In this study, we demonstrate that the fluorescence of fluorescein dye molecules can be significantly modified in both the weak and strong coupling regimes by placing the molecules inside a perturbative or non-perturbative Fabry-Perot cavity. By controlling the cavity thickness and dye concentration, we selectively altered the frequency and number of cavity transmission peaks, thereby establishing conditions for weak or strong coupling for fluorescein molecules. Using steady-state fluorescence spectroscopy, we confirmed that both the excitation and emission spectra were substantially tuned in these coupling regimes, enabling tunable and multicolor fluorescence from a single type of dye molecule, fluorescein.

We present a novel design approach for vibrational strong coupling (VSC) that enables spectrally accessible and controllable vibrational-polaritonic states using a graphene-integrated deep silver (Ag) grating. The deep Ag grating supports strong infrared resonances arising from hybrid magnetic polariton and surface plasmon modes, facilitating coherent coupling with the molecular vibrations of a test molecule, poly(methyl methacrylate) (PMMA). Integrating graphene into the deep Ag grating introduces discrete graphene plasmon (GP) modes that interact with the vibrational-polaritonic modes, providing spectral tunability and control over otherwise static polaritonic states. Consequently, the upper and lower polaritonic modes split into two distinct branches due to the sharp GP modes. The mixing ratio among the grating mode, molecular vibration, and GP mode is significantly modulated by adjusting the chemical potential applied to the graphene and varying the number of graphene layers incorporated into the grating. This ability to spectrally access and control polaritonic states makes the graphene-integrated Ag grating a promising platform for VSC applications, which potentially enables the use of polaritonic states as distinct quantum states for polaritonic chemistry.

Data to reproduce Figures in paper "Modification of ground state chemical reactivity via light-matter coherence in infrared cavities" published in DOI:0000/0000000

Reaction-rate modifications for chemical processes due to strong coupling between reactant molecular vibrations and the cavity vacuum have been reported; however, no currently accepted mechanisms explain these observations. In this work, reaction-rate constants were extracted from evolving cavity transmission spectra, revealing resonant suppression of the intracavity reaction rate for alcoholysis of phenyl isocyanate with cyclohexanol. We observed up to an 80% suppression of the rate by tuning cavity modes to be resonant with the reactant isocyanate (NCO) stretch, the product carbonyl (CO) stretch, and cooperative reactant-solvent modes (CH). These results were interpreted using an open quantum system model that predicted resonant modifications of the vibrational distribution of reactants from canonical statistics as a result of light-matter quantum coherences, suggesting links to explore between chemistry and quantum science.

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.

Quantum emitters in the so-called strong coupling regime, create new hybrid light-matter states called polaritons. Recently, strong coupling between molecular vibrations and optical cavity modes has been shown to alter chemical reaction rates, product ratios, and charge exchange equilibria. In this work, we examine a cavity-modified addition reaction by monitoring alcoholysis of phenyl isocyanate with cyclohexanol, which yields urethane monomers. Since the reactants, products, and solvent all have strong vibrational modes, we examine the impact of cavity coupling to each and identify bands most active in modifying this reaction. A strong cavity-tuning dependence was found with reaction rate constants decreasing by a factor of 5 for cavities tuned to the reactant isocyanate stretch mode (NCO) and reduced by half for cavities tuned to product carbonyl stretch modes as well as for cavities tuned to CH modes shared by both the solvent and reactants. The reaction progress was tracked by extracting the time-dependent reactant concentration from fits to cavity-coupled transmission spectra. Quantitative measure of reactant concentration was necessity for analyzing this second order reaction. Our results extend the understanding of cavity-modified chemistry by examining the impact of coupling to reactant, solvent, and product modes within the same system, extracting reactant concentration directly from fits to strongly coupled spectra, and by providing rigorous verification of the effect itself.

Strong cavity coupling can have profound effects on fundamental material properties. In this work, we examine the Raman scattering response of a poly(methyl methacrylate) (PMMA) carbonyl band under...

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.

Quantum emitters strongly coupled to optical cavity modes create new hybrid states called polaritons, resulting in a vacuum Rabi splitting (Ω). Strikingly, the magnitude of this splitting correlates with modified emission properties and chemical reaction rates. However, active control of this coupling strength is difficult due to the fixed properties of the coupled oscillators (both the quantum emitter and optical resonator). Here, we demonstrate active tuning of excitonic strong coupling in a system where organic dyes strongly couple to propagating surface plasmon polaritons (SPPs). After electropolymerization of a methylene blue (MB) film on a SPP-supporting Au surface, we demonstrated active control of coupling strength through reversible redox cycling of the MB film. Excitonic strong coupling was effectively cycled on and off with the electrode potential either continuously tuned (transient) or held at a fixed value (static) and was quantitatively correlated with the simultaneously measured electrochemical charge. Switching between reduced and oxidized forms of the dye resulted in Ω values tuned from ∼0 meV to ∼280 meV, i.e., ∼14% of the transition energy. The ability to control coupling strengths in a given emitter–cavity coupled system is a key capability for utilizing polaritonic states for cavity-mediated chemical reactions or optical devices.

Similar to excitonic materials interacting with optical cavity fields, vibrational absorbers coupled to resonantly matched optical modes can exhibit new hybridized energy states called cavity polaritons. The delocalized nature of these hybrid polaritonic states can potentially modify a material's physical and chemical characteristics, with the promise of a significant impact on reaction chemistry. In this study, we investigate the relationship between the spatial distribution of vibrational absorbers and the cavity mode profile in vibrational strong coupling by systematically varying the location of a 245-nm-thick poly(methyl methacrylate) (PMMA) film within a few-micrometer-thick Fabry-Perot cavity. Angle-tuning the cavity reveals that the first- and second-order cavity resonances couple to molecular absorption lines of PMMA (the C=O and C-H stretching bands at 1731 and 2952 cm(-1), respectively), resulting in quantifiable vacuum Rabi splittings in the dispersion response. These splittings, as extracted from experiment, transfer-matrix calculations, and an analytical treatment, display a consistent and strong dependence on the molecular spatial distribution within a cavity. Furthermore, we demonstrate the response of two physically separated molecular layers by measuring and calculating the vacuum Rabi splitting for cavities loaded with single and widely spaced pairs of PMMA layers. The results provide evidence that extended cavity polariton modes sample these separate layers simultaneously and, more broadly, provide guidance for controlling the coupling strength, and potentially chemical reactivity, of a given region through modification of the cavity mode profile or through introducing a remotely located molecular layer.

Strong coupling between vibrational modes and cavity optical modes leads to the formation of vibration-cavity polaritons, separated by the vacuum Rabi splitting. The splitting depends on the square root of the concentration of absorbers confined in the cavity, which has important implications on the response of the coupled system after ultrafast infrared excitation. In this work, we report on solutions of W(CO)6 in hexane with a concentration chosen to access a regime that borders on weak coupling. Under these conditions, large fractions of the W(CO)6 oscillators can be excited, and the anharmonicity of the molecules leads to a commensurate reduction in the Rabi splitting. We report excitation fractions > 0.4, depending on excitation pulse intensity, and show drastic increases in transmission that can be modulated on the picosecond time scale. In comparison to previous experiments, the transient spectra that we observe are much simpler because excited-state transitions lie outside of the transmission spectrum of the cavity, thereby contributing only weakly to the spectra. We find that the Rabi splitting recovers with the characteristic vibrational relaxation lifetime and anisotropy decay of uncoupled W(CO)6, implying that polaritons are not directly involved in the relaxation we observe after the first few ps. The results help corroborate the model that we proposed to describe the results at higher concentrations and show that the ground-state bleach of cavity-coupled molecules has a broad, multisigned spectral response.

Non-radiative plasmon decay in noble metals generates highly energetic carriers under visible light irradiation, which opens new prospects in the fields of photocatalysis, photovoltaics, and photodetection. While localized surface plasmon-induced hot carrier generation occurs in diverse metal nanostructures, inhomogeneities typical of many metal-semiconductor plasmonic nanostructures hinder predictable control of photocarrier generation and therefore reproducible carrier-mediated photochemistry. Here, we generate traveling surface plasmon polaritons (SPPs) at the interface between a noble metal/titanium dioxide (TiO2) heterostructure film and aqueous solution, enabling simultaneous optical and electrochemical interrogation of plasmon-mediated chemistry in a system whose resonance may be continuously tuned via the incident optical excitation angle. To the best of our knowledge, this is the first experimental demonstration of SPP-induced hot carrier generation for photocatalysis. We found electrochemical photovoltage and photocurrent responses as SPP-induced hot carriers drive both solution-based oxidation of methanol and the anodic half-reaction of photoelectrochemical water-splitting in sodium hydroxide solution. A strong excitation angle dependence and linear power dependence in the electrochemical photocurrent confirm that the photoelectrochemical reactions are SPP-driven. SPP-generated hot carrier chemistry was recorded on gold and silver and with two different excitation wavelengths, demonstrating potential for mapping resonant charge transfer processes with this technique. These results will provide the design criteria for a metal-semiconductor hybrid system with enhanced hot carrier generation and transport, which is important for the understanding and application of plasmon-induced photocatalysis.

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 structures contain plasmonic components embedded in a defined photonic environment to create synergistic interactions between photonic and plasmonic components. Here, we show that chains of optical microspheres containing gold nanoparticles in their evanescent field combine the light guiding properties of a microsphere chain with the light localizing properties of a plasmonic nanoantenna. We implement these materials through template guided self-assembly and investigate their fundamental electromagnetic working principles through combination of electromagnetic simulations and experimental characterization. We demonstrate that optoplasmonic chains implemented by directed self-assembly achieve a significant reduction in guiding losses when compared with conventional plasmonic waveguides and, at the same time, retain the light localizing properties of plasmonic antennas at pre-defined locations. The results reinforce the potential of optoplasmonic structures for realizing low-loss optical interconnects with high bandwidth.

United States. Department of Energy. Office of Basic Energy Science. Division of Materials Sciences and Engineering (DOE DE-SC0010679)

Optoplasmonic networks consisting of dielectric microsphere resonators and plasmonic nanoantennas in a morphologically well-defined on-chip platform support unique electromagnetic signatures that are hybrids of photonic whispering gallery modes and localized surface plasmon resonances. Here we explore the dependence of their near- and far-field responses on the key structural parameters, including the size of the gold nanoparticles forming the plasmonic elements, the separation between the microspheres, and the geometry of the chain. The high degree of structural flexibility, which is experimentally accessible through template guided self-assembly approaches, makes these optoplasmonic structures a unique electromagnetic material for tuning spectral shapes and intensities.