Tsujimoto, H; Yagi, S; Asuka, H; Inui, Y; Ikawa, S; Maeda, T; Nakazumi, H; Sakurai, Y; ,
In order to develop highly emissive red phosphorescent materials for OLED application, novel bis-cyclometalated iridium(III) complexes were developed using the 1-(dibenzo[b,d] furan-4-yl) isoquinolinato- N,C-3' (dbfiq) cyclometalating ligand. When 1,3-bis(3,4-dibutoxyphenyl) propane-1,3-dionate (bdbp) is employed as an ancillary ligand, Ir(dbfiq) 2(bdbp) 1 exhibits red photoluminescence (PL) at 640 nm with a quantum yield (Phi(PL)) of 0.61 (in toluene, 298 K). Replacement of bdbp to dipivaloylmethanate (dpm) and acetylacetonate (acac) (Ir(dbfiq) 2(dpm) 2 and Ir(dbfiq) 2(acac) 3, respectively) does not affect the PL spectrum, but reduces Phi(PL) to 0.55 and 0.49 for 2 and 3, respectively. Similar tendency is also found in the doped poly(methyl methacrylate) (PMMA) film, and 1 is more emissive (Phi(PL) 0.17) than 2 and 3 (Phi(PL) 0.08 and 0.06, respectively). Using 1 as a phosphorescent dopant, polymer light-emitting diodes (PLEDs) were fabricated, of which structure was ITO/PEDOT: PSS (40 nm)/PVCz: 1: PBD (100 nm)/CsF (1 nm)/Al (250 nm). Pure red electroluminescence (EL) is obtained from the fabricated PLEDs, affording a CIE chromaticity coordinate of (0.68, 0.31). When 0.51 mol% of 1 is incorporated in the PVCz-based emitting layer, the PLED shows maximum luminance of 7270 cd m(-2) at 16.5 V, power efficiency of 1.4 lm W-1 at 7.5 V, and external quantum efficiency of 6.4% at 9.0 V. PLEDs with the same structure and components were also fabricated using 2 and 3, and their device characteristics were investigated. In proportion to the PL quantum yields, 1 affords better device performance than 2 and 3. Owing to four butoxy groups introduced to the bdbp ligand, 1 exhibits high solubility in organic solvents such as chloroform and toluene, and thus, is an excellent red phosphorescent dopant for solution-processed OLEDs. (C) 2010 Elsevier B. V. All rights reserved.