Probing Nanostructural Organization in the Intermolecular and Orientational Dynamics of Small Molecules in Ionic Liquids Using Optical Kerr Effect Spectroscopy

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Professor Edward Quitevis of Texas Tech University is being supported by the Chemical Structure, Dynamics and Mechanism Program to study the role of nanostructural organization in determining the intermolecular and orientational dynamics of small molecules in ionic liquids (ILs). The main approach will be to use optical Kerr effect (OKE) spectroscopy to probe dynamics in molecular liquid-IL mixtures. Novel ILs will be synthesized with specific structural features that allow the local environment of the molecular solute to be varied systematically. The significance of this work is that specific interactions of the IL with functional groups on a solute molecule often underlie solute-IL interactions. In order to understand, for example, the effect of ILs on chemical reactions, it is therefore important to study the interactions of ILs with small solute molecules that mimic the functional groups on larger molecules. This research will address the following questions: (1) How are the intermolecular and orientational dynamics of nonpolar molecules in the nonpolar domains of ILs similar to or different from that of nonpolar molecules in alkane solvents? (2) Are the OKE data for mixtures of ILs and polar liquids consistent with polar solute molecules being localized at the polar-nonpolar interface? (3) What can OKE measurements on mixtures of ILs and aromatic liquids tell us about the difference between dynamics of aromatic molecules in polar domains and dynamics of aromatic molecules in nonpolar domains? The outcomes are expected to help elucidate the complex solute-solvent interactions in ILs from the perspective of nanosegregation. Although many of the physicochemical properties of ILs can be understood using standard molecular liquid concepts, there is great interest in discovering IL properties that are atypical of conventional molecular solvents. Nanoscale structural heterogeneity in ILs is one of those properties. The idea that ILs can be thought of as "2-in-1" solvents has broad implications from the standpoint of solvation of solute molecules and, ultimately, chemical reaction dynamics in ILs. The main goal of the investigator's research is to understand molecular scale organization in ILs for the purpose of using this property in basic science and technological applications. This research will provide fundamental knowledge that is critical to the rational design of task-specific ILs for current and future applications that contribute to the goal of achieving a sustainable society, such as lithium-ion batteries, biomass processing, and carbon dioxide capture. Aside from the technological benefits, the project provides strong educational training to undergraduate, graduate, and postdoctoral researchers in areas ranging from chemical synthesis to lasers and optics. In particular, the PI has developed a pilot summer undergraduate research program at Texas Tech that provides underrepresented minority students the opportunity to participate in this project.