Association of indopolymethine cyanine cations with anions of sulfonephthalein and xanthene dyes in water

Abstract

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 (104to 7 × 107 mol-1 L). In all the cases a substantial hypochromic effect is observed for the Vis absorption band of the cation (λmax = 737 nm). The interaction of indotrimethinium cation (λmax = 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. ©2005 Sociedade Brasileira de Química.