Enhanced intersystem crossing in the oxygen quenching of aromatic hydrocarbon triplet states with high energies

Abstract

The yields of singlet oxygen resulting from the reactions of oxygen with the triplet states of some aromatic hydrocarbons were found to be less than unity. This means that the oxygen quenching of the triplet states of these aromatic hydrocarbons is not solely due to energy transfer as was previously believed to be the case.

For all the compounds studied, the energies of the charge-transfer complex formed between the triplet states and oxygen, calculated from their oxidation potentials, were less than the energies of the isolated triplet states. It is concluded that the oxygen–triplet-state quenching encounters which do not involve energy transfer are proceeding through charge-transfer intermediates with energies lower than those of the isolated triplet states.