Rational Design and Construction of Hierarchical Superstructures Using Shape-Persistent Organic Cages: Porphyrin Box-Based Metallosupramolecular Assemblies

We
report a new approach to building hierarchical superstructures
using a shape-persistent porous organic cage, which acts as a premade
secondary building unit, and coordination chemistry. To illustrate
the principle, a zinc-metalated porphyrin box (Zn-PB),
a corner-truncated cubic porous cage, was connected by suitable dipyridyl
terminated bridging ligands to construct PB-based hierarchical
superstructures (PSSs). The PSSs were stabilized
not only by the coordination bonds between Zn ions and bipyridyl-terminated
ligands but also by π–π interactions between the
corners of the Zn-PB units. By varying the length of
the linker, we identified an optimum range of the linker length for
construction of PSSs. The PSSs have large
void volumes and an extrinsic surface area compared to the parent
PBs, which can be exploited for the selective encapsulation and interior
functionalization of the PSSs for various applications,
including catalysis. We observed that singlet oxygen induced synthesis
of the natural product, juglone, is more efficiently catalyzed by PSS-1 than its constituent component Zn-PB.