COMPARATIVE PHOTOPHYSICAL STUDY OF ROSE-BENGAL, EOSIN-Y AND THEIR MONOMETHYL AND DIMETHYL DERIVATIVES

The fluorescence quantum yields and lifetimes of rose bengal, eosin Y, their ionized or neutral methyl esters, and the methyl ethers of the methyl esters, in 1:1 mixtures of dioxane with pH 0.5 or pH 8 aqueous buffer, are much higher when the phenol group in the xanthenic moiety is ionized than when it is in neutral or methylated form. On the contr ary, the influence of the state of the carboxylic group in the phenyl moiety is much lower. Non-emissive molecules, very probably aggregates , have been observed by fluorescence excitation spectroscopy in 2 x 10 (-6) M solutions of the neutral forms.