Photolysis mechanism of a squarylium dye

The photodegradation mechanism of a squarylium dye was investigated by analyzing the photoproducts using a UV–Vis spectrometer, MALDI-TOF-MASS, HPLC and GC–MS. We found that a squarylium dye was likely decomposed into smaller species by way of an intermediate species which was an adduct of an original dye with a solvent molecule or solvent radical. The reaction mechanism was confirmed using the quantum chemical calculation by estimating the structure of the intermediate species. Since the solvent molecules are involved in the reaction, the reaction rate depended on the used solvent, and the photodegradation rate was much faster in a chloromethane than in an alcohol.