Achieving Bright and Long‐Lived Aqueous Room‐Temperature Phosphorescence of Carbon Nitrogen Dots Through In Situ Host–Guest Binding

The development of bright and long‐lived aqueous room‐temperature phosphorescent (RTP) materials holds paramount importance in broadening the application scope of RTP material system. However, the conventional RTP materials usually exhibit low efficiency and short lifetime in aqueous solution. Herein, an in situ host–guest strategy is proposed to achieve cyanuric acid (CA)‐derived phosphorescent carbon nitrogen dots (CNDs) composite (CNDs@CA) that demonstrates a significant enhancement of both quantum yield (QY) and lifetime mediated by water. Detailed investigations reveal that the robust hydrogen bonding networks between CNDs@CA and water effectively stabilize triplet excitons and suppress nonradiative decays, as well as facilitate efficient energy transfer from CA to CNDs, thereby prolonging the lifetime and enhancing the efficiency of RTP. The phosphorescent QY and lifetime of CNDs@CA can be increased to 26.89% (3.9‐fold increase) and 951.25 ms (5.5‐fold increase), respectively, with the incorporation of 50 wt% water under ambient conditions. Even in fully aqueous environments (with up to 400 wt% water added), CNDs@CA exhibits persistent water‐boosted RTP properties, demonstrating exceptional stability. The robust water‐boosted RTP property of CNDs@CA in aqueous solutions presents significant potential for high signal‐to‐noise ratio afterglow bioimaging as well as advanced information encryption. The present study successfully develops an efficient in situ host–guest approach for synthesizing water‐boosted phosphorescent carbon nitrogen dots through a one‐pot pyrolysis of cyanuric acid. This material exhibits bright and long‐lived aqueous room‐temperature phosphorescence, even in fully aqueous environments, thereby demonstrating significant potential for high signal‐to‐noise ratio afterglow bioimaging both in vitro and in vivo, as well as advanced information encryption applications.