The discovery and creation of new forms of carbon have always transformed the scientific landscape. For example, the discoveries of fullerenes, carbon nanotubes (CNTs), and graphenes have opened doors to the science of nanometer-sized carbon allotropes, otherwise known as nanocarbons. Since then, researchers worldwide have unveiled their outstanding physical and chemical properties, and a number of applications and technologies have arisen in not only materials science but also biological research fields. The synthesis and study of this privileged class of “single-molecule” compounds has become one of the most engaging subjects in chemistry and holds huge promise to establish new fields in molecular science. However, there have been huge gaps between established small-molecule chemistry and nanocarbon science. In the particular case of CNTs, it is still not possible to access structurally uniform CNTs. Although a wide range of synthetic methods have been reported, CNTs are generally accessed as a mixture of various structures. One logical strategy to achieve full synthetic control over CNTs is to build up from a template molecule with structural precision (the so-called “growth-from-template” strategy), where a short CNT segment molecule represents an initial synthetic target. To this end, organic synthesis techniques are our most powerful tools to synthesize short CNT segments such as carbon nanorings and carbon nanobelts. This Account highlights our 16-year campaign in the synthesis and application of carbon nanorings and carbon nanobelts. The first topic is the synthesis of carbon nanorings (cycloparaphenylenes) as substructures of CNTs. The second topic is the synthesis of armchair and zigzag carbon nanobelts, which consist solely of fully fused hexagonal rings and provide a continuous double-stranded cylindrical framework. The third topic is the synthesis of methylene-bridged cycloparaphenylene, an aromatic belt containing nonhexagonal rings, in which the cyclic paraphenylene chain is ladderized by methylene bridges. This nonalternant aromatic belt can be regarded as segments of nonconventional CNTs. During our extensive investigation, we found that the careful design of strainless macrocyclic precursors is crucial to the success of the synthesis of these curved π-conjugated nanorings and nanobelts. In the final section, some of the representative size-dependent properties of these nanorings/belts, including their HOMO–LUMO energies, strain energies, and photophysical properties, are summarized. In addition to basic properties, the utilization of these compounds as supramolecular hosts and organic materials is also briefly introduced. We hope this Account will inspire the development of new forms of nanocarbon molecules that would open doors to new fields and applications.

中文翻译：

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碳纳米环和纳米带的化学合成

新形式碳的发现和创造一直在改变科学格局。例如，富勒烯、碳纳米管 (CNT) 和石墨烯的发现为纳米级碳同素异形体（也称为纳米碳）的科学打开了大门。此后，世界范围内的研究人员揭开了其优异的物理和化学性质，不仅在材料科学领域，而且在生物研究领域也出现了许多应用和技术。合成和研究这一特殊类别的“单分子”化合物已成为化学中最具吸引力的学科之一，并有望在分子科学中建立新的领域。然而，已建立的小分子化学与纳米碳科学之间存在巨大差距。在碳纳米管的特殊情况下，仍然无法获得结构均匀的碳纳米管。尽管已经报道了广泛的合成方法，但碳纳米管通常以各种结构的混合物形式获得。实现对 CNT 的完全合成控制的一种逻辑策略是从具有结构精确性的模板分子构建（所谓的“模板生长”策略），其中短的 CNT 片段分子代表初始合成目标。为此，有机合成技术是我们合成碳纳米环和碳纳米带等碳纳米管短链段的最有力工具。该帐户重点介绍了我们在碳纳米环和碳纳米带的合成和应用方面的 16 年活动。第一个主题是合成碳纳米环（环对亚苯基）作为碳纳米管的亚结构。第二个主题是扶手椅和锯齿形碳纳米带的合成，它们仅由完全融合的六边形环组成，并提供连续的双链圆柱形框架。第三个主题是亚甲基桥连环对亚苯基的合成，这是一种含有非六方环的芳香带，其中环状对亚苯基链由亚甲基桥梯级化。这种非交替芳香带可以看作是非常规碳纳米管的片段。在我们的广泛研究中，我们发现无应变大环前体的精心设计对于这些弯曲的 π 共轭纳米环和纳米带的合成成功至关重要。在最后一部分，这些纳米环/带的一些具有代表性的尺寸相关特性，包括它们的 HOMO-LUMO 能量、应变能、和光物理性质，进行了总结。除了基本性质外，还简要介绍了这些化合物作为超分子主体和有机材料的利用。我们希望这个帐户将激发新形式纳米碳分子的开发，为新领域和应用打开大门。