TEMPERATURE EFFECTS ON S1-]SO-S1-]T1 BRANCHING RATIO IN RADIATIONLESS TRANSITIONS OF N-HETEROCYCLIC COMPOUNDS

In both protic and aprotic solvents, the fluorescence and triplet formation yields of quinoline and isoquinoline decrease with increasing temperature. This is interpreted in terms of an increased S1 → S0 internal conversion rate, resulting from thermal populations of low frequency out-of-plane vibrations, coupling the lowest energy nππ* and Ππ* singlet states. The temperature sensitivity of the radiationless decay rate is predicted to be common for N-heterocyclic compunds with closely spaced, lowest energy, nππ* and ππ* states. © 1979.