Department of Chemistry, Hong Kong Branch of Chinese National Engineering Research Center for Tissue Restoration and Reconstruction and Institute for Advanced Study, The Hong Kong University of Science and Technology, Clear Water Bay, Kowloon, Hong Kong 999077, China.
State Key Laboratory of Coordination Chemistry, Jiangsu Key Laboratory of Advanced Organic Materials, School of Chemistry and Chemical Engineering, Nanjing University, Nanjing 210023, China.
J Am Chem Soc. 2021 Aug 4;143(30):11820-11827. doi: 10.1021/jacs.1c05647. Epub 2021 Jul 22.
Molecular motions are essential natures of matter and play important roles in their structures and properties. However, owing to the diversity and complexity of structures and behaviors, the study of motion-structure-property relationships remains a challenge, especially at all levels of structural hierarchy from molecules to macro-objects. Herein, luminogens showing aggregation-induced emission (AIE), namely, 9-(pyrimidin-2-yl)-carbazole (PyCz) and 9-(5-R-pyrimidin-2-yl)-carbazole [R = Cl (ClPyCz), Br (BrPyCz), and CN (CyPyCz)], were designed and synthesized, to decipher the dependence of materials' structures and properties on molecular motions at the molecule and aggregate levels. Experimental and theoretical analysis demonstrated that the active intramolecular motions in the excited state of all molecules at the single-molecule level endowed them with more twisted structural conformations and weak emission. However, owing to the restriction of intramolecular motions in the nano/macroaggregate state, all the molecules assumed less twisted conformations with bright emission. Unexpectedly, intermolecular motions could be activated in the macrocrystals of ClPyCz, BrPyCz, and CyPyCz through the introduction of external perturbations, and synergic strong and weak intermolecular interactions allowed their crystals to undergo reversible deformation, which effectively solved the problem of the brittleness of organic crystals, while endowing them with excellent elastic performance. Thus, the present study provided insights on the motion-structure-property relationship at each level of structural hierarchy and offered a paradigm to rationally design multifunctional AIE-based materials.
分子运动是物质的基本属性，在物质的结构和性质中起着重要作用。然而，由于结构和行为的多样性和复杂性，运动-结构-性质关系的研究仍然是一个挑战，尤其是在从分子到宏观物体的所有结构层次上。在此，设计并合成了表现出聚集诱导发光（AIE）性质的发荧光团，即 9-（嘧啶-2-基）咔唑（PyCz）和 9-（5-R-嘧啶-2-基）咔唑[R=Cl（ClPyCz）、Br（BrPyCz）和 CN（CyPyCz）]，以解析材料的结构和性质对分子在分子和聚集态水平上运动的依赖性。实验和理论分析表明，所有分子在单分子水平上的激发态中存在的活性分子内运动赋予了它们更扭曲的结构构象和较弱的发光。然而，由于在纳米/宏观聚集态中分子内运动受到限制，所有分子都呈现出较少扭曲的构象，并表现出强烈的发光。出人意料的是，通过引入外部扰动，可以在 ClPyCz、BrPyCz 和 CyPyCz 的大晶体中激活分子间运动，协同的强和弱分子间相互作用使它们的晶体能够发生可逆变形，有效地解决了有机晶体脆性的问题，同时赋予它们优异的弹性性能。因此，本研究为每个结构层次的运动-结构-性质关系提供了深入的了解，并为合理设计基于 AIE 的多功能材料提供了范例。
