Abstract: In this paper the photo-oxidation of cyanine dyes with different typical structures in ethanol solution has been studied. It was showed that the structure of the cyanine dye acted an important role in photooxidation and photostability of dyes. Photostability of dyes, with three typical structures, was in such order: benzoxazol>benselenazole>benzothiazole. It also indicated that the spectral energy distribution of the light source had some effects on photo oxidation. The concentration of singlet oxygen, which was produced by dye photosensitized, could be worked out by the β value, as well as the photooxidetion rate constants of dyes.

Key words: cyanine dye, photooxidation, singlet oxygen