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 benzimid azoles (BI's) have been studied in cetyltrimethyl ammonium bromide (CT AB) at different pH. Absorption and fluorescence band maxima of the BI 's are hardly affected in the micelles, but the fluorescence quantum y ield of each BI decreases with increase of [CTAB], and this decrease d epends on the position of the substituent rather than on their number. On the other hand, the fluorescence quantum yields of monoanions incr ease 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 dep rotonation reaction decrease in CTAB, and this effect of detergent con centration can be explained with the help of the pseudophase ion excha nge model (PIE).