Insight into the effect of functional groups on visible-fluorescence emissions of graphene quantum dots

Graphene quantum dots (GQDs) with a variety of functional groups are studied by adjusting the pH of the solvents and through reduction using chemical methods. Our study suggests that the -CO-OH and -CO-N(CH3)(2) groups could contribute to the green fluorescence emission (peak at 500-520 nm), and the -CO-N(CH3)(2) group could form the green fluorescence emission state more effectively. Additionally, -OH groups and free zigzag sites may contribute to the blue fluorescence emission (peak at around 420 nm). The edge states and functional groups commonly constitute fluorescence emission centers. Additionally, both blue and green fluorescence emission centers corresponding to the molecule-like states could be quenched using the electron acceptor methyl viologen, which barely affects the intrinsic state of the carbon honeycomb flat structure.