Photoinduced double charge accumulation in a molecular compound

Photochemistry involves elementary steps in which single electrons are transferred, but artificial photosynthesis requires multi-electron reactions. This discrepancy necessitates light-driven charge accumulation, which has so far proved very difficult to achieve without sacrificial redox reagents. Here we report a molecular donor-photosensitizer-acceptor compound in which light absorption leads to the reversible accumulation of two positive and two negative charges. The resulting photoproduct forms with an overall quantum yield of 37%, has a lifetime of more than 100 ns and stores 3.0 eV of energy. The use of a structurally well-defined molecular compound provides fundamental insights into how light-driven multi-electron transfer can generally be performed efficiently and sustainably, at irradiance levels orders of magnitude below those required in comparable systems. This represents a step towards more application-oriented research on solar fuels from fundamental studies of photoinduced (single) electron transfer.