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.

中文翻译：

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振动强耦合下的溶剂极性

当分子振动与光学腔的模式混合时，就会发生振动强耦合（VSC），这是一种由真空涨落介导的相互作用。VSC 已被证明会影响化学反应的速率和选择性。然而，对其作用机制的清晰理解仍然难以捉摸。在这里，我们表明 VSC 会影响溶剂的极性，这是众所周知的影响反应性的参数。Reichardt 染料 (RD) 的强溶剂化显色响应可用于量化可见波长下一系列醇溶剂的极性。我们观察到，通过同时耦合醇的 OH 和 CH 振动带，Reichardt 染料的最大吸收红移高达 ∼15.1 nm，对应于 5.1 kJ·mol –1 的能量^变化。对于脂肪醇，观察到 RD 吸收变化的大小与烷基链长度、分子表面积和极化率有关，表明色散力受到强耦合的影响。因此，我们认为色散相互作用本身源于真空波动，在强耦合下受到影响，因此对于理解 VSC 如何影响化学至关重要。