Strong light-matter coupling for optical switching through the fluorescence and FRET control

Resonant interaction between excitonic transitions of molecules and localized electromagnetic field forms the hybrid polaritonic states. Tuneable microresonators may change the light-matter coupling strength and modulate them from weak to strong and ultra-strong coupling regimes. In this work we have realised strong coupling between the tuneable open-access cavity mode and the excitonic transitions in oligonucleotide-based molecular beacons with their terminus labelled with a pair of organic dye molecules demonstrating an efficient donor-to-acceptor Förster resonance energy transfer (FRET). We show that the 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". The data show the possibility for confined electromagnetic fields to control and mediate polariton-assisted remote energy transfer. Obtained results open the avenues to quantum optical switching and other applications.