Construction of Chiroptical Switch on Silica Nanoparticle Surface via Chiral Self-assembly of Side-chain Azobenzene-containing Polymer

In this contribution, we utilized surface-initiated atom transfer radical polymerization (SI-ATRP) to prepare organic-inorganic hybrid core/shell silica nanoparticles (NPs), where silica particles acted as cores and polymeric shells (PAzoMA*) were attached to silica particles via covalent bond. Subsequently, chiroptical switch was successfully constructed on silica NPs surface taking advantage of supramolecular chiral self-assembly of the grafted side-chain Azo-containing polymer (PAzoMA*). We found that the supramolecular chirality was highly dependent on the molecular weight of grafted PAzoMA*. Meanwhile, the supramolecular chirality could be regulated using 365 nm UV light irradiation and heating-cooling treatment, and a reversible supramolecular chiroptical switch could be repeated for over five cycles on silica NPs surface. Moreover, when heated above the glass transition temperature (Tg) of PAzoMA*, the organic-inorganic hybrid nanoparticles (SiO2@PAzoMA* NPs) still exhibited intense DRCD signals. Interestingly, the supramolecular chirality could be retained in solid film for more than 3 months. To conclude, we have prepared an organic-inorganic hybrid core/shell chiral silica nanomaterial with dynamic reversible chirality, thermal stability and chiral storage functions, providing potential applications in dynamic asymmetric catalysis, chiral separation and so on.