Solvatochromism of symmetrical 2,6-distyrylpyridines. An experimental and theoretical study

Abstract

Seven symmetrical 2,6-distyrylpyridines, phenyl-substituted with hydrogen-bond donors, hydrogen-bond acceptors, halogens and hydrophobic moieties were synthesized and their spectroscopic characterization was done. Solvent effects on the absorption and fluorescence spectra were analyzed and quantified using the Kamlet-Taft and Catalán approach. The obtained results were rationalized by comparison of electrostatic potentials of the molecules in the ground and in excited state and by comparison of the frontier molecular orbitals (HOMO and LUMO), derived from quantum-mechanical calculations (HF, DFT, MP2). Analysis of the results revealed an important influence of non-specific (dispersive) interactions on the solvatochromic behavior of the compounds. 1D and 2D NMR data, in silico obtained conformational assembly of the compound, and the NMR analysis of molecular flexibility in solution (NAMFIS), were used to estimate population of conformers and to deconvolute the UV-Vis spectrum of representative derivative; inferring that the conformational assembly is more complex than was assumed in so far published literature data for this class of compounds. Along with this, the emission spectra of the representative compounds were decomposed by the Multivariate Curve Resolution analysis.

Keywords: Conformational preferences; Fluorescence spectroscopy; UV–Vis spectroscopy.