A nuclear magnetic resonance study of the solvatochromism of a pyridinium betaine

Abstract

The ¹H and ¹³C nuclear magnetic resonance spectra of the solvatochromic indicator 2,4,6-triphenylpyridinium-N-3,5-diphenylphenol betaine have been measured in CDCl₃, CD₃OD, [²H₆]DMSO and [²H₆]acetone solvents and 1:1 molar mixtures of CDCl₃–DMSO, CDCl₃–CD₃OD, CDCl₃–acetone, DMSO–acetone, DMSO–D₂O and CD₃OH–D₂O. An attempt has been made to assign the resonance signals and to measure the changes in resonance positions with change of solvent. The major changes in resonance positions that accompany change of solvent are for those parts in the molecule close to the centres of charge. The effects of the differences in solvation at these centres, which are likely to be associated with the extreme solvatochromic properties of the betaine, are also transmitted to other parts of the molecule.