Time-resolved Raman study on the photoinduced intermolecular electron-transfer reaction of biphenyl in alcohols

Time-resolved Raman spectroscopy has uncovered a new type of photoinduced i ntermolecular electron-transfer reaction of biphenyl in alcohols. The Raman bands of the first excited singlet (S-1) state, the cation radical and the anion radical of biphenyl were simultaneously observed in the time range 0 -200 ns after photoexcitation. The two ion radicals exhibit distinct rise a nd decay behaviors from each other. A kinetic analysis shows that the elect ron-transfer reaction consists of the following three elementary processes; (i) monophotonic formation of a biphenyl cation radical and a solvated ele ctron via the S-1 state, (ii) migration of the electron in the solvent medi um, and (iii) anion radical formation resulting from the capture of the ele ctron by a biphenyl molecule in the ground state. The formation of the cati on radical from the S-1 state is a slow process with a rate not greater tha n 10(-7) s(-1). (C) 1999 American Institute of Physics. [S0021-9606(99)5191 7-X].