An Investigation of Certain Solvent Effect in Absorption Spectra

Abstract

A study of the solvent effects in the spectra of non‐ionic compounds to whose structure a zwitter ion form makes appreciable contribution (particularly in the excited state) has revealed three distinct effects: 1. A shift of absorption bands to greater wavelength with increasing refractive index, as predicted by Kundt's rule. This is ascribed to the effect of electronic polarizability on the zwitter ion structure, and is seen unmixed with the other effects only when the solvents are hydrocarbons or aryl halides. 2. A further shift which appears with most solvents other than hydrocarbons and aryl halides, and is ascribed to orientation of molecules of nonuniform polarizability. 3. The Kuhn‐Brockmann effect—a large shift which appears whenever hydrogen bonds between the solvent and solute occur. This is believed to be due to the stabilization of the zwitter ion by the electrostatic nature of the hydrogen bond. No correlations of the spectra of phenolphthalein, p‐rosaniline hydrochloride, or iodine with the properties of the solvent were found.