Supramolecular Polymers Capable of Controlling Their Topology
Supramolecular Polymers Capable of Controlling Their Topology
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能够控制其拓扑结构的超分子聚合物
DOI：
10.1021/acs.accounts.8b00660
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发表时间：
2019
期刊：
影响因子：
18.3
通讯作者：
B. Adhikari
中科院分区：
文献类型：
--
作者：
S. Yagai;Y. Kitamoto;S. Datta;B. Adhikari
一维拉长超分子聚合物是一类重要的超分子材料，其中单体通过可逆的分子间相互作用相互作用而形成纤维状结构。与通常报道的基于主客体相互作用的常规超分子聚合物不同，由一维堆积的π共轭分子组成的超分子聚合物可以通过刚性芳香单体的合作缔合来编码具有高度内部有序性的分子，从而赋予这种超分子聚合物非凡的性质和功能。然而，它们的内部有序还没有被用来操纵超分子聚合物主链上明确定义的状态的复杂景观，这可能会诱导出超出骨架固有性质的新功能。本文将重点介绍我们研究的具有高内有序度的超分子聚合物的起步阶段，这些超分子聚合物能够赋予其骨架内在的曲率。最初，我们开发了一种用巴比妥酸官能化的萘分子，通过形成氢键的环状六聚体(玫瑰花环)，形成直径约16 nm的均匀环形短纤维。由于我们认为环状尺寸的一致性是由玫瑰花环堆积产生的本征曲率引起的，所以我们利用这种本征曲率通过扩展这种分子π体系来设计连续弯曲的延伸超分子聚合物。具有更多扩展的π体系的单体产生的本征曲率确实使我们能够在扩展的超分子聚合物中获得从随机折叠到螺旋折叠的更高阶结构(拓扑)。我们将讨论用于拓扑控制的内禀曲率的产生的动力学方面，包括闭环过程导致的环状结构的形成。对于具有明确定义的拓扑的扩展超分子聚合物，我们将讨论外部刺激对明确定义的态的复杂景观的操纵。将光响应偶氮苯发色团引入到原始的萘分子支架中，使得我们可以通过反式顺光异构化来可逆地破坏或恢复主链的曲率。借助于这种光可控的曲率，我们已经证明了光诱导的螺旋折叠结构变成完全拉伸的结构。此外，π共轭核心的直接延伸为我们提供了获得前所未有的超分子聚合物的途径，这些聚合物具有紧急的依赖于时间的拓扑转变。以萘为核的分子与两个亚苯基共轭，动力学地提供了由螺旋折叠和错误折叠的结构域组成的超分子聚合物。在老化超分子聚合物溶液后，我们观察到错误折叠的结构域在几天的时间尺度上自发折叠，最终获得了类似于蛋白质三级结构的超分子聚合物拓扑结构。这些具有无与伦比的活性拓扑结构的超分子聚合物为超分子聚合物作为一维纳米材料提供了新的前景。
ConspectusOne important class of supramolecular materials is one-dimensionally elongated supramolecular polymers, in which monomers are associated by reversible intermolecular interactions, yielding a fibrous morphology. Unlike frequently reported conventional supramolecular polymers based on, for instance, host–guest interactions, those composed of one-dimensionally stacked π-conjugated molecules can be encoded with high degrees of internal order by cooperative association of the rigid aromatic monomers, endowing such supramolecular polymers with extraordinary properties and functionality. However, their internal order has not yet been exploited to manipulate the complex landscape of well-defined states of the supramolecular polymer backbone, which may induce new functionalities beyond the intrinsic properties of the backbones.This Account will focus on the inceptive phase of our research on supramolecular polymers with high degrees of internal order able to impart intrinsic curvature to their backbones. Initially, we developed a naphthalene molecule functionalized with barbituric acid, which forms uniform toroidal short fibers with diameters of approximately 16 nm via the formation of hydrogen-bonded cyclic hexamers (rosettes). As we thought the uniformity of the toroid size to arise from the intrinsic curvature generated upon stacking of the rosettes, we exploited this intrinsic curvature to design continuously curved extended supramolecular polymers by extension of such molecular π-systems. The intrinsic curvature produced by the monomers with more expanded π-systems indeed gave us access to higher-order structures (topologies) ranging from randomly folded to helically folded coils in extended supramolecular polymers. We will discuss the kinetic aspects of the generation of intrinsic curvature for topology control, including the formation of toroidal structures resulting from ring-closing processes.For extended supramolecular polymers with well-defined topologies, we will discuss manipulation of a complex landscape of well-defined states by external stimuli. The incorporation of a photoresponsive azobenzene chromophore in the original naphthalene molecular scaffold allowed us to reversibly destroy or recover the curvature of the main chain throughtrans–cisphotoisomerization. By means of this photocontrollable curvature, we have demonstrated light-induced unfolding of helically folded structures into entirely stretched structures. Furthermore, a direct extension of the π-conjugated core provided us with access to unprecedented supramolecular polymers with emergent time-dependent topology transitions. Molecules with a naphthalene core conjugated with two phenylene units kinetically afforded supramolecular polymers that consist of helically folded and misfolded domains. Upon aging the supramolecular polymer solution, we observed spontaneous folding of the misfolded domains in a time scale of days, eventually obtaining a supramolecular polymer topology analogous to the tertiary structure of proteins. These supramolecular polymers with unrivaled and active topologies provide new prospects for supramolecular polymers as one-dimensional nanomaterials.