A Redox-Active Heterocyclic Capsule: Radical Generation, Oxygenation, and Guest Uptake/Release

Abstract

For the development of a redox-active supramolecular capsule with host function, we synthesized a bent heterocyclic amphiphile using phenothiazine panels capable of adopting three different states, i.e., neutral, radical, and oxygenated states. In water, the new amphiphiles spontaneously and quantitatively assemble into a heterocycle-based capsule with an average diameter of ∼2 nm, through the hydrophobic effect and π-stacking interactions. The product structure was confirmed by the combination of NMR, UV–visible, DLS, AFM, and molecular modeling studies. Electrochemical and chemical oxidation of the capsule generates relatively stable radical cation capsules at room temperature in a reversible fashion. The neutral capsule efficiently takes up large hydrophobic compounds (e.g., pigment blue 15 and fullerene C60) into the heterocyclic cavity through a grinding protocol and subsequent chemical oxidation of the products generates radical host–guest complexes. Moreover, chemical oxygenation of the host–guest complexes was shown to induce guest release in water via disassembly of the capsular structure through dioxygenation of the phenothiazine panels.