Rational Design and Functions of Electron Donor–Acceptor Dyads with Much Longer Charge-Separated Lifetimes than Natural Photosynthetic Reaction Centers

The natural photosynthetic reaction center utilizes sequential multi-step electron transfer from the excited chromophore to the terminal electron acceptor via electron mediators to attain a long lifetime of the final charge-separated (CS) state. Contrary to natural systems, simple electron donor–acceptor dyads have been developed to attain a long-lived CS state, where the donor and acceptor molecules are linked with a short spacer. In the case of a directly linked zinc chlorin–fullerene dyad, the lifetime of the CS state at −150 °C is as long as 120 s. This value is the longest CS lifetime ever reported for porphyrin-based donor–acceptor linked systems. The use of 9-mesityl-10-methylacridinium ion, which has an extremely long-lived CS state, enables the construction of highly efficient photocatalytic systems such as oxygenation of aromatic compounds and hydrogen evolution.