Charge Separation in a Copper(I) Donor-Chromophore-Acceptor Assembly for both Photoanode and Photocathode Sensitization

A copper(I) donor-chromophore-acceptor triad D-Cu(I)-A bearing 1,8-napthalenemonoimide as the electron acceptor and triphenylamine as the electron donor was synthesized using HETPhen methodology. Photophysical and electrochemical characterization suggest stepwise photoinduced charge separation upon excitation of the copper(I) metal-to-ligand charge transfer (MLCT) excited state. Corresponding dyads with only acceptor or donor moieties are also reported for comparison purposes. Analysis of femtosecond transient absorption data of the triad show that intersystem crossing (ISC) of the 1MLCT to 3MLCT state happens first and two electron-transfer steps occur from the 3MLCT state with time constants of 20 ps and 722 ps, respectively. The presumed final charge-separated state •+D-Cu(I)-A•- 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.