Electroluminescence of Bisindolylmaleimide Derivatives Containing Pentafluorophenyl Substituents

• Published in: Chemistry of materials Vol. 18; no. 3; pp. 832 - 839
• Main Authors: Yeh, Tzu-San, Chow, Tahsin J, Tsai, Sheng-Heng, Chiu, Ching-Wen, Zhao, Cheng-Xue
• Format: Journal Article
• Language: English
• Published: American Chemical Society 07-02-2006
• ISSN: 0897-4756; 1520-5002
• DOI: 10.1021/cm052198y

Bisindolylmaleimide derivatives containing nonfluorinated (1−3) and fluorinated (1F−4F) substituents were synthesized, and their performances on electroluminescence devices were compared. Two kinds of devices were fabricated, in which either AlQ3 (tris(8-hydroxyquinolinato)aluminum) or TPBI (2,2‘,2‘ ‘-(1,3,5-benzenetriyl)tris(1-phenyl-1H-benzimidazole)) was used as an electron-transporting (ET) medium. For nonfluorinated materials 1−3, a red emission was obtained in devices with an ITO/NPB/1−3/TPBI/Mg:Ag configuration (ITO and NPB denote indium−tin oxide and 4,4‘-bis[N-(1-naphthyl)-N-phenylamino]biphenyl, respectively), whereas dual emissions were observed in others using AlQ3 as the ET material. For fluorinated materials 1F−4F, dual emissions were observed in both kinds of devices. The second emission came from the ET layer, although a certain number of holes were annihilated with the electrons there. Compounds bearing pentafluorophenyl moieties exhibited a reduced potential energy for both the HOMO and LUMO levels and thus lowered the barrier for the hole moving across the film interface. Typical devices with an ITO/NPB/dye/TPBI/Mg:Ag configuration exhibited a red to purple color, which showed turn-on voltages of ∼4 V, a maximum luminescence of 2700−5400 Cd/m2 at 14 V, and an external quantum efficiency of 0.3−0.6%. Devices with an ITO/NPB/dye/AlQ3/Mg:Ag configuration exhibited a yellow to green color, which showed turn-on voltages of ∼4 V, a maximum luminescence of 7000−16000 Cd/m2 at 13 V, and an external quantum efficiency of 0.4−0.7%.