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

德克萨斯理工大学的Edward Quitevis教授正得到化学结构、动力学和机制计划的支持，研究纳米结构组织在确定离子液体(ILS)中小分子的分子间和取向动力学中的作用。主要的方法将是使用光学克尔效应(OKE)光谱来探测分子液体-IL混合物中的动力学。将合成具有特殊结构特征的新型ILS，使分子溶质的局部环境能够系统地改变。这项工作的意义在于，IL与溶质分子上官能团的特定相互作用往往是溶质-IL相互作用的基础。例如，为了了解ILS对化学反应的影响，研究ILS与模拟大分子上的官能团的小溶质分子的相互作用是很重要的。这项研究将解决以下问题：(1)ILS非极性区域中非极性分子的分子间和取向动力学与烷烃溶剂中非极性分子的分子间和取向动力学有何相似或不同？(2)ILS和极性液体混合物的OKE数据是否定位在极性-非极性界面上？(3)ILS和芳香族液体混合物的OKE测量可以告诉我们极性区域芳香分子动力学和非极性溶剂芳香分子动力学之间的差异吗？这一结果将有助于从纳米分离的角度阐明离子液体中复杂的溶质-溶剂相互作用。尽管可以使用标准的分子液体概念来理解ILS的许多物理化学性质，但人们对发现ILS的非典型的传统分子溶剂的性质非常感兴趣。离子液体的纳米尺度结构异质性就是这些特性之一。从溶质分子的溶剂化和最终的化学反应动力学的角度来看，ILS可以被认为是“2合1”溶剂的想法具有广泛的意义。研究人员的主要研究目标是了解ILS中的分子尺度组织，以便在基础科学和技术应用中利用这一性质。这项研究将提供对合理设计特定任务ILS的基础知识，这些ILS适用于当前和未来的应用，有助于实现可持续社会的目标，如锂离子电池、生物质加工和二氧化碳捕获。除了技术优势，该项目还为从化学合成到激光和光学等领域的本科生、研究生和博士后研究人员提供了强有力的教育培训。特别是，PI在德克萨斯理工大学制定了一个试点暑期本科生研究计划，为代表人数较少的少数族裔学生提供参与这个项目的机会。

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.