[UV-Vis spectroscopic characterization of Sudan series in organic solution]

The UV-Vis spectroscopic characterization of Sudan I, Sudan III and Sudan IV in nonpolar solvent ligarine, polar solvent acetonitrile, and acetonitrile-water mixture was studied. The characteristic absorption peaks of sudan series were a little red shifted in polar solvent compared to that in nonpolar solvent. In acetonitrile-water mixture the red shift of characteristic absorption peaks of sudan I and sudan III is respectively 13 and 8 nm, but the characteristic absorption peaks of sudan IV are red shifted before blue shifted. The increased adsorption strength of Sudan I, Sudan III and Sudan IV is 34.5%, 11% and 2.5% respectively. For these, the important reason is that the destroyed intramolecular hydrogen bond in Sudan series enlarges the scope of the pi delocalized bond in polar solvent.