ISSN:
0021-8383
Keywords:
Chemistry
;
Organic Chemistry
Source:
Wiley InterScience Backfile Collection 1832-2000
Topics:
Chemistry and Pharmacology
Notes:
MO-LCAO Calculations on Polymethines. XI. Local Spectral Excitations in Polynuclear Cyanine DyesVarious branched-conjugated cyanine dyes display long-wavelength absorption bands similar in position to those of their straight-chain substructures. According to the analysis of results of PPP-type calculations this close similarity results from a partial localization of the electronic transitions, whereas the participating electronic states are highly delocalized. The long-wavelength absorptions of symmetrically-branched trinuclear cyanine dyes have an entire molecular chromophore origin resulting from twofold degenerate electronic transitions. Lowering of the symmetry brings about a splitting of the colour-band.In contrast to the branched-conjugated cyanine dyes various tetranuclear cyanine dyes can be considered as being composed of two subchromophores either directly linked or joined through a conjugative bridge. In accordance with PPP configuration analyses and LHM-type calculations the splitting of the colour band is best understood by composite-molecule approaches. In this context the applicability of the simple molecular exciton theory is discussed.
Additional Material:
5 Ill.
Type of Medium:
Electronic Resource
URL:
http://dx.doi.org/10.1002/prac.19793210315
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