NMR structural elucidation of photochromic quinolone photoproducts

UV irradiation of 3-benzoyl-2-benzyl-6,7-difluoro-1-propyl-1H-quinolin-4-one leads to the formation of a mixture of photoproducts, with different evolutions. The structure of each of them has been obtained by one- and two-dimensional multinuclear NMR experiments. Two photoenols, which are thermally reversible, have been identified. All of the other photoproducts have been assigned to degradation. Based on the structural identification and the photochemical and thermal evolution of samples, a plausible mechanism is proposed.