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((CC)-C-<^>:)(3), where (CC)-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 (phi(PL)) in solution decrease on going from nonpolar to polar solvents; however, all the complexes are efficient emitters in polystyrene at room temperature (phi(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 (approximate to 18 +/- 1%) and brightness (29 000 cd m(-2)) at low current density.