Low-Energy Electronic Spectra of 2-[(4-Sulfanylphenyl)azo]-4,5-diphenylimidazole

The visible electronic spectra of the title azo compound (HA) in a number of organic solvents have been examined. It was concluded that the compound exists in solutions in an azo __ hydrazone quilibrium, while in DMF (S) solution the dye exhibits an acid-base equilibrium of the type HA + S __ A − + HS + . The proportional concentration of the conjugate base form A − is largely dependent upon the concentration of the dye, the basicity of the solvent, and the tendency of the ionized form to be stabilized by H-bonding interaction with the solvent molecules. The bands displayed by the different forms of the compound have been assigned to the possible electronic transitions. The visible spectral behaviour of compound in mixed organic solvents has been investigated. The effect of temperature on the compound in DMF at the longer-wavelength visible bands has been also investigated.