New amorphous electron-transporting materials based on Tris-benzimidazoles for all wet-process OLED devices

New amorphous electron-transporting materials 1,3,5-tris[1-(phenoxy phenyl)-1H-benzimidazol-2-yl]benzene (6a and 6b) were synthesized by dehydration reaction of corresponding triamides and fully characterized. Compounds 6a and 6b showed high thermal stability (Tg = 108 to 110 °C) and good solubility in common organic solvents, such as acetone, 2-methoxyetanol, tetrahydrofuran, chloroform, and 2-butanone. Pinhole-free transparent films were obtained by spin-casting the 2-butanone solution. 6a and 6b were fabricated as electron-transporting layer by spin-casting on a hole-transporting layer that was deposited by spin-cast beforehand and was insoluble in 2-butanone. Both devices showed no emission, but carrier transporting property was observed (400 mA/cm2). The device showed a blue emission (35 cd/m2) from 9,10-diphenylanthracene (DPA) when 10 wt.% DPA was mixed into the 6b layer.