  Electronic Energy Transfer (EET) between chromophores is fundamental in many
natural light-harvesting complexes, serving as a critical step for solar energy
funneling in photosynthetic plants and bacteria. The complicated role of the
environment in mediating this process in natural architectures has been
addressed by recent scanning tunneling microscope (STM) experiments involving
EET between two molecules supported on a solid substrate. These measurements
demonstrated that EET in such conditions has peculiar features, such as a steep
dependence on the donor-acceptor distance, reminiscent of a short-range
mechanism more than of a Forster-like process. By using state of the art hybrid
ab initio electromagnetic modeling, here we provide a comprehensive theoretical
analysis of tip-enhanced EET. In particular, we show that this process can be
understood as a complex interplay of electromagnetic-based molecular plasmonic
processes, whose result may effectively mimic short range effects. Therefore,
the established identification of an exponential decay with Dexter-like effects
does not hold for tip-enhanced EET, and accurate electromagnetic modeling is
needed to identify the EET mechanism.
