Light-driven electron transfer between a photosensitizer and a proton-reducing catalyst Co-adsorbed to NiO

While intermolecular hole-hopping along the surface of semiconductors is known, there are no previous examples of electron-hopping between molecules on a surface. Herein, we present the first evidence of electron transfer from the photoreduced sensitizer Coumarin-343 (C343) to complex 1, both bound on the surface of NiO. In solution, 1 has been shown to be a mononuclear Fe-based proton-reducing catalyst. The reduction of 1 is reversible and occurs within 50 ns after excitation of C343. Interfacial recombination between the reduced 1^(-) and NiO hole occurs on a 100 μs time scale by non-exponential kinetics. The observed process is the first essential step in the photosensitized generation of H₂ from a molecular catalyst in the absence of a sacrificial donor reagent.