Determination of structure and dynamics of liquid crystalline molecules by state-correlated 2D NMR spectroscopy

将一种新颖的二维核磁共振实验--状态相关二维核磁共振应用于液晶样品，研究了液晶分子的结构和动力学。第一年，对核磁共振探头的微波部分进行了改进，以提高温度跳跃的效率。结果，我们成功地获得了4‘-甲氧基亚甲基-4-乙酰氧基苯胺(APAPA)和4’-乙氧基亚甲基-4-正丁基苯胺(EBBA)的向列相-各向同性相关联2D核磁共振谱。在第二年，我们重点研究了液晶分子的结构和动力学，并取得了以下结果。在10毫秒内完成了从向列相到各向同性相的相变，从而分别观察到APAPA中单个质子的偶极图样。在α-甲基质子中观察到强度比为1：2：1的三重态。这一事实表明存在三个具有相同偶极耦合价值的质子。2，6和3，5芳香族质子的分裂频率为9.7 kHz，呈现明显的双重态，APAPA的有序参数为0.41。由于自旋交换效应，观察到了截面的混合。我们发现，被认为是液晶分子核心基团的芳环内的自旋交换比芳香质子和α-甲基质子之间的自旋交换更有效。光谱分析可以对具有少量自旋的亚自旋系统进行，而不是对整个自旋系统进行。用直径3 mm的样品管在5毫秒内完成了EBBA从向列相到各向同性相的相变，并分别测定了丁基各质子的偶极分裂。

A novel two dimensional NMR experiment, state-correlated 2D NMR, were applied in liquid crystalline samples to investigate the structure and the dynamics of the liquid crystalline molecules. In the first year, the microwave part of the NMR probe head was modified to improve the efficiency of temperature jump. As a results, we have succeeded to obtain nematic-isotropic phase correlated 2D NMR spectra of 4'-methoxybenzylidene-4-acetoxyaniline(APAPA) and 4'-ethoxybenzylidene-4-n-butylaniline(EBBA). In the second year, we have focused attention on investigating the structure and dynamics of liquid crystalline molecules and obtained the following results.1. Phase transition from nematic to isotropic phase was completed within 10 msec so that the dipolar patterns for individual protons in APAPA were separately observed.2. A triplet pattern with the intensity ratio of 1 : 2 : 1 was observed for the alpha methyl protons. This fact indicates the presence of three protons with equal value of dipolar couplings. A doublet pattern was clearly seen for 2,6 and 3,5 aromatic protons with a splitting frequency of 9.7 kHz and the order parameter was determined to be 0.41 for APAPA.3. A mixing of the cross sections due to the spin exchange effects was observed. We found that spin exchange occurs more efficiently within the aromatic ring, which is considered to be a core group of the liquid crystal molecule, than between the aromatic and alpha methyl protons.4. Spectral analysis could be performed for a subspin system with a small number of spins rather than the entire spin system.5. Phase transition from nematic to isotropic phase was completed within 5 msec for EBBA by using a sample tube of 3 mm diameter and the dipolar splittings for the individual protons of the butyl group were separately determined.