A H-2 NMR study of orientational order and spin relaxation in the mesogen p-hexyloxybenzylidene-p'-fluoroaniline

H-2 NMR measurements of orientational order and spectral densities in the nematic, smectic A and smectic B phases of p-hexyloxybenzylidene-p'-fluoroaniline (FAB-OC6) deuterated in the benzylidene methine group and in the aniline ring are reported. The orientational order parameters obtained indicate a high order of the aromatic core in the smectic phases. The Wimperis pulse sequence was used to measure the Zeeman and quadrupolar spin-lattice relaxation times at the frequency of 46.04 MHz. The spectral densities are discussed within rotational diffusion models for the reorientational motions, taking also into account internal rotations and collective fluctuations.