Color Tuning of Multi-Resonant Thermally Activated Delayed Fluorescence Emitters Based on Fully Fused Polycyclic Amine/Carbonyl Frameworks

Two novel -extended amine/carbonyl-based multi-resonance thermally activated delayed fluorescence (MR-TADF) emitters have been designed and synthesized. The two emitters are isomeric, comprised of nine fused rings and show green-yellow emission. Sym-DiDiKTa and Asym-DiDiKTa possess tert-butyl groups distributed in a symmetrical and asymmetrical fashion, respectively, which significantly impact the single-crystal packing structure. The two compounds possess similar singlet-triplet energy gaps, EST, of around 0.23 eV, narrowband emission characterized by a full width half maximum, FWHM, of 29 nm and a photoluminescence quantum yield, PL, of 70% and 53% for the symmetric and asymmetric counterparts, respectively, in toluene. Investigation in OLEDs demonstrated that the devices with Sym-DiDiKTa and Asym-DiDiKTa displayed electroluminescence maxima of 543 and 544 nm, and maximum external quantum efficiencies (EQEmax) of 9.8% and 10.5%, respectively. The maximum EQE was further improved to 19.9% by employing a hyperfluorescence strategy. We further present the first example of a neutral MR-TADF emitter incorporated in a LEC device where Sym-DiDiKTa acts as the emitter. The LEC shows a EL at 551 nm and FWHM of 60 nm with luminance of 300 cd/m2 and a fast turn-on time of less than 2 s to 100 cd/m2.