Water-Dispersible Glassy Organic Dots Exhibiting Near-Infrared Delayed Emission for Bioimaging

Red to near-infrared (NIR) emitting thermally activated delayed fluorescence (TADF) emitters and room temperature phosphorescence (RTP) emitters are attractive for time-gated biological imaging. Luminophores that emit red to NIR light can operate within the biological transparency window (650–1350 nm), enabling deeper penetration into tissue while also being easier to distinguish from cellular autofluorescence. Herein, we report a TADF emitter NAI-Q-MeOTPA and an RTP emitter NAI-Py-MeOTPA which incorporate the strong electron-donating group bis(4-methoxyphenyl)amine and strong acceptor cores quinoxaline-naphthalimide and pyrido[2,3-b]pyrazine-naphthalimide, respectively. Delayed emission was observed for both luminophores with emission maxima for NAI-Q-MeOTPA and NAI-Py-MeOTPA of 746 and 749 nm in toluene, respectively. When encapsulated into glassy organic dots (g-Odots), the luminophores still maintained NIR emission with significant delayed lifetimes. The NAI-Q-MeOTPA and NAI-Py-MeOTPA g-Odots were probed for bioimaging in HeLa cells in which g-Odot uptake was observed and demonstrated bioimaging capability in the 630–740 nm imaging window.