A Simple and Strong Electron‐Deficient 5,6‐Dicyano[2,1,3]benzothiadiazole‐Cored Donor‐Acceptor‐Donor Compound for Efficient Near Infrared Thermally Activated Delayed Fluorescence

Abstract

Despite the success of thermally activated delayed fluorescent (TADF) materials in steering the next generation of organic light-emitting diodes (OLEDs), effective near infrared (NIR) TADF emitters are still very rare. Here, we present a simple and extremely high electron-deficient compound, 5,6dicyano[2,1,3]benzothiadiazole (CNBz), as a strong electronaccepting unit to develop a sufficiently strong donor-acceptor (DÀ A) interaction for NIR emission. End-capping with the electron-donating triphenylamine (TPA) unit created an effective DÀ AÀ D type system, giving rise to an efficient NIR TADF emissive molecule (λ em = 750 nm) with a very small ΔE ST of 0.06 eV. The electroluminescent device using this NIR TADF emitter exhibited an excellent performance with a high maximum radiance of 10020 mW Sr À 1 m À 2 , a maximum EQE of 6.57% and a peak wavelength of 712 nm.

Green‐, Red‐, and Infrared‐Emitting Polymorphs of Sterically Hindered Push–Pull Substituted Stilbenes

“…In 2010, Shimizu and Hiyama expressed an essential requirement to obtain red fluorophores with PLQY over 30 % from neat solids and fulfilled it in 2012 for first time with the observed emission with a maximum over 700 nm (702 nm) and PLQY over 30 % (33 %) at the same time [11] . Although, since then, the impressive values of NIR emission have been reported for polycrystalline powders (for example, 735 nm/11 %), [9b] water dispersions of nanoparticles (for example, 685 nm/20.7 %), [12] and neat films (for example, 756 nm/17 % [13] or 750 nm/21 %), [14] the >700 nm/>30 % limit still remains a challenge [15] . There are generally two ways to tune the position of emission maxima.…”

“…There are generally two ways to tune the position of emission maxima. The first one, intramolecular, modifies the strength of (usually) the electron acceptor, [14] for example, by adding an additional CN group [10] or by a conjugation extension, [16] whereas the second, intermolecular, modifies the structure to form emitting aggregates, for example, of J‐type [4c] or X‐type [16] . Structural change, transforming the continuous H‐type dimeric stacking to discrete dimers, showing intense (54.8 %) excimer fluorescence with a maximum at 690 nm, seems also promising [17]…”

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

“…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). A deep red/NIR emission with a peak at 712 nm could attribute to the strong electron-withdrawing ability of the acceptor 5,6-dicyano[2,1,3]benzothiadiazole.…”

Highly Efficient Near‐Infrared Electrofluorescence from a Thermally Activated Delayed Fluorescence Molecule

“…Among other light-sources, organic LEDs (OLEDs) [5] are considered to be a potential alternative because of their intrinsic advantages such as ultra-flexibility, ultra-lightweight, high uniformity of light emission, and the possibility for low-cost fabrication. Indeed, many organic [6][7][8][9][10][11][12][13][14][15][16][17][18][19][20][21] and organometallic [22][23][24][25] com-pounds have been developed and applied as emitters for NIR-OLEDs. However, NIR-OLEDs suffer from low external EL quantum efficiency (EQE) caused by unbalanced charge trapping, [25] aggregation-caused quenching, [15] and accelerated nonradiative deactivation of the excitons through a vibration coupling with a ground state, that is, energy-gap law.…”

“…[29] Recently, there has been a great deal of interest in NIR-TADF OLEDs. Particularly, considerable progress has been made in the field of NIR-TADF emitters, such as phenanthropyrazine, [6][7][8] acenaphthopyrazine (AP), [9][10][11][12] dibenzophenazine, [13] quinoxaline, [14,15] benzothiadiazole, [16] boron-curcuminoid, [17][18][19] and dipyridophenazine [20,21] derivatives, and the OLEDs demonstrated EQE higher than 10 % at wavelengths beyond 700 nm. [10] However, NIR-OLEDs suffer from a high EQE rolloff at the high current region > 100 mA cm À2 .…”