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 H-3-O<^>N<^>C<^>O ligands has been synthesized and employed as a trianionic scaffold for preparing [Ir-III(O<^>N<^>C<^>O)(L)(2)], with L = a wide variety of neutral ligands, and also [Ir-III(O<^>N<^>C<^>O)(C NAr)(NH2Ar)], [Ir-III(O<^>N<^>C<^>O)(C NAr)(X)] (Ar = 2,6-Me2C6H3; X = 1-methylimidazole, PPh3, pyridine), and [Ir-III(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 nano-second 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).