Microwave-Assisted Buchwald-Hartwig Double Amination: A Rapid and Promising Approach for the Synthesis of TADF Compounds

We herein report a microwave-assisted Buchwald-Hartwig double amination reaction to synthesize potential thermally activated delayed fluorescence compounds, forming C(sp2)-N bonds between donor and acceptor units. Our approach reduces reaction times from 24 h to 10-30 min and achieves moderate to excellent yields, outperforming conventional heating methods. The method is compatible with various aryl bromides and secondary amines, including phenoxazine, phenothiazine, acridine, and carbazole. Density functional theory calculations have attributed the lack of reactivity with high energy barriers in the reductive elimination (RE) steps. Electron-withdrawing groups such as CF3 increase the RE barrier, resulting in a 0% yield, while substituting carbazole with acridine lowers the barriers and enhances higher yields. Distortion-interaction analysis highlights steric hindrance as a key factor affecting the reaction outcome when the RE barrier is low and steric hindrance is minimal. This microwave-assisted method not only demonstrates a superior performance in terms of higher yields and shorter reaction times but also offers significant potential for reducing production costs of these materials.

Modulating the Electron-Donating Ability of Acridine Donor Units for Orange-Red Thermally Activated Delayed Fluorescence Emitters

The development of thermally activated delayed fluorescence (TADF) emitters with orange-red emission still lags behind that of their blue, green, and yellow counterparts. Recent research to address this problem mainly focused on developing new acceptor units. There were few donor units designed especially for orange-red emitters. Herein, with benzothiophene fused to a diphenylacridine donor unit, a new donor moiety, namely, 5,5-diphenyl-5,13-dihydrobenzo[4,5]thieno[3,2-c]acridine (BTDPAc), was designed and synthesized. Benefiting from the strong electron-donating ability of the new donor moiety, a new TADF emitter, 2-[4'-(tert-butyl)(1,1'-biphenyl)-4-yl]-6-[5,5-diphenylbenzo[4,5]thieno[3,2-c]acridin-13(5H)-yl]-1H-benzo[de]isoquinoline-1,3(2H)-dione (BTDPAc-PhNAI), shows an orange-red emission with a maximum at 610 nm in dilute toluene solution. Also, with the help of the diphenyl rings of the donor unit, high photoluminescence quantum yields were achieved for BTDPAc-PhNAI over a wide concentration range. Consequently, an orange-red organic light-emitting diode based on BTDPAc-PhNAI achieved a high external quantum efficiency of nearly 20 %, which was comparable to state-of-the-art device performances with similar emission spectra.

A simple and effective strategy to lock the quasi-equatorial conformation of acridine by H–H repulsion for highly efficient thermally activated delayed fluorescence emitters

A novel donor, namely, TMDBP was designed by angularly fusing two acridine moieties. TMDBP-based TADF emitters presented a dominant QE conformation and excellent electroluminescence performances.

Fused tetracyclic tris[1,2,4]triazolo[1,3,5]triazine as a novel rigid electron acceptor for efficient thermally activated delayed fluorescence emitters

Tris[1,2,4]triazolo[1,3,5]triazine, a new acceptor based on a fused triazole and triazine moiety, is utilized to construct D₃–A star-shaped tristriazolotriazine derivatives, named 3,7,11-tris(4-(10H-phenoxazin-10 yl)phenyl)tris([1,2,4]triazolo)[1,3,5]triazine (TTT-PXZ) and 3,7,11-tris(4-(9,9-dimethylacridin-10(9H)yl)phenyl)tris([1,2,4])triazolo[1,3,5]triazine (TTT-DMAC). Both TTT-PXZ and TTT-DMAC emitters feature TADF activities and AIEE properties. Consequently, solution processed OLEDs based on TTT-PXZ green emitters exhibited good performances, with an external quantum efficiency (EQE) of up to 6.2%.

Tris[1,2,4]triazolo[1,3,5]triazine, a new acceptor based on a fused triazole and triazine moiety, has been utilized to construct two new star-shaped TADF emitters.