Molecular vibrations can couple to optical cavities to create new hybrid states called polaritons. The magnitude of this coupling, measured as the vacuum Rabi splitting (Ω), correlates with modified materials processes such as photon emission, molecular energy transfer, and chemical reaction rates. In this talk, I will first discuss active control of cavity coupling strength. We demonstrate active tuning of excitonic strong coupling in a system where organic dyes strongly couple to propagating surface plasmon polaritons (SPPs) and modulation of vibrational strong coupling in a Fabry-Perot cavity coupled to an organic charge shuttling molecule. Next, I will discuss results indicating modified chemical reaction rates for an alcoholysis addition reaction forming urethane monomers. Cavity tuning was used to selectively couple to reactant, solvent, and product vibrational modes resulting in a chemical response that is cavity tuning dependent. Lastly, and in light of the search for an understanding of the mechanisms leading to modified chemical and physical properties, I will present a theoretical description of the density of polariton states relative to molecular dark states. This work will also discuss the differences between polariton states generated in microcavities, slabs, and in the bulk.
Materials with adaptable properties could impact optoelectronics (tunable sensors or filters) and chemical reactivity (triggered reactivity). It is widely known that strong material absorptions resonant with an optical cavity can lead to the formation of new hybrid light-matter states called polaritons. Strikingly, cavity-modified material properties (e.g., electrical conductivity, optical emission/absorption, chemical reaction rates and branching ratios) have been demonstrated and, the degree to which they are modified, shown to depend on the energy positions of these new hybrid states. Our work shows real-time tuning of these states through electrochemical cycling and optical excitation of the coupled species.
We will focus on approaches which make use of light-matter interactions to alter the chemical behavior of a target molecular species. This is done through cavity coupling to a molecular vibration. Coupling vibrational transitions to resonant optical modes creates vibrational polaritons shifted from the uncoupled molecular resonances and provides a convenient way to modify the energetics of molecular vibrations. This approach is a viable method to explore controlling chemical reactivity and energy relaxation. Here, we demonstrate frequency domain results for vibrational bands strongly coupled to optical cavities. We experimentally and numerically describe strong coupling between a Fabry-Pérot cavity and several molecular species (e.g., poly-methylmethacrylate, thiocyanate, hexamethyl diisocyanate). We investigate strong and weak coupling regimes through examination of cavities loaded with varying concentrations of a urethane monomer. Rabi splittings are in excellent agreement with an analytical description using no fitting parameters. We show that coupling strength is a function of molecule/cavity mode overlap by systematically altering the position of a molecular slab throughout a first order cavity with results agreeing well with analytical and transfer matrix predictions. Further, remote molecule-molecule interaction will be explored by placing discrete and separated molecular layers throughout a cavity. In addition to establishing that coupling to an optical cavity modifies the energy levels accessible to the coupled molecules, this work points out the possibility of systematic and predictive modification of the excited-state kinetics of vibration-cavity polariton systems. Opening the field of polaritonic coupling to vibrational species promises to be a rich arena amenable to a wide variety of infrared-active bonds that can be studied in steady state and dynamically.
Optoplasmonic materials that contain both metallic (plasmonic) and dielectric building blocks can sustain synergistic
electromagnetic interactions between photonic and plasmonic resonances and, thus, pave the way to overcoming the
limitations of the respective building blocks. A significant challenge in realizing the full potential of these unique
electromagnetic materials is the integration of building blocks with different chemical compositions and sizes into
defined morphologies. We demonstrate in this paper that template guided self-assembly strategies show great promise in
realizing intricate discrete and extended optoplasmonic materials. Selected examples of optoplasmonic materials and the
underlying fabrication methods are discussed. The first example combines dielectric microspheres as whispering gallery
mode resonators with plasmonic antennas. The latter are located at defined locations in close vicinity of (but not attached
to) the dielectric microsphere. The interactions of WGMs with plasmonic resonators located in their evanescent field are
analyzed. The second example describes two-dimensional interdigitated arrays of 250 nm diameter TiO2 NPs and
clusters of electromagnetically strongly coupled 60 nm gold nanoparticles. It is demonstrated that delocalized photonic–
plasmonic modes in the arrays achieve a cascaded E-field enhancement in the gap junctions of the gold NP clusters.
Opto-electronic coupling of plasmonic nano-antennas in the near infrared water window in vitro and in vivo is of
growing interest for imaging contrast agents, spectroscopic labels and rulers, biosensing, drug-delivery, and optoplasmonic
ablation. Metamaterials composed of nanoplasmonic meta-atoms offer improved figures of merit in many
applications across a broader spectral window. Discrete and coupled dipole approximations effectively describe
localized and coupled resonance modes in nanoplasmonic metamaterials. From numeric and experimental results have
emerged four design principles to guide fabrication and implementation of metamaterials in bio-related devices and
systems. Resonance intensity and sensitivity are enhanced by surface-to-mass of meta-atoms and lattice constant. Fano
resonant coupling is dependent on meta-atom polarizability and lattice geometry. Internal reflection in plasmonic metaatom-
containing polymer films enhances dissipation rate. Dimensions of self-assembled meta-atoms depend on
balancing electrochemical and surface forces. Examples of these principles from our lab compare computation with
images and spectra from ordered metal-ceramic and polymeric nanocomposite metamaterials for bio/opto theranostic
applications. These principles speed design and description of new architectures for nanoplasmonic metamaterials that
show promise for bioapplications.
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