Saturated red phosphorescent Iridium(III) complexes containing phenylquinoline ligands for efficient organic light-emitting diodes

Abstract

Saturated red iridium phosphors are strongly desired for application in organic light-emitting diodes (OLEDs). Most of the reported iridium complexes with 2-arylquinoline or its derivatives as cyclometalating ligands are orange-red phosphorescent with peak wavelength below 620 nm. Herein trifluoromethyl (CF3) or Fluorine (F) is introduced into the 6-site of quinoline ring to design and synthesize the cyclometalated ligands 2-phenyl-6-CF3/F-quinoline (CF3-phq or F-phq) and heteroleptic iridium complexes Ir(CF3-phq)2(acac) (Ir-1), Ir(CF3-phq)2(tmd) (Ir-2), Ir(F-phq)2(acac) (Ir-3) and Ir(F-phq)2(tmd) (Ir-4). Owing to the electron-deficient feature of CF3 and F, the electron affinity of these complexes are increased, the corresponding LUMOs are pulled downwards, and the phosphorescence of CF3-containing iridium complexes are saturated red with peaks at 627–632 nm in photoluminescence. At the same time, by varying the ancillary ligand from acetylacetonate (acac) to 2,2,6,6-tetrametylheptane-3,5-dionate (tmd), the emitting performance are dramatically improved. As a result, the Ir(CF3-phq)2(tmd) based red OLED realized pure red electroluminescence with Commision Internationale de L'Eclairage (CIE) coordinates of (0.67, 0.33) with a high brightness of 12695 cd m−2 and a maximum external quantum efficiency of 14.96%, respectively, which maintained as high as 9.62% at a practical luminance of 1000 cd m−2. This is the first example of saturated red iridium phosphors with structure modification at the 6-site of quinoline ring of 2-phenylquinoline ligand.