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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 identi ed that the most vulnerable molecular site in an Ir-phenylimidazole dopant is the benzylic C-H bond and predicted that deuteration may lower the deactivation pathway involving C-H/D cleavage notably. Experiments showed that the device lifetime (T 70 ) of a prototype phosphorescent OLED device could be doubled to 355 hours with a maximum external quantum e ciency 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.

Purely organic phosphorescent emitters have been developed with the incorporation of alkyl substituents into the N-phenylphenoselenazine core. The new emitter displayed efficient phosphorescence in amorphous film and featured pure phosphorescence...

Dual emission featuring both thermally activated delayed fluorescence (TADF) and phosphorescence was engineered into a single metal-free molecule, phenyl(10-phenyl-10H-phenoselenazin-3-yl)methanone. Selenium incorporated into the molecule increases the spin−orbit coupling to facilitate both TADF and phosphorescence, whereas donor−acceptor units promote TADF emission. The relative contribution of the green TADF and yellow phosphorescence can be controlled by the driving voltage of the devices. At low voltage, phosphorescence emission dominates the electroluminescence, whereas TADF is the major component at high voltages. The mechanism of dual emission was explored using experimental and theoretical methods.