Nanoengineering of Curved Supramolecular Polymers: Toward Single-Chain Mesoscale Materials,Accounts of Materials Research

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Nanoengineering of Curved Supramolecular Polymers: Toward Single-Chain Mesoscale Materials
Accounts of Materials Research ( IF 14.0 ) Pub Date : 2022-01-07 , DOI: 10.1021/accountsmr.1c00241
Sougata Datta ₁ , Sho Takahashi ₂ , Shiki Yagai _{1,

2,

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Affiliation

Recently, supramolecular polymers (SPs), which depend on the formation of reversible bonds between monomers, have attracted attention as a class of materials that can overcome the potential environmental problems of conventional polymeric materials. The development of various supramolecular polymers is important not only for their direct application as materials but also because their unique polymerization processes and dynamic properties have a profound influence on the development of polymeric and small-molecule-based functional materials. In other words, by limiting the dimensionality of molecular assemblies to one dimension, we can discover the essential aspects of self-assembly and self-organization. In particular, supramolecular polymerization, in which π-electron-rich planar molecules are stacked one-dimensionally via multiple interactions, is interesting because it gives “π-stacked SPs” with one-dimensional crystal-like order. The excellent intrinsic (internal) structural order of π-stacked SPs is difficult to observe in higher-order structures that exhibit only a monotonous linear structure. However, our research has shown that when internal structural order intrinsically generates curvature, the curvature appears as a major feature of the entire polymer chain. This intrinsic curvature allows the formation of diverse topologies such as toroids, random coils, waves, spirals, and helicoids using π-stacked SPs and also allows structural changes at the single-polymer-chain level along a topology-dependent energy landscape. In other words, π-stacked SP-based nanomaterials could enable free control of the structure at the single-polymer-chain level. This Account will focus on our research into curved supramolecular polymers (CSPs) during the last five years. CSPs are formed by the hydrogen bonding between barbiturate-containing π-conjugated molecules to produce giant supramolecular monomers. We first give an overview of the molecular design of the monomers required for the formation of CSPs, the unique energy landscape of CSPs, and their evaluation and analysis methods, before describing the four specific properties of CSPs. The first is structural controllability via the introduction of photoresponsive units such as azobenzene and diarylethene moieties. The isomerization of these photochromic molecules within the CSP main chain has a local effect on the curvature and allows photocontrol of their entire topology. The second is the copolymerization of different molecules via the formation of rosettes. Here, two extreme examples, block and alternating copolymerization, are discussed. Third, we describe a structural transition that involves the rearrangement of hydrogen bonds. This is a new property, which enables a structural transition from a soft and highly soluble supramolecular polymer to a hard and poorly soluble crystalline structure and thus expands the applicability of CSPs to environmentally important and electronic materials. Finally, self-assembled polycatenanes are described as an example of an entirely new “topological self-organization” using CSP formation on CSP surfaces, i.e., secondary nucleation. This work is also a turning point in our CSP research and includes concepts that are broadly applicable to the creation of self-organized functional materials. At the end of this Account, we will discuss how CSPs can contribute to nanotechnology or mesotechnology as single-chain-polymer materials. We hope that the landscape depicted in this Account will guide the development of a variety of new functional materials.

中文翻译：

弯曲超分子聚合物的纳米工程：迈向单链中尺度材料

最近，依赖于单体之间形成可逆键的超分子聚合物（SPs）作为一类可以克服传统聚合物材料潜在环境问题的材料而受到关注。各种超分子聚合物的开发不仅对它们作为材料的直接应用具有重要意义，而且因为它们独特的聚合过程和动态特性对聚合物和小分子基功能材料的开发产生了深远的影响。换句话说，通过将分子组装的维度限制为一维，我们可以发现自组装和自组织的基本方面。特别是超分子聚合，其中富含π电子的平面分子通过多重相互作用一维堆叠，很有趣，因为它给出了具有一维晶体状秩序的“π-stacked SPs”。在仅表现出单调线性结构的高阶结构中，难以观察到 π 堆叠 SP 的优异内在（内部）结构顺序。然而，我们的研究表明，当内部结构有序内在地产生曲率时，曲率表现为整个聚合物链的主要特征。这种固有曲率允许使用 π 堆叠 SP 形成不同的拓扑结构，例如环形、无规线圈、波浪、螺旋和螺旋体，并且还允许在单聚合物链水平上沿着依赖于拓扑结构的能量景观发生结构变化。换句话说，π 堆叠的基于 SP 的纳米材料可以在单聚合物链水平上自由控制结构。本报告将重点关注我们在过去五年中对弯曲超分子聚合物 (CSP) 的研究。CSPs是由含有巴比妥酸盐的π共轭分子之间的氢键形成的，以产生巨大的超分子单体。我们首先概述了形成 CSPs 所需的单体的分子设计、CSPs 独特的能量景观及其评估和分析方法，然后描述了 CSPs 的四个具体特性。首先是通过引入光响应单元如偶氮苯和二芳基乙烯部分来实现结构可控性。CSP 主链中这些光致变色分子的异构化对曲率有局部影响，并允许对其整个拓扑结构进行光控制。第二种是不同分子通过花环形成的共聚。这里讨论了两个极端的例子，嵌段共聚和交替共聚。第三，我们描述了涉及氢键重排的结构转变。这是一种新的特性，它能够从柔软且高度可溶的超分子聚合物结构转变为坚硬且难溶的晶体结构，从而扩展了 CSP 在环境重要和电子材料中的适用性。最后，自组装聚链烷被描述为一个全新的“拓扑自组织”的例子，它使用 CSP 表面上的 CSP 形成，即二次成核。这项工作也是我们 CSP 研究的一个转折点，包括广泛适用于创建自组织功能材料的概念。在本报告的最后，我们将讨论 CSP 如何作为单链聚合物材料为纳米技术或介观技术做出贡献。我们希望本文所描绘的景观能够指导各种新功能材料的开发。

更新日期：2022-01-07

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