Mechanisms of Temperature Control of Singlet Fission in an Optical Cavity.

We investigate the mechanisms of temperature control in conical-intersection-mediated singlet fission (SF) within optical cavities. Using the multiple Davydov D₂ Ansatz combined with the thermo-field dynamics formalism, we model the quantum dynamics of a rubrene dimer coupled to an optical cavity at finite temperatures. The work explores the influence of temperature, cavity-matter coupling strength, photon frequency, and cavity loss on the triplet-triplet population dynamics. Results reveal that temperature enhances SF efficiency via thermal activation of coupling modes and assists in overcoming potential barriers between singlet and triplet states. It is found that strong photon-matter coupling and high photon frequencies also promote SF under conditions of resonance with excited vibronic states, while cavity losses and increased photon numbers can inhibit the process. Increased average photon numbers suppress SF as the polaritonic conical intersections shift away from the Franck-Condon region, although a photon-assisted SF effect is revealed for specific values of the average photon number at low temperatures. The study provides insights into the temperature control mechanisms of SF in optical cavities, offering potential directions for designing functional optical cavities to enhance SF efficiency, with implications for organic photovoltaics and other energy transfer technologies.