Abstract
It has been shown with the use of the HMO, PPP, and CNDO/2 approximations that the distribution of the electron density in asymmetric polymethine dyes at the ends of the polymethine chain is determined mainly by the electron-donor ability of the nearby terminal groups, whereas in the middle their influence becomes weaker as the chain becomes longer. The asymmetry of the dyes causes a decrease in the alternation of the charges on the atoms and an increase in the alternation of the bond populations. These phenomena are most clearly displayed in the SCF approximations, which always emphasize alternation. The closer are the electron-donor properties of the terminal groups and the longer is the polymethine chain, the smaller is the difference in the distribution of the electron density near the terminal residues in asymmetric and symmetric dyes.
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Translated from Teoreticheskaya i Éksperimental'naya Khimiya, Vol. 22, No. 3, pp. 347–351, May–June, 1986.
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Dyadyusha, G.G., Repyakh, I.V. & Kachkovskii, A.D. Quantum-chemical investigation of the distribution of the electron density in asymmetric polymethine dyes. Theor Exp Chem 22, 332–336 (1986). https://doi.org/10.1007/BF00521161
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DOI: https://doi.org/10.1007/BF00521161