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A associação do corante catiônico indoeptametinocianina com vários corantes aniônicos (quatro sulfonaftaleínas e cinco xantinas) em solução aquosa foi investigada usando espectroscopia de absorção no visível. Os valores das constantes de associação estão na faixa de 10 4 a 7 × 10 7 mol -1 L. Em todos os casos, um efeito hipocrômico significativo foi observado para a banda de absorção do cátion (λ max = 737 nm). O mesmo foi observado para a interação do cátion indotrimetínio (λ max = 540 nm) com espécies aniônicas. Interações eletrostáticas, de Van der Waals e hidrofóbicas são identificadas como as forças que dirigem esta associação. A adição de surfatantes iônicos destrói os compostos de associação do corante, primeiramente devido à interação com os íons de corante com carga oposta. Este processo é acompanhado pela restauração dos espectros de absorção visível dos corantes aniônico e catiônico.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 (λ max = 737 nm). The interaction of indotrimethinium cation (λ max = 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.

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Di , tetra , and hexamethine merocyanines derived from malononitrile and heterocycles with moderate (dyes 1-6), strong (7-9), and weak (10 and 11) electron releasing ability were synthesized. The electronic structures of merocyanines 10 and 11 are similar to the neutral polyene state, whereas those of 7-9 are similar to the ideal polymethine state. These tenden cies become more pronounced with increasing length of the polymethine chain. The merocyanines derived from heterocyclic residues with weak or moderate electron releasing ability exhibit a positive solvatochromism, whereas those with strong electron releasing ability show a negative solvatochromism. An increase in the polarity of the solvent makes the former compounds more similar to polymethines, whereas the latter become more similar to polyenes bearing opposite charges on the end groups. The nature of the factors (nonspecific solvation, specific nucleophilic and electrophilic solvation, and vibronic interactions) responsible for the observed characteristic features was analyzed.

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TCF as the acceptor group of merocyanines, having its own extended π-system, gives access to deeply coloured dyes exhibiting good fluorescence efficiency in the red and near-IR spectral range.