Visible Light Induced Catalytic Water Reduction without an Electron Relay

Protons from water are reduced by a catalytic system composed of a heteroleptic iridium(III) photosensitizer [Ir(ppy)2(bpy)]+, platinum catalyst, and sacrificial reductant. The hydrogen quantum yield reaches 0.26 in this study, which proceeds via reductive quenching of the excited photosensitizer by triethanolamine. This simplified approach allows the characterization of degradation products that are otherwise obscured in more complex systems. A novel 16‐well setup for parallel kinetic analysis of H2 evolution enables high‐throughput screening of reaction conditions and quantization of the decaying reaction rate. DFT calculations rationalize the differences between this and previous studies on tris‐diimine ruthenium(II) photosensitizers. The long‐lived triplet state of a cyclometalated IrIII complex was used to reduce protons from water photo‐catalytically to H2. The kinetics of the hydrogen evolution were monitored with a novel photoreactor and a maximum quantum yield of 26 % was measured for this electron relay deficient system.