Tunable enforced cavities inside self-assembled capsules‡

Controlling and tuning the molecular recognition properties is a crucial task in host–guest chemistry. The size and dimension of the guest-binding space inside self-assembled capsules 1a–c is successfully determined by installing the substituents at the 6′-position of 2,2′-bipyridyl arms. X-ray diffraction analysis and DFT calculations at the M06-2X/6-31G(d,p)+LanL2DZ level of theory demonstrate that the p-methoxyphenyl group expands the dihedral angle of the 2,2′-bipyridyl arms through its π-stacking interaction to the 2,2′-bipyridyl arm, whereas the steric interaction of the isopropyl group to the neighboring bipyridyl arm slightly reduces the dihedral angle of the two bipyridyl groups. The Cu(I)-united 2,2′-bipyridyl arms function as a hinge; accordingly, installing the p-methoxyphenyl group extends the cavity by ca. 2 Å, whereas the isopropyl group shrinks the cavity more than that of the capsule 1a with methyl groups at the 6′-positions. These steric interactions influence the molecular recognition of the capsules 1a–c for rigid ditopic guest 2a as well as flexible ones 2b–f. The guest selectivity inside the enforced cavity is determined by varying the substituents.