Theoretical studies on full-color thermally activated delayed fluorescence molecules

Thermally activated delayed fluorescence (TADF) materials have attracted wide attention due to the full utilization of triplet and singlet excitons. Beyond the typical donor-acceptor (D-A) TADF compounds, D-p-A-p-D TADF emitters were reported recently. In this paper, we study the dynamic nature of excited states of four D-p-A-p-D TADF molecules with full color emission at the first principles level. It shows thatMAC-PNhas good TADF efficiency benefiting from the large reverse intersystem crossing (RISC,k_risc) and radiative decay (k_r) rates.PX-PNandMCZ-DPPNmolecules have a reduced TADF efficiency, owing to the largely increased non-radiative decay rate (k_nr) by two orders of magnitude and decreasedk_risc, respectively, whilePX-CNPshows the worst TADF performance, becausek_nris five orders of magnitude larger thank_r. Moreover, reorganization energy analysis reveals that the RISC process is largely manipulated by the torsional vibration of the dihedral angle, while the non-radiative process mainly happens through the channels of bond stretching vibration. These calculations agree well with the experimental efficiency trend among the four TADF molecules and uncover the intrinsic TADF mechanisms, providing the possibility of further engineering the molecules with improved TADF efficiency.