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Bulletin of the Korean Chemical Society (BKCS)

ISSN 0253-2964(Print)
ISSN 1229-5949(Online)
Volume 33, Number 11
BKCSDE 33(11)
November 20, 2012 

Blue Emitting Cationic Iridium Complexes Containing Two Substituted 2-Phenylpyridine and One 2,2'-Biimidazole for Solution-Processed Organic Light-Emitting Diodes (OLEDs)
Seong-Jae Yun, Hoe-Joo Seo, Myungkwan Song, Sung-Ho Jin, Young Inn Kim*
Cationic iridium compound, Solution-processed, OLEDs, Blue phosphorescence
Two new blue emitting cationic iridium(III) complexes with two substituted 2-phenlypyridine ligands as main ligands and one 2,2'-biimidazole as an ancillary ligand, [(L1)2Ir(biim)]Cl (1) and [(L2)2Ir(biim)]Cl (2), where L1 = 2-(2',4'-difluorophenyl)-4-methylpyridine, L2 = 2-(2',4'-difluoro-3'-trifluoromethylphenyl)-4-methylpyridine and biim = 2,2'-biimidazole, were synthesized for applications in phosphorescent organic lightemitting diodes (PhOLEDs). Their photophysical, electrochemical and electroluminescent (EL) device performances were examined. The photoluminescent (PL) spectra revealed blue phosphorescence in the 450 to 485 nm range with a quantum yield of more than 10%. The iridium(III) compounds studied showed good solubility in organic solvents with no solvatochromism dependent on the solvent polarity. The solutionprocessed OLEDs were prepared with the configuration, ITO/PEDOT:PSS (40 nm)/mCP:Ir(III) (70 nm)/ OXD-7 (20 nm)/LiF (1 nm)/Al (100 nm), by spin coating the emitting layer containing the mCP host doped with the iridium phosphors. The best performance of the fabricated OLEDs based on compound 1 showed an external quantum efficiency of 4.5%, luminance efficiency of 8.52 cd A−1 and blue emission with the CIE coordinates (x,y) of (0.16, 0.33).
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