Photobleaching of metal phthalocyanine sulfonates under UV and visible light irradiation over TiO2 semiconductor

The stability of eleven metal phthalocyanine sulfonates against UV (λ > 320 nm) or visible light (λ > 450 nm) in the presence of TiO2 semiconductor was studied in an aqueous medium. Although all the dyes were quite photostable in a homogeneous solution, they underwent notably photobleaching in the presence of TiO2. The degree of dye bleaching was strongly dependent on the central metal in the complex, whereas for each complex the bleaching rate under UV irradiation was much faster than that under visible light irradiation. The spectral analysis showed that the dye photobleaching led to complete destruction of the phthalocyanine ring. In addition, the visible light stability of the dye was greatly affected by physical properties of TiO2 semiconductor, and the dye photostability could be improved by addition of electron sacrifice such as 4-chlorophenol.