Supramolecular tuning of energy transfer efficiency and direction in a bis(styryl) dye–crown ether conjugate

The control of the energy transfer (FRET) in a novel bischromophoric styryl(pyridinium) dye bearing two different crown ether residues is presented. Complexation of the dye with metal cations allows to tune the FRET efficiency without changing the transfer direction or to switch the FRET off, whereas protonation launches the FRET process in the opposite direction relative to the molecular structure.