Switching of Adsorption Properties in a Zwitterionic Metal–Organic Framework Triggered by Photogenerated Radical Triplets

A new metal–organic framework (MOF) that features photoreactive zwitterionic pyridinium 4-carboxylate units has been designed. Upon UV light irradiation, these units form radical triplets permitted by intramolecular electron transfer between anionic carboxylate and cationic pyridinium groups. This reversible light-responsive behavior creates on/off switchable charge gradients localized at the MOF’s major adsorption sites and, thus, allows significant control of the gas sorption process. It is shown that this strategy offers new design routes for accessing stimulus-responsive materials.