Postsynthetic modification (PSM) has been widely used in porous crystalline materials to gain better performance in adsorptive separation of gases or hydrocarbons. We here report that guest adsorption selectivity in a kind of nonporous crystalline materials, namely nonporous adaptive crystals (NACs), can be readily and precisely tuned via a facile substituent-size-dependent solid-vapor PSM method. Before PSM, NACs of pillar[4]arene[1]quinone EtP4Q1 show negligible selectivity for C5 hydrocarbons. PSM with a larger substituent, cyclopentylamine, onto EtP4Q1 NACs does not improve the selectivity, while EtP4Q1 NACs after PSM with a slightly smaller substituent, cyclobutylamine, is endowed with very high preference of n-pentane over cyclopentane. Comprehensive structural analyses confirm that the intermolecular interactions among the host compounds and host-guest interactions between the adsorbent and the adsorbate are the two major factors in determining the guest selectivity.
Keywords: Host-Guest Systems; Molecular Separations; Nonporous Adaptive Crystals; Postsynthetic Modification; Supramolecular Chemistry.
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