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Porous Organic Cage Nanocrystals by Solution Mixing

Hasell, Tom, Chong, Samantha Y., Jelfs, Kim E., Adams, Dave J., Cooper, Andrew I.
Journal of the American Chemical Society 2012 v.134 no.1 pp. 588-598
chemical interactions, dispersions, mixing, nanocrystals, particle size, porosity, porous media, solubility, solvents, stereoisomerism, surface area, surfactants, temperature
We present here a simple method for the bottom-up fabrication of microporous organic particles with surface areas in the range 500–1000 m² g–¹. The method involves chiral recognition between prefabricated, intrinsically porous organic cage molecules that precipitate spontaneously upon mixing in solution. Fine control over particle size from 50 nm to 1 μm can be achieved by varying the mixing temperature or the rate of mixing. No surfactants or templates are required, and the resulting organic dispersions are stable for months. In this method, the covalent synthesis of the cage modules can be separated from their solution processing into particles because the modules can be dissolved in common solvents. This allows a “mix and match” approach to porous organic particles. The marked solubility change that occurs upon mixing cages with opposite chirality is rationalized by density functional theory calculations that suggest favorable intermolecular interactions for heterochiral cage pairings. The important contribution of molecular disorder to porosity and surface area is highlighted. In one case, a purposefully amorphized sample has more than twice the surface area of its crystalline analogue.