Photoelectric Conversion Based on Proton-Coupled Electron Transfer Reactions

Making efficient use of solar energy is one of the biggest challenges of our time. In nature, solar energy can be harvested by photosynthesis where proton-coupled electron transfer (PCET) plays a critical role. Here, PCET is utilized for the first time to directly convert light energy to electrical energy. Quinone/hydroquinone PCET redox couples were used to produce a photovoltage along with spiropyrans, photoswitchable compounds that undergo reversible transformation between a ring-closed (Sp) and ring-opened form (Mc). The Mc form is more basic than the Sp form, and the open-circuit voltage (V_oc) is related to the proton concentration and that of the Sp/Mc ratio controlled by light. V_oc values from 100 to 140 mV were produced. In addition to direct current (J_sc ca. 9 μA cm^–2), alternating current in the range of 0.1 to 200 Hz was also produced by manipulating the input light.