Control Synthesis of Multicolor Emitting Carbonized Polymer Dots Using Different Dihydroxynaphthalene Isomers

Carbonized polymer dots (CDs) with sizes smaller than 10 nm have gained significant interest, particularly in the pursuit of multicolor fluorescence, which is a fascinating field of research. Here, we report the control synthesis of multicolor CDs with tunable emissions via the rational selection of isomer-based reaction precursors. Using cost-friendly dihydroxynaphthalene (DHN) isomers (1,7-DHN, 1,6-DHN, or 2,7-DHN) and l-methionine as the precursors, multicolor CDs with blue, green, and red fluorescence were obtained under ethanol-thermal conditions. It can be observed that structural changes in the coordination of the hydroxyl group within the aromatic compound DHN lead to a significant redshift in the emission of the synthesized CDs. Notably, the red-emitting CDs (r-CDs, 10 μM) at very low concentrations exhibit high sensitivity to tetracycline (TC), and the ratiometric fluorescent probe based on r-CDs enables quantitative and visual detection of TC. Compared with ratiometric fluorescent probes containing metal and rare earth elements, CDs-based ratiometric fluorescent probes are more cost-effective and environmentally friendly.