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The endeavor to develop high‐performance narrowband blue organic light‐emitting diodes (OLEDs) with low efficiency roll‐off represents an attractive challenge. Herein, we introduce a hetero‐acceptor design strategy centered around the heptagonal diimide (BPI) building block to create an efficient thermally activated delayed fluorescence (TADF) sensitizer. The alignment of a twisted BPI unit and a planar diphenyltriazine (TRZ) fragment imparts remarkable exciton dynamic properties to 26tCz‐TRZBPI, including a fast radiative decay rate (kR) of 1.0×107 s−1 and a swift reverse intersystem crossing rate (kRISC) of 1.8×106 s−1, complemented by a slow non‐radiative decay rate (kNR) of 6.0×103 s−1. Consequently, 26tCz‐TRZBPI facilitates the fabrication of high‐performance narrowband pure‐blue TADF‐sensitized fluorescence OLEDs (TSF‐OLEDs) with a maximum external quantum efficiency (EQEmax) of 24.3 % and low efficiency roll‐off even at a high brightness level of 10000 cd m−2 (EQE10000: 16.8 %). This showcases a record‐breaking external quantum efficiency at a high luminance level of 10000 cd m−2 for narrowband blue TSF‐OLEDs. [ABSTRACT FROM AUTHOR]

Narrowband organic light‐emitting diodes (OLEDs) are receiving significant attention and have demonstrated impressive performance in blue and green OLEDs. However, developing high‐performance narrowband red OLEDs remains a highly desired yet challenging task. Herein, we have developed narrowband red fluorescent emitters by utilizing a boron‐dipyrromethene (BODIPY) skeleton in combination with a methyl‐shield strategy. These emitters exhibit small full‐width at half‐maxima (FWHM) ranging from 21 nm (0.068 eV) to 25 nm (0.081 eV) and high photoluminescence quantum yields (ΦPL) ranging from 88.5 % to 99.0 % in toluene solution. Using BODIPY‐based luminescent materials as emitters, high‐performance narrowband red OLEDs have been assembled with external quantum efficiency as high as 18.3 % at 623 nm and 21.1 % at 604 nm. This work represents, to our knowledge, the first successful case of achieving NTSC pure‐red OLEDs with the Commission Internationale de l'Éclairage (CIE) coordinates of [0.67, 0.33] based on conventional fluorescent emitters. [ABSTRACT FROM AUTHOR]

Suppressing aggregation‐caused quenching (ACQ) effect and reducing device efficiency roll‐off are both crucial yet challenging for multi‐resonance (MR) emitters. Herein, we put forward a medium‐ring strategy to design efficient MR emitters that feature heptagonal tribenzo[b,d,f]azepine (TBA) donors. The highly twisted conformation enlarges the intermolecular distances between the MR‐emitting cores, and thus suppresses ACQ effect. Meanwhile, the introduction of heptagonal donors enhances spin‐orbital coupling, so as to accelerate reverse intersystem crossing (RISC) process. This medium‐ring strategy gives rise to the first example of blue MR emitter that simultaneously possesses radiative decay rate as fast as 108 s−1 and RISC rate as fast as 106 s−1. Accordingly, DTBA‐B2N3 enables to assemble high‐performance blue organic light‐emitting diodes (OLEDs) with maximum external quantum efficiency (EQEmax) of 30.9 % and alleviated efficiency roll‐off (EQE1000: 20.5 %). [ABSTRACT FROM AUTHOR]

The development of intramolecular‐lock strategy is an appealing task for designing efficient thermally activated delayed fluorescence (TADF) molecules, but only limited examples have been reported so far. Herein we present a "medium ring"‐lock strategy to develop TADF emitters for improving the efficiency of organic light‐emitting diodes (OLEDs). The installation of an electron‐deficient heptagonal diimide lock onto a highly rotatable biphenyl‐based emitter not only enhances electron‐withdrawing ability of acceptor that decreases singlet‐triplet energy gap (ΔEST), but also endows the skeleton with modest rigidity and flexibility that increases photoluminescence quantum yield (PLQY) in neat film. In particular, the integration of the diimide lock also leads to an increase in horizontal orientation factor (Θ//) from 69 % to 83 %. Consequently, this modified intramolecular‐lock strategy enables an efficient TADF emitter to assemble high‐performance non‐doped OLEDs with a high external quantum efficiency of 26.2 % and a power efficiency of 76.6 lm W−1. [ABSTRACT FROM AUTHOR]

The development of high‐performance blue organic light‐emitting diodes (OLEDs) remains a challenging task. While exploiting new blue emitters has attracted great interest, developing host materials that considerably determine device performance obviously lags behind. Herein, we present an ease of access to the structurally diverse benzoheteroaromatic‐fused pyridine skeletons by the iridium‐catalyzed intramolecular C−H/C−H coupling reaction, which unlocks an unparalleled opportunity to rapidly assemble a library of pyridine‐fused bipolar host materials. As an illustrated example, the benzo[4,5]thieno[2,3‐b]pyridine skeleton (BTP) has been made to a pseudo‐symmetric host (DCz‐BTP). The merging of a pyridine fragment enables strong intermolecular interactions, leading to satisfactory bipolar transporting properties. Utilizing DCz‐BTP as the host, blue thermally activated delayed fluorescent OLEDs (TADF‐OLEDs) exhibit a low turn‐on voltage of 2.8 V and a high maximum external quantum efficiency (EQEmax) of 29.0 % and blue TADF‐sensitized florescent OLEDs (TSF‐OLEDs) give an EQEmax as high as 20.5 %, revealing the potential of the BTP skeleton for the construction of high‐performance host materials. [ABSTRACT FROM AUTHOR]

The emitting layer based on a host–guest system plays a crucial role in organic light‐emitting diodes (OLEDs). While emitters have witnessed rapid progress in structural diversity, hosts still rely heavily on traditional structures and are underdeveloped. Herein a "medium‐ring" strategy has been put forward to design structurally nontraditional host molecules, which are not only rotatable enough to suppress close π–π stacking, thus reducing exciton annihilation, but also rigid enough to prevent excessive conformational flipping, thus inhibiting non‐radiative decay. Accordingly, a brand‐new type of bipolar hosts with a twisted "butterfly‐shaped heptagonal acceptor (EtBP), which features an electron‐deficient benzophenone fragment with a flexible ethylidene bridge, has been developed. With satisfactory morphological stability and well‐balanced hole‐ and electron‐transporting properties, the EtBP‐based bipolar hosts enable high‐performance RGB phosphorescent OLEDs with small efficiency roll‐off, which are superior to those of acyclic benzophenone‐based devices. [ABSTRACT FROM AUTHOR]

Herein disclosed is the first example of diarylation/annulation of benzoic acids via an iridium catalyst system. This protocol provides a step‐economic and highly efficient pathway to 1‐aryl, 1,3‐diaryl, 1,7‐diaryl and 1,3,7‐triaryl spirobifluorenes from readily available starting materials. The applications of multi‐aryl spirobifluorenes as pure hydrocarbon (PHC) hosts for red, green, and blue (RGB) phosphorescent organic light‐emitting diodes (PhOLEDs) were explored. Due to high triplet energies, 1,3‐diaryl spirobifluorenes exhibit the potential as the host material of blue PhOLEDs. 1,7‐Diaryl spirobifluorene can serve as the host of green PhOLEDs. 1,3,7‐Triaryl spirobifluorene is a high‐performance host for red PhOLEDs, which exhibits a high external quantum efficiency (EQE) up to 27.3 %. This work not only exemplifies the great potential of multi‐aryl spirobifluorenes as PHC hosts, but also offers a new approach for the synthesis of these PHC hosts. [ABSTRACT FROM AUTHOR]

Disclosed here is a palladium‐catalyzed direct [4+1] spiroannulation of ortho‐C−H bonds of naphthols with cyclic diaryliodonium salts to construct spirofluorenyl naphthalenones (SFNP) under mild reaction conditions. This spiroannulation directly transforms the hydroxy group into a carbonyl group, and also tolerates reactive functional groups such as the halo groups, which provide an opportunity to rapidly assemble structurally new thermally activated delayed fluorescent (TADF) materials that feature a carbonyl group with an adjacent spirofluorenyl unit as the acceptor. As an illustrated example, the OLED device utilizing the assembled DMAC‐SFNP as the host material exhibits a low turn‐on voltage of 2.5 V and an ultra‐high external quantum efficiency of 32.2 %. This work provides inspiration for structurally new TADF materials, and also displays the potential of C−H activation as a synthetic strategy for the innovation of optoelectronic materials. [ABSTRACT FROM AUTHOR]

The development of efficient non‐doped organic light‐emitting diodes (OLEDs) is highly desired but very challenging because of a severe aggregation‐caused quenching effect. Herein, we present a heptagonal diimide acceptor (BPI), which can restrict excessive intramolecular rotation and inhibit close intermolecular π–π stacking due to well‐balanced rigidity and rotatability of heptagonal structure. The BPI‐based luminogen (DMAC‐BPI) shows significant aggregation‐induced delayed florescence with an extremely high photoluminescence quantum yield (95.8 %) of the neat film, and the corresponding non‐doped OLEDs exhibit outstanding electroluminescence performance with maximum external quantum efficiency as high as 24.7 % and remarkably low efficiency roll‐off as low as 1.0 % at 1000 cd m−2, which represents the state‐of‐the‐art performance for non‐doped OLEDs. In addition, the synthetic route to DMAC‐BPI is greatly streamlined and simplified through oxidative Ar−H/Ar−H homo‐coupling reaction. [ABSTRACT FROM AUTHOR]

• Two high-performance triazolotriazine-based TADF hosts were developed. • A mixed host strategy was employed to enhance the performance of red Ph-OLEDs. • Pure-red Ph-OLEDs with ultra-low efficiency roll-off were achieved. The development of high-performance pure-red phosphorescent organic light-emitting diodes (Ph-OLEDs) especially with low efficiency roll-off at high brightness is still an appealing yet challenging task. Despite success of well-documented 1,3,5-triazine (TRZ)-based thermally activated delayed fluorescence (TADF) hosts in green Ph-OLEDs, the limited electron-withdrawing ability of the TRZ acceptor makes the TADF hosts unsuitable enough for usage in the assembly of high-performance red Ph-OLEDs. Herein, pure-red Ph-OLEDs with ultra-low efficiency roll-off at luminance above 10000 cd m−2 are achieved by developing two triazolotriazine-based TADF hosts (23aIC-TAZTRZ and 32aIC-TAZTRZ) with balanced bipolar transporting property, good morphological stability and high photoluminescence quantum yield in neat film. Particularly, the phosphor-doped 23aIC-TAZTRZ and 32aIC-TAZTRZ emitting layers display high horizontal orientation factors (Θ //) of 84% and 85%, respectively. Ph-OLEDs utilizing 50 wt% 23aIC-TAZTRZ and 50 wt% 32aIC-TAZTRZ as the mixed host exhibit pure-red emission with Commission Internationale de l'Eclairage (CIE) coordinate of [0.66, 0.34], high maximum external quantum efficiency (EQE max) of 27.4% and ultra-low efficiency roll-off at 10000 cd m−2 (EQE 10000 = 23.9%). This work not only discloses the potential of triazolotriazine acceptor for the construction of efficient TADF hosts, but also provides alternative candidates to TRZ-based hosts for the assembly of high-performance red Ph-OLEDs. [ABSTRACT FROM AUTHOR]

Herein disclosed the adjustment of the dual emission of keto and enol forms of excited-state intramolecular proton transfer (ESIPT) emitters via intramolecular charge transfer (ICT) effects. Introducing electron-donating triphenylamine (TPA) and electron-withdrawing triphenylboron (TPB) substituents into the para -position of the phenolic hydroxyl group or the side of the oxazole of 2-(2′-hydroxyphenyl)oxazole skeleton endows the resulting compounds (6a - 6d) with different photophysical properties. Owing to the ICT effect from electronic donor to acceptor, introducing TPA into the side of oxazole and TPB into the para -position of phenolic hydroxyl is conducive to an enol-form emission (6a). Exchanging the two substituents, namely introducing TPB into the side of oxazole and TPA into the para -position of phenolic hydroxyl, would be beneficial to a keto-form emission (6b). Synchronously introducing two identical substituents, whether TPA or TPB, into two sides of 2-(2′-hydroxyphenyl)oxazole skeleton (6c and 6d) would lead to the dual emission of keto and enol forms due to the excited-state equilibrium of ESIPT reactions, which are further verified by DFT calculation. The organic light-emitting diode (OLED) devices with 6a and 6c as emitters were fabricated, both of which exhibit hybridized local and charge transfer (HLCT) excited-state characters with high external quantum efficiencies (EQEs) of 4.9% and 5.6%, respectively. • The adjustment of keto/enol emission of ESIPT emitters was systematically investigated for the first time. • ICT effect was deduced to be the main driving force to lead to the different luminescence properties of these ESIPT emitters. • The excited-state equilibrium of ESIPT reactions is verified by DFT calculation. • OLEDs based on ESIPT emitters exhibit high external quantum efficiencies. • The HLCT characters of ESIPT emitters were confirmed by experimental data and theoretical calculations. [ABSTRACT FROM AUTHOR]