Design of efficient photoinduced charge separation in donor-copper(i)-acceptor triad

A pure and stable copper(I)-based donor-Cu(I)-acceptor triad was synthesized featuring an efficient stepwise photoinduced charge separation upon excitation of the copper(I) metal-to-ligand charge transfer (MLCT) excited state. The heteroleptic copper(I) complex is composed of two phenanthrolines, one substituted by a naphthalene bisimide (NDI) as electron acceptor and the other by a ferrocene (Fc) as electron donor. The synthesis of two dyads with different spacers between the electron acceptor and Cu(I) center and the charge separation mechanism and dynamics were determined by electrochemical and femtosecond transient experiments, which show that two parallel electron-transfer routes occur from the unrelaxed ¹MLCT and flattened ³MLCT states with time constants of 540 fs and 162 ps, respectively. The final charge-separated state Fc⁺-Cu(I)-NDI^- has a 34 ns lifetime in acetonitrile and is formed with a quantum yield of 90% upon excitation on the MLCT transition of the copper(I) complex.