Behaviour of Aklyloxybenzylidenealkylanilines in the Smectic G Phase

Abstract

The liquid crystalline smectic G phases of two alkyloxybenzylidenealkylanilines (nO.m) were studied by means of ¹³C-NMR. The spectral patterns provide information about order and orientation of the sample. The asymmetry parameter ν of 50.6 was found to be very small. ν < 0.02; for all chemical shift tensors of the aromatic core. the shielding tensors are averaged by fast molecular motions practically to rotational symmetry. Thc principal axis z of the time averaged interaction is unchanged at the S< _F-S_G transition. In contrast, the spectra of 70.4 show that the orientation of the z-axes tilts with respect to their original orientation c at the S_C-S_G transition. From the angular dependence of the spectra in the S_G-phase, we conclude that the molecular rotation is strongly hindered; the ν values are increased by at least one order of magnitude. Thc local order parameter of the benzene rings was found to be S = 0.90 in the S_G phase of both suhstances. The results are compared with ²H-investigations.