Fluorescent nitrogen-doped carbon nanodots synthesized through a hydrothermal method with different isomers

In this work, we have developed a novel fabrication technique for preparing N-functionalized carbon nanodots (CNDs) through one-pot hydrothermal route using various isomers, exhibiting highly intense fluorescence under blue light illumination. Three types of isomers, o-, m-, and p-phenylenediamine (PD), serving as the carbon and nitrogen sources were employed where the N/C atomic ratio in the CNDs structure was precisely tuned within the range of 20.2–25.7 at.% via tailoring the isomer precursors. The application of the m-PD precursor resulted in implanting the “lattice N” functionalities while the o-PD precursor enabled the formation of N-oxide groups. The CND suspensions in highly-polarity solvents (e.g., water and ethanol) emit intense fluorescence with ultrahigh quantum yield (QY: 85‒99%), whereas the fluorescence from the CND suspensions in propylene glycol methyl ether acetate is significantly quenched. The ultrahigh QY is majorly due to an intense radiative emission mechanism induced by the substitutional N atoms (via high electron-withdrawing) and N- and O-rich edge groups as the major contributors for boosting the affinity to high-polar solvents. Given the widespread applications of quantum dots as high-performance nanomaterials, this study paves the way for engineering N-functionalized CNDs to be used in optical, sensing, energy storage/conversion, and biological devices.