Anisotropic Contraction of a Polyaromatic Capsule and Its Cavity-Induced Compression Effect.

Anisotropic contraction of a spherical polyaromatic capsule was demonstrated through simple meta-to-ortho modification of the bent polyaromatic ligands. The resultant capsule, composed of two metal ions and four ortho-substituted ligands, possesses a spheroidal cavity (1.1 nm × 1.5 nm × 1.5 nm) fully encircled by a polyaromatic framework. One large planar or bowl-shaped molecule (e.g., porphine or sumanene) is quantitatively bound by the capsule, in which the cavity-induced compression effect causes the acceleration of the bowl-to-bowl inversion of sumanene. Temperature-dependent 1H NMR analysis revealed that the activation energy of the inversion decreases greatly (ΔG⧧ = -2.8 kcal mol-1 at 318 K) upon encapsulation, whereas the opposite effect was observed in the spherical cavity of the previous polyaromatic capsule.