Studies on electro-optical properties of conjugated polymers and novel metal complexes for nanocrystalline titanium oxide photovoltaic cells and sensors

Several new approaches towards the development of dye and polymer sensitized photovoltaic cells and fluorescence sensors are the focus of this thesis. A new Ru(II) complex has been designed and synthesized introducing two types of ligands, 5-amino-1,10-phenanthroline and 4,4′-dicarboxylic acid-2,2′-bipyridine. This Ru(II) complex is capable of grafting onto nanocrystalline titanium dioxide and can be incorporated into solid polymer electrolytes. A series of analogous ruthenium complexes have also been synthesized and investigated to compare the effects of functional groups on various ligands by measuring spectroscopic and photovoltaic properties.; A mononuclear Ru(II) complex using terpyridine and bipyridine ligands has been synthesized and compared to analogous homometallic dinuclear Ru(II) complex. The photophysical and photovoltaic (PV) properties have been investigated.; Carboxylated polythiophenes have also been investigated as photosensitizers and charge transfer mediators for nanocrystalline TiO₂ PV cells and show potential as a new class of light harvesting photosensitizers. In the present study, by introducing a chelating group such as a carboxylic acid into the side chain of polythiophenes, enhancements in photovoltaic properties are observed. We believe the carboxylic groups in the side chains enhance the adsorptions of these polythiophenes giving higher solar energy conversion efficiencies. The effects of the chelating group in the side chain of polythiophene have been investigated using a variety of analytical techniques.; Cationic nanocrystalline TiO₂ particles have been synthesized for which the size and composition of the nanoparticles were analyzed by TEM and EDXS. Multilayered films have been fabricated by sequential adsorption of TiO₂ nanoparticles and poly (3-thiophene acetic acid). Each layer of the nanoparticles and PTAA in the thin film has also been characterized by XPS, AFM, and UV-vis spectroscopy. It is believed that these types of multilayered nanocomposite films can be used for the fabrication of efficient light harvesting photovoltaic cells.; Investigations on water-soluble carboxylated polythiophenes show strong fluorescence quenching at low concentrations by methyl viologen in solution as well as in solid state. A high Stern-Volmer constant (Ksv) of ∼3.5 × 106 was measured in the solution state. This may be due to efficient photoinduced electron transfer between the anionic polythiophenes and cationic methyl viologen. Fluorescence quenching in self assembled thin films of these polythiophenes was also observed in diluted methyl viologen solution. The effects of concentration and pH of methyl viologen on fluorescence quenching are investigated.