Biradiate-Shaped Trifluoromethyl-Carbazole-Based Donor-Acceptor-Donor Materials Serving as Hosts in Green Phosphorescent OLEDs

A novel series of biradiate-shaped D-A-D bipolar host materials, derived from 3,6-bis(trifluoromethyl)-9H-carbazole (CF3Cz) as a donor and pyrimidine or pyridine as acceptors, was synthesized. Various derivatives, including CF3Cz-l to CF3Cz-5, were designed with distinct substituents. The strong electron-withdrawing CF3 groups stabilized the HOMO energy level, while electron-donating groups affected the LUMO energy level. The green phosphorescent OLED device using CF3Cz-3 as a sole bipolar host exhibited remarkable electroluminescent properties, achieving a maximum EQE of 18.5% and luminescence efficiency of 64.6 cd/A, with a low tum-on voltage of 2.6 V. Introducing the electron-transporting B3PyMPM to form a co-host (CF3Cz-3:B3PyMPM (3:7)) improved charge balance, resulting in green OLEDs with an outstanding maximum EQE of 19.8% and luminescence efficiency of68.8 cd!Aat a low tum-on voltage of 2.4 V These findings highlight the potential of these CF3Cz-based compounds for practical OLED applications as a green phosphorescent host.