IMPROVING PHOTOLYTIC WATER REDUCTION THROUGH ORCHESTRATED ELECTRON TRANSFER USING ADSORBING IRIDIUM PHOTOSENSITIZERS

Abstract

The need for alternative, non-fossil fuels has driven the search for reliable and efficient methods of solar water splitting. Though progress has been made on both the water oxidation and water reduction half reactions, the lack of success in forming a complete reaction and the sensitivity of these systems to even small changes in their composition highlights the need for more research into new and more robust catalytic systems. Because artificial photosynthesis requires control of kinetically driven reactions, our aim was to improve electron transfer efficiency from photosensitizer to catalyst by localizing the photosensitizer on the catalyst using adsorbing moieties.

This thesis describes the synthesis and characterization of bipyridyl ligands containing adsorbing pendant pyridyl moieties, and iridium heteroleptic complexes containing those ligands. The Ir complexes were then evaluated in hydrogen producing photoreactions. The new photosensitizers outperform the control molecules that did not contain adsorbing moieties. Electrochemical evaluation of the new iridium photosensitizers revealed that the adsorbing moieties cause unusual, irreversible electrochemistry compared to iridium complexes without adsorbing moieties, and adsorbing complexes containing osmium instead of iridium.

Furthermore, phenylpyridyl ligands with pendant carboxylic groups were synthesized. The ligands were used to create novel iridium compounds that could adsorb onto metal oxides. Possible future work utilizing these carboxylic-functionalized iridium complexes is outlined.