High‐Performance Non‐doped OLEDs with Nearly 100 % Exciton Use and Negligible Efficiency Roll‐Off

Non‐doped organic light‐emitting diodes (OLEDs) possess merits of higher stability and easier fabrication than doped devices. However, luminescent materials with high exciton use are generally unsuitable for non‐doped OLEDs because of severe emission quenching and exciton annihilation in neat films. Herein, we wish to report a novel molecular design of integrating aggregation‐induced delayed fluorescence (AIDF) moiety within host materials to explore efficient luminogens for non‐doped OLEDs. By grafting 4‐(phenoxazin‐10‐yl)benzoyl to common host materials, we develop a series of new luminescent materials with prominent AIDF property. Their neat films fluoresce strongly and can fully harvest both singlet and triplet excitons with suppressed exciton annihilation. Non‐doped OLEDs of these AIDF luminogens exhibit excellent luminance (ca. 100000 cd m^?2), outstanding external quantum efficiencies (21.4–22.6 %), negligible efficiency roll‐off and improved operational stability. To the best of our knowledge, these are the most efficient non‐doped OLEDs reported so far. This convenient and versatile molecular design is of high significance for the advance of non‐doped OLEDs.     

Aggregation‐Induced Delayed Fluorescence Luminogens for Efficient Organic Light‐Emitting Diodes

Aggregation‐induced delayed fluorescence (AIDF) can be regarded as a special case of aggregation‐induced emission (AIE). Luminogens with AIDF can simultaneously emit strongly in solid state and fully utilize the singlet and triplet excitons in organic light‐emitting diodes (OLEDs). In this work, two new AIDF luminogens, DMF‐BP‐DMAC and DPF‐BP‐DMAC, with an asymmetric D–A–D′ structure, are designed and synthesized. The characteristics of both luminogens are systematically investigated, including single crystal structures, theoretical calculations, photophysical properties and thermal stabilities. Inspired by their AIDF nature, the green‐emission non‐doped OLEDs based on them are fabricated, which afford good electroluminescence performances, with low turn‐on voltages of 2.8 V, high luminance of 52560 cd m^?2, high efficiencies of up to 14.4 %, 42.3 cd A^?1 and 30.2 lm W^?1, and very small efficiency roll‐off. The results strongly indicate the bright future of non‐doped OLEDs on the basis of robust AIDF luminogens.     

High‐Performance Blue OLEDs Based on Phenanthroimidazole Emitters via Substitutions at the C6‐ and C9‐Positions for Improving Exciton Utilization

Donor–acceptor (D–A) molecular architecture has been shown to be an effective strategy for obtaining high‐performance electroluminescent materials. In this work, two D–A molecules, Ph‐BPA‐BPI and Py‐BPA‐BPI, have been synthesized by attaching highly fluorescent phenanthrene or pyrene groups to the C6‐ and C9‐positions of a locally excited‐state emitting phenylamine–phenanthroimidazole moiety. Equipped with good physical and hybridized local and charge‐transfer properties, both molecules show high performances as blue emitters in nondoped organic light‐emitting devices (OLEDs). An OLED using Ph‐BPA‐BPI as the emitting layer exhibits deep‐blue emission with CIE coordinates of (0.15, 0.08), and a maximum external quantum efficiency (EQE), current efficiency (CE), and power efficiency (PE) of 4.56 %, 3.60 cd A^?1, and 3.66 lm W^?1, respectively. On the other hand, a Py‐BPA‐BPI‐based, sky‐blue OLED delivers the best results among nondoped OLEDs with CIE_y values of < 0.3 reported so far, for which a very low turn‐on voltage of 2.15 V, CIE coordinates of (0.17, 0.29), and maximum CE, PE, and EQE values of 10.9 cd A^?1, 10.5 lm W^?1, and 5.64 %, were achieved, respectively. More importantly, both devices show little or even no efficiency roll‐off and high singlet exciton‐utilizing efficiencies of 36.2 % for Ph‐BPA‐BPI and 39.2 % for Py‐BPA‐BPI.     

Highly Luminescent Pincer Gold(III) Aryl Emitters: Thermally Activated Delayed Fluorescence and Solution‐Processed OLEDs

Herein are described the synthesis, photophysical properties and applications of a series of luminescent cyclometalated Au^III complexes having an auxiliary aryl ligand. These complexes show photoluminescence with emission quantum yields of up to 0.79 in solution and 0.84 in thin films (4 wt % in PMMA) at room temperature, both of which are the highest reported values among Au^III complexes. Thermally activated delayed fluorescence (TADF) is the emission origin for some of these complexes. Solution‐processed OLEDs made with these complexes showed sky‐blue to green electroluminescence with external quantum efficiencies (EQEs) of up to 23.8 %, current efficiencies of up to 70.4 cd A⁻¹, and roll‐off of down to 1 %, highlighting the bright prospect of Au^III‐TADF emitters in OLEDs.     

Non‐Doped Sky‐Blue OLEDs Based on Simple Structured AIE Emitters with High Efficiencies at Low Driven Voltages

Blue organic light‐emitting diodes (OLEDs) are necessary for flat‐panel display technologies and lighting applications. To make more energy‐saving, low‐cost and long‐lasting OLEDs, efficient materials as well as simple structured devices are in high demand. However, a very limited number of blue OLEDs achieving high stability and color purity have been reported. Herein, three new sky‐blue emitters, 1,4,5‐triphenyl‐2‐(4‐(1,2,2‐triphenylvinyl)phenyl)‐1H‐imidazole (TPEI), 1‐(4‐methoxyphenyl)‐4,5‐diphenyl‐2‐(4‐(1,2,2‐triphenylvinyl)phenyl)‐1H‐imidazole (TPEMeOPhI) and 1‐phenyl‐2,4,5‐tris(4‐(1,2,2‐triphenylvinyl)phenyl)‐1H‐imidazole (3TPEI), with a combination of imidazole and tetraphenylethene groups, have been developed. High photoluminescence quantum yields are obtained for these materials. All derivatives have demonstrated aggregation‐induced emission (AIE) behavior, excellent thermal stability with high decomposition and glass transition temperatures. Non‐doped sky‐blue OLEDs with simple structure have been fabricated employing these materials as emitters and realized high efficiencies of 2.41 % (4.92 cd A⁻¹, 2.70 lm W⁻¹), 2.16 (4.33 cd A⁻¹, 2.59 lm W⁻¹) and 3.13 % (6.97 cd A⁻¹, 4.74 lm W⁻¹) for TPEI, TPEMeOPhI and 3TPEI, with small efficiency roll‐off. These are among excellent results for molecules constructed from the combination of imidazole and TPE reported so far. The high performance of a 3TPEI‐based device shows the promising potential of the combination of imidazole and AIEgen for synthesizing efficient electroluminescent materials for OLED devices.     

A Novel Spiro[acridine‐9,9′‐fluorene] Derivatives Containing Phenanthroimidazole Moiety for Deep‐Blue OLED Application

Typical π–π stacking and aggregation‐caused quenching could be suppressed in the film‐state by the spiro conformation molecular design in the field of organic light‐emitting diodes (OLEDs). Herein, a novel deep‐blue fluorescent material with spiro conformation, 1‐(4‐(tert ‐butyl)phenyl)‐2‐(4‐(10‐phenyl‐10H ‐spiro[acridine‐9,9′‐fluoren]‐2‐yl)phenyl)‐1H ‐phenanthro[9,10‐d ]imidazole ( SAF‐BPI ), was designed and synthesized. The compound consists of spiro‐acridine‐fluorene (SAF) as donor part and phenanthroimidazole (BPI) as acceptor part. Owing to the rigid SAF skeleton, this compound exhibits a high thermal stability with a glass transition temperature (T _g) of 198 °C. The compound exhibits bipolar transporting characteristics demonstrated by the single‐carrier devices. The non‐doped OLEDs based on the SAF‐BPI as the emitting layer shows maximum emission at 448 nm, maximum luminance of 2122 cd m⁻², maximum current efficiency (CE) of 3.97 cd A⁻¹, and a maximum power efficiency of 2.08 lm W⁻¹. The chromaticity coordinate is stable at (0.15, 0.10) at the voltage of 7–11 V. The device shows a slow efficiency roll‐off with CE of 3.35 and 2.85 cd A⁻¹ at 100 and 1000 cd m⁻², respectively.     

Constructing a Novel Dendron for a Self‐Host Blue Emitter with Thermally Activated Delayed Fluorescence: Solution‐Processed Nondoped Organic Light‐Emitting Diodes with Bipolar Charge Transfer and Stable Color Purity

Self‐host thermally activated delayed fluorescence (TADF) materials have recently been identified as effective emitters for solution‐processed nondoped organic light‐emitting diodes (OLEDs). However, except for the carbazole unit, few novel dendrons have been developed to build self‐host TADF emitters. This study reports two self‐host blue materials, tbCz‐SO and poCz‐SO, with the same TADF emissive core and different dendrons. The influence of the peripheral dendrons on the photophysical properties and electroluminescent performances of the self‐host materials were systematically investigated. The transient fluorescence and electroluminescence spectra indicated that the diphenylphosphoryl carbazole units could effectively encapsulate the emissive core to reduce the concentration quenching effect and to enhance reverse intersystem crossing. By using tbCz‐SO and poCz‐SO as host‐free blue emitters, the performance of the solution‐processed nondoped OLED device demonstrated that a more balanced charge transfer from the bipolar dendrons would offer a better current efficiency of 10.5 cd A⁻¹ and stable color purity with Commission Internationale de L'Eclairage units of (0.18, 0.27).     

Efficient Nondoped Pure Blue Organic Light‐Emitting Diodes Based on an Anthracene and 9,9‐Diphenyl‐9,10‐dihydroacridine Derivative

Organic light‐emitting diodes (OLEDs) have been greatly developed in recent years owing to their abundant advantages for full‐color displays and general‐purpose lightings. Blue emitters not only provide one of the primary colors of the RGB (red, green and blue) display system to reduce the power consumption of OLEDs, but are able able to generate light of all colors, including blue, green, red, and white by energy transfer processes in devices. However, it remains a challenge to achieve high‐performance blue electroluminescence, especially for nondoped devices. In this paper, we report a blue light emitting molecule, DPAC‐AnPCN, which consists of 9,9‐diphenyl‐9,10‐dihydroacridine and p‐benzonitrile substituted anthracene moieties. The asymmetrically decoration on anthracene with different groups on its 9 and 10 positions combines the merits of the respective constructing units and endows DPAC‐AnPCN with pure blue emission, high solid‐state efficiency, good thermal stability and appropriate HOMO and LUMO energy levels. Furthermore, DPAC‐AnPCN can be applied in a nondoped device to effectively reduce the fabrication complexity and cost. The nondoped device exhibits pure blue electroluminescence (EL) locating at 464 nm with CIE coordinates of (0.15, 0.15). Moreover, it maintains high efficiency at relatively high luminescence. The maximum external quantum efficiency (EQE) reaches 6.04 % and still remains 5.31 % at the luminance of 1000 cd m^?2 showing a very small efficiency roll‐off.     

Tri‐Spiral Donor for High Efficiency and Versatile Blue Thermally Activated Delayed Fluorescence Materials

Blue thermally activated delayed fluorescence (TADF) emitters that can simultaneously achieve high efficiency in doped and nondoped organic light‐emitting diodes (OLEDs) are rarely reported. Reported here is a strategy using a tri‐spiral donor for such versatile blue TADF emitters. Impressively, by simply extending the nonconjugated fragment and molecular length, aggregation‐caused emission quenching (ACQ) can be greatly alleviated to achieve as high as a 90 % horizontal orientation dipole ratio and external quantum efficiencies (EQEs) of up to 33.3 % in doped and 20.0 % in nondoped sky‐blue TADF‐OLEDs. More fascinatingly, a high‐efficiency purely organic white OLED with an outstanding EQE of up to 22.8 % was also achieved by employing TspiroS‐TRZ as a blue emitter and an assistant host. This compound is the first blue TADF emitter that can simultaneously achieve high electroluminescence (EL) efficiency in doped, nondoped sky‐blue, and white TADF‐OLEDs.     

C−H Direct Arylated 6H‐Indolo[2,3‐b]quinoxaline Derivative as a Thickness‐Dependent Hole‐Injection Layer

A novel perfluoro‐1,4‐phenylenyl 6H ‐indolo[2,3‐b ]quinoxaline derivative ( TFBIQ ) was designed and synthesized by using a C−H direct arylation method. The optoelectrical properties of the obtained TFBIQ were fully characterized by UV/Vis spectroscopy, photoluminescence spectroscopy, cyclic voltammetry, and a group of Alq₃‐based green organic light‐emitting diodes (OLEDs). Device A, which used 0.5 nm‐thick TFBIQ as the interfacial modification layer, exhibited the five best advantages of device performance including a minimum turn‐on voltage as low as 3.1 V, a maximum luminescence intensity as high as 26564 cd m⁻², a highest current density value of 348.9 mA cm⁻² at a voltage of 11 V, the smallest efficiency roll‐off, as well as the greatest power efficiency of 1.46 lm W⁻¹ relative to all of the other tested devices with thicker TFBIQ and also 10 nm‐thick MoO₃ as hole‐injection layers (HILs). As a promising candidate for an organic HIL material, the as‐prepared TFBIQ exhibited a strong thickness effect on the performance of corresponding OLEDs. Furthermore, the theoretical calculated vertical ionization potential of the fluorinated TFBIQ suggests better anti‐oxidation stability than that of the non‐fluorinated structure.     

Highly Efficient Near‐Infrared Organic Light‐Emitting Diode Based on a Butterfly‐Shaped Donor–Acceptor Chromophore with Strong Solid‐State Fluorescence and a Large Proportion of Radiative Excitons

The development of near‐infrared (NIR) organic light‐emitting diodes (OLEDs) is of growing interest. Donor–acceptor (D–A) chromophores have served as an important class of NIR materials for NIR OLED applications. However, the external quantum efficiencies (EQEs) of NIR OLEDs based on conventional D–A chromophores are typically below 1 %. Reported herein is a butterfly‐shaped D–A compound, PTZ‐BZP. A PTZ‐BZP film displayed strong NIR fluorescence with an emission peak at 700 nm, and the corresponding quantum efficiency reached 16 %. Remarkably, the EQE of the NIR OLED based on PTZ‐BZP was 1.54 %, and a low efficiency roll‐off was observed, as well as a high radiative exciton ratio of 48 %, which breaks through the limit of 25 % in conventional fluorescent OLEDs. Experimental and theoretical investigations were carried out to understand the excited‐state properties of PTZ‐BZP.     

Four‐Coordinate Boron Emitters with Tridentate Chelating Ligand for Efficient and Stable Thermally Activated Delayed Fluorescence Organic Light‐Emitting Devices

A new class of four‐coordinate donor‐acceptor fluoroboron‐containing thermally activated delayed fluorescence (TADF) compounds bearing a tridentate 2,2′‐(pyridine‐2,6‐diyl)diphenolate (dppy) ligand has been successfully designed and synthesized. Upon varying the donor moieties from carbazole to 10H‐spiro[acridine‐9,9′‐fluorene] to 9,9‐dimethyl‐9,10‐dihydroacridine, these boron derivatives exhibit a wide range of emission colors spanning from blue to yellow with a large spectral shift of 2746 cm^?1, with high PLQYs of up to 96 % in the doped thin film. Notably, vacuum‐deposited organic light‐emitting devices (OLEDs) made with these boron compounds demonstrate high performances with the best current efficiencies of 55.7 cd A^?1, power efficiencies of 58.4 lm W^?1 and external quantum efficiencies of 18.0 %. More importantly, long operational stabilities of the green‐emitting OLEDs based on 2 with half‐lifetimes of up to 12 733 hours at an initial luminance of 100 cd m^?2 have been realized. This work represents for the first time the design and synthesis of tridentate dppy‐chelating four‐coordinate boron TADF compounds for long operational stabilities, suggesting great promises for the development of stable boron‐containing TADF emitters.     

A Versatile Triphenylamine/Fluoranthene‐Based Derivative as a Nondoped Green‐Emitting,Hole‐Transporting Interlayer for Electroluminescent Devices

A new triphenylamine‐bridged fluoranthene derivative, 4‐(7,10‐diphenylfluoranthen‐8‐yl)‐N‐[4‐(7,10‐diphenylfluoranthen‐8‐yl)phenyl]‐N‐phenylaniline (BDPFPA), with a high glass transition temperature of 220 °C has been synthesized and characterized. BDPFPA is a highly fluorescent and versatile material that can be used as a nondoped green emitter and as a hole transporter. BDPFPA was used in a standard trilayer device as the emitting layer, which showed a low turn‐on voltage (<3 V) and a high efficiency of 11.6 cd A^?1. The device also shows little efficiency roll‐off at high brightness. For example, the efficiency can still be maintained at 11.4 cd A^?1 (5.4 lm W^?1) at a brightness of 10 000 cd m^?2. These results are among the best reported for nondoped fluorescent green organic light‐emitting diodes. A simple bilayer device, in which BDPFPA serves as a hole‐transporting layer, has a maximum power efficiency of 3.3 lm W^?1 and the performance is nearly 40 % higher than that of an N,N′‐bis(1‐naphthyl)‐N,N′‐ diphenyl‐1,1′‐biphenyl‐4,4′‐diamine (NPB)‐based standard device.     

Highly Efficient Orange and Warm White Phosphorescent OLEDs Based on a Host Material with a Carbazole–Fluorenyl Hybrid

A new carbazole–fluorenyl hybrid compound, 3,3′(2,7‐di(naphthaline‐2‐yl)‐9H‐fluorene‐9,9‐diyl)bis(9‐phenyl‐9H‐carbazole) (NFBC) was synthesized and characterized. The compound exhibits blue‐violet emission both in solution and in film, with peaks centered at 404 and 420 nm. In addition to the application as a blue emitter, NFBC is demonstrated to be a good host for phosphorescent dopants. By doping Ir(2‐phq)₃ in NFBC, a highly efficient orange organic light‐emitting diode (OLED) with a maximum efficiency of 32 cd A^?1 (26.5 Lm W^?1) was obtained. Unlike most phosphorescent OLEDs, the device prepared in our study shows little efficiency roll‐off at high brightness and maintains current efficiencies of 31.9 and 26.8 cd A^?1 at a luminance of 1000 and 10 000 cd m^?2, respectively. By using NFBC simultaneously as a blue fluorescence emitter and as a host for a phosphorescent dopant, a warm white OLED with a maximum efficiency of 22.9 Lm W^?1 (21.9 cd A^?1) was also obtained.     

Non-Doped Blue AIEgen-Based OLED with EQE Approaching 10.3 %

Aggregation-induced emission (AIE) luminogens (AIEgens) are attractive for the construction of non-doped blue organic light-emitting diodes (OLEDs) owning to their high emission efficiency in the film state. However, the large internal inversion rate (k_IC^(Tn)) between high-lying triplet levels (T_n) and T_n-1 causes a huge loss of triplet excitons, resulting in dissatisfied device performance of these AIEgens-based non-doped OLEDs. Herein, we designed and synthesized a blue luminogen of DPDPB-AC by fusing an AIEgen of TPB-AC and a DMPPP, which feature hot exciton and triplet-triplet annihilation (TTA) up-conversion process, respectively. DPDPB-AC successfully inherits the AIE feature and excellent horizontal dipole orientation of TPB-AC. Furthermore, it owes smaller k_IC^(Tn) than TPB-AC. When DPDPB-AC was applied in OLED as non-doped emitting layer, an outstanding external quantum efficiency of 10.3 % and an exceptional brightness of 69311 cd m⁻² were achieved. The transient electroluminescent measurements and steady-state dynamic analysis confirm that both TTA and hot exciton processes contribute to such excellent device performance. This work provides a new insight into the design of efficient organic fluorophores by managing high-lying triplet excitons.     

Silicon‐Based Material with Spiro‐Annulated Fluorene/Triphenylamine as Host and Exciton‐Blocking Layer for Blue Electrophosphorescent Devices

A novel silicon‐based compound, 10‐phenyl‐2′‐(triphenylsilyl)‐10H‐spiro[acridine‐9,9′‐fluorene] (SSTF), with spiro structure has been designed, synthesized, and characterized. Its thermal, electronic absorption, and photoluminescence properties were studied. Its energy levels make it suitable as a host material or exciton‐blocking material in blue phosphorescent organic light‐emitting diodes (PhOLEDs). Accordingly, blue‐emitting devices with iridium(III) bis[(4,6‐difluorophenyl)‐pyridinato‐N,C²′]picolinate (FIrpic) as phosphorescent dopant have been fabricated and show high efficiency with low roll‐off. In particular, 44.0 cd A^?1 (41.3 lm W^?1) at 100 cd m^?2 and 41.9 cd A^?1 (32.9 lm W^?1) at 1000 cd m^?2 were achieved when SSTF was used as host material; 28.1 lm W^?1 at 100 cd m^?2 and 20.6 lm W^?1 at 1000 cd m^?2 were achieved when SSTF was used as exciton‐blocking layer. All of the results are superior to those of the reference devices and show the potential applicability and versatility of SSTF in blue PhOLEDs.     

Versatile Benzimidazole/Triphenylamine Hybrids: Efficient Nondoped Deep‐Blue Electroluminescence and Good Host Materials for Phosphorescent Emitters

Two new bipolar compounds, N,N,N′,N′‐tetraphenyl‐5′‐(1‐phenyl‐1H‐benzimidazol‐2‐yl)‐1,1′:3′,1′′‐terphenyl‐4,4′′‐diamine ( 1 ) and N,N,N′,N′‐tetraphenyl‐5′‐(1‐phenyl‐1H‐benzimidazol‐2‐yl)‐1,1′:3′,1′′‐terphenyl‐3,3′′‐diamine ( 2 ), were synthesized and characterized, and their thermal, photophysical, and electrochemical properties were investigated. Compounds 1 and 2 possess good thermal stability with high glass‐transition temperatures of 109–129 °C and thermal decomposition temperatures of 501–531 °C. The fluorescence quantum yield of 1 (0.52) is higher than that of 2 (0.16), which could be attributed to greater π conjugation between the donor and acceptor moieties. A nondoped deep‐blue fluorescent organic light‐emitting diode (OLED) using 1 as the blue emitter displays high performance, with a maximum current efficiency of 2.2 cd A⁻¹ and a maximum external efficiency of 2.9 % at the CIE coordinates of (0.17, 0.07) that are very close to the National Television System Committee’s blue standard (0.15, 0.07). Electrophosphorescent devices using the two compounds as host materials for green and red phosphor emitters show high efficiencies. The best performance of a green phosphorescent device was achieved using 2 as the host, with a maximum current efficiency of 64.3 cd A⁻¹ and a maximum power efficiency of 68.3 lm W⁻¹; whereas the best performance of a red phosphorescent device was achieved using 1 as the host, with a maximum current efficiency of 11.5 cd A⁻¹, and a maximum power efficiency of 9.8 lm W⁻¹. The relationship between the molecular structures and optoelectronic properties are discussed.     

Synthesis and electroluminescent performance of thermally activated delayed fluorescence‐conjugated polymers with simple formylphenyl as pendant acceptor

Formylphenyl has been demonstrated to act as an acceptor to construct thermally activated delayed fluorescence (TADF) emitter, and therefore a series of the TADF‐conjugated polymers with formylphenyl as pendant acceptor and carbazole/acridine as backbone donor are designed and synthesized. All polymers involve the twisted donor/acceptor structural moieties with the sufficiently spatial separation between the highest occupied molecular orbital and the lowest unoccupied molecular orbital as well as a small singlet/triplet splitting, and exhibit the legible TADF features confirmed by theoretical calculation and their transient decay spectra. The solution‐processed organic light‐emitting diodes using neat film of the polymers as emissive layer achieve excellent performance with the maximum external quantum efficiency (EQE) of up to 10.6%, the maximum current efficiency of up to 35.3 cd A⁻¹ and the low turn‐on voltage of 2.7 V. Moreover, the EQE still remains 10.3% at the luminance of 1000 cd m⁻² with the low driving voltage of 4.4 V and extremely small efficiency roll‐off. © 2018 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2018 , 56, 1989–1996     

Alignment of Heptagonal Diimide and Triazine Enables Narrowband Pure-Blue Organic Light-Emitting Diodes with Low Efficiency Roll-Off

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 (k_R) of 1.0×10⁷ s⁻¹ and a swift reverse intersystem crossing rate (k_RISC) of 1.8×10⁶ s⁻¹, complemented by a slow non-radiative decay rate (k_NR) 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 (EQE_max) 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.     

Molecular Design of Non‐doped OLEDs Based on a Twisted Heptagonal Acceptor: A Delicate Balance between Rigidity and Rotatability

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.