The electronic absorption spectra of 4-((2-ethylphenyl)diazenyl)benzene-1,3-diol and 2((2-ethylphenyl)diazenyl)benzene-1,3,5-triol molecules in the nine different solvent variable electronic characters have been recorded. The solvent dependent maximum absorption band (pi-pi* transitions) shifts, nu(max), were analyzed using a wide range of parameters such as refractive index, dielectric constant and Kamlet-Taft parameters [hydrogen bond donating ability (alpha) and hydrogen bond accepting ability (beta)]. The electronic transitions are assigned and the solvent-induced spectral shifts have been analyzed in relation to the different solute-solvent interaction mechanism using computational chemistry. The intermolecular interaction types in the azobenzene derivatives solutions have been established on the basis of a multiple linear regression analysis. The fitting coefficients obtained from this analysis allowed us to estimate the contribution of each type of interactions to the total spectral shifts in the studied solutions. (C) 2008 International Association for Hydrogen Energy. Published by Elsevier Ltd. All rights reserved.