Porous Organic Cages: A modular and Predictable Alternative to Nanoporous Networks

摘要

Research in nanoporous frameworks~1 has shown explosive growth recently, prompted by societally important applications in separation, energy storage, catalysis, and gas sequestration. Empirical rules exist for the assembly of these frameworks based upon the geometry and bonding patterns of the constituent nodes and linkers. It is still challenging, however, to control the placement and segregation of mixed functionality in three-dimensional porous solids. Indeed, recent studies on mixed frameworks suggest a tendency for random distribution of functionalities throughout the pores~(2-3) rather than, for example, the functional group localisation found in the reactive sites of enzymes~4. 'One-pot' chemical syntheses of porous frameworks from relatively simple starting materials may ultimately limit our scope to mimic more complex, compartmentalized biological structures. An alternative strategy is to prepare nanoporous solids from molecular organic pores~(5-16). In principle, functional pore modules could be covalently prefabricated and then assembled in a mix-and-match fashion to produce materials with specific properties~(7,11). We show here that ordered porous solids can be produced via the cocrystallization of two or more different organic cage modules via chiral recognition. The constituent modules are synthesized on gram scales and in high yields in a one-step procedure. Moreover, assembly of the porous cocrystals is as simple as combining the modules in solution and removing the solvent, thus leading to thermally-stable nanoporous solids. The method is not limited to one molecular combination but can be generalised based on the recognition of chirality between modules in a lock-and-key assembly that has analogues in biochemistry. We also show that the assembly mode can be predicted a priori, in a manner that is currently unique for porous solids (Fig. 1). We will also discuss for the first time the extension of this strategy to ternary cocrystals containing three or more separate modules (Fig. 2).