Mesomeric betaine chemistry in solution: Solvent effect on the structure and spectra of uracilyl–pyridinium betaine

Abstract

The presence of positive and negative delocalized charges in a heterocyclic conjugated system gives rise to an interesting class of molecules known as mesomeric betaines. These can be conveniently represented by dipolar canonical formulae. Among them, cross-conjugation appears when the charges are placed in separated parts of the common π-electron system. This fact makes cross-conjugated mesomeric betaines (CCMB) suitable systems to study intramolecular electron transfer processes. In this paper, we studied Raman and electronic spectra of an uracilyl–pyridinium CCMB in solution. Vibrational results demonstrated that the presence of a polar environment quinoidizes the cationic part and aromatizes the anionic moiety of this molecule, which gave us useful information to propose the more relevant mesomeric structures of this molecule in solution. Raman spectroscopy was able to account for cross-conjugation by characterizing conjugational-sensitive bands. The effect of the solvent polarity was studied by electronic spectroscopy, allowing us to establish spectroscopy–structure relationships.