Investigation on Tunable Optical Properties and Structures of Graphene Quantum Dots Doped with Sulfur-Containing Groups

Abstract

Due to quantum confinement and edge effects, graphene quantum dots (GQDs) have demonstrated numerous novel chemical and physical properties. Doping GQDs with heteroatoms is an effective way to tailor their electronic and optical properties. However, due to different synthesis methods, the potential use of GQDs doped with heteroatoms is hindered by the poor understanding of their intrinsic optical properties and mechanisms. In this work, optical spectrum, HOMO–LUMO gap, and electronic density of GQDs doped with sulfur (S) atoms are calculated to reveal electron transition processes. It is found that S=O can reduce the absorption intensity of GQDs, and the calculated absorption spectra tend to be blueshifted when the number of S-containing groups decreases. The S-doped GQDs containing S atom in pentatomic ring has a broad UV−Vis absorption band with a weak shoulder at 300 nm, which is blueshifted by 60 nm with respect to that of pristine GQDs. Moreover, the thioether-S configuration plays remarkable effect on tailoring optical properties of GQDs, and the recombination of electron-hole pairs can result in weakened absorption intensity. This study will provide valuable knowledge for understanding electronic and optical properties of GQDs and give important insights for the development of methods to controllably synthesize GQDs.