SPECTROSCOPIC STUDY OF STRUCTURE AND INTERACTIONS IN COSOLVENT-MODIFIED SUPERCRITICAL FLUIDS

Cosolvents can be used to tailor supercritical fluid solvents for incr eased selectivity by increasing the solvent polarity or polarizability and participating in specific interactions with solutes. Specific int eractions in these fluids are often inferred from thermodynamic measur ements although independent confirmation of the structure of cosolvent /solute interactions is lacking. The solutes 2-naphthol, 5-cyano-2-nap hthol, and 7-azaindole exhibit well-characterized spectral responses t o an organized, hydrogen-bonded solvent environment in liquids. We des cribe fluorescence and UV absorption experiments to probe the structur e and interaction between polar cosolvents and these solutes in a vari ety of supercritical fluids. In addition, new solubility data are repo rted for 7-azaindole in supercritical CO2 with and without methanol an d in supercritical ethane. The results suggest that the interaction be tween cosolvent and solute can be strong yet exhibit no evidence for a ctual complexes in solution.