Wide‐Gamut and Reversible Phosphorescence Tuning From Green to NIR in Carbon Dots via Acid‐Responsive Protonation‐Assembly Strategy

Abstract The development of stimulus‐responsive room‐temperature phosphorescence (RTP) materials with wide color ranges is crucial but challenging. A new strategy that integrates acid‐triggered carbon dots (CDs) protonation and assembly to realize a wide color RTP variable among green, orange, and near‐infrared (NIR) was reported. The synthesized neutral CDs solution exhibited bright green RTP after being printed on paper and dried. Upon acidic treatment, the phosphate groups on the CD surfaces undergo protonation and trigger their self‐assembly. As a result, the originally green RTP transforms into orange and NIR dual‐mode emission, accompanied by enhanced emission intensity. Notably, the phosphorescence quantum yield increased from 10.3% to 26.0%. Upon further stimulation with water, only NIR RTP is observed. Detailed investigations revealed that acid‐induced protonation of phosphate groups enhances π‐electron delocalization, resulting in a redshift of RTP emission to the orange region; moreover, the large conjugated core state induced by assembly leads to NIR RTP emission even in the presence of water. Additionally, acid‐triggered CDs protonation and assembly greatly enhance hydrogen bond interactions, effectively suppress nonradiative decay, and increase the RTP intensity. Furthermore, tamper‐evident labels with multiple dimensions have been developed and further applied to the fields of information authentication and food freshness detection.