Synthesis and Luminescence Property of Two New Blue Phosphorescent Iridium(Ⅲ) Diazine Complexes

We designed and synthesized two new iridium(Ⅲ) diazine complexes [(DFPPM)2IrCl-(PPh3)] and [(DFPPM)2Ir(CN)(PPh3)],where Ph= phenyl,containing 2-(2,4-difluorophenyl)-pyrimidine(DFPPM) as the cyclometalated ligands.OLEDs with iridium(Ⅲ) diazine complexes as phosphor have high-efficiency and long luminance half-life,however,diazine compounds show a significantly redshift of the emission band than pyridine compounds.Therefore,it will be a great challenge to synthesize blue phosphorescent materials with diazine compounds as ligands.The complexes were characterized by nuclear magnetic resonance(NMR) spectroscopy and mass spectrometry(MS) and their photophysical properties were investigated by UV-Vis spectroscopy and photoluminescence(PL) technique.The PL spectrum of [(DFPPM)2IrCl(PPh3)] in solution has its maximum emission peak at 472 nm and 489 nm,whereas [(DFPPM)2Ir(CN)(PPh3)] has its maximum emission peak at 447 nm and 472 nm.The luminescence of [(DFPPM)2IrCl(PPh3)] shifts to the blue region compared to that of(DFPPM)2Ir(acac),indicating that the HOMO-LUMO gap is increased due to the higher ligand field strength of the phosphine.Compared with [(DFPPM)2IrCl-(PPh3)],[(DFPPM)2Ir(CN)(PPh3)] shows a significantly blue-shift of the emission band.The ligand field strength of CN is larger than Cl due to its strong σ donor and π acceptor ability.This causes larger splitting of the d-orbital and consequently more lowering of the metal-centered HOMO.Complex of(DFPPM)2Ir(CN)(PPh3) emits deep blue light with Commission Internationale de l'Eclairage(CIE) coordinates of(0.14,0.15).Electroluminescence(EL) device was fabricated when the complex of [(DFPPM)2Ir(CN)(PPh3)] was doped into polymer host polyvinylcarbazole(PVK).Compared to the photoluminescence spectrum,a red-shifted of emission was observed from the electroluminescence spectrum.The reason of red-shift of EL spectra is in progress.