PHOTOCHEMICAL REACTIVITY OF PARA-AMINOBENZOPHENONE IN POLAR AND NONPOLAR-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 hyd rogen abstraction In polar N,N-dimcthylformamide (DMF), the tripler yi eld is 0.1,but the reaction quantum yield is below 10(-5); other react ive benzophenones are photoreduced efficiently in the same solvent. Th is difference in photoreactivity is related to the nature of the lowes t tripler excited state, which is n-pi (reactive) in non-polar solven ts but of ''charge transfer'' (CT) type in polar media. In polar, prot ic solvents, such as ethanol, the triplet yield is very low as a resul t of quenching of the CT singlet excited state by proton transfer.