LONG-LIVED PHOTOINDUCED CHARGE SEPARATION IN A REDOX SYSTEM TRAPPED IN A SOL-GEL GLASS

A KEY feature in the mechanism of photosynthesis is the initial storage of a substantial fraction of the light energy in the form of a long-lived radical pair 1. In attempts to mimic this process in artificial systems 2-4, impressive progress has been made in increasing the efficiency of the charge-separation reaction between an excited photosensitizer and an appropriate electron acceptor, but prevention of the energy-wasting back-reaction to neutral species still constitutes a major challenge. The back-reaction limits the length of time during which charge separation (and thus energy storage) can be maintained. Here we report exceedingly long-lived (up to a few hours) photoinduced charge separation in an artificial photosynthetic system that does not require a secondary substrate to react with the charged species. Our system uses pyrene (Py*) as the photosensitized electron donor and N,N'-dimethyl-4,4'-bipyridinium (methyl viologen, MV2+) as the electron acceptor, both immobilized in a porous sol-gel silica glass 5. The redox reaction is carried out by the mediation of a third mobile charge carrier in the intrapore space 6. The spatial separation between the donor and acceptor inhibits the back-reaction to produce the long lifetimes of the charge-separated air.