Photochromic activity of thiazine dye/amine systems was investigated under visible light irradiation with adjusting acidity in PVA matrix and in aqueous solution. The influence of acidity on the photochromic rate is significant

the optimum pH values for thionine/EDTA and thionine/triethanolamine in PVA matrix are 6.4 and 8.4 respectively. The best effect was found when the higher contents of protonated species of triplet dye match with the higher contents of effective reductive species of donor. On the other hand

the influence of different amine donors on the photochromic rates and the fluorescence emission spectra were studied and found that amine donors with donating group attacted to nitrogen atoms or those being able to associate with dye can increase the photochromic activity.