Structure-Activated Copper Photosensitisers for Photocatalytic Water Reduction

A series of phenanthroline-based ligands have been synthesised and their influence as bidentate nitrogen ligands in heteroleptic [Cu(P^P)(N^N)]⁺ photosensitisers in light-driven water reduction has been studied. In this noble-metal-free Cu-Fe-based photocatalytic water reduction system, the structural effects of the nitrogen ligands have been explored, including the steric and electronic effects of substituents at the 2,9- and 4,7-positions of phenanthroline. Ligands were prepared that led to increased hydrogen generation, with turnover numbers (TON_Cu ) of up to 1388 being observed. All the new complexes were electrochemically and photophysically characterised. We demonstrate for the first time that the presence of fluorine in nitrogen ligands increases the efficacy of copper complexes in photocatalytic hydrogen production.