Verification of the electron/proton coupled mechanism for phenolic H-atom transfer using a triplet π,π∗ carbonyl

Evidence for the coupled electron/proton transfer mechanism of the phenolic H-atom transfer between triplet π,π∗ 3,3′-carbonylbis(7-diethylaminocoumarin) and phenol derivatives is obtained by using laser photolysis techniques. It was confirmed that the quenching rate constants of triplet CBC by phenols having positive Hammett constants do not follow the Rehm–Weller equation for electron transfer while those by phenols with negative Hammett constants do it. From the viewpoint of thermodynamic parameters for electron transfer, the crucial factors for phenolic H-atom transfer to π,π∗ triplet are discussed.