Blue Emissive fac/mer‐Iridium (III) NHC Carbene Complexes and their Application in OLEDs

Abstract The photophysical and electrochemical properties of N‐heterocyclic carbene complexes of Iridium (III) (Ir(C^{^}C:)₃, where C^{^}C: = N‐phenyl,N‐methyl‐pyrazinoimidazol‐2‐yl (pmpz), N,N‐di‐p‐tolyl‐pyrazinoimidazol‐2‐yl (tpz)) are reported. Facial and meridional isomers of Ir(pmpz)₃ are prepared, but only the facial isomer can be isolated for Ir(tpz)₃. The fac‐Ir(pmpz)₃ and fac‐Ir(tpz)₃ complexes have emission maxima at 465 nm in polystyrene, whereas the emission maximum of mer‐Ir(pmpz)₃ is redshifted to 495 nm. The emission energies and photoluminescent quantum yield (Φ_PL) in solution decrease on going from nonpolar to polar solvents; however, all the complexes are efficient emitters in polystyrene at room temperature (Φ_PL = 88–96%) and 77 K. Blue phosphorescent organic light emitting diodes employing fac‐Ir(tpz)₃ as an emissive dopant achieves a high external electroluminescence efficiency (≈18 ± 1%) and brightness (29 000 cd m⁻²) at low current density.