Quenching of aromatic triplet states in solution by nitric oxide and other free radicals

Abstract

The rate constants for quenching of aromatic hydrocarbon triplets by nitric oxide and by the free radical di-t-butyl nitroxide have been measured by the laser flash photolysis technique. For low energy triplets the efficiency of quenching is inversely proportional to triplet energy. At high triplet energy the rates are proportional to triplet energy and there is a large effect of solvent polarity.These data are analysed in terms of an enhanced intersystem crossing process catalysed by the doublet state nitric oxide molecule. The data are shown to be consistent with important contributions from charge-transfer interactions for high triplet energy compounds in non-polar solvents.