Drzewicz Anna, Rossi Martina, Cifelli Mario, Saielli Giacomo, Tykarska Marzena, Domenici Valentina
Institute of Nuclear Physics Polish Academy of Sciences, PL-31342 Krakow, Poland.
Dipartimento di Chimica e Chimica Industriale, University of Pisa, via Moruzzi 13, Pisa 56124, Italy.
Soft Matter. 2025 Feb 26;21(9):1646-1661. doi: 10.1039/d4sm01321b.
In the field of chiral smectic liquid crystals, orthoconic antiferroelectric liquid crystals (OAFLCs) have attracted the interest of the scientific community due to the very high tilt angle, close to 45°, and the consequent optical properties. In the present study, the first H NMR investigation is reported on two samples, namely 3F5HPhF9 and 3F7HPhF8, showing the phase sequence isotropic-SmC*-SmC* and the phase sequence isotropic-SmA-SmC*-SmC*, respectively, when cooling from the isotropic to the crystalline phases. To this aim, the liquid crystals were doped with a small amount of deuterated probe biphenyl-4,4'-diol-d. The trend of H NMR spectra temperature indicates the presence of very high values of the tilt of the deuterated probe in the antiferroelectric phase for both samples. The trend of the local order parameters and that of the tilt angle were compared with the results obtained for the same samples by means of different experimental techniques, namely X-ray diffraction and electrooptical measurements. Moreover, a computational study was performed on the sample labelled 3F5HPhF9 using fully atomistic classical molecular dynamics simulation of the orthoconic phase. The results obtained from the MD simulations show a very large molecular tilt of the molecules (about 42°) when packed in layers and this value is in very good agreement with experimental results. The present research aims to give additional clues about the molecular origin of the very peculiar high tilt angle of orthoconic liquid crystals in the antiferroelectric phase.
在手性近晶型液晶领域，正锥反铁电液晶（OAFLCs）因其非常高的倾斜角（接近45°）以及由此产生的光学性质而引起了科学界的关注。在本研究中，报道了对两个样品3F5HPhF9和3F7HPhF8的首次氢核磁共振研究，结果表明，当从各向同性相冷却到结晶相时，它们的相序列分别为各向同性-SmC*-SmC和各向同性-SmA-SmC-SmC*。为此，向液晶中掺杂了少量的氘代探针联苯-4,4'-二醇-d。氢核磁共振谱随温度的变化趋势表明，在反铁电相中，两个样品中氘代探针的倾斜度都非常高。将局部有序参数的变化趋势和倾斜角的变化趋势与通过不同实验技术（即X射线衍射和电光测量）对相同样品获得的结果进行了比较。此外，还使用正锥相的全原子经典分子动力学模拟对标记为3F5HPhF9的样品进行了计算研究。分子动力学模拟结果表明，分子在堆积成层时具有非常大的分子倾斜度（约42°），这一数值与实验结果非常吻合。本研究旨在为反铁电相中正锥液晶非常特殊的高倾斜角的分子起源提供更多线索。
