Excited state intramolecular proton transfer of 2-(2[prime ]-hydroxyphenyl)benzimidazole in non-ionic micelles:Brijs
Abstract
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 ≈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 (εeff) of the site where neutral 2-HPBI is present is 20±2, whereas εeff 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≈7 decreases with increase of Brij number. At pH ≈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 pKa values of the prototropic reactions are determined in different Brijs and are discussed.