MAGNETIC-FIELD EFFECTS ON THE PHOTOINDUCED ELECTRON-TRANSFER REACTIONS BETWEEN HEXAMETHYLDISILANE AND AROMATIC NITRILES IN BRIJ-35 MICELLAR SOLUTIONS

Transient absorptions due to the anion radicals of several aromatic nitriles were measured in their electron-transfer reactions from hexamethyldisilane by means of a nanosecond laser flash photolysis technique. With direct excitation, the yields of the escaped anion radicals of p- and o-dicyanobenzenes increased with increasing magnetic field strength from 0 to 1.35 T. At 1.35 T, the yield of the p-dicyanobenzene anion radical became 1.23 +/-0.05 times as large as that at 0 T. With triplet sensitization of p-dicyanobenzene and 1,2,4,5-tetracyanobenzene, the yields at 1.0 T were 1.61 +/- 0.1 5 and 1.11 +/- 0.05 times as large as those at 0 T, respectively. These magnetic field effects can be interpreted by hyperfine coupling and relaxation mechanisms in the case of triplet radical pairs. The effect reveals that electron transfer partially occurs through triplet states of aromatic nitriles even with direct excitation.