Role of edge nitrogen doping in nonradiative decay dynamics of graphene quantum dots: a Fermi’s golden rule analysis

Nitrogen-doped graphene quantum dots (NGQDs) are appealing materials for light-emitting devices due to their chemical stability, high quantum yield, and tunable electronics. However, the complex N-doping configurations greatly impede the development and applications of NGQDs for optoelectronics. In the current work, we perform density functional theory calculations to investigate the electronic, optical, and nonradiative properties of NGQDs bearing various N functionalities, based on Fermi’s golden rule principle. Our results show that the pyrazole and pyrrolic N induce the hybridization in both occupied and unoccupied energy levels, reducing the band gaps and redshift absorption spectra of the NGQDs. The pyrrolic N increases the electron localization in NGQDs, leading to larger electron–phonon coupling, which, accordingly, increases the effective Huang-Rhys factor that contributes to a very efficient nonradiative decay. On the contrary, the NGQD-bearing pyridinic N exhibits the most inefficient nonradiative decay among all NGQDs because of the large optical gap, small solvent reorganization energy, and electronic coupling.