Excited state intramolecular proton transfer of 2-(2′-hydroxyphenyl)benzimidazole in non-ionic micelles:: Brijs']js

Excited state intramolecular proton transfer (ESIPT) of 2-(2'-hydroxyphenyl)benzimidazole (2-HPBI) has been studied in four different Brijs, i.e. Brij-35, Brij-58, Brij-78 and Brij-99. In comparison to water, fluorescence maxima of the tautomer band is red shifted by approximate to 20 nm, whereas that of normal fluorescence is not affected much. The fluorescence quantum yield of the tautomer band increases and that of the normal band decreases. The effective relative permittivity (epsilon(eff)) of the site where neutral 2-HPBI is present is 20 +/- 2, whereas epsilon(eff) of the sites where monocation-neutral and neutral-monoanion equilibria are taking place are higher. The critical micelle concentration (c.m.c.) of the Brijs at pH approximate to 7 decreases with increase of Brij number. At pH approximate to 1.0 (ionic strength 0.3 M), the c.m.c. of the Brijs are larger, by nearly two orders of magnitude than at pH 7. The pK(a) values of the prototropic reactions are determined in different Brijs and are discussed.