Insights of Shadow Trapping States and Intramolecular Charge Transfer on Simultaneous Redshift and Efficiency Enhancement of Electrochemiluminescence in Carbon Dots

While highly efficient electrochemiluminescence (ECL) emitters with finely tunable emission wavelengths are crucial for practical applications, the simultaneous modulation of ECL efficiency and emission wavelength, along with the deep understanding of the mechanism in the molecular level, remain elusive. Herein, we reported carbon dots (CDs) with both fine-tuned ECL efficiency and emission wavelength were achieved by phosphorus (P) doping, e.g., the ECL emission was finely tuned from 425 nm to 645 nm, and the efficiency (relative to the Ru(bpy)32+/K2S2O8 system) was promoted from 10.6% to 57.4%. Experimental and theoretical studies revealed the P dopants in the form of P-C and P-O groups not only imported shadow trapping states but also promoted a significant intramolecular charge transfer (ICT), which jointly induced the redshift and boosted the ECL performance of CDs. This work would provide a clue for the rational design of CDs to tune the ECL properties for advanced biomedical applications finely.