Photoreaction Boosting Phosphorescence Cascade Energy Transfer Based on Cucurbit[8]Uril Biaxial Polypseudorotaxane

Cascade energy capturers based on supramolecular assembly have recently generated great research interest in the field of luminescent materials. Herein is reported a cucurbit[8]uril (CB[8])-encapsulated coumarin-bridged phenylpyridinium salt (G) to form biaxial polypseudorotaxane (G subset of CB[8]), which not only induces the phosphorescence of the guest G, but also activates the photodimerization of coumarin functional group in the CB[8] cavity (G-dimer subset of CB[8]) to further boost its phosphorescence emission, extending the phosphorescence lifetime from 271.3 to 430.3 mu s and the quantum yield from 5.1% to 25.7% in aqueous solution. After co-assembly with amphiphilic calixarene (SC4AD), the supramolecular biaxial polypseudorotaxane G-dimer subset of CB[8] is changed to the nanoparticle. Compared with the alone G-dimer subset of CB[8], the phosphorescence intensity of G-dimer subset of CB[8]@SC4AD is significantly enhanced with the phosphorescence lifetime extending to 2.11 ms. Subsequently, by doping commercial dye rhodamine B (RhB) in the G-dimer subset of CB[8]@SC4AD assembly, an ultrahighly efficient phosphorescence-harvesting energy transfer process occurs with an energy transfer efficiency (phi(ET)) of 72.3% and an antenna effect of 396.8. Furthermore, the cascaded room temperature phosphorescence harvesting system is constructed via introducing the secondary near-infrared (NIR) acceptors Nile blue or Cy5 in the G-dimer subset of CB[8]@SC4AD:RhB system, which possesses a good biocompatibility and is successfully applied to NIR delayed fluorescence targeted imaging in HeLa cell.

Automated summary

Cascade energy capturers based on supramolecular assembly have attracted great research interest in luminescent materials. A cucurbit[8]uril (CB[8])-encapsulated coumarin-bridged phenylpyridinium salt (G) was reported to form a biaxial polypseudorotaxane (G subset of CB[8]), which not only induced the phosphorescence of the guest G, but also activated the photodimerization of coumarin functional group in the CB[8] cavity (G-dimer subset of CB[8]), resulting in enhanced phosphorescence emission. The system showed potential for targeted imaging in HeLa cells.