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%.