Polymer Dots Exhibiting Multi‐Resonant Thermally Activated Delayed Fluorescence for Cellular Imaging

Abstract Materials exhibiting multiple resonance thermally activated delayed fluorescence (MR‐TADF) have attracted attention in organic electronics because of their high photoluminescence quantum yield and narrowband emission. While these superior properties are also desirable for probes for biological imaging, MR‐TADF emitters have yet to be broadly exploited in this field. Here, the MR‐TADF emitter QAO is incorporated into polymer nanoparticles to construct biological imaging probes with narrowband emission and delayed fluorescence. A monomer QAO‐NB is first designed by incorporating a norbornene polymerization handle onto the QAO core, which is then incorporated into a polymer backbone by ring‐opening metathesis polymerization to afford water‐dispersible fluorescent polymer dots, or Pdots. Photophysical characterization confirmed that narrowband emission is preserved in both the polymers and Pdots (λ_max = 467–478 nm, FWHM ≤ 50 nm), with a delayed fluorescence lifetime of 455 µs in the Pdots. Multichannel fluorescence imaging studies using comparisons against donor‐acceptor TADF materials underscore the potential of MR‐TADF for the development of narrowband emissive bioimaging probes.