Edge-oxidation induced non-radiative recombination dynamics in graphene quantum dots: a theoretical insight from Fermi's golden rule

The photoluminescence quantum yield of graphene quantum dots (GQDs) can be tuned by chemical functionalization. A rational design of fluorescent probes based on GQDs requires an understanding of the relationship between the chemical structure and the non-radiative recombination decay of GQDs. The oxygen-containing groups modify the edge states and alter the non-radiative decay of GQDs. In this work, we perform density functional theory (DFT) calculations to investigate the non-radiative decay dynamics of GQDs functionalised with different oxygen-containing groups, e.g. carbonyl, hydroxyl, and carboxyl, based on the principle of Fermi's golden rule. The carbonyl group oxidises the GQD edges, reducing the bandgap and red-shifting the absorption spectra. The carboxyl group increases the strength of electron-vibrational coupling of the high-frequency modes, resulting in faster non-radiative decay. The hydroxyl group, on the other hand, reduces the strength of electron-vibrational coupling in the high-frequency modes, thereby reducing non-radiative decay. Overall, this research extends our current knowledge of the role of individual oxygen-containing groups in the non-radiative decay of GQDs.