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.