Derivatives of 2-Pyridone Exhibiting Hot-Exciton TADF for Sky-Blue and White OLEDs

Development of emissivematerials for utilization inorganic light-emittingdiodes (OLEDs) remains a highly relevant research field. One of themost important aspects in the development of efficient emitters forOLEDs is the efficiency of triplet-to-singlet exciton conversion.There are many concepts proposed for the transformation of tripletexcitons to singlet excitons, among which thermally activated delayedfluorescence (TADF) is the most efficient and widespread. One of thevariations of the TADF concept is the hot exciton approach accordingto which the process of exciton relaxation into the lowest energyelectronic state (internal conversion as usual) is slower than intersystemcrossing between high-lying singlets and triplets. In this paper,we present the donor-acceptor materials based on 2-pyridoneacceptor coupled to the different donor moieties through the phenyllinker demonstrating good performance as components of sky-blue, green-yellow,and white OLEDs. Despite relatively low photoluminescence quantumyields, the compound containing 9,9-dimethyl-9,10-dihydroacridinedonor demonstrated very good efficiency in sky-blue OLED with thesingle emissive layer, which showed an external quantum efficiency(EQE) of 3.7%. It also forms a green-yellow-emitting exciplex with4,4 & PRIME;,4 & DPRIME;-tris[phenyl(m-tolyl)amino]triphenylamine.The corresponding OLED showed an EQE of 6.9%. The white OLED combiningboth exciplex and single emitter layers demonstrated an EQE of 9.8%together with excellent current and power efficiencies of 16.1 cdA(-1) and 6.9 lm W-1, respectively.Quantum-chemical calculations together with the analysis of photoluminescencedecay curves confirm the ability of all of the studied compounds toexhibit TADF through the hot exciton pathway, but the limiting factorreducing the efficiency of OLEDs is the low photoluminescence quantumyields caused mainly by nonradiative intersystem crossing dominatingover the radiative fluorescence pathway.