  Long-range energy transfer in organic molecules has been experimentally
obtained by strongly coupling their electronic excitations to a confined
electromagnetic cavity mode. Here, we shed light into the polariton-mediated
mechanism behind this process for different configurations: donor and acceptor
molecules either intermixed or physically separated. We numerically address the
phenomenon by means of Bloch-Redfield theory, which allows us to reproduce the
effect of complex vibrational reservoirs characteristic of organic molecules.
Our findings reveal the key role played by the middle polariton as the
non-local intermediary in the transmission of excitations from donor to
acceptor molecules. We also provide analytical insight on the key physical
magnitudes that helps to optimize the efficiency of the long-range energy
transfer.
