A Flexible HOF with Reversible Structural Transformation for Selective Separation of Chlorobenzene from Chlorocyclohexane

The separation of chlorobenzene (ClBz) and chlorocyclohexane (ClCy) represents a critical industrial challenge owing to their similar boiling points and polarities, which renders traditional distillation energy-intensive and inefficient. Herein, we report a novel flexible hydrogen-bonded organic framework (HOF), X−HOF−12, assembled from a non-planar tetracyano-functionalized 1,4-dihydropyrrolo[3,2-b]pyrrole building block (DPTCN). Single-crystal X-ray diffraction demonstrates that X−HOF−12 adopts a three-dimensional hydrogen-bonded network with penetrating channels, where guest ClBz molecules are stabilized by multiple CN···Cl and C−H···π interactions. Upon thermal removal of ClBz, X−HOF−12 undergoes a reversible structural transformation to a dense, nonporous phase (X−HOF−12a). X−HOF−12a displays exceptional selective adsorption of ClBz over ClCy through a guest-responsive “open-gate” adsorption mechanism, and the purity of ClBz released from the HOF reaches 94.81%. Furthermore, the material preserves high selectivity and structural integrity over multiple adsorption−desorption cycles. This work not only offers a high-performance flexible HOF adsorbent for energy-efficient ClBz/ClCy separation but also provides a design principle for constructing guest-responsive porous materials for precise molecular separations.