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.