EFFECT OF CATIONIC MICELLES ON THE DEPROTONATION EQUILIBRIA OF BENZIMIDAZOLES IN THE GROUND AND 1ST EXCITED SINGLET-STATES

Spectral characteristics of six methyl and phenyl substituted benzimidazoles (BI's) have been studied in cetyltrimethyl ammonium bromide (CTAB) at different pH. Absorption and fluorescence band maxima of the BI's are hardly affected in the micelles, but the fluorescence quantum yield of each BI decreases with increase of [CTAB], and this decrease depends on the position of the substituent rather than on their number. On the other hand, the fluorescence quantum yields of monoanions increase by a factor of 10 to 15, and the band maxima are blue shifted in comparison to an aqueous medium. The apparent pK(a) values for the deprotonation reaction decrease in CTAB, and this effect of detergent concentration can be explained with the help of the pseudophase ion exchange model (PIE).