ORBITAL SYMMETRY EFFECTS IN PHOTOINDUCED BIMOLECULAR ELECTRON-TRANSFER REACTIONS

The rate constants for electron-transfer (ET) reactions between the photoexcited acceptor 9-cyanoanthracene and two series of vinylogous hydrocarbon donors are reported. The HOMOs of these donors alternate in symmetry which leads to the expectation of a 'saw-tooth' relationship for the ET quenching rate constants. This is indeed observed but the effect is quite small, the rate constants varying by a factor of < 10 between 'allowed' and 'forbidden' orbital symmetries.