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'-cyanobiphen yl (50CB) and its one-to-one mixture with 1-(4'-cyanophenyl)-4-propylc yclohexane (PCH3) in their nematic phases has been obtained by measuri ng local dipolar couplings of individual protons in state-correlated t wo-dimensional (SC-2D) H-1 NMR experiments (Naito et al., J. Magn. Res on. 1990, 87, 429). Nematic-to-isotropic phase transitions (from withi n 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 fou nd to decrease toward the end of the aliphatic chain. Secondary splitt ings of the ring protons give an estimate of the torsional angle betwe en the two phenyl rings to be in the range 47-52 degrees at 67.1 degre es C. In a one-to-one mixture of 50CB and PCH3, the local orders of bo th the rings and the aliphatic chain of 50CB are significantly increas ed, while those of the rings of PCH3 are decreased. Interproton cross relaxation and spin diffusion are found to be quite sensitive to the d ynamics and molecular interactions in pure and mixed liquid crystals.