The association of the cationic dye indoheptamethine cyanine with various anionic dyes (four sulfonephthaleins and five xanthenes) in aqueous solutions was detected using the Vis-spectroscopic method. The values of the association constants are within the range (10(4) to 7×10(7) mol-1 L). In all the cases a substantial hypochromic effect is observed for the Vis absorption band of the cation (lambdamax = 737 nm). The interaction of indotrimethinium cation (lambdamax = 540 nm) with anionic species manifests itself in analogous manner. Electrostatic, Van der Waals, and hydrophobic interactions are regarded as driving forces of the association. Addition of ionic surfactants destroys the dye associates, primarily due to interactions with the oppositely charged dye ions. This process is accompanied by the restoration of the initial Vis absorption bands of both the cationic and the anionic dye.
polymethine cyanine dyes with indoline end groups; sulfonephthaleins; xanthenes; Vis absorption spectra; ion association in water; ionic surfactants
