Deuterium magnetic resonance study of a smectic liquid crystal

Abstract

The compound terephthal‐bis(butylaniline) (TBBA) has been prepared with selective deuteration on the central benzene ring and the two methine positions. The deuterium magnetic resonance of this material was studied as a function of temperature and sample rotation in the nematic, smectic A, smectic C, and smectic B phases. It is concluded that in the nematic and smectic A phases the direction of molecular alignment (the ``director'') makes an angle of 8° with the para axis of the central benzene ring. There is also good evidence that the molecular conformation is not planar, i.e., the outer benzene rings are rotated out of the plane of the central ring. Results for the smectic C phase confirm a model in which the long axes of the molecules are free to realign while keeping a constant angle with the smectic planes; there is no indication that in this phase rotation of the molecules about their long axes is inhibited, as suggested by a recent theory. Observations on the smectic B phase suggest that its structure resembles the smectic C in some aspects, but results are less conclusive in this case.