Programming Host-Guest Interactions in Covalent Organic Frameworks with Arylazopyrazole Photoswitches

Programming host-guest interactions in porous crystalline materials using external stimuli offers a promising strategy for adaptive molecular separations but remains challenging because adsorption is often governed by pore structure rather than tunable molecular interactions. Here, we report a series of photoresponsive covalent organic frameworks (LACOF-1) incorporating arylazopyrazole (AAP) photoswitches that enable light-controlled modulation of CO₂ adsorption through molecular photoisomerization. The framework-embedded AAP units undergo efficient E-Z photoisomerization with an exceptional thermal half-life of ∼76 days while preserving crystallinity and permanent porosity of the framework. Despite exhibiting a lower surface area than the corresponding Z-state, the E-state displays stronger CO₂ adsorption enthalpies, demonstrating that adsorption can be regulated independently of overall pore accessibility. Combined molecular simulations and density functional theory calculations reveal that this behavior arises from enhanced local CO₂ binding within adsorption pockets created by the extended E-AAP configuration. These molecular-level changes translate directly into reversible dynamic CO₂ capture under dry, dilute, and humid conditions, with excellent cycling stability and facile regeneration under ambient conditions. This work establishes molecular photoswitching as an effective strategy for programming adsorption energetics in crystalline porous materials and provides a general design principle for adaptive, stimulus-responsive gas separations.