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A simple strategy to simultaneously achieve fast reverse intersystem crossing (RISC) and low non‐radiative decay rates in thermally activated delayed fluorescence (TADF) emitters is still lacking. Here, the green TADF emitters containing aromatic ketones and prepared D‐Ph and D‐PhCz containing different amounts of deuterium are deuterated to study the mechanism of deuterium on the performance improvement of TADF devices. Due to the heavy atom effect of deuterium, the non‐radiative transition rate constant (knr) of D‐Ph and D‐PhCz decreases. Most importantly, deuterium reduces the reorganization energy (λ) of (T1‐S1), which greatly improves the reverse intersystem crossing rate constant (kRISC) and the exciton utilization efficiency. The results show that the external quantum efficiency of D‐Ph and D‐PhCz increases to 25.69% and 24.92%, respectively. This study provides a simple and efficient strategy for reducing non‐radiative energy loss and increasing kRISC to achieve high‐performance TADF emitters. [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]

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]

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]

Developing red thermally activated delayed fluorescence (TADF) emitters for high‐performance OLEDs is still facing great challenge. Herein, three red TADF emitters, pDBBPZ‐DPXZ, pDTBPZ‐DPXZ, and oDTBPZ‐DPXZ, are designed and synthesized with same donor–acceptor (D‐A) backbone with different peripheral groups attaching on the A moieties. Their lowest triplet states change from locally excited to charge transfer character leading to significantly enhance reverse intersystem crossing process. In particular, oDTBPZ‐DPXZ exhibits efficient TADF feature and exciton utilization. It not only achieves an external quantum efficiency (EQE) of 20.1 % in red vacuum‐processed OLED, but also realize a high EQE of 18.5 % in a solution‐processed OLED, which is among the best results in solution‐processed red TADF OLEDs. This work provides an effective strategy for designing red TADF molecules by managing energy level alignments to facilitate the up‐conversion process and thus enhance exciton harvesting. [ABSTRACT FROM AUTHOR]

Thermally activated delayed fluorescence (TADF) provides great potential for the realization of efficient and stable organic light‐emitting diodes (OLEDs). However, it is still challenging for blue TADF emitters to simultaneously achieve high efficiency, high brightness, and low Commission Internationale de l'Eclairage (CIE) y coordinate (CIEy) value. Here, the design and synthesis of two new benzonitrile‐based TADF emitters (namely 2,6‐di(9H‐carbazol‐9‐yl)‐3,5‐bis(3,6‐diphenyl‐9H‐carbazol‐9‐yl)benzonitrile (2PhCz2CzBn) and 2,6‐di(9H‐carbazol‐9‐yl)‐3,5‐bis(3,6‐di‐tert‐butyl‐9H‐carbazol‐9‐yl)benzonitrile (2tCz2CzBn)) with a symmetrical and rigid heterodonor configuration are reported. The TADF OLEDs doped with both the emitters can achieve a high external quantum efficiency (EQE) over 20% and narrowband blue emission of 464 nm with a CIEy < 0.2. Moreover, the incorporation of a terminal tert‐butyl group can weaken the intermolecular π–π stacking in the nondoped TADF emitter, and thus significantly suppress self‐aggregation‐caused emission quenching for enhanced delayed fluorescence. A peak EQE of 21.6% is realized in the 2tCz2CzBn‐based nondoped device with an extremely low turn‐on voltage of 2.7 V, high color stability, a high brightness over 20 000 cd m−2, a narrow full‐width at half‐maximum of 70 nm, and CIE color coordinates of (0.167, 0.248). [ABSTRACT FROM AUTHOR]

Developing red thermally activated delayed fluorescence (TADF) emitters, attainable for both high‐efficient red organic light‐emitting diodes (OLEDs) and non‐doped deep red/near‐infrared (NIR) OLEDs, is challenging. Now, two red emitters, BPPZ‐PXZ and mDPBPZ‐PXZ, with twisted donor–acceptor structures were designed and synthesized to study molecular design strategies of high‐efficiency red TADF emitters. BPPZ‐PXZ employs the strictest molecular restrictions to suppress energy loss and realizes red emission with a photoluminescence quantum yield (ΦPL) of 100±0.8 % and external quantum efficiency (EQE) of 25.2 % in a doped OLED. Its non‐doped OLED has an EQE of 2.5 % owing to unavoidable intermolecular π–π interactions. mDPBPZ‐PXZ releases two pyridine substituents from its fused acceptor moiety. Although mDPBPZ‐PXZ realizes a lower EQE of 21.7 % in the doped OLED, its non‐doped device shows a superior EQE of 5.2 % with a deep red/NIR emission at peak of 680 nm. [ABSTRACT FROM AUTHOR]

Abstract: Multifunctional emitting materials are scarce and need to be further explored. Now, a newly anthraquinone derivative, 2‐(phenothiazine‐10‐yl)‐anthraquinone (PTZ‐AQ) was designed and synthesized and found to demonstrate polymorphism, multi‐color emission, aggregation‐induced emission (AIE), mechanochromic luminescence (MCL), and thermally activated delayed fluorescence (TADF) in its different solid forms. It is shown for the first time that TADF properties of a compound can be systematically tuned via its aggregation state. The optimized PTZ‐AQ crystal shows a small singlet–triplet energy splitting of 0.01 eV and exhibits red TADF with a photoluminescence quantum yield as high as 0.848. This study shows that the unique multiple functions can be integrated into one single compound through controlling the aggregation states, which provides a new strategy for the investigation and application of multifunctional organic materials. [ABSTRACT FROM AUTHOR]

To develop high-performance thermally activated delayed fluorescence (TADF) exciplex emitters, a novel strategy of introducing a single-molecule TADF emitter as one of the constituting materials has been presented. Such a new type of exciplex TADF emitter will have two reverse intersystem crossing (RISC) routes on both the pristine TADF molecules and the exciplex emitters, benefiting the utilization of triplet excitons. Based on a newly designed and synthesized single-molecule TADF emitter MAC, a highly efficient exciplex emitter MAC:PO-T2T has been obtained. The device based on MAC:PO-T2T with a weight ratio of 7:3 exhibits a low turn-on voltage of 2.4 V, high maximum efficiency of 52.1 cd A−1 (current efficiency), 45.5 lm W−1 (power efficiency), and 17.8% (external quantum efficiency, EQE), as well as a high EQE of 12.3% at a luminance of 1000 cd m−2. The device shows the best performance among reported organic light-emitting devices based on exciplex emitters. Such high-efficiency and low-efficiency roll-off should be ascribed to the additional reverse intersystem crossing process on the MAC molecules, showing the advantages of the strategy described in this study. [ABSTRACT FROM AUTHOR]

Charge-Transfer Complexes: Deep-Red/Near-Infrared Electroluminescence from Single-Component Charge-Transfer Complex via Thermally Activated Delayed Fluorescence Channel (Adv. Funct. Keywords: intermolecular charge transfer; near-infrared; organic light-emitting diode; single-component charge-transfer complex; thermally activated delayed fluorescence Intermolecular charge transfer, near-infrared, organic light-emitting diode, single-component charge-transfer complex, thermally activated delayed fluorescence. [Extracted from the article]

Formation of a single‐component charge‐transfer complex (SCCTC) is unveiled in solid state of an intermolecular charge‐transfer molecule 2‐(4‐(1‐phenyl‐1H‐phenanthro[9,10‐d]imidazol‐2‐yl)phenyl)anthracene‐9,10‐dione (PIPAQ). Intermolecular donor–acceptor interactions between two PIPAQ molecules is the primary driving force for self‐association and contributes to intermolecular charge transfer. The SCCTC character is fully verified by crystallographic, photophysical, electron spin resonance, and vibrational characterizations. The PIPAQ‐based SCCTC is first applied in light‐emitting devices as an emissive layer to realize efficient deep‐red/near‐infrared electroluminescence. This work provides new insights into SCCTC and represents an important step toward their applications in optoelectronic devices. [ABSTRACT FROM AUTHOR]

C.‐J. Zheng, C.‐S. Lee, X.‐H. Zhang, and co‐workers report, on page 2002, a new type of exciplex emitter formed by introducing single‐molecule thermally activated delayed fluorescence emitter. The organic LED based on this novel emitter shows a low turn‐on voltage and excellent efficiency, benefitting from the utilization of triplet excitons and offering a new strategy for designing efficient exciplex emitters. [ABSTRACT FROM AUTHOR]

The long-/short-range charge-transfer (LR/SR-CT) type thermally activated delayed fluorescence (TADF) emitter is designed to solve the problem of slow reverse intersystem crossing rate (k RISC) of the traditional MR-TADF emitter and obtain the full-color emission. However, the introduction of LR-CT transition inevitably leads to the broadening of the emission spectrum. In the design of LR/SR-CT type TADF emitters, it is still quite difficult to balance the smaller singlet-triplet energy gap (Δ E ST) and the narrower full-width at half-maximum (FWHM). Here, we investigated the LR-CT and SR-CT proportion of LR/SR-CT TADF emitters by adjusting the strength and position of the peripheral electron-donating units on the MR skeleton (TSBA), and prepared three MR-TADF emitters. The investigation of photophysical properties reveals that the increase in the strength and number of donors significantly reduces the Δ E ST and accelerates the RISC process. The double substitution strategy of the TSBA skeleton effectively reduces the dihedral angle between the MR skeleton and the electron donor unit, and the highest occupied molecular orbital (HOMO)/hole is more distributed on the MR skeleton, which realizes the increase of the excited state SR-CT component. Consequently, the dual-substituted DTPA-TSBA emitter overcomes the contradiction between the small Δ E ST and the narrow FWHM, and achieves the reduction of both. The corresponding device based on DTPA-TSBA achieved a green light emission with a maximum external quantum efficiency (EQE max) of 26.2 % and a FWHM of only 55 nm. This work provides profound guidance for the development of high-performance narrowband TADF emitters. In this paper, the conformation and excited state characteristics of the emitters are adjusted by adjusting the strength and position of the peripheral substituents, endows the long-/short-range charge-transfer (LR/SR-CT) type TADF emitter with a smaller singlet-triplet energy gap (Δ E ST) and a narrower full-width at half-maximum (FWHM). This work provides profound guidance for the development of high-performance narrowband full-color emitters. [Display omitted] • The excited state characteristics of LR/SR-CT type emitters are regulated by peripheral substitution. • By increasing the proportion of SR-CT in the S 1 state of the LR/SR-CT type emitters to achieve a smaller FWHM. • The multi-donor strategy significantly reduces Δ E ST , accelerates RISC process and increases EQE. [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]

• 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]