Purely organic phosphorescent organic light emitting diodes using alkyl modified phenoselenazine

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 in electroluminescence devices due to strong spin–orbit coupling for triplet to singlet transition. The steric bulk of the alkyl substituent, which could hamper triplet-exciton-quenching, is found to be essential for high efficiency of the device, and the tert-butyl group induces the highest external quantum efficiency (EQE) of 9.0%.