How to develop efficient red-emitting organometallics of earth-abundant copper­(I) is a formidable challenge in the field of organic light-emitting diodes (OLEDs) because Cu­(I) complexes have weak spin-orbit coupling and a serious excited-state reorganization effect. Here, a red Cu­(I) complex, MAC*-Cu-DPAC, was developed using a rigid 9,9-diphenyl-9,10-dihydroacridine donor ligand in a carbene-metal-amide motif. The Cu­(I) complex achieved satisfactory red emission, a high photoluminescence quantum yield of up to 70%, and a sub-microsecond lifetime. Thanks to a linear geometry and the acceptor and donor ligands in a coplanar conformation, the complex exhibited a high horizontal dipole ratio of 77% in the host matrix, first demonstrated for coinage metal­(I) complexes. The resulting OLEDs delivered high external quantum efficiencies of 21.1% at a maximum and 20.1% at 1000 nits, together with a red emission peak at ∼630 nm. These values represent the state-of-the-art performance for red-emitting OLEDs based on coinage metal complexes.

The development of red thermally activated delayed fluorescence (TADF) emitters having excellent optoelectronic properties and satisfactory electroluminescence efficiency is full of challenges due to strict molecular design principles. Two red TADF molecules, 3-(9,9-dimethylacridin-10(9H)-yl) acenaphtho[1,2-b]quinoxaline-9,10-dicarbonitrile and 3-(2,7-dimethyl-10Hspiro[acridine-9,9′-fluoren]-10-yl)acenaphtho[1,2-b]quinoxaline-9,10-dicarbonitrile, are developed by adopting a donor-acceptor molecular architecture bearing an electron-accepting acenaphtho[1,2-b]quinoxaline-9,10-dicarbonitrile (ANQDC) moiety and a 9,9-dimethyl-9,10-dihydroacridine or 2,7-dimethyl-10H-spiro[acridine-9,9′-fluorene] electron donor. The combined effects of rigid and planar D/A moieties and highly steric hindrance between D and A groups endow both molecules with high rigidity to suppress nonradiative decay processes, resulting in high photoluminescence quantum efficiencies (Φ PL s) of up to 95%. Attributed to the linear and planar acceptor motif and rod-like molecular configuration, both emitters achieve high horizontal ratios of emitting dipole orientation of ≈80%. The organic light-emitting diodes (OLEDs) based on both emitters exhibit red emissions peaking at ≈615 nm and successfully afford ultrahigh electroluminescence performance with an external quantum efficiency of nearly 28% and a power efficiency of above 50 lm W −1 , on par with the state-of-the-art device efficiency for red TADF OLEDs. This presents a feasible design strategy for excellent TADF emitters simultaneously possessing high Φ PL s and horizontally aligned emitting dipoles.

Regulated by the fused heterocyclic units on the frame of acridine, two TADF emitters showed very different emissions from orange to pure red and excellent OLED performances.

No abstract

No abstract

Rigid electron donors (D) and acceptors (A) have been widely used in recent years for the construction of D-A type thermally activated delayed fluorescence (TADF) materials. However, the chromophore robustness...

This work reports the incorporation of a triphenylamine‐based macrocyclic donor to design new donor‐π‐acceptor‐configured blue thermally activated delayed fluorescence (TADF) emitters. The X‐ray structure analyses manifest the degree of twisted conformations that can be modulated by methyl substituents of the π‐bridge and macrocyclic donor, leading to well‐separated highest occupied natural transition orbital and lowest unoccupied natural transition orbital frontier orbitals, thus sufficiently small singlet–triplet energy difference (ΔEST) for TADF. The theoretical analyses elucidate the structure–property relationship and reveal the beneficial effect of macrocyclic donor on increasing reverse intersystem crossing (RISC) process that can contribute to improved triplet‐upconversion efficiency. The blue device employing c‐NN‐TRZ as emitter gave a maximum external quantum efficiecny (EQEmax) of 26.3% as compared to that (19.1%) of the device using the model compound DPA‐MeTRZ without the macrocyclic donor, suggesting the contribution of macrocyclic donor to enhance device performance. Benefiting from the combined advantages of macrocyclic donor and methyl substituents, the device incorporating c‐NN‐MeTRZ as emitter achieves an outstanding EQEmax of 32.2%, which is attributed to the more horizontally oriented emission dipoles as well as the significantly accelerated RISC rate constant (kRISC) resulting from reduced ΔEST. This work represents a new strategy of designing twisted TADF emitter incorporating macrocyclic donor to achieve highly efficient blue device.

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.