Bound states in the continuum (BIC) have emerged as an effective platform for realizing vibrational strong coupling (VSC) in the midinfrared spectrum because of their highly localized electric field and extremely low optical loss. However, the traditional VSC system based on quasi-BIC (QBIC) is constrained by the static structure design, lacking real-time control capabilities, which severely limits its practical application potential. Here, we proposed a chiral metasurface constructed by the phase-change material ${\mathrm{Ge}}_2{\mathrm{Sb}}_2{\mathrm{Te}}_5$ (GST) and successfully realized a chiral QBIC mode with circular dichroism (CD) value reaching 0.99 by synergistically breaking in-plane and out-of-plane symmetries. We achieved strong coupling between chiral QBIC modes and molecular vibrations for the first time by integrating a PMMA molecular layer onto the metasurface, observing the Rabi splitting of 13 meV. Using the coupled oscillator model, we revealed the coupling strength of the hybrid system and the evolution of the chiral QBIC mode and molecules in the vibrational polariton. We also demonstrated dynamic tuning of coupling strength through phase transitions between crystalline and amorphous states of GST materials, which originates from the positive correlation between electric field intensity of chiral QBIC modes and the volume fraction $f$ of GST. Notably, the chiral strong coupling system exhibits coherent energy exchange processes exceeding 2000 fs (approximately six Rabi cycles), which is significantly longer than that observed in conventional plasmonic systems. Our studies not only deepen the understanding of chiral light-matter interactions but also provide a universal platform for developing chiral quantum optoelectronic devices in the midinfrared frequency range.

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• Bound states in the continuum
• Metasurfaces
• Photonics
• Polaritons