NMR studies of molecular ordering and molecular dynamics in a chiral liquid crystal with the SmCα* phase

Molecular dynamics of the antiferroelectric liquid crystal 4'-(octyloxy)biphenyl-4-carboxylate2-fluoro-4-[(octyl-2-yloxy)carbonyl]phenyl (abbreviated as D16) was investigated using different nuclear magnetic resonance (NMR) techniques. D16 molecules form a smectic-C-alpha* phase (SmC alpha*) in an extremely wide temperature range (similar to 10 degrees C). Due to a small tilt of the molecules, this phase is characterized by short switching times, important for new photonic applications. The proton spin-lattice relaxation times were measured in isotropic (Iso), smectic-A (SmA), and SmC alpha* phases over a wide frequency range of five decades, with conventional and fast field-cycling NMR techniques. This approach allowed a comparison of the essential processes of molecular dynamics taking place in these phases. On the basis of NMR relaxometry measurements, we present a description of the motional behavior of liquid crystal molecules forming SmC alpha*. Pretransitional effects were observed in wide temperature ranges in both the isotropic and SmA phases in D16. The H-1 fast field-cycling NMR measurements were supplemented with NMR diffusometry and F-19 NMR spectroscopy.