(96e) Determination of Relative Polarity by Spectroscopic Analysis of Gas Expanded Liquids

Gas eXpanded Liquids (GXLs) are organic solvents pressurized with carbon dioxide that maintain a high degree of solvent strength but also possess intermolecular properties similar to that of supercritical fluids. GXLs are a highly tunable class of solvents that have applications in but not limited to gas anti-solvent methods and nutraceutical extractions. Previous studies have demonstrated a relationship between solvent polarity and the cis-trans isomerization rates of a probe molecule, 4-(diethylamino)-4'-nitroazobenzene (DENAB). This work analyzes the ability to control the DENAB isomerization reaction rates in GXLs and thus the tunability of the GXL solvent polarity as a function of CO2 pressure. Spectroscopic analyses of the cis-trans isomerization rates of relaxation were measured versus CO2 pressure in multiple GXLs. Conclusions regarding the local (around the probe molecule) and bulk solvent properties address the results of this investigation and provide rationalization to the coexisting high degree of transportability, solvent strength, and user tunability of GXLs.