Solvent Polarity under Vibrational Strong Coupling

Abstract

Vibrational strong coupling (VSC) occurs when molecular vibrations hybridize with the modes of an optical cavity, an interaction mediated by vacuum fluctuations. VSC has been shown to influence the rates and selectivity of chemical reactions. However, a clear understanding of the mechanism at play remains elusive. Here, we show that VSC affects the polarity of solvents, which is a parameter well-known to influence reactivity. The strong solvatochromic response of Reichardt’s dye (RD) was used to quantify the polarity of a series of alcohol solvents at visible wavelengths. We observed that, by simultaneously coupling the OH and CH vibrational bands of the alcohols, the absorption maximum of Reichardt’s dye redshifted by up to ∼15.1 nm, corresponding to an energy change of 5.1 kJ·mol–1. With aliphatic alcohols, the magnitude of the absorption change of RD was observed to be related to the length of the alkyl chain, the molecular surface area, and the polarizability, indicating that dispersion forces are impacted by strong coupling. Therefore, we propose that dispersion interactions, which themselves originate from vacuum fluctuations, are impacted under strong coupling and are therefore critical to understanding how VSC influences chemistry.

Machine Learning for Polaritonic Chemistry: Accessing Chemical Kinetics

“…The latter is essential for investigating potential modification of solvation dynamics induced by strong coupling. 18,88,90 Polaritonic chemistry remains an equally fascinating and puzzling domain of research. While major questions are yet to be answered, [2][3][4]6 especially the connection between local chemistry and collective coupling as well as the interplay with solvation, the continuous growth of theoretical methodology and additional experiments draw an optimistic picture for the future of polaritonics.…”

Non‐Polaritonic Effects in Cavity‐Modified Photochemistry

“…[7] It potentially opens up a new avenue to modify material properties such as energy transfer, [8] ferromagnetism, [9] ionic conductivity, [10] and solvent DOI: 10.1002/adma.202309393 polarity. [11] This could lead to the development of novel smart materials with useful functionalities. Perhaps the most exciting area of study is polaritonic (or vacuummodified) chemistry: [1,[12][13][14][15][16] if, as hoped, strong coupling changes the energy levels of molecules and their coherent interaction, can it modify chemical processes?…”

Collective Strong Coupling Modifies Aggregation and Solvation

“…For example, their spectral absorption and emission can be altered by their interplay with the solvent (solvatochromic) or by the close proximity to identical molecules (concentration-dependent). Experiments under strong coupling often use organic molecules that are sensitive to their surroundings, show intense excitations, or even form aggregates. − ,− The chemical environment can then play an active role and exert significant influence, as emphasized by several vibrational strong coupling (VSC) experiments showing modification of assembly − and reactivity. ,, For a clear chemical understanding of polaritonic processes, we must then investigate the coexisting roles of the molecule, the solvent (chemical environment), and the cavity (optical environment). To this end, ab initio quantum electrodynamics (QED) merges the knowledge of quantum optics and quantum chemistry to explore single-molecule effects retaining the chemical complexity. − Even if collective states can show larger contributions from selected molecules, , local changes tend to reduce as a result of collective delocalization and an increasing number of quasi-dark states .…”

“…Three polaritonic branches, the lower polariton (LP), middle polariton (MP), and upper polariton (UP) emerge. The electron and electron–photon correlation are accurately described by the ab initio QED-CC ansatz wave function, thus capturing any modification of inter- (dispersion) and intramolecular forces. ,,,, Nevertheless, as a result of the low coupling strength, the molecular ground state, here, is essentially unaffected by the embedding in the optical environment and polaritonic effects effectively arise from collective coupling. The dimers are indirectly coupled through the cavity, establishing an interplay between longitudinal (Coulomb) and transverse (photon) fields.…”