Molecular dynamics in the smectic A and C* phases in a long-chain ferroelectric liquid crystal:: 2H NMR, dielectric properties, and a theoretical treatment

In this work, the rotational-diffusion coefficients D-parallel to and D-perpendicular to for the ferroelectric smectogen (+)-(S)-4-[4'-(1-methylheptyloxy)] biphenyl 4-(10-undecenyloxy)benzoate have been studied by means of H-2 NMR spectroscopy in the smectic C* phase, using a new theoretical approach (Domenici,V.; Geppi, M.; Veracini, C. A. Chem. Phys. Lett. 2003, 382, 518). The analysis of spin-lattice relaxation times has been performed in terms of the diffusional. constant and the activation energy of the internal and overall molecular-reorientational motions, and the results are compared to the smectic A (SmA) phase. Moreover, from the H-2 NMR data in the SmA phase, the dielectric permittivity and the dielectric relaxation time functions tau(mn)(L) are investigated using a theoretical approach. The longitudinal and transverse components of the real R chi(gamma)(omega) and imaginary chi(gamma)(omega) (gamma = parallel to, perpendicular to) parts of the complex susceptibility tensor and the nematic-like rotational-viscosity coefficients, lambda(2) and lambda(5), are calculated.