Switch-over in photochemical reaction mechanism from hydrogen abstraction to exciplex-induced quenching: interaction of triplet-excited versus singlet-excited acetone versus cumyloxyl radicals with amines.

摘要: The fluorescence and phosphorescence quenching of acetone by 13 aliphatic amines has been investigated. bimolecular rate constants lie in the range 108−109 M-1 s-1 for singlet-excited 106−108 triplet case. data indicate that a direct hydrogen abstraction process dominates acetone, while charge-transfer mechanism, namely, exciplex-induced quenching, becomes important acetone. Pronounced stereoelectronic effects toward H abstraction, e.g., 1,4-diazabicyclo[2.2.2]octane (DABCO), significant steric hindrance effects, N,N-diisopropyl-3-pentylamine, are observed. A negative activation energy (Ea = −0.9 ± 0.2 kcal mol-1 triethylamine DABCO) absence solvent effect on indicative involvement exciplexes. Full electron transfer can be ruled out basis low reduction potential which was found to below −3.0 V vers...