Can we control the electronic energy transfer in molecular dyads through metal nanoparticles? A QM/continuum investigation

Metal nanoparticles (MNPs) can have a dramatic effect on the electronic energy transfer (EET) between donor and acceptor molecular dyes. In addition, such an effect can be modulated by the presence of a solvent. Here we present a novel multiscale QM/continuum approach which can both treat MNP-solvent-mediated EET and take into account the effects of the MNPs in all the photophysical processes into play (absorption and emission), including the competitive energy transfer from the molecular systems to the metal. By applying such a unified theoretical framework, we show that the excitonic interactions in stacked dimers are generally reduced by the presence of MNPs. In contrast, for setups in which the two transferring moieties are separated by the MNPs, the presence of the metal results in a direct enhancement of the coupling but, when the competing process of quenching by the MNP is also considered, the final effect is almost invariably a reduction of the efficiency of the EET process. Only for particular donor-MNP-acceptor setups, the model shows that waveguide-like behavior can be obtained, in these cases the excitation energy of the donor can be transferred to the acceptor over distances much longer than those allowed by the conventional Forster mechanism.