Elucidation of the Hydrogen Evolution Reaction on a Photochemical Molecular Device

Abstract

The direct conversion of solar energy to produce useful chemical products such as molecular hydrogen is one of the ultimate goals of photocatalysis. Photochemical molecular devices enable such a process cost-efficiently while offering additional benefits like repairability. We present here a full mechanism for the complete photo-induced catalytic hydrogen evolution reaction by combining a Ru-containing photocenter and a Pt-based catalytically active center in one molecular device. State-of-the-art quantum-chemical calculations shed light on the interplay between light-driven electron transfer processes and activation of protons as substrates. They reveal an induction process and the crucial role of the formation of unpaired electronic states corresponding to a doublet and subsequent higher spin multiplicities. Furthermore, the study indicates that sacrificial donors not only provide electrons but also act as a proton regulator in combination with the bridging ligand acting as a base. Based on the mechanistic understanding derived from the detailed atomistic calculations, our study provides design principles for operative photochemical molecular devices. Thus, our results that are validated through the comparison with experimental spectroscopic data are expected to alter the perspective on elementary concepts of artificial photosynthesis.