Reversible C 60 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 (mPy) exTTF to the host-guest complex [C-60 subset of 1], leading to fullerene C-60 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-60 encapsulation. The C-60 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.