Mobility of side chains in a discotic liquid crystal studied by deuteron spin relaxation

A hexaether-substituted rufigallol mesogen is studied by measuring deuteron spin–lattice relaxation times T1Z and T1Q in the hexagonal Dho phase. Small-step rotations of discotic molecules within each column are described by the so-called ‘anisotropic viscosity’ model, giving rotational diffusion constants Dα and Dβ for rotations of the disc normal around and perpendicular to the director. A libration model is used to describe the wagging motions in different side chains as seen by the first CD bonds, which diffuse in a circular arc within a defined apex angle. The chain libration rates and corresponding apex angles are also derived.