Organic Thermally Activated Delayed Fluorescence Host-Guest Nanoparticles for Super-Resolution Imaging

It is significantly important to design fluorescent probes with excellent stimulated emission (SE) efficiency for low-power stimulated emission depletion (STED) imaging. Herein, 4,6-bis((E)-4-(dibenzothiophene)styryl)-5(ethoxycarbonyl)-2,2-difluoro-2H-1,3,2- dioxaborinin-1-ium-2-uide (BBSF) is chosen as guest fluorescence molecule and 4,4 '-bis9H-carbazol-9-ylbiphenyl (CBP) selected as host matrix. It is demonstrated that BBSF@CBP microcrystals possess outstanding amplified stimulated emission (ASE) behavior and thermally activated delayed fluorescent (TADF) characteristics, which are beneficial for achieving low-power STED imaging through decreasing the saturation intensity. Moreover, BBSF and CBP molecules are encapsulated into polyethylene-polypropylene glycol (Pluronic F127) to form amphipathic BBSF@CBP nanoparticles (NPs), which show bright red emission with extraordinary fluorescence quantum yield (phi) of 0.375, large Stokes' shift of 190 nm, appropriate long-lived lifetime of 16.17 ns, and high photostability. The measured saturation intensity and lateral resolution of BBSF@CBP NPs are 0.28 MW cm-2 and 73.77 nm, respectively. Moreover, STED imaging in living HeLa cells with enhanced resolution of 72.20 nm is also achieved by utilizing the prepared BBSF@CBP NPs. This study demonstrates the high performance of TADF NPs, making them promising as fluorescent probes for low-power STED imaging in living cells. High stimulated emission (SE) efficiency molecule BBSF and high crystallization CBP are chosen as guest and host matrix, respectively. The organic thermally activated delayed fluorescence BBSF@CBP nanoparticles possess the merits of excellent SE performance, large Stokes's shift, and high photostability, which realize dynamic STED imaging in living cells with a resolution of approximate to 72 nm.image