PHOTOREDUCTION OF 4,4'-BIPYRIDINE BY TRIETHYLAMINE AND BY 1,4-DIAZABICYCLO[2.2.2]OCTANE IN ACETONITRILE AS STUDIED BY NANOSECOND ABSORPTION AND RAMAN SPECTROSCOPIES

The transients that are produced in the photoreduction of 4,4'-bipyridine by triethylamine and by 1,4-diazabicyclo[2.2.2]octane in acetonitrile have been examined by use of nanosecond laser photolysis and time-resolved absorption and Raman spectroscopies. The reaction arises from initial quenching of the 4,4'-bipyridine triplet state by electron transfer (k(Q)(DABCO) = 8.8 x 10(9) M-1 s-1; k(Q)(TEA) = 4.0 x 10(9) M-1 s-1). A mechanism involving the rapid formation of a triplet ion pair followed by ionic dissociation in competition with intrapair proton transfer is proposed. This mechanism is similar to that governing the reduction of triplet ketones by amines in polar solvents.