Excited state intramolecular proton transfer reactions in 2-(2-hydroxyphenyl)benzimidazole in micellar solutions

Spectral characteristics of 2-(2-hydroxyphenyl)benzimidazole (HPBI) have been studied in solutions containing different compositions of dioxane-water mixtures, aqueous sodium dodecyl sulfate (SDS), hexadecyltrimethylammonium bromide (HTAB), and Triton X-100 (TX-100). The correlation curve between the fluorescence band maxima ((v) over bar(a)) and the dielectric constant of dioxane-water solutions provides a better rule than the pure solvents to find the polarity at the binding site of the fluorophore in micelles. The effective dielectric constant at the binding sites of SDS, HTAB, and TX-100 are found to be 40, 20, and 20, respectively. The values of the binding constants of HPBI to these micelles conform to the above results. pK(a) values for various proton transfer reactions were determined at different concentrations of SDS, HTAB, and TX-100, both in the ground and singlet states, and these are discussed.