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Polycyclic heteroaromatics (PHAs) are a highly versatile class of functional materials, especially applicable as efficient luminophores in organic light‐emitting diodes (OLEDs). Those constructed by tethered phenyl surrounding the main group center attract extensive attention due to their excellent OLED device performance. However, the development of such a class of emitters is often limited to boron, nitrogen‐doped π‐conjugated heterocycles. Herein, we proposed a novel kind of blue emitter by constructing a donor‐acceptor molecular configuration, utilizing a dual sulfone‐bridged triphenylamine (BTPO) core and mono/di‐diphenylamine (DPA) substituents. The twisted D−A molecular structures and appropriate donor strength facilitate the effective separation of natural transition orbitals, endowing the emitters with charge‐transfer dominant hybridized local and charge‐transfer characteristics for the excited states. Both BTPO‐DPA and BTPO‐2DPA own small S1–T1 splitting energy, thus demonstrating blue thermally activated delayed fluorescence. The more symmetrical structure and enhanced CT features brought by additional DPA moiety confer BTPO‐2DPA with a shorter delayed fluorescence lifetime, a higher fluorescence quantum yield and narrower emission. Therefore, BTPO‐2DPA based OLED devices exhibit superior blue electroluminescence performance, with external quantum efficiencies reaching 12.31 %. [ABSTRACT FROM AUTHOR]

Emitters with a hot exciton mechanism are regarded as one of the most promising candidates for organic light‐emitting diodes (OLEDs). In this study, a deep‐blue emitter with the hot exciton mechanism is reported, namely 2An‐PCz, by integrating a pair of carbazole groups with a 9,9′‐bi‐anthracene nucleus. Owing to the symmetric molecular architecture and intrinsic local excited state character, multiple high‐lying reverse intersystem cross (hRISC) channels and large overlaps of frontier molecular orbits (FMOs) can be formed, facilitating rapid hRISC processes as well as enhancement of radiative transition rates simultaneously. Combined with the strong luminescence properties brought by the unique X‐packing mode, a high photoluminescence quantum yield of 60.5% is achieved in the non‐doped state. Strikingly, non‐doped deep‐blue OLEDs exhibited a maximum external quantum efficiency (EQE) of 10.50% with minimal efficient roll‐off, which is one of the highest values for deep‐blue organic light‐emitting devices based on hot exciton emitters thus far. The magneto‐electroluminescence (MEL) experiment and transient electroluminescence measurements corroborated that both the high EQE and suppressed efficiency roll‐off are attributable to the rapid "hot exciton" channels. [ABSTRACT FROM AUTHOR]

Due to the hydrophobic organic cations, quasi‐two‐dimensional (quasi‐2D) lead halide perovskite materials have shown better moisture resistance. However, the inappropriate multiphase structure in the quasi‐2D perovskite films seriously affects the efficient transport of energy from low‐n domains to high‐n domains, especially when prepared in air. Herein, the study develops efficient quasi‐2D perovskite films in 30% ± 10% humidity and studies their amplified spontaneous emission (ASE) properties. It can be seen that the phase disproportionation of the quasi‐2D perovskite films prepared in air is greatly suppressed by manipulating the crystallization kinetics of the multiphase structure via using the organic additive benzimidazole (BI), thereby enabling a narrowed phase distribution. Due to the improvement in energy transfer efficiency, surface roughness, and humidity stability, the ASE with a low threshold of 13.4 µJ cm−2 is realized under the quasi‐continuous pumping condition, which is significantly <28.8 µJ cm−2 of the pristine film. Furthermore, the introduction of BI organic additive enhanced the number of peak intensity half‐decay pulses to as high as 5.6 × 107, indicating a good operating stability of the BI‐treated films. This work suggests that the BI‐treated quasi‐2D perovskite films provide the possibility for preparing high‐performance lasers in air. [ABSTRACT FROM AUTHOR]

Aggregation-induced emission (AIE) materials can be well utilized to fabricate high-efficiency blue fluorescence organic light-emitting diodes (OLEDs) due to their fast reverse intersystem crossing (hRISC) from the high-lying triplet state (Tn ≥ 2) to low-lying singlet state (S1) and high photoluminescence (PL) quantum efficiency in the solid film, which should be conducive to the preparation of high-efficiency white OLEDs (WOLEDs). In this study, we fabricated high-efficiency two-color and four-color hybrid WOLEDs based on an AIEgen of 4′-(4-(diphenylamino)phenyl)-5′phenyl-[1,1′:2′,1′′-terphenyl]-4-carbonitrile (TPB-AC) as the blue emitter and host of yellow phosphor, and the efficiency and efficiency roll-off were greatly improved by incorporating a triplet–triplet fusion (TTF) layer in the TPB-AC blue emitter. Finally, the two-color WOLED exhibited a low turn-on voltage of 2.6 V, and the maximum EQE, CE, and PE of 23.2%, 73.2 cd A−1, and 78.7 lm W−1, respectively. The CE, PE, and EQE were maintained at 21.1%, 63.2 cd A−1, and 58.3 lm W−1, respectively, at the luminance of 1000 cd m−2, achieving an extremely low-efficiency roll-off. The optimized four-color hybrid WOLED also showed the maximum EQE, CE, and PE of 24.9%, 49.6 cd A−1, and 51.9 lm W−1, respectively, with low-efficiency roll-off and CRI was over 85. Our results fully demonstrate the potential application value of AIEgens in the preparation of high-performance WOLEDs. [ABSTRACT FROM AUTHOR]

Excellent stability is an essential premise for organic diradicals to be used in organic electronic and spintronic devices. We have attached two tris(2,4,6‐trichlorophenyl)methyl (TTM) radical building blocks to the two sides of perylene bisimide (PBI) bridges and obtained two regioisomeric diradicals (1,6‐TTM‐PBI and 1,7‐TTM‐PBI). Both of the isomers show super stability rather than the monomeric TTM under ambient conditions, due to the increased conjugation and the electron‐withdrawing effects of the PBI bridges. The diradicals show distinct and reversible multistep redox processes, and a spectro‐electrochemistry investigation revealed the generation of organic mixed‐valence (MV) species during reduction processes. The two diradicals have singlet ground states, very small singlet–triplet energy gaps (ΔES‐T) and a pure open‐shell character (with diradical character y0=0.966 for 1,6‐TTM‐PBI and 0.967 for 1,7‐TTM‐PBI). This work opens a window to developing very stable diradicals and offers the opportunity of their further application in optical, electronic and magnetic devices. [ABSTRACT FROM AUTHOR]

High‐quality near‐ultraviolet/deep‐blue organic emitters are urgently needed but still rare. Here, three V‐shape donor‐acceptor‐donor (D‐A‐D) emitters based on pyrazine cores, namely, VDMP‐PhCz, VDMP‐36PhCz, and VDMP‐TPA, are designed and synthesized. Their doped devices using a high‐polar host show remarkable electroluminescence (EL) performances with maximum external quantum efficiency (EQE) values up to 7.37%, 7.55%, and 9.03%, and corresponding CIE coordinates of (0.160,0.040), (0.161,0.039), and (0.149,0.072), respectively. Supported by theoretical calculations and experimental results, the high EL performances of these emitters are achieved by their planarized intramolecular charge transfer (PLICT) features, high triplet‐excitons utilization from "hot exciton" channels, and high horizontal dipole orientations. Furthermore, these PLICT‐based emitters can also function as efficient hosts for green or yellow multi‐resonance (MR) narrowband emissive guests, providing high EQEs of over 32% with alleviated efficiency roll‐offs. [ABSTRACT FROM AUTHOR]

The lifetime of blue organic light-emitting diodes (OLEDs) has always been a big challenge in practical applications. Blue OLEDs based on triplet–triplet annihilation (TTA) up-conversion materials have potential to achieve long lifetimes due to fusing two triplet excitons to one radiative singlet exciton, but there is a lack of an in-depth understanding of exciton dynamics on degradation mechanisms. In this work, we established a numerical model of exciton dynamics to study the impact factors in the stability of doped blue OLEDs based on TTA up-conversion hosts. By performing transient electroluminescence experiments, the intrinsic parameters related to the TTA up-conversion process of aging devices were determined. By combining the change of excess charge density in the emitting layer (EML) with aging time, it is concluded that the TTA materials are damaged by the excess electrons in the EML during ageing, which is the main degradation mechanism of OLEDs. This work provides a theoretical basis for preparing long-lifetime blue fluorescent OLEDs. [ABSTRACT FROM AUTHOR]

The pursuit for efficient deep blue material is an ever‐increasing issue in organic optoelectronics field. It is a long‐standing challenge to achieve high external quantum efficiency (EQE) exceed 10% at brightness of 1000 cd m−2 with a Commission International de L'Eclairage (CIEy) <0.08 in non‐doped organic light‐emitting diodes (OLEDs). Herein, this study reports a deep blue luminogen, PPITPh, by bonding phenanthro[9,10‐d]imidazole moiety with m‐terphenyl group via benzene bridge. The non‐doped OLED based on PPITPh exhibits an exceptionally high EQE of 11.83% with a CIE coordinate of (0.15, 0.07). The EQE still maintains 10.17% at the brightness of 1000 cd m−2, and even at a brightness as high as 10000 cd m−2, an EQE of 7.5% is still remained, representing the record‐high result among non‐doped deep‐blue OLEDs at 1000 cd m−2. The unprecedented device performance is attributed to the reversed intersystem crossing process through hot exciton mechanism. Besides, the maximum EQE of orange phosphorescent OLED with PPITPh as host is 32.02%, and remains 31.17% at the brightness of 1000 cd m−2. Such minimal efficiency roll‐off demonstrates that PPITPh is also an excellent phosphorescent host material. The result offers a new design strategy for the enrichment of high‐efficiency deep blue luminogen. [ABSTRACT FROM AUTHOR]

"Hot exciton" molecules that allow the transition of excitons from a high‐lying triplet state (Tn, n≥ 2) to singlet states (Sm, m≥1) by a reverse intersystem crossing (hRISC) process have become an effective strategy to achieve high efficiency fluorescence organic light emitting diodes (OLEDs). However, the understanding of the dynamic behavior of the "hot exciton" process is still very lacking. Herein, the exciton dynamics of an aggregation‐induced emission (AIE) molecule TPA‐An‐mPhCz with the "hot exciton" property are deeply investigated, and the proportion between hRISC and internal inversion (IC) of excitons on Tn is successfully quantified by in situ transient electroluminescent measurements and theoretical calculation. It is found that the IC process increases severe energy loss of Tn excitons. By introducing a triplet–triplet annihilation up‐conversion layer in the emissive layer to efficiently recapture the IC excitons and further doping a blue fluorescent emitter in the TPA‐An‐mPhCz layer to achieve high photoluminescence quantum yield (PLQY), the resulting OLED achieves a maximum external quantum efficiency of 12.5% with negligible efficiency roll‐off. More impressively, the operational lifetime LT75 (lifetime to 75% of the initial luminance) of the device with efficient triplets utilization performs a remarkable 116 h under 1000 cd m−2. This work provides the fundamentals for the design of hot exciton materials with efficient exciton utilization to develop efficient blue fluorescence OLEDs. [ABSTRACT FROM AUTHOR]

The development of thermally activated delayed fluorescence (TADF) emitters for high efficiency and low roll-off red organic light-emitting diodes (OLEDs) is challenging. In this paper, three red TADF molecules are developed by adopting a donor–acceptor molecular architecture. It can be seen that the delayed fluorescence lifetime is dependent on the intensity and quantity of donors. Furthermore, by changing the dipole moment and regulating the intensity of charge transfer between the host and emitter, high efficiency red OLEDs with the maximum EQE of 21.1% are achieved due to the improvement of horizontal dipole orientations and charge transport balance. Through the analysis of the exciton dynamics model, the polaron–exciton annihilation is suppressed with a faster reverse intersystem crossing (RISC) process, which is highly beneficial to the improvement of efficiency roll-off at high luminance. Our results demonstrate that the selection of highly efficient TADF emitters and matched hosts is crucial for realizing high performance red TADF-based OLEDs. [ABSTRACT FROM AUTHOR]