Effect of Increasing Ligand Conjugation in Cu(I) Photosensitizers on NiO Semiconductor Surfaces

Dye-sensitized photoelectrochemical cells may be used as heterogeneous catalysts for fuel-forming and redox reactions. We describe here the synthesis, characterization, and study of ground and excited state properties of three Cu(I) complexes involving three different ligands with varying electron accepting capacities. Femtosecond and nanosecond transient absorption studies confirm the formation of a singly reduced acceptor ligand after photoexcitation of the Cu(I) centre. These complexes are surface anchored onto nanostructured NiO on conductive fluorine-doped tin oxide on glass to fabricate photocathodes. It was found that even though the ligands with increasing conjugation have effects on the formation of the final excited state in solution, they exhibit similar photocurrents upon white light illumination suggesting hole transfer to NiO happening in advance of the formation of the final excited state.