Efficient electroluminescence of sky-blue iridium(III) complexes for organic light-emitting diodes

Two novel sky-blue iridium(III) complexes Ir(dfppy)(2)pypzpy and Ir(dfppy)(2)phpzpy were synthesized, in which 2-(2,4-difluorophenyl)pyridine (dfppy) was used as main ligand, 2,2'-(1H-pyrazole-3,5-diypdipyridine (pypzpy) and 2-(3-2-(3-phenyl-1H-pyrazol-5-yl)pyridine (phpzpy) were introduced as the ancillary ligands, respectively. Both Ir(III) complexes showed similar emissions peaked at 469 and 472 nm with high quantum efficiencies of 0.82 and 0.86, respectively. Moreover, the organic light-emitting diodes (OLEDs) with the structure of ITO/HATCN (hexaazatriphenylenehexacabonitrile, 5 nm)/TAPC (bis[4-(N,N-ditolylamino)-phenyl] cyclohexane, 40 nm)/mCP (1,3-bis(9H-carbazol-9-yl)benzene, 5 nm)/Ir(dfPpY)(2)Pypzpy or Ir(dfppy)2phpzpy (10 wt%): PPO21 (3-(diphenylphosphoryl)-9-(4- (diphenylphosphoryl)phenyl)-9H-carbazole, 10 nm)/TmPyPB (1,3,5-tri[(3-pyridy1)-phen-3-y1] benzene, 30 nm)/LiF (1 nm)/Al (100 nm) exhibited high efficiency with low efficiency roll-off. Especially, the device based on Ir(dfppy)(2)phpzpy complex shows the better device performances with a maximum luminance of 38 200 cd/m(2), a maximum current efficiency of 58.74 cd/A, a maximum power efficiency of 49.85 lm/W and a maximum external quantum efficiency of 29.30% with Commission Internationale de l'Eclairage (CIE) color coordinates at (0.18, 0.34).