Spectroscopic and photochemical studies of xanthene and azo dyes on surfaces:cellophane as a mimic of paper and cotton

Steady-state UV¯visible absorption spectra of a xanthene dye, Acid Red 52, and an azo dye, Direct Blue 1, have been studied in aqueous solution, on paper (Acid Red 52) or cotton ( Direct Blue 1), and in cellophane films. Distinct spectral changes are observed when these dyes are deposited from solution on to paper or cotton, and the respective spectral changes are replicated on incorporation into a cellophane film. Dye photofading has also been studied in these media: the photofading of Acid Red 52 and Direct Blue 1 in solution was found to be very slow, with a low quantum yield; the photofading of each dye was significantly faster on paper or on cotton; and the photofading of each dye in cellophane was found to be significantly faster than in solution and similar to that on paper or cotton. Similar spectral changes were observed during the photofading of Acid Red 52 in cellophane and on paper, and of Direct Blue 1 in cellophane and on cotton. These similarities, both in steady-state spectra and in photofading properties, show that cellophane can be used as a good mimic for studying dye fading on paper or cotton; loading into cellophane is straightforward and it has the additional advantage, for spectroscopic studies, of being transparent.