STUDIES OF SOLUTE SOLVENT INTERACTIONS IN MIXTURES OF SUPERCRITICAL FLUIDS USING FLUORESCENCE SPECTROSCOPY

Solute-solvent interactions of (dimethylamino)benzonitrile and ethyl (dimethylamino)benzoate in mixtures of supercritical trifluoromethane and carbon dioxide are studied using fluorescence spectroscopy. The density dependence of solvation in the mixtures is similar to that in the pure supercritical fluids. The polar component CHF3 in the mixtures clusters preferentially about a solute molecule. This clustering is also density dependent. Bulk and local (microscopic) solvent effects in the in different density regions are rationalized based on the Onsager reaction field model and on the concepts of local density and composition.