Permanently porous cycloparaphenylene nanohoops via supramolecular engineering

Abstract

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.