Bulky Iridium NHC Complexes for Bright, Efficient Deep-Blue OLEDs

Four new deep-blue-emitting iridium(III) NHC complexes containing sterically demanding ligands are synthesized. The four complexes show bright, deep-blue emission, with emission maxima between 420 and 427 nm in both acetonitrile solution and 30 wt% doped films in TSPO1; the two meridional isomers showing photoluminescence quantum yields, phi(PL), in doped films of 80% and 89%. The two meridional isomers are used to assess the impact of emitters containing bulky, sterically demanding ligands on the performance of organic light-emitting diodes (OLEDs). OLEDs employing a stepped doping profile with mer-Ir(tfpi_tmBn)(3) as the emitter produce the highest performing devices in this study, with these devices exhibiting deep-blue [lambda(EL) = 429 nm, CIE = (0.16, 0.08)] emission and a maximum external quantum efficiency (EQE(max)) of 14.9%, which decreases to 11.7% at 100 cd m(-2). The performance of the OLEDs shows very good efficiencies and moderate efficiency roll-offs in comparison to reported phosphorescent deep-blue OLEDs with CIEy <= 0.08, as required for commercial displays. The promising results suggest that the design strategy of adding steric bulk to blue emitting iridium complexes containing NHC ligands is a useful strategy for reducing intermolecular interactions between emitters in OLEDs.

Automated summary

The synthesis of four new deep-blue-emitting iridium(III) NHC complexes with sterically demanding ligands shows promising results for application in organic light-emitting diodes.