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首页> 外文期刊>The journal of physical chemistry, B. Condensed matter, materials, surfaces, interfaces & biophysical >Electric-Field-Induced Reorientation of a Ferroelectric Liquid Crystal Molecule without a Carboxylate Group near the Stereocenter Studied by Time-Resolved Infrared Spectroscopy Combined with Normalized Sample-Sample Two-Dimensional Correlation Spectr
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Electric-Field-Induced Reorientation of a Ferroelectric Liquid Crystal Molecule without a Carboxylate Group near the Stereocenter Studied by Time-Resolved Infrared Spectroscopy Combined with Normalized Sample-Sample Two-Dimensional Correlation Spectr

机译：时间分辨红外光谱结合归一化样品-样品二维相关光谱研究的在中心附近没有羧酸基的铁电液晶分子的电场诱导取向

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摘要

The orientation dynamics of a ferroelectric liquid crystal (FLC) with a naphthalene ring and without a carboxylate group near the stereocenter (FLC-2) during the electric-field-induced switching has been investigated by time-resolved infrared (IR) spectroscopy combined with normalized sample-sample two-dimensional (2D) correlation spectroscopy. To reveal the orientation dynamics, we have proposed a normalized sample-sample 2D correlation spectroscopy that is calculated by normalizing a sample-sample 2D correlation spectrum over every column or row. An important advantage of the normalized sample-sample 2D correlation spectroscopy over sample-sample 2D correlation spectroscopy is that the excessive information is deleted and more precise information therefore can be extracted even from spectra with a rather low signal-to-noise ratio. The normalized sample-sample 2D correlation spectroscopy allows us to explore the differences in the dynamics of each segment more clearly than the usual sample-sample 2D correlation spectroscopy. Time-resolved IR spectra of FLC-2 in a planar-aligned cell were measured over two delay time ranges from 0 to 150 μs and from 200 to 350 μs at an interval of 10 μs with the polarization angle of 45.0° under a rectangular electric field of ±3 V with a 2.5 kHz repetition rate in the smectic-C~* (Sm-C~*) phase at 115 ℃. The normalized sample-sample correlation spectroscopy was applied to these time-resolved spectra. We explored the reorientation process of the alkyl chains, the core, and the carboxylate group of FLC-2 in the positive and negative half-periods of the electric-field-induced switching. It has been found from the present study that the reorientation track of the core in the positive half-period is different from that in the negative half-period, while the reorientation tracks of the C=O dipole moment and alkyl chains are very similar between the positive and negative half-periods. The present study has also revealed that the orientation profile of the core moiety is different from those of the alkyl chains and the C=O dipole moment, and the difference in the profile depends on the change of dc electric field from -3 to +3 V and from +3 to -3 V at an interval of 0.25V. It seems that the core moiety functions in the presence of memory properties. Furthermore, a tilt angle for FLC-2 with a naphthalene ring and without a carboxylate group near the stereocenter is smaller than other similar FLCs with a naphthalene ring and a carboxylate group near the stereocenter. It is been suggested from the analysis of the polarization-angle dependent spectra under the external dc electric field of two polarities that the carboxylate group near the stereocenter plays an important role in forming a large tilt angle and that the carboxylate group in the core moiety is responsible for the emergence of ferroelectricity.
机译：通过时间分辨红外（IR）光谱法结合电场研究了带萘环且在中心附近（FLC-2）附近没有羧酸根基团的铁电液晶（FLC）的取向动力学。归一化样本-样本二维（2D）相关光谱。为了揭示方向动力学，我们提出了归一化的样本-样本2D相关光谱，通过对每列或每一行的样本-样本2D相关光谱进行标准化来计算。归一化的样品-样品2D相关光谱比样品-样品2D相关光谱的重要优势在于，即使从信噪比非常低的光谱中，也可以删除过多的信息，因此可以提取更精确的信息。归一化的样品-样品2D相关光谱使我们比普通的样品-样品2D相关光谱更清楚地探索每个段的动力学差异。在矩形电镜下，在极化角为45.0°的情况下，以10μs的间隔在0至150μs和200至350μs的两个延迟时间范围内测量了平面排列电池中FLC-2的时间分辨红外光谱。层列C〜*（Sm-C〜*）相在115℃时的重复频率为±3 V，重复率为2.5 kHz。将归一化的样品-样品相关光谱应用于这些时间分辨光谱。我们探讨了电场诱导的开关的正半周期和负半周期中FLC-2的烷基链，核心和羧酸酯基团的重新取向过程。从本研究中发现，在正半周期中核的重新定向轨迹与在负半周期中的核不同，而C = O偶极矩和烷基链的重新定向轨迹在两者之间非常相似。正和负半周期。本研究还表明，核心部分的取向分布与烷基链和C = O偶极矩不同，并且分布的差异取决于直流电场从-3到+3的变化。 V和+3至-3 V，间隔为0.25V。似乎核心部分在存在记忆特性的情况下起作用。此外，具有萘环且在立构中心附近不具有羧酸基的FLC-2的倾斜角小于其他具有萘环且在立构中心附近具有羧酸基的FLC-2的倾斜角。从两种极性的外部直流电场下与偏振角相关的光谱分析表明，立构中心附近的羧酸根基团在形成大的倾斜角方面起着重要作用，并且核心部分的羧酸根基团是负责铁电的出现。

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