Highly efficient solution-processed pure red phosphorescent organic light-emitting diodes using iridium complexes based on 2,3-diphenylquinoxaline ligand

We synthesized two highly efficient red phosphorescent Ir(III) complexes, bis[2,3-diphenylquinoxalinato-N,C2′]iridium(III) pyrazinate (dpq)₂Ir(prz) (1) and bis[2,3-diphenylquinoxalinato- N,C2′]iridium(III) 5-methylpyrazinate (dpq)₂Ir(mprz) (2), which are both based on the use of 2,3-diphenylquinoxaline as the ligand, and investigated their photophysical, electrochemical, and electroluminescence (EL) properties. Both Ir(III) complexes are soluble in common organic solvents and uniform thin films can be readily spin-coated onto substrates. Phosphorescent organic light-emitting diodes (PhOLEDs) produced using the ITO/PEDOT:PSS/TCTA:TPBi:Ir(III) complex/cathode configuration, had a maximum external quantum efficiency of 7.32% and a luminance efficiency of 7.15 cd/A with a CIE coordinate of (0.70, 0.30) for compound 2. CIE coordinates remained stable on increasing current density. To the best of our knowledge, the efficiencies of these PhOLEDs are higher than those previously reported for solution-processed pure red PhOLEDs.