Peripheral Amplification of Multi‐Resonance Induced Thermally Activated Delayed Fluorescence for Highly Efficient OLEDs

Abstract

Multi-resonance induced by boron and nitrogen atoms in opposite resonance positions endows a thermally activated delayed fluorescence (MR-TADF) emitter with a strikingly small full width at half maximum of only 26 nm and excellent photoluminescence quantum yield of up to 97.48 %. The introduction of a carbazole unit in the para position of the B-substituted phenyl-ring can significantly boost up the resonance effect without compromising the color fidelity, subsequently enhancing the performances of the corresponding pure blue TADF-OLED, with an outstanding external quantum efficiency (EQE) up to 32.1 % and low efficiency roll-off, making it one of the best TADF-OLEDs in the blue region to date. Furthermore, utilizing this material as host for a yellow phosphorescent emitter, the device also shows a significantly reduced turn-on voltage of 3.2 V and an EQE of 22.2 %.

Intramolecular Borylation via Sequential B−Mes Bond Cleavage for the Divergent Synthesis of B,N,B‐Doped Benzo[4]helicenes

“…In contrast to their charge transfer (CT) governed, donor–acceptor analogues, MR‐TADF molecules exhibit a narrow π→π* emission band, improving the color purity of the corresponding OLEDs significantly. Notably, only a few MR‐TADF emitters are known so far and optimization of their photophysical properties relies on early‐stage introduction of donor units, which greatly hinders a systematic exploration of this new class of emitters . With the aim of achieving new B,N,B‐doped helicenes such as 3 —an inverted DABNA with respect to B and N positions (Scheme )—we discovered a new and highly effective borylation method using 1,4‐B,N‐anthracene borinic acid 1 as the precursor, which enabled the synthesis of a series of symmetric and unsymmetric B,N,B‐benzo[4]helicenes.…”

Multi‐Resonance Induced Thermally Activated Delayed Fluorophores for Narrowband Green OLEDs

“…As depicted in Figure c, remarkably, maximum EQEs (EQE max ) and power efficiencies (PE max ) of 22.0 % and 69.8 lm W −1 , 22.7 % and 72.3 lm W −1 , as well as 20.9 % and 51.3 lm W −1 were observed for devices based on 2F‐BN, 3F‐BN, and 4F‐BN, respectively, which are among the best device performances based on MR‐TADF emitters . To our knowledge, the power efficiencies here are the record‐high values among all MR‐TADF OLEDs . Contrarily, the reference device with 4CzIPN as the emitter only showed EQE max and PE max of 19.6 % and 55.1 lm W −1 , which are both inferior to other devices.…”

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

“…The breakthrough within this category was made in 2018. Our group reported a peripheral amplification method of enhancing both the multi‐resonance effect and increasing the device performances drastically . Through addition of a carbazole unit on the periphery of the rigid framework, the HOMO and LUMO energy levels are simultaneously lowered, whereas the oscillating strength is enhanced (Figure ).…”

“… Illustration of enhancement of multi‐resonance effect to create better MR‐TADF emitters. Reproduced with permission from Ref . Copyright 2018, Wiley‐VCH.…”