Regulatory mechanisms of the charge-transfer-state-mediated singlet fission by an optical cavity.

We utilize an accurate, fully quantum multiple Davydov ansatz method to numerically elucidate the regulatory mechanisms governing charge-transfer-state-mediated singlet fission under the influence of a single-mode optical cavity and a phonon environment. Our principal findings are as follows: strong vibronic coupling to the triplet state accelerates singlet fission through vibronic polaritonic resonances; cavity parameters synergize with phonons to modulate dynamics; an optimal charge-transfer-state energy promotes vibronic polariton-assisted tunneling; and environmental phonons exert dissipative effects under strong coupling or catalytic enhancement under weak coupling. These results furnish critical insights into engineering cavity-enhanced charge-transfer-state-mediated singlet fission systems.