In the ever-evolving field of nanotechnology, carbon continues to astonish. From diamond to graphene, this element has a remarkable ability to reinvent itself at the atomic scale. Now, scientists are uncovering a new carbon-based marvel: single-walled carbon nanobelts (CNBs).

Structurally, CNBs are tiny loops of curved graphene. More precisely, they are short belt-like slices of single-walled carbon nanotubes (SWCNTs) with unique shapes that confer exceptional electronic properties. Already they have been identified as being ideal candidates for applications in nanoscale electronics and flexible optoelectronic devices.

Despite their promise however, synthesising CNBs is a formidable challenge.

Most synthesised nanobelts have an all-benzenoid structure, with benzene rings fused along the zigzag edge of the backbone. In such structures, electrons do not flow freely across the entire molecule but are instead confined to individual benzene rings. This limits their electronic properties and reduces their usefulness in practical devices.

More ambitious targets, such as fully conjugated cyclacenes suffer from extreme strain and instability. Their curved geometry introduces high reactivity, often resulting in partial or degraded forms during synthesis.

Synthetic strategy

To overcome these limitations, Associate Professor Chi Chunyan from NUS Chemistry developed a new class of fully π-conjugated, non-alternant pentagon-embedded CNBs that allows better electronic properties through deoxygenative aromatisation approach, a chemical process that forms aromatic rings by removing oxygen atoms from oxygenated precursors. In this strategy, oxo-bridged belt precursors are synthesised via a Diels–Alder reaction between benzyne and furan derivatives. These intermediates are then subjected to reductive aromatisation using tin(II) chloride (SnCl₂) and hydrobromic acid (HBr), affording two fully π-conjugated carbon nanobelts of different sizes. The stepwise buildup of strain energy, together with the moderate overall strain in the final structures, accounts for the successful formation of both nanobelts—long-standing targets in synthetic chemistry.

These CNBs showed improved electronic properties, including stronger red-light emission and smaller energy gaps. These features are particularly important for advancing technologies that rely on efficient light-matter interactions, such as organic photovoltaic (solar cell) and organic light-emitting diodes (OLEDs). Moreover, the smaller carbon nanobelt can be oxidised to its dicationic form, which possesses an open-shell singlet ground state and exhibits intriguing global aromaticity.

Theoretical studies suggest that the dication adopts a structure consisting of two weakly coupled [32]annulenes with Baird-type aromaticity along its edges. As charge separation plays a pivotal role in organic semiconducting devices, this insight offers a deeper understanding of the electronic delocalisation behaviour of CNBs in their charged states.

This study presents a new strategy for the design and synthesis of carbon nanobelts and related complex carbon nanostructures with enhanced π-conjugation and electron delocalisation. No longer appreciated solely for their topological novelty, these all-carbon systems are now emerging as functional materials with promising applications as topological organic semiconductors. Their ability to support spin-state manipulation suggests potential use in devices that are faster and more energy-efficient than traditional charge-based electronics. Additionally, their lightweight, chemically robust, and synthetically tunable nature offers a compelling alternative to conventional magnetic materials, positioning CNBs as attractive candidates for the development of next-generation quantum materials and spintronic technologies.

“Our discoveries provide a new platform for exploring the behaviour of correlated electrons in a highly controlled, tunable carbon-based system,” Chi explained.

As carbon nanobelts transition from synthetic challenge to functional platform, their future looks increasingly dynamic. With an all-carbon modular design, CNBs offer a versatile foundation for engineering next-generation materials. As fabrication techniques advance and theoretical models deepen, CNBs are poised to become powerful tools not just in nanotechnology, but in reimagining the very architecture of future electronics and quantum systems.