LOCAL ORDER, CONFORMATION, AND INTERACTION IN NEMATIC 4-(N-PENTYLOXY)-4'-CYANOBIPHENYL AND ITS ONE-TO-ONE MIXTURE WITH 1-(4'-CYANOPHENYL)-4-PROPYLCYCLOHEXANE - A STUDY BY STATE-CORRELATED H-1 2-DIMENSIONAL NMR-SPECTROSCOPY

Microscopic ordering of the molecule of 4-(n-pentyloxy)-4'-cyanobiphenyl (50CB) and its one-to-one mixture with 1-(4'-cyanophenyl)-4-propylcyclohexane (PCH3) in their nematic phases has been obtained by measuring local dipolar couplings of individual protons in state-correlated two-dimensional (SC-2D) H-1 NMR experiments (Naito et al., J. Magn. Reson. 1990, 87, 429). Nematic-to-isotropic phase transitions (from within several degrees below T-c) are realized within 5-25 ms by microwave irradiation within the NMR probe. In pure 50CB, the local order is found to decrease toward the end of the aliphatic chain. Secondary splittings of the ring protons give an estimate of the torsional angle between the two phenyl rings to be in the range 47-52 degrees at 67.1 degrees C. In a one-to-one mixture of 50CB and PCH3, the local orders of both the rings and the aliphatic chain of 50CB are significantly increased, while those of the rings of PCH3 are decreased. Interproton cross relaxation and spin diffusion are found to be quite sensitive to the dynamics and molecular interactions in pure and mixed liquid crystals.