The coupling between molecular vibrations and an optical resonator not only facilitates the detection of the molecular vibrational resonance as a local probe of chemical environments, but also alters the reactivity of associated chemical bonds. Of particular interest is the opportunity to control the spatially varying molecule-resonator coupling of infrared active molecular vibrations to tunable IR nano-wire antennas and its ultrafast dynamics. Here, we apply infrared scattering scanning near-field optical microscopy to molecule-antenna-resonator hybrid systems to sensitively detect and control the vibration-resonator coupling and associated dynamics with nanometer-femtosecond scale spatio-spectral resolution in the strong light-matter interaction regime. We first demonstrate the excitation of C=O and C-H functional group of PMMA spin-coated on top of gold nanowires which support tunable radiative bright and non-radiative dark modes. Through the strong three resonator coupling between scanning tip, molecules, and gold nanowire, we were able to control the electromagnetically induced scattering spectrum by tuning the nanowire resonance and tip position on the nanowire. To further increase and control the light-matter coupling strength, we then resort to gold nanowires chemically functionalized with molecular monolayer containing a metal carbonyl complex, which simultaneously provides a strong infrared transition dipole moment and small mode volume. By controlling the nanowire resonance, femtosecond pulse excitation polarization, and nanoscale excitation and relative phase by the positioning of the tip, we achieve efficient hybridization, sensitive detection, high Purcell enhancement, and precise control of the strongly enhanced antenna coupled vibrational response as measured through heterodyne detection of the near-field vibrational free-induction decay. This tip-enhanced strong coupling (TESC) in the infrared, with configurable nano-cavity, femtosecond coherent excitation, and scanning tip phase control provides for new pathways toward single molecule/oscillator detection and reactivity control over small ensemble.

Nano-imaging and -control of infrared vibrational molecular-antenna hybrid states in the strong coupling regime

Macromolecular Chemistry: The Second Century

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ACS Spring 2020 National Meeting & Expo

The official archive and repository for all ACS Meetings & Expositions abstracts and select posters or presentations.