A dual-responsive cationic acridinium nanohoop: redox activity and acid/base-controlled reversible guest capture and...

In this work, we report a fully conjugated, radially cationic nitrogen-doped cycloparaphenylene derivative, Ad[10]CPP⁺, constructed using the acridinium moiety as a functional building block. This compound exhibits remarkable reversibility in structural transformations under chemical stimuli and tunable redox behavior under electrochemical stimuli. Cyclic voltammetry reveals that Ad[10]CPP⁺ possesses multiple oxidation states and demonstrates significant redox versatility. Furthermore, Ad[10]CPP⁺ can reversibly transform from a near-circular configuration to a water-droplet shape upon hydroxide attack on the acridinium moiety when the acid concentration is lowered. The host-guest interaction between fullerene (C₆₀) and Ad[10]CPP⁺ was confirmed by NMR spectroscopy and single-crystal X-ray diffraction. Significantly, the host-guest system exhibits excellent fatigue resistance, enabling at least five consecutive cycles of chemically triggered fullerene capture and release through reversible structural transformations.