Porphyrin Boxes: Rationally Designed Porous Organic Cages.

The porphyrin boxes (PB-1 and PB-2), which are rationally designed porous organic cages with a large cavity using well-defined and rigid 3-connected triangular and 4-connected square shaped building units are reported. PB-1 has a cavity as large as 1.95 nm in diameter and shows high chemical stability in a broad pH range (4.8 to 13) in aqueous media. The crystalline nature as well as cavity structure of the shape-persistent organic cage crystals were intact even after complete removal of guest molecules, leading to one of the highest surface areas (1370 m(2) g(-1)) among the known porous organic molecular solids. The size of the cavities and windows of the porous organic cages can be modulated using different sized building units while maintaining the topology of the cages, as illustrated with PB-2. Interestingly, PB-2 crystals showed unusual N2 sorption isotherms as well as high selectivity for CO2 over N2 and CH4 (201 and 47.9, respectively at 273 K at 1 bar).