Photochromism of 2-benzyl-3-benzoyl-4(1H)-quinolone derivatives

A series of 2-benzyl-3-benzoyl-4(1H)-quinolone derivatives was investigated. The UV–vis spectra of all photochromic derivatives and the corresponding colored photoenols are similar and almost solvent independent. In contrast, the stability of the photoenols depends strongly on the substituents at the quinolone moiety and solvent. We conclude that conversion of the photoinduced forms into the initial quinolones occurs through ionization rather than usual for photochromic compounds thermal relaxation or sigmatropic H-shift. The experimental observations are in good agreement with the results of quantum mechanical calculations.