Flexible Hydrogen-Bonded Organic Framework with Anthracene Core for Recognition of Benzene Over Cyclohexane

Flexibility is considered one of the most critical features of framework materials, playing a vital role in applications such as adsorption and separation. Hydrogen-bonded organic frameworks (HOFs) exhibit unique flexibility derived from their weak, reversible hydrogen-bonding interactions; however, realizing controlled and functional flexible behavior in HOFs remains a synthetic challenge. Herein, we report a flexible hydrogen-bonded organic framework, HOF-FJU-119, constructed from an anthracene-core, that exhibits multimode guest-responsive behavior. Upon activation, HOF-FJU-119a undergoes distinct gate-opening transformations in response to CO₂ at 196 K and benzene vapor at room temperature. Single-crystal X-ray diffraction (SCXRD) and vapor adsorption isotherms reveal the emergence of new adsorption sites in the benzene-loaded phase, driven by strong interactions and the flexibility of C≡N⋯H─C hydrogen bonds, enabling selective benzene/cyclohexane separation. Notably, the adsorption of benzene induces a visible color change in fluorescence emission and a red shift of approximately 60 nm. Structural and density functional theory (DFT) analyses confirm increased molecular planarity, extended conjugation, and a narrowed bandgap. This work demonstrates a rare integration of selective adsorption, molecular recognition, and signal transduction within a single crystalline framework, offering a versatile platform for the development of intelligent porous materials with real-time visual tracking capabilities.