Ultraviolet absorbers and singlet oxygen

Photooxygenation of 9,10-dimethylanthracene (DMA) was carried out with eosi ne as photosensitizer in ethyl cellulose films to investigate the behaviour of the three UV absorbers, 2-(2-hydroxy-4-methoxyphenyl)-4,6-diphenyl-1,3, 5-triazine (M-OH-P), 2-(2-hydroxy-4-methoxyphenyl)-4,6-bis(2,4-dimethylphen yl)-1,3,5-triazine (M-OH-X) and 2-(2-hydroxy-5-methylphenyl)benzotriazole ( Tinuvin P, TIN P), in the presence of singlet oxygen O-2 ((1)Delta(g)). Non e of the UV absorbers displays significant reaction with singlet oxygen aft er 50 h of irradiation with a 500 W mercury lamp. Quenching experiments in ethanol reveal that these UV absorbers do not attenuate the reaction of DMA with singlet oxygen, i.e. there is no detectable physical quenching of sin glet oxygen. M-OH-P produces a minute amount of singlet oxygen with either M-OH-X or TIN P, no measurable quantities of singlet oxygen are generated. These W absorbers, therefore, have no significant capacity for generating s inglet oxygen. (C) 1999 Elsevier Science S.A. All rights reserved.