Properties and applications of tetrahedral organic molecules; new tripodal titanium dioxide sensitizers

This thesis includes three chapters related to two projects. The first chapter describes a new approach for studying fixed distance electron transfer at molecule-nanoparticle interface. The general strategy is to utilize a tripod-shaped organic molecule as a rigid, three-point anchor that positions a sensitizer at fixed distance with respect to the surface of semiconductor nanoparticles. The tripods are unsymmetrical adamantane derivatives with three rigid-rod arms terminating with ester groups and a fourth arm terminating with a Ru II-polypyridine complex as a sensitizer. The synthetic methodology that we have developed allowed us to synthesize a variety of tripods. These were anchored to TiO₂ nanoparticles by the formation of an ester bond. High binding constants and high surface coverages on TiO₂ surface were observed for all tripods. The absorption difference spectra of the TiO₂ bound tripods indicate rapid interfacial electron transfer (k_cs > 108 s−1 and fast charge recombination (200 μs). A specific application of Ru(II) sensitizers is as photoanodes in regenerative solar cells, and we have demonstrated that the tripods can be employed to prepare cells that convert light into electricity as efficiently as other Ru(II) complexes.; The second chapter describes a study of the motif-forming characteristics of weak intermolecular interactions (BrBr, C≡CHC≡C and C≡CBrC≡C) in the crystals of tetraphenylmethane and 1,3,5,7-tetraphenyladamantane derivatives substituted at the four vertices with bromo, ethynyl and bromoethynyl groups. The crystals of the bromo- and ethynyl-substituted tetraphenylmethane derivatives exhibited diamondoid lattices sustained by weak interactions between the bromo- and ethynyl substituents. It was observed that when the bromo- and ethynyl groups were interchanged in these compounds, their solid-state structures did not change significantly. The crystals of tetrakis(4-bromoethynyphenyl)methane, as well as 1,4- and 1,3,5-bromoethynylbenzene, were sustained by rare, T-shaped C≡CBrC≡C contacts, but a comparison between these solid-state structures showed significant differences in the ways bromoethynyl groups interact.