温度响应型pi-共轭聚合物的自组装与多功能集成研究（领域序号：二）

Regulating the interactions between assembly building blocks on the molecular level is one of the key strategies to modulate the self-assembly behavior and thus the properties of the assembles. While the generation of self-assembled nanocrystals of pi-conjugated polymers is a prospective target, two issues of particular relevance to such nanocrystals, are how can we modulate the self-assembly process from the polymer chains to the nanocrystals, which is not satisfactorily understood, and the fact that fluorescence of the nanocrystals is usually non-sensitive to the changes on the environmental temperature. To address those issues, in this project, we aim to synthesis a series of polythiophenes with ethylene glycol (EG) short side-chains, denoted as P3EGxT (2≤x≤5), via molecular design and Ni-catalyzed polymerization of the monomers. Those P3EGxT will be designed to be temperature-responsive. The temperature-responsiveness will then utilized to the self-assembly behavior of the pi-conjugated polymers. Furthermore, temperature-responsive nanogels will be fabricated on the basis of the P3EGxT assembles, and made into multifunctional. Those interesting functions we desired, including ratiometric fluorescence sensing of environmental temperature, and fluorescence cellular-labeling and imaging, will be integrated into a single nanobject. Under the framework of the national research project “Controllable self-assembly systems and their functionalization”, it is anticipated that a series of original results should be achieved on the methodology for the modulation of the self-assembly behavior, as well as on the multifunctional systems on the basis of assembles towards biological applications.

在分子水平上调节自组装基元间相互作用是调控自组装行为，进而调控自组装体物性的重要策略之一。针对当前pi-共轭聚合物纳米晶存在的两个挑战性问题（自组装形成纳米晶的过程调控问题尚无令人满意的答案；现有报道的纳米晶可用于细胞荧光标记成像，但其荧光对环境温度变化不产生响应），在本项目中，我们通过单体设计、催化缩聚合成出具有适当长度氧乙烯短支链的聚噻吩类聚合物（P3EGxT，2≤x≤5），使其具备温度响应性构象相转变特性，建立利用该特性来调控刚性pi-共轭主链在选择性溶剂对中自组装行为的方法，进而构建结构稳定、具有体积相转变特性的组装体纳米凝胶，并在单个的该纳米凝胶颗粒中主要集成环境温度——荧光信号定量转换、细胞荧光标记成像等多种功能。本项目是面向“可控自组装体系及其功能化”重大研究计划目标，在自组装过程调控的探索、以生物学功能为导向的多功能集成自组装体系的构建等方面做出原创性工作。

针对当前π-共轭高分子纳米晶所存在的挑战性科学问题，本项目合成了含低聚氧乙烯短支链的聚噻吩P3OExT（即P3EGxT；x = 2、3、4）。P3OE2T、P3OE3T、P3OE4T水溶液均表现出温度响应特性，LCST随支链长度增长而增大。为了突出利用温度响应特性来调控自组装，对于具有不同LCST的P3OET，建立了相应自组装方法，制备出P3OET组装体、组装体纳米凝胶及更高级次自组装材料，获得可设计的光电性质，实现多种功能：细胞成像，自适应温度、氨气等波动并转换为光/电信号，导电和储能等。（1）对于LCST适中的P3OE3T：在良溶剂四氢呋喃中发射橙色荧光；在水中形成稳定的球形组装体，荧光峰相对红移、强度减弱；而在甲醇中，形成丝状组装体，荧光峰相对蓝移、强度增强。选取在水中形成的组装体继续实验，结果显示：当水温升高，荧光峰蓝移，荧光强度增强；可进入细胞，用于成像；进一步用热台加热，或用解偶联剂、抗癌药物等化学刺激使细胞活动产生热量时，荧光随细胞温度升高而发生蓝移、强度增强等规律性变化。（2）对于LCST较低的P3OE2T：一方面，在1:9乙醇/水中得到组装体，并作为成核中心，经双官能化大单体自由基聚合、表面修饰，制备出具有网络半互穿结构的P3OET组装体纳米凝胶；另一方面，通过设计合成氨气、H2O2、葡萄糖等响应性高分子纳米凝胶、筛选作为组装模板，采用表面自组装方法，制备以响应性高分子纳米凝胶为核、P3OET组装体为壳层的“核-壳”式组装体纳米凝胶。该组装体纳米凝胶能够集成P3OE2T的光学性质、纳米凝胶的体积相转变特性等，并协同产生温度响应荧光、氨气响应导电性等性质，为测定细胞温度波动、呼出气体中氨气等应用提供了可能性。（3）对于LCST较高的P3OE4T：在探索以纳米凝胶为基元制备自组装材料的方法的基础上，根据P3OE4T溶于水而不利于自组装等情况，通过单体设计、催化缩聚、端基双键化、与单质硫共聚，合成S-P3OET，并合成具有网络半互穿结构的S-P3OET组装体纳米凝胶，进而以纳米凝胶为基元制备自组装材料。与S-P3OET组装体相比，纳米凝胶自组装材料具有更好的导电和储能等性能。综上所述，本项目体现了可控自组装体系及其功能化在光电材料设计制备的应用，为理解普遍认为最关键的问题——从分子到终端材料的不同层次的组装——提供有价值的视角。