FLUORESCENCE FROM THE TWISTED INTRAMOLECULAR CHARGE-TRANSFER COMPOUND BIS(4,4'-DIMETHYLAMINOPHENYL)SULFONE IN ETHANOL CO2 - A PROBE OF LOCAL SOLVENT COMPOSITION

Fluorescence spectra and decays of bis(4,4'-dimethylaminophenyl)sulfone (DMAPS) in mixed ethanol/CO2 supercritical fluid solution have been examined in order to evaluate the local solvent polarity of the mixed fluid solvents. Solvatochromic shifts and band intensities have been determined by nonlinear regression analysis, and are compared with shifts and intensities observed in liquid n-alcohols. The spectral parameters of DMAPS in the mixed supercritical fluid solvents have been used to estimate enrichment of the local solvent composition in the polar modifier, under the assumption that the increase in solvent polarity over that calculated for the bulk fluid is the result of augmentation of the fluid composition in the region immediately surrounding the solute molecule. The analysis indicates that the local composition is enriched by a factor of five to ten over the bulk composition.