Control of molecular energy redistribution pathways via surface plasmon gating

Strong coupling of molecular electronic states with tunable surface plasmon resonances is used to control electronic energy redistribution pathways in molecules adsorbed on a silver film. Ultrafast excitation of porphyrinic molecular J aggregates into the S2 state is followed by a second pulse of varying incident wave vector to produce a tunable plasmon in the film. When the plasmon overlaps the S1 state, energy flows from S2 to S1 at high efficiency. If the plasmon hybridizes with the S2 state, the excitation remains in the S2 vibrational manifold during quenching to the ground state. These results could have significant impact on the design of active molecular devices.