Photochemical reactivity of para-aminobenzophenone in polar and non-polar solvents

In non-polar cyclohexane solution, para-aminobenzophenone (PAB) has a triplet yield of 0.82 and a reaction quantum yield of 0.21 towards hydrogen abstraction In polar N,N-dimcthylformamide (DMF), the tripler yield is 0.1,but the reaction quantum yield is below 10(-5); other reactive benzophenones are photoreduced efficiently in the same solvent. This difference in photoreactivity is related to the nature of the lowest tripler excited state, which is n-pi* (reactive) in non-polar solvents but of ''charge transfer'' (CT) type in polar media. In polar, protic solvents, such as ethanol, the triplet yield is very low as a result of quenching of the CT singlet excited state by proton transfer.