Molecular Vibrational Polariton Dynamics: What Can Polaritons Do?

Abstract

Metrics & MoreArticle Recommendations CONSPECTUS: When molecular vibrational modes strongly couple to virtual states of photonic modes, new molecular vibrational polariton states are formed, along with a large population of dark reservoir modes. The polaritons are much like the bonding and antibonding molecular orbitals when atomic orbitals form molecular bonds, while the dark modes are like nonbonding orbitals. Because the polariton states are half-matter and half-light, whose energy is shifted from the parental states, polaritons are predicted to modify chemistry under thermally activated conditions, leading to an exciting and emerging field known as polariton chemistry that could potentially shift paradigms in chemistry. Despite several published results supporting this concept, the chemical physics and mechanism of polariton chemistry remain elusive. One reason for this challenge is that previous works cannot differentiate polaritons from dark modes. This limitation makes delineating the contributions to chemistry from polaritons and dark states difficult. However, this level of insight is critical for developing a solid mechanism for polariton chemistry to design and predict the outcome of strong coupling with any given reaction. My group addressed the challenge of differentiating the dynamics of polaritons and dark modes by ultrafast two-dimensional infrared (2D IR) spectroscopy. Specifically, (1) we found that polaritons can facilitate intra-and intermolecular vibrational energy transfer, opening a pathway to control vibrational energy flow in liquid-phase molecular systems, and (2) by studying a single-step isomerization event, we verified that indeed polaritons can modify chemical dynamics under strong coupling conditions, but in contrast, the dark modes behave like uncoupled molecules and do not change the dynamics. This finding confirmed the central concept of polariton chemistry: polaritons modify the potential energy landscape of reactions. The result also clarified the role of dark modes, which lays a critical foundation for designing cavities for future polariton chemistry. Aside from using 2D IR spectroscopy to study polariton chemistry, we also used the same technique to develop molecular polaritons into a potential quantum simulation platform. We demonstrated that polaritons have Rabi oscillations, and using a checkerboard cavity design, we showed that polaritons could have large nonlinearity across space. We further used the checkerboard polaritons to simulate coherence transfer and visualize it. A unidirectional coherence transfer was observed, indicating non-Hermitian dynamics. The highlighted efforts in this Account provide a solid understanding of the capability of polaritons for chemistry and quantum information science. I conclude this Account by discussing a few challenges for moving polariton chemistry toward being predictable and making the polariton quantum platform a complement to existing systems.

Coherent state switching using vibrational polaritons in an asymmetric double-well potential

“…So far, the changes in the molecular properties caused by vibrational strong coupling (VSC) in a cavity have been probed using various spectroscopy methods, including linear infrared (IR) spectroscopy, 14,15 Raman spectroscopy 11,[16][17][18] as well as 2D-IR spectroscopy. [19][20][21] Among the various properties that could be altered under VSC, energy transport, photochemical reactivity and thermally driven ground-state chemical reactions have been scrutinized. 15,[22][23][24][25][26] However, the difficulties inherent to these experiments 27 have raised a number of controversies regarding their reproducibility 28,29 and interpretation.…”

Molecular Polaritons for Chemistry, Photonics and Quantum Technologies

“…This Review is structured as follows: section provides an introduction to the fundamental theory underpinning polaritons; section explores a variety of cavity types with potential applications in molecular polaritons; section encapsulates the ongoing endeavors aimed at leveraging polaritons for manipulation of reactions and other macroscopic properties; section delves into the pursuit of revealing the intricate interplay between dark modes and polariton states using ultrafast multidimensional spectroscopy; section outlines the latest advancements in harnessing molecular polaritons to establish photonic and quantum technology platforms; last, section elucidates the prospective pathways toward controlling polariton polarization. We would like to point out the wealth of insightful prior reviews ,,,,,− and the current thematic issue. − Furthermore, our focus remains intentionally concentrated on experimental works and pertinent theoretical studies. For a more comprehensive overview of theoretical studies of polariton chemistry, we refer the audience to the following reviews from the groups of Yuen-Zhou, Nitzan, Rubio, , Feist, Huo, García-Vidal, Yelin, Owrutsky, and Herrera and Spano …”

Ultrafast Spectroscopy under Vibrational Strong Coupling in Diphenylphosphoryl Azide

“…These polariton modes are energetically separated by Rabi splitting, ℏ Ω R . Vibrational polaritons are a kind of polariton composed of infrared-active vibrational transitions and cavity photons. − Following the pioneering works by Ebbesen et al, , vibrational strong coupling (VSC) is now recognized as a new tool to modulate the vibrational potential energy surface in the electronic ground state, allowing for systematic modification of chemical reactivity and manipulation of bulk material properties by the formation of delocalized collective states. − A number of groups have reported exciting results, including reaction selectivity, ,, increased ionic conductivity, enhanced driving of DNA origami coassembly, and acceleration and suppression of ground-state reactivity. , Despite continued reports of modified molecular properties and chemical reactivity, the mechanisms behind them have still not been clearly elucidated. One major unsolved problem is, for example, the relation between the coherent and delocalized nature of the vibrational polaritons and the modified properties of VSC systems.…”