Revealing the mechanism behind the highly selective separation of 1,4-butyrolactone from n-methylpyrrolidone using nonporous adaptive crystals of perethylated pillar[5]arene

N-Methylpyrrolidone is widely used across various sectors; however, the energy-efficient removal of 1,4-butyrolactone impurity from NMP remains a significant challenge due to their nearly identical molecular size and properties. Herein, we synthesize a series of flexible molecular materials, perethylated pillar[n]arene (n = 5, 6) with enhanced crystallization efficiency under the induce of dichloromethane solvent. Through a size-specific recognition and varied host–guest interaction, EtP5 demonstrates exceptional 99 % selectivity for GBL against NMP; single-crystal structure analyses and theoretical calculations unveil intricate C-H···O hydrogen bonding interactions, and π-π stacking interactions between EtP5 and GBL. The single-crystal structure of the two-guest complexes has proved the existence of adsorption transition states, and it comprehensively elucidates the dynamic adsorption process of EtP5 with GBL, supported by theoretical calculations. Reuse experiments validate these crystals could be fully reused without loss of performance.