Designing Noble Benzimidazole-Based Bipolar Hosts for Blue Organic Light-Emitting Diodes Using Thermally Activated Delayed Fluorescence Materials.

We designed a novel thermally activated delayed fluorescence (TADF) host molecules for blue elec-trophosphorescence by combining the electron acceptor benzimidazole (BI) unit and the electron donor acridine derivatives into a single molecular unit based on density functional theory (DFT). We obtained the energies of the first singlet () and the first triplet () excited states of the TADF materials by performing DFT and time-dependent DFT (TD-DFT) calculations on the ground state using dependence on charge transfer amounts for the optimal Hartree-Fock percentage in the exchange-correlation of TD-DFT. The DFT and TD-DFT calculations showed that the large separation between the highest occupied molecular orbital and the lowest unoccupied molecular orbital caused a small difference in energy (Δ) between the and states. The host molecules retained a high triplet energy and demonstrated a great potential for use in blue phosphorescent organic light-emitting diodes. The results showed that these molecules are promising host materials for TADF OLEDs because they have a low barrier to hole and electron injection, a balanced charge transport for both holes and electrons, and a small Δ.