Condition-triggered single-to-double peak transition of CPDs for visual detection of water content in DMSO

Herein, we have synthesized blue fluorescent carbonized polymer dots (CPDs) via a facile hydrothermal method using p-aminophenol and ethylenediaminetetraacetic acid. The reduced density gradient (RDG) analysis reveals that the supramolecular interactions between hydrogen-bonded polyamide chains result in a strong blue emission, whereas the orange emission arises from the hydrogen-bond-induced excited-state intramolecular proton transfer (ESIPT) between the CPDs and water. Density functional theory (DFT) calculations have confirmed that phenolic hydroxyl groups play a key role in the fluorescence redshift as the synthesis temperature increases. It is worth noting that the constructed dual emission ratio probe exhibits a good linear relationship at a moisture content of 10-40% through the fluorescence intensity ratio (I₄₅₈/I₅₆₄), with a detection limit of 0.0538% and a correlation coefficient R² of 0.9971. The fluorescence color of the probe solution changes from blue to orange yellow, indicating its potential for on-site visual detection. It has been successfully applied to detect trace water in various organic solvents, edible oils, and traditional Chinese medicines.