Highly efficient green-emitting electrophosphorescent iridium complexes with enhanced steric hindrance.

Two novel iridium complexes, bis[2-(1,1',2',1"-terphen-3-yl)pyridinato-C,N]iridium(III) (acetylacetonate) (tphpy)2Ir(acac) and bis[2-(5,5,8,8-tetramethyl-5,6,7,8-tetrahydronaphthalen-2-yl)pyridinato-C,N]- iridium(III) (acetylacetonate) (tmhppy)2Ir(acac), were synthesized and characterized using the various spectroscopic methods. Multilayered, organic light-emitting diodes (OLEDs) were fabricated by using the complexes as dopant materials. A maximum luminance of 57840 cd/m2 at 14 V and a luminance efficiency of 40 cd/A at 20 mA/cm2 were achieved. The peak wavelength of the electroluminescence was at 527 nm with CIE coordinates of (0.34, 0.63), and the device showed a stable color chromaticity at various voltages. Significantly improved operational lifetime was achieved using (tphpy)2Ir(acac) and (tmhppy)2Ir(acac) compared to that using (ppy)2Ir(acac), at the same doping level.