Photophysics and Homoconjugation Effect of the Acid‐base Complex between 2,4,6‐Trimethoxy‐2‐styrylquinoline and Protic Acids

Abstract

The influence of hydrogen bonding and protonation on an intra‐molecular charge transfer (ICT) compound, 2,4,6‐trimethoxy‐2‐styrylquinoline (2‐StQ‐2,4,6–30Me), was investigated in the ground state and the excited state. The acid concentration strongly influences the acid‐base reaction between 2‐StQ‐2,4,6–30Me and trifluoroacetic acid (TFA) in a non‐polar solvent. The homoconjugation effect (HE) induced by the presence of an acid was quantified by the red shift of absorption maxima. In strong protic acids, the HE was not observed. For non‐polar to moderate polar solvents, the HE value increases as solvent polarity increases. When the solvent dielectric constant was higher than that of TFA, the HE value is reduced when the solvent polarity increases.