反射-荧光双重模式胆甾相液晶材料的光调控

Photoresponsive cholesteric liquid crystals (CLCs) may represent one of the most ideal candidates to construct active color units as ‘photonic ink’ and develop color reflective displays and rewritable devices, breaking the limitation of showing single color images caused by bistable E-ink. However, such CLC systems is restricted to the fact that the structural color can be seen in the light field and disappears in the dark field. In this project, a reflection-fluorescence dual-mode CLC system is constructed by introducing the fluorescence performance into the CLC materials. This project intends to design and prepare fluorescence chiral switches with different structures and fluorescence molecules of liquid-crystal-like structures. Based on these materials, two methods are used to prepare fluorescence CLCs. Parameters of the optimized system are analyzed, such as fluorescence intensity, physical and chemical properties of liquid crystals, and tuning range of the structural color. In order to master the effective ways in which reflection mode and fluorescence mode complement each other, the relationship between the tuning of reflection wavelength and the intensity of fluorescence emission will be carefully studied. In the light field, we can use the energy-saving and eye-protected reflection mode; while in the dark field, the system can continue to be used with the fluorescence mode, which expands the application of the CLC materials and meets the growing demand for multi-functional materials, laying the material foundation for the promotion of the CLCs in flexible display technology, multilevel security and optical information encryption.

光响应胆甾相液晶（CLC）有望作为“光子墨水”构筑显示系统中的可调控颜色单元，突破双稳态“电子墨水”在电场模式下仅能显示单色图案的瓶颈，开发彩色反射型显示器和可擦写设备。然而，结构色在明场可见、暗场“失活”的短板限制了CLC的进一步应用。本项目将荧光性能引入CLC中，构建反射-荧光双重模式光响应CLC材料。项目拟设计制备不同结构的手性荧光分子开关和类液晶结构的荧光分子，并以此为材料基础分别采用两种方法开发荧光CLC体系，分析优化体系的荧光强度、液晶理化性质、反射波长调控范围等参数；深入研究反射波长的调控和荧光发光强度之间的关系，掌握反射模式和荧光模式相辅相成的有效途径；实现节能、护眼的反射模式（明场）和荧光模式（暗场）的不间断使用，满足对多功能材料日益增长的需求，为推动CLC在柔性显示、多级防伪和光学信息加密等领域的应用奠定基础。

光响应反射-荧光双模式胆甾相液晶结合了胆甾相液晶的物理排列和刺激响应性以及荧光材料的化学结构，兼具可调结构色和自发光两种光学特征，是一类新兴的显示材料，有望应用于反射式显示器、信息存储和光学防伪等领域。然而，构筑反射-荧光双模式胆甾相液晶并实现结构色的可控光调控存在巨大挑战：一方面，传统光调控胆甾相液晶的螺距处于不稳定的过渡态，难以精确调节结构色；另一方面，受限于液晶独特的物理性质，绝大部分荧光材料难以与其兼容。本项目首先提出了利用光响应二元手性分子体系调控胆甾相液晶结构色的新策略，探索了手性分子开关在光激发下分子构型变化对整体螺旋扭曲力的影响，揭示了二元手性分子体系螺旋扭曲力变化和调控胆甾相液晶螺距间的规律，建立了激发光源波长与反射波长间的对应关系，实现了反射波长在410-660 nm范围内的精确光调控，获得了6种处于光稳态的结构色。利用该结构色可光精确调控的胆甾相液晶，我们构筑了“力写电擦光调色”的新型光子纸，突破了传统光子纸仅能“写入-擦除”的单一功能。该光子纸的书写精度可达0.8 mm，与市面上手写板书写精度相当。进一步，本项目首次实现了将自发光性质引入胆甾相液晶材料的设想，设计了与液晶结构相似且量子效率高（φTHF = 85.7%，φSolid = ~100%）的荧光材料，并利用掺杂的方法制备了荧光胆甾相液晶。借助毛细管微流控技术将该荧光胆甾相液晶制备成结构色可调、荧光颜色不变的“双色光子墨水”，并基于其构筑反射和荧光模式下携带完全不同信息的双重防伪标签，拓展了单一荧光分子或光子晶体无法实现的功能。综上，本项目不仅解决了现有光调控胆甾相液晶存在的问题，还验证了构筑荧光胆甾相液晶的可行方法，在开发光调控反射-荧光双模式胆甾相液晶材料的研究领域中起着“承上启下”的作用，为胆甾相液晶乃至其他光子晶体材料在反射式显示领域的应用提供了新的思路。