Exciplex forming a Phenyl-Spaced Phenoxazine D–A Cohost for a Highly Efficient Red-Phosphorescent Organic Light-Emitting Diode

Spaced bipolar D–A molecules were designed for application as host materials for phosphorescent organic light-emitting diode (PhOLED) devices. Three molecules (POZ–PQ, POZ-SA, and PTZ–PQ) with a phenyl linker between the donor (phenoxazine and phenothiazine) and acceptor were synthesized and characterized. Their thermal, photophysical, and electrochemical properties were studied and then applied in the emitting layer (EML) of the PhOLED device. A promising exciplex-forming tendency of the molecules led us to explore their application as cohosts in the EML. An excellent external quantum yield of 14.9% was achieved for the POZ–PQ:CN-T2T device.