Changes induced by solvent polarity in electronic absorption spectra of some azo disperse dyes

The electronic absorption spectra of some azo disperse dyes in various solvents of different polarities have been studied at room temperature. The solvent effects on the wavenumbers of the absorption band maxima (ṽmax) were discussed using the following solvent parameters, refractive index, n, dielectric constant, ε and empirical Kamlet-Taft solvent parameters, π* (dipolarity/polarizability), α (hydrogen bond donating capacity) and β (hydrogen bond accepting ability). The solute-solvent interactions were determined on the basis of multilinear solvation energy relationships concept. The fitting coefficients obtained from this analysis allowed us to estimate the contribution of each type of interactions to the total spectral shifts in solution. The established dependences between ṽmax and the solvent parameters emphasize that the visible band of the studied molecules is affected by both non-specific and specific solute-solvent interactions.