Solvatochromic behavior of the electronic absorption spectra of gallic acid and some of its azo derivatives

The electronic absorption spectra of gallic acid and its azo derivatives have been studied in various solvents of different polarities. Multiple regression techniques were applied to calculate the regression and correlation coefficients based on an equation that relates the wavenumbers of the absorption band maxima (υmax−) to the solvent parameters; refractive index (n), dielectric constant (D), empirical Kamlet–Taft solvent parameters, π*(dipolarity/polarizability), α (solvent hydrogen-bond donor acidity) and β (solvent hydrogen-bond acceptor basicity). The fitting coefficient obtained from this analysis allows estimating the contribution of each type of interactions relative to total spectral shifts in solution. The dependence of υmax− on the solvent parameters indicates that the obtained bands are affected by specific and non-specific solute-solvent interactions.

Graphical abstractFigure optionsDownload full-size imageDownload as PowerPoint slideHighlights► The electronic absorption spectra of gallic acid and some of its azo derivatives were studied in different solvents. ► Multiple regression techniques were applied including empirical Kamlet–Taft overviews. ► The radius of solutes in different solvents are calculated.