Is self-sensitized photo-oxidation a significant pathway in the photofading of azo dyes?

Abstract

The photofading in aerated solution of 4-diethylaminoazobenzene (1) and of the corresponding 4′-methoxy (2) and 4′-nitro derivatives (3) under various conditions has been examined and compared with naphthol derivatives which are subject to azo–hydrazone tautomerism. Dyes (1)–(3) are efficient physical quenchers of singlet oxygen but show very little chemical reactivity with oxygen. Their ability to sensitize oxygen is low. More efficient photo-oxidative fading is observed upon short-wavelenght irradiation, which results from the reaction of oxygen with hydrazyl radicals, formed by initial hydrogen abstraction from the solvent.