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 , 65.7 lm W , and 18.4 %, and a negligible current efficiency roll-off of 1.2 % at 1000 cd m . Exploring AIDF luminogens for the construction of nondoped OLEDs could be a promising strategy to advance device efficiency and stability.

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 ), 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.

Organic emitters with persistent phosphorescence have shown potential application in optoelectronic devices. However, rational design and phosphorescence tuning are still challenging. Here, a series of metal-free luminophores without heavy atoms and carbonyl groups from commercial/lab-synthesized carbazole and benzene were synthesized to realize tunable molecular emission from fluorescence to phosphorescence by simply substituent variation. All the molecules emit blue fluorescence in both solution and solid state. Upon removal of excitation source, the fluorinated luminophores show obvious phosphorescence. The labsynthesized carbazole based molecules exhibit a huge lifetime difference to the commercially purchased ones due to the existence of isomer in the latter samples. The small energy gap between singlet and triplet state and low reorganization energy help enhance intersystem crossing to contribute to a more competitive radiative process from triplet to ground state. Blue and white organic light-emitting devices are fabricated by using fluorinated luminophore as emitting layer.

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.

Raising triplet exciton utilization of pure organic luminescent materials is of significant importance for efficiency advancement of organic light-emitting diodes (OLEDs). Herein, by introducing bromine atom(s) onto a typical molecule (bis(carbazol-9-yl)-4,5-dicyanobenzene) with thermally activated delayed fluorescence, we demonstrate that the heavy atom effect of bromine can increase spin-orbit coupling and promote the reverse intersystem crossing, which endow the molecules with more distinct delayed fluorescence. In consequence, the triplet exciton utilization is improved greatly with the increase of bromine atoms, affording apparently advanced external quantum efficiencies of OLEDs. Utilizing the enhancement effect of bromine atoms on delayed fluorescence should be a simple and promising design concept for efficient organic luminogens with high exciton utilization.

Blue organic luminescent materials play a crucial role in full-color display and white lighting but efficient ones meeting commercial demands are very rare. Herein, the design and synthesis of tailor-made bipolar blue luminogens with an anthracene core and various functional groups are reported. The thermal stabilities, photophysical properties, electronic structures, electrochemical behaviors, carrier transport abilities, and electroluminescence performances are systematically investigated. The luminogen TPE-TAPBI containing a tetraphenylethene moiety shows aggregation-induced emission, while another luminogen TriPE-TAPBI bearing a triphenylethene unit exhibits light aggregationcaused quenching. In comparison with TriPE-TAPBI, TPE-TAPBI has stronger blue emission in neat film and functions more efficiently in nondoped organic light-emitting diodes (OLEDs). High maxima current, power, and external quantum efficiencies of 7.21 cd A −1 , 6.78 lm W −1 , and 5.73%, respectively, are attained by the nondoped blue OLED of TPE-TAPBI (CIE x,y = 0.15, 0.16). Moreover, efficient two-color hybrid warm white OLEDs (CIE x,y = 0.457, 0.470) are achieved using TPE-TAPBI neat film as the blue-emitting component, which provide total current, power, external quantum efficiencies of up to 70.5 lm W −1 , 76.0 cd A −1 , and 28% at 1000 cd m −2 , respectively. These blue and white OLEDs are among the most efficient devices with similar colors in the literature.

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.H erein, 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 quenchinga nd exciton annihilation are well-suppressed, whichl eads to high emission efficiencies and efficient exciton utilization in neat films. Their nondoped OLEDs providee xcellent electroluminescence efficiencies of 59.1 cd A À1 ,65.7 lm W À1 ,and 18.4 %, and anegligible current efficiency roll-off of 1.2 %at1000 cd m À2 . Exploring AIDF luminogens for the construction of nondoped OLEDs could be ap romising strategy to advance device efficiency and stability.

(1 of 11)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) 2 acac, 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 forwardviewing 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.luminous efficiencies and efficient exciton utilization approaching 100%. [2] However, commercial phosphors depend on rare metal elements such as iridium and platinum, and thus are usually expensive. What is more, high doping concentrations (5-20 wt%) of phosphors were recently reported to optimize the device performance, leading to a high manufacturing cost. [3] As promising alternatives, Adachi and co-workers developed purely organic luminescent materials with thermally activated delayed fluorescence (TADF), which can fully utilize the electrogenerated excitons in OLEDs and thus afford excellent external quantum efficiencies (ƞ ext ) of >20% via reverse intersystem crossing (RISC) process based on small singlet-triplet energy gaps (ΔE ST ≤ 0.3 eV) of the molecules. [4] However, on account of the long triplet lifetimes, most phosphors and TADF emitters suffer from negative nonradiative processes in OLEDs, such as aggregation and concentration caused quenching, [5] triplet-triplet annihilation (TTA), [6] singlet-triplet annihilation (STA), [7] and so on, [8] which greatly limits their practical applications. To address the issue, robust luminogens that can alleviate emission quenching and exciton annihilation are extremely desired. According to the previous works, reducing the intermolecular interactions (e.g., π-π interactions) has been evidenced to be an effective strategy to develop efficient luminescent materials with high photoluminescence quantum yields (Φ F s) in neat films and prominent delayed fluorescence. [9] By this way, the emitters are usually insensitive ...