Efficient photocatalytic hydrogen evolution without an electron mediator using a simple electron donor-acceptor dyad

A highly efficient photocatalytic hydrogen evolution system without an electron mediator such as methyl viologen (MV²⁺) has been constructed using 9-mesityl-10-methylacridinium ion (Acr⁺-Mes), poly(N-vinyl-2-pyrrolidone)-protected platinum nanoclusters (Pt-PVP) and NADH (β-nicotinamide adenine dinucleotide, reduced form) as the photocatalyst, hydrogen evolution catalyst and electron donor, respectively. The photocatalyst (Acr⁺-Mes) undergoes photoinduced electron transfer (ET) from the Mes moiety to the singlet excited state of the Acr⁺ moiety to produce an extremely long-lived ET state, which is capable of oxidizing NADH and reducing Pt-PVP, leading to efficient hydrogen evolution. The hydrogen evolution efficiency is 300 times higher than that in the presence of MV²⁺ because of the much faster reduction rate of Pt-PVP by Acr^.-Mes compared with that by MV^.+. When the electron donor (NADH) is replaced by ethanol in the presence of an alcohol dehydrogenase (ADH), NADH is regenerated during the photocatalytic hydrogen evolution.