Hydrophobic interaction of amphiphilic hemicyanine dyes with cationic and anionic surfactant micelles

The hydrophobic interaction of amphiphilic hemicyanine dyes, i.e. (dimethylamino) stilbazolium butyl sulphonate (I) and (dihexylamino)stilbazolium butyl sulphonate (II) with cetyltrimethyl ammonium bromide (CTAB), a cationic surfactant and lithium dodecyl sulphate (LDS), an anionic surfactant, was studied through absorption spectra as a function of the concentration of surfactants above and below their critical micelle concentrations. The different lengths of dialkyl chains present on these dyes exhibited hydrophobic interaction with micelles of CTAB and LDS; as a result visible spectra of both the dyes exhibited red shifts of different magnitudes when the dye molecules were solubilized into micelles. The approximate number of dye molecules per micelle was also estimated at a particular concentration of each surfactant. The solubilization depends on the dilakyl chain length of the dye together with the nature of surfactant head groups. (C) 1997 Elsevier Science B.V.