QUENCHING BY OXYGEN OF EXCITED-STATES OF DYES ON COTTON INVESTIGATED WITH DIFFUSE-REFLECTANCE LASER FLASH-PHOTOLYSIS AND SINGLET OXYGEN DETECTION

Diffuse reflectance laser flash photolysis was successfully employed t o study the triplet states of dyes adsorbed on or chemically attached to cotton. This technique, together with the detection of singlet oxyg en from dyes on cotton, made it possible to investigate the diffusion of oxygen in cotton fibres and the mobility of dyes adsorbed onto cott on. Absorption by the triplet states of aluminium phthalocyanine chlor ide and eosin and the phosphorescence of singlet oxygen produced by se nsitisation with rose bengal was used to monitor oxygen diffusion and dye mobility by measuring differences in triplet lifetimes, singlet ox ygen lifetimes and in signal intensities. It was found that swollen co tton allows diffusion of oxygen in the fibres. However, a noticeable e ffect on the triplet state of adsorbed aluminium phthalocyanine chlori de is only observed if oxygen is removed or added by thorough evacuati on or oxygenation of the samples over several days. Singlet oxygen was quenched dynamically by adsorbed dyes, which were found to be immobil ised on the fibres, demonstrating that oxygen is mobile within the fib res at the molecular level.