Blue Phosphorescent Iridium Complexes with Fluorine‐free Main Ligands for Efficient Organic Light‐emitting Diodes

Two heteroleptic iridium(III) complexes with fluorine‐free pyridylpyrimidine main ligands were designed and synthesized for use as blue phosphorescent emitters in organic light‐emitting diodes (OLEDs). Complexes 1 and 2 have a molecular formula of Ir(C∧N)2(L∧X), where C∧N = 2‐tert‐butyl‐5‐(pyridin‐2‐yl)pyrimidine (b5ppmH) is the main ligand and L∧X = picolinic acid (pic) and 2‐(1H‐tetrazol‐5‐yl)pyridine (ptz) are ancillary ligands. The thermal, photophysical, and electrochemical properties of these complexes were investigated. Even without electron‐withdrawing fluorine substituents, the complexes emitted blue light at 463 and 455 nm with moderate quantum efficiencies (ΦPL = 0.54 and 0.43), respectively. Furthermore, the replacement of the pyridine ring with a pyrimidine ring allowed blue emission without fluorine substituents. An organic light‐emitting device fabricated using complex 2 as a dopant and 1,3‐bis(N‐carbazolyl)benzene (mCP) as a host exhibited a maximum external quantum efficiency of 11.5% and color coordinates of (0.17, 0.26) at 100 cd/m2.