~(13)C-NMR Spin Lattice Relaxation Time Observation on the Smectic A and Smectic C~* Phases of a Chiral Smectic Liquid Crystal, (S)-4-(1-methylhexyloxycarbonyI)phenyl 4′-octyloxybiphenyl-4-carboxylate

摘要

In order to study molecular rotation around the long axis in chiral smectic phases, the temperature dependence of the spin-lattice relaxation time T_1 is investigated in a ferroelectric liquid crystal, (S)-4-(1-methylhexyloxycarbonyl)phenyl 4′-octyloxybiphenyl-4-carboxylate (S-MH(6)POBC) by means of solid-state ~(13)C-NMR spectroscopy. The spin-lattice relaxation time T_1 of the aromatic core increases with increasing temperature in the smectic A (SmA) and chiral smectic C (SmC~*) phases, because the frequency of the molecular rotation dominating the spin-lattice relaxation process is higher than the Larmor frequency ω_0 of 100 MHz in the present measurement. In addition, the temperature dependence of T_1 reveals that the activation energy of the molecular rotation in the SmC~* phase is lower than that in the SmA phase.