Computational insights into tuning TADF properties via multiple donor–acceptor linkages
摘要
Traditionally, thermally activated delayed fluorescence (TADF) molecular design has focused on donor–acceptor (D–A) structures. However, this study explores alternate molecular configurations that extend beyond the conventional models. Using density functional theory (DFT) and time-dependent DFT calculations, we systematically investigated the impact of various donor and acceptor arrangements, such as D_A, D_A_D, A_D_A, D_A_D_A, and D_A_A_D, on the TADF properties of emitters using 5,10-dihydrophenazine (DHPZ) as the donor and benzophenone (BP) as the acceptor. In tetrad systems, the electronic structure of TADF emitters strongly depends on the spatial arrangement of the donor and acceptor units. For instance, in the D_A_D_A configuration, the lowest three singlet and triplet states exhibit charge transfer character. In contrast, the D_A_A_D configuration reveals significant Frenkel-type character in T3 and T4 states. The involvement of these higher triplet states enhances the spin–orbit coupling value and improves the reverse intersystem crossing (RISC) rates. Additionally, the configuration of donor and acceptor units influences the number of potential RISC channels. Overall, the D_A_A_D configuration emerges as a promising design, demonstrating superior TADF performance through multiple efficient exciton utilization pathways (up to 10 RISC channels) and faster RISC rates (> 105 to 108 s–1) compared to D_A_D_A.
Graphical abstractThe D_A_A_D configuration emerged as a promising design, demonstrating superior TADF character through multiple efficient exciton utilization pathways (10 channels) and faster RISC (> 105 to 108 s−1) rates compared to D_A_D_A.