Controlling Intramolecular Vibrational Redistribution with an Infrared Photonic Cavity

Using ultrafast dual-frequency two-dimensional infrared spectroscopy (DF-2DIR), we probed how the strong coupling of high-frequency molecular vibrations to surface lattice resonances of infrared antennas, which act as a photonic cavity, affects intramolecular vibrational relaxation (IVR). DF-2DIR allows one to probe the IVR pathways beyond the vibrational state subspace of the polaritons and reservoir states, which is typically accessed in conventional 2DIR experiments. We observed anharmonic coupling between lower polariton and high-frequency molecular vibrational modes not coupled to the cavity directly, which appeared in the strongly coupled system by virtue of the polariton's molecular component, and alternation of the rate of excitation energy excess transfer from the polariton to a distant molecular vibrational mode, which depended on the polariton transition frequency. These are in contrast with the weak coupling regime, where enhanced fields magnify molecular vibrational signals without affecting their dynamics. Our work demonstrates a promising experimental approach toward understanding of polariton chemistry phenomena.