Understanding Vibrational Spectroscopic Probes of the Structure and Dynamics of Liquids Confined in Mesoporous Materials

堪萨斯大学的沃德·汤普森教授正在接受大分子、超分子和纳米化学项目的奖励。理论和计算方法用于获奖项目中，用于询问振动光谱技术可以揭示限制在不同尺寸（直径约2.4至4.5 nm）和表面功能（羟基和烷基封端）的纳米级二氧化硅孔中的液体和溶液的性质。在分子水平的液体结构和动力学的戏剧性的变化发生在这样的纳米级的限制，但这些效果是不容易观察到的线性红外（IR）光谱。通过分析振动光谱探针，该项目揭示了纳米限制液体的复杂结构和动力学。该项目的重点是密闭乙腈和相关系统。应用的选择是基于一个戏剧性的蓝移CN拉伸频率氢键和相对缓慢的振动弛豫，这允许检查较长的时间尺度的动态时的存在。结合分子动力学，巨正则蒙特卡罗模拟，电子结构计算，和混合量子经典MD的选择方法。拟研究的特性包括：i）确定腈和异腈的线性红外光谱中氢键和非氢键峰的相对强度，ii）预测限制在不同表面化学的二氧化硅孔中的CH 3 CN的IR泵浦-探测光谱，iii）预测限制在不同表面化学的二氧化硅孔中的CH 3 CN的IR光子回波光谱，多孔二氧化硅材料在催化、分离和传感方面是人们感兴趣的，并且是在各种应用中同样重要的更广泛类别的多孔氧化物材料的一部分。此外，纳米限制液体存在于许多其他系统中，包括超分子组件、模板材料、反胶束、生物系统、水凝胶、膜、燃料电池电极和非线性光学材料。该项目更广泛的影响目标是获得更深入的机械理解液体如何在纳米限制结构内移动和相互作用，以及如何通过光谱学探测这些机制，以帮助设计和表征利用受限环境中液体独特物理特性的应用程序。研究生和本科生参与这项研究，为他们提供理论和计算技术的培训以及物理化学的广泛背景。继续鼓励代表性不足的群体参与这一研究小组。

Professor Ward Thompson of the University of Kansas is receiving an award from the Macromolecular, Supramolecular and Nanochemistry Program. Theoretical and computational approaches are used in the awarded project for inquiring what vibrational spectroscopic techniques can reveal about the properties of liquids and solutions confined in nanoscale silica pores of varying size (~2.4 to 4.5 nm in diameter) and surface functionality (hydroxyl- and alkyl-terminated). Dramatic changes in the molecular-level liquid structure and dynamics occur upon such nanoscale confinement, yet these effects are not readily observable in the linear infrared (IR) spectra. By analyzing vibrational spectroscopic probes, this project sheds light on the complex structure and dynamics of nanoconfined liquids. The project focuses on confined acetonitrile and related systems. The application choice is based on the presence of a dramatic blue shift in the CN stretching frequency upon hydrogen bonding and the relatively slow vibration relaxation, which permits examination of longer timescale dynamics. A combination of molecular dynamics, grand canonical Monte Carlo simulations, electronic structure calculations, and mixed quantum-classical MD are the chosen methodologies. The proposed properties to be studied include: i) determination of the relative intensities of hydrogen bonded and non-hydrogen bonded peaks in the linear infrared spectra of nitriles and isonitriles, ii) prediction of the IR pump-probe spectroscopy of CH3CN confined in silica pores of varying surface chemistry, iii) prediction of the IR photon echo spectroscopy of CH3CN confined in silica pores of varying surface chemistry, and iv) simulation of the spectroscopy of solutes in nanoconfined CH3CN and of a CH3CN solute in other nanoconfined liquids.Porous silica materials are of interest in catalysis, separations, and sensing and are part of a wider class of porous oxide materials similarly important in a variety of applications. Moreover, nanoconfined liquids are present in a number of other systems including supramolecular assemblies, templated materials, reverse micelles, biological systems, hydrogels, membranes, fuel cell electrodes, and nonlinear optical materials. The broader impact aim of this project is to gain deeper mechanistic understanding of how liquids move and interact within nanoconfined structures and how these mechanisms can be probed via spectroscopy to assist in the design and characterization of applications that exploit the unique physical properties of liquids in confined environments. Graduate and undergraduate students are involved in this research, providing them with training in theoretical and computational techniques and a broad background in physical chemistry. The participation of underrepresented groups continues to be encouraged within this research group.