Novel Iridium Complex with Carbazol-2-yl-β-diketone Derivative: Low-energy Excitation and Red Electrophosphorescent Devices

A novel iridium-complex, (BPPBI)₂Ir(2-TFDBC)BPPBI=2-(biphenyl-4-yl)-1-phenyl-1H-benzod]imi- dazole, 2-TFDBC=1-(9-ethyl-9H-carbazol-2-yl)-4,4,4-trifluorobutane-1,3-dione], was synthesized, and its structure and component were confirmed by ¹H NMR and element analysis, respectively. UV-Vis absorption and photoluminescent(PL) spectra of (BPPBI)₂Ir(2-TFDBC) in dichloromethane were investigated. The Ir-complex exhibited a long wavelength excitation of 470 nm, i.e., low-energy excitation. So, it is a promising candidate for phosphorescent probe and PL material. (BPPBI)₂Ir(2-TFDBC)-based electroluminescent devices, ITO/MoO₃(10 nm)/NPB(80 nm)/ CBP:x(BPPBI)₂Ir(2-TFDBC)(20 nm)/TPBi(45 nm)/LiF/Al, were fabricated, where x(%) was of 4% or 8% doping concentration(mass fraction); ITO=indium tin oxides; NBP=N,N'-bis-(1-naphthalenyl)-N,N'-bis-phenyl-(1,1'-biphenyl)- 4,4'-diamine, CBP=4,4'-bis(N-carbazolyl)-1,1'-biphenyl, TPBi=1,3,5-tris(1-phenyl-1H-benzimidazol-2-yl)benzene. The devices showed a red emission of 620 nm. The maximum current efficiency and brightness were 1.7 cd/A and 4063 cd/m² for a device of 8%(mass fraction) doping level, respectively. The moderate luminous efficiency was due to the inadequate energy transfer from the host material to the guest material.