The role of singlet molecular oxygen in the photodegradation of 1-arylazo-2-naphthols in methanol and on cotton

The contribution of a type II singlet oxygen mechanism to the photodegradation in the visible region amongst several 1-arylazo-2-naphthols in methanol was established and shown to be in the range from 10% to 30%. The quantum yield for photodegradation, the quantum yield for the production of singlet oxygen together with the total and reactive quenching constants for reaction with singlet oxygen were measured by steady-state irradiation and time-resolved emission experiments. The values for a type II contribution towards the photodegradation are the first experimentally determined percentages giving quantitative information about different photodegradation pathways of azo compounds. On cotton linters, the dyes were found to quench singlet oxygen and to degrade in the presence of thermally generated singlet oxygen. (C) 1999 Elsevier Science S.A. All rights reserved.