Molecular Product Design for Ionic Liquids with Refrigerant Gases Samantha E. McLeese, John C. Eslick, Aaron M. Scurto, and Kyle V. Camarda* The University of Kansas, Dept. of Chemical and Petroleum Engineering, 4132 Learned Hall, 1530 West 15th Street, Lawrence, KS 66045-7609 *Corresponding Author. Email: firstname.lastname@example.org Ionic liquids (ILs) are currently being considered for novel uses in hydrofluorocarbon (refrigerant) gas separations and as solvents in absorption refrigeration systems. Due to the low to immeasurable volatility of ILs, these compounds may be well-suited for such applications, and could potentially be considered as environmentally-benign solvents. Their molecularly-tunable nature yields an extraordinary number of possible cation and anion combinations, the majority of which have never been synthesized. This project applies newly developed quantitative structure-property relations (QSPRs) along with an optimization framework to design novel ionic liquids possessing targeted values of such important properties as solubility in a given refrigerant, diffusivity, viscosity, toxicity, molar volume, and melting and decomposition temperatures. The electronic structure of ionic liquids is quantified using modified connectivity indices, which describe bonding environments, charge distribution, orbital hybridization and other interactions within and between ions, and between the ions and the refrigerant molecules present. The resulting expressions are integrated within a computational molecular design framework, which combines the QSPRs with structural feasibility constraints in a combinatorial optimization problem. The problem is solved using Tabu Search, a stochastic optimization algorithm which generates many near-optimal solutions, which are candidate structures for use as environmentally benign solvents with refrigerant gases. The examples provided show the efficacy of the approach in terms of computational efficiency.