The discovery of electroluminescence of organic molecules is one of the ground-breaking and promising breakthroughs in the last century. Owing to it and to the progress in the field of organic electronics over the last half-century, nowadays, we are surrounded by organic light-emitting diodes (OLEDs) products. In addition to lightness, flexibility, and low production cost, the major advantage of using organic emitters for OLEDs is the possibility to tailor their properties by designing and modifying their molecular structures. From the view point of emission mechanisms, there are two type of emitters: fluorescence and phosphorescence emitters. Fluorescence emitters are the first generation of electroluminescence emitters for OLEDs, but they are fatally restricted by the upper limit of internal quantum efficiency (IQE) of 25%, due to spin statistics. The second generation emitter, phosphorescence emitters, are more efficient and for this reason, are commonly used in OLED-based displays. However, nothing is perfect: phosphorescence emitters that are currently used in organic electronics are organometallic complexes comprising of very expensive and rare heavy metals such as Ir and Pt. To overcome this problem, the search for all-organic TADF (Thermally Activated Delayed Fluorescence) and RTP (Room Temperature Phosphorescence) emitters is conducted.
Herein we present a new approach to the design of metal-free organic thermally activated delayed fluorescence and room temperature phosphorescence emitters for organic light-emitting diodes. The subtle tuning of the energy difference between the singlet and triplet excited states allows for tailored emission properties and switching of emission channels between thermally activated delayed fluorescence and room temperature phosphorescence. Moreover, we have realized an efficient and heavy atom-free room temperature phosphorescence organic light-emitting diodes using the developed emitter.