DIELECTRIC-PROPERTIES OF A BINARY CRYOELECTROCHEMICAL SOLVENT ACCORDING TO A SOLVATOCHROMIC PROBE

The application of a solvatochromic dye to determination of the dielec tric properties of organic solvent mixtures is described. The dye 2,6- diphenyl-4-(2,4,6-triphenylpyridino)phenolate (Reichardt's dye) featur es an intramolecular charge transfer band in its visible spectrum with a large associated change in dipole moment between the ground and exc ited states. The position of the charge transfer band is sensitive to local dielectric environment and so is an indicator of solvation of th e dye. Room-temperature spectra of Reichardt's dye in the cryoelectroc hemical solvent system 2:1 (v/v) ethyl chloride/butyronitrile and in t he neat components are reported and related to the dielectric properti es of the mixture. The effective dielectric properties of the mixture scale with the value of the Pekar factor, 1/epsilon(OP) - 1/epsilon(S) , that is predicted from the mole fraction-weighted (or volume fractio n-weighted) sum of the dielectric constants for the pure components, s uggesting that strongly selective solvation of the dye by one componen t of the solvent mixture does not occur. The results are pertinent to a recent study of electrode kinetics in the solvent mixture.