Polymorphism of [6]cycloparaphenylene for packing structure-dependent hostguest interaction

Molecular carbon nanorings, [n]cycloparaphenylenes ([n]CPP), are a unique class of porous molecules with allbenzene surface. Herein, we report the preparation of polymorphs of [6]CPP crystals for the first time, and the discovery of their packing structure-dependent properties. We found that the herringbone-packed structure is thermodynamically more stable than the tubular-packed structure. We revealed that their hostguest interaction depends on the packing structures of [6]CPP: the tubular-packing affords one-dimensional open channels for weak guest sorption, while the herringbone-packing gives closed cavities for strong guest entrapment. This study exemplifies that the solid-state hostguest chemistry of CPP crystals can be directed by controlling their packing structures.