigated. The second part of the work concerns the ion pair formation between the oppositely double charged species of complex catalyst and electron acceptor and Photosensitizer and complex catalyst are investigated. This study should bring solid evidence on the influence of each component in photosystem through the ion pair association and dissociation. In the third part, we study a synthetic sensitizer-catalyst system that can photoactivate a water molecule bound to the catalytic unit through a two-electron, two-proton abstraction, performed all the photophysical characterization of the dyad. Therefore, studying molecular complexes for artificial photosynthesis provides diverse direction to develop the utilization efficiency of solar energy.

Der Gegenstand der vorliegenden Arbeit ist die Untersuchung von photoinduzierten Energietransferprozessen (EET) und Elektronentransferprozessen (ET) in Modellsystemen, die als potentiell geeignet für eine Nutzung in der artifiziellen Photosynthese angesehen werden. Den beiden wesentlichen Zugängen zur Architektur artifizieller Photosynthese-Systeme entsprechend wurden vergleichend kovalente und sich selbst organisierende Systeme untersucht. In beiden Zugängen wurden ähnliche chemische Komponenten als optisch aktive Moleküle eingesetzt, insbesondere Phthalocyanine mit einem Silizium-Zentralatom (SiPc). Durch eine Kombination von stationären und zeitaufgelösten optisch-spektroskopischen Methoden konnten die lichtinduzierten ET- und EET-Prozesse identifiziert und quantifiziert werden. Im ersten Teil der Arbeit wurden mehrere kovalent gebundene Triaden und eine Pentade untersucht. In allen Systemen finden sehr effiziente ET und EET Prozesse statt. Es wurde gezeigt, dass das Lösungsmittel großen Einfluss auf die photophysikalischen Eigenschaften der Systeme ausübt. Die Lebensdauer des ladungsseparierten Zustandes variiert von 1,7 ns in Toluol bis 30 ps in DMF. Im zweiten Teil der Arbeit wurde erstmals gezeigt, dass sich in wässriger Lösung ein supramolekularer Komplex, bestehend aus einem Beta-Cyklodextrin (CD), einem konjugierten Subphthylocyanin (SubPc), einem Porphyrin (Por) und einem SiPc bilden kann. Letzteres wurde über unterschiedliche Ketten an zwei CDs kovalent gebunden. Die Selbstorganisation wird über hydrophobe Wechselwirkungen vermittelt und die Bildung der Komplexe ist sehr effizient. Nach selektiver Anregung von SubPc finden sequenzielle ET- und EET-Prozesse von SubPc zu SiPc statt. Das Por spielt die Rolle einer energetischen und elektronischen Brücke und ermöglicht die ET und EET-Prozesse von SubPc zu SiPc. Die Ladungsrekombination in den Grundzustand geschieht innerhalb von 1,7 ns. / The main objective of the present thesis was to conduct investigations of photo-induced electron transfer (ET) and excitation energy transfer (EET) processes in model compounds that are considered potentially appropriate for use in artificial photosynthesis. Two approaches have been used to construct the artificial photosynthetic systems, namely covalent and supramolecular approach. In both systems similar optically active molecules have been employed, particularly silicon-based phthalocyanines (SiPc). A comparative study between the covalently-linked and self-assembled systems had been conducted. For these purposes, thorough spectroscopic measurements in the UV/Vis range had been performed on these conjugates. A combination of steady-state and time-resolved experiments allowed an identification and quantification of the photo-induced ET and EET processes. In the first part of the work several covalently bound triads and a pentad bearing a central SiPc unit were studied. In all systems highly efficient ET and EET processes take place. It was found that the solvent exerts great influence on the photophysical properties of the systems. The lifetime of the charge-separated state varied from 1.7 ns (toluene) down to 30 ps (DMF). In the second part of the thesis, for the first time the formation of ternary supramolecular complexes consisting of a beta-cyclodextrin (CD), a conjugated subphthalocyanine (SubPc), a porphyrin (Por) and a series of SiPcs substituted axially with two CDs via different spacers was shown. These components are held in water by host-guest interactions and the formation of these host-guest complexes was found to be very efficient. Upon excitation of the SubPc-part of the complex sequential ET and EET processes from SubPc to SiPc take place. The Por dye acts as a transfer bridge enabling these processes. The probability of ET is controlled by the linker between CD and SiPc. Charge recombination to the ground state occurs within 1.7 ns.