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Deep‐red (DR) and near‐infrared (NIR) organic light‐emitting diodes (OLEDs) based on purely organic materials hold great potential in various frontier applications, but purely organic DR/NIR materials are far from satisfactory. Herein, a series of tailor‐made delayed fluorescence luminophores comprised of electron‐withdrawing dipyrido[3,2‐a:2″,3″‐c]phenazine‐11,12‐dicarbonitrile and various electron‐donating triarylamines are developed, and their thermal and electrochemical stabilities, electronic structures, photophysical properties and electroluminescence (EL) performances are investigated. They exhibit strong NIR emissions (758−767 nm) in neat films and DR/NIR emissions (680−691 nm) with good photoluminescence quantum yields (48−60%) in doped films, and prefer ordered horizontal alignment with high horizontal dipole ratios of 82−90%, which are attributed to the hybrid transition components of excited states, extended molecular plane and intramolecular hydrogen‐bonding. Their non‐doped OLEDs emit purely NIR light peaking at 820−834 nm with maximum external quantum efficiencies (ηext,maxs) of 0.66−1.06%, and thier doped OLEDs radiate DR/NIR emissions peaking at 656−748 nm with superb ηext,maxs of 14.4–31.0%. They present even better EL performances in sensitized OLEDs, with DR emissions peaking at 648−656 nm and higher ηext,maxs of 29.7−32.9%. These state‐of‐the‐art EL performances demonstrate the great potential of the developed DR/NIR delayed fluorescence luminophores in practical application. [ABSTRACT FROM AUTHOR]

Organic light‐emitting diodes (OLEDs) radiating near ultraviolet (NUV) light are of high importance but rarely reported due to the lack of robust organic short‐wavelength emitters. Here, we report a short π‐conjugated molecule (POPCN‐2CP) with high thermal and morphological stabilities and strong NUV photoluminescence. Its neat film exhibits an electroluminescence (EL) peak at 404 nm with a maximum external quantum efficiency (ηext,max) of 7.5 % and small efficiency roll‐off. The doped films of POPCN‐2CP in both non‐polar and polar hosts at a wide doping concentration range (10–80 wt%) achieve high‐purity NUV light (388–404 nm) and excellent ηext,maxs of up to 8.2 %. The high‐level reverse intersystem crossing improves exciton utilization and accounts for the superb ηext,maxs. POPCN‐2CP can also serve as an efficient host for blue fluorescence, thermally activated delayed fluorescence and phosphorescence emitters, providing excellent EL performance via Förster energy transfer. [ABSTRACT FROM AUTHOR]

Developing orange to red purely organic luminescent materials having external quantum efficiencies (ηexts) exceeding 30% is challenging because it generally requires strong intramolecular charge transfer, efficient reverse intersystem crossing (RISC), high photoluminescence quantum yield (ΦPL), and large optical outcoupling efficiency (Φout) simultaneously. Herein, by introducing benzoyl to dibenzo[a,c]phenazine acceptor, a stronger electron acceptor, dibenzo[a,c]phenazin‐11‐yl(phenyl)methanone, is created and employed for constructing orange–red delayed fluorescence molecules with various acridine‐based electron donors. The incorporation of benzoyl leads to red‐shifted photoluminescence with accelerated RISC, reduced delayed lifetimes, and increased ΦPLs, and the adoption of spiro‐structured acridine donors promotes horizontal dipole orientation and thus renders high Φouts. Consequently, the state‐of‐the‐art orange–red organic light‐emitting diodes are achieved, providing record‐high electroluminescence (EL) efficiencies of 33.5%, 95.3 cd A−1, and 93.5 lm W‒1. By referring the control molecule without benzoyl, it is demonstrated that the presence of benzoyl can exert significant positive effect over improving delayed fluorescence and enhancing EL efficiencies, which can be a feasible design for robust organic luminescent materials. [ABSTRACT FROM AUTHOR]

Tailor‐made red thermally activated delayed fluorescence (TADF) molecules comprised of an electron‐withdrawing pyrazino[2,3‐f][1,10]phenanthroline‐2,3‐dicarbonitrile core and various electron‐donating triarylamines are developed. They can form intramolecular hydrogen‐bonding, which is conducive to improving emission efficiency and promoting horizontal orientation and show near infrared (NIR) emissions (692–710 nm) in neat films and red delayed fluorescence (606–630 nm) with high photoluminescence quantum yields (73–90%) in doped films. They prefer horizontal orientation with large horizontal dipole ratios in films, rendering high optical out‐coupling factors (0.39–0.41). Their non‐doped OLEDs exhibit NIR lights (716–748 nm) with maximum external quantum efficiencies (ηext,max) of 1.0–1.9%. And their doped OLEDs radiate red lights (606–648 nm) and achieve record‐beating ηext,max of up to 31.5%. These new red TADF materials should have great potentials in display and lighting devices. [ABSTRACT FROM AUTHOR]

Exploring molecular design strategy for efficient luminescent materials is of high academic and industrial significance. In this work, it is demonstrated that the introduction of the functional group 4‐(phenoxazin‐10‐yl)benzoyl to the conventional chromophores of carbazole‐substituted fluorene derivatives can generate robust luminogens with aggregation‐induced delayed fluorescence (AIDF), and subtle molecular structure modulation can result in prodigious differences in photoluminescence (PL) and electroluminescence (EL). The obtained new AIDF materials exhibit high thermal and electrochemical stabilities, but their PL quantum yields and delayed fluorescence can be altered greatly. In consequence, these luminogens show varied EL performances in nondoped organic light‐emitting diodes (OLEDs) with external quantum efficiencies (ηext) ranging from 19.0% to 3.3%. In doped OLEDs, these luminogens can afford higher ηext values of 21.7−24.4% because of enhanced PL efficiencies and/or improved exciton recombination efficiencies. Noticeably, both nondoped OLEDs and doped OLEDs at high doping concentrations enjoy very small efficiency roll‐offs. These findings reveal that the proposed design strategy is feasible and applicable for constructing new AIDF luminogens for the fabrication of high‐performance OLEDs with greatly advanced efficiency stability. [ABSTRACT FROM AUTHOR]

Increasing exciton utilization and reducing exciton annihilation are crucial to achieve high performance of organic light‐emitting diodes (OLEDs), which greatly depend on molecular engineering of emitters and hosts. A novel luminogen (SBF‐BP‐DMAC) is synthesized and characterized. Its crystal and electronic structures, thermal stability, electrochemical behavior, carrier transport, photoluminescence, and electroluminescence are investigated. SBF‐BP‐DMAC exhibits enhanced photoluminescence and promotes delayed fluorescence in solid state and bipolar carrier transport ability, and thus holds multifunctionality of emitter and host for OLEDs. Using SBF‐BP‐DMAC as an emitter, the nondoped OLEDs exhibit maximum electroluminescence (EL) efficiencies of 67.2 cd A−1, 65.9 lm W−1, and 20.1%, and the doped OLEDs provide maximum EL efficiencies of 79.1 cd A−1, 70.7 lm W−1, and 24.5%. A representative orange phosphor, Ir(tptpy)2acac, is doped into SBF‐BP‐DMAC for OLED fabrication, giving rise to superior EL efficiencies of 88.0 cd A−1, 108.0 lm W−1, and 26.8% for orange phosphorescent OLEDs, and forward‐viewing EL efficiencies of 69.3 cd A−1, 45.8 lm W−1, and 21.0% for two‐color hybrid warm‐white OLEDs. All of these OLEDs can retain high EL efficiencies at high luminance, with very small efficiency roll‐offs. The outstanding EL performance demonstrates the great potentials of SBF‐BP‐DMAC in practical display and lighting devices. [ABSTRACT FROM AUTHOR]

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

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

Purely organic emitters that can efficiently utilize triplet excitons are highly desired to cut the cost of organic light-emitting diodes (OLEDs), but most of them require complicated doping techniques for their fabrication and suffer from severe efficiency roll-off. Herein, we developed novel luminogens with weak emission and negligible delayed fluorescence in solution but strong emission with prominent delayed components upon aggregate formation, giving rise to aggregation-induced delayed fluorescence (AIDF). The concentration-caused emission quenching and exciton annihilation are well-suppressed, which leads to high emission efficiencies and efficient exciton utilization in neat films. Their nondoped OLEDs provide excellent electroluminescence efficiencies of 59.1 cd A−1, 65.7 lm W−1, and 18.4 %, and a negligible current efficiency roll-off of 1.2 % at 1000 cd m−2. Exploring AIDF luminogens for the construction of nondoped OLEDs could be a promising strategy to advance device efficiency and stability. [ABSTRACT FROM AUTHOR]

Luminescent materials with thermally activated delayed fluorescence (TADF) can harvest singlet and triplet excitons to afford high electroluminescence (EL) efficiencies for organic light-emitting diodes (OLEDs). However, TADF emitters generally have to be dispersed into host matrices to suppress emission quenching and/or exciton annihilation, and most doped OLEDs of TADF emitters encounter a thorny problem of swift efficiency roll-off as luminance increases. To address this issue, in this study, a new tailor-made luminogen (dibenzothiophene-benzoyl-9,9-dimethyl-9,10-dihydroacridine, DBT-BZ-DMAC) with an unsymmetrical structure is synthesized and investigated by crystallography, theoretical calculation, spectroscopies, etc. It shows aggregation-induced emission, prominent TADF, and interesting mechanoluminescence property. Doped OLEDs of DBT-BZ-DMAC show high peak current and external quantum efficiencies of up to 51.7 cd A−1 and 17.9%, respectively, but the efficiency roll-off is large at high luminance. High-performance nondoped OLED is also achieved with neat film of DBT-BZ-DMAC, providing excellent maxima EL efficiencies of 43.3 cd A−1 and 14.2%, negligible current efficiency roll-off of 0.46%, and external quantum efficiency roll-off approaching null from peak values to those at 1000 cd m−2. To the best of the authors' knowledge, this is one of the most efficient nondoped TADF OLEDs with small efficiency roll-off reported so far. [ABSTRACT FROM AUTHOR]

Organic materials with aggregation‐induced delayed fluorescence (AIDF) have exhibited impressive merits for improving electroluminescence efficiency and decreasing efficiency roll‐off of nondoped organic light‐emitting diodes (OLEDs). However, the lack of comprehensive insights into the underlying mechanism may impede further development and application of AIDF materials. Herein, AIDF materials consisting of benzoyl serving as an electron acceptor, and phenoxazine and fluorene derivatives as electron donors are reported. They display greatly enhanced fluorescence with increased delayed component upon aggregate formation. Experimental and theoretical investigations reveal that this AIDF phenomenon can be rationally ascribed to the suppression of internal conversion and the promotion of intersystem crossing in solid. Moreover, the theoretical calculations disclose that the efficient solid‐state delayed fluorescence originates from the higher energy electronic excited state (e.g., S2) rather than the lowest energy‐excited state (S1), demonstrating an anti‐Kasha behavior. The excellent AIDF property allows high exciton utilization and thus superb performance of OLEDs using these new materials as light‐emitting layers. Aggregation‐induced delayed fluorescence (AIDF) can be interpreted as a consequence of the suppression of internal conversion and the promotion of intersystem crossing in the aggregated state. Moreover, efficient solid‐state delayed fluorescence of some AIDF molecules can originate from the higher energy electronic excited state rather than the lowest energy one, demonstrating an anti‐Kasha behavior. [ABSTRACT FROM AUTHOR]

A robust luminescent material with aggregation‐induced emission (AIE) and thermally activated delayed fluorescence (TADF) is reported by Zujin Zhao, Shi‐Jian Su, Zhong Tang, and co‐workers in article number 1606458. The cover vividly describes the design and property of the molecule, which generates high‐performance doped and non‐doped OLEDs with very small efficiency roll‐off thanks to the synergistic effect of AIE and TADF. [ABSTRACT FROM AUTHOR]