Synthesis And Electroluminescence Properties Of Iridium(Ⅲ) Complexes Based On Pyridazine Derivatives With C^n=n Structure

Phosphorescent transition-metal complexes have attracted extensive attention in recent years, due to their ability of harvesting both singlet and triplet exciton in organic light-emitting diodes (OLEDs), theoretically enabling internal quantum efficiency of 100%, while the up-limitation for fluorescent OLEDs is 25%. Among these materials, iridium complexes are the most promising emitters for OLEDs since they usually have the good features of strong luminescence, tunable emission-color, good thermal and electrochemical stability, as well as being able to form neutral compounds for vacuum deposition. Therefore,design and synthesis of new organic ligands in iridium(Ⅲ) complexes are signifieant in the exploration of different light emitting diodes.In this work, a series of tris-cyclometalated iridium(Ⅲ) complexes are synthesized with pyridazine derivatives and Ir(acac)₃ ( or IrCl₃), on the basis of reference to the research in phosphorescent iridium(Ⅲ) complexes at home and abroad. These complexes are [Ir(BFPPya)₃: tris[3,6-bis(4'-fluorophenyl)pyridazinato-N¹,C^2']iridium; Ir(BDFPPya)₃: tris[3,6-bis(2',4'-diflu- orophenyl)pyridazinato-N¹,C^2']iridium; Ir(MDFPPya)₃: tris[3-methyl-6-(2',4'-difluorophenyl)- pyridaziato-N¹,C^2']iridium]. New compounds are characterized by 1^HNMR and elemental analysis. These data are consistent with the proposed molecular structures. Photophysical properties, electrochemical and thermogravitometric analysis of the complexes are investigated. The absorption spectra of all the complexes show intense transition 1^π-π^* (from 250 nm to 340 nm) originating from ligand parts, as well as comparatively weak and broad transition in the region of low band energy (from 350 nm to 630 nm) due to the singlet and triplet metal to ligand charge-transfer. All these complexes present strong green or red photoluminescence with wavelengths ranging from 500 nm to 630 nm. Thermo-gravitometric analysis (TGA) shows that these complexes are very thermal stable (T_d > 400℃).Electrophosphorescent organic light-emitting diodes have been fabricated with the structure of ITO/NPB/Ir complexes-doped TPBI /LiF/Al, in which Ir complexes (e.g. Ir(BFPPya)₃, Ir(BDFPPya)₃ and Ir(MDFPPya)₃) worked as the phosphorescent dopant emitter, TPBI as the host material, and NPB are used to serve as the Hole-transporting layer. Here NPB and TPBI represent N,N'-bis-(1-naphthyl)-N,N'-diphenyl-1,1'-biphenyl-4,4'-diamine and 1,3,5-Tris(1- phenyl-1H-benzimidazol-2-yl)benzene. Among these PHOLEDs device, the best performance is obtained based on Ir(MDFPPya)₃, with a very high current efficiency of approximately 35.09 cd/A, and a power efficiency of approximately 36.56 lm/W.