Influence on Optical and Electronic Properties of Graphene Quantum Dots Originating from S-Doping: A Theoretical Investigation

Abstract

The optical and electronic properties of sulfur-doped graphene quantum dots (GQDs) have been theoretically investigated using DFT/TDDFT methods in water (B3LYP/6-31G/SMD). Both edge and core sites for doping have been considered. Simulation results reveal that edge-doped sulfydryl (-SH) presents no significant influence on electronic and optical properties of the GQD, however, the nonzero oscillator strength (S0-S1) of edge-doped S-GQDs enables fluorescence emission (@~450 nm) of GQD and this explains the contribution of surficial -SH to the bright blue fluorescence emission which is commonly achieved by N/S co-doping. Moreover, the S doping of GQDs at skeleton sites dramatically raises the HOMO energy level, and regulates the electron transfer process and corresponding density of states during electron transition. This eventually decreases the HOMO-LUMO gaps, enabling strong fluorescence emission in near infrared (NIR) region which suggests the S-doped GQDs at skeleton sites have great potential for application in bioimaging field.

Keywords: graphene quantum dots, sulfur doping, NIR fluorescence, theoretical investigation, DFT, TDDFT