Spectroscopic studies on styryl-, thienylethenyl- and furylethenyl-pyridines: molecular orbital treatment and effect of positional isomerism

Abstract

The electronic absorption spectra of 2-, 3- and 4-styrylpyridines and 2- and 4-thienylethenyl and furylethenylpyridines in polar and non-polar solvents have been investigated. Different spectra were obtained for the different positional isomers. Solvent–solute interactions caused a shift in band maxima with solvent polarity that was dependent on the specific isomer under investigation. Spectral investigation indicated an extensive electronic interaction between the two heterocyclic rings joined through an ethylenic linkage.

Molecular orbital calculations, using the INDO/S-CI procedure, were performed. The nature of the MO, whether localized or delocalized was a function of the specific isomer. The contribution of CT configuration to the electronic transition was different for different isomers. The solvent–solute interaction was calculated at the MO level. Satisfactory correspondence was found between calculated and experimental results.