Efficient Low Driving Force Charge Separation in an Electron Deficient Zn-Porphyrin-Fullerene Donor-Acceptor Conjugate

Here, we present a novel conjugate based on a weakly electron-donating Zn(II)-meso-tetrakis(pentafluorophenyl)porphyrin linked to a strongly electron-accepting C60. From spectroscopic and electrochemical investigations a 1.9 eV high charge-separated state is derived. Transient absorption spectroscopy measurements analyzed by global target analysis confirmed the successful charge separation with a quantum yield of 72% despite an overall small driving force of only -0.2 eV. The charge-separated state lifetime is in the nanosecond range. Considering that 90% of the singlet excited state energy is transiently stored in the charge-separated state, we conclude a charge separation energy efficiency of 65%.