Modification of Urethane Addition Reaction via Vibrational Strong Coupling

Quantum emitters in the so-called strong coupling regime, create new hybrid light-matter states called polaritons. Recently, strong coupling between molecular vibrations and optical cavity modes has been shown to alter chemical reaction rates, product ratios, and charge exchange equilibria. In this work, we examine a cavity-modified addition reaction by monitoring alcoholysis of phenyl isocyanate with cyclohexanol, which yields urethane monomers. Since the reactants, products, and solvent all have strong vibrational modes, we examine the impact of cavity coupling to each and identify bands most active in modifying this reaction. A strong cavity-tuning dependence was found with reaction rate constants decreasing by a factor of 5 for cavities tuned to the reactant isocyanate stretch mode (NCO) and reduced by half for cavities tuned to product carbonyl stretch modes as well as for cavities tuned to CH modes shared by both the solvent and reactants. The reaction progress was tracked by extracting the time-dependent reactant concentration from fits to cavity-coupled transmission spectra. Quantitative measure of reactant concentration was necessity for analyzing this second order reaction. Our results extend the understanding of cavity-modified chemistry by examining the impact of coupling to reactant, solvent, and product modes within the same system, extracting reactant concentration directly from fits to strongly coupled spectra, and by providing rigorous verification of the effect itself.