Carbon dots structural characterization by solution-state NMR and UV-visible spectroscopy and DFT modeling

Abstract

A combination of experimental and theoretical results was used for the structural characterization of Carbon dots (Cdots). The synthesis of the Cdots was performed using glucose as a precursor and via the microwave method (“bottom-up” route) as a simple and environmentally friendly method. The experimental data obtained by UV–visible, fluorescence, IR and solution-state NMR spectroscopy techniques were correlated with density functional theory calculations results. Particularly, the results obtained by solution-state NMR spectroscopy suggested Cdots structures of Polymer dots (PDs) and/or polymer Carbon dots (PCDs) kind. PDs are characterized by being formed only of polymer structures and PCDs by being formed of a small carbonized core surrounded by polymer structures. Calculations allow us to predict the UV–visible absorption and IR spectra behavior of the species detected by the NMR technique, and propose a structure that can explain the experimentally observed features and infer the presence or absence of a carbon core in the proposed structures. Density of states curves were used to analyze and interpret the theoretical spectra peaks. Additionally, a calculation of the IR spectra for the models proposed, was performed. The complement of experimental and theoretical results represents a useful tool for the structural characterization of Cdots.