Influence of Vibrational Strong Coupling on an Ordered Liquid Crystal

Vibrational strong coupling and the formation of vibrational polaritons are a result of strong light-matter interaction between a cavity photon and a molecular vibrational mode. The Rabi splitting parameter, which reflects the microscopic light-matter interaction strength, reveals information about the molecular alignment and concerted vibrational motion inside the cavity. We have investigated vibrational strong coupling of 4-cyano-4 '-octylbiphenyl liquid crystal molecules in isotropic and smectic A phases. We observed a similar to 30% change in the Rabi splitting with the phase transition from isotropic to smectic A by controlling the temperature, together with the onset of polarization-dependent anisotropy of the Rabi splitting in the smectic A phase. Based on the estimated orientational distribution function, we show that the observed Rabi splitting difference in the isotropic and smectic A phases can only be explained by taking into account the influence of collective vibrational motion in the cavity, which affects the molecular properties under the vibrational strong coupling regime.

Automated summary

Vibrational strong coupling and the formation of vibrational polaritons are the result of strong light-matter interaction. The Rabi splitting parameter reflects the strength of the interaction and provides information about molecular alignment and vibrational motion. In this study, we investigated the vibrational strong coupling in liquid crystal molecules and observed changes in the Rabi splitting with the phase transition, as well as polarization-dependent anisotropy in a specific phase. Our results suggest that the collective vibrational motion inside the cavity affects the molecular properties under the vibrational strong coupling regime.