New heteroleptic Tris-cyclometalated iridium complex for red electrophosphorescent light-emitting diodes

New heteroleptic Tris-cyclometalated iridium complex having two different (C∧N) ligands, [Ir(dpq)2(dpq-3F)] (dpq = 2,4-diphenylquinoline, dpq-3F = 2-(3′-fluorophenyl)-4-phenyl quinoline), have been synthesized and characterized for an efficient red organic light-emitting diodes (OLEDs). The iridium phosphors emit bright red light with its maximum at 615 nm. The heteroleptic Tris-cyclometalated iridium complex [Ir(dpq)2(dpq-3F)] is shown to be a more efficient electrophosphor than the homoleptic Tris-cyclometalated iridium complex [Ir(dpq-3F)3] to avoid the triplet–triplet (T–T) annihilation by decreasing the number of the luminescent ligand. The highest occupied molecular orbital (HOMO) energy level of Ir(dpq-3F)3 is lower than that of Ir(dpq)3. Thus, the luminescence of the heteroleptic Ir(dpq)2(dpq-3F) occurs mainly at the dpq-3F ligand because the Ir(dpq-3F)3 has more MLCT characteristic. To analyze luminescent mechanism, we calculated these complexes theoretically by using computational method.