Photophysics of graphene quantum dots: Insights from electronic structure calculations

Understanding electronic excitations in graphene nanostructures plays a crucial role in utilizing these recently emerging systems in optoelectronics and photonics. Based on time-dependent density functional theory, we elucidate on optical selection rules in isolated graphene quantum dots (QDs) and their relation to the system symmetry and bring the general results into a broader context with other semiconductor QD systems. The dark nature that we find for the lowest singlet transitions and the degeneracy of the lowest optically bright transition have important consequences for any optical application of graphene QDs.