Beijing National Laboratory for Molecular Sciences, Centre for Soft Matter Science and Engineering, Key Lab of Polymer Chemistry & Physics of the Ministry of Education, College of Chemistry , Peking University , Beijing 100871 , China.
Key Laboratory for Advanced Materials, School of Chemistry and Molecular Engineering , East China University of Science and Technology , Shanghai 200237 , China.
J Am Chem Soc. 2018 May 2;140(17):5764-5773. doi: 10.1021/jacs.8b01463. Epub 2018 Apr 23.
Completely understanding the working mechanisms of sophisticated supramolecular self-assembly exhibiting competing paths is very important for chemists en route to acquiring the ability of constructing supramolecular systems with controlled structures and designed functions. Here, the self-aggregation behaviors of an N-heterocyclic aromatic dicarboximide molecule 1, boasting two competing paths that give rise to different supramolecular structures and exhibit distinct thermodynamic features, are carefully examined. First, a group of H-aggregates are observed when providing a medium driving force for aromatic stacking, and their formation is manifested as an anticooperative process. When exposed to enhanced strength of aromatic interactions, these H-aggregates are found to transform into J-aggregates via a cooperative assembly mechanism. With the assistance of a mathematic model accommodating two competing polymerization pathways, calculations are conducted to simulate and explain the thermodynamic equilibria of such a unique supramolecular system. The calculation results are highly consistent with the experimental observations, and some important properties are elucidated. Specifically, the anticooperative assembly mechanism generally promotes the formation of low to medium oligomers, whereas the cooperative path is more competent at producing high polymers. If the anticooperative and cooperative routes coexist and compete for the same molecule, the cooperative formations of high polymers are significantly suppressed unless a very high degree of polymerization can be achieved. Such a unique feature of concurring anticooperative and cooperative paths emerges to the H- and J-aggregates of molecule 1 and thus brings about the interesting sequential appearances of the two types of aggregates under conditions of continuously enlarged driving force for self-aggregation. Finally, based on the knowledge acquired from this study and by analyzing the steric features of 1 that influence its supramolecular packing motifs, a slightly modified molecular structure is designed, with which the intermediate H-aggregation state was successfully suppressed, and a single cooperative J-aggregation path is manifested.
完全理解表现出竞争路径的复杂超分子自组装的工作机制对于化学家来说非常重要，这是他们获得构建具有受控结构和设计功能的超分子系统能力的关键。在这里，仔细研究了具有两种竞争途径的 N-杂环芳香二羧酸酰亚胺分子 1 的自组装行为，这两种竞争途径导致不同的超分子结构并表现出不同的热力学特征。首先，当提供芳香堆积的中等驱动力时，观察到一组 H-聚集体，其形成表现为反协同过程。当暴露于增强的芳香相互作用强度时，发现这些 H-聚集体通过协同组装机制转化为 J-聚集体。借助一个容纳两种竞争聚合途径的数学模型，进行了计算以模拟和解释这种独特超分子系统的热力学平衡。计算结果与实验观察高度一致，并阐明了一些重要性质。具体来说，反协同组装机制通常促进低聚物至中聚物的形成，而协同途径更有利于高聚物的形成。如果反协同和协同途径共存并竞争同一分子，则除非达到非常高的聚合度，否则协同高聚物的形成会受到显著抑制。这种共存的反协同和协同途径的独特特征出现在分子 1 的 H-和 J-聚集体中，从而导致在不断增大的自组装驱动力下两种类型的聚集体的有趣顺序出现。最后，基于从这项研究中获得的知识，并通过分析影响其超分子堆积模式的 1 的空间特征，设计了一个稍微修改的分子结构，成功抑制了中间 H-聚集态，并表现出单一协同 J-聚集途径。
