Carbon Nanorings and Nanobelts: Material Syntheses, Molecular Architectures, and Applications

Abstract

Carbon nanorings (CNRs) and carbon nanobelts (CNBs) of various sizes and innovative molecular architectures have ushered improvement in research in recent years. This serves as a prerequisite for further advances and applications, such as organic semiconductors and bottom‐up synthesis of single‐walled carbon nanotubes. Nevertheless, challenges such as high strain energy, excessive reactivity, end‐product stability, low‐scale yields, and side reactions inhibit material synthesis and applications. In this review, CNRs, CNBs, and other heteroatom‐doped molecular belts are discussed based on their molecular structural characteristics, with a special focus on their developments in the past two years. Furthermore, current applications, research obstacles, and future developments related to CNRs and CNBs are discussed. For the first time, studies and advancements in organic field‐effect transistors (OFETs) have been summarized in detail.

Enumeration, Nomenclature, and Stability Rules of Carbon Nanobelts

“…Moreover, owing to their double-stranded cylindrical skeleton, the radial π-conjugation in CNBs brings about more efficient orbital overlaps than those of the linear conjugation. As a result, CNBs are supposed to have remarkable charge transport properties and be generally more conductive than linear conjugated semiconductors, which was confirmed by both experimental and computational studies . Lastly, photophysical measurements , and excited-state simulations , demonstrated that CNBs exhibit peculiar photophysical and fluorescent properties, and as envisioned in ref , we could make use of the supramolecular chemistry of CNBs to modulate these properties by varying the guest species.…”

“…The translation vector, T⃗ = n ′ a 1 → + m ′ a 2 → , which is perpendicular to C⃗ , becomes the periodic (axial) direction of the resultant CNT. Accordingly, CNB structures have usually been designated the same chiral indices ( n , m ) as those for the CNTs where the CNBs are cut out from. ,− ,, Figure a demonstrates the construction of CNB (7,0) (represented by green rings) by rolling up the graphene nanosheet along the horizontal direction, C⃗ = O C = 7 a 1 → .…”

“…Carbon nanobelts (CNBs) are an intriguing family of aromatic macrocyclic hydrocarbons that have recently received escalating attention in the chemical community. − Structurally, they can be regarded as sidewall cutouts of carbon nanotubes (CNTs) and are conventionally defined as closed molecular loops consisting solely of fully unsaturated and fused benzene rings. Compared with the analogous carbon nanorings (CNRs), ,− for a CNB, we need to break at least two C–C bonds to open its macrocyclic framework, whereas the cleavage of only one bond is required in the CNR case. , As a more strict definition, CNBs are considered by many chemists as double-stranded structures with a single layer of benzene rings, ,,,− although multilayered nanobelts, such as the Vögtle belt, , are also frequently known. ,, …”

“…The distinctive structures of CNBs endow them with unique properties and potential applications in electronics, photonics, and optoelectronics. First, CNBs have been proposed as molecular seeds or templates for the bottom-up, precise synthesis of uniform, single-chirality CNTs, which is regarded as one of the ultimate goals in the CNT industry. , As another application in synthetic chemistry, CNBs can be exploited as building blocks for making more complex nanocarbon architectures, as exemplified by the synthesis of cycloiptycenes from CNBs . On the other hand, the electron-rich macrocyclic framework of CNBs makes them ideal hosts to selectively capture guest molecules .…”

Carbon Nanobelts: Brief History and Perspective

“…In addition to aromatic hydrocarbon-based CNBs, heteroatom-embedded CNBs have also been reported. − In 2019, Tanaka et al synthesized the first oxygen-embedded CNB by rhodium-catalyzed alkyne cyclotrimerization . Since then, CNBs with various topologies such as the armchair, zigzag, and Möbius-type CNBs, have been synthesized through the strategy developed by Tanaka’s group. − Nitrogen-embedded CNBs have also been synthesized by our group, Wu et al, and Chen et al − These heteroatom-containing nanobelts are also one of emerging molecules because of their unique properties derived from synergies between nanobelts and heteroatoms . Phenine nanotubes, which were first synthesized by Isobe et al in 2019, are also a kind of nanobelts when referring to the definition by Scott. , Long segments of CNTs are of great interest and should be one of the ultimate targets in synthetic chemistry.…”