π-Armor: Shape-Complementary Encapsulation of Aromatics

Host-guest binding can be classified into two well-separated modes, i.e., reversible binding under thermodynamic control and permanent encapsulation via kinetic trapping during host formation. However, combining both modes within a single π-conjugated host on the basis of host-guest shape complementarity has remained challenging. Here, we present the design and synthesis of a neutral D3-symmetric π-conjugated cage (1), wherein two curved hexa-cata-hexabenzocoronene (c-HBC) panels are bridged by dibenzodiazocine (DBDA) units to form three orifices and a biconvex nanocavity. Cage 1 reversibly encapsulates aromatic guests, whereby binding affinities are governed by dispersion arising from shape complementarity. In contrast, bulky guests that are too large to pass through the orifices are incorporated during cage formation and permanently entrapped, affording thermally robust carceplexes. Even a π-extended guest exceeding the cavity size was entrapped, with its aryl groups protruding through the three orifices to form a mechanically interlocked molecule. Thus, cage 1 behaves as a dual-mode host controlled by shape complementarity, representing a "π-armor" that sandwiches aromatic guests between its π-surfaces.