Molecular Dynamics in Smectic and Crystalline Phases Studied by¹³C-NMR Spin Lattice Relaxation Time Observation

Abstract

The temperature dependence of the spin-lattice relaxation time T 1 is investigated in the chiral smectic liquid crystal (S)-4-(1-methylhexyloxycarbonyl)phenyl 4 -octyloxybiphenyl-4-carboxylate (S-MH(6)POBC) by solid-state 13 C-NMR spectroscopy.The T 1 of an aromatic carbon belonging to the core part of the liquid-crystalline molecule decreases from 1 s to 0.2 s with decreasing temperature in smectic phases, where the frequency of the molecular rotation around its long axis is higher than the Larmor frequency of 100 MHz in the present study. Because the molecular rotation freezes during the phase transformation from the smectic phase to the crystalline phase, T 1 rapidly increases from 0.2 s to 16 s.