A pH-Responsive Cu-Corrole-Based Cage That Reversibly Encapsulates Fullerene in a Shapeshifting Low-Symmetry Cavity.

Artificial hosts combining chemical functionalities (recognition sites and stimuli-responsive behavior) in a low-symmetrical and guest-adaptive environment are of major interest to better understand and mimic protein receptors. However, molecular cages are generally restricted to symmetrical cavities built from rigid subunits. For instance, porphyrin building blocks have a time-honored role in the preparation of receptors and confined catalysts. Here, we introduce a new design for molecular cages based on corroles, the low-symmetry analogue of porphyrins, breathing life into desymmetrized cavities. A (CuIII)corrole complex was equipped with a shapeshifting cyclotriveratrylene (CTV) roof via pH-responsive side arms. The latter enables the first metallocorrole-based cage CuIII(Hm-Cor) to reversibly bind fullerenes in a unique low-symmetry, conformationally adaptive, and pH-responsive cavity. Experimental and computational studies evidence flipping of the CTV roof upon fullerene binding, enabling structural reconfiguration of the host to adapt its size and shape to selectively accommodate the guest. Such conformational change also responds to the protonation of the cage's side arms. This pH-responsive cavity allows fullerene release and reuse of the host. Beyond establishing a key precedent for preparation of caged metallocorroles, the present study provides a unique approach for the on-demand fullerene encapsulation in a low-symmetry environment, enabling precise positioning of the guest and control over its functionalization.