Heteroleptic copper(I) photosensitizers with carbazole-substituted phenanthroline ligands: Synthesis, photophysical properties and application to photocatalytic H₂ generation

A series of novel 4,7-dicarbazol-1,10-phenanthroline bidentate N-ligands have been designed and synthesized, and applied in heteroleptic copper complexes [Cu(PˆP)(NˆN)]⁺ as photosensitizers (PS) for light-driven water reduction. In combination with a water reduction catalyst (WRC), Fe₃CO₁₂, photocatalytic performances up to 1036 turnover numbers (TON) were reached. This excellent performance can be attributed to the introduction of carbazole groups to the phenanthroline backbone, which can increase the fluorescence quantum yield, decrease the reduction potential of the copper complexes and switch the excited state quenching mechanism from reductive to oxidative. By means of DFT calculations, it has been established that the carbazole substituent contributes most significantly to the HOMO of these complexes.