The Design, Synthesis and Characterization of 21,23-Dithiaporphyrins for Organic Materials

Abstract

Due to the inherent ability of porphyrins to harvest light, researchers have been striving to expand upon their optical and electronic properties. This thesis investigates the design and improvement of the ability of porphyrins to collect light for applications as donor materials to organic electronics. Derivatives of 21,23-dithiaporphyrins were investigated for their optical and electrochemical properties, in addition to studying the possibility of long-range ordering through the formation of liquid crystalline mesogens. It was found that these dithiaporphyrin derivatives are likely soft-crystalline and through their ability to long-range order, were able to increase their conductivity in a thin-film. The improvements of optical, electrochemical and self-assembling ability of these 21,23-dithiaporphyrins compared to their tetra pyrrolic analogues, prompted the inclusion of these molecules, as a light harvester, into a dye-sensitized solar cell. While the cell was unsuccessful, new dithiaporphyrin chemistry was explored and the optical and electrochemical properties of dithiaporphyrins were studied. To further improve the ability of dithiaporphyrins to harvest light, synthetic changes were made to incorporate planar ethynyl meso-spacers, as well as fuse polycyclic aromatic hydrocarbons to the back bone of the macrocyclic, porphyrin core. Through the gradual improvement in the design of these dithiaporphyrins, it was found that the absorption profile of these compounds broadened and red-shifted to lower wavelengths, compared to tetra pyrrolic analogues. Additionally, it was found that these compounds could oxidize more readily, while still maintaining electronic energy levels, compatible with acceptor materials, for organic photovoltaic applications. Acenaphthene fused dithiaporphyrins exhibited the most encouraging light harvesting properties compared to all the derivatives within this work. These electron rich, highly delocalized dithiaporphyrins, displayed red-shifted absorbance profiles which were capable of harvesting low energy photons beyond 1000 nm. Additionally, these derivatives were able to oxidize at very low potentials, while maintaining stability in air. While these molecules did not display long-range ordering ability, they did show promising, non-covalent, interactions with the common fullerene acceptor material, C60.