Molecular engineering of photosensitizers for fast and stable photocatalytic hydrogen generation

•Iridium(III) complexes with a general structure [Ir(C^N)2(N^N)]PF6 are synthesized.•Iridium(III) complexes are explored as photosensitizers for hydrogen generation.•Introduction of fluorinated C^N ligand leads to much faster electron transfer.•N^N ligands with adsorbing groups improve greatly hydrogen-generation duration.•At a low formyl Ir-PS concentration, turnover number over 10,000 is demonstrated.

A family of iridium(III) complexes with a general structure, [Ir(C^N)2(N^N)]PF6 (C^N is cyclometalating ligand and N^N is bipyridyl ligand), was synthesized and explored as photosensitizers (PSs) for photocatalytic hydrogen generation using a three-component system containing an electron donor, triethylamine (TEA), a colloidal platinum catalyst and water. The introduction of a novel fluorinated C^N ligand, 2-(2,4-difluorophenyl)-4-methylquinoline, leads to much faster electron transfer from TEA to the excited-state Ir-PSs, as confirmed from Stern–Volmer measurements. In combination with the employment of various N^N ligands attached with surface-adsorbing groups including vinyl, formyl, cyano, and pyridyl, the photocatalytic hydrogen-generation duration is significantly extended. This might be related to the fast quenching of the reduced state (Ir-PS−) resulting from the enhanced interaction between the Ir-PSs and the Pt catalyst. In photocatalytic reactions at relatively low Ir-PS concentrations, turnover numbers of over 10,000 for hydrogen generation can be attained using the formyl Ir-PS.

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