A H-2 NMR study of orientational order, phase transitions and dynamics in a liquid crystalline compound

H-2-NMR spectroscopy is employed to investigate the orientational order in the nematic and smectic A, B, and crystal G phases formed by 4-(2-methylbutyl)phenyl 4'n-heptylbiphenyl-4-carboxylate-d(18). Evidence of the lock in the trans-conformation of the first two methylene groups of the n-heptyl chain is found in the S-B and G phases. The dynamics of the aromatic molecular core are studied in a temperature interval including the S-A-S-B transition, by the analysis of the deuterium Zeeman and Quadrupolar relaxation times using the rotational diffusion model. Hence the diffusion constants related to the molecular spinning and tumbling motions are evaluated.