Reversible C Ejection from a Metallocage through the Redox-Dependent Binding of a Competitive Guest.

The reversible encapsulation of a tetrapyridyl extended-tetrathiafulvalene (exTTF)-based ligand (m-Py)exTTF by a tetragonal Zn-porphyrin-based prismatic nanocage (1) is described. The reversible uptake and release of the (m-Py)exTTF guest proceeds through drastic electronic and conformational changes occurring upon oxidation of the latter. This reversible system has been explored in a guest-exchange process, by addition of (m-Py)exTTF to the host-guest complex [C ⊂1], leading to fullerene C ejection from the host cavity. Remarkably, the subsequent redox-triggered ejection of (m-Py)exTTF, leads to the recovery of the empty cage 1, which remains available for further C encapsulation. The C ejection is justified by the preferable coordination of the pyridine anchors of (m-Py)exTTF to the two Zn-porphyrin units of 1. This approach, based on the use of a switchable competitive guest, offers a promising new strategy for guest-delivery control.