| Popis: |
Features of the electron transitions in a vinylogous series of polymethine dyes and α,ω-disubstituted polyenes are considered. It is shown that the vinylene shift of the longwave length band on chain lengthening by one vinylene group depends on the degree of π-bond equalization within the chromophore. In polymethines with end groups charaterized by the highest or lowest basicity, the vinylene shift essentially decreases. In polyenes, the magnitude of the vinylene shift is determined by both the topological indices of residues and the polyene form, neutral or charged. On chain lengthening, the difference between the transition energies in different forms increases regularly. Theoretical conclusions are illustrated by both quantum-chemical calculations and experimental data. |
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