Heavy Atom Effect of Selenium for Metal-Free Phosphorescent Light-Emitting Diodes

Room-temperature phosphorescence from metal-free purely organic molecules has recently gained much interest. We devised metal-free organic phosphors by incorporating selenium (Se) to promote spin-orbit coupling by its nonmetal heavy atom effect. The Se-based organic phosphors showed bright phosphorescent emission in organic light-emitting diodes (OLEDs) and photo-excited phosphorescence in an amorphous film state. Large orbital angular momentum change (Delta L) during the electron transition process and heavy atom effect of Se render a PL quantum yield of 0.33 +/- 0.01 and a high external quantum efficiency (EQE) of 10.7 +/- 0.14% in phosphorescent LEDs. This work demonstrates the rational molecular design of metal-free organic phosphorescent emitters with Se as an alternative novel class of materials to the conventional organometallic phosphors for OLEDs.