The Role of Atomistic Tip Morphology in Tip-Enhanced Electronic Energy Transfer

Tip-enhanced photoluminescence in scanning tunneling microscopy nanocavities has emerged as a powerful tool to probe intermolecular electronic energy transfer (EET) at the single-molecule level. Single-atom modifications at a metallic tip apex can drastically alter the near-field, yet their quantitative impact on intermolecular EET has remained elusive. By exploiting a multiscale fully atomistic quantum mechanical (QM)/electrodynamical approach, we show a nontrivial modulation of the EET-driven fluorescence, jointly determined by the atomistic morphology and single-atom features of the silver tip apex. Remarkably, we demonstrate that a fully atomistic QM/Classical description, able to treat systems of more than ten thousand atoms, is essential to capture how subtle apex rearrangements affect intermolecular EET. Our results quantitatively reproduce experimental fluorescence spectra and Förster-type distance behaviors, providing a direct structure-property connection at the atomistic level, crucial for predictive simulations of tip-enhanced spectroscopies.