Vibrational strong coupling (VSC)occurs when molecularvibrationshybridize with the modes of an optical cavity, an interaction mediatedby vacuum fluctuations. VSC has been shown to influence the ratesand selectivity of chemical reactions. However, a clear understandingof the mechanism at play remains elusive. Here, we show that VSC affectsthe polarity of solvents, which is a parameter well-known to influencereactivity. The strong solvatochromic response of Reichardt'sdye (RD) was used to quantify the polarity of a series of alcoholsolvents at visible wavelengths. We observed that, by simultaneouslycoupling the OH and CH vibrational bands of the alcohols, the absorptionmaximum of Reichardt's dye redshifted by up to similar to 15.1nm, corresponding to an energy change of 5.1 kJ center dot mol(-1). With aliphatic alcohols, the magnitude of the absorption changeof RD was observed to be related to the length of the alkyl chain,the molecular surface area, and the polarizability, indicating thatdispersion forces are impacted by strong coupling. Therefore, we proposethat dispersion interactions, which themselves originate from vacuumfluctuations, are impacted under strong coupling and are thereforecritical to understanding how VSC influences chemistry.
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