Towards reliable description of rotational and translational motion in ionic liquids by means of field cycling and high field NMR relaxometry as well as molecular dynamics simulations

在这个项目中，我们希望通过高场（HF）和场循环（FC）NMR弛豫法以及分子动力学（MD）模拟来研究离子液体（IL）中的旋转和平移运动。结合特殊合成的离子液体，我们能够在宽频率和温度范围内进行测量和模拟。我们的方法可以测试常用的NMR弛豫模型的适用性，并建议模型更复杂的现象。这样，我们克服了早期的问题，在太窄的温度范围和小的数据集限制科学家的应用程序的简单的Bloembergen-Purcell-磅（BBP）relationship. In这里，首先，我们研究了纯粹的分子内四极（2 H）松弛的分子矢量ND和OD的阳离子离子在离子液体中，这都涉及到氢键。宽的液体范围下至玻璃化转变温度，提供频率相关的信息，并允许考虑更复杂的模型，包括各向异性或内部运动。我们还确定可靠的氘四极耦合常数和旋转相关时间的特点是氢键与不同的强相互作用的阴离子的债券。其次，我们确定旋转和平移动力学的偶极弛豫率（1H和19 F）FC弛豫测量宽的温度和频率范围内解开的光谱密度的细节。在这里，面临的挑战是解剖的总弛豫速率的核磁弛豫色散（NMRD）配置文件内和分子间的贡献，以可靠的方式。这一过程将支持使用部分氘离子液体抑制1H弛豫。在阳离子和阴离子内寻址不同的分子载体允许验证各向异性或内部旋转。由此产生的平移扩散系数，我们比较从低频色散定律和脉冲场梯度NMR得到的。第三，对于最相关的离子液体，我们确定的相关函数，耦合参数和弛豫率从经典的MD模拟。这里的挑战是通过实验解决重叠的温度范围。这允许证明我们用于评估测量的弛豫数据的基础弛豫模型。除了验证弛豫模型，这种实验和模拟方法的结合提供了深入了解离子液体在分子水平上的结构和动力学。

In this project we want to study the rotational and translational motion in ionic liquids (ILs) by means of high field (HF) and field cycling (FC) NMR relaxometry as well as molecular dynamics (MD) simulations. In combination with specially synthesized ILs, we are able to measure and simulate over broad frequency and temperature ranges. Our approach allows testing the applicability of commonly used NMR relaxation models and suggesting models for more complex phenomena. This way, we overcome earlier problems, where too narrow temperature ranges and small data sets constrained scientists to the application of the simple Bloembergen-Purcell-Pound (BBP) relation.Here firstly, we study purely intramolecular quadrupolar (2H) relaxation for molecular vectors ND and OD of the cations in the ILs, which are all involved in hydrogen bonding. The broad liquid ranges down to glass transition temperature, provide frequency dependent information and allow for considering more sophisticated models including anisotropic or internal motion. We also determine reliable deuteron quadrupole coupling constants and rotational correlation times for bonds characterized by hydrogen bonds with differently strong interacting anions. Secondly, we determine rotational and translational dynamics from dipolar relaxation rates (1H and 19F) measured by FC relaxometry for broad temperature and frequency ranges to unravel details of the spectral densities. Here, the challenge is to dissect the total relaxation rates of the nuclear magnetic relaxation dispersion (NMRD) profiles into intra- and intermolecular contributions in a reliable way. This procedure will be supported by using partially deuterated ILs for suppressing 1H relaxation. Addressing different molecular vectors within the cations and anions allow validating anisotropic or internal rotation. The resulting translational diffusion coefficients we compare with those obtained from the low frequency dispersion law and pulsed field gradient NMR. Thirdly, for the most relevant ILs we determine the correlation functions, coupling parameters and relaxation rates from classical MD simulations. The challenge here is to address overlapping temperature ranges with experiment. That allows justifying the underlying relaxation models we used for evaluating the measured relaxation data. Beyond validating the relaxation models this combination of experimental and simulation methods provides insight into structure and dynamics of ILs at the molecular level.