Suppression of photo-oxidation of organic chromophores by strong coupling to plasmonic nanoantennas

Controlling Molecular Dynamics by Exciting Atoms in a Cavity

Placing an atom and a molecule in a cavity opens the door to initialize molecular dynamics by exciting a level of the atom. This approach enlarges the range of choosing the light source to trigger molecular dynamics substantially. The interplay of the atomic, molecular, and photonic populations gives rise to rich dynamics. The cavity photon plays the role of a mediator between the atom and the molecule and it is found that the photonic population is rather low throughout and its evolution follows that of the molecule. Cavities are known to be subject to losses. In spite of the losses it is demonstrated that the presence of the atom gives rise to a long-lived dynamics that should be of relevance for experimental investigations. The presence of more atoms and molecules is expected to further enrich the dynamics.

Global Spectral Analysis of Polaritonic Coupling of Multiple Organic Dyes to a Tunable Fabry-Pérot Resonator Operating with Mirror Separations up to 10 μm

We study strong optical coupling and the formation of hybrid polaritons by a donor-acceptor pair of J-aggregated dyes separated by up to 11 μm in a tunable Fabry-Pérot resonator. Fitting a phenomenological Hamiltonian to the white light transmission spectra of different cavity-J-aggregate-configurations, for which several hundred spectra were recorded sequentially as function of cavity length, allows us to determine coupling energies as a function of the effective cavity distances. The theoretical analysis shows that certain hybrid polaritons contain contributions from both dyes, making this system a promising platform for polariton-mediated energy transfer at very large distances.

Optical-cavity manipulation strategies of singlet fission systems mediated by conical intersections: Insights from fully quantum simulations

We offer a theoretical perspective on simulation and engineering of polaritonic conical-intersection-driven singlet-fission (SF) materials. We begin by examining fundamental models, including Tavis-Cummings and Holstein-Tavis-Cummings Hamiltonians, exploring how disorder, non-Hermitian effects, and finite temperature conditions impact their dynamics, setting the stage for studying conical intersections and their crucial role in SF. Using rubrene as an example and applying the numerically accurate Davydov Ansatz methodology, we derive dynamic and spectroscopic responses of the system and demonstrate key mechanisms capable of SF manipulation, viz. cavity-induced enhancement/weakening/suppression of SF, population localization on the singlet state via engineering cavity-mode excitation, polaron/polariton decoupling, and collective enhancement of SF. We outline unsolved problems and challenges in the field and share our views on the development of the future lines of research. We emphasize the significance of careful modeling of cascades of polaritonic conical intersections in high excitation manifolds and envisage that collective geometric phase effects may remarkably affect the SF dynamics and yield. We argue that the microscopic interpretation of the main regulatory mechanisms of polaritonic conical-intersection-driven SF can substantially deepen our understanding of this process, thereby providing novel ideas and solutions for improving conversion efficiency in photovoltaics.

Semiclassical Truncated-Wigner-Approximation Theory of Molecular Exciton-Polariton Dynamics in Optical Cavities

Molecular exciton polaritons, hybrid states formed through the strong coupling of molecular electronic excitations with optical cavity modes, offer a powerful avenue for controlling photophysical and photochemical processes in molecular systems. Here, we present a semiclassical framework for investigating the dynamics of molecular exciton polaritons using the truncated Wigner approximation (TWA). This approach extends the prior TWA method developed for molecular vibration-polariton dynamics ( J. Chem. Theory Comput. 2024, 20, 3019-3027) by incorporating semiclassical treatment of quantum coherence between ground and excited molecular states. To validate the framework, we first apply it to a simplified system of two-level (spin-1/2) molecules without vibronic coupling, demonstrating strong agreement between semiclassical and fully quantum simulations in systems with a large molecular ensemble. We further extend the model to include molecular vibronic coupling, revealing the dynamic polaron decoupling effect, where the quantum coherence between molecular excitations persists under strong light-matter coupling. These findings provide critical insights into the collective behavior and coherence preservation in polaritonic systems with implications for designing cavity-mediated molecular processes.

Nonlinear optical spectroscopy of open quantum systems

The development of experimental techniques at the nanoscale has enabled the performance of spectroscopic measurements on single-molecule current-carrying junctions. These experiments serve as a natural intersection for the research fields of optical spectroscopy and molecular electronics. We present a pedagogical comparison between the perturbation theory expansion of standard nonlinear optical spectroscopy and the (non-self-consistent) perturbative diagrammatic formulation of the nonequilibrium Green's functions method (which is widely used in molecular electronics), highlighting their similarities and differences. By comparing the two approaches, we argue that the optical spectroscopy of open quantum systems must be analyzed within the more general Green's function framework.

Disentangling collective coupling in vibrational polaritons with double quantum coherence spectroscopy

Vibrational polaritons are formed by strong coupling of molecular vibrations and photon modes in an optical cavity. Experiments have demonstrated that vibrational strong coupling can change molecular properties and even affect chemical reactivity. However, the interactions in a molecular ensemble are complex, and the exact mechanisms that lead to modifications are not fully understood yet. We simulate two-dimensional infrared spectra of molecular vibrational polaritons based on the double quantum coherence technique to gain further insight into the complex many-body structure of these hybrid light-matter states. Double quantum coherence uniquely resolves the excitation of hybrid light-matter polaritons and allows one to directly probe the anharmonicities of the resulting states. By combining the cavity Born-Oppenheimer Hartree-Fock ansatz with a full quantum dynamics simulation of the corresponding eigenstates, we go beyond simplified model systems. This allows us to study the influence of self-polarization and the response of the electronic structure to the cavity interaction on the spectral features even beyond the single-molecule case.

Comparing parameterized and self-consistent approaches to ab initio cavity quantum electrodynamics for electronic strong coupling

Molecules under strong or ultra-strong light-matter coupling present an intriguing route to modify chemical structure, properties, and reactivity. A rigorous theoretical treatment of such systems requires handling matter and photon degrees of freedom on an equal quantum mechanical footing. In the regime of molecular electronic strong or ultra-strong coupling to one or a few molecules, it is desirable to treat the molecular electronic degrees of freedom using the tools of ab initio quantum chemistry, yielding an approach referred to as ab initio cavity quantum electrodynamics (ai-QED), where the photon degrees of freedom are treated at the level of cavity QED. We analyze two complementary approaches to ai-QED: (1) a parameterized ai-QED, a two-step approach where the matter degrees of freedom are computed using existing electronic structure theories, enabling the construction of rigorous ai-QED Hamiltonians in a basis of many-electron eigenstates, and (2) self-consistent ai-QED, a one-step approach where electronic structure methods are generalized to include coupling between electronic and photon degrees of freedom. Although these approaches are equivalent in their exact limits, we identify a disparity between the projection of the two-body dipole self-energy operator that appears in the parameterized approach and its exact counterpart in the self-consistent approach. We provide a theoretical argument that this disparity resolves only under the limit of a complete orbital basis and a complete many-electron basis for the projection. We present numerical results highlighting this disparity and its resolution in a particularly simple molecular system of helium hydride cation, where it is possible to approach these two complete basis limits simultaneously. In this same helium hydride system, we examine and compare the practical issue of the computational cost required to converge each approach toward the complete orbital and many-electron bases limit. Finally, we assess the aspect of photonic convergence for polar and charged species, finding comparable behavior between parameterized and self-consistent approaches.

Toward Polaritonic Molecular Orbitals for Large Molecular Systems

A comprehensive understanding of electron-photon correlation is essential for describing the reshaping of molecular orbitals in quantum electrodynamics (QED) environments. The strong coupling QED Hartree-Fock (SC-QED-HF) theory tackles these aspects by providing consistent molecular orbitals in the strong coupling regime. The previous implementation, however, has significant convergence issues that limit the applicability. In this work, we introduce two second-order algorithms that significantly reduce the computational requirements, thereby enhancing the modeling of large molecular systems in QED environments. Furthermore, the implementation will enable the development of correlated methods based on a reliable molecular orbital framework as well as multi-level methodologies able to model the inclusion of solvent effects in this kind of complex systems.

Quantized embedding approaches for collective strong coupling-Connecting ab initio and macroscopic QED to simple models in polaritonics

Collective light-matter interactions have been used to control chemistry and energy transfer, yet accessible approaches that combine ab initio methodology with large many-body quantum optical systems are missing due to the fast increase in computational cost for explicit simulations. We introduce an accessible ab initio quantum embedding concept for many-body quantum optical systems that allows us to treat the collective coupling of molecular many-body systems effectively in the spirit of macroscopic quantum electrodynamics while keeping the rigor of ab initio quantum chemistry for the molecular structure. Our approach fully includes the quantum fluctuations of the polaritonic field and yet remains much simpler and more intuitive than complex embedding approaches such as dynamical mean-field theory. We illustrate the underlying assumptions by comparison to the Tavis-Cummings model. The intuitive application of the quantized embedding approach and its transparent limitations offer a practical framework for the field of ab initio polaritonic chemistry to describe collective effects in realistic molecular ensembles.

Controlling Plasmonic Catalysis via Strong Coupling with Electromagnetic Resonators

Plasmonic excitations decay within femtoseconds, leaving nonthermal (often referred to as "hot") charge carriers behind that can be injected into molecular structures to trigger chemical reactions that are otherwise out of reach─a process known as plasmonic catalysis. In this Letter, we demonstrate that strong coupling between resonator structures and plasmonic nanoparticles can be used to control the spectral overlap between the plasmonic excitation energy and the charge injection energy into nearby molecules. Our atomistic description couples real-time density-functional theory self-consistently to an electromagnetic resonator structure via the radiation-reaction potential. Control over the resonator provides then an additional knob for nonintrusively enhancing plasmonic catalysis, here more than 6-fold, and dynamically reacting to deterioration of the catalyst─a new facet of modern catalysis.

Microfluidics and Nanofluidics in Strong Light-Matter Coupling Systems

The combination of micro- or nanofluidics and strong light-matter coupling has gained much interest in the past decade, which has led to the development of advanced systems and devices with numerous potential applications in different fields, such as chemistry, biosensing, and material science. Strong light-matter coupling is achieved by placing a dipole (e.g., an atom or a molecule) into a confined electromagnetic field, with molecular transitions being in resonance with the field and the coupling strength exceeding the average dissipation rate. Despite intense research and encouraging results in this field, some challenges still need to be overcome, related to the fabrication of nano- and microscale optical cavities, stability, scaling up and production, sensitivity, signal-to-noise ratio, and real-time control and monitoring. The goal of this paper is to summarize recent developments in micro- and nanofluidic systems employing strong light-matter coupling. An overview of various methods and techniques used to achieve strong light-matter coupling in micro- or nanofluidic systems is presented, preceded by a brief outline of the fundamentals of strong light-matter coupling and optofluidics operating in the strong coupling regime. The potential applications of these integrated systems in sensing, optofluidics, and quantum technologies are explored. The challenges and prospects in this rapidly developing field are discussed.

Non-equilibrium rate theory for polariton relaxation dynamics

We derive an analytic expression of the non-equilibrium Fermi's golden rule (NE-FGR) expression for a Holstein-Tavis-Cumming Hamiltonian, a universal model for many molecules collectively coupled to the optical cavity. These NE-FGR expressions capture the full-time-dependent behavior of the rate constant for transitions from polariton states to dark states. The rate is shown to be reduced to the well-known frequency domain-based equilibrium Fermi's golden rule (E-FGR) expression in the equilibrium and collective limit and is shown to retain the same scaling with the number of sites in non-equilibrium and non-collective cases. We use these NE-FGR to perform population dynamics with a time-non-local and time-local quantum master equation and obtain accurate population dynamics from the initially occupied upper or lower polariton states. Furthermore, NE-FGR significantly improves the accuracy of the population dynamics when starting from the lower polariton compared to the E-FGR theory, highlighting the importance of the non-Markovian behavior and the short-time transient behavior in the transition rate constant.

The paradox of thermal vs. non-thermal effects in plasmonic photocatalysis

The debate surrounding the roles of thermal and non-thermal pathways in plasmonic catalysis has captured the attention of researchers and sparked vibrant discussions within the scientific community. In this review, we embark on a thorough exploration of this intriguing discourse, starting from fundamental principles and culminating in a detailed understanding of the divergent viewpoints. We probe into the core of the debate by elucidating the behavior of excited charge carriers in illuminated plasmonic nanostructures, which serves as the foundation for the two opposing schools of thought. We present the key arguments and evidence put forth by proponents of both the non-thermal and thermal pathways, providing a perspective on their respective positions. Beyond the theoretical divide, we discussed the evolving methodologies used to unravel these mechanisms. We discuss the use of Arrhenius equations and their variations, shedding light on the ensuing debates about their applicability. Our review emphasizes the significance of localized surface plasmon resonance (LSPR), investigating its role in collective charge oscillations and the decay dynamics that influence catalytic processes. We also talked about the nuances of activation energy, exploring its relationship with the nonlinearity of temperature and light intensity dependence on reaction rates. Additionally, we address the intricacies of catalyst surface temperature measurements and their implications in understanding light-triggered reaction dynamics. The review further discusses wavelength-dependent reaction rates, kinetic isotope effects, and competitive electron transfer reactions, offering an all-inclusive view of the field. This review not only maps the current landscape of plasmonic photocatalysis but also facilitates future explorations and innovations to unlock the full potential of plasmon-mediated catalysis, where synergistic approaches could lead to different vistas in chemical transformations.

Theory of Magnetic Properties in Quantum Electrodynamics Environments: Application to Molecular Aromaticity

In this work, we present ab initio cavity quantum electrodynamics (QED) methods which include interactions with a static magnetic field and nuclear spin degrees of freedom using different treatments of the quantum electromagnetic field. We derive explicit expressions for QED-HF magnetizability, nuclear shielding, and spin-spin coupling tensors. We apply this theory to explore the influence of the cavity field on the magnetizability of saturated, unsaturated, and aromatic hydrocarbons, showing the effects of different polarization orientations and coupling strengths. We also examine how the cavity affects aromaticity descriptors, such as the nucleus-independent chemical shift and magnetizability exaltation. We employ these descriptors to study the trimerization reaction of acetylene to benzene. We show how the optical cavity induces modifications in the aromatic character of the transition state leading to variations in the activation energy of the reaction. Our findings shed light on the effects induced by the cavity on magnetic properties, especially in the context of aromatic molecules, providing valuable insights into understanding the interplay between the quantum electromagnetic field and molecules.

Plexcitonic Nanorattles as Highly Efficient SERS-Encoded Tags

Plexcitonic nanoparticles exhibit strong light-matter interactions, mediated by localized surface plasmon resonances, and thereby promise potential applications in fields such as photonics, solar cells, and sensing, among others. Herein, these light-matter interactions are investigated by UV-visible and surface-enhanced Raman scattering (SERS) spectroscopies, supported by finite-difference time-domain (FDTD) calculations. Our results reveal the importance of combining plasmonic nanomaterials and J-aggregates with near-zero-refractive index. As plexcitonic nanostructures nanorattles are employed, based on J-aggregates of the cyanine dye 5,5,6,6-tetrachloro-1,1-diethyl-3,3-bis(4-sulfobutyl)benzimidazolocarbocyanine (TDBC) and plasmonic silver-coated gold nanorods, confined within mesoporous silica shells, which facilitate the adsorption of the J-aggregates onto the metallic nanorod surface, while providing high colloidal stability. Electromagnetic simulations show that the electromagnetic field is strongly confined inside the J-aggregate layer, at wavelengths near the upper plexcitonic mode, but it is damped toward the J-aggregate/water interface at the lower plexcitonic mode. This behavior is ascribed to the sharp variation of dielectric properties of the J-aggregate shell close to the plasmon resonance, which leads to a high opposite refractive index contrast between water and the TDBC shell, at the upper and the lower plexcitonic modes. This behavior is responsible for the high SERS efficiency of the plexcitonic nanorattles under both 633 nm and 532 nm laser illumination. SERS analysis showed a detection sensitivity down to the single-nanoparticle level and, therefore, an exceptionally high average SERS intensity per particle. These findings may open new opportunities for ultrasensitive biosensing and bioimaging, as superbright and highly stable optical labels based on the strong coupling effect.

Strongly coupled plasmon-exciton polaritons for photobleaching suppression

Strong light-matter interactions have received a lot of attention, for example in the pursuit of plasmonic-excitonic structures as coherent light sources with low-power threshold. In this study, we investigate the influence of room temperature strong coupling between surface plasmon polaritons (SPP) and excitons on fluorescence lifetimes and photobleaching effects. Our plasmonic-photonic structure, comprising of thin silver (Ag) and gold (Au) layers with a Rhodamine 6G (R6G) dye layer, shows a clear shift in the plasmon resonance and R6G absorption lines with varying incident angles, indicative of strong coupling, with a measured Rabi splitting of approximately 90 meV. Fluorescence lifetime imaging microscopy (FLIM) was then employed to assess photobleaching, revealing a significant reduction in photobleaching effect for in strongly coupled plasmonic-excitonic structures compared to single Rhodamine R6G layers. Our findings indicate the pivotal role of strong light-matter interactions in reducing photobleaching effects and stabilizing fluorescence intensities, offering promising avenues for developing quantum multiparticle nanophotonic devices with enhanced stability and performance.

Electromagnetic Enantiomer: Chiral Nanophotonic Cavities for Inducing Chemical Asymmetry

Chiral molecules, a cornerstone of chemical sciences with applications ranging from pharmaceuticals to molecular electronics, come in mirror-image pairs called enantiomers. However, their synthesis often requires complex control of their molecular geometry. We propose a strategy called "electromagnetic enantiomers" for inducing chirality in molecules located within engineered nanocavities using light, eliminating the need for intricate molecular design. This approach works by exploiting the strong coupling between a nonchiral molecule and a chiral mode within a nanocavity. We provide evidence for this strong coupling through angular emission patterns verified by numerical simulations and with complementary evidence provided by luminescence lifetime measurements. In simpler terms, our hypothesis suggests that chiral properties can be conveyed on to a molecule with a suitable chromophore by placing it within a specially designed chiral nanocavity that is significantly larger (hundreds of nanometers) than the molecule itself. To demonstrate this concept, we showcase an application in display technology, achieving efficient emission of circularly polarized light from a nonchiral molecule. The electromagnetic enantiomer concept offers a simpler approach to chiral control, potentially opening doors for asymmetric synthesis.

Quantum engineering of the radiative properties of a nanoscale mesoscopic system

Despite the recent advances in quantum technology, the problem of controlling the light emission properties of quantum emitters used in numerous applications remains: a large spectral width, low intensity, blinking, photodegradation, biocompatibility, etc. In this work, we present the theoretical and experimental investigation of quantum light sources - mesoscopic systems consisting of fluorescent molecules in a thin polydopamine layer coupled with metallic or dielectric nanoparticles. Polydopamines possess many attractive adhesive and optical properties that promise their use as host media for dye molecules. However, numerous attempts to incorporate fluorescent molecules into polydopamines have failed, as polydopamine has been shown to be a very efficient fluorescence quencher through Förster resonance energy transfer and/or photoinduced electron transfer. Using the system as an example, we demonstrate new insights into the interactions between molecules and electromagnetic fields by carefully shaping its energy levels through strong matter-wave coupling of molecules to metallic nanoparticles. We show that the strong coupling effectively suppresses the quenching of fluorescent molecules in polydopamine, opening new possibilities for imaging.

Cavity Controlled Upconversion in CdSe Nanoplatelet Polaritons

Exciton-polaritons provide a versatile platform for investigating quantum electrodynamics effects in chemical systems, such as polariton-altered chemical reactivity. However, using polaritons in chemical contexts will require a better understanding of their photophysical properties under ambient conditions, where chemistry is typically performed. Here, we used cavity quality factor to control strong light-matter interactions and in particular the excited state dynamics of colloidal CdSe nanoplatelets (NPLs) coupled to a Fabry-Pérot optical cavity. With increasing cavity quality factor, we observe significant population of the upper polariton (UP) state, exemplified by the rare observation of substantial UP photoluminescence (PL). Excitation of the lower polariton (LP) states results in upconverted PL emission from the UP branch due to efficient exchange of population between the LP, UP and the reservoir of dark states present in collectively coupled polaritonic systems. In addition, we measure time scales for polariton dynamics ∼100 ps, implying great potential for NPL based polariton systems to affect photochemical reaction rates. State-of-the-art quantum dynamical simulations show outstanding quantitative agreement with experiments, and thus provide important insight into polariton photophysical dynamics of collectively coupled nanocrystal-based systems. These findings represent a significant step toward the development of practical polariton photochemistry platforms.

Thermal disorder prevents the suppression of ultra-fast photochemistry in the strong light-matter coupling regime

Strong coupling between molecules and confined light modes of optical cavities to form polaritons can alter photochemistry, but the origin of this effect remains largely unknown. While theoretical models suggest a suppression of photochemistry due to the formation of new polaritonic potential energy surfaces, many of these models do not account for the energetic disorder among the molecules, which is unavoidable at ambient conditions. Here, we combine simulations and experiments to show that for an ultra-fast photochemical reaction such thermal disorder prevents the modification of the potential energy surface and that suppression is due to radiative decay of the lossy cavity modes. We also show that the excitation spectrum under strong coupling is a product of the excitation spectrum of the bare molecules and the absorption spectrum of the molecule-cavity system, suggesting that polaritons can act as gateways for channeling an excitation into a molecule, which then reacts normally. Our results therefore imply that strong coupling provides a means to tune the action spectrum of a molecule, rather than to change the reaction.

Visual Sensor with Host-Guest Specific Recognition and Light-Electrical Co-Controlled Switch

Perception of UV radiation has important applications in medical health, industrial production, electronic communication, etc. In numerous application scenarios, there is an increasing demand for the intuitive and low-cost detection of UV radiation through colorimetric visual behavior, as well as the efficient and multi-functional utilization of UV radiation. However, photodetectors based on photoconductive modes or photosensitive colorimetric materials are not conducive to portable or multi-scene applications owing to their complex and expensive photosensitive components, potential photobleaching, and single-stimulus response behavior. Here, a multifunctional visual sensor based on the "host-guest photo-controlled permutation" strategy and the "lock and key" model is developed. The host-guest specific molecular recognition and electrochromic sensing platform is integrated at the micro-molecular scale, enabling multi-functional and multi-scene applications in the convenient and fast perception of UV radiation, military camouflage, and information erasure at the macro level of human-computer interaction through light-electrical co-controlled visual switching characteristics. This light-electrical co-controlled visual sensor based on an optoelectronic multi-mode sensing system is expected to provide new ideas and paradigms for healthcare, microelectronics manufacturing, and wearable electronic devices owing to its advantages of signal visualization, low energy consumption, low cost, and versatility.

Extending the Tavis-Cummings model for molecular ensembles-Exploring the effects of dipole self-energies and static dipole moments

Strong coupling of organic molecules to the vacuum field of a nanoscale cavity can be used to modify their chemical and physical properties. We extend the Tavis-Cummings model for molecular ensembles and show that the often neglected interaction terms arising from the static dipole moment and the dipole self-energy are essential for a correct description of the light-matter interaction in polaritonic chemistry. On the basis of a full quantum description, we simulate the excited-state dynamics and spectroscopy of MgH+ molecules resonantly coupled to an optical cavity. We show that the inclusion of static dipole moments and the dipole self-energy is necessary to obtain a consistent model. We construct an efficient two-level system approach that reproduces the main features of the real molecular system and may be used to simulate larger molecular ensembles.

Tunable single emitter-cavity coupling strength through waveguide-assisted energy quantum transfer

The emitter-cavity strong coupling manifests crucial significance for exploiting quantum technology, especially in the scale of individual emitters. However, due to the small light-matter interaction cross-section, the single emitter-cavity strong coupling has been limited by its harsh requirement on the quality factor of the cavity and the local density of optical states. Herein, we present a strategy termed waveguide-assisted energy quantum transfer (WEQT) to improve the single emitter-cavity coupling strength by extending the interaction cross-section. Multiple ancillary emitters are optically linked by a waveguide, providing an indirect coupling channel to transfer the energy quantum between target emitter and cavity. An enhancement factor of coupling strengthg ̃ / g > 10 can be easily achieved, which dramatically release the rigorous design of cavity. As an extension of concept, we further show that the ancillae can be used as controlling bits for a photon gate, opening up new degrees of freedom in quantum manipulation.

Influence of molecular structure on the coupling strength to a plasmonic nanoparticle and hot carrier generation

Strong coupling between metal nanoparticles and molecules mixes their excitations, creating new eigenstates with modified properties such as altered chemical reactivity, different relaxation pathways or modified phase transitions. Here, we explore excited state plasmon-molecule coupling and discuss how strong coupling together with a changed orientation and number of an asymmetric molecule affects the generation of hot carriers in the system. We used a promising plasmonic material, magnesium, for the nanoparticle and coupled it with CPDT molecules, which are used in organic optoelectronic materials for organic electronic applications due to their facile modification, electron-rich structure, low band gap, high electrical conductivity and good charge transport properties. By employing computational quantum electronic tools we demonstrate the existence of a strong coupling mediated charge transfer plasmon whose direction, magnitude, and spectral position can be tuned. We find that the orientation of CPDT changes the nanoparticle-molecule gap for which maximum charge separation occurs, while larger gaps result in trapping hot carriers within the moieties due to weaker interactions. This research highlights the potential for tuning hot carrier generation in strongly coupled plasmon-molecule systems for enhanced energy generation or excited state chemistry.

Hybrid architectures for terahertz molecular polaritonics

Atoms and their different arrangements into molecules are nature's building blocks. In a regime of strong coupling, matter hybridizes with light to modify physical and chemical properties, hence creating new building blocks that can be used for avant-garde technologies. However, this regime relies on the strong confinement of the optical field, which is technically challenging to achieve, especially at terahertz frequencies in the far-infrared region. Here we demonstrate several schemes of electromagnetic field confinement aimed at facilitating the collective coupling of a localized terahertz photonic mode to molecular vibrations. We observe an enhanced vacuum Rabi splitting of 200 GHz from a hybrid cavity architecture consisting of a plasmonic metasurface, coupled to glucose, and interfaced with a planar mirror. This enhanced light-matter interaction is found to emerge from the modified intracavity field of the cavity, leading to an enhanced zero-point electric field amplitude. Our study provides key insight into the design of polaritonic platforms with organic molecules to harvest the unique properties of hybrid light-matter states.

Self-Hybridized Vibrational-Mie Polaritons in Water Droplets

We study the self-hybridization between Mie modes supported by water droplets with stretching and bending vibrations in water molecules. Droplets with radii >2.7  μm are found to be polaritonic on the onset of the ultrastrong light-matter coupling regime. Similarly, the effect is observed in larger deuterated water droplets at lower frequencies. Our results indicate that polaritonic states are ubiquitous and occur in water droplets in mists, fogs, and clouds. This finding may have implications not only for polaritonic physics but also for aerosol and atmospheric sciences.

Controlling Molecular Photoisomerization in Photonic Cavities through Polariton Funneling

Strong coupling between photonic modes and molecular electronic excitations, creating hybrid light-matter states called polaritons, is an attractive avenue for controlling chemical reactions. Nevertheless, experimental demonstrations of polariton-modified chemical reactions remain sparse. Here, we demonstrate modified photoisomerization kinetics of merocyanine and diarylethene by coupling the reactant's optical transition with photonic microcavity modes. We leverage broadband Fourier-plane optical microscopy to noninvasively and rapidly monitor photoisomerization within microcavities, enabling systematic investigation of chemical kinetics for different cavity-exciton detunings and photoexcitation conditions. We demonstrate three distinct effects of cavity coupling: first, a renormalization of the photonic density of states, akin to a Purcell effect, leads to enhanced absorption and isomerization rates at certain wavelengths, notably red-shifting the onset of photoisomerization. This effect is present under both strong and weak light-matter couplings. Second, kinetic competition between polariton localization into reactive molecular states and cavity losses leads to a suppression of the photoisomerization yield. Finally, our key result is that in reaction mixtures with multiple reactant isomers, exhibiting partially overlapping optical transitions and distinct isomerization pathways, the cavity resonance can be tuned to funnel photoexcitations into specific reactant isomers. Thus, upon decoherence, polaritons localize into a chosen isomer, selectively triggering the latter's photoisomerization despite initially being delocalized across all isomers. This result suggests that careful tuning of the cavity resonance is a promising avenue to steer chemical reactions and enhance product selectivity in reaction mixtures.

Molecular Polaritons for Chemistry, Photonics and Quantum Technologies

Molecular polaritons are quasiparticles resulting from the hybridization between molecular and photonic modes. These composite entities, bearing characteristics inherited from both constituents, exhibit modified energy levels and wave functions, thereby capturing the attention of chemists in the past decade. The potential to modify chemical reactions has spurred many investigations, alongside efforts to enhance and manipulate optical responses for photonic and quantum applications. This Review centers on the experimental advances in this burgeoning field. Commencing with an introduction of the fundamentals, including theoretical foundations and various cavity architectures, we discuss outcomes of polariton-modified chemical reactions. Furthermore, we navigate through the ongoing debates and uncertainties surrounding the underpinning mechanism of this innovative method of controlling chemistry. Emphasis is placed on gaining a comprehensive understanding of the energy dynamics of molecular polaritons, in particular, vibrational molecular polaritons─a pivotal facet in steering chemical reactions. Additionally, we discuss the unique capability of coherent two-dimensional spectroscopy to dissect polariton and dark mode dynamics, offering insights into the critical components within the cavity that alter chemical reactions. We further expand to the potential utility of molecular polaritons in quantum applications as well as precise manipulation of molecular and photonic polarizations, notably in the context of chiral phenomena. This discussion aspires to ignite deeper curiosity and engagement in revealing the physics underpinning polariton-modified molecular properties, and a broad fascination with harnessing photonic environments to control chemistry.

Non-Hermitian molecular dynamics simulations of exciton-polaritons in lossy cavities

The observation that materials can change their properties when placed inside or near an optical resonator has sparked a fervid interest in understanding the effects of strong light-matter coupling on molecular dynamics, and several approaches have been proposed to extend the methods of computational chemistry into this regime. Whereas the majority of these approaches have focused on modeling a single molecule coupled to a single cavity mode, changes to chemistry have so far only been observed experimentally when very many molecules are coupled collectively to multiple modes with short lifetimes. While atomistic simulations of many molecules coupled to multiple cavity modes have been performed with semi-classical molecular dynamics, an explicit description of cavity losses has so far been restricted to simulations in which only a very few molecular degrees of freedom were considered. Here, we have implemented an effective non-Hermitian Hamiltonian to explicitly treat cavity losses in large-scale semi-classical molecular dynamics simulations of organic polaritons and used it to perform both mean-field and surface hopping simulations of polariton relaxation, propagation, and energy transfer.

Machine Learning for Polaritonic Chemistry: Accessing Chemical Kinetics

Altering chemical reactivity and material structure in confined optical environments is on the rise, and yet, a conclusive understanding of the microscopic mechanisms remains elusive. This originates mostly from the fact that accurately predicting vibrational and reactive dynamics for soluted ensembles of realistic molecules is no small endeavor, and adding (collective) strong light-matter interaction does not simplify matters. Here, we establish a framework based on a combination of machine learning (ML) models, trained using density-functional theory calculations and molecular dynamics to accelerate such simulations. We then apply this approach to evaluate strong coupling, changes in reaction rate constant, and their influence on enthalpy and entropy for the deprotection reaction of 1-phenyl-2-trimethylsilylacetylene, which has been studied previously both experimentally and using ab initio simulations. While we find qualitative agreement with critical experimental observations, especially with regard to the changes in kinetics, we also find differences in comparison with previous theoretical predictions. The features for which the ML-accelerated and ab initio simulations agree show the experimentally estimated kinetic behavior. Conflicting features indicate that a contribution of dynamic electronic polarization to the reaction process is more relevant than currently believed. Our work demonstrates the practical use of ML for polaritonic chemistry, discusses limitations of common approximations, and paves the way for a more holistic description of polaritonic chemistry.

Understanding the Nature of Vibro-Polaritonic States in Water and Heavy Water

Very recent experiments on vibrational strong coupling tend to modify chemical reactivity, energy transfer, and many other physical properties of the coupled system. This is achieved without external stimuli and is very sensitive to the vibrational envelope. Water is an excellent vibrational oscillator, which is being used for similar experiments. However, the inhomogeneously broad OH/OD stretching vibrational band make it complicated to characterize the vibro-polaritonic states spectroscopically. In this paper, we performed vibrational strong coupling and mapped the evolution of vibro-polaritonic branches from low to high concentration of H2 O and measured the on-set of strong coupling. The refractive index dispersion is correlated with the cavity tuning experiments. These results are further compared with transfer matrix simulations. Simulated data deviate as noted in the dispersion spectra as the system enters into ultra-strong coupling due to enhanced self-dipolar interactions. Hopfield coefficients calculation shows that even at ±400 cm-1 detuning, the vibro-polaritonic states still possess hybrid characteristics. We systematically varied the concentration of H2 O and mapped the weak, intermediate, and strong coupling regimes to understand the role of inhomogeneously broad OH/OD stretching vibrational band. Our finding may help to better understand the role of H2 O/D2 O strong coupling in the recent polaritonic chemistry experiments.

Cavity Quantum Electrodynamics Complete Active Space Configuration Interaction Theory

Polariton chemistry has attracted great attention as a potential route to modify chemical structure, properties, and reactivity through strong interactions among molecular electronic, vibrational, or rovibrational degrees of freedom. A rigorous theoretical treatment of molecular polaritons requires the treatment of matter and photon degrees of freedom on equal quantum mechanical footing. In the limit of molecular electronic strong or ultrastrong coupling to one or a few molecules, it is desirable to treat the molecular electronic degrees of freedom using the tools of ab initio quantum chemistry, yielding an approach we refer to as ab initio cavity quantum electrodynamics, where the photon degrees of freedom are treated at the level of cavity quantum electrodynamics. Here, we present an approach called Cavity Quantum Electrodynamics Complete Active Space Configuration Interaction theory to provide ground- and excited-state polaritonic surfaces with a balanced description of strong correlation effects among electronic and photonic degrees of freedom. This method provides a platform for ab initio cavity quantum electrodynamics when both strong electron correlation and strong light-matter coupling are important and is an important step toward computational approaches that yield multiple polaritonic potential energy surfaces and couplings that can be leveraged for ab initio molecular dynamics simulations of polariton chemistry.

Collective Strong Coupling Modifies Aggregation and Solvation

Intermolecular (Coulombic) interactions are pivotal for aggregation, solvation, and crystallization. We demonstrate that the collective strong coupling of several molecules to a single optical mode results in notable changes in the molecular excitations around a single perturbed molecule, thus representing an impurity in an otherwise ordered system. A competition between short-range coulombic and long-range photonic correlations inverts the local transition density in a polaritonic state, suggesting notable changes in the polarizability of the solvation shell. Our results provide an alternative perspective on recent work in polaritonic chemistry and pave the way for the rigorous treatment of cooperative effects in aggregation, solvation, and crystallization.

Non-Polaritonic Effects in Cavity-Modified Photochemistry

Strong coupling of molecules to vacuum fields is widely reported to lead to modified chemical properties such as reaction rates. However, some recent attempts to reproduce infrared strong coupling results have not been successful, suggesting that factors other than strong coupling may sometimes be involved. In the first vacuum-modified chemistry experiment, changes to a molecular photoisomerization process in the ultraviolet-visible spectral range are attributed to strong coupling of the molecules to visible light. Here, this process is re-examined, finding significant variations in photoisomerization rates consistent with the original work. However, there is no evidence that these changes need to be attributed to strong coupling. Instead, it is suggested that the photoisomerization rates involved are most strongly influenced by the absorption of ultraviolet radiation in the cavity. These results indicate that care must be taken to rule out non-polaritonic effects before invoking strong coupling to explain any changes of properties arising in cavity-based experiments.

Strong coupling in mechanically flexible free-standing organic membranes

Strong coupling of a confined optical field to the excitonic or vibronic transitions of a molecular material results in the formation of new hybrid states called polaritons. Such effects have been extensively studied in Fabry-Pèrot microcavity structures where an organic material is placed between two highly reflective mirrors. Recently, theoretical and experimental evidence has suggested that strong coupling can be used to modify chemical reactivity as well as molecular photophysical functionalities. However, the geometry of conventional microcavity structures limits the ability of molecules "encapsulated" in a cavity to interact with their local environment. Here, we fabricate mirrorless organic membranes that utilize the refractive index contrast between the organic active material and its surrounding medium to confine an optical field with Q-factor values up to 33. Using angle-resolved white light reflectivity measurements, we confirm that our structures operate in the strong coupling regime, with Rabi-splitting energies between 60 and 80 meV in the different structures studied. The experimental results are matched by transfer matrix and coupled oscillator models that simulate the various polariton states of the free standing membranes. Our work demonstrates that mechanically flexible and easy-to-fabricate free standing membranes can support strong light-matter coupling, making such simple and versatile structures highly promising for a range of polariton applications.

Ultrafast dynamics of CN radical reactions with chloroform solvent under vibrational strong coupling

Polariton chemistry may provide a new means to control molecular reactivity, permitting remote, reversible modification of reaction energetics, kinetics, and product yields. A considerable body of experimental and theoretical work has already demonstrated that strong coupling between a molecular vibrational mode and the confined electromagnetic field of an optical cavity can alter chemical reactivity without external illumination. However, the mechanisms underlying cavity-altered chemistry remain unclear in large part because the experimental systems examined previously are too complex for detailed analysis of their reaction dynamics. Here, we experimentally investigate photolysis-induced reactions of cyanide radicals with strongly-coupled chloroform (CHCl3) solvent molecules and examine the intracavity rates of photofragment recombination, solvent complexation, and hydrogen abstraction. We use a microfluidic optical cavity fitted with dichroic mirrors to facilitate vibrational strong coupling (VSC) of the C-H stretching mode of CHCl3 while simultaneously permitting optical access at visible wavelengths. Ultrafast transient absorption experiments performed with cavities tuned on- and off-resonance reveal that VSC of the CHCl3 C-H stretching transition does not significantly modify any measured rate constants, including those associated with the hydrogen abstraction reaction. This work represents, to the best of our knowledge, the first experimental study of an elementary bimolecular reaction under VSC. We discuss how the conspicuous absence of cavity-altered effects in this system may provide insights into the mechanisms of modified ground state reactivity under VSC and help bridge the divide between experimental results and theoretical predictions in vibrational polariton chemistry.

The Rise and Current Status of Polaritonic Photochemistry and Photophysics

The interaction between molecular electronic transitions and electromagnetic fields can be enlarged to the point where distinct hybrid light-matter states, polaritons, emerge. The photonic contribution to these states results in increased complexity as well as an opening to modify the photophysics and photochemistry beyond what normally can be seen in organic molecules. It is today evident that polaritons offer opportunities for molecular photochemistry and photophysics, which has caused an ever-rising interest in the field. Focusing on the experimental landmarks, this review takes its reader from the advent of the field of polaritonic chemistry, over the split into polariton chemistry and photochemistry, to present day status within polaritonic photochemistry and photophysics. To introduce the field, the review starts with a general description of light-matter interactions, how to enhance these, and what characterizes the coupling strength. Then the photochemistry and photophysics of strongly coupled systems using Fabry-Perot and plasmonic cavities are described. This is followed by a description of room-temperature Bose-Einstein condensation/polariton lasing in polaritonic systems. The review ends with a discussion on the benefits, limitations, and future developments of strong exciton-photon coupling using organic molecules.

Control of Photoswitching Kinetics with Strong Light-Matter Coupling in a Cavity

Most photochemistry occurs in the regime of weak light-matter coupling, in which a molecule absorbs a photon and then performs photochemistry from its excited state. In the strong coupling regime, enhanced light-matter interactions between an optical field and multiple molecules lead to collective hybrid light-matter states called polaritons. This strong coupling leads to fundamental changes in the nature of the excited states including multi-molecule delocalized excitations, modified potential energy surfaces, and dramatically altered energy levels relative to non-coupled molecules. The effect of strong light-matter coupling on covalent photochemistry has not been well explored. Photoswitches undergo reversible intramolecular photoreactions that can be readily monitored spectroscopically. In this work, we study the effect of strong light-matter coupling on the kinetics of photoswitching within optical cavities. Reproducing prior experiments, photoswitching of spiropyran/merocyanine photoswitches is decelerated in a cavity. Fulgide photoswitches, however, show the opposite effect, with strong coupling accelerating photoswitching. While modified merocyanine switching can be explained by changes in radiative decay rates or the amount of light in the cavity, modified fulgide switching kinetics suggest direct changes to excited-state reaction kinetics.

Quantum dynamics simulations of the 2D spectroscopy for exciton polaritons

We develop an accurate and numerically efficient non-adiabatic path-integral approach to simulate the non-linear spectroscopy of exciton-polariton systems. This approach is based on the partial linearized density matrix approach to model the exciton dynamics with explicit propagation of the phonon bath environment, combined with a stochastic Lindblad dynamics approach to model the cavity loss dynamics. Through simulating both linear and polariton two-dimensional electronic spectra, we systematically investigate how light-matter coupling strength and cavity loss rate influence the optical response signal. Our results confirm the polaron decoupling effect, which is the reduced exciton-phonon coupling among polariton states due to the strong light-matter interactions. We further demonstrate that the polariton coherence time can be significantly prolonged compared to the electronic coherence outside the cavity.

Theoretical Advances in Polariton Chemistry and Molecular Cavity Quantum Electrodynamics

When molecules are coupled to an optical cavity, new light-matter hybrid states, so-called polaritons, are formed due to quantum light-matter interactions. With the experimental demonstrations of modifying chemical reactivities by forming polaritons under strong light-matter interactions, theorists have been encouraged to develop new methods to simulate these systems and discover new strategies to tune and control reactions. This review summarizes some of these exciting theoretical advances in polariton chemistry, in methods ranging from the fundamental framework to computational techniques and applications spanning from photochemistry to vibrational strong coupling. Even though the theory of quantum light-matter interactions goes back to the midtwentieth century, the gaps in the knowledge of molecular quantum electrodynamics (QED) have only recently been filled. We review recent advances made in resolving gauge ambiguities, the correct form of different QED Hamiltonians under different gauges, and their connections to various quantum optics models. Then, we review recently developed ab initio QED approaches which can accurately describe polariton states in a realistic molecule-cavity hybrid system. We then discuss applications using these method advancements. We review advancements in polariton photochemistry where the cavity is made resonant to electronic transitions to control molecular nonadiabatic excited state dynamics and enable new photochemical reactivities. When the cavity resonance is tuned to the molecular vibrations instead, ground-state chemical reaction modifications have been demonstrated experimentally, though its mechanistic principle remains unclear. We present some recent theoretical progress in resolving this mystery. Finally, we review the recent advances in understanding the collective coupling regime between light and matter, where many molecules can collectively couple to a single cavity mode or many cavity modes. We also lay out the current challenges in theory to explain the observed experimental results. We hope that this review will serve as a useful document for anyone who wants to become familiar with the context of polariton chemistry and molecular cavity QED and thus significantly benefit the entire community.

Theory for Cavity-Modified Ground-State Reactivities via Electron-Photon Interactions

We provide a simple and intuitive theory to explain how coupling a molecule to an optical cavity can modify ground-state chemical reactivity by exploiting intrinsic quantum behaviors of light-matter interactions. Using the recently developed polarized Fock states representation, we demonstrate that the change of the ground-state potential is achieved due to the scaling of diabatic electronic couplings with the overlap of the polarized Fock states. Our theory predicts that for a proton-transfer model system, the ground-state barrier height can be modified through light-matter interactions when the cavity frequency is in the electronic excitation range. Our simple theory explains several recent computational investigations that discovered the same effect. We further demonstrate that under the deep strong coupling limit of the light and matter, the polaritonic ground and first excited eigenstates become the Mulliken-Hush diabatic states, which are the eigenstates of the dipole operator. This work provides a simple but powerful theoretical framework to understand how strong coupling between the molecule and the cavity can modify ground-state reactivities.

The role of dephasing for dark state coupling in a molecular Tavis-Cummings model

The collective coupling of an ensemble of molecules to a light field is commonly described by the Tavis-Cummings model. This model includes numerous eigenstates that are optically decoupled from the optically bright polariton states. Accessing these dark states requires breaking the symmetry in the corresponding Hamiltonian. In this paper, we investigate the influence of non-unitary processes on the dark state dynamics in the molecular Tavis-Cummings model. The system is modeled with a Lindblad equation that includes pure dephasing, as it would be caused by weak interactions with an environment, and photon decay. Our simulations show that the rate of pure dephasing, as well as the number of two-level systems, has a significant influence on the dark state population.

Strong coupling in plasmonic metal nanoparticles

The study of strong coupling between light and matter has gained significant attention in recent years due to its potential applications in diverse fields, including artificial light harvesting, ultraefficient polariton lasing, and quantum information processing. Plasmonic cavities are a compelling alternative of conventional photonic resonators, enabling ultracompact polaritonic systems to operate at room temperature. This review focuses on colloidal metal nanoparticles, highlighting their advantages as plasmonic cavities in terms of their facile synthesis, tunable plasmonic properties, and easy integration with excitonic materials. We explore recent examples of strong coupling in single nanoparticles, dimers, nanoparticle-on-a-mirror configurations, and other types of nanoparticle-based resonators. These systems are coupled with an array of excitonic materials, including atomic emitters, semiconductor quantum dots, two-dimensional materials, and perovskites. In the concluding section, we offer perspectives on the future of strong coupling research in nanoparticle systems, emphasizing the challenges and potentials that lie ahead. By offering a thorough understanding of the current state of research in this field, we aim to inspire further investigations and advances in the study of strongly coupled nanoparticle systems, ultimately unlocking new avenues in nanophotonic applications.

Sub-picosecond collapse of molecular polaritons to pure molecular transition in plasmonic photoswitch-nanoantennas

Molecular polaritons are hybrid light-matter states that emerge when a molecular transition strongly interacts with photons in a resonator. At optical frequencies, this interaction unlocks a way to explore and control new chemical phenomena at the nanoscale. Achieving such control at ultrafast timescales, however, is an outstanding challenge, as it requires a deep understanding of the dynamics of the collectively coupled molecular excitation and the light modes. Here, we investigate the dynamics of collective polariton states, realized by coupling molecular photoswitches to optically anisotropic plasmonic nanoantennas. Pump-probe experiments reveal an ultrafast collapse of polaritons to pure molecular transition triggered by femtosecond-pulse excitation at room temperature. Through a synergistic combination of experiments and quantum mechanical modelling, we show that the response of the system is governed by intramolecular dynamics, occurring one order of magnitude faster with respect to the uncoupled excited molecule relaxation to the ground state.

Molecular Chemistry in Cavity Strong Coupling

The coherent exchange of energy between materials and optical fields leads to strong light-matter interactions and so-called polaritonic states with intriguing properties, halfway between light and matter. Two decades ago, research on these strong light-matter interactions, using optical cavity (vacuum) fields, remained for the most part the province of the physicist, with a focus on inorganic materials requiring cryogenic temperatures and carefully fabricated, high-quality optical cavities for their study. This review explores the history and recent acceleration of interest in the application of polaritonic states to molecular properties and processes. The enormous collective oscillator strength of dense films of organic molecules, aggregates, and materials allows cavity vacuum field strong coupling to be achieved at room temperature, even in rapidly fabricated, highly lossy metallic optical cavities. This has put polaritonic states and their associated coherent phenomena at the fingertips of laboratory chemists, materials scientists, and even biochemists as a potentially new tool to control molecular chemistry. The exciting phenomena that have emerged suggest that polaritonic states are of genuine relevance within the molecular and material energy landscape.

Modification of ground-state chemical reactivity via light-matter coherence in infrared cavities

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.

Validation of Calcein Violet as a New Marker of Semen Membrane Integrity in Domestic Animals

Many fluorochromes routinely used in semen quality analysis emit in the green and red channels, limiting their possible combination for multiple parameter analysis. The use of fluorophores emitting in different light channels broadens the possibilities of combination to expand the range of simultaneously evaluated criteria. This is of great interest in cases of small ejaculated volumes, such as those naturally occurring in roosters, small dog breeds and drones (Apis mellifera). The purpose of this experiment is to establish Calcein Violet (CaV), a blue fluorochrome, as a marker of viability and acrosomal integrity in domestic animals in order to free the red and green channels. SYBR®14/Propidium Iodide (PI) was used as reference dye, heat-treated samples as negative controls, serial staining combination for validation and epifluorescence microscopy for observation. Dead spermatozoa marked in red with PI showed no blue fluorescence either from the head or the tail. Live spermatozoa showed a decreasing blue emission from head to tail when single stained with CaV. Unreacted acrosomes showed intense blue fluorescence irrespective of plasma membrane integrity. This needs to be further confirmed for species with small and difficult to observe heads. Establishment of CaV as a marker of membrane integrity by fluorescence microscopy is a decisive first step towards further technical development and use with flow cytometry.

Control and Enhancement of Single-Molecule Electroluminescence through Strong Light-Matter Coupling

The energetic positions of molecular electronic states at molecule/electrode interfaces are crucial factors for determining the transport and optoelectronic properties of molecular junctions. Strong light-matter coupling offers a potential for manipulating these factors, enabling a boost in the efficiency and versatility of these junctions. Here, we investigate electroluminescence from single-molecule junctions in which the molecule is strongly coupled with the vacuum electromagnetic field in a plasmonic nanocavity. We demonstrate an improvement in the electroluminescence efficiency by employing the strong light-matter coupling in conjunction with the characteristic feature of single-molecule junctions to selectively control the formation of the lowest-energy excited state. The mechanism of efficiency improvement is discussed based on the energetic position and composition of the formed polaritonic states. Our findings indicate the possibility to manipulate optoelectronic conversion in molecular junctions by strong light-matter coupling and contribute to providing design principles for developing efficient molecular optoelectronic devices.

Chiral Polaritonics: Analytical Solutions, Intuition, and Use

Preferential selection of a given enantiomer over its chiral counterpart has become increasingly relevant in the advent of the next era of medical drug design. In parallel, cavity quantum electrodynamics has grown into a solid framework to control energy transfer and chemical reactivity, the latter requiring strong coupling. In this work, we derive an analytical solution to a system of many chiral emitters interacting with a chiral cavity similar to the widely used Tavis-Cummings and Hopfield models of quantum optics. We are able to estimate the discriminating strength of chiral polaritonics, discuss possible future development directions and exciting applications such as elucidating homochirality, and deliver much needed intuition to foster the newly flourishing field of chiral polaritonics.

Quantitative Investigation of the Rate of Intersystem Crossing in the Strong Exciton-Photon Coupling Regime

Strong interactions between excitons and photons lead to the formation of exciton-polaritons, which possess completely different properties compared to their constituents. The polaritons are created by incorporating a material in an optical cavity where the electromagnetic field is tightly confined. Over the last few years, the relaxation of polaritonic states has been shown to enable a new kind of energy transfer event, which is efficient at length scales substantially larger than the typical Förster radius. However, the importance of such energy transfer depends on the ability of the short-lived polaritonic states to efficiently decay to molecular localized states that can perform a photochemical process, such as charge transfer or triplet states. Here, we investigate quantitatively the interaction between polaritons and triplet states of erythrosine B in the strong coupling regime. We analyze the experimental data, collected mainly employing angle-resolved reflectivity and excitation measurements, using a rate equation model. We show that the rate of intersystem crossing from the polariton to the triplet states depends on the energy alignment of the excited polaritonic states. Furthermore, it is demonstrated that the rate of intersystem crossing can be substantially enhanced in the strong coupling regime to the point where it approaches the rate of the radiative decay of the polariton. In light of the opportunities that transitions from polaritonic to molecular localized states offer within molecular photophysics/chemistry and organic electronics, we hope that the quantitative understanding of such interactions gained from this study will aid in the development of polariton-empowered devices.