A Red Thermally Activated Delayed Fluorescence Emitter Simultaneously Having High Photoluminescence Quantum Efficiency and Preferentially Horizontal Emitting Dipole Orientation

Abstract

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.

Recent Advances in Solid‐State Lighting Devices Using Transition Metal Complexes Exhibiting Thermally Activated Delayed Fluorescent Emission Mechanism

“…[ 187 ] Che et al have successfully prepared red‐ and white‐emitting OLEDs with the highest EQEs of 10.2% and 16.8%, respectively. [ 113,114 ] Although these values are lower than those reported for organic TADF emitters—that is, EQE values of 37% for blue [ 65 ] and around 30% for green/yellow [ 10,66 ] and orange/red [ 67,201 ] ( Table 10 ), they are remarkable enough to encourage new breakthroughs in the future.…”

Rational design of perfectly oriented thermally activated delayed fluorescence emitter for efficient red electroluminescence

“…In the past decade, thermally activated delayed fluorescence (TADF) emitters are particularly attractive in OLEDs because of their merits in harvesting triplet excitons without using noble metals [15][16][17][18][19]. To further boost device performance of TADF OLEDs, many efforts have been made to control the EDO of TADF emitters [20][21][22]. In virtue of variable molecular structures, TADF emitters' molecular conformation can be easily altered to linear or planar shape, leading to favorable anisotropic orientation [23][24][25][26].…”

Harvesting triplet excitons for near-infrared electroluminescence via thermally activated delayed fluorescence channel

“…The doped device with embedded APDC-DTPA in Zn(BTZ) 2 can harvest further redshift emission with high device efficiency (peak at 728 nm and an EQE of 5.1%). 32 The unique molecular structure and excellent performance of APDC-DTPA have encouraged researchers to explore acenaphtho[1,2-b]pyrazine derivatives for photo electricity functional materials (Gong et al, 2020a(Gong et al, , 2020bLi et al, 2020b). In 2019, Congrave et al proposed a D-A dyad emitter, CAT-1, which could be considered as replacing one triphenylamine unit with a cyan group in APDC-DTPA ( (Kumsampao et al, 2020).…”