荧光超分子液晶聚合物及嵌段共聚物的组装和响应性研究

Stimuli-responsive polymers have received a great deal of attention due to their fundamental interest and practical applications, in which their physical properties or functions can be controlled by various stimuli such as temperature, light, pH, mechanical force, chemicals, and an electric field. They have intensive applications in smart devices, biotechnology, actuators, sensors, etc. Toward achieving more complicated functional properties and multiple responsive behaviors in one system in different dimensions and time scale, one of the most used strategies is integrating different functional molecular motives into a system and precisely programing their responsive properties. While with increasing the composition and complicity of system, the challenge to control and manipulate various responses increases dramatically. Single molecular motif exhibiting versatile responsive properties can be considered as the candidate to reduce the complicity of multi-component integrated functional systems. α-Cyanostilbene and its derivatives are linear conjugated molecules that show aggregation-induced emission (AIE) behavior. This phenomenon is due to a synergetic effect of the restricted environment of the solid phase and J-aggregation. Their fluorescence can be modulated under various stimuli, exhibiting such as mechanochromic, thermochromic, and solvatochromic responsive properties. Moreover, under UV irradiation, α-cyanostilbene moiety can undergo Z/E isomerization that could subsequently induce self-assembled structure and fluorescence changes. So α-Cyanostilbene moiety gathers Z/E isomerization, mesogenic, and AIE properties together and can be considered as an all-round building block bearing luminogen, AIEgen, mesogen and chromophore characteristics. Although a variety of responsive properties for α-cyanostilbene derivatives have been explored so far, the multi-stimuli responsive behavior only exists in small molecular systems. In this proposal, we design and synthesize three series of cyanostilbene derivatives and introduce them into supramolecular side-chain polymers or block copolymers via hydrogen bonding interaction. Their mesomorphic structures, hierarchical self-assembled structures and multi-responsive properties will be systemically investigated. Meanwhile, both Z and E isomers of α-cyanostilbene derivatives would be synthesized and purified. The different self-assembled structures and fluorescence properties of supramolecular polymers containing Z or E isomers will be studied. Multiple external stimuli, such as temperature, light, solvent, and mechanical force, will be programmed and introduced into the supramolecular polymer systems. The induced morphological, structural, and surface property changes with concomitant fluorescence switching or modulation in supramolecular polymer systems will be investigated thoroughly.

刺激响应性聚合物材料在光、电、热等刺激下其物理性质以及功能性会随之发生改变，是智能材料的重要组成部分。氰基二苯乙烯不仅可作为液晶基元来构筑各类液晶材料，而且具有聚集诱导发光（AIE）、热致变色、力至变色、光致异构化、溶剂变色等刺激响应性质，是一类多功能响应基团。在本项目中，我们通过控制氢键作用强度，将不同结构的氰基二苯乙烯衍生物引入聚合物体系中，构筑具有多重刺激响应行为的超分子侧链液晶荧光聚合物以及嵌段共聚物。利用氢键作用来调控氰基二苯乙烯衍生物在聚合物体系中的有序排列，系统研究小分子的形状和结构设计及其Z、E异构体对超分子聚合物液晶相结构以及AIE性质的影响。研究不同刺激条件下的超分子聚合物及其嵌段共聚物的发光性质、液晶态、多层级结构以及薄膜表面性质等响应行为以及变化规律，探索聚合物材料从分子尺度到介观乃至宏观的一系列刺激响应的内在机理。

刺激响应性聚合物材料是智能材料的重要组成部分。很多材料的刺激响应变化过程经历了从微观到宏观不同尺度之间的传递和放大，因此在材料设计上需要兼顾分子本身的化学结构到聚集态结构最后到宏观性质之间的相互作用和相互影响。该项目从氰基二苯乙烯这类具有多重刺激响应行为的荧光生色团入手，系统研究了含有这类生色团的小分子、聚合物、超分子聚合物以及嵌段共聚物体系的刺激响应行为以及由此导致的各类物理化学性质和聚集态结构变化规律，探讨这类响应材料从分子尺度到介观乃至宏观的一系列多重刺激响应性的内在机理。在项目执行期间，首先通过分子设计来调整氰基二苯乙烯类生色团以及衍生物的分子结构，研究了其光响应行为的内在分子结构和分子堆积的影响规律，发现生色团之间的分子间作用力会在一定程度上影响到分子在光响应过程中采取不同的光化学反应机制，因此可通过引入不同的芳香环以及柔性链等来对分子间作用力进行调整，从而实现对光响应行为的可控调节，在具有强相互作用的联苯类氰基二苯乙烯体系发现了无定形态下也可实现高效的[2+2]原位光化学反应。通过对光化学机制的调控，在氰基二苯乙烯类薄膜材料里实现了室温下全光控可逆荧光变色响应。其次研究发现在本体中材料的发光性质和光响应行为也受到柔性烷基链的影响，通过调节柔性链的含量不仅实现了超分子液晶有序结构以及发光效率的可控调节，同时也发现了一类反常的光致荧光增强效应。最后，项目所设计研究的氰基二苯乙烯类材料还在纤维、凝胶、溶液组装体中均表现出优异的光响应行为，除了荧光颜色的变化，表现出光致形变、光致溶胶凝胶转变，光致手性转变等多种刺激响应过程。该项目的研究结果为多功能刺激响应材料的构筑提供了很好的设计思路。