Molecular dynamics in smectic A and chiral smectic C phases by deuteron spin relaxation study

Quantitative analyses of deuterium spectral densities of motion for three deuteron sites (ring and Cα) at two different Larmor frequencies are reported in the smectic A and C* phases of a partially deuterated smectogen. The motional model is the small step rotational diffusion for reorientations plus internal rotations. In the chiral C* phase, the helical axes are aligned along the external magnetic field and the deuteron spins appear to relax in a macroscopically uniaxial environment. After including the molecular tilt, the reorientation processes in the C* phase were found to have higher activation energies than those in the smectic A phase.