Photochemical behaviour of rhodamine 6G in Nafion membrane

Abstract

Sorption of laser dye rhodamine 6G in perfluorosulphonate cation-exchange membrane (Nafion) from aqueous solution has been investigated by optical absorption and emission studies. In the H⁺ form, the optical absorption spectra changes with water content in the membrane and is attributed to the change in H⁺ ion concentration in dry and wet (with water) conditions of the membrane. The dye is present in the protonated form in the dry membrane and in the cationic form in the wet membrane. In the Na⁺ form, rhodamine 6G is present in the cationic form and the optical absorption spectra do not show changes in dry and water-wet conditions of the membrane. The fluorescence lifetime of rhodamine 6G is 3.97 ns and decay is single exponential. In the Na⁺ and H⁺ forms of the membrane, the fluorescence decay is biexponential. The lifetime and the relative ratio vary for the Na⁺ and H⁺ forms and also with the water content in the membrane. Owing to the large size of the dye low values for the diffusion coefficient are observed (3.2 × 10^–11 and 2.0 × 10^–8 cm² s^–1 for Na⁺ and H⁺ form of Nafion, respectively). As compared to aqueous solutions, rhodamine 6G in Nafion membrane is observed to be photostable.