Protecting Benzylic C-H Bonds by Deuteration Doubles the Operational Lifetime of Deep-Blue Ir-Phenylimidazole Dopants in Phosphorescent OLEDs

Abstract

Much effort has been dedicated to increase the operational lifetime of blue phosphorescent materials in organic light-emitting diodes (OLEDs), but the reported device lifetimes are still too short for the industrial applications. An attractive method for increasing the lifetime of a given emitter without making any chemical change is exploiting the kinetic isotope effect, where key C-H bonds are deuterated. A computer model identifies that the most vulnerable molecular site in an Ir-phenylimidazole dopant is the benzylic C-H bond and predicts that deuteration may hamper the deactivation pathway involving C-H/D bond cleavage notably. Experiments show that the device lifetime until the initial luminance diminishes to 70% (LT70) of a prototype phosphorescent OLED device can be doubled to 355 hours with a maximum external quantum efficiency of 25.1% at 1000 cd m(-2). This is one of the best operational performances of blue phosphorescent OLEDs observed to date in a single stacked cell.