In Situ Synthesis of Dual‐Emissive Carbon Dots: Mechanistic Insights into Growth and Luminescence and Ratiometric Fluorescence Sensing of Hydrogen Sulfide

Dual‐emissive carbon dots (CDs) hold significant potential for sensing and bioimaging, but achieving intrinsic, precisely controlled dual emissions with self‐calibration capability without post‐modification remains challenging. Herein, a novel in situ synthesis of dual‐emissive CDs using pyronin Y as the sole precursor via a one‐pot hydrothermal method is presented. This strategy directly generates CDs exhibiting homogeneous dual‐fluorescence and intrinsic self‐calibration properties. Systematic investigation reveals that the dual emissions arise from the synergistic interplay between green emission centers scattered on the carbon core and orange‐emissive surface‐bound aromatic molecular fluorophores derived from the precursor. Green emission centers form rapidly at 160 °C (8 h reaction), comprising three‐ring aromatics functionalized with aldehyde, amide, amino, hydroxyl, and methyl groups. Leveraging this unique optical signature, a ratiometric fluorescent sensor is fabricated for hydrogen sulfide (H 2 S) detection, achieving rapid, highly sensitive (detection limit: 6.93 n m ), and selective sensing over a wide range (10 n m –70 µ m ). Furthermore, the CDs enable effective ratiometric imaging of exogenous and endogenous H 2 S in living cells. This single‐precursor approach provides a versatile platform for intrinsically dual‐emissive nanomaterials and advances the rational design of high‐performance sensing and bioimaging agents through fundamental mechanistic insights.