Reimplementing Guest Shape Sorting of Nonporous Adaptive Crystals via Substituent‐Size‐Dependent Solid‐Vapor Postsynthetic Modification

Abstract 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 C 5 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.