Cost-effective synthesis of oc-carboline/pyridine hybrid bipolar host materials with improved electron-transport ability for efficient blue phosphorescent OLEDs

Two ct-carboline/pyridine hybrid bipolar host materials, 2,6-bis(9-H-pyrido[2,3-b]indol-9-yppyridine (2,6CbPy) and 9,9',9 ''-(pyridine-2,4,6-triyptris(9-H-pyrido[2,3-blindole) (2,4,6-CbPy) are designed and synthesized through an efficient one-step catalyst-free C-N coupling reaction. The thermal, electrochemical and photoluminescence properties of the two host materials have been fully investigated. The introduction of the alpha-carboline instead of carbazole in 2,6-CbPy and 2,4,6-CbPy significantly improves the electron transporting abilities, and simultaneously maintains the good hole transporting properties with 2,6-CzPy and 2,4,6-CzPy. By using them as hosts for Flrpic-doped blue phosphorescent OLEDs, a maximum current efficiency of 44.1 cd A(-1) and power efficiency of 38.5 Ern W-1 has been achieved for the 2,4,6-CbPy-based device. The maximum current efficiency is higher than 42.1 cd A(-1) of the carbazole-containing 2,4,6-CzPy under the same device conditions.