Selective Loading of Xylene Isomers in Self-Assembled Triphenylamine bis-Urea Macrocycles

Supramolecular self-assembly of brominated triphenyl amine bis-urea macrocycles leads to the formation of porous organic crystals with small elliptical 4.3 angstrom x 6.5 angstrom unidirectional pores. Here, this porous material has been applied in a simple vapor loading technique for the enrichment of isomeric mixtures of xylene. The host exhibits selectivity toward loading linear isomers present in the mixture that better match the channel topography. The same crystals were reused for multiple separations, highlighting the robust nature of the crystals. Host-guest complexes with each xylene constitutional isomer as well as with ethylbenzene were separately prepared by single-crystal-to-single-crystal guest exchange and their structures analyzed by single-crystal X-ray diffraction. Room-temperature xylene isomer enrichment employing these porous organic crystals provides insight toward energy efficient alternatives for separating complex petrochemical feed mixtures.