摘要/Abstract
胆甾相液晶是一类具有周期性螺旋超结构的软光子晶体，能够选择性地反射不同波长的光产生结构色.在向列相液晶中掺杂光响应手性分子是制备光响应胆甾相液晶的普遍方法.在外界光源的刺激下，光响应手性分子的空间结构改变，诱导螺旋超结构的螺距发生变化，从而调控胆甾相液晶的结构色，因此光响应胆甾相液晶在滤光器、传感器、可调光学激光器和动态显示等领域具有广阔的应用前景.总结了不同光响应手性分子构筑的胆甾相液晶体系，分析了手性分子结构设计对胆甾相液晶结构色调控的影响，最终讨论了光响应胆甾相液晶目前面临的挑战以及未来的发展方向.
关键词: 胆甾相液晶, 光响应手性分子, 结构色, 螺旋超结构, 偶氮苯
Cholesteric liquid crystals (CLCs) are a kind of intriguing soft photonic crystal materials, in which the orientation of LC molecules varies in a helical fashion, and selectively reflect light, known as structural color, according to Bragg's law. Moreover, the structural color determined by the pitch length of the helices in CLCs can be tuned owing to the dynamic control of inherent self-organized helical superstructures in response to external stimuli. Currently, light-driven CLCs have attracted extensive interest because light, compared to other stimuli, has unique advantages of remote, temporal, local and spatial manipulation. Such elegant systems are generally formulated by doping light-driven chiral switches, mainly consisting of chiral centers and photoswitches, into a nematic LC host. The chiral centers are able to twist the nematic LC host into helical superstructures, which is represented by helical twisting power (HTP). The photoswitches undergo configurational changes upon photoisomerization, leading to the variation in HTP and the pitch length of the helices, and consequently tune the structural color of the CLCs. These light-driven CLCs provide opportunities for various photonic applications such as tunable filters, sensors, tunable optical lasers, and optically addressed displays. In this review, we summarize diverse light-driven CLC systems according to the type of the photoswitch in doped chiral switches. Azobenzene-and motor-based chiral switches usually have high HTP and large variation in HTP, which enables the tuning range of the resultant CLC to cover visible spectrum. Besides, chiral switches based on dithienylethenes have also been synthesized and utilized to tune the reflection of the CLC across red, green and blue colors that remain unchanged in darkness even after one week because of the excellent thermal stability of dithienylethenes. Chiral switches based on dicyanoethene are used to construct an optically tunable reflective-photoluminescent CLC system. Importantly, the design of the light-driven chiral switches is analyzed in detail to reveal the structure-property correlation. Potential and demonstrated practical applications of light-driven CLCs are discussed, and forecast of existing challenges and opportunities in CLC systems are concluded.
Key words: cholesteric liquid crystal, light-driven chiral switch, structural color, helical superstructure, azobenzene
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