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

采用一种新的二维核磁共振实验——状态相关二维核磁共振，在液晶样品中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，提高了温度跳变的效率。结果，我们成功地获得了4'-甲氧基苄基-4-乙酰氧基苯胺（APAPA）和4'-乙氧基苄基-4-正丁苯胺（EBBA）的向列各向同性相关联的二维核磁共振波谱。在第二年，我们重点研究了液晶分子的结构和动力学，得到了以下结果：1。从向列相到各向同性相的相变在10毫秒内完成，因此APAPA中单个质子的偶极模式被单独观察到。在α -甲基质子中观察到强度比为1:2:1的三重态模式。这一事实表明存在三个具有相等偶极偶联值的质子。在分裂频率为9.7 kHz的情况下，2,6和3,5个芳族质子明显呈现双重模式，APAPA.3的序参量为0.41。由于自旋交换效应，观察到截面的混合。我们发现自旋交换在芳香环（被认为是液晶分子的核心基团）内比芳香和α甲基质子之间发生得更有效。光谱分析可以用于具有少量自旋的子自旋系统，而不是整个自旋系统。利用直径为3 mm的样品管，EBBA在5 msec内完成了从向列相到各向同性相的相变，并分别测定了丁基单个质子的偶极分裂。

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.