Three cationic iridium(III) complexes with 1,10-phenanthroline or compounds containing 1,10-phenanthroline unit as auxiliary ligands: Synthesis and application in polymer light-emitting diodes

• Using 1,10-phenanthroline or compounds containing 1,10-phenanthroline unit as ancillary ligands.
• Lmax are 8733 cd m−2, 8878 cd m−2 and 13019 cd m−2, LEmax are 13.7 cd A−1, 12.5 cd A−1 and 17.5 cd A−1.
• The complex with bipolar property exhibits the best EL performances.
• EL performances are lowered by steric hindrance and distorted conjugated plane.

Three yellow-green phosphorescent cationic iridium(III) complexes [(CBT)2Ir(phen)]PF6, [(CBT)2Ir(BCP)]PF6 and [(CBT)2Ir(o-phen)]PF6 were synthesized (phen: 1,10-phenanthroline, BCP: bathocuproine, o-phen: 2-(4-tert-butylphenyl)-5-(4-(1-ethyl-H-imidazo[4,5-f][1,10]phenanthrolin-2-yl)phenyl)-1,3,4-oxadiazole, CBT: 2-(9-(2-ethylhexyl)-9H-carbazol-3-yl)benzo[d]thiazole). All of them were successfully applied in polymer light-emitting diodes: ITO/PEDOT: PSS (40 nm)/PVK: PBD: complex (mass ratios 100: 40: x, x = 1.0, 3.0, and 5.0) (80 nm)/CsF (1.5 nm)/Al (100 nm). The maximum luminances were 8733 cd m−2, 8878 cd m−2 and 13019 cd m−2, the maximum luminance efficiencies were 13.7 cd A−1, 12.5 cd A−1 and 17.5 cd A−1 respectively. Because the steric hindrance of two methyls increase the distance between central Ir3+ and BCP, and the conjugated plane of 1,10-phenanthroline unit in BCP are distorted by two benzene rings, the flow of electrons are partly hindered, [(CBT)2Ir(BCP)]PF6 exhibits the lowest electroluminescent performances. Due to the electron-transporting functional group 2,5-diphenyl-1,3,4-oxadiazole and hole-transporting functional group carbazole providing good bipolar property, [(CBT)2Ir(o-phen)]PF6 exhibits the best electroluminescent performances.

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