A Mechanical sp 2 ‐ Jail for C 60 Fullerene

Being an iconic spherical molecule exclusively composed of sp 2 carbon atoms, the development of increasingly efficient synthetic receptors for C 60 fullerene remains a pressing challenge in supramolecular chemistry. However, as tighter hosts that employ most of their cavity volumes to complementarily encapsulate C 60 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 sp 2 ‐receptor that acts as a “mechanical jail” for C 60 . 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 ( K a > 10 9 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.