Helical Twist Sense and Spontaneous Polarization Direction in Ferroelectric Smectic Liquid Crystals.
Helical Twist Sense and Spontaneous Polarization Direction in Ferroelectric Smectic Liquid Crystals.
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铁电近晶液晶中的螺旋扭转方向和自发极化方向。
DOI：
10.1002/chin.198650052
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发表时间：
1986
期刊：
影响因子：
--
通讯作者：
J. Patel
中科院分区：
文献类型：
--
作者：
J. Goodby;E. Chin;T. Leslie;J. Geary;J. Patel
光学活性材料的液晶系统与纯无定形液体或手性材料溶液的液晶系统不同，其平面偏振光的旋光符号表现出规则的交替。在给定的同系物中，随着不对称中心沿着末端碳骨架逐渐远离分子的中央芳香核，存在交替效应。当手性中心从一个位置移动到下一个位置时，旋转会从右旋到左旋交替。对胆甾相的研究已将这种行为与相中分子的宏观螺旋排序的扭曲感、分子结构中手性中心的位置以及不对称中心的空间构型联系起来。目前的研究表明，类似的效应也发生在螺旋铁电近晶相中，但在这种情况下，存在更复杂的规则，将上述因素与相对于单斜相倾斜轴的自发极化方向以及关于手性中心本身的电子分布相关联。开发了与这些因素相关的一般规则，这些规则允许直接根据所讨论的smectogen的分子结构来预测各种光学和电学特性。分子螺旋排序的扭转方向被证明具有偶极起源，因此它对不对称中心周围电子分布的变化敏感。类似地，自发极化的方向也取决于横向偶极性质和手性中心相对于分子长轴的方向。因此，近晶的原始规则会发生变化，具体取决于该中心的偶极子方向。这些一般规则也适用于近晶晶体修饰的铁电性质和胆甾型晶体的螺旋性质。
Liquid-crystalline systems of optically active materials, unlike those of pure amorphous liquids or solutions of chiral materials, exhibit regular alternations for the signs of theiroptical rotations of plane polarized light. In a given homologous series, there is an alternation effect as the asymmetric center is moved incrementally along the terminal carbonskeleton away from the central aromatic core of the molecule. The rotation alternates dextro to levo as the chiral center is moved from one position to the next. Studies on cholesteric phases have related this behavior to the twist sense of the macroscopic helical ordering of the molecules in the phase, to the position of the chiral center within the molecular structure, and to the spatial configuration of the asymmetric center. This present investigation shows that a similar effect also occurs in helical ferroelectric smectic phases, but in this case there are more complex rules relating the above factors to the directionof the spontaneous polarization with respect to the tilt axis of the monoclinic phase, and to the electron distribution aboutthe chiral center itself. General rules that relate these factors are developed which allowfor the predictions of various optical and electrical properties to be made directly from the molecular structure of the smectogen in question. The twist sense of the helical ordering of the molecules is shown to have dipolar origins, and it is therefore sensitive to changes in the electron distribution about the asymmetric center. Similarly, the direction of the spontaneous polarization is also dependent on the lateral dipolar nature and orientationof the chiral center with respect to the long axis of the molecule. Thus variations in the original rules occur for smectics depending on the dipole direction at this center. These general rules also apply to the ferroelectric properties of smectic crystal modifications and to the helical properties in cholesterics.