A Relay-Type Solid-State Macrocyclic Host-Guest System for Selective Isomer Adsorption, Controlled Release, and Turn-On Colorimetric Sensing of 1-/2-Bromoalkanes.

Macrocycle-based adaptive crystals have gained significant attention for their precise adsorption and separation capabilities. However, achieving controlled analyte release under nonthermal stimuli remains a major challenge. Here, a relay-type solid-state host-guest system based on a fluorinated pillararene derivative, EtFLP6, is presented, which enables selective adsorption of 1-/2-bromoalkane isomers, room-temperature-controlled desorption, and turn-on colorimetric sensing. Activated EtFLP6 crystals selectively adsorb 1-bromoalkanes from mixtures of 1-/2-positional isomers and release them at room temperature upon introduction of electron-deficient aromatic acceptors (4-nitrobenzonitrile and 1,5-difluoro-2,4-dinitrobenzene), triggering a distinct color change from colorless to orange. Single-crystal structures incorporating X-ray powder diffraction and spectral analyses reveal that the desorption and color change result from the disassembly of solid-state host-guest complexes, driven by competitive binding with acceptors. This process is governed by the dynamic intermolecular interactions and selective molecular recognition of EtFLP6 in the solid state. This work bridges traditional macrocyclic adsorbents with functional organic cocrystals, offering a novel strategy for designing intelligent supramolecular materials.