Theoretical study on thermally activated delayed fluorescent molecules based on space charge transfer

Thermally Activated Delayed Fluorescent (TADF) molecules with through-space charge transfer (TSCT) have broad application potential in organic light-emitting diodes. In this paper, five TPA-ace based molecules with different electron-withdrawing groups and TSCT property are investigated using polarizable continuum model (PCM) combined with density functional theory (DFT) and time-dependent functional theory (TD-DFT) in Methylcyclohexane, Toluene and Dichloromethane. It is found that stronger electron-withdrawing ability of acceptors could induce redshift of emission and smaller energy gap between the first singlet excited state (S1) and the first triplet excited state (ΔEST). The ratio of TSCT to through bond charge transfer (TBCT) for S1 of TPA-ace-TRZ is calculated quantitatively, which further confirmed the TSCT character of TPA-ace-TRZ. The TADF property is also analyzed based on the calculation of spin-orbit coupling and the (reverse) intersystem crossing rates between S1 and T1. Our calculation results would favor the understanding of TSCT-TADF.