Tuning the Excited-State Intramolecular Proton Transfer in Carbon Dots via Coordination with Metal Ion

Although carbon dots (CDs) are widely used in the detection of heavy metal ions, rationally designing high-performance CDs for metal ion detection remains a significant challenge due to the limited understanding of their interaction mechanism. Here, we reveal the excited-state intramolecular proton transfer (ESIPT) in CDs and provide an effective strategy for switching the ESIPT by coordinating with metal ions. This work demonstrates that Zn²⁺ has strong coordination capacity toward CDs, while Mn²⁺ has the mildest coordination mode that can effectively sense other metal ions. Reasonable design of CDs with unique responses to heavy metal ions is achieved by doping Zn²⁺ or Mn²⁺ to regulate the ESIPT process. Therefore, a fluorescent sensor array for the sensitive identification of 10 kinds of heavy metal ions in real samples is constructed, which shows consistent detection results with ICP-OES. This work deepens the understanding of the fundamental fluorescence mechanism of CDs, opens new avenues for the rational tuning the emissive process, and provides a simple yet reliable platform to design nanoprobes for heavy metal ions as well as other molecules.