Electron Donor, Acceptor, and Concentration-Dependent Quenching of Photoluminescent Carbon Nanodots

Carbon nanodots (CNDs) are 0D-carbon nanomaterials with distinct fluorescence properties. Due to the poor understanding of the fluorescent origin and its connection to the structural complexity of CNDs, the full potential in applications of CNDs is still in a stagnant stage. Herein, we present the photoluminescence properties of two CNDs prepared from di-ammonium citrate and tri-ammonium citrate. Synthesis of CNDs was done by pyrolysis of ammonium citrates at 180 °C and 40 h under ambient conditions. We monitored the pyrolysis process using thermogravimetric analysis (TGA) both under air and inert atmospheres, which allowed for the proposal of reaction stoichiometry and structural analyses of CNDs in combination with spectroscopic means. Both CNDs possess strong photoluminescence (PL) emissions at ∼450 nm upon excitation at 365 nm. Concentration-dependent PL emission kinetics were studied to reveal both nanoparticle-like behaviors of CNDs with the enhancement of PL emission upon dilution and aggregation-induced quenching of PL emission that is common for molecular fluorophores. Quenching of CNDs’ emission with the benzophenone as a triplet sensitizer or an acceptor and the dimethoxy benzene as a donor was also studied to present additional PL emission dynamics of CNDs in support of the proposed structure for CNDs. The extensive aggregation and stacking of the proposed CNDs structure were verified using molecular dynamics simulations.