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This thesis describes the synthesis and study of two types of ruthenium(II) bipyridyl complexes that were developed to study sensitization processes on TiO2 surfaces. The thesis will be separated into two parts: the synthesis, characterization, and study of rigid rod dyes to investigate Voc and recombination, and the synthesis and preliminary results of thiol-substituted dyes that were developed to study the influence of platinum catalysis on redox mediator processes in dye-sensitized solar cells. Rigid rod dyes, AK0, AK1, and AK2, a series of bis(bipyridyl) bis(thiocyanate) ruthenium(II) dyes (N3-type), were synthesized to study how dye structure affects voltage. Dyes AK0-2 were synthesized through a one-pot complexation reaction with modified dipyridyl ligands containing 0, 1, or 2 oligo(phenyleneethynylene) bridge units, respectively, to study the effect of the chromophore-semiconductor distance. The dyes were characterized and their photophysical and photoelectrochemical properties were studied in solution and on TiO2 films. In DSSCs, the dyes showed an increase in Voc due to decreased charge recombination rates with increasing semiconductor-chromophore distance. The recombination rate also showed decreased sensitivity to TiO2 electron concentrations as the chromophore-semiconductor distance increased. A second series of rigid-rod, N3-type dyes, AK3 and AK4, was synthesized through a two-step complexation process proceeding through isolation of a p-cymene ruthenium(II) intermediate. These dyes contained long, saturated alkyl chain (nonyl) substituents on the ancillary bipyridyl ligand, with the goal of increasing solubility and facilitating solution characterization. These dyes were characterized synthetically and currently are being studied for I2-adduct formation. The modified thiol dyes were targeted for studying the catalytic process of redox mediator regeneration. As platinum has been shown to catalyze the I-/I3- redox reaction, it was thought that by incorporating platinum nanoparticles into DSSCs the large overpotential for the I-/I3- redox mediator could be reduced. A modified N3-type dye was designed with carboxylic acid groups for anchoring to TiO2 in the DSSC on one bipyridyl ligand and thiols on the other for attachment to platinum. The synthesis of the novel thiolane bipyridyl ligand was followed by a two-step complexation process and both ligand and dye were successfully synthesized and characterized. The dye, AK6, shows positive current and efficiencies of approximately 3% when used as a sensitizer in an operational DSSC. It has also been shown to bind to platinum wire. These preliminary results suggest that this dye may allow for incorporation of platinum nanoparticles into the DSSC, which is currently being investigated. |
