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

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.