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

Professor Ward Thompson of the University of Kansas is receiving an award from the Macromolecular, Supramolecular and Nanochemistry Program.获奖项目使用理论和计算方法来探究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特性。在这种纳米级限制下，分子级液体结构和动力学发生了巨大的变化，但这些效应在线性红外（IR）光谱中不容易观察到。 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.应用选择是基于氢键作用下 CN 拉伸频率的显着蓝移以及相对较慢的振动弛豫，这允许检查较长时间尺度的动力学。选择的方法论结合了分子动力学、大正则蒙特卡罗模拟、电子结构计算和混合量子经典MD。拟研究的性质包括：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) 预测不同表面化学的二氧化硅孔中限制的 CH3CN 的红外泵浦探针光谱，iii) 预测不同表面化学的二氧化硅孔中限制的 CH3CN 的红外光子回波光谱，以及 iv) 模拟纳米限制的 CH3CN 和纳米级 CH3CN 中溶质的光谱。其他纳米限制液体中的 CH3CN 溶质。多孔二氧化硅材料在催化、分离和传感方面具有重要意义，并且是更广泛的多孔氧化物材料类别的一部分，在各种应用中同样重要。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更深入地了解液体如何在纳米受限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，以协助设计和表征在受限环境中利用液体独特物理性质的应用。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广泛的物理化学背景。 The participation of underrepresented groups continues to be encouraged within this research group.

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.