EVIDENCE OF NONEMISSIVE PROTONATED FORMS IN METHYL-ESTERS OF ROSE-BENGAL AND EOSIN-Y IN ACIDIC MEDIUM

Differences between the shapes of the absorption and fluorescence exci tation spectra of the neutral forms of the methyl ester of Eosin Y, th e methyl ester-methyl ethers of the same dye and of Rose-Bengal (MeEO, DMeEO and DMeRB, respectively) in 10(-6) m solutions in 1:1 v/v dioxa ne-pH 0.5 aqueous buffer, is explained by the existence in the ground state of small proportions of the corresponding protonated forms, whic h are only detectable through these differences.