Redox tuning in Pt(bpy)-viologen catalyst-acceptor dyads enabling photocatalytic hydrogen evolution from water.

A Pt(ii)-based photo-hydrogen-evolving molecular device tethered to dimethyl-substituted viologens (Pt(bpy)(dmMV2+)2), providing higher driving force for hydrogen evolution reaction (HER) than the non-methylated analogue (Pt(bpy)(MV2+)2), is found to exhibit improved photocatalytic performance. The observed behaviors are explained by the multiple HER pathways taken by evolving H2 by the doubly and triply reduced species generated via consecutive photo-driven steps. Although the activity is still killed by the Dexter-type energy transfer quenching, our results provide new design strategies towards the development of more finely tuned molecular devices controlling the photocatalytic HER.