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

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.