Controlled Hierarchical Self-Assembly of Catenated Cages

Constructing hierarchical
superstructures to achieve comparable
complexity and functions to proteins with four-level hierarchy is
challenging, which relies on the elaboration of novel building blocks
with complex structures. We present a series of catenated cages with
unique structural complexity and tailorability. The rational design
was realized as such: A catenane of two symmetric cages (CSC), CSC-1, with all rigid imine panels was converted to a catenane
of two dissymmetric cages (CDC), CDC-1, with two exterior
flexible amine panels, and CDC-5 was tailored from CDC-1 by introducing an additional methyl group on each blade
to increase lateral hindrance. CDC-1s with the most irregular
and flexible configuration formed supramolecular dimers, which self-organized
into 3D continuous wavelike plank with a three-level hierarchy, previously
undiscovered by conventional building blocks. A drastically different
3D triclinic crystalline phase with a four-level hierarchy and trigonal
phase with a three-level hierarchy were constructed of distorted CSC-1s and the most symmetric CDC-5s, respectively.
The wavelike plank exhibited the lowest order, and the triclinic phase
had a lower order than the trigonal phase which had the highest order.
It correlates with the configuration of the primary structures, namely,
the most disordered shape of CDC-1, the low-order configuration
of CSC-1, and the most ordered geometry of CDC-5. The catenated cages with subtle structural differences therefore
provide a promising platform for the search of emerging hierarchical
superstructures that might be applied to proton conductivity, ferroelectricity,
and catalysis.