Stereoisomerism of Meso Substituted Carbocyanines and Its Influence on J-aggregate Formation

Publisher Website
Google Scholar
Abstract
Three dimensional X-ray data, obtained from a meso ethyl substituted thiacarbocyanine dye, showed that crystals of this dyestuff exist as mono-cis stereoisomers. J-aggregates are formed with this isomer, the geometry of which has been shown by X-ray analysis to be similar to a brickstone-work structure formed of sandwich-like dimers. Studies of the stereoisomeric equilibrium in alcoholic solutions of meso methyl and meso ethyl substituted thiacarbocyanines revealed the presence of considerable amounts of mono-cis isomer in equilibrium at room temperature. The all-trans form was shown to be prevalent in polar solutions of meso unsubstituted and meso phenyl substituted thiacarbocyanines. The influence of stereochemical equilibria on J-aggregate formation was studied in oriented monolayers and in layers adsorbed from solution on large silver halide monocrystals. In oriented monolayers, all-trans J-aggregates, absorbing at longest wave-lengths, are observed. Their absorption maxima are independent of the nature and the periodicity of the substrate on which these layers have been coated. In thiacarbocyanine layers which were adsorbed to silver halide monocrystals from aqueous ethanolic solution, either the all-trans (J2) or a shorter wavelength J-aggregate (J1) or both are formed, following the nature and the periodicity of the adsorbent. For meso methyl and meso ethyl substituted thiacarbocyanines, J1-aggregates are more frequently observed in adsorbed layers on silver halides.

This publication has 0 references indexed in Scilit: