N-Bordered Rylene Arches via Programmable Curved π-Extension

Curved molecular carbons have attracted considerable interest owing to their distinctive properties relative to planar analogues and their structural relevance to diverse nonplanar carbon allotropes. Aromatic ribbons with continuously and directionally curved π-surfaces, predicted as key building blocks for circular carbon architectures, remain challenging synthetic targets, with only a few examples reported to date. Herein, we report the synthesis and properties of arch-shaped nitrogen-bordered nanoribbons featuring rylene backbones fused with five-membered rings at the armchair edges, achieved through a programmable curved π-extension strategy. X-ray crystallography reveals well-defined arched topologies and continuously curved π-surfaces, while variable-temperature proton nuclear magnetic resonance experiments and theoretical calculations demonstrate high arch-to-arch inversion barriers. The resulting quaterrylene arch exhibits an enhanced fluorescence quantum yield in solution and forms host-guest complexes with fullerene C₆₀ in both solution and the solid state. This work provides a foundation for the synthesis of long-sought-after carbon nanobelts.