Molecular dynamics in chiral smectic liquid-crystalline phases studied by solid state 13C-NMR measurements

The temperature dependence of the spin-lattice relaxation time T-1 is investigated in an antiferroelectric liquid crystal, (S)-4-(1-methylheptyloxy-carbonyl)phenyl 4'-octyloxybiphenyl-4-carboxylate (S-MHPOBC) by means of solid-state C-13-NMR spectroscopy. The spin-lattice relaxation time T-1 of almost all of aromatic carbons has a minimum at the temperature region of the SmCA* phase in the temperature dependent curves, because the correlation time tau(c) of the molecular motion corresponds to the Larmor frequency omega(0) of 100 MHz in the present measurements. As for the aliphatic carbons in a flexible chain, the value of T-1 increases with increasing temperature, because the molecular motion characterized by tau(c) is faster than the Larmor frequency omega(0).