Chromophore and Spin–Orbit Coupling Engineering for Highly Efficient Purely Organic Phosphorescent Emitters

In this work, a design methodology to develop purely organic phosphorescent (POP) emitters was studied to improve the photoluminescence quantum yield (PLQY) and external quantum efficiency (EQE) of organic light-emitting diodes (OLEDs). The molecular design was directed to have a strong spin–orbit coupling through a phenoselenazine core for triggering phosphorescence and an expanded chromophore using an aromatic extended structure to enhance radiative transition probability. As a result, a 3-(9-phenyl-9H-carbazol-3-yl)-10-(p-tolyl)-10H-phenoselenazine (PSe3Cz) emitter achieved high PLQY of 50.2% and EQE of 13.2% in POPLEDs. The EQE of this work is one of the highest EQE values reported in heavy metal-free phosphorescent OLEDs.