基于硼螯合锁定效应的扩展共轭结构二维席夫碱共价有机框架半导体材料：分子设计、合成及性质

Covalent organic frameworks (COFs) feature versatile precise chemical structure, highly regular pore morphology as well as light weight and high stability, thus exhibiting a broad prospective in the fundamental research and application of optoelectronics, catalysis and biomedicine etc. For two-dimensional Schiff base COFs, their imine-linked conjugated backbones display only a moderate electron delocalization. However, owing to its high polarization, the imine linkage in the network is not very beneficial to supporting π-delocalization between the connected units, and is also susceptible to hydrolysis. With these in our mind, the present project will be focused on resolving these key issues. Lewis acid boron atoms will be introduced into the networks of the target COFs. These boron cores will be coordinated with the nitrogen atoms of imine units. The resulting chelated effect through the formation of tetra-coordinated boron core will create the fused structure and weaken the polarization of the imine unit, and thus improve the π-delocalization capability and stability of imine unit. On the other hand, variation of the substituents on the boron core will tune the electronic structures and layer-layer packing mode, and then creating rich optoelectronic properties and mesocopic morphologies. Meanwhile, the efficient strategy approach to obtain highly dispersed samples, will also be explored. The target two dimensional Schiff base COFs semiconductors with high stability and activity will be developed within the framework of this project, and their device fabrication will be performed. In general, these results will be hopefully contributed to promote the practical application of COFs-based optoelectronic materials.

共价有机框架材料拥有丰富多样的精确化学结构、高度规整的孔道形貌以及质轻和稳定性高等优点，在光电、催化和生物医药等基础和应用领域具有广阔的发展前景。其中，二维席夫碱型共价有机框架材料，其共轭骨架通过亚胺键连接而成，可在面内传导电子，有潜力用于高性能有机半导体器件，然而，亚胺键的极化性质束缚了电子在二维骨架离域和传导能力的提升，并导致骨架稳定性降低，易于水解。本项目针对这些关键问题，拟将路易斯酸硼原子引入二维席夫碱型共价有机框架，通过与亚胺单元形成硼氮配位键来构建四配位硼核螯合的稠合结构，并减低亚胺键极性，提高亚胺单元离域π-电子能力和稳定性；通过硼原子上取代基变化调节材料的电学性质和层间堆叠，来丰富材料的光电性质和介观形貌，并开发样品的分散剥离技术；获得具有良好稳定性和活性的二维席夫碱型共价有机框架半导体材料，研究其器件加工工艺，推动共价有机框架光电材料的实用化进程。

有机框架材料（COFs）作为一种新兴的晶态孔材料，具有多样化结构设计和丰富的周期性孔道，在催化，能源和环保等领域有着巨大的发展潜力，但传统COFs由极性动态共价键连接而成，因而，稳定性和电子离域性较弱，极大限制了这类材料的应用范围。基于此，本项目设立了通过降低连接COFs结构动态共价键的极性来改善此类框架材料的稳定性和电子离域特性为研究目标。首先，开发了稳定性明显提高的酰腙动态共价键共轭多孔结构，利用这种连接基团丰富的氢键等弱作用，建立了基于单体纳米结构为模板的自模板诱导的微纳中空管束制备策略，揭示了Kirkendall效应形成聚合物中空有序结构的合理机制，进而研究了所制备共轭多孔聚合物纳米管束作为锂或钠离子电池电极材料的电化学活性，展示了优良的充放电倍率性能，证明了微管束独特的多级有序形貌有助于氧化-还原活性位点的充分利用，以及电解质的快速传输和电子的快速交换/转移。此外，开发了以脑文格缩合反应制备乙烯基动态共价键为连接桥的COFs材料的通用制备策略，相继开发了多个三甲基取代芳基关键功能单体，如3,5-二氰-2,4,6-三甲基吡啶、2,4,6-三甲基-1,3,5-三嗪、三氰基均三甲苯，这些单体与二倍或三倍对称性多取代芳香醛缩合构建高结晶性多个系列无取代乙烯基桥连COFs；粉末X射线衍射、高分辨透射电子显微镜和氮气等温吸脱附测试等表征分析，充分证明了这类材料高的比表面积(>1000 m2 g−1)、开放规则纳米孔道和长程有序蜂窝状网络结构；这种基于非极性碳碳双键连接的晶态多孔框架结构，具有优异的抗强酸、强碱稳定性，以及突出的电子离域行为；初步探索了这类COFs的结构与性能间关系，发现了一些构筑单元对其半导体活性、形貌和拓扑结构等的影响规律，为后续对此类新型材料的基础和应用性深入研究奠定了基础。