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.