Separation of p‑Xylene from C8 Alkylaromatics by Nonporous Adaptive Crystals of Leggero Pillar[4]arene[1]quinone

The separation and purification of C8 aromatics under nonthermal conditions remain a significant challenge in the chemical industry. Here, we report a new leggero pillararene containing one benzoquinone unit, namely, leggero pillar[4]­arene[1]­quinone (P­[4]­Q­[1]­L), which exhibits excellent guest sorting ability and vapochromic properties. Nonporous adaptive crystals (NACs) of P­[4]­Q­[1]­L can adsorb p-xylene from equal volume mixtures of C8 aromatics with high purity (97.5%), along with a color change from red to black. Single-crystal structures and powder X-ray diffraction data reveal that the high selectivity is attributed to the fact that p-xylene can trigger the structural rearrangement of P­[4]­Q­[1]­L NACs and form the corresponding host–guest assembly in the solid state. Moreover, P­[4]­Q­[1]­L NACs material is highly recyclable, because of the reversible transformation between guest-free and guest-loaded structures.