A swing-type solid-state host–guest system enabling spontaneous adsorption–desorption cycling

Macrocycle-based solid-state adsorbents offer molecularly precise platforms for the selective capture of volatile organic molecules. However, regeneration of these materials commonly relies on thermal or solvent stimulation, limiting energy efficiency and the recovery of adsorbed molecules. Developing solid-state adsorption systems that enable reversible guest release under mild conditions remains challenging, particularly for structurally similar volatile molecules. Here we show a swing-type solid-state host–guest system based on a fluorinated pillar[5]arene that enables reversible adsorption–desorption cycling of volatile methylpyridines at ambient temperature without heat or solvent stimulation. Competitive binding of nonvolatile electron-deficient acceptors drives the transformation of volatile guest inclusion phases into charge-transfer phases, releasing the volatile guests and producing a visible chromic response. Re-exposure to excess volatile vapor reverses the phase transformation, with the direction and extent of switching influenced by the relative stability of the competing host–guest assemblies and further modulated by guest size and lattice accessibility. These findings highlight an appropriate degree of thermodynamic proximity between competing solid-state complexes as an important design consideration for reversible guest exchange. More broadly, this strategy provides a route to adaptive macrocycle-based adsorbents for low-energy, visually traceable adsorption–desorption processes. Solid-state host–guest complexes derived from macrocycles provide a direct pathway from molecular recognition to adaptive functional materials, but desorption typically requires thermal activation. Here, the authors report a solid-state host–guest system with a swing-type adsorption–desorption cycle without heat or solvent stimulation.