Pyridine-terminated small molecular photocatalyst for water reduction

Photocatalytic water reduction into hydrogen using solar energy is an ideal way for the storage of renewable energy. Currently, a great number of photocatalysts with high activity and stability have been developed for hydrogen evolution. The use of metal components is commonly indispensable for highly efficient hydrogen evolution, and the catalytic mechanism at the molecular level remains ambiguous for heterogeneous systems. We report here a pyridine-terminated organic small molecular photocatalyst with superior hydrogen-evolution activity under visible-light irradiation in non-acidic aqueous media, with a turnover number of 281 being achieved in 28 h. Combined experimental and theoretical studies suggest that the water reduction occurs via a homolytic elimination of two pyridine-hydrogen radicals generated by multistep light-induced proton-coupled electron transfer processes. The success of this small molecular organic photocatalyst with both structural integration and functional separation for light harvesting and catalysis opens a revolutionary prospect for simple and low-cost solar energy utilization.