SOLVATION IN MIXED SUPERCRITICAL FLUIDS - TICT SPECTRA OF BIS(4,4'-AMINOPHENYL) SULFONE IN ETHANOL/CO2

We present an examination of the fluorescence spectra of bis(aminophenyl) sulfone (APS) dissolved in mixed ethanol/CO2 supercritical fluid solvents having cosolvent concentrations in the 1-10 mol % range. Peak shifts and areas of the locally excited (LE) and charge-transfer (CT) components of the spectra are determined from two component spectral fits and are compared to similar measurements in a series of liquid n-alcohols. Measures of the supercritical fluid solvent polarity are obtained by correlation of the spectral parameters of the fluid samples with parameters of the liquid samples. Simple mixing rules are proposed for the estimation of the mixed fluid refractive index and the dielectric constant and are used to calculate the values of two different solvent polarity functions under various fluid conditions. It is found that calculated values of the solvent polarity functions match the measured values over a wide range of fluid conditions only when the local fluid environment is assumed to be enriched in the ethanol concentration by up to an order of magnitude over the bulk concentration. Because APS is insoluble in pure CO2 under the conditions of our study, these results provide important information regarding cosolvent-enhanced solubility in supercritical fluid solutions.