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Thermally activated delayed fluorescence (TADF) emitters with a high horizontal orientation are highly essential for improving the external quantum efficiency (EQE) of organic light‐emitting diodes; however, pivotal molecular design strategies to improve the horizontal orientation of solution‐processable TADF emitters are still scarce and challenging. Herein, a phenyl bridge is adopted to connect the double TADF units, and generate a dimerized TADF dendrimer, D4CzBNPh‐SF. Compared to its counterpart with a single TADF unit, the proof‐of‐the‐concept molecule not only exhibits an improved horizontal dipole ratio (78 %) due to the π‐delocalization‐induced extended molecular conjugation, but also displays a faster reversed intersystem crossing rate constant (6.08×106 s−1) and a high photoluminescence quantum yield of 95 % in neat film. Consequently, the non‐doped solution‐processed device with D4CzBNPh‐SF as the emitter achieves an ultra‐high maximum EQE of 32.6 %, which remains at 26.6 % under a luminance of 1000 cd/m2. Furthermore, when using D4CzBNPh‐SF as a sensitizer, the TADF‐sensitized fluorescence device exhibits a high maximum EQE of 30.7 % at a luminance of 575 cd/m2 and a full width at half maximum of 36 nm. [ABSTRACT FROM AUTHOR]

Ir(III) carbene complexes have been explored as one of the best blue phosphors for their high performance. Herein, the authors designed and synthesized a series of blue‐emitting Ir(III) phosphors (f‐ct9a–c), featuring fac‐coordinated cyano‐imidazo[4,5‐b]pyridin‐2‐ylidene cyclometalates. These Ir(III) complexes exhibit true‐blue emission with a peak maximum spanning 448–467 nm, with high photoluminescence quantum yields of 81–88% recorded in degassed toluene. Moreover, OLED devices bearing phosphors f‐ct9a and f‐ct9b deliver maximum external quantum efficiencies (EQEmax) of 25.9% and 30.3%, together with Commission Internationale de L'Eclairage (CIEx,y) coordinates of (0.157, 0.225) and (0.142, 0.169), respectively. Remarkably, the f‐ct9b‐based device displays an incredible EQE of 29.0% at 5000 cd·m−2. The hyper‐OLED device based on f‐ct9b and ν‐DABNA exhibits an EQEmax of 34.7% and CIEx,y coordinates of (0.122, 0.131), affirming high potentials in achieving efficient blue electroluminescence. [ABSTRACT FROM AUTHOR]

Narrowband emissive multiple resonance (MR) emitters promise high efficiency and stability in deep‐blue organic light‐emitting diodes (OLEDs). However, the construction of ideal ultra‐narrow‐band deep‐blue MR emitters still faces formidable challenges, especially in balancing bathochromic‐shift emission, spectral narrowing, and aggregation suppression. Here, DICz is chosen, which possesses the smallest full‐width‐at‐half‐maximum (FWHM) in MR structures, as the core and solved the above issue by tuning its peripheral substitution sites. The 1‐substituted molecule Cz‐DICz is able to show a bright deep‐blue emission with a peak at 457 nm, an extremely small FWHM of 14 nm, and a CIE coordinate of (0.14, 0.08) in solution. The corresponding OLEDs exhibit high maximum external quantum efficiencies of 22.1%–25.6% and identical small FWHMs of 18 nm over the practical mass‐production concentration range (1–4 wt.%). To the best of the knowledge, 14 and 18 nm are currently the smallest FWHM values for deep‐blue MR emitters with similar emission maxima under photoluminescence and electroluminescence conditions, respectively. These discoveries will help drive the development of high‐performance narrowband deep‐blue emitters and bring about a revolution in OLED industry. [ABSTRACT FROM AUTHOR]

Recently, boron (B)/nitrogen (N)‐embedded polycyclic aromatic hydrocarbons (PAHs), characterized by multiple resonances (MR), have attracted significant attention owing to their remarkable features of efficient narrowband emissions with small full width at half maxima (FWHMs). However, developing ultra‐narrowband pure‐green emitters that comply with the Broadcast Service Television 2020 (BT2020) standard remains challenging. Precise regulation of the MR distribution regions allows simultaneously achieving the emission maximum, FWHM value, and spectral shape that satisfy the BT2020 standard. The proof‐of‐concept molecule TPABO‐DICz exhibited ultrapure green emission with a dominant peak at 515 nm, an extremely small FWHM of 17 nm, and Commission Internationale de l′Eclairage (CIE) coordinates of (0.17, 0.76). The corresponding bottom‐emitting organic light‐emitting diode (OLED) exhibited a remarkably high CIEy value (0.74) and maximum external quantum efficiency (25.8 %). Notably, the top‐emitting OLED achieved nearly BT2020 green color (CIE: 0.14, 0.79) and exhibited a state‐of‐the‐art maximum current efficiency of 226.4 cd A−1, thus fully confirming the effectiveness of the above strategy. [ABSTRACT FROM AUTHOR]

Extending the π‐skeletons of multi‐resonance (MR) organoboron emitters can feasibly modulate their optoelectronic properties. Here, we first adopt the indolo[3,2‐b]indole (32bID) segment as a multi‐nitrogen bridge and develop a high‐efficiency π‐extended narrowband green emitter. This moiety establishes not only a high‐yield one‐shot multiple Bora–Friedel–Crafts reaction towards a π‐extended MR skeleton, but a compact N‐ethylene‐N motif for a red‐shifted narrowband emission. An emission peak at 524 nm, a small full width at half maximum of 25 nm and a high photoluminescence quantum yield of 96 % are concurrently obtained in dilute toluene. The extended molecular plane also results in a large horizontal emitting dipole orientation ratio of 87 %. A maximum external quantum efficiency (EQE) of 36.6 % and a maximum power efficiency of 135.2 lm/W are thereafter recorded for the corresponding device, also allowing a low efficiency roll‐off with EQEs of 34.5 % and 28.1 % at luminance of 1,000 cd/m2 and 10,000 cd/m2, respectively. [ABSTRACT FROM AUTHOR]

Fusing condensed aromatics into multi‐resonance (MR) frameworks has been an exquisite strategy to modulate the optoelectronic properties, which, however, always sacrifices the small full width at half maxima (FWHM). Herein, we strategically embed B−N/B−O contained heterocycles as fusion locker into classical MR prototypes, which could enlarge the π‐extension and alleviate the steric repulsion for an enhanced planar skeleton to suppress the high‐frequency stretching/ scissoring vibrations for ultra‐narrowband emissions. Sky‐blue emitters with extremely small FWHMs of 17–18 nm are thereafter obtained for the targeted emitters, decreased by (1.4–1.9)‐fold compared with the prototypes. Benefiting from their high photoluminescence quantum yields of >90 % and fast radiative decay rates of >108 s−1, one of those emitters shows a high maximum external quantum efficiency of 31.9 % in sensitized devices, which remains 25.8 % at a practical luminance of 1,000 cd m−2 with a small FWHM of merely 19 nm. Notably a long operation half‐lifetime of 1,278 h is also recorded for the same device, representing one of the longest lifetimes among sky‐blue devices based on MR emitters. [ABSTRACT FROM AUTHOR]

Though the flourishment of materials with multiple resonance (MR) in blue to green regions, red‐emissive MR emitters are still rare in literatures, which definitely should be resolved for further applications. Herein, we report a simple molecular design strategy for the construction of pure‐red MR emitters by conjugate charge transfer, which could greatly enhance the π‐conjugation degree and charge‐transfer property of the target molecule while maintaining the basic feature of MR, leading to a significant redshift of more than 128 nm compared to the selected parent MR core. The proof‐of‐concept emitter PPZ‐BN exhibited a pure‐red emission with a dominant peak at 613 nm and a small full‐width‐at‐half‐maximum of 0.16 eV (48 nm). The optimized organic light‐emitting diode showed a high external quantum efficiency of 26.9 %, a small efficiency roll‐off, and an excellent operation stability (LT99) of more than 43 hours at an initial luminance of 10 000 cd m−2. [ABSTRACT FROM AUTHOR]

Although helically chiral heterohelicenes are widely adopted in chiroptical studies, those with circularly polarized thermally activated delayed fluorescence (CP‐TADF), which are highly valuable for circularly polarized organic light‐emitting diodes (CP‐OLEDs), are rarely realized. Moreover, the core skeletons of known CP‐TADF heterohelicenes are limited to the p‐ and n‐doped structures with multiresonance effect. In this study, a new type of helically chiral CP‐TADF heterohelicenes featuring a fused donor–acceptor core skeleton is successfully designed and constructed. Enantiomers possessing high configurational stability are achieved and separated, and they efficiently emit CP light with dissymmetry factors reaching 3.1 × 10−3 in doped films. Owing to the excellent photophysical properties, a high‐performance CP‐OLED with the maximum external quantum efficiency of up to 20.0% and an electroluminescence dissymmetry factor reaching 2.9 × 10−3 is obtained. This new type of CP‐TADF heterohelicenes provides a large space for the development of high‐performance CP‐TADF materials for various applications. [ABSTRACT FROM AUTHOR]

Pure organic phosphors capable of room-temperature phosphorescence show a great potential in organic light-emitting diodes, while it is limited by the big challenge to realize efficient electroluminescence under electric excitation. Herein, we develop a class of organic phosphors based on acridine as the electron donor, triazine as the electron acceptor and oxygen as the bridge between them. Benefitting from the characteristic donor-oxygen-acceptor geometry, these compounds are found to behave an exciting aggregation-induced organic room-temperature electrophosphorescence, and achieve a record-high external quantum efficiency of 15.8% for non-doped devices. Furthermore, they can sensitize multi-resonant emitters in the absence of any additional wide bandgap host, leading to an effective narrowband emission with a peak external quantum efficiency of 26.4% and a small full-width at half maximum of 26 nm. The results clearly indicate that donor-oxygen-acceptor geometry is a promising strategy to design organic phosphors suitable for organic light-emitting diodes. Pure organic room-temperature phosphorescencent materials draw much attention but realising electroluminescence under electric excitation is challenging. Here the authors propose a donor-oxygen-acceptor molecular design realizing aggregation-induced organic room-temperature electrophosphorescence with high external quantum efficiency. [ABSTRACT FROM AUTHOR]

Comprehensive Summary: Emitters with narrowband spectra are of great importance nowadays because of the growing demand for ultra‐high‐definition displays in the fields of panel displays and solid‐state lighting. Though the reported multiple resonance (MR) emitters have been widely studied with extremely sharp spectra and color‐tunable emissions, the electrophilic borylation synthetic strategies and stable narrowband blue devices still face great challenges. Herein, by virtue of the advantages of both the MR effect of conventional indolocarbazole skeleton and the easy‐to‐access of B—N covalent bonds, the linear tert‐butyl benzene and carbazole groups modified 6,12‐diphenyl‐5,11‐dihydroindolo[3,2‐b]carbazole derivatives (tPh[BN] and Cz[BN]) containing two B—N covalent bonds are easily constructed through amine‐directed double borylation strategy. Both emitters behaved bright blue emission with full‐width‐at‐half‐maximum (FWHM) of 20—27 nm in solution, high fluorescence quantum efficiency over 90%, and excellent stability toward moisture. By employing triplet‐triplet annihilation electroluminescent mechanism, blue OLED devices based on them showed a small FWHM of 48 nm and maximum external quantum efficiency of ~7.1% with negligible efficiency roll‐off, and long operational lifetime (LT80) of 87 h at an initial brightness of 1000 cd·m−2, demonstrating the enormous application potential of B—N bonds embedded emitters in achieving ideal narrowband blue emitters. [ABSTRACT FROM AUTHOR]

A novel macrocycle of B/N‐doped calix[4]arene (C‐BN) was synthesized by a one‐shot double boronation. Owing to the structural tension and electron‐donating properties of the nitrogen atoms in the macrocycle, reaction selectively proceeds between the adjacent benzene rings outside the macrocycle. C‐BN shows a highly centrosymmetric structure with two multiple resonance (MR) fragments bridged by tertiary amine groups at the 1,3 positions of the benzene ring. Benefiting from the large intermolecular distance (>4.6 Å) between adjacent MR‐emitting cores, C‐BN also exhibits excellent narrowband emitting features against aggregation‐induced quenching and spectrum broadening. Optimized organic light‐emitting diode devices based on C‐BN exhibit high maximum external quantum efficiencies of 24.7–26.6 % and small full width at half maximums of 25–28 nm over a wide doping range of 1–12 wt %. [ABSTRACT FROM AUTHOR]

Strategies to enhance the ratio of the molecular horizontal emitting dipole orientation (Θ∥) for thermally activated delayed fluorescence (TADF) emitters have unlocked the full potential of efficiencies for the evaporated devices, which, however, remain elusive for the solution‐processed ones. Here, a strategic molecular design for solution processable TADF emitters featuring high Θ∥s is proposed by attaching flexible chains ended with bipolar 9,9′‐spirobi[fluorene] subunits as anchoring groups onto TADF emitting core. It's unveiled that the anchoring groups not only enhance the horizontal orientation via enlarging molecular planarity, but also benefit the high photoluminescence in pristine films. The corresponding non‐doped solution processable OLEDs substantiate an unprecedented maximum external quantum efficiency (EQEmax)>30 %. Meanwhile, combining these compounds as TADF sensitizers, and multiple resonance final emitter, solution‐processed OLEDs achieve an EQEmax of 25.6 % with a narrow full width at half maximum of 29 nm. [ABSTRACT FROM AUTHOR]

Despite the remarkable multiple resonance (MR) optoelectronic properties of organic nanographenes with boron and nitrogen atoms disposed para to each other, the synthetic procedures are sophisticated with low yields and the molecular skeletons are limited. Here, a new paradigm of easy‐to‐access MR emitter is constructed by simplifying the multiborylation through amine‐directed formation of B−N bonds while introducing an additional para‐positioned nitrogen atom to trigger the MR effect. The proof‐of‐concept molecules exhibit narrowband emissions at 480 and 490 nm, with full width at half maxima (FWHMs) of only 29 and 34 nm. The devices based on them showed external quantum efficiencies (EQE) of >33.0 %, which remained above 24.0 % even at a high brightness of 5000 cd m−2. This is the first example of MR emitters with a B−N covalent bond, not only decreasing the synthesis difficulty but also increasing the diversity of MR skeletons for emerging new optoelectronic properties. [ABSTRACT FROM AUTHOR]

Polycyclo‐heteraborin multi‐resonance (MR) emitters are promising for high color‐purity organic light‐emitting diodes (OLEDs). Here, unlike the most common heteroatom ternary‐doped (X/B/N) frameworks, a binary‐doped (B/N) skeleton is reported with a large energy band for wide‐range color tunability. Based on this parent‐segment, a "one‐pot" catalyst‐free borylation method is developed which generates deep blue to pure green MR emitters from readily available starting materials, with peaks at 426–532 nm and full‐width‐at‐half‐maxima of 27–38 nm. Impressively, a maximum external quantum efficiency of nearly 40 % is recorded for the corresponding device with Commission Internationale de l′Eclairage coordinates of (0.14, 0.16), representing the state‐of‐the‐art performances. This work presents a new paradigm and synthesis of B/N‐doped MR emitters and will motivate the study of other novel frameworks. [ABSTRACT FROM AUTHOR]

Herein, we report a general strategy for achieving ultra‐pure green emissions by suppressing the shoulder peaks in the emission spectra of conventional polycyclic aromatic hydrocarbons (PAHs). Through precise synthetic fusion of multi‐resonance (MR) fragments with conventional PAH, extended π‐conjugation lengths, increased molecular rigidity, and reduced vibrational frequency could be simultaneously realized. The proof‐of‐concept emitters exhibited ultra‐pure green emissions with dominant peaks at ca. 521 nm, photoluminescence quantum yields that are greater than 99 %, a small full‐width‐at‐half‐maximum of 23 nm, and CIE coordinates of (0.16, 0.77). The bottom‐emitting organic light‐emitting diode (OLED) exhibited a record‐high CIEy value of 0.74 and a high maximum external quantum efficiency of 30.5 %. The top‐emitting OLED not only achieved a BT.2020 green color (CIE: 0.17, 0.78) for the first time but also showed superior performance among all green OLED devices, with a current efficiency of 220 cd A−. [ABSTRACT FROM AUTHOR]

Surface chemistry mediated direct optical patterning represents an emerging strategy for incorporating colloidal nanocrystals (NCs) in integrated optoelectronic platforms including displays and image sensors. However, the role of photochemistry of crosslinkers and other photoactive species in patterning remains elusive. Here we show the design of nitrene‐ and carbene‐based photocrosslinkers can strongly affect the patterning capabilities and photophysical properties of NCs, especially quantum dots (QDs). Their role beyond physical linkers stems from structure‐dictated electronic configuration, energy alignment and associated reaction kinetics and thermodynamics. Patterned QD layers with designed carbene‐based crosslinkers fully preserve their photoluminescent and electroluminescent properties. Patterned light emitting diodes (QLEDs) show a maximum external quantum efficiency of ≈12 % and lifetime over 4800 h, among the highest for reported patterned QLEDs. These results would guide the rational design of photoactive species in NC patterning and create new possibilities in the monolithic integration of NCs in high‐performance device platforms. [ABSTRACT FROM AUTHOR]

Nitrogen‐containing polycyclic heteroaromatics have exhibited fascinating multi‐resonance (MR) characteristics for efficient narrowband emission, but strategies to bathochromic shift their emissions while maintaining the narrow bandwidths remain exclusive. Here, homogeneous hexatomic rings are introduced into nitrogen‐embedded MR skeletons to prolong the π‐conjugation length for low‐energy electronic transitions while retaining the non‐bonding character of the remaining parts. The proof‐of‐the‐concept emitters exhibit near unity photoluminescence quantum yields with peaks at 598 nm and 620 nm and small full‐width‐at‐half‐maximums of 28 nm and 31 nm, respectively. Optimal organic light‐emitting diodes exhibit a high external quantum efficiency of 18.2 %, negligible efficiency roll‐off, and ultra‐long lifetime with negligible degradation at an initial luminance of 10 000 cd m−2 after 94 hours. [ABSTRACT FROM AUTHOR]

Thermally activated delayed fluorophors (TADF) featuring through‐space charge transfers (TSCT) suffer from low radiative decay rates (krs), especially for blue emitters. Here, a xanthene bridge is adopted to construct space‐confined face‐to‐face donor–acceptor alignment and minimize their distances down to 2.7–2.8 Å, even shorter than the interlayer distance of graphite and thus strengthening the electronic interactions. The resulting blue TSCT‐TADF emitters exhibit peaks around ≈460 nm, photoluminescence quantum yields of >90 %, and krs of nearly 107 s−1, almost 2–10 times higher than previously observed values with comparable reverse intersystem crossing rates. The corresponding blue organic light‐emitting diodes show maximum external quantum efficiencies of 27.8 % and 34.7 % with Commission Internationale de L'Eclairage y coordinates of 0.29 and 0.15 using those molecules as emitters and sensitizers, respectively. [ABSTRACT FROM AUTHOR]

Thermally activated delayed fluorescence (TADF) materials with through‐space charge transfers (CT) have attracted particularly interest recently. However, the slow reverse intersystem crossing (RISC) and radiative decay always limit their electroluminescence performances. Herein, TADF molecules with ortho‐linked multiple donors‐acceptor (ortho‐Dn‐A) motif are developed to create near‐degenerate excited states for the reinforcement of spin‐orbit coupling. The incorporation of both through‐bond and through‐space CT enlarges oscillator strength. The optimal ortho‐D3‐A compound exhibits a photoluminescence quantum yield of ca. 100 %, a high RISC rate of 2.57×106 s−1 and a high radiative decay rate of 1.00×107 s−1 simultaneously. With this compound as the sensitizer, a TADF‐sensitized‐fluorescent organic light‐emitting diode shows a maximum external quantum efficiency of 31.6 % with an ultrapure green Commission Internationale de L'Eclairage y coordinate value of 0.69. [ABSTRACT FROM AUTHOR]

Blue TADF emitters with both linear donor‐π‐donor and acceptor‐π‐acceptor structures are constructed to facilitate delocalized excited states for enhanced mixing between charge‐transfer and locally excited states. Consequently, high kRISCs over 106 s‐1 can be achieved. When utilizing these materials to sensitize a blue multiple‐resonance TADF emitter, a TADF sensitized fluorescence (TSF) OLED realized maximum external quantum efficiency up to 35% and high stability. [ABSTRACT FROM AUTHOR]

Pure green emitters are essential for realizing an ultrawide color gamut in next‐generation displays. Herein, by fusing the difficult‐to‐access aza‐aromatics onto B (boron)–N (nitrogen) skeleton, a hybridized multi‐resonance and charge transfer (HMCT) molecule AZA‐BN was successfully synthesized through an effective one‐shot multiple cyclization method. AZA‐BN shows pure green fluorescence with photoluminance quantum yield of 99.7 %. The corresponding green device exhibits a maximum external quantum efficiency and power efficiency of 28.2 % and 121.7 lm W−1, respectively, with a full width half maximum (FWHM) of merely 30 nm and Commission Internationale de l'Eclairage (CIE) coordinate y of 0.69, representing the purest green bottom‐emitting organic light‐emitting diode. [ABSTRACT FROM AUTHOR]

Ultrapure colors are vital for displays to obtain the highly desired wide color‐gamut. Till now, only boron‐dipyrromethene derivatives (BODIPYs) have demonstrated ultrapure full‐colors but suffer from low excitons utilization efficiency as dopants in organic light‐emitting diodes. It is proposed here that with a thermally activated delayed fluorophore to sensitize BODIPYs, all excitons can be recycled, which, still, is challenged by exciton loss through Dexter energy transfer (DET) from sensitizer to dopant and direct charge trapping on BODIPYs. Hence, a sterically hindered BODIPY‐type dopant with a bulk substituent on the meso‐position is developed to suppress DET, exhibiting a high photo‐luminance quantum yield of 98% and a small full width at half maximum of 28 nm. Moreover, the device structure is elaborately designed, successfully modulating carriers and excitons to avoid charge trapping on dopant and also trigger multiple‐sensitizing processes to reduce exciton loss. Consequently, a state‐of‐the‐art maximum external quantum efficiency/power efficiency of 19.0%/85.7 lm W−1 are realized together with an ultrapure‐green emission of Commission Internationale de l'Eclairage coordinates of (0.26, 0.67) and a long half‐lifetime of 2947 h at an initial luminance of 1000 cd m−2. [ABSTRACT FROM AUTHOR]

White organic light‐emitting diodes (WOLEDs) with thermally activated delayed fluorophor sensitized fluorescence (TSF) have aroused wide attention, considering their potential for full exciton utilization without noble‐metal containing phosphors. However, performances of TSF‐WOLEDs with a single‐emissive‐layer (SEL) still suffer from low exciton utilization and insufficient blue emission for proper white balance. Here, by modulating Förster and Dexter interactions in SEL‐TSF‐WOLEDs, high efficiencies, balanced white spectra, and extended lifetimes are realized simultaneously. Given the different dependencies of Förster and Dexter interactions on intermolecular distances, sterically shielded blue thermally activated delayed fluorescence (TADF) emitters and orange conventional fluorescent dopants (CFDs) with electronically inert peripheral units are adopted to enlarge distances of electronically active chromophores, not only blocking the Dexter interaction to prevent exciton loss but also finely suppressing the Förster one to guarantee balanced white emission with sufficient blue components. It thus provides the possibility to maximize device performances in a large range of CFD concentrations. A record high maximum external quantum efficiency/power efficiency of 19.6%/52.2 lm W−1, Commission Internationale de L'Eclairage coordinate of (0.33, 0.45), and prolonged half‐lifetime of over 2300 h at an initial luminance of 1000 cd m−2 are realized simultaneously for SEL‐TSF‐WOLEDs, paving the way toward practical applications. [ABSTRACT FROM AUTHOR]

The low efficiency of blue devices has been a bottleneck problem for OLED panel manufacturers for a long time. In recent years, TASF‐OLED has attracted great attention because of the high external quantum efficiency and color purity, which makes it a promising technology for high efficiency deep blue OLEDs. In this paper, we present our latest development of TADF material for deep blue TASF‐OLEDs with an emission peak at 460 nm and a high external quantum efficiency up to 31 %. [ABSTRACT FROM AUTHOR]

Despite the proliferation of multiple resonance (MR) materials in the blue to green spectral ranges, red MR emitters remain scarce in the literature, an area that certainly warrants attention for future applications. Here, through a clever application of classic Clar's aromatic π‐sextet rule, we triumphantly constructed the first red MR emitter by substituting the conventional benzene ring core with anthracene (fewer π‐sextets). Theoretical studies indicate that the quantity of π‐sextets ultimately determines the optical band gap of a molecule, rather than the number of fused benzene rings. Benefiting from the high photoluminescence quantum yield of ~94 % and horizontal dipole ratio of ~90 %, the corresponding narrowband red (luminescence wavelength: 608 nm) organic light‐emitting diode shows a high external quantum efficiency of 27.3 %, with only a slight decrease of 3.7 % at an elevated luminance level of 100,000 cd/m2. [ABSTRACT FROM AUTHOR]

Here, we strategically propose an efficient asymmetric structure design strategy aimed at simultaneously optimizing the horizontal emitting dipole orientation and aggregation state properties of the deep-blue multi-resonance emitters. The corresponding electroluminescent device exhibited leading performance for deep-blue OLEDs, with a CIEy coordinate of 0.08, an external quantum efficiency up to 41.5%, and an excited state energy down to 2.68 eV. [Display omitted] Narrowband emitters offer significant advantages in the fabrication of next-generation deep-blue organic light-emitting diodes (OLEDs) due to their wide color gamut, high stability, and high efficiency. It is a pressing challenge to increase the light outcoupling efficiency to further boost device performance, even though 100% internal quantum efficiency is already achievable through rational molecular design. Here, we strategically propose a novel asymmetric structure design strategy aimed at simultaneously optimizing the horizontal emitting dipole orientation and aggregation state properties of the deep-blue multi-resonance (MR) emitters. This proof-of-concept emitter A-BN is capable of displaying ultrapure deep-blue emission with a peak of ∼461 nm, a small full-width-at-half-maximum of ∼25 nm, a CIEy coordinate of ∼0.08, a high horizontal dipole ratio of ∼90 %, and a near-unity photoluminescence quantum yield of ∼98 % in the practical mass-production concentration range (1–3 wt%). The corresponding non-sensitized device achieves a maximum external quantum efficiency of 41.5% without any external light extraction techniques, representing state-of-the-art performance for deep-blue OLEDs. These findings will help drive the development of highly efficient and stable narrowband deep-blue emitters and lead to a revolution in OLED technology. [ABSTRACT FROM AUTHOR]

High cost of phosphors, efficiency roll-off and short lifetime are the main factors that limited phosphorescent organic light-emitting diodes' (PHOLED) application. In this work, we report red emission PHOLED with low dopant concentration, low efficiency roll-off and long operation lifetime based on a novel host material 2,4-bisbiphenyl-6-(12-phenylindole[2,3 - a ]carbazole-11-yl)-1,3,5-triazine (BBPICT), with thermally activated delayed fluorescent (TADF) properties. The devices displayed a maximum external quantum efficiency of 20.9% and low efficiency roll-off of 1.7% at 1000 cd m −2 , and the operation lifetime of the device at a brightness of 1000 cd m −2 is 1390 h. [ABSTRACT FROM AUTHOR]

Achieving efficient blue emission is an exigent challenge for the application of thermally activated delayed fluorescent organic light-emitting diodes (TADF-OLEDs). Carbazole benzonitrile-based TADF molecules exhibit promising performance in achieving the goal. Here, by replacing the cyano group in the sensitizer with the isocyano group, a 9 nm hypochromatic shift in photoluminescence spectra of the sensitizer and an enhanced efficiency of the Förster energy transfer (FET) in TADF-sensitized fluorescence (TSF) is found. By using the isocyano-based compounds as sensitizers, a maximum external quantum efficiency of 24.5 % is obtained in solution-processed OLEDs, surpassing the cyano-based counterparts with similar structures. Moreover, the full width at half maximum (FWHM) of the emitter in the electroluminescence spectrum is also decreased from 47 nm to 38 nm, indicating a more complete energy transfer. [Display omitted] • Replacing cyano groups with isocyano groups enhances the sensitizers' performance. • Introduction of cyano groups leads to an significant luminescent blue-shift. • OLEDs using 4tCzBN-PhNC as sensitizers have a higher external quantum efficiency. • OLEDs using 4tCzBN-PhNC as sensitizers exhibit a 9 nm narrower FWHM of electroluminescence spectrum from 47 nm to 38 nm. [ABSTRACT FROM AUTHOR]

Comprehensive Summary: Emitters with narrowband spectra are of great importance nowadays because of the growing demand for ultra‐high‐definition displays in the fields of panel displays and solid‐state lighting. Though the reported multiple resonance (MR) emitters have been widely studied with extremely sharp spectra and color‐tunable emissions, the electrophilic borylation synthetic strategies and stable narrowband blue devices still face great challenges. Herein, by virtue of the advantages of both the MR effect of conventional indolocarbazole skeleton and the easy‐to‐access of B—N covalent bonds, the linear tert‐butyl benzene and carbazole groups modified 6,12‐diphenyl‐5,11‐dihydroindolo[3,2‐b]carbazole derivatives (tPh[BN] and Cz[BN]) containing two B—N covalent bonds are easily constructed through amine‐directed double borylation strategy. Both emitters behaved bright blue emission with full‐width‐at‐half‐maximum (FWHM) of 20—27 nm in solution, high fluorescence quantum efficiency over 90%, and excellent stability toward moisture. By employing triplet‐triplet annihilation electroluminescent mechanism, blue OLED devices based on them showed a small FWHM of 48 nm and maximum external quantum efficiency of ~7.1% with negligible efficiency roll‐off, and long operational lifetime (LT80) of 87 h at an initial brightness of 1000 cd·m−2, demonstrating the enormous application potential of B—N bonds embedded emitters in achieving ideal narrowband blue emitters. [ABSTRACT FROM AUTHOR]

A new type of triazolotriazine acceptor has been designed to construct highly efficient TADF materials by fusing triazine and triazole together and achieve the state-of-the-art performance yellow TSF-OLEDs. [Display omitted] Thermally activated delayed fluorescence (TADF) sensitized fluorescent organic light-emitting diodes (TSF-OLEDs) have shown great potential for the realization of high efficiency with low efficiency roll-off and good color purity. However, the superior examples of TSF-OLEDs are still limited up to now. Herein, a trade-off strategy is presented for designing efficient TADF materials and achieving high-performance TSF-OLEDs via the construction of a new type of triazolotriazine (TAZTRZ) acceptor. The enhanced electron-withdrawing ability of TAZTRZ acceptor, fused by triazine (TRZ) and triazole (TAZ) together, enables TADF luminogens with small singlet-triplet energy gap (Δ E ST) values. Meanwhile, the increased planarity from the TRZ-phenyl linkage (6:6 system) to the TAZ-phenyl linkage (5:6 system) can compensate the decrease of oscillator strength (f) while lowing Δ E ST , thus achieving a trade-off between small Δ E ST and high f. As a result, the related TSF-OLED achieved an extremely low turn-on voltage of 2.1 V, an outstanding maximum external quantum efficiency (EQE max) of 23.7% with small efficiency roll-off (EQE 1000 of 23.2%; EQE 5000 of 20.6%) and an impressively high maximum power efficiency of 82.1 lm W−1, which represents the state-of-the-art performance for yellow TSF-OLEDs. [ABSTRACT FROM AUTHOR]

• A symmetrical Bee-shaped host was constructed by intramolecular π-π interaction. • The host exhibited deep blue emission with a moderate polarity. • Blue TADF devices based on this host exhibited high performance and color purity. • Full-TADF white device with single-emissive-layer realized high performance. An ideal host for blue emitters with thermally activated delayed fluorescence (TADF) should bear a moderate polarity to relax charge transfer (CT) states of dopant for a reduced singlet-triplet energy gap (Δ E ST) while utter-mostly keeping blue emission, a high triplet energy to confine exciton, and a small Δ E ST for feasible charge injection. However, it is rather challenging to simultaneously fulfill all those requirements as the strong CT characteristic necessary for a small Δ E ST usually enlarge polarity and lower energy levels. Here, a symmetrical ortho -linked diphenylphosphine oxide (DPO)/carbazole derivative is developed, of which the configuration resembles the bee with carbazoles as front wings, phenyl rings on DPO as back wings, hooked together by π-π interaction. This motif features a short distance of charges for a moderate polarity of 3.45 D, a twisted non-conjugation structure for a small Δ E ST of 0.24 eV with a high triplet of 2.98 eV and multiple intermolecular interactions for enhanced charge transport. The corresponding blue TADF device realizes a compromise between efficiency and colors with a maximum external quantum efficiency (EQE max) of 35.7% and a CIE y of 0.20. Furthermore, a full-TADF white device with this host realizes a EQE max of 26.1%, representing the state-of-the-art performance. [ABSTRACT FROM AUTHOR]

• A novel molecule, CyPA·HBr is synthesized and adopted to construct a mixed 2D/3D perovskite. • The CyPA·HBr can help to tune the perovskite growth and passivate of the defect, along with fine phase control. • The optimized PeLEDs exhibit a pure green emission with FWHM of 22 nm, EQE of 6.55%, and a maximum brightness of 9408 cd m−2. • The CyPA·HBr-based device shows a half-lifetime two times longer than the one based on a traditional ligand PEA·HBr. The mixed 2D/3D perovskite has been proved to be a promising candidate to increase the exciton binding energy in perovskite light-emitting diodes (PeLEDs). However, the complex phase distribution and impurity (usually referring to ligands) limit the stability of the corresponding PeLEDs. Here, a novel molecule, cyclopentanamine hydrobromide (CyPA·HBr), is adopted to construct a mixed 2D/3D perovskite by partial substitution of FA with CyPA, realizing fine phase control for improved device stability. The adoption of CyPA·HBr helps to tune perovskite grain growth and passivate the defect, resulting in high coverage and smooth thin film with improved photoluminescence property. The PeLEDs with an optimized CyPA·HBr concentration of a molar ratio of 40% exhibit a pure green emission with a full width at half maximum of 22 nm, an external quantum efficiency of 6.55%, and a maximum brightness of 9408 cd m−2 simultaneously. Interestingly, the CyPA·HBr-based device shows a half-lifetime two times longer than the one based on the most commonly used ligand of phenethylammonium bromide (PEA·HBr), assigned to the better phase control ability of CyPA·HBr in 2D/3D perovskite. Those results testify the importance of ligands to modulate perovskite phase along with efficient passivation defects for better stability of PeLEDs. [ABSTRACT FROM AUTHOR]