Spectroscopic Study of Erythrosin B in PVA Films

The effects of increasing concentration (10-7−2.5 × 10-3 mol/g) of Erythrosin B (Ery B) in poly(vinyl alcohol) films on its visible absorption spectrum have been investigated. In a concentration range of 2 × 10-7−10-5 mol/g, no effects on the absorption spectrum are found. By contrast, within this concentration range, time-resolved fluorescence experiments (fluorescence and anisotropy decay) reveal the presence of energy transfer between Ery B molecules, followed by fluorescence at low concentrations and fluorescence quenching at higher concentrations. At a concentration of ≈5 × 10-5 mol/g, the absorption spectrum broadens as compared to the monomeric spectrum and fluorescence is almost completely quenched. A further increase of the concentration results in a blue shift of the absorption spectrum. Using molecular mechanics calculations, it is shown that the initial broadening can be ascribed to excitonic interactions between randomly oriented molecules, whereas the blue shift at higher concentrations can be explained by the formation of oligomeric structures. At concentrations of ≥2.5 × 10-3 mol/g, the molecules are closely packed, resulting in a contribution at the red edge of the absorption spectrum.