Alkyl Chain Length-Selective Vapor-Induced Fluorochromism of Pillar[5]arene-Based Nonporous Adaptive Crystals

Developing new vapochromic fluorescent sensing materials with selectivity is in great demand due to serious air pollution caused by volatile organic compounds. Here we report the first nonporous adaptive crystals with vapor-induced fluorochromism. The emission of anthracene conjugated pillar[5]­arene P5en crystals blue shifts from bright yellow to green upon exposure to vapors of linear alkyl ketones with alkyl chain length selectivity. Powder and single crystal X-ray diffraction analyses reveal the relationship between vapor-induced crystal structural transformation and fluorochromism. After exposure to 2-butanone, 2-pentanone, and 2-hexanone, the anthracene groups in P5en exist as monomers in the solid state, while after exposure to heptanone and octanone, the anthracene groups instead aggregate as excimers in the solid state. By solid-state NMR and thermogravimetric analysis, we further find that the size fit between ketone molecules and interspaces in P5en crystals lead to the alkyl chain length selectivity. This work provides a new strategy to design vapochromic fluorescent crystalline materials and crystalline transformation systems.