Search

Deep‐blue multi‐resonance (MR) emitters with stable and narrow full‐width‐at‐half‐maximum (FWHM) are of great importance for widening the color gamut of organic light‐emitting diodes (OLEDs). However, most planar MR emitters are vulnerable to intermolecular interactions from both the host and guest, causing spectral broadening and exciton quenching in thin films. Their emission in the solid state is environmentally sensitive, and the color purity is often inferior to that in solutions. Herein, a molecular design strategy is presented that simultaneously narrows the FWHM and suppresses intermolecular interactions by combining intramolecular locking and peripheral shielding within a carbonyl/nitrogen‐based MR core. Intramolecularly locking carbonyl/nitrogen‐based bears narrower emission of 2,10‐dimethyl‐12,12‐diphenyl‐4H‐benzo[9,1]quinolizino[3,4,5,6,7‐defg]acridine‐4,8(12H)‐dione in solution and further with peripheral‐shielding groups, deep‐blue emitter (12,12‐diphenyl‐2,10‐bis(9‐phenyl‐9H‐fluoren‐9‐yl)−4H‐benzo[9,1]quinolizino[3,4,5,6,7‐defg]acridine‐4,8(12H)‐dione, DPQAO‐F) exhibits ultra‐pure emission with narrow FWHM (c.a., 24 nm) with minimal variations (∆FWHM ≤ 3 nm) from solution to thin films over a wide doping range. An OLED based on DPQAO‐F presents a maximum external quantum efficiency (EQEmax) of 19.9% and color index of (0.134, 0.118). Furthermore, the hyper‐device of DPQAO‐F exhibits a record‐high EQEmax of 32.7% in the deep‐blue region, representing the first example of carbonyl/nitrogen‐based OLED that can concurrently achieve narrow bandwidth in the deep‐blue region and a high electroluminescent efficiency surpassing 30%. [ABSTRACT FROM AUTHOR]

Rationally tuning the emission position and narrowing the full width at half‐maximum (FWHM) of an emitter is of great importance for many applications. By synergistically improving rigidity, strengthening the resonant strength, inhibiting molecular bending and rocking, and destabilizing the HOMO energy level, a deep‐blue emitter (CZ2CO) with a peak wavelength of 440 nm and an ultranarrow spectral FWHM of 16 nm (0.10 eV) was developed via intramolecular cyclization in a carbonyl/N resonant core (QAO). The dominant υ0‐0 transition character of CZ2CO gives a Commission Internationale de I'Éclairage coordinates (CIE) of (0.144, 0.042), nicely complying with the BT.2020 standard. Moreover, a hyper‐fluorescent device based on CZ2CO shows a high maximum external quantum efficiency (EQEmax) of 25.6 % and maintains an EQE of 22.4 % at a practical brightness of 1000 cd m−2. [ABSTRACT FROM AUTHOR]

High‐performance nondoped organic light‐emitting diodes (OLEDs) are promising technologies for future commercial applications. Herein, we synthesized two new thermally activated delayed fluorescence (TADF) emitters that enable us, for the first time, to combine three effective approaches for enhancing the efficiency of nondoped OLEDs. First, the two emitters are designed to have high steric hindrances such that their emitting cores will be suitably isolated from those of their neighbors to minimize concentration quenching. On the other hand, each of the two emitters has two stable conformations in solid films. In their neat films, molecules with the minority conformation behave effectively as dopants in the matrix composing of the majority conformation. One hundred percent exciton harvesting is thus theoretically feasible in this unique architecture of "self‐doped" neat films. Furthermore, both emitters have relatively high aspect ratios in terms of their molecular shapes. This leads to films with preferred molecular orientations enabling high populations of horizontal dipoles beneficial for optical out‐coupling. With these three factors, OLEDs with nondoped emitting layers of the respective emitters both achieve nearly 100% exciton utilization and deliver over 30% external quantum efficiencies and ultralow efficiency roll‐off at high brightness, which have not been observed in reported nondoped OLEDs. [ABSTRACT FROM AUTHOR]

Multiple resonance (MR) type thermally activated delayed fluorescence (TADF) material is currently a research hotspot in organic light‐emitting diodes (OLEDs) due to their high color purity and high exciton utilization. However, there are only a handful of MR‐TADF emitters with emissions beyond the blue‐to‐green region. The very limited emission colors for MR‐TADF emitters are mainly caused by the fact that so far molecular modifications of MR‐TADF do not offer much change in the emission colors. Here, we report a new approach to modifying a prototypical MR core of DABNA by fusing carbazoles to the MR framework. The carbazole‐fused molecule (TCZ‐F‐DABNA) basically maintains the MR‐dominated features of DABNA while red‐shifting the emission. Its OLED achieves an external quantum efficiency of 39.2 % with a peak at 588 nm, which is a record‐high efficiency for OLEDs with peaks beyond 560 nm. This work provides a new approach for significantly tunning emission colors of MR‐TADF emitters. [ABSTRACT FROM AUTHOR]

Non‐doped organic light‐emitting diodes (OLEDs) are particularly appealing due to the merit of the extremely simple device structure. However, the performance of non‐doped OLEDs is usually far inferior than that of doped devices, mainly due to the lack of desirable emitters. An ideal emitter for non‐doped OLEDs should not merely be highly emissive in the host matrix but also be capable of delivering excellent properties in its condensed state. Herein, through molecular engineering, an "axial and equatorial carbazolyl extension" approach to manipulate the molecular packing behavior is developed, and thus, the emitter is awarded with superior properties in its neat film. Based on this approach, through simply modifying the conventional acridine donor in a thermally activated delayed fluorescence (TADF) emitter with carbazole moieties in the way of hyper‐conjugation, two new TADF emitters with the molecular skeleton being extended both horizontally and vertically by carbazole moieties are constructed. The resulted TADF emitters reveal superb properties with simultaneous excellent thermal and morphological stabilities, photophysical behaviors, and charge transporting ability in their neat film. Owing to the merits of these synergistic superior properties, highly efficient non‐doped green emissive OLED with the state‐of‐the‐art external quantum efficiency of nearly 30% is realized. [ABSTRACT FROM AUTHOR]

Upon fusing the pyrazinyl pyrazole entity in giving pyrazolo[3,4‐f]quinoxaline chelate, the corresponding Os(II) based NIR emitter exhibited "invisible" and efficient electroluminescence with a peak maximum at 811 nm. A maximum external quantum efficiency of 0.97 % and a suppressed efficiency roll‐off till a current density of 300 mA cm−2 was also exhibited. [ABSTRACT FROM AUTHOR]

The conformational distribution and mutual interconversion of thermally activated delayed fluorescence (TADF) emitters significantly affect the exciton utilization. However, their influence on the photophysics in amorphous film states is still not known due to the lack of a suitable quantitative analysis method. Herein, we used temperature‐dependent time‐resolved photoluminescence spectroscopy to quantitatively measure the relative populations of the conformations of a TADF emitter for the first time. We further propose a new concept of "self‐doping" for realizing high‐efficiency nondoped OLEDs. Interestingly, this "compositionally" pure film actually behaves as a film with a dopant (quasi‐equatorial form) in a matrix (quasi‐axial form). The concentration‐induced quenching that may occur at high concentrations is thus expected to be effectively relieved. The "self‐doping" OLED prepared with the newly developed TADF emitter TP2P‐PXZ as a neat emitting layer realizes a high maximum external quantum efficiency of 25.4 % and neglectable efficiency roll‐off. [ABSTRACT FROM AUTHOR]

Nondoped organic light‐emitting diodes (OLEDs) have drawn enormous attention for their merits of process simplicity, reduced fabrication cost, and phase stability. Herein, a novel approach of utilizing intermolecular hydrogen bonding for enhancing performance of nondoped OLEDs with a new thermally activated delayed fluorescence (TADF) emitter 10‐(4‐(2,6‐di(pyrimidin‐5‐yl)pyridin‐4‐yl)phenyl)‐10H‐phenoxazine (DPmP‐PXZ) is investigated. Endowing with suitable intermolecular hydrogen bonds linking the ends of neighboring DPmP‐PXZ molecules, the molecules tend to form extended 1D molecular chain in solid. This 1D structure effectively keeps the electron‐rich PXZ cores in neighboring molecules apart from each other such that triplet‐related exciton quenching can be well suppressed. In addition, it also improves the balance of carrier mobilities and the optical out‐coupling from the emitting layer. With these merits, OLEDs using DPmP‐PXZ as a dopant emitter, from 10 to 100 wt%, can maintain high external quantum efficiencies (EQEs) of over 20%. More importantly, its nondoped OLED shows a yellow emission and an excellent maximum EQE of 21.8% with little efficiency roll‐off which is even comparable with state‐of‐the‐art yellow OLEDs. These results provide new insight on the role of hydrogen bonding in molecular packing and its subsequent influences on the performance of OLEDs. [ABSTRACT FROM AUTHOR]

Organic light‐emitting diodes (OLEDs) with simple nondoped device structure are extremely attractive for real applications since excitons can be utilized without considering the possible charge trapping and morphology issues in the host–dopant systems. Emitters with suppressed concentration annihilation capability are essential for nondoped devices. Herein, two thermally activated delayed fluorescence (TADF) emitters based on a novel 3D electron donor, namely, TDMAC, are constructed. The TDMAC donor consists of a conventional donor with fused triptycene scaffold. Benefitting from the unique rigid and bulky triptycene moiety, these TADF emitters exhibit excellent thermal, morphological, and photophysical properties. Consequently, highly efficient OLEDs with external quantum efficiencies up to 24.2% and 23% are realized for doped and nondoped devices, respectively. [ABSTRACT FROM AUTHOR]

Near‐infrared (NIR) organic‐light emitting devices (OLEDs) with high radiance are useful for applications including invisible marking, communication, and biomedical imaging. However, performances of NIR OLEDs are typically limited by their severe efficiency roll‐offs at high current density. Herein, three isoquinolinyl azolate based Os(II) complexes (Isq‐1–3) with short radiative decay lifetime (in hundreds of ns), and photoluminescence with peak wavelengths > 745 nm and quantum yield up to 48% as doped thin films, are reported. Upon concomitant employment of exciplex‐forming co‐host (tris(4‐carbazoyl‐9‐ylphenyl)amine and 2,4,6‐tris(biphenyl‐3‐yl)‐1,3,5‐triazine), efficiency roll‐off is greatly reduced, giving external quantum efficiency of 9.66% at a current density of 300 mA cm−2. A maximum radiance over 170 W sr−1 m−2 is also achieved in devices based on Isq‐2 and Isq‐3. [ABSTRACT FROM AUTHOR]

While monochrome organic light‐emitting diodes (OLEDs) based on thermally activated delayed fluorescence (TADF) emitters have achieved over 30% external quantum efficiencies (EQEs), all‐TADF white OLEDs (WOLEDs) are still lagging behind. Herein, a simple system based on two color‐complementary TADF emitters is exploited to realize high‐performance WOLEDs. By doping a high‐performance orange–red TADF fluorophor (BPPZ‐DPXZ) into a blue TADF host (DBFCz‐Trz), energy transfer, and triplet‐to‐singlet conversion in the host‐dopant system can be optimized to simultaneously achieve full exciton utilization and color balance. With this design, all‐TADF single‐emitting‐layer WOLEDs with a maximum EQE up to 32.8% are demonstrated. This high efficiency surpasses EQEs of reported WOLEDs based on both TADF as well as phosphorescence. It is expected that this finding can provide new insight for designing highly efficient all‐TADF WOLEDs. [ABSTRACT FROM AUTHOR]

Near‐infrared organic light‐emitting diodes (NIR OLEDs) enable many unique applications ranging from night‐vision displays and photodynamic therapies. However, the development of efficient NIR OLEDs with a low efficiency roll‐off is still challenging. Here, a series of new heteroleptic Pt(II) complexes (1–4) flanked by both pyridyl pyrimidinate and functional azolate chelates are synthesized. The reduced ππ* energy gap of the pyridyl pyrimidinate chelate, and strong intermolecular interaction and high crystallinity in vacuum‐deposited thin films engender strong intermolecular charge transfer transition including metal–metal‐to‐ligand charge transfer; thereby, exhibiting efficient photoluminescence within 776–832 nm and short radiative lifetimes of 0.52–0.79 µs. Consequently, nondoped NIR‐emitting OLEDs based on these Pt(II) complexes are fabricated, to which Pt(II) complexes 2 and 4 give record high maximum external quantum efficiency of 10.61% at 794 nm and 9.58% at 803 nm, respectively. Moreover, low efficiency roll‐off is also observed, among which the device efficiencies of 2 and 4 are at least four times higher than that of the best NIR‐emitting OLEDs recorded at current density of 100 mA cm−2. [ABSTRACT FROM AUTHOR]

The design of square‐planar Pt(II) complexes with highly efficient solid‐state near infrared (NIR) luminescence for electroluminescence is attractive but challenging. This study presents the fine‐turning of excited‐state properties and application of a series of isoquinolinyl pyrazolate Pt(II) complexes that are modulated by steric demanding substituents. It reveals that the bulky substituents do not always disfavor metallophilic Pt···Pt interactions. Instead, π–π stacking among chelates, which are fine‐tuned by the associated substituents, also exerts strong influence to the metal‐metal‐to‐ligand charge transfer (MMLCT) transition character. Theoretical calculations indicate that Pt···Pt contacts become more relevant in the trimers rather than the dimers, especially in their T1 states, associated with a change from mixed 3LC/3MLCT transition in the monomer/dimer to mixed 3LC/3MMLCT transition character in the trimer. Electroluminescence devices affording intense deep‐red/NIR emission (near 670 nm) with unprecedentedly high external quantum efficiency over 30% are demonstrated. This work provides deep insights into formation MMLCT transition of square‐planar Pt(II) complexes and efficient molecular design for deep‐red/NIR electroluminescence. [ABSTRACT FROM AUTHOR]

A novel host material featuring a spiro-annulated benzimidazole configuration is exploited for blue phosphorescent organic light-emitting devices (PhOLEDs). The new material exhibits a high triplet energy (3.07 eV) and a bipolar characteristic and is effective as the host for FIrpic-, FIr6- and FK306-based blue PhOLEDs with high performances. [ABSTRACT FROM AUTHOR]

• Boron-doped aromatics have demonstrated valuable optoelectrical application in the past few years. In this mini review, our focus was on three-coordinated boron-doped aromatics. The recent progress of their applications in organic light-emitting diodes, organic field-effect transistors, chemical sensing, imaging and organic photovoltaics were highlighted. The structure and optoelectronic performance of three-coordinated boron-doped aromatic compounds were discussed, in order to gain a fundamental insight into the design strategy of the molecules and the related applications. Boron-doped polycyclic aromatic hydrocarbons are an emerging class of material. The incorporation of electrophilic boron atoms into aromatic system can modify the electronic property, leading to strutures with new photophysical and optoelectronic properties. The advances in synthetic chemistry promoted the generation of new boron-doped aromatic species and their applications in optoelectronics have been further explored. This review highlights the recent progress of three-coordinated boron-doped aromatic compounds for their applications in organic light-emitting diodes, organic field-effect transistors, chemical sensing, imaging and organic photovoltaics. [ABSTRACT FROM AUTHOR]

While exciplex formation is considered to have a negative impact on the performance of organic light-emitting devices (OLEDs), it can be utilized as a simple means for manipulating the emission colors. Here, we explore various important factors influencing the exciplex formation in order to provide a simple way for tailoring the emission color of OLEDs involving exciplex emission. In addition to the well-known effects of the energy difference between electron affinity and ionization potential (IP) of organic materials used, we found that electron mobility and IP of electron-transporting layer (ETL) are also critical factors in controlling the intensity of exciplex emission via the influence on charge accumulation intensity at the organic/organic interface. Interestingly, devices with green, blue, and white electroluminescence colors can be attained by simply replacing different ETL materials in contact with the same blue fluorophore underneath. The underlying mechanism for the color change in OLEDs will be discussed. [ABSTRACT FROM AUTHOR]

We report polymeric light-emitting diodes (PLEDs) made from pinene-substituted iridium(III) phosphorescent dopants: tris(5-(4-difluoro phenyl)-10,10-dimethyl-4-aza-tricycloundeca-2,4,6-triene) iridium (III) [Ir(F-pppy)3] and tris(5-(2,4-difluorophenyl)-10,10-dimethyl-4-aza-tricycloundeca-2,4,6-triene) iridium (III) [Ir(F2-pppy)3]. The pinene substitution introduces steric hindrance to molecular structure of the dopant that reduces triplet-triplet annihilation between dopants and consequently enhances device performance. Via endothermic energy transfer from poly(vinylcarbazole) to Ir(F-pppy)3 and Ir(F2-pppy)3, a peak electroluminescent efficiency of 32.8 cd/A or 12.3 cd/A at 12 wt % Ir(F-pppy)3 or 15 wt % Ir(F2-pppy)3 doped and solution-processed PLEDs have been obtained. These values represent significant improvement in performance over previously reported endothermic energy-transfer based electrophosphorescent devices. [ABSTRACT FROM AUTHOR]

An efficient nondoped green organic light-emitting device was demonstrated by using a dual-functional electroluminescent material, 4,4′,4″-tris[8-(7,10-diphenylfluoranthenyl)] phenylamine (TDPFPA). TDPFPA was shown to be a good hole transporting [with a mobility of (1.1–1.2)×10-4 cm2 V-1 s-1 at (1.8–5.6)×105 V cm-1] and efficient fluorescent material with an exceptionally high glass transition temperature of 237 °C. The device with a simple structure of indium tin oxide/TDPFPA/4,7-diphenyl-1,10-phenanthroline/LiF/Al showed green emission with Commission Internationale de L’Eclairage coordinates of (0.24, 0.54), a current efficiency of 9.9 cd/A, and power efficiency of 10.6 lm/W. [ABSTRACT FROM AUTHOR]

High-efficiency nondoped white organic light-emitting devices (WOLEDs) were demonstrated by using both the intrinsic and exciplex emissions from a single electroluminescent material, 4,4′,4″-trispyrenylphenylamine (TPyPA). The simple device structure of indium tin oxide/N,N′-bis(1-naphthyl)-N,N′-diphenyl-1,1′-biphenyl-4,4′-diamine/TPyPA/4,7-diphenyl-1,10-phenanthroline/LiF/Al exhibited a luminance of 10 000 cd/m2 at a low driving voltage of 4.5 V, and high current and power efficiencies of 9.4 cd/A and 9.0 lm/W, respectively. Such WOLED showed excellent color stability and purity with the Commission Internationale de L’Eclairage coordinates of (0.31, 0.35), which remained unchanged over a wide range of luminance from 100 to 20 000 cd/m2. [ABSTRACT FROM AUTHOR]

We demonstrated an organic red-light-emitting device (ORLED) using a host, 5,6-bis-[4-(naphthalene-1-yl-phenyl-amino)-phenyl]-pyrazine-2,3-dicarbonitrile (BNPPDC), and a dopant, 2,3-bis[[[(2-hydroxy-4-diethylamino)phenyl] (methylene)] amino]-2-butanedinitrile (BDPMB). The device achieved a brightness of 9730 cd/m2 at a 11 V, a power efficiency of 2.35lm/W, a current efficiency of 3.36 cd/A at 4.5 V, and a low turn-on voltage of 3.0 V, with nearly saturated red emission. The device is superior or equal to the best fluorescent ORLEDs reported. BNPPDC generally induced a significant blueshift in dopant emission, thus it may serve as a host for dopants emitting at long wavelengths in ORLEDs with improved performance. [ABSTRACT FROM AUTHOR]

In article number 1801534, Yan‐Qing Li, Feng Gao, Chun‐Sing Lee, Jian‐Xin Tang, and co‐workers propose a method for the synergetic morphology control over cesium lead bromide perovskite films. Bright perovskite light‐emitting diodes (PeLEDs) are achieved due to the synergetic interplay of small grain sizes for efficient energy funneling and defect passivation for suppressing nonradiative recombination losses. Efficient flexible PeLEDs on plastics are also realized, showing great potential for commercially viable applications. [ABSTRACT FROM AUTHOR]

[Display omitted] • A clear inverse relationship between efficiencies and dipole moments was found. • Three new blue molecules were designed and synthesized as proof-of-concept. • Record-high performance in non-doped blue OLEDs was achieved. • State-of-the-art performances were delivered in non-doped, doped and hyper-OLEDs. Non-doped and solution-processable deep blue emitters can greatly reduce the manufacturing cost of organic light-emitting diodes (OLEDs). However, influences of parameters concerning intermolecular interactions in solid state have not yet been explored. Herein, we proposed molecular dipole moment as a pre-experimental parameter to evaluate an emitter's performance in the solid state. By extracting efficiency data of OLEDs based on blue-emitting molecules from literature and calculating the dipole moments of these molecules, we found a clear inverse relationship. Three deep blue TADF emitters with similar molecular emitting properties were designed and synthesized. The PL efficiency of their solid films and device performance was found to decrease as the molecular dipole increased. Specifically, TDBA-SPQ with the smallest dipole moments of 1.86 D delivered much better performance in both vacuum-processed and solution-processed non-doped OLEDs with record-high EQE max of 22.7% and 15.2% with CIE-y coordinates of 0.136 and 0.123, respectively. [ABSTRACT FROM AUTHOR]

[Display omitted] • Fullerene fragments are used as acceptor to prepare TADF emitters for the first time. • OLED using one of the fullerenes fragment-based TADF emitter shows high EQE of 20.2%. • Acceptor without heteroatom can be used for designing efficient TADF emitter. • This strategy may open a new path for enhancing operation stability of TADF emitters. Fragments of fullerene are used as acceptor segments for the first time to construct two thermally activated delayed fluorescence (TADF) compounds DBCP and FAP. Both compounds exhibit similar highly twisted geometries and separated frontier molecular orbital distributions. While on the other hand, their locally exited triplet energy levels from acceptor moieties (3LE A) are fine-tunable owning to the different structural stress in the fragments, resulting in different lowest triplet excited state (T 1) features. In DBCP, the 3LE A is the high lying state and thus DBCP exhibits a small singlet–triplet energy difference of 0.10 eV and a high photoluminescence quantum yield (Φ PL) of 89% with excellent TADF characteristics; while T 1 of FAP is 3LE A , and thus, FAP displays poor triplet exciton utilization with Φ PL of only 54%. In organic light-emitting diodes (OLEDs) based on DBCP and FAP as dopants, maximum external quantum efficiencies of 20.2% and 12.8% are respectively achieved. This work not only demonstrates for the first time that fullerene fragments can be used as key building blocks for TADF emitters, it also proves in principle that pure hydrocarbon mobilities without any electronegative heteroatom can also be employed as acceptor segment in high performance TADF emitters. [ABSTRACT FROM AUTHOR]

Abstract: A new multifunctional compound, 4,4′-di-(1-pyrenyl)-4′′-[2-(9,9′-dimethylfluorene)]-triphenylamine (DPFA) has been designed, synthesized and applied respectively as host-emitter, electron- and hole-transporters in organic light-emitting devices (OLEDs). The compound exhibits good thermal stability with a glass transition temperature (T g) of 161°C and shows blue emissions in both solution and films. OLEDs with DPFA playing various roles have been fabricated and characterized. The results show that DPFA has efficient bipolar charge transport properties for both hole and electron. By using DPFA as a blue emitter in a typical three layer device with a configuration of ITO/NPB(50nm)/DPFA(20nm)/TPBI(30nm)/LiF(0.5nm)/MgAg, highly efficient blue emission with a maximum luminescence efficiency of 5.1cd/A (5.3lm/W) is obtained. [ABSTRACT FROM AUTHOR]

Abstract: Interfacial electronic structures of WO3-based intermediate connectors used in tandem organic light-emitting diodes were studied with photoemission spectroscopy. Important factors controlling their functional effectiveness for charge carrier generation and injection were analyzed. By systematically characterizing the electronic properties and chemical structures for various intermediate connectors, it is identified that the WO3 interlayer is capable of pronouncedly modifying the energy level alignment of the intermediate connectors and thereby the adjacent emission units. Substantial interface dipole and energy level bending caused by the oxide connector are shown to be beneficial to carrier injection into the suitable molecular energy levels of adjoining emission units. [Copyright &y& Elsevier]

Abstract: A high-efficiency, undoped, blue, organic light-emitting device was devised that employed a novel electroluminescent material 4-(7,10-diphenylfluoranthen-8-yl)-N,N-diphenylbenzenamine as electrofluorescence emitter. The device with a simple structure of ITO/N,N′-bis(1-naphthyl)-N,N′-diphenyl-1,1′-biphenyl-4,4′-diamine/4-(7,10-diphenylfluoranthen-8-yl)-N,N-diphenylbenzenamine/4,7-diphenyl-1,10-phenanthroline/LiF/Al exhibited stable blue light emission of CIE chromaticity coordinates (x =0.19±0.01 and y =0.45±0.02), and a current efficiency of 6.0cd A−1 and a power efficiency of 4.6lm W−1. [Copyright &y& Elsevier]

We report two donor-acceptor type blue luminophores based on an azaryl-ketone derivative, phenyl(3-phenylimidazo[1,2- a ]pyridin-2-yl)methanone (pBZ), as respectively emitter and host materials for organic light-emitting diodes (OLEDs). The two new compounds pBZ-TPA and pBZ-DPA having varying lengths of phenylene linkers are prepared through a facile synthetic method and systematically investigated with thermal, photophysical, electroluminescent, and theoretical studies. They exhibit obvious aggregation-induced emission (AIE) characters. The electron-deficiency pBZ and the electron-rich arylamine (triphenylamine or diphenylamine) respectively serve as electron acceptor and donor, rendering bipolar electronic properties. The two AIE luminophores (AIEgens) exhibit obvious charge transfer character evidenced by positive solvatochromic effect in their photoluminescence. It is also found that the (bi)phenylene π-linker attached in donor would tune the molecular conjugation and degree of charge transfer. The versatility of pBZ-TPA and pBZ-DPA is demonstrated in blue OLEDs as emitters and in red phosphorescent devices as hosts with decent performance and mild efficiency roll-offs. Novel azaryl-ketone-based blue AIEgens are developed for blue OLEDs as emitters and for red phosphorescent devices as hosts with decent performance and mild efficiency roll-offs. [Display omitted] • Two novel azaryl-ketone-based blue luminophores with a D-A type structure were rationally designed and synthesized. • Charge transfer state can be modulated by modifying the π linker to realize blue emission. • The azaryl ketones provide rich intermolecular interaction and AIE properties, facilitating solid-state emission. • The new luminophores are employed as host materials for red phosphorescence OLEDs with EQE max near 20%. [ABSTRACT FROM AUTHOR]

[Display omitted] • Molecular design of anthracene-based deep-blue fluorescent emitter is presented. • External quantum efficiency improvement is achieved by TTA. • High efficiency with small roll-off in deep-blue nondoped OLED is realized. Three new anthracene-based emitters, 4-(10-(9,9′-spirobi[fluoren]-2-yl)anthracen-9-yl)benzonitrile (SBF - AnCN), 4-(10-(9,9-diphenyl-9 H -fluoren-2-yl)anthracen-9-yl)benzonitrile (DPF-AnCN) and 4-(10-(9,9-dimethyl-9 H -fluoren-2-yl)anthracen-9-yl)benzonitrile (DMF-AnCN) are developed for deep blue organic light-emitting diodes (OLEDs). Their photophysical properties, thermal properties, molecular configurations and device performances have been systematically investigated. As verified by crystallographic study, these anthracene derivatives possess highly twisted configuration, leading to deep-blue light emission by restraining π-conjugation extension. Furthermore, the difference in the molecular packing manner may influence the photoluminescence quantum yields (PLQYs) in solid state and the proportion of singlet exciton harvested by triplet–triplet annihilation (TTA) process. A nondoped device fabricated using DPF-AnCN as emitter exhibits a maximum external quantum efficiency (EQE) of 7.1% with insignificant efficiency roll-off (6.6%@1000 nit) and Commission Internationale de L'Eclairage (CIE) index of (0.149, 0.104), approaching the standard blue index of the National Television System Committee (NTSC) of (0.14, 0.08). It is demonstrated that TTA is responsible for the excellent electroluminescence (EL) performance. In comparison with doped OLEDs, transient EL decay measurements demonstrate that TTA process is more efficient in the nondoped device. This work would provide an efficient method for designing deep-blue nondoped EL materials. [ABSTRACT FROM AUTHOR]

• Two sterically shielded anthracene derivatives are developed with modification of peripheral phenyl groups (PPGs). • The influence of PPGs decoration on the photoluminescence and electroluminescence properties is studied to unveil the structure-property relationship. • PPGs can significantly suppress electronic coupling in solid state due to its steric-demanding geometry • High efficiency with EQE of up to 5.05% and deep-blue electroluminescence with color index of (0.15, 0.09) are demonstrated. Two new anthracene derivatives are designed with a sterically shielded strategy for deep-blue electroluminescence applications. The naphthyl groups of the widely used blue emitter 9,10-di-(2-naphthyl)anthracene (ADN) were modified with four peripheral phenyl groups (PPGs) to enhance intermolecular spacing in solid-state thin film for suppressing electronic coupling. Influence of the PPGs decoration on photoluminescence and electroluminescence are investigated to reveal the structure-property relationship. A nondoped organic light-emitting diode with the new emitter 9-(naphthalen-2-yl)-10-(5,6,7,8-tetraphenylnaphthalen-2-yl)anthracene (M1) exhibits excellent performance with a maximum external quantum efficiency of 5.05% and deep-blue color index of (0.15, 0.09). Although the use of bulky peripheral substituents does improve device performance, it should be paid attention to the non-conductive effect induced by the larger molecular spacing in the design of deep-blue electroluminescence materials. This work provides a promising molecular design for deep-blue electroluminescence materials. [Display omitted] [ABSTRACT FROM AUTHOR]

• Facile synthesis of 3,5-dicyanapyridine acceptors with different side substituents. • Three TADF emitters with rigid structures achieve high photoluminescent quantum yield. • Highly efficient TADF-OLEDs with external quantum efficiency up to 29.1%. As the blooming of thermally activated delayed fluorescent (TADF) materials, organic light-emitting diodes (OLEDs) possessing high external quantum efficiency (EQE) and low efficiency roll-off are under eager pursuit. Herein, three molecules, 4-(4-(9,9-dimethylacridin-10(9 H)-yl)phenyl)-2,6-diphenylpyridine-3,5-dicarbonitrile (Ph-DMAC), 4-(4-(9,9-dimethylacridin-10(9 H)-yl)phenyl)-2,6-di(naphthalen-1-yl)pyridine-3,5-dicarbonitrile (Na-DMAC) and 4′-(4-(9,9-dimethylacridin-10(9 H)-yl)phenyl)-[3,2′:6′,3″-terpyridine]-3′,5′-dicarbonitrile (3Py-DMAC) with a twisted donor–acceptor structure comprising 3,5-dicynanopryidine with different 2,6-substutents as acceptor and 9,10-dimethylacridan as donor were designed and synthesized. With the highly twisted conformations, effective TADF is achieved in these molecules. Ph-DMAC delivers a high photoluminescent quantum yield (PLQY) of 89% ascribed to its rigid acceptor geometry. Na-DMAC and 3Py-DMAC suffer a slight decrease in efficiency due to excess vibration induced by their naphthyl and pyridinyl moieties. A Ph-DMAC based OLED achieves a very high maximum EQE of 29.1% due to its high PLQY and efficient TADF. With a relatively short delayed lifetime, 3Py-DMAC based OLEDs show only mild efficiency roll-off. [ABSTRACT FROM AUTHOR]