H-bond Dynamics Modification Under Vibrational Strong Coupling: The Role of Energy Disorder

Polaritons, quasiparticles that exhibit both light and matter characteristics, are formed by coupling molecular vibrations with confined light fields in Fabry-Pérot cavities, achieving vibrational strong coupling (VSC). Under VSC, changes in chemical reactivity and energy transfer have been observed, but conflicting reports of null effects suggest that crucial factors may be overlooked. In our study, we identify energy disorder as a key parameter influencing polariton delocalization under VSC.

Our model system focuses on the H-bond dynamics of 2,6-Di-tert-butylphenol in both its liquid and solid phases, which involve H-bond association and dissociation. In the solid phase, the well-ordered molecular packing leads to a sharp OH stretch vibration with minimal energy disorder, while the liquid phase exhibits significant energy disorder in the same mode. This contrast allows us to systematically investigate the role of energy disorder on polariton behavior.

Through 2DIR and polarization-dependent pump-probe, we observed energy transfer within the cavity in the solid phase, driven by polariton delocalization. However, in the liquid phase, there was no discernible difference in H-bond dynamics inside versus outside the cavity, which we attribute to the loss of polariton delocalization caused by energy disorder.

Our findings suggest that minimizing energy disorder is critical to sustaining polariton delocalization, highlighting their importance in modifying molecular dynamics under VSC.

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