UV–Vis spectroscopic study of solvation in the ternary mixture methanol + ethanol + 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-triphenyl 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.