The role of excited singlet molecular oxygen in the photodegradation of functional squarylium dyes

Abstract

Stern–Volmer analysis and competitive photo–oxidation experiments of some squarylium dyes with nickel bis(dithiobenzil), an efficient singlet oxygen quencher, have been carried out in chloroform solution and cellulose acetate film, in order to study the photodegradation mechanism of the dyes for optical data storage systems. From both sets of experiments it was found that the photodegradation reactions of squarylium dyes involve oxidation by singlet oxygen in a self–sensitised process, and that singlet oxygen quenchers such as nickel dithiolato complexes have an inhibiting effect on the photoreaction of the dyes. The relative rate constants for the reaction with singlet oxygen from the competitive photo–oxidation experiments were determined. It is shown that the use of singlet oxygen quenchers is effective for improving the light fastness of thin layers of squarylium dyes on polycarbonate substrates.