ORGN 896 |
| Absorption and Fluorescence spectra of some cyanine dyes in solutions and films show an intense and narrow band (J-band) red-shifted with respect to the typical spectra of these dyes in monomeric form. This band is attributed to the formation of an excitonic state among tightly packed molecules in molecular aggregates; however, its nature is not completely understood yet. Previously we reported that formation of the J-band in the absorption and emission spectra of 1, 1'-Diethyl-2, 2'-Cyanine Iodide is accompanied by changes in the aromatic region of its proton-NMR spectra. Complicity of the spectra did not allow to clearly assign the changes. In this paper we report on changes in proton-NMR spectra of 5, 6-Dichloro-2-[3-[5, 6-dichloro-1-ethyl-3-(3-sylfopropyl)-2(3H)-benzimidazolidene]-1-propenyl]-1-ethyl-3-(3-sulfopropyl) benzimidazolium hydroxide, inner salt, sodium salt (TDBC) and similar dyes accompanying the formation of the J-band in their solutions. These dyes have only two aromatic protons that makes much easier to analyze the changes in the NMR spectra. Possible explanations structural changes /changes in electronic density distributions responsible for the formation of the J-band are discussed. |
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Physical Organic Chemistry: Calculations, Mechanisms, Photochemistry, and High-Energy Species
8:00 AM-12:00 PM, Thursday, 17 March 2005 Convention Center -- Room 11A, Oral
Division of Organic Chemistry |