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Synthesis,1H-NMR and Electronic Absorption Spectra, and Halochromic Properties of Bis(1,2-dimethyl-3-indolizinyl)hetarylmethane Dyes

Authors
Journal
Dyes and Pigments
0143-7208
Publisher
Elsevier
Publication Date
Volume
4
Issue
2
Identifiers
DOI: 10.1016/0143-7208(83)85003-7

Abstract

Abstract A series of bis(1,2-dimethyl-3-indolizinyl)hetarylmethane dyes has been synthesised, where the hetaryl substituents are 2-benzoxazolyl, 2-benzothiazolyl, 1-methyl-2-benzimidazolyl, 4- and 2-pyridyl and 4-quinolyl. The interpretations of the 1H-NMR spectra supported the postulated structure of these dyes. The dependence of the electronic absorption spectra on the variation of the hetaryl substituents as well as on the pH * conditions of the water/methanol solvent mixture (halochromism) is discussed on the basis of PPP-CI and HMO calculations. Analogously to trihetarylmethane dyes described earlier 1 a second-order perturbational effect could be shown to make the main contribution to the bathochromic shift on substituting the chromophoric di-indolizinylmonomethincyanine fragment at the central carbon atom. This effect was superimposed on the general first-order perturbational shift induced by the increased out-of-plane rotation of the chromophore on substitution with the bulky hetarenes. Lower dissociation constants K * and K R * in comparison with the di-indolylhetarylmethane series 1 confirmed the calculated better delocalisation of the positive charge on the central carbon in the present system.

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