High-resolution Solid Nuclear Magnetic Resonance Research Articles

Different Molecular Conformations in Ferroelectric and Antiferroelectric Liquid Crystals Studied by 19F-NMR Spectroscopy

In order to discuss the relationship between molecular conformation and phase sequence, static 19F-NMR measurements were performed using a high-resolution solid nuclear magnetic resonance spectrometer. In the homologous series of 10BIMFn, dipole coupling constants between fluorines of the phenyl ring and CF3 were found to be larger in the antiferroelectric compounds (n=8 and 10) than in the ferroelectric ones (n=7 and 9). This result indicates that the molecules exhibiting SmC* have a different conformation around the chiral part from those exhibiting SmCA*. Based on the MOPAC calculation in 10BIMF7, which gives two stable conformations with bent and extended chiral end chains, two different conformations obtained by NMR in 10BIMFn are suggested to correspond to the bent and extended structures in antiferroelectric and ferroelectric compounds, respectively.