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 Ir I atom increased triplet d π →π* transitions ( 3 MLCT), 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 3 ππ 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 cd m −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 Ir I complexes in OLED applications.