  Resonant interaction between excitonic transitions of molecules and localized
electromagnetic field allows the formation of hybrid light-matter polaritonic
states. This hybridization of the light and the matter states has been shown to
be able to significantly alter the intrinsic properties of molecular ensembles
placed inside the optical cavity. Here, we have achieved strong coupling
between the excitonic transition in typical oligonucleotide-based molecular
beacons labelled with a pair of organic dye molecules, demonstrating an
efficient donor to acceptor resonance energy transfer, and the tuneable
open-access cavity mode. The photoluminescence of this hybrid system under
non-resonant laser excitation and the dependence of the relative population of
light-matter hybrid states on cavity detuning have been characterized.
Furthermore, by analysing the dependence of the relaxation pathways between
energy states in this system, we have demonstrated that predominant strong
coupling of the cavity photon to the exciton transition in the donor dye
molecule can lead to such a large an energy shift that the energy transfer from
the acceptor exciton reservoir to the mainly donor lower polaritonic state can
be achieved, thus yielding the chromophores donor-acceptor role reversal or
carnival effect. Our experimental data confirm the theoretically predicted
possibility for confined electromagnetic fields to control and mediate
polariton-assisted remote energy transfer thus paving the way to new approaches
to remote-controlled chemistry, energy harvesting, energy transfer and sensing.
