Preparation and luminescent mechanism of dual-emissive red carbon dots for Pb2+/Fe3+ ion sensing and water content detection

Carbon dots (CDs), as emerging fluorescent carbon nanomaterials, boast exceptional optical properties and hold significant potential for various applications. In this study, novel dual-emissive red carbon dots (R-CDs) were synthesized from o -phenylenediamine (oPD) and 2, 2′-dithiobisbenzoic acid (DTSA) in ethanol, exhibiting emission wavelengths at 600 and 650 nm and a high photoluminescence quantum yield (QY) of 30.64 %. Notably, R-CDs exhibit excellent photostability, solvent-dependent fluorescence, and excitation wavelength-independent fluorescence properties. Based on liquid chromatography-mass spectrometry (LC-MS) and the 1 H nuclear magnetic resonance spectra ( 1 H NMR), the luminescent mechanism of R-CDs was systematically investigated to verify that 5,14-dihydroquinoxalinolo[2,3-b] phenazine (DHQP) is the fluorophore of R-CDs and a possible structural formation pathway has been proposed. For application testing, R-CDs demonstrated high sensitivity and selectivity toward Pb 2+ and Fe 3+ , exhibiting good linearity in the concentration ranges of 0–40 μM and 0–60 μM, with the detection limits (LOD) of 0.086 μM and 0.265 μM, respectively. Due to their polarity sensitivity, R-CDs can function as fluorescent sensors for detecting water content in organic solvents. Meanwhile, according to the sensitivity of R-CDs to Fe 3+ , an on-off-on fluorescent sensor was developed to detect F − , L-cys and EDTA with LOD of 9.446, 0.413 and 0.078 μM, respectively. Therefore, this study not only develops novel dual-emissive red carbon dots, but also establishes the foundation for the subsequent advancement of fluorescent sensors.