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

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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.