Reversible Light-Controlled CO Adsorption via Tuning π-Complexation of Cu⁺ Sites in Azobenzene-Decorated Metal-Organic Frameworks

Light-responsive adsorbents capture significant attention due to their tailorable performance upon light irradiation. The modulation of such adsorbents is mainly based on weak (physical) interactions caused by steric hindrance while tuning strong interaction with target adsorbates is scarce. Here we report smart π-complexation adsorbents, which can adjust the π-complexation of active sites via light irradiation. A typical metal-organic framework, MIL-101-NH₂, was decorated with azobenzene motifs, and Cu⁺ as π-complexation active sites were introduced subsequently. The reversible light-induced isomerization of azobenzene regulates the surface electrostatic potentials around Cu⁺ from −0.038 to 0.008 eV, causing shielding and exposure effects. The alteration of CO uptake is achieved up to 54 % via changing light, while that on MIL-101-NH₂ is negligible. This study provides a clue for designing target-specific smart materials to meet the practical stimuli-responsive adsorption demands.