Iridium(I) pyridyl azolate complexes with saturated red metal-to-ligand charge transfer phosphorescence; Fundamental and potential applications in organic light-emitting diodes

Preparation of a new series of neutral metal complexes [(cod)Ir-(fppz)] (1), [(cod)Ir(bppz)] (2), [(cod)Ir(fptz)] (3) and [(cod)Ir(bptz)] (4). bearing one cod ligand and a pyridyl azolate chelate are reported. A single-crystal X-ray diffraction study of 3 reveals the expected distorted square-planar geometry. The lowest absorption band consists of Ir¹ atom increased triplet d_π-→* transitions (³MLCT), the assignment of which is firmly supported by the theoretical approaches. Complexes 1-4 exhibit weak phosphorescence in degassed solution at room temperature, whereas much more intense, solid-state phosphorescence appears in the range 622-649 nm. The pure MLCT emission was used as a prototypical model to address its remarkable spectral differences from the Ir^III isoquinoline pyrrolide complex (5), which has mainly ³ππ phosphorescence. Complex 3 was used as a dopant to fabricate red-emitting phosphorescent organic light-emitting diodes (OLEDs). For the 7% doped device, a maximum brightness of 3010 cdm^-2 was achieved at an applied voltage of 15 V and with CIE coordinates of (0.56, 0.33). demonstrating for the first time the potential of neutral Ir¹ complexes in OLED applications.