Glassy organic dots exhibiting near-infrared TADF with quantum yields >40% for cellular imaging

Near-infrared (NIR) thermally activated delayed fluorescence (TADF) imaging integrates the benefits of both NIR emission and TADF mechanisms, offering enhanced sensitivity and deeper tissue penetration while enabling time-resolved imaging for biological and medical applications. In this study, we synthesized and studied a donor-acceptor (D-A) type TADF emitter, 7,8-bis(4-(di([1,1'-biphenyl]-4-yl)amino)phenyl)phenazine-2,3-dicarbonitrile (DPPZ), which exhibits strong NIR fluorescence. The photophysical properties of DPPZ were characterized in both toluene and poly(methyl methacrylate) (PMMA) films. In degassed toluene, DPPZ displayed a maximum emission peak at 724 nm with a high photoluminescence quantum yield (<i>Φ</i>_PL) of 54.4%, while maintaining a <i>Φ</i>_PL of 43.9% in PMMA film under aerated conditions. Upon encapsulation into glassy organic dots (g-Odots), the emitter retained its NIR emission, a <i>Φ</i>_PL of 40.1%, and a notably long delayed lifetime (<i>τ</i>_d) of up to 225.5 μs. These NIR-emissive g-Odots were subsequently applied for lysosome-targeted bioimaging in HeLa cells, demonstrating their potential as effective probes for subcellular imaging.