Narrow carbon pentaheptite nanoribbon as a covalent metal

Metallic carbon-based nanoribbons are sought after^1,2 as atomically defined one-dimensional conductors with potential relevance to future carbon-based electrodes and interconnects³, ideally with quantum-limited conductance comparable to metallic carbon nanotubes⁴. Metallic graphene nanoribbons have been realized by band engineering, notably through zero-mode superlattices¹. However, atomically precise metallic nanoribbons of fully non-benzenoid carbon allotropes, such as the theorized metallic carbon pentaheptites^5,6, remain unexplored. The realization of these nanoribbons could enable bottom-up fabrication of all-carbon electronics^7,8 compatible with semiconducting graphene nanoribbons^9-13 and nanographenes^14,15, along with their fascinating properties^16-20. Here we report a hierarchical approach for the on-surface synthesis of planar carbon pentaheptite nanoribbons (CPHNs) by laterally fusing well-aligned polypentalene chains transformed from pre-synthesized polycyclooctadiene chains. Two distinct types of narrow pentaheptite nanoribbon share a similar basal structure consisting of a central heptagon chain flanked by either identically (CPHN 1) or differently (CPHN 2) oriented polypentalene chains on opposite lateral edges. CPHN 1 is an intrinsic metal, whereas CPHN 2 is a narrow-bandgap semiconductor. The CPHN 1 ribbon exhibits near-ballistic conductance approaching one conductance quantum, comparable to metallic carbon nanotubes⁴. This highlights CPHN 1 as a promising planar carbon metal and suggests a possible route towards carbon quantum wires, although further synthetic optimization will be required for device integration.