Photodegradation of Some 1:2 Metal-complexed Formazan Dyes in an Amide Environment

The photodegradation of some representative metallised formazan dyes has been investigated. Photofading was examined in N,N-dimethylformamide (DMF) at wavelength of 300 and 350 nm, and in daylight. The measured quantum yields of photodegradation depended on the metal present in the dye molecule and the photolysis wavelength. It was found that the UV light under anaerobic conditions the presence of ketone sensitisers such as benzophenone accelerated photofading, confirming that hydrogen abstraction is responsible for degradation. Oxygen also played an important role in the photolytic behaviour under daylight exposure conditions. Co(III) complexed formazan dyes, unlike their Fe(III) analogues, were found to be effective singlet oxygen quenchers. Photofading of the metallised formazan dyes on polyamide fabric was also examined. Fading rates were directly related to the reciprocal of the light fastness of polyamide dyeings. The expected direct relationship between log quantum yield and the reciprocal of light fastness was also observed