New heteroleptic cyclometalated iridium(III) complexes containing 2-(2′,4′-difluorophenyl)-4-methylpyridine for organic light-emitting diode applications

Two phosphorescent iridium(III) complexes (dfpmpy)₂Ir(ppc) and (dfpmpy)₂Ir(prz) [dfpmpy=2-(2′,4′-difluorophenyl)-4- methylpyridine, ppc=pipecolinate, prz=2-pyrazine carboxylate] were synthesized from the reaction of the chloro-bridged dimeric complex [(dfpmpy) ₂Ir(μ-Cl)]₂ and the ancillary ligand. Their structures and photoluminescence properties were investigated and device performances for application in organic light-emitting diodes (OLEDs) were studied. The complexes adopt a distorted, octahedral geometry around the iridium metal, exhibiting cis CC and trans NN arrangements. The photoluminescent (PL) properties reveal that (dfpmpy)₂Ir(ppc) emits in the blue-green region (λ _max=497 nm), whereas (dfpmpy)₂Ir(prz) shows red phosphorescence (λ_max=543 nm) in the film state (5% wt. doped in PMMA). The (dfpmpy)₂Ir(ppc)-and (dfpmpy)₂Ir(prz)-based OLEDs exhibited sky-blue and greenish-yellow electroluminescence with similar currentvoltage characteristics, repectively. Maximum current efficiency of (dfpmpy)₂Ir(ppc) and (dfpmpy)₂Ir(prz) were 4.4 and 7.4 cd/A, respectively. Maximum luminance values were approximately 10,000 cd/m ² for the both compounds.