• Blue light emission;
  • Cationic iridium complexes;
  • LECs;
  • 2-(1H-pyrazol-1-yl) pyridine;
  • Light-emitting electrochemical cells


Two blue-emitting cationic iridium complexes with 2-(1H-pyrazol-1-yl)pyridine (pzpy) as the ancillary ligands, namely, [Ir(ppy)2(pzpy)]PF6 and [Ir(dfppy)2(pzpy)]PF6 (ppy is 2-phenylpyridine, dfppy is 2-(2,4-difluorophenyl) pyridine, and PF6 is hexafluorophosphate), have been prepared, and their photophysical and electrochemical properties have been investigated. In CH3CN solutions, [Ir(ppy)2(pzpy)]PF6 emits blue-green light (475 nm), which is blue-shifted by more than 100 nm with respect to the typical cationic iridium complex [Ir(ppy)2(dtb-bpy)]PF6 (dtb-bpy is 4,4′-di-tert-butyl-2,2′-bipyridine); [Ir(dfppy)2(pzpy)]PF6 with fluorine-substituted cyclometalated ligands shows further blue-shifted light emission (451 nm). Quantum chemical calculations reveal that the emissions are mainly from the ligand-centered 3ππ* states of the cyclometalated ligands (ppy or dfppy). Light-emitting electrochemical cells (LECs) based on [Ir(ppy)2(pzpy)]PF6 gave green-blue electroluminescence (486 nm) and had a relatively high efficiency of 4.3 cd A−1 when an ionic liquid 1-butyl-3-methylimidazolium hexafluorophosphate was added into the light-emitting layer. LECs based on [Ir(dfppy)2(pzpy)]PF6 gave blue electroluminescence (460 nm) with CIE (Commission Internationale de L'Eclairage) coordinates of (0.20, 0.28), which is the bluest light emission for iTMCs-based LECs reported so far. Our work suggests that using diimine ancillary ligands involving electron-donating nitrogen atoms (like pzpy) is an efficient strategy to turn the light emission of cationic iridium complexes to the blue region.