Adaptive Pillar[5]arene Co-Crystals Showing Vapochromic Behavior to 5-Membered Heterocyclic Compounds

Macrocycle-based crystalline materials have recently gained significant attention in supramolecular chemistry for their vapor adsorption properties in the solid state. Here, we demonstrate that the binary adaptive co-crystals (P5-PDIα), assembled from electron-rich pillar[5]arene (P5) and an electron-deficient pyromellitic diimide derivative (PDI), show selective vapochromic behavior toward 5-membered heterocyclic compounds (5-MHCs). The co-crystals undergo remarkable color transitions from white to yellow or orange upon exposure to specific vapors. Powder and single-crystal X-ray diffraction analyses confirm that these chromic behaviors originate from vapor-induced solid-state structural rearrangements, resulting in the formation of charge-transfer (CT) cocrystals. Notably, spin-coated thin films of the P5-PDI system maintain excellent vapochromic performance with remarkable reversibility and cycling stability.