Fabrication,Modulation And Functions Of Supramolecular Free Radicals

Modulating the activity of free radicals is crucial for their applications on radical-based functional materials and radical-mediated reactions or polymerizations.In spite of the significant advances,most of the research is focused on the stabilization of radicals,which has limited the modulating methodology and impaired the functions of radicals to some extent.To address this issue,we have proposed and extended the new concept of“supramolecular free radicals”,which refers to the free radicals stabilized or activated by noncovalent interactions.Different from the radicals constructed by traditional covalent chemistry,supramolecular free radicals can be not only fabricated in a facile way,but also endowed with various dynamic properties such as reversibility,adaptivity and stimuli-responsiveness.In this thesis,based on the host-guest chemistry of cucurbit[7]uril(CB[7]),we have constructed a series of supramolecular free radicals.Owing to the steric effect and electrostatic interaction of CB[7],the radicals can be stabilized,activated or endowed with adaptive reactivity.These supramolecular free radicals exhibit diverse applications on supramolecular materials and supramolecular catalysis.Three main achievements are summarized as follows:1)A stabilized supramolecular radical anion has been fabricated as a new kind of near-infrared(NIR)photothermal system.Through the steric hindrance of CB[7],the aggregation and quenching of perylene diimide radical anion can be suppressed,thus greatly improving the radical yield in aqueous solution.Furthermore,benefitting from the increase of radical anion,the NIR absorption of the system is enhanced,which induces a more effective NIR photothermal conversion.It is anticipated that this stabilized supramolecular radical anion is a promising candidate for new organic NIR materials.2)An activated supramolecular radical cation has been constructed for the significant acceleration of Fenton oxidation reaction.Through the electrostatic effect of CB[7],the spin distribution and SOMO energy level of diketopyrrolopyrrole radical cation can be regulated,which improves the reactivity of the radical cation.As the key intermediate of Fenton oxidation,this activated supramolecular radical cation leads to a drastic decrease on the apparent activation energy and greatly increases the reaction rate.In contrast to the usual efforts on the stabilization of radicals,this strategy of supramolecular activation could enrich the realm of supramolecular catalysis.3)A reaction intermediate with adaptive reactivity has been designed for highly efficient supramolecular catalysis.Taking advantage of the dynamic nature of host-guest interactions,TEMPO~+,the key catalytic intermediate of the biphasic alcohol oxidation,can be endowed with adaptive reactivity.Specifically,TEMPO~+is stabilized by the host-guest complexation and the electrostatic effect of CB[7]in aqueous phase,thus promoting the formation and inhibiting side reactions of TEMPO~+.Moreover,during the migration into organic phase,TEMPO~+recovers the high reactivity through the dissociation from CB[7],which can drive a fast oxidation of substrates.The adaptive reactivity of TEMPO~+induces an integral optimization of the catalytic cycle and greatly improves the conversion of reaction.This strategy highlights the unique advantages of dynamic noncovalent interactions on modulating the activity of reaction intermediates,which may open new horizons for supramolecular catalysis.