Orange electrophosphorescence based on bis(3,5-dimethylphenyl)pyridine iridium (III) complexes for non-halogenated solution processable phosphorescent organic light-emitting diodes

Two heteroleptic iridium complexes, (dmppy)2Ir(tmd) and (dmppy)2Ir(acac), which consist of phenylpyridin (ppy) as main ligand with dimethyl substituents on both the phenyl ring and the pyridine ring, and heptanedione (tmd) and acetyl acetonate (acac) as ancillary ligands were synthesized and characterized regarding their suitability as orange organic light-emitting diodes (OLEDs). The photoluminescence (PL) of (dmppy)2Ir(tmd) and (dmppy)2Ir(acac) produced orange emissions with maximum emission peaks at 577 and 570 nm, respectively. The highest occupied molecular orbital (HOMO) and lowest unoccupied molecular orbital energy (LUMO) levels of (dmppy)2Ir(tmd) and (dmppy)2Ir(acac) were −5.03/-2.83 and −5.02/-2.77 eV, respectively. An optimized non-halogenated solution-processed (dmppy)2Ir(tmd) device showed a high current efficiency of 52.7 cd/A and exhibits an efficiency of 89% when compared to a vacuum-deposited device that showed 66.7 cd/A at 1000 cd/m2.