Molecular dynamics of chiral, racemic, and achiral smectic liquid crystals studied by 13C-NMR spectroscopy

Abstract

The temperature dependence of the spin-lattice relaxation time T1 is investigated in the enantiomer and the racemate of 4-(1-methylhexyloxycarbonyl)phenyl 4'-octyloxybiphenyl- 4-carboxylate (MH(6)POBC) by solid-state 13C-NMR spectroscopy. In the case of the enantiomer, the T1 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, T1 rapidly increases from 0.2 s to 16 s.