Polarography and Solvatochromism: Part 2.—Comparison of Electrochemical and Spectral Properties of 5'-Methoxy-2'-hydroxy-Ar-methyl-4-stilbazolium Iodide

Abstract

When polarographic half-wave potentials of 5′-methoxy-2′-hydroxy-N-methyl-4-stilbazolium iodide were measured at pH > 13 in mixtures of water with DMF and DMSO, practically no solvent effect was observed. In this pH-range the betaine form of the stilbazole derivative is reduced. Spectra of the betaine form (II) in the solvent mixtures have shown shifts of electronic absorption bands of up to 100 nm. Either changes in the solvent–solute interaction in the excited state or different solvent–solute interactions in the bulk of the solution and at the electrode surface, where the solute is oriented or adsorbed, are considered to explain this difference. Changes in spectra and heights of polarographic waves and shifts of half-wave potentials indicate interaction of the phenolic form (I) of the stilbazole derivative with a form of boric acid.