A Dual-Responsive Cationic Acridinium Nanohoop: Redox Activity and Acid/Base-Controlled Reversible Guest Capture and Release

Abstract

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.