While the contribution of singlet oxygen quenchers to synthetic dyes has been investigated previously by several workers, there have been few studies pertaining to the use of singlet oxygen quenchers as a means of improving the light fastness of natural dyes. In this paper, the influence of various additives on the photofading of carthamin has been examined in cellulose acetate film. The rate of photofading of the colour was remarkably suppressed in the presence of nickel hydroxyarylsulphonates, while the addition of UV absorbers afforded little retardation in the rate of fading. O H HO H HO
JapanSelf-sensitized and Rose Bengal-sensitized photo-oxidation of 4,4'-bisacetamidostilbene (BAAS) in solution gives pacetamidobenzaldeh yde and p-acetamidobenzoic acid via the reaction of singlet oxygen with the trans isomer (fa). The rate of the photo-oxidation is retarded in the presence o f effective singlet oxygen quenchem. On the other hand, cis-BAAS (lbl is more stable to visible light under the conditions of Rose Bengal-sensitized photo-oxidation than t ra nsstilbene.
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