Chemistry, University of Southampton, Highfield, Southampton, SO17 1BJ, United Kingdom.
Department of Chemistry, Center for Magnetic Resonance, University of Florence, Sesto Fiorentino (FI) 50019, Italy.
Phys Rev E. 2017 Dec;96(6-1):062702. doi: 10.1103/PhysRevE.96.062702. Epub 2017 Dec 15.
The orientational order of the molecules in the bent mesogen CB6OCB has been studied throughout the range of temperature stability of both the N_{U} and N_{TB} liquid-crystal phases by ^{13}C NMR spectroscopy. These spectra provide local order parameters for the para axes of both of the nonequivalent cyanobiphenyl groups and show how they change on entering the twist-bend nematic phase. A key feature of the order parameters is a weak, but clear maximum in the temperature variation of the order parameter prior to the N_{TB} phase. This suggests that the directors in both the N_{U} and N_{TB} phases are tilted with respect to the magnetic field of the spectrometer. Significantly the conformational states of the spacer are comparable in both phases, although the low temperature nematic is chiral but not that at high temperature. It is proposed that the higher temperature, tilted phase could be the splay-bend nematic phase.
通过 13C NMR 光谱研究了分子在弯曲介晶 CB6OCB 中的取向序，涵盖了 N_{U}和 N_{TB}液晶相的整个温度稳定范围。这些光谱为两个不等效的氰基联苯基团的 para 轴提供了局部有序参数，并展示了它们在进入扭曲向列相时如何变化。有序参数的一个关键特征是在进入 N_{TB}相之前，有序参数随温度的变化出现微弱但明显的最大值。这表明在 N_{U}和 N_{TB}相中，指向矢相对于光谱仪的磁场倾斜。重要的是，尽管低温向列相是手性的，但高温向列相不是，两个相中间隔基的构象状态是可比的。有人提出，较高温度的倾斜相可能是伸展弯曲向列相。
