Stable Luminescent Radicals and Radical-Based LEDs with Doublet Emission

Radical-based light-emitting diodes are an innovative type of organic light-emitting diodes (OLEDs), which adopt luminescent radicals as emitters, aiming at improving the external quantum efficiency (EQE) of OLEDs. Research on luminescent radicals and the corresponding devices is a multidisciplinary field involving organic chemistry, solid-state physics, photochemistry, electronics, and others. The relevant theories have been established step-by-step in recent years. Considering the rapid development tendency, it is time to systematically summarize and discuss the doublet emissionmechanism in devices, as well as the design principles of stable luminescent radicals. It is also of great importance to point out future developments in this area. In this minireview, the relevant advancements on radical-based OLEDs and stable radicals, especially those possessing luminescent properties, are summarized, respectively. Besides, the doublet emissionmechanism is elaborated systematically. Some novel findings on stable luminescent radicals are also introduced. Finally, future developments and challenges in this field are presented.