Two-dimensional materials as ideal substrates for molecular quantum emitters

The generation and manipulation of non-classical light states is central to emerging quantum technologies. Color centers in insulating crystals have been extensively studied for single-photon generation, but organic molecules immobilized on substrates have gained attention due to their superior scalability, large oscillator strengths, and tunable emission frequency. Here, we use first principles calculations to investigate the photoemission spectrum of organic molecules adsorbed on various 2D materials. Machine learning interatomic potentials are combined with density functional theory to accelerate the search for stable adsorption configurations. The calculated zero phonon line (ZPL) energies and emission lineshapes show excellent agreement with experiments. Our results indicate that the 2D substrate couples weakly to the molecular transitions and that emission characteristics are almost universal across different substrates. The unique effect of the 2D substrate is to introduce a sharp sideband(s) near the ZPL as a fingerprint of hindered rotational and translational modes of the molecule.