However, there exists obvious deviation between the calculated and experimental rates, attributed to the inaccurate excited-state PESs produced by TDA and improperly accounting for the complex experimental situation. Like many other MR-type TADF emitters, 7-PhQAD holds a strongly electron correlation. Though its low-lying excited states are single excitation dominated states, more than 10% second-order dynamic correlation shown by ADC(2) calculated results suggests that the more sophisticated quantum chemistry methods should be used to exactly describe its excited states. The TDDFT method not only overestimates ∆E ST but also the difference of the PESs between S 1 and S 0 states. The latter results in the significant enhancement of the vibrational motion, leading to the broadband absorption and emission when the difference of PESs between S 1 and S 0 states is taken into account. The calculation with VG approximation can successfully reproduce the experimental spectral lineshape. Additionally, in this theoretical calculation, a single molecule is assumed to be embedded by the dielectric continuum media, so that the solute-solute and explicit solute-solvent interactions and the environmental fluctuation are neglected, leading to the overestimated rate coefficients. This work demonstrates a way to quantitatively predict the ISC and RISC rates of TADF emitters with including the vibronic coupling effect. Our calculations unveil the dynamical mechanism for highly efficient OLED emission and open design routes that go beyond the