General Scheme for Oxidative Quenching of a Copper Bis-Phenanthroline Photosensitizer for Light-Driven Hydrogen Production

A new, general reaction scheme for photocatalytic hydrogen production is presented based on oxidative quenching of a homoleptic copper(I) bis-1,10-phenanthroline photosensitizer (PS) by 1-methyl-4-phenyl-pyridinium (MPP+) as the electron relay and subsequent regeneration of the so formed copper(II) complex by a sacrificial electron donor. Electron transfer from the relay to various cobalt based water reduction catalysts and subsequent H-2 production was shown to close the catalytic cycle. Transient absorption experiments unambiguously confirmed the proposed pathway, both the oxidative quenching and subsequent regeneration of oxidized PS. Photocatalytic test runs further confirmed the role of MPP+ and up to 10turnovers were achieved in the relay. The performance limiting factor of the system was shown to be the decomplexation of the copper PS. Quantum yields of the system were 0.03 for H-2 production, but 0.6 for MPP. formation, clearly indicating that unproductive pathways still prevail.