II—Evidence for the Formation of Singlet Oxygen by Phototendering Vat Dyes

Abstract

The reaction of tetraphenylcyclopentadienone (TPC) with singlet oxygen has been used as a probe for the photochemical formation of singlet oxygen by phototendering vat dyes. The dyes C.I. Vat Yellow 1, 2 and 26 and C.I. Vat Orange 9 sensitised the oxidation of TPC in phenol‐methylene chloride solution by the action of visible light. In each case the sole photo‐oxidation product was cis‐dibenzoylstilbene, indicating the intermediacy of singlet oxygen. Similar results were obtained when the dyes were applied to cotton fabric, although the relative efficiencies of the dyes as sensitisers differed from those observed in solution. The singlet‐oxygen‐sensitising efficiencies of the dyes on cotton parralleled their relative phototendering activities towards cellulose, providing evidence in favour of the singlet‐oxygen theory of phototendering. Quenching studies of the dye‐sensitised oxidation of TPC confirmed that the reaction proceeded by a singlet‐oxygen mechanism rather than a radical process.

Analysis of the photofading of phenylazo-aniline and phenylazo-pyridone disperse dyes on poly(ethylene terephthalate) substrate using the semiempirical molecular orbital PM5 method

“…(14)] and E N HOMO [HOMO energy of the nuceophile, a in Eq. (15)], is crucial to the successful application of superdelocalizability, especially when comparing the reactivity against different reagents [10,23].…”

Photofading of phenylazo‐aniline, ‐pyridone and ‐quinolone disperse dyes on a nylon 6 substrate

“…The fading mechanism of disperse dyes on PET fabric was analysed, assuming that only photo‐oxidation occurred on exposure in air [5,6]. Catalytic fading of mixed dyeings demonstrated the photo‐oxidation in the fading on PET fabric [5,6,11–14]. In previous papers [5,6], the catalytic fading of the phenylazo‐pyridone and ‐quinolone dyes by CI Disperse Blue 165 on a PET substrate was analysed in terms of the reactivity, k 0, i (mol −1 dm 3 s −1 ); the second‐order rate constant of reaction of a dye towards 1 O 2 and the photosensitivity, f i (−); and the quantum yield of the 1 O 2 formation, as in the case of a reactive dye–cellulose system [15–18].…”