UV-Vis spectroscopic study of solvation in the ternary mixture methanol plus ethanol plus acetone

We report for the first time a study of solvation characteristics of a solute in a completely miscible ternary solvent mixture by means of electronic absorption spectroscopy. The solvatochromic charge transfer band of two indicator dyes, viz, 2,6-diphenyl-4-(2,4,6-triplienyl pyridinium-1-yl) phenolate and N-ethyl-4-cyanopyridinium iodide has been studied in methanol + ethanol + acetone as a function of solvent composition at a fixed temperature. The transition energy in a ternary solvent mixture differs significantly from the average value of transition energy in component solvents weighted by the mole fraction of the solvents. To explain the results we have proposed a realistic model of solvation in a ternary solvent mixture. The excess or deficit of solvent composition in the immediate vicinity of solute over that in the bulk has been calculated. (C) 2002 Elsevier Science B.V. All rights reserved.