Gengwei Lin

Sky-blue nondoped OLEDs based on new AIEgens: ultrahigh brightness, remarkable efficiency and low efficiency roll-off

Two novel AIEgens decorated with fluorenyl and dimesitylboryl groups are prepared. They show high thermal stability and excellent solid-state photoluminescence efficiency. Sky-blue nondoped OLEDs are achieved based on them, affording remarkable electroluminescence efficiencies (12.2 cd A−1 and 5.3%), ultrahigh brightness (92810 cd m−2) and low efficiency roll-off (11.0 cd A−1 at 1000 cd m−2).

Improving Electron Mobility of Tetraphenylethene-Based AIEgens to Fabricate Nondoped Organic Light-Emitting Diodes with Remarkably High Luminance and Efficiency

Robust light-emitting materials with strong solid-state fluorescence as well as fast and balanced carrier transporting ability are crucial to achieve high-performance organic light-emitting diodes (OLEDs). In this contribution, two linear tetraphenylethene (TPE) derivatives (TPE-TPAPBI and TPE-DPBI) that are functionalized with hole-transporting triphenylamine and/or electron-transporting 1,2-diphenyl-1H-benzimidazole groups are synthesized and fully characterized. Both TPE-TPAPBI and TPE-DPBI have aggregation-induced emission attributes and excellent photoluminescence quantum yields approaching 100% in vacuum deposited films. They also possess good thermal property, giving high decomposition temperatures (480 and 483 °C) and glass-transition temperatures (141 and 157 °C). TPE-TPAPBI and TPE-DPBI present high electron mobilities of 1.80 × 10(-5) and 1.30 × 10(-4) cm(2) V (-1) s(-1), respectively, at an electric field of 3.6 × 10(5) V cm(-1), which are comparable or even superior to that of 1,3,5-tri(1-phenylbenzimidazol-2-yl)benzene. The nondoped OLED device employing TPE-TPAPBI as active layer performs outstandingly, affording ultrahigh luminance of 125 300 cd m(-2), and excellent maximum external quantum, power and current efficiencies of 5.8%, 14.6 lm W(-1), and 16.8 cd A(-1), respectively, with very small roll-offs, demonstrating that TPE-TPAPBI is a highly promising luminescent material for nondoped OLEDs.

The synthesis of novel AIE emitters with the triphenylethene-carbazole skeleton and para-/meta-substituted arylboron groups and their application in efficient non-doped OLEDs

Four novel aggregation-induced emission (AIE)-active luminogens (p-DPDECZ, p-DBPDECZ, m-DPDECZ and m-DBPDECZ) with triphenylethene-carbazole skeleton and para-/meta-substituted arylboron groups have been synthesized. Their structures are fully characterized using elemental analysis, mass spectrometry and proton nuclear magnetic resonance spectroscopy. The thermal stabilities, photophysical properties, electronic structures, and electrochemical properties of these molecules are investigated systematically using thermal analysis, UV-vis absorption spectroscopy, fluorescence spectroscopy, theoretical calculation and electrochemical methods. The effects of donor–acceptor interaction and conjugation degree on the photoluminescent and electroluminescent properties of these compounds are investigated. The results show that these donor–AIE–acceptor type compounds exhibit good thermal stability and electrochemical stability as well as AIE properties. Non-doped fluorescent OLEDs fabricated by using para-linked p-DPDECZ as an emitting layer emits a green light with a turn-on voltage of 4.8 V, a maximum brightness of 30 210 cd m−2 and a maximum current efficiency of 9.96 cd A−1. While the OLED prepared with meta-linked m-DBPDECZ exhibits efficient blue light emission with a maximum current efficiency of 4.49 cd A−1 and a maximum luminance of 16 410 cd m−2. The electroluminescence properties of these compounds demonstrate their potential application in OLEDs.

High-Performance Doping-Free Hybrid White OLEDs Based on Blue Aggregation-Induced Emission Luminogens

Doping-free white organic light-emitting diodes (DF-WOLEDs) have aroused research interest because of their simple properties. However, to achieve doping-free hybrid WOLEDs (DFH-WOLEDs), avoiding aggregation-caused quenching is challenging. Herein, blue luminogens with aggregation-induced emission (AIE) characteristics, for the first time, have been demonstrated to develop DFH-WOLEDs. Unlike previous DFH-WOLEDs, both thin (<1 nm) and thick (>10 nm) AIE luminogen (AIEgen) can be used for devices, enhancing the flexibility. Two-color devices show (i) pure-white emission, (ii) high CRI (85), and (iii) high efficiency. Particularly, 19.0 lm W1- is the highest for pure-white DF-WOLEDs, while 35.0 lm W1- is the best for two-color hybrid WOLEDs with CRI ≥ 80. A three-color DFH-WOLED shows broad color-correlated temperature span (2301-11628 K), (i) the first sunlight-like OLED (2500-8000 K) operating at low voltages, (ii) the broadest span among sunlight-like OLED, and (iii) possesses comparable efficiency with the best doping counterpart. Another three-color DFH-WOLED exhibits CRI > 90 at ≥3000 cd m-2, (i) the first DF-WOLED with CRI ≥ 90 at high luminances, and (ii) the CRI (92.8) is not only the highest among AIE-based WOLEDs but also the highest among DF-WOLEDs. Such findings may unlock an alternative concept to develop DFH-WOLEDs.

Dimesitylboryl-functionalized tetraphenylethene derivatives: efficient solid-state luminescent materials with enhanced electron-transporting ability for nondoped OLEDs

Organic electroluminescent materials that can simultaneously serve as light-emitting and electron-transporting layers in one organic light-emitting diode (OLED) are very useful for simplifying device configuration, but there are not many. In this work, three tailored luminescent materials (TPE-DB, TPE-BPDB and TPE-TPDB) adopting tetraphenylethene (TPE) and dimesitylboryl groups as the π-conjugated backbone and the electron-deficient functional group, respectively, are synthesized and fully characterized. Their thermal, photophysical, electronic, electrochemical, and electroluminescent properties are investigated systematically. The results reveal that these new dimesitylboryl-functionalized TPE derivatives feature aggregation-induced emission (AIE) characteristics with high fluorescence quantum yields of 81–86% in solid films. They possess high glass-transition temperatures of 134–168 °C and very low LUMO energy levels down to −2.9 eV. The OLED device [ITO/HATCN (20 nm)/NPB (40 nm)/TPE-DB (60 nm)/LiF (1 nm)/Al (100 nm)] that is fabricated by adopting TPE-DB as both the light emitter and electron transporter exhibits excellent electroluminescent performance, with high efficiencies of up to 13.5 cd A−1 and 4.6%, which are advanced noticeably relative to those attained from the device with an additional electron-transporting layer (TPBi). The results demonstrate that these new TPE derivatives are promising n-type solid-state luminescent materials with practical utility in nondoped OLEDs.

Solution-processable, star-shaped bipolar tetraphenylethene derivatives for the fabrication of efficient nondoped OLEDs

Organic light-emitting diodes (OLEDs) based on solution-processable small molecules are attracting intense attention, as such technology combines the merits of low-cost solution processability of polymers and finely defined structural uniformity of small molecules. Small-molecule tetraphenylethene (TPE) derivatives are excellent solid-state light emitters featuring aggregation-induced emission (AIE) characteristics, however those that can be used in solution-processable devices are very rare. To address this issue, herein, a series of novel star-shaped bipolar TPE derivatives are synthesized and characterized. Their thermal stabilities, photophysical properties, electronic structures, electrochemical behaviors, and application in solution-processed OLEDs are investigated systematically. These luminogens exhibit AIE characteristics and excellent fluorescence quantum yields up to 95% in the solid state. Nondoped OLEDs are successfully fabricated through a spin-coating method. The solution-processed OLEDs [ITO (130 nm)/PEDOT:PSS (40 nm)/emitter (70 nm)/TPBi (30 nm)/Ba (4 nm)/Al (120 nm)] adopting star-shaped TPE derivatives as light-emitting layers show peak luminance of 11 665 cd m−2 and high electroluminescence (EL) efficiencies up to 8.3 cd A−1, 2.6% and 7.5 lm W−1. These results demonstrate a promising avenue towards efficient nondoped OLEDs based on solution-processable AIE-active small molecules.

3,4-Donor- and 2,5-acceptor-functionalized dipolar siloles: synthesis, structure, photoluminescence and electroluminescence

Siloles are a group of outstanding silicon-containing five-membered heterocyclics with intense solid-state fluorescence and superior electron-transporting ability. However, most studies focus on functionalization at the 1,1- and 2,5-positions of siloles, and siloles functionalized with electron donor and acceptor moieties at the 2,3,4,5-positions are scarcely investigated. Herein, two new silole derivatives functionalized with acceptors of cyano or dimesitylboryl groups at their 2,5-positions and donors of diphenylamino groups at their 3,4-positions are successfully synthesized and fully characterized via spectroscopy, thermal analysis, crystallography, electrochemistry and theory calculations. These two functionalized silole derivatives are thermally stable and exhibit aggregation-induced emission (AIE) characteristics with intense fluorescence in solid films. Their HOMO energy levels are increased because of the incorporation of diphenylamino groups, whereas they have lowered LUMO energy levels due to the additional electron acceptors. The application of these new siloles as light-emitting materials for OLEDs is evaluated, where the nondoped OLEDs based on them display good device performances. These dipolar siloles can be useful models to further understand the structure–property relationship of siloles and provide a useful design principle for solid-state luminescent materials.

Long-Term Tracking of the Osteogenic Differentiation of Mouse BMSCs by Aggregation-Induced Emission Nanoparticles

Bone marrow-derived mesenchymal stem cells (BMSCs) have shown great potential for bone repair due to their strong proliferation ability and osteogenic capacity. To evaluate and improve the stem cell-based therapy, long-term tracking of stem cell differentiation into bone-forming osteoblasts is required. However, conventional fluorescent trackers such as fluorescent proteins, quantum dots, and fluorophores with aggregation-caused quenching (ACQ) characteristics have intrinsic limitations of possible interference with stem cell differentiation, heavy metal cytotoxicity, and self-quenching at a high labeling intensity. Herein, we developed aggregation-induced emission nanoparticles decorated with the Tat peptide (AIE-Tat NPs) for long-term tracking of the osteogenic differentiation of mouse BMSCs without interference of cell viability and differentiation ability. Compared with the ability of the commercial Qtracker 655 for tracking of only 6 passages of mouse BMSCs, AIE-Tat NPs have shown a much superior performance in long-term tracking for over 12 passages. Moreover, long-term tracking of the osteogenic differentiation process of mouse BMSCs was successfully conducted on the biocompatible hydroxyapatite scaffold, which is widely used in bone tissue engineering. Thus, AIE-Tat NPs have promising applications in tracking stem cell fate for bone repair.

A new blue AIEgen based on tetraphenylethene with multiple potential applications in fluorine ion sensors, mechanochromism, and organic light-emitting diodes

In this work, we report a new blue AIEgen, (9,9-dimethyl-7-(4-(1,2,2-triphenylvinyl)phenyl)-9H-fluoren-2-yl)dimesitylborane (TPE-FB), composed of dimesitylboryl, fluorene and tetraphenylethene (TPE) groups. The thermal stability, electronic structure, optical properties, transient fluorescence decay and electroluminescence of TPE-FB are studied. TPE-FB shows high thermal stability and good aggregation-induced emission (AIE) properties. Due to the presence of the dimesitylboryl group, TPE-FB can interact with fluorine ions to cause a blue-shift in the absorption spectrum and an apparent decrease in the emission spectrum. TPE-FB also exhibits mechanochromic properties, and the fluorescence color of its solid can be reversibly switched between blue and sky-blue by simple grinding and heating (fuming). TPE-FB can function as a light-emitting layer in nondoped sky-blue OLEDs with good performances.

Efficient red AIEgens based on tetraphenylethene: synthesis, structure, photoluminescence and electroluminescence

Red emitters are very important for colour displays and white lighting devices. However, efficient red emitters are relatively rare because they often suffer from the problem of aggregation-caused quenching. In this work, a series of robust red molecules consisting of tetraphenylethene, benzo-2,1,3-thiadiazole, phenanthro[9,10-d]imidazole and triphenylamine moieties are synthesized and fully characterized. The photophysical properties, transient fluorescence decay, thermal stability, and electrochemical behaviors and electronic structures are thoroughly investigated. The results show that these molecules have high thermal and electrochemical stabilities. They show aggregation-induced emission (AIE) properties and emit strong red fluorescence in the aggregated state, which can be well modulated by functional groups. Nondoped OLEDs are fabricated using these red molecules as light-emitting layers, offering red electroluminescence at 650 nm (CIEx,y = 0.665, 0.334) and a high luminance and an external quantum efficiency of up to 6277 cd m−2 and 2.17%, respectively. Moreover, a solution-processed red OLED with good performance is also achieved. This work not only presents efficient red emitters for nondoped OLEDs, but also provides useful structure–property relationship insights for further development of efficient red luminescent materials.