The association of cyanine dye cations with phenol red anions in aqueous solutions

The interaction of pinacyanol (PNC) and quinaldine red (QR) cyanine dye cations with single-and doubly charged phenol red (PR) anions in aqueous solution was investigated in detail. In spite of fundamentally different geometries, noticeable interaction between the counterions leads to the formation of ion associates. The energies of PNC, QR, PR, and their associates were calculated. The addition of cationic or anionic surfactants destroyed the associates. The nontrivial character of for the destruction of the PNC⁺-PR^? associate offers promise for the development of quantitative and test methods for the determination of cationic surfactants in solution.