Highly Efficient Red Thermally Activated Delayed Fluorescence Nanoparticles for Real‐Time in Vivo Time‐Resolved Luminescence Imaging

Thermally activated delayed fluorescence (TADF) nanoparticles are used importantly in time‐resolved luminescence imaging for eliminating the background signals from scattering and short‐lived autofluorescence. However, TADF nanoparticles are seldom used for real‐time time‐resolved luminescence imaging, due to their limited luminescence efficiency and lifetimes. To detect delayed fluorescence, multiple excitation cycles with adequate delay times are usually required, leading to long detecting durations and low imaging speed. Herein, highly efficient red TADF nanoparticles are developed through doping a guest molecule, TPAAQ (2,6‐bis[4‐(diphenylamino) phenyl] anthraquinone), in a host (4,4′‐bis(carbazol‐9‐yl)biphenyl, CBP) matrix. With a low doping concentration, the nanoparticles can exhibit obvious TADF with luminescence lifetimes over 0.1 ms and photoluminescence quantum yield up to 35%. A cell‐penetrating peptide is used together with the amphiphilic compound for assembling nanoparticles, which can easily penetrate cells and greatly increase the TADF signals for luminescence lifetime imaging. Thanks to the long‐lived and highly efficient TADF, real‐time in vivo time‐gated luminescence imaging of zebrafish is realized on a chopper‐based wide‐field microscope. This low‐cost time‐resolved luminescence imaging method showed a great potential for real‐time detection of life activities in many organisms with high autofluorescence. Host‐guest thermally activated delayed fluorescence nanoparticles are assembled with cell‐penetrating peptides for fast biological imaging. With highly efficient long‐lived fluorescence, real‐time in vivo time‐resolved luminescence imaging of zebrafish activity is achieved on a chopper‐based wide‐field microscope, avoiding the strong autofluorescence from organisms.