A Mechanical sp2-Jail for C60 Fullerene.

Being an iconic spherical molecule exclusively composed of sp2 carbon atoms, the development of increasingly efficient synthetic receptors for C60 fullerene remains a pressing challenge in supramolecular chemistry. However, as tighter hosts that employ most of their cavity volumes to complementarily encapsulate C60 are developed, steric constraints may emerge that mechanically trap this ball-shaped guest within their lumen. Here we explore this unprecedented scenario with a rigid bisporphyrin sp2-receptor that acts as a "mechanical jail" for C60. This exceptional host presents the tightest 3D cavity reported for this spherical guest, occupying 77% of the internal volume and enabling strong π-π and CH⋯π interactions, which result in exceptionally high binding affinities (Ka > 109 M- 1). Unlike related cage and basket analogues, encapsulation in this perfectly fitted host is kinetically hindered, leading to guest release dynamics that are extremely slow above 400 K and essentially suppressed at room temperature.