Molecular Dynamics in Smectic and Crystalline Phases Studied by ¹³C-NMR Spin Lattice Relaxation Time Observation

Abstract

The temperature dependence of the spin-lattice relaxation time T₁ is investigated in the chiral smectic liquid crystal (S)-4-(1-methylhexyloxycarbonyl)phenyl 4′-octyloxybiphenyl-4-carboxylate (S-MH(6)POBC) by solid-state ¹³C-NMR spectroscopy. 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.

Keywords:

• Ferroelectric liquid crystal
• ferroelectricity
• hindered rotation
• molecular dynamics
• NMR
• smectic liquid crystals

Acknowledgment

This work was supported by a Grant-in-Aid for Scientific Research C (No. 20550167) from the Ministry of Education, Culture, Sports, Science and Technology (MEXT).