Studies on solvatochromic behavior of some monoazo derivatives using electronic absorption spectra

The electronic absorption spectra of 2′,4′-dihydroxy-2-methoxyazobenzene and 4,2′,4′-trihydroxyazobenzene molecules have been investigated in solvents with different polarities. The solvent dependent UV–vis spectral shifts, νmax, were analysed using some physical parameters such as refractive index, dielectric constant, Kamlet–Taft parameters, α (hydrogen bond donating ability) and β (hydrogen bond accepting ability). The electronic transitions are assigned and the solvent induced spectral shifts have been analysed in relation to different solute–solvent interaction mechanisms using linear regression analysis. The results of fitting coefficients obtained from the analysis helped us to estimate the contribution of each type of interaction to the spectral shift in the molecule under consideration. It is concluded that the electronic character of the chemical nature of the solvent and the electronic character of substituents are the important factor for the observed solvatochromism.