Electronic spectroscopy of aromatic Schiff bases. V. Specific interactions involved between some typical benzylideneaniline molecules and small polar molecules

Abstract

Fluorescence quantum yields [Formula: see text], theoretical first-singlet radiative decay constants (kF(t)), and first-singlet non-radiative decay constants (knr) of some benzylideneanilines (BA) dissolved in methylcyclohexane have been obtained. High values of knr are interpreted by the twisting of the molecules around the azomethine bond (C=N) in the first singlet excited state. The absorption spectra of some BA's have also been obtained in methylcyclohexane with various added amounts of polar molecules. BA's with strong electron-donor and/or strong electron-acceptor substituents in the para positions give rise to the formation of ground state complexes with small polar molecules. The stoichiometry of the complex is one BA molecule for two polar solvent molecules; when ethanol is used as a polar solvent, it is further involved in hydrogen bonding formation. The fluorescence spectra of 4-dimethylaminobenzylidene-4′-nitroaniline have been obtained in methylcyclohexane with various added amounts of polar species. The results are interpreted by the formation of exciplexes with polar compound. The Lippert–Mataga theory and the more generalized Kawski theory failed to explain the solute-solvent interactions disussed in this paper.