Influence of solvent polarity and base concentration on the photochemistry of ketoprofen:: independent singlet and triplet pathways

The photochemistry of ketoprofen in aqueous solutions is strongly influenced by its acid-base chemistry. While the acid form of ketoprofen behaves as a typical benzophenone chromophore, the ketoprofen carboxylate undergoes efficient photodecarboxylation involving a carbanion intermediate. In the present work we have conducted studies in organic solvent-water mixtures in attempts to establish the nature of the carbanion precursor. We find a dual photochemical behavior of ketoprofen depending on the protic state of the ground state absorbing species. The detection of both the ketoprofen triplet and the carbanion during the photolysis of ketoprofen in these mixtures, and the experimentally determined independence of both pathways indicates that the carbanion originates from the singlet state in the system under study.