Separation of Cyclohexanone and Cyclohexanol by Adaptive Pillar[5]arene Cocrystals Accompanied by Vapochromic Behavior

The separation of cyclohexanone (CHA-one) and cyclohexanol
(CHA-ol)
mixtures is of great importance in the chemical industry. Current
technology exploits multiple steps of energy-intensive rectification
due to their close boiling points. Herein, we report a new and energy-efficient
adsorptive separation method employing binary adaptive macrocycle
cocrystals (MCCs) built with π-electron-rich pillar[5]arene
(P5) and an electron-deficient naphthalenediimide derivative (NDI)
that can selectively separate CHA-one from an equimolar CHA-one/CHA-ol
mixture with >99% purity. Intriguingly, this adsorptive separation
process is accompanied by vapochromic behavior from pink to dark brown.
Single-crystal and powder X-ray diffraction analyses reveal that the
adsorptive selectivity and vapochromic property are derived from the
CHA-one vapor inside the cocrystal lattice voids triggering solid-state
structural transformations to yield charge-transfer (CT) cocrystals.
Moreover, the reversible transformations make the cocrystalline materials
highly recyclable.