Guo Xiuxiu, Mao Tianhui, Wang Zhifang, Cheng Peng, Chen Yao, Ma Shengqian, Zhang Zhenjie
State Key Laboratory of Medicinal Chemical Biology, College of Chemistry, Nankai University, Tianjin 300071, China.
Renewable Energy Conversion and Storage Center, Nankai University, Tianjin 300071, China.
ACS Cent Sci. 2020 May 27;6(5):787-794. doi: 10.1021/acscentsci.0c00260. Epub 2020 Apr 21.
Seeking new photoresponsive materials with high energy conversion efficiency, good mechanical properties, as well as well-defined photoactuation mechanisms is of paramount significance. To address these challenges, we first introduced crystalline covalent organic frameworks (COFs) into the photoactuator field and created a facile fabrication strategy to directly install photoresponsive functional groups (i.e., acylhydrazone) on the skeletons of COFs. Herein, an approach to use polyethylene glycol (PEG) cross-linked dimers as the building blocks of the platform was developed and afforded a series of uniform and freestanding membranes () with outstanding mechanical properties (e.g., high flexibility and mechanical strength). Notably, these membranes possessed a fast mechanical response (e.g., bending) to UV light and good reversibility upon blue light or heating. After an in-depth investigation of the photoactuation mechanism via various techniques, we proposed a mechanism for the photoresponsive performance of : configurational change of acylhydrazone (i.e., E ↔ Z isomerization) accompanied by an excited-state intramolecular proton transfer (ESIPT) process intramolecularly transferring hydrogens from hydrogen donors (N-H) to hydrogen acceptors (oxygen in PEG). Moreover, attributed to the PEG moieties, also demonstrated a vapor-responsive performance. This study not only broadens the application scopes of COFs but also provides new opportunities for the construction of multi-stimuli-responsive materials.
寻找具有高能量转换效率、良好机械性能以及明确光驱动机制的新型光响应材料具有至关重要的意义。为应对这些挑战，我们首先将结晶共价有机框架（COF）引入光驱动器领域，并创建了一种简便的制备策略，以直接在COF骨架上安装光响应功能基团（即酰腙）。在此，开发了一种使用聚乙二醇（PEG）交联二聚体作为该平台构建单元的方法，并得到了一系列具有出色机械性能（如高柔韧性和机械强度）的均匀且独立的膜。值得注意的是，这些膜对紫外光具有快速的机械响应（如弯曲），并且在蓝光或加热时具有良好的可逆性。通过各种技术对光驱动机制进行深入研究后，我们提出了该材料光响应性能的一种机制：酰腙的构型变化（即E↔Z异构化）伴随着激发态分子内质子转移（ESIPT）过程，分子内氢从氢供体（N-H）转移到氢受体（PEG中的氧）。此外，由于PEG部分，该材料还表现出蒸汽响应性能。这项研究不仅拓宽了COF的应用范围，也为构建多刺激响应材料提供了新的机遇。
