A series of new bipolar CBP derivatives with introduction of a electron-deficient moiety for efficient green organic light-emitting diodes

By introducing pyridine, benzimidazole and triazine groups, three novel CBP derivatives host materials, 9,9 '-(2-(pyridin-3-yl)-[1,1 '-biphenyl]-4,4 '-diyl)bis(9H-carbazole) (CBPPY), 9,9 '-(4 ''-(1- phenyl-1H-benzo[d]imidazol-2-yl)-[1,1 ':2 ',1 ''-terphenyl]-4,4 '-diyl)bis(9H-carbazole) (CBPBM) and 9,9 '-(3 ''-(4,6-diphenyl-1,3,5-triazin-2-yl)-[1,1 ':2 ',1 ''-terphenyl]-4,4 '-diyl)Bis (9H-carbazole) (CBPTZ) were designed and synthesized. These three compounds exhibited high thermal stabilities, appropriate HOMO-LUMO energy levels and improved electroluminescent (EL) performance compared with CBP compound in Ir(ppy)(3) doped green organic light emitting diodes (OLED). In addition, devices based on CBPPY, CBPBM and CBPTZ showed lower driving voltages of 3.0, 2.6 and 2.5 V, and all devices achieved higher EL efficiencies. Especially, the CBPBM-based device reached the optimal external quantum efficiencies (EQE) of 18.9% with the maximum power efficiency (PE) of 56.71 m/W, which suggested that CBPPY, CBPBM and CBPTZ were promising bipolar host materials for green OLEDs.