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

Two α-carboline/pyridine hybrid bipolar host materials, 2,6-bis(9-H-pyrido[2,3-b]indol-9-yl)pyridine (2,6-CbPy) and 9,9′,9′′-(pyridine-2,4,6-triyl)tris(9-H-pyrido[2,3-b]indole) (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 α-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 FIrpic-doped blue phosphorescent OLEDs, a maximum current efficiency of 44.1 cd A^-1 and power efficiency of 38.5 lm 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.