Effect of the Environment, Charge, Chemical Structure, and Size of an Azo Dye on its Energy and Optical Properties

Calculations with consideration of solvation of methylsulfonic acid showed that the hydrogen bond is weakened in substitution of a methyl group for a chromophore in an azo dye due to delocalization of excess electrons from oxygen atoms in the sulfo group and more uniform electron density distribution over the conjugation system of the dye molecule. It was shown that the PM3 method satisfactorily reproduces the energy and geometric parameters of hydrogen bond systems and in calculating the electron, UV, and optical spectra, more correct results are obtained using the geometry of supramolecular solvate systems obtained in the 3-21G nonempirical basis set.