Modulating the activity of radicals is crucial for radical-mediated reactions and radical-based materials. For this aim, we proposed the new concept of “supramolecular free radicals”, which refers to the free radicals stabilized or activated by noncovalent interactions.

　Based on this concept, several kinds of supramolecular free radicals were constructed by the host-guest interactions with cucurbiturils (CBs). Cucurbiturils possess significant electrostatic effect owing to the many carbonyl groups and steric hindrance effect based on the bulky size. These structural features of CB are advantageous for the rational modulation on the activity of radicals.

　Radical anions can be stabilized by the electrostatic effect or steric effect of CB, which provides a new method for fabricating NIR organic materials and constructing selective antibacterial systems.

　Radical cations can be activated by the electrostatic effect of CB, opening new horizons for supramolecular catalysis. For example, the introduction of CB can activate the radical cations of dye molecules, the key intermediates of Fenton oxidation. Such supramolecular activation induces a drastic decrease of the apparent activation energy and accelerates the Fenton oxidation.

　Moreover, owing to the dynamic nature of noncovalent interactions, supramolecular free radicals can be endowed with adaptive reactivity. It means that the stabilized state and the activated state of radicals can be converted reversibly under the different microenvironments. In this way, we can make use of the unique advantages of supramolecular catalysis for improving the efficiency of reactions.