Proton-Mediated ROS Amplification in Hydrazone-Linked Pillararene Microspheres for Photocatalysis

Smart materials that adapt to environmental stimuli have massive technological potential. Translating well-established molecular-level responsiveness to macroscopic systems, particularly complex systems for photocatalysis, remains a significant hurdle. Herein, we introduce a new approach using a hydrazone-linked pillararene microsphere (NP5-TF-HPM) as a smart stimuli-responsive photocatalyst. NP5-TF-HPM showcases unique proton responsiveness owing to electron-rich cavities, resulting in a proton-induced structural rearrangement from the enol-imine to keto-amine form. Experiments and density functional theory calculations reveal that pillararenes in the protonated framework function as activity amplifiers. These molecules donate π-electrons from their cavities to another building unit, not only shifting the framework's conduction band to a more negative potential, which enhances its electron-donating capability, but also inducing a nonuniform charge distribution in the donor-acceptor moiety, thereby resulting in an intramolecular built-in electric field. Consequently, protonated HPM exhibits amplified photo-oxidation activity, efficiently catalyzing sulfide photo-oxidation with high conversions (up to 99%).