Fluorescent Quenching of Lanthanide-Doped Upconverting Nanoparticles by Photoresponsive Polymer Shells

A photoresponsive amphiphilic polymer was synthesized and used to encapsulate upconverting lanthanide-doped nanoparticles to produce a novel water-dispersible nanoassembly with a high loading of emission quenchers. The nanoassembly exhibits fluorescent emission in the visible region upon irradiation with 980 nm light, which can be reversibly modulated by toggling the isomeric state of photoresponsive chromophores attached to the polymer's backbone using UV and visible light. Photon counting experiments show that the quenching mechanism for this new nanoassembly is a combination of Förster resonance energy transfer (FRET) and emission-reabsorption. Compared to the similar nanoassembly prepared from a reported "plug-and-play" method, this new nanoassembly has higher overall quenching efficiency due to the increased photoswitch loading (14 times compared to the existing nanoassembly).