A theoretical investigation of benzothiadiazole derivatives for high efficiency OLEDs

It is of great importance and worthy of efforts to give a clear structure-property relationship and microscopic mechanism of fluorescence emitters with high quantum yield. In this work, we perform a detailed computational investigation to give an explanation to the high efficiency of a fluorescence emitter XBTD-NPh based TADF sensitized fluorescence (TSF) OLEDs, and construct a symmetry structure DSBNA-BTD. Theoretical calculations show that XBTD-NPh is a long-time phosphorescent material at 77 K and TADF is attributed to the RISC of T-1 to S-1 state. For DSBNA-BTD, excitons arrived at T-1 state comes to a large rate of nonradiatively path to the ground state, meaning it is may not be an efficient TADF molecule. For both molecules, the fast IC between T-2 and T-1 state results in that the hot exciton channel T-1-T-n-S-1 makes no contribution to the TADF.