Charge separation in a copper(I) donor-chromophore-acceptor assembly for both photoanode and photocathode sensitization.

A copper(I) donor-chromophore-acceptor triad bearing 1,8-napthalenemonoimide as the electron acceptor and triphenylamine as the electron donor was synthesized. Photophysical and electrochemical characterization suggest stepwise photoinduced charge separation upon excitation of the copper(I)-based metal-to-ligand charge transfer (MLCT) transition. Analyses of femtosecond transient absorption data of the triad show that intersystem crossing from the 1 MLCT to the 3 MLCT state is followed by two electron-transfer steps with time constants of 20 ps and 722 ps yielding a presumed final charge-separated state with a radical cation on the donor and radical anion on the acceptor that has an 18 ns lifetime in acetonitrile. Finally, this triad was anchored onto n-type (ZnO) and p-type (NiO) semiconductor surfaces to construct a photoanode and photocathode respectively. Successful photocurrent generation from both electrodes upon white light illumination confirms the potential utilization of such systems in dye-sensitized photoelectrochemical cells.