The photochemistry of the semi-oxidized form of eosin Y and rose bengal in aqueous sodium dodecylsulphate solutions

Abstract

In aerobic aqueous solutions, the semi-oxidized form of the halofluorescein dyes disappears via a bimolecular reaction with itself and via the formation of an adduct with OH − ions. In aerobic aqueous solutions of sodium dodecylsulphate, semi-oxidized rose bengal is solubilized in the micelles, and its exit rate from the micellar aggregates is lower than 60 s −1. The properties of semi-oxidized eosin Y in sodium dodecylsulphate solutions are interpreted in terms of a model based on an adsorption equilibrium between water-bound and micelle-bound dye radicals. This equilibrium depends on the surfactant concentration between the critical micelle concentration and 80 mmol dm −3. Over this range, the reactivity of the semi-oxidized form with itself and towards hydrophilic quenchers decreases when the surfactant concentration is increased. The reaction of the semi-oxidized form with itself is involved in the bleaching of these dyes and the photoproduct is clearly able to react with the semi-oxidized radical of the xanthene dyes.