The Design And Synthesis Of Blue Iridium Complexes Based On C^N=N Type Ligand And The OLEDs Study

The neutral iridium(III) complexes have been studied during the last two decades for high performance phosphorescent organic light emitting diodes(PhOLEDs), owing to their short exciton lifetimes, as well as high photoluminescence quantum efficiency. Among them, blue iridium(III) complexes and the corresponding PhOLED devices are the most difficult to achieve, mainly because of the large energy gap of blue phosphors as well as the elevated energy of their triplet state. Therefore, the designs of blue iridium complexes as well as their device architecture are challenging. This work focused on the developing new blue iridium(III) complexes and studying their PhOLEDs, which includes the following aspects:(1) Firstly, by introducing difluoropyridinyl(dfpy) moiety to C^N=N type ligand, two new iridium(III) complexes were synthesized i.e., iridium(III) bis[3-methyl-6-(2′,4′-difluoro-pyridinato)-pyridazine] trifluoromethylated-triazole(1) and iridium(III) bis[3-methyl-6-(2′,4′-difluoro-pyridinato) pyridazine] picolinate(2). The two new iridium(III) complexes 1 and 2 exhibit strong blue/sky-blue photoluminescence with peaks of 488 nm and 494 nm, respectively. Based on experimental results and quantum chemistry calculations, the link between molecular structures and properties was disclosed. It was found that in iridium complexes, ancillary ligand with strong electron withdrawing property can significantly influence the HOMO electron distribution.(2) Secondly, using the above two complexes as the dopant, devices with mCP(N,N′-dicarbazolyl-3,5-benzene) as host were fabricated. By varying dopant concentration(8 wt% to 18 wt%), the optimized performance was obtained at 10 wt% for compound 1 and 14 wt% for 2, with the maximum current efficiencies of 23.6 cd A-1 and 48.9 cd A-1, respectively.(3) Finally, to further improve the efficiencies of the devices, mCP and B3PYMPM(bis-4,6-(3,5-di-3-pyridylphenyl)-2-methylpyrimi-dine) were employed as the exciplex-forming co-host for dopant 1 and 2.The efficiencies of devices were significant improved, which attribute to the more balanced electron and hole owing to the co-host of mCP and B3 PYMPM. The maximum efficiencies were 20.1%(41.6cd A-1) for 1 based device and 26.5%(62.8cd A-1) for 2 based device. These are the first promising performance with device using blue emitters based on C^N=N type ligand so far.