Permanently porous cycloparaphenylene nanohoops via supramolecular engineering

Cycloparaphenylenes, also called carbon nanohoops, are a class of strained macrocycles recognized for their unique size-dependent optoelectronic properties, rich host-guest chemistry, and resemblance to carbon nanotubes. In this work, we establish carbon nanohoops as versatile tectons for permanently porous molecular crystals with well-defined supramolecular architectures and novel functionality. Using fluorinated nanohoops as precursors, we have synthesized seven new difluorodibenzodioxin-, methoxy-, and catechol boron bromide-functionalized derivatives. Structural characterization by single crystal X-ray and electron diffraction reveals porous structures stabilized by diverse noncovalent interactions, including π-π, CH-π, and boron-π interactions. In difluorodibenzodioxin nanohoops, robust intratubular π-π stacking guides the formation of nanotubular arrays with surface areas up to 910 m² g^-1, the highest value reported for cycloparaphenylenes to date. Remarkably, the nanotubular structure persists even in the presence of peripheral functionalization, enabling the formation of surface-decorated nanotubes. In contrast, boron bromide-derivatized nanohoops adopt an unusual 3D pore network that maximizes boron-π interactions. Due to the unique curvature of the carbon nanohoops, dense molecular packing is frustrated and the Lewis acidic boron centers remain partially exposed, leading to enhanced CO₂ binding. This work provides a blueprint on how substituted cycloparaphenylenes can be used to achieve permanently porous molecular materials with targeted structure and function.