Zig‐Zag Acridine/Sulfone Derivative with Aggregation‐Induced Emission and Enhanced Thermally Activated Delayed Fluorescence in Amorphous Phase for Highly Efficient Nondoped Blue Organic Light‐Emitting Diodes

Abstract

weight, flexibility as well as low-cost device production for lighting and displaying applications. In the past decades, emissive materials that can harvest both singlet (25%) and triplet (75%) excitons have attracted significant interest. Followed the phosphorescent noblemetal complexes, thermally activated delayed fluorescent (TADF) materials were emerged and were considered as an important breakthrough. [1][2][3] This is because these purely organic emitters, as inexpensive alternatives, are able to convert excitons from the lowest triplet excited state (T 1 ) to the lowest singlet excited state (S 1 ) through reverse intersystem crossing (RISC), thus giving theoretical maximum internal electroluminescence quantum efficiency up to 100%. [4,5] Motivated by this, numerous TADF materials that comprise of electron donor (D) and electron acceptor (A) segments to yield charge transfer systems with a thermally accessible energy gap between S 1 and T 1 have been developed. [6][7][8][9][10] However, to meet the demand of high-quality singleand full-color OLEDs in practical applications, highly efficient blue TADF emitters are of great significance but still rare. [10][11][12][13][14][15][16] Moreover, despite a few important precedents with neglectable concentration quenching, [17,18] most of the reported blue TADF molecules that suffer from aggregationcaused quenching have to be applied in doped OLEDs, which challenged in precise control of the doping concentration, complicated structure, and expensive fabrication.To overcome this limitation, emissive materials with aggregation-induced emission (AIE) characteristics of which possess intense luminescence in the aggregated state become a promising strategy as emitting layers (EML) for efficient nondoped OLEDs. [19][20][21][22][23][24] In addition, to achieve high performance and good repeatability, the most efficient devices are still fabricated under thermal evaporation processing, in which the emissive materials are used in their amorphous phase. Therefore, several issues about the emissive materials are significant Luminescent materials simultaneously exhibiting aggregation-induced emission (AIE), superior luminous efficiency, and thermally activated delayed fluorescence (TADF) properties in amorphous phase are eagerly required for highly efficient nondoped organic light-emitting diodes. In this contribution, an acridine/sulfone derivative, bis(3-(9,9-dimethyl-9,10-dihydroacridine) phenyl)sulfone (mSOAD), designed and synthesized by combing a diphenylsulfone (DPS) core with bi-9,9-dimethyl-9,10-dihydroacridine (DMAC) substituted at the 3,3′-positions is demonstrated. The highly twisted zig-zag configuration endows the compound with desired frontier orbital distribution for extremely small energy gap between singlet and triplet states (ΔE ST = 0.02 eV) of TADF molecule and prominent AIE characteristic. More importantly, its amorphous sample displays enhanced quantum fluorescence yield as well as superior TADF characteristic, which exhibits advantage for device fabrica...

Thermally Activated Delayed Fluorescence Materials: Towards Realization of High Efficiency through Strategic Small Molecular Design

“…Another successful attempt in modulating the twist and lowering the Δ E ST was accomplished by Guo et al. in 2018 . Through a highly‐twisted zig‐zag conformation, the resulting TADF emitter, bis(3‐(9,9‐dimethyl‐9,10‐dihydroacridine)phenyl)sulfone (mSOAD), with acridine as donor and sulfone as acceptor, exhibits a much smaller Δ E ST of only 0.02 eV.…”

“…The OLEDsi ncorporating two TADF emitterse xhibit decent EQE max values of 11.7 %f or DTC-pBPSB and 5.5 %f or DTC-mBPSB, respectively.A nother successful attempti nm odulating the twist and lowering the DE ST was accomplished by . [34] Through ah ighly-twisted zig-zagc onformation, the re-sultingT ADF emitter,b is (3-(9,9-dimethyl-9,10-dihydroacridine)phenyl)sulfone (mSOAD), with acridine as donor and sulfone as acceptor, exhibits am uch smaller DE ST of only 0.02 eV.T he zigzag conformation also endows the emitter with AIE capability. Consequently,t he OLEDse xhibit ac oncentration-insensitive property,w ith the EQE max data of 14-16.6 %f or doped and non-doped devices due to the negligible p-p stacking and the bipolar property of the material.…”

Efficient Deep-Blue Electrofluorescence with an External Quantum Efficiency Beyond 10%

“…The DMPA-based device B1 also showed excellent efficiency of 8.05% with an FWHM of 51 nm. To the best of our knowledge, the EQEs of devices A1 and B1 are the highest among the reported deep-blue devices with CIE y <0.06 ( Tang et al., 2018 , Hu et al., 2014 , Li et al., 2018 ). Furthermore, device B1 displayed an efficiency roll-up at low luminance and extremely low-efficiency roll-off at high luminance.…”

Recent Developments in AIEgens for Non‐doped and TADF OLEDs

“…Recently, Guo and co‐workers showed that the isomer of the well‐known blue TADF dye bis‐[4‐(9, 9‐dimethyl‐9,10‐dihydroacridine)‐phenyl]‐sulfone (DMAC‐DPS) obtained by linking the electron donor DMAC groups to the diphenyl sulfone (DPS) unit in meta position, exhibits AIDF properties and blue emission . The non‐doped OLED employing the bis(3‐(9,9‐dimethyl‐9,10‐dihydroacridine)phenyl)sulfone (mSOAD) achieves very remarkable performance as blue electroluminescent device with emission maximum at 488 nm and EQE of 14.0 %.…”

“…The high performance of the AIDF OLED employing the isomer of DMAC‐DPS was confirmed later by Yang and co‐workers, which reported highly efficient sky‐blue solution‐processed OLEDs by using two different isomers . Besides the isomers bis‐[3‐(9, 9‐dimethyl‐9,10‐dihydroacridine)‐phenyl]‐sulfone ( m ‐ACSO2) indicated as mSOAD by Guo and co‐workers, they prepare also the bis‐[2‐(9,9‐dimethyl‐9,10‐dihydroacridine)‐phenyl]‐sulfone ( o ‐ACSO2) compound. Both molecules maintain good TADF properties with excellent solubility and AIE effect thanks to the large twisted angles between donors and acceptor unit.…”