Luminescent Iridium(III) Complexes Supported by a Tetradentate Trianionic Ligand Scaffold with Mixed O, N, and C Donor Atoms: Synthesis, Structures, Photophysical Properties, and Material Applications

A panel of tetradentate H3-O∧N∧C∧O ligands has been synthesized and employed as a trianionic scaffold for preparing [IrIII(O∧N∧C∧O)­(L)2], with L = a wide variety of neutral ligands, and also [IrIII(O∧N∧C∧O)­(CNAr)­(NH2Ar)], [IrIII(O∧N∧C∧O)­(CNAr)­(X)] (Ar = 2,6-Me2C6H3; X = 1-methylimidazole, PPh3, pyridine), and [IrIII(O∧N∧C∧O)­(NHC)]2 (NHC = N-heterocyclic carbene). X-ray crystal structure analysis and photophysical studies (including variable-temperature emission lifetime measurements and nanosecond time-resolved emission and absorption spectroscopy) were performed. [Ir­(O∧N∧C∧O)­(L)2] display a moderately strong phosphorescence at room temperature (emission quantum yields up to 18% in solution, 51% in PMMA film), with the luminescent properties being strongly affected by axial L ligands. The use of [Ir­(O∧N∧C∧O)­(NHC)2] as a phosphorescent emitter in a solution-processed organic light-emitting diode device generated a red electrophosphorescence with an EQE of 10.5% and CIE chromaticity coordinates of (0.64, 0.36).