增强型液晶物理凝胶中胆甾相螺距的光调控及稳定化

It is still a problem to controllably tune the pitch of cholesteric liquid crystals (CLCs) and to stabilize the pitch at will, as well as to concurrently endow the CLC materials self-supporting ability. In this proposal, a novel series of ortho-halogeneated azobenzene dopants bearing binaphthyl group are designed and synthesized. On the one hand, the powerful axial chirality of binaphthyl group can easily induce commercial-available nematic liquid crystals (NLCs) into CLCs. On the other hand, the electron-withdrawing ortho-halogen atom substitution can decrease the energy difference of the highest occupied molecular orbitals between cis- and trans- isomers, which effectively prolongs the half-life time of cis-trans isomerization and promotes the thermal stability of cis-isomer at room temperature. Meanwhile, this substitution can also separate the energy bands for n-π* excitation of trans- and cis- isomers. As a result, the photo-switching and stabilizing of both the ratio of trans- / cis- isomers and the cholesteric pitch of CLCs can be realized via two specific monochromatic visible lights with different wavelengths and exposure time. Following, in order to endow these CLC materials good self-supporting ability, when the mixture of NLCs, dopant and gelator experiences the isotropic-nematic transition of LCs, followed by the sol-gel transition, a new kind of photo-switchable CLC physical gels is constructed. The CLCs are induced by the pre-oriented surface of substrate. The chosen gelators are temperature-responsive sorbitol derivatives. The mechanical performance is reinforced by loading inorganic nanoparticles. The pitch of CLCs in physical gels can be controlled reversibly by two specific monochromatic visible lights under a certain intensity and exposure time, leading to a large range variation of the color reflection and an on-demand stabilization of the reflection wavelength. Combined with the chemical structure of the dopants, condensed microstructure of the CLC gels, as well as the macroscopic properties including liquid crystal transition behavior, sol-gel transition behavior, and reflection spectrum, the effect of the substituent halogen atoms on the photo-isomerization behavior and the helical twist power of dopants in LCs, will be investigated systematically. The correlation of the CLC pitch to the specific monochromatic lights, the intensity and exposure time will be established. Finally, reinforced physical gel composites will be fabricated on the basis of these photo-switchable and stabilizable CLCs. This study can provide theoretical and practical fundamentals to the design and preparation of such materials, especially for their applications in electro-optic devices, information storage, high-tech anti-counterfeit, etc.

同时实现胆甾相液晶(CLC)螺距的调控及稳定化、赋予材料较强力学支撑能力仍是一个难题。本申请拟设计合成邻位卤代的联萘偶氮苯掺杂剂，其中，联萘轴向手性的强螺旋扭曲能力易诱导向列相液晶形成CLC；邻位卤代则一方面缩小顺反异构体最低能量之间的差别，抑制顺式向反式的快速回复，提升顺式的室温稳定性，另一方面拉开顺反异构体的n-π*跃迁能级，以便由不同波长的可见光来调控及稳定化顺反异构体的比例与CLC的螺距。采用热响应凝胶因子将之凝胶化，并以无机纳米粒子进一步增强凝胶，赋予体系较强的力学支撑能力。结合掺杂剂化学结构、凝胶微结构、液晶相转变、溶胶-凝胶转变和反射光谱等宏观性能，揭示偶氮苯掺杂剂中取代基种类对光致异构化和螺旋扭曲能力的影响规律，阐明螺距对光照条件的依赖关系，构筑基于螺距可光调控及稳定化的增强型凝胶复合材料，为此类材料的设计、制备及在电光器件、信息存储和高端防伪等领域的应用奠定基础。

掺杂型胆甾相液晶（CLC）由于具有独特的螺旋结构和刺激响应性质而备受青睐。实现螺旋扭曲能力（HTP）的精准调控、刺激源的清洁无毒，以及CLC体系反射颜色的长期稳定是难点；与此同时，当前的研究绝大部分集中在流动体系，体系的力学支撑性能亦有待提高。本项目首先采用重氮偶联、亲核取代、点击化学反应合成了4种末端烷基/烷氧基长度递增的偶氮苯联萘基轴手性掺杂剂。基于溶解度参数和DSC表征结果分析了掺杂剂与向列相液晶P0616A的相容性，制备了反射光波长/颜色不同的CLC。通过对紫外和可见光照射下HTP的分析，结合指数衰减（增长）规律，实现了HTP、体系反射光波长和颜色的精准调控。其次，采用Mills反应，通过调控氨基氧化为亚硝基的时间制备了4种氟取代偶氮苯手性掺杂剂（F-azo）。F-azo在550nm绿光和450nm蓝光交替照射下能够可逆异构化反应，避免了紫外光的引入。特别地，命名为D-4F的F-azo顺式异构体最大含量、半衰期分别高达49%和67h，满足CLC反射颜色大范围调控与长期稳定的要求。基于溶解度参数匹配原则，利用简单的共掺杂策略有效改善了CLC的相容性。实现了体系RGB三基色的快速转变，每一种颜色在暗室下均可稳定保存~24h，显著提高了体系超螺旋结构及其性能的稳定性。再次，在上述体系中添加山梨醇类衍生物DBS，制得了CLC凝胶，精准调控了CLC在可见光下的螺距、反射波长及颜色，且将每种颜色稳定至少1天。最后，设计合成了一种集手性、全可见光响应和温度响应于一体的凝胶因子S-4F-AG。在绿光和蓝光交替照射下，S-4F-AG表现出良好的光致顺反异构化行为，且顺式异构体的最大含量、半衰期分别是35%和89h。另外，S-4F-AG对掺杂剂2/P0616A的最低凝胶化浓度低至2.0wt%。在保持自支撑性的同时，所制备的CLC凝胶的反射光波长和颜色对温度和绿光有良好的响应行为，并几乎覆盖了整个可见光区域。初步探索了上述材料在图案信息擦写方面的应用。本项目的实施，为此类软物质材料的设计、制备及其在信息存储、传感、高端防伪等领域的应用提供了理论基础和实验依据。