Supramolecular interactions via hydrogen bonding contributing to citric-acid derived carbon dots with high quantum yield and sensitive photoluminescence

Herein, we report the characterization of highly fluorescent citric-acid derived carbon dots (CACDs) synthesized by hydrothermal treatment of citric acid and diethylenetriamine below 200 degrees C. After being purified using a gel permeation chromatography cleanup system, the complexity and chemical composition of the CACDs were evaluated by liquid chromatography coupled with high-resolution Fourier transform ion cyclotron resonance mass spectrometry. The fluorophores consisted of five-membered ring fused 2-pyridones identified as the photoluminescence origin. M06-2X density functional calculations, surface tension and morphological studies suggested DETA@5CA serves as the main building block to fabricate supramolecular aggregates. Then we proposed that the dimeric and trimeric fluorophores coupled with DETA@5CA led to "dot" topologies in the CACDs solution under the effect of hydrogen bonding. In aqueous solution, the CACDs exhibited narrowly dispersed optical properties and a high fluorescent quantum yield (similar to 98%). Moreover, the supramolecular interaction induced CACDs have high sensitivity under various ambient conditions, such as pH, organic solvents and metal ions.