Photochemical reactions of 1H-pyrazolo[1,5-b][1,2,4]triazole azomethine dyes

The photochemical reactions of 1H-pyrazolo[1,5-b][1,2,4]triazole azomethine dyes have been studied both in solution and in film. There are two different reaction pathways. (1) Under visible (VIS) light illumination, the reactive species are the lowest excited state of the dimer of the pyrazolotriazole dyes. The reaction proceeds by a one-photon process. (2) Under ultraviolet (UV) light illumination, the reactive species is the upper excited state of the monomeric pyrazolotriazole dye. The reaction may proceed by a step-by-step two-photon process.A series of additives were tested to improve the light-fastness of pyrazolotriazole dyes. Of the various stabilizers, spiroindane derivatives quench the fluorescence of the dimeric pyrazolotriazole dyes with a maximum value of 1.1 × 102 dm3 mol–1 for the product of kqτ0. These compounds efficiently reduce the photochemical reactions of pyrazolotriazole dyes in film.