Solvatochromism of π-Extended Pyridinium-Thienylene-Phenolates

Abstract

The synthesis and solvatochromic behavior of two series of pyridinium-thienylene-phenolates, which differ in the relative orientation and length of their donor/acceptor pairs, are reported. Increasing the donor/acceptor distance significantly influences the spectral behavior of the dyes, transforming the negative solvatochromism exhibited by the shorter analogs into a highly symmetrical inverted solvatochromic response when the π-system is increased. Through the application of multiparametric analysis, ¹H NMR spectroscopy, and density functional theory (DFT) calculations, it was determined that the transition from negative to inverted solvatochromism is the result of an enhanced sensitivity of the π-extended dyes to solvent polarizability, with the 2,4-thienylene ring present in the bridge playing a crucial role.