Solvation spectra. Part 17.—Water-induced dimerization of various dye and related paramagnetic ions studied by optical and electron spin resonance spectroscopy

Abstract

Analysis of the electron spin resonance spectra of aqueous and alcoholic solutions of the methyl viologen cation and the tetracyanoquinodimethane anion confirms that the association process responsible for the concentration-dependent colour change involves dimerization of the organic ions rather than cation-anion pairing. The ways in which water favours such association are discussed, and the dependence of the absorption spectrum of methylene blue on solvent, dye concentration and the concentration of various solutes, is examined in terms of the specific role of water.