Juan Zhao

Recent advances in mechano-responsive luminescence of tetraphenylethylene derivatives with aggregation-induced emission properties

Since the realization in 2011 that most aggregation-induced emission (AIE) molecules exhibit mechano-responsive luminescence (MRL), research regarding the MRL of AIE molecules has drawn much attention, and this area has been expanding tremendously. As one of the most extensively studied AIE cores, tetraphenylethylene (TPE) has been widely used to construct MRL molecules. This review will focus on recent advances in MRL of TPE derivatives with AIE properties, including a brief history of mechano-responsive AIE-active materials, mechanistic studies on MRL, mechano-responsive luminogens based on TPE, mechano-responsive luminogens containing multiple AIE-active units, mechano-memory chromism and mechanoluminescence of TPE derivatives. Moreover, this review will give a perspective on the possible opportunities and future challenges that exist in this research area.

An efficient yellow thermally activated delayed fluorescence emitter with universal applications in both doped and non-doped organic light-emitting diodes

Thermally activated delayed fluorescence (TADF) emitters have aroused serious attention for their use in organic light-emitting diodes (OLEDs). However, TADF emitters providing both doped and non-doped OLEDs with high device performance are rare. In this work, we present a yellow TADF emitter (OPDPO) meeting the above requirements. The OPDPO-based doped OLEDs show a maximum external quantum efficiency (EQE) of 26.7%, which is amongst the highest ever reported for doped yellow TADF-based OLEDs. The EQE remains as high as 22.1% at a luminance of 1000 cd m−2. Meanwhile, the OPDPO-based non-doped OLEDs afford a maximum EQE of 16.6% at a high luminance of 3600 cd m−2, which is amongst the best performances of non-doped yellow TADF-based OLEDs. Moreover, simple and efficient white OLEDs are implemented by combining a blue conventional fluorescent emitter with either a doped or non-doped OPDPO emissive layer, confirming the universal applications of OPDPO in high-performance OLEDs.

Recent progress in the mechanofluorochromism of cyanoethylene derivatives with aggregation-induced emission

As a class of smart materials, mechanofluorochromic (MFC) luminogens have promising applications in mechanosensors, security papers, and optical storage primarily based on their alternation in emission behaviors in response to mechanical stimuli. It has been discovered that most molecules having aggregation-induced emission (AIE) exhibit mechanofluorochromism. As one of the essential AIE cores, cyanoethylene has been widely used to build MFC molecules. This review focuses on the latest advances in the mechanofluorochromism of cyanoethylene derivatives with AIE properties, which incorporates mechanistic studies on mechanofluorochromism and MFC luminogens based on cyanoethylene. We hope that this review will provide a clear outlook on these novel functional materials to a broad range of scientists within exclusive disciplinary areas and attract more researchers to devote themselves to this exciting research area.

Highly-efficient fully non-doped white organic light-emitting diodes consisting entirely of thermally activated delayed fluorescence emitters

Thermally activated delayed fluorescence (TADF) emitters can harvest singlet and triplet excitons for light emission to afford highly efficient organic light-emitting diode (OLED) devices, especially for all-TADF white OLEDs (WOLEDs). However, the majority of TADF emitters suffer from concentration quenching effects and require complicated doping techniques for device fabrication. Herein, we demonstrate a yellow TADF emitter that enables non-doped OLED systems, which is beneficial for the simplification of the OLED device structure and fabrication. The non-doped yellow OLED achieves a maximum external quantum efficiency (EQE) of 16.7% at a high luminance of 3600 cd m−2, in which such a high magnitude is rarely reported. More significantly, by the combination of the yellow TADF emitter with a blue TADF emitter, a fully non-doped emissive layer (EML) strategy has been demonstrated for the fabrication of an all-TADF WOLED, in which the non-doped yellow and blue TADF emissive layers are closely stacked together without any interlayers. The fully non-doped WOLEDs show a maximum EQE of up to 19.8%, along with high quality white-light emission. This is the first report regarding the fully non-doped all-TADF WOLEDs, and the presented design strategy provides a universal route towards the fabrication of simple and efficient WOLEDs.

Efficient triplet harvesting in fluorescence–TADF hybrid warm-white organic light-emitting diodes with a fully non-doped device configuration

Warm-white organic light-emitting diodes (WOLEDs) fabricated with hybrid fluorescence-based emitters, consisting of traditional fluorescence and thermally activated delayed fluorescence (TADF) emitters can achieve high efficiency without the use of expensive organometallic phosphors. However, most of these types of OLEDs require complicated fabrication techniques, especially host–guest doping systems and multiple interlayers. Herein, an efficient design strategy for hybrid fluorescence WOLEDs is presented, in which a traditional blue fluorescence emitter is simply stacked together with a yellow TADF emitter without any interlayers. Due to the high triplet excited state of the chosen blue emitter, its intrinsically non-radiative triplet excitons can be efficiently utilized for light emission, by exoergic transfer to the adjacent yellow TADF emitter. Following this idea, a maximum external quantum efficiency of 20.8% at a high luminance of 400 cd m−2 is achieved for a fully non-doped WOLED when using a blue fluorescent emitter with the aggregation-induced emission property. This strategy provides a universal approach for the fabrication of highly-efficient fluorescence–TADF hybrid WOLEDs based on the fully non-doped device configuration.

Alkyl Chain Introduction: In Situ Solar‐Renewable Colorful Organic Mechanoluminescence Materials

Mechanoluminescence (ML) materials are environmentally friendly and emit light by utilizing mechanical energy. This has been utilized in light sources, displays, bioimaging, and advanced sensors. Organic ML materials are strongly limited to application by in situ unrepeatable ML. Now, in situ solar-renewable organic ML materials can be formed by introducing a soft alkyl chain into an ML unit. For the first time, the ML from these polycrystalline thin films can be iteratively produced by simply recrystallizing the fractured crystal in situ after a contactless exposure to sunlight within a short time (≤60 s). Additionally, their ML color and lifetime can be also easily tuned by doping with organic luminescent dyes. Therefore, large-area sandwich-type organic ML devices can be fabricated, which can be repeatedly used in a colorful piezo-display, visual handwriting monitor, and sensitive optical sensor, showing a lowest pressure threshold for ML of about 5 kPa.

Recent progress in the mechanofluorochromism of distyrylanthracene derivatives with aggregation-induced emission

Mechanofluorochromic (MFC) luminogens, as a group of evidence-based, practical smart materials, have established immense interest with respect to mechanical stimuli, due to their promising applications in various fields like mechanosensors, safety papers, and optical storage. However, MFC luminogens were rare earlier than 2010. After the discovery that MFC is an essential unique feature of aggregation-induced emission (AIE)-active molecules in 2011, researchers are encouraged to pay more attentions toward MCF luminogens, in which field the investigations are hastened steadily and focused distinctly. As one of the most vital AIE cores, distyrylanthracene (DSA) has been extensively used to assemble MFC motifs. As part of the interest in MFC luminogens, this contemporary overview is targeted on recent advances in the mechanofluorochromism of DSA derivatives with AIE properties and mechanistic study, which encourages more researchers to dedicate themselves to this interesting exploration discipline.

Organic Mechanoluminescence with Aggregation‐Induced Emission

Mechanoluminescence (ML) involves the emission of light from various organic and inorganic materials upon mechanical stimulus. In this review, we contemplate the advances of metal-free, purely organic ML compounds with aggregation-induced emission (AIE), which give strong emission upon mechanical force. We show the new ML-AIE based materials can be used explore the basic of ML properties with structure-property relationships and molecular interactions. The flourishing idea of ML-AIE may help to find the characteristic and elusive component of ML as it partners with AIE, which upgrades the emission property in solids or aggregates. Recent advances in ML-AIE information could increase the wide scope of research in this expanding area, as these materials have promising applications in different optoelectronic areas.