Spectroscopic study of erythrosin B in PVA films

The effects of increasing concentration (10(-7)-2.5 x 10(-3) mol/g) of Eryt hrosin B (Ery B) in poly(vinyl alcohol) films on its visible absorption spe ctrum have been investigated. In a concentration range of 2 x 10(-7)-10(-5) mol/g, no effects on the absorption spectrum are found. By contrast, withi n this concentration range, time-resolved fluorescence experiments (fluores cence and anisotropy decay) reveal the presence of energy transfer between fry B molecules, followed by fluorescence at low concentrations and fluores cence quenching at higher concentrations. At a concentration of approximate to5 x 10(-5) mol/g, the absorption spectrum broadens as compared to the mo nomeric spectrum and fluorescence is almost completely quenched. A further increase of the concentration results in a blue shift of the absorption spe ctrum. Using molecular mechanics calculations, it is shown that the initial broadening can be ascribed to excitonic interactions between randomly orie nted molecules, whereas the blue shift at higher concentrations can be expl ained by the formation of oligomeric structures. At concentrations of great er than or equal to2.5 x 10(-3) mol/g, the molecules are closely packed, re sulting in a contribution at the red edge of the absorption spectrum.