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

Abstract

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 H2 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 10 turnovers 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 H2 production, but 0.6 for MPP(.) formation, clearly indicating that unproductive pathways still prevail.

Elucidating the Nature of the Excited State of a Heteroleptic Copper Photosensitizer by using Time‐Resolved X‐ray Absorption Spectroscopy

“…As a result, a low‐energy excited state is formed, known as an “exciplex”, which exhibits a fast emission decay to the ground state with shortened excited‐state lifetimes on the order of ps–ns . Although significant advances have been made in the fine‐tuning of the diimine ligands and the improvement of the resulting bis‐diimine complexes, these homoleptic Cu I compounds have only found restricted use in the photocatalytic reduction of protons from water . In contrast, a large number of the heteroleptic complexes exhibit increased excited‐state lifetimes, which even exceed some of the commonly applied Ru II photosensitizers .…”

Mononuclear and dinuclear heteroleptic Cu(I) complexes based on pyridyl-triazole and DPEPhos with long-lived excited-state lifetimes

“…There are still very few Cu(I)-based PS applied to artificial photosynthesis; nevertheless, they are quite promising. [35][36][37][38][39][40] We are interested in the development of new PS based on copper(I), which can be used in the homogeneous reduction of CO2. In this work three heteroleptic Cu(I) coordination compounds based on pyrid-2´-yl-1H-1,2,3-triazole ligand and bis[(2diphenylphosphino)phenyl] ether (DPEPhos) are presented.…”

Structure–Activity and Stability Relationships for Cobalt Polypyridyl‐Based Hydrogen‐Evolving Catalysts in Water

“…For instance, quantities are strongly influenced even by subtle variations of the different components (e.g., SED, PS, pH, concentrations/ratios, and light source) . There is a great deal of reported information on the initial steps of photocatalysis in homogeneous solutions, that is, the study of the processes that follow excitation of the photosensitizer (reductive/oxidative quenching, first electron transfer to cobalt, and follow‐up reactions of oxidized electron donors), both in organic and aqueous media, as well as in mixtures . There are, from a spectroscopic point of view, only few studies focusing on the follow‐up reactions of the reduced cobalt species in water or organic solvents .…”