[New highly phosphorescent heteroleptic tris-cyclometalated iridium (III) complexes: synthesis and photophysical...

New heteroleptic tris-cyclometalated iridium(III) complexes (ppy)2 Ir(LX) (ppy==2-phenylpyridine, LX==Sal (salicylic acid), Msal (4-methylsalicylic acid), FSal(4-trifluoro methyl salicylic acid)) was synthesized and characterized. The molecular structure, photophysical properties and thermal stability were tested and analyzed. The results show that the absorption peaks were located around 270, 370, 450 and 484 nm respectively at room temperature. The two former peaks at 270 and 370 nm should belong to 1pi--pi* transition at ppy and transition from salicylic acid ligands to 2-phenylpyridine; The peaks around 450 and 484 nm can be assigned to the charge transfer transition from Ir to ligand (1MLCT and 3MLCT) and 3pi--pi* transition respectively. The PL emission peaks were located at 520, 522, and 510 nm, respectively. The emission of (ppy), Ir(Sal) and (ppy), Ir (MSal) was mainly ascribed to the radiation transition of triple state 3MLCT, while the emission of (ppy)2 Ir(FSal) was mainly from the radiation transition between Sal and ppy, partly from the radiation transition of single state 1MLCT and triple state 3MLCT. The quantum efficiencies of these complexes were 0.37, 0.33 and 0.29 respectively. The thermal decomposition temperature was from 306 to 328 degrees C. (ppy)2 Ir(LX), being a series of efficient phosphorescent materials with good thermal stability, can be used in the organic electroluminescent devices.