Fig. 3: Multiplets structure and the JT process.

a The possible optical excitation cycle among ground state and excited states. Blue arrow indicates the allowed optical transition by electric dipole moment interaction. The black dots denote the structures with C_s symmetry. The E_JT are 139 meV and 89.9 meV for ¹E and ³E, respectively. Red dash lines indicate selective non-radiative ISC between different spin multiplicity. Intrinsic SOC splitting λ_z separates the spin sublevels in the triplet ³E excited state which is reduced by p < 1 Ham reduction factor due to Jahn-Teller (JT) interaction. b APES of the JTE between C_3v and C_s symmetry for C\({}_{\,{{\mbox{S}}}\,}^{0}\). The line is the fitted curve and dot is the DFT result. The C_3v configuration is refered to Q = 0. The standard deviation is less than 1%. c Polaronic eigenstates for energy levels in ³E with SOC ⊗ DJT interaction included. The inset shows the lowest vibronic solution for the three states.