From molecular tweezers to pliers: a significant enhancement of fullerene grasping capability

Abstract

A molecular design leap from simple tweezers to precision pliers is achieved by substituting planar bisporphyrins with curved calixarenes. A series of pH-responsive cavitand hybrids that reversibly switch between vase and kite conformations has been synthesized. Host–guest experiments demonstrated that the rigid host 2a binds to C₆₀ more strongly, whereas the flexible host 2b binds to C₇₀ (2.47 × 10⁵ M⁻¹) with higher affinity. These are the highest binding constants reported to date for a supramolecular host–guest complex involving partial-wrapping fullerenes that can be subsequently released on demand.