Visible light induced photo-oxidation of water. Formation of intermediary hydroxyl radicals through the photoexcited triplet state of perfluorophenazine

Abstract

1,2,3,4,5,6,7,8-Octafluorophenazine (F-Phen) has an absorption spectrum in the longer wavelength extending to the visible-light region and has a more positive oxidation potential than for unfluorinated phenazine. F-Phen has been photolysed with water in acetonitrile under visible-light irradiation to produce stoichiometrically 1,3,4,5,6,7,8-heptafluoro-2-hydroxyphenazine (F-Phen-2-OH). Photolysis of F-Phen with water in the presence of benzene leads to the formation of phenol followed by the disappearance of F-Phen. EPR analysis and laser flash photolysis reveal that the photoexcited triplet state of F-Phen participates in water oxidation to hydroxyl radicals with concurrent conversion to F-Phen-2-OH. The mechanism is discussed with the results of semi-empirical molecular orbital calculations.