Nevertheless, the experimental ISC and RISC rates actually reach 1.5×10 8 and 6.4×10 3 s -1 , respectively, which indicates the significant impact of the vibronic coupling effects. Here we calculate the vibrationally resolved absorption and fluorescence spectra as well as its ISC and RISC rates with HTVC effect to verify the microscopic mechanism of TADF process. We aim to describe its photophysical properties, quantitatively predict the ISC and RISC rates, and unveil the behind mechanisms. The time-dependent correlation function approaches will be adopted.