SPECTROSCOPIC CHARACTERISTICS OF AN AMPHIPHILIC MEROCYANINE DYE - A PROBE OF POLARITY IN MICELLES

The amphiphilic merocyanine dye C16M was synthesized and its absorption spectra were investigated in organic solvents of varying polarities and solutions of different pH. The spectral behavior was also studied in aqueous and in reversed micelles of two differently charged detergents, CDBA (cetyldimethylbenzylammonium chloride) and AOT (sodium bis 2-ethylhexyl sulfosuccinate). The results show that the pKa value of C16M is more acidic by four pKa units in aqueous micelles than that in methanolic buffer solutions. The spectral changes observed in methanol/H2O mixtures are indicative of self-aggregation of C16M forming miscelles. It was found that this molecule exhibits an extreme negative solvatochromic effect, which permits its use as a chemical probe to monitor the polarity of aqueous micellar systems as well as the polarity of the water pools in reversed micelles.