Polymorphism of [6]Cycloparaphenylene for Packing Structure-dependent Host–Guest Interaction

Molecular carbon nanorings, [n]cycloparaphenylenes ([n]CPP), are a unique class of porous molecules with all-benzene 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 host–guest 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 host–guest chemistry of CPP crystals can be directed by controlling their packing structures.