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To address the threat of bacterial infection in the following post-antibiotic era, developing effective antibacterial approaches is of utmost urgency. Theranostic medicine integrating diagnosis and therapy is a promising protocol to fight against pathogenic bacteria. But numerous reported antibacterial theranostic materials are disclosed to be trapped in the excessive invasiveness to living mammal cells, leading to false positives and possible biosafety risks. Herein, a series of cationic pyridinium-substituted phosphindole oxide derivatives featuring aggregation-induced emission are designed, and alkyl chain engineering is conducted to finely tune their hydrophobicity and investigate their bioaffinity preference for living mammal cells and pathogenic bacteria. Most importantly, an efficient theranostic agent (PyBu-PIO) is acquired that is free from living cell invasiveness with negligible cytotoxicity and yet holds a good affinity for Gram-positive bacteria, including drug-resistant strains, with a superior inactivating effect. Externally applying PyBu-PIO onto Gram-positive bacteria-infected skin wounds can achieve creditable imaging effects and successfully accelerate the healing processes with reliable biosafety. This work proposes living cell invasiveness as a criterion for antibacterial theranostic materials and provides important enlightenment for the design of antibacterial theranostic materials.

The construction of multivalued logic circuits by multiple quantum-interfered states at the molecular level can make full use of molecular diversity and versatility, broadening the application of molecular electronics. Understanding charge transport through different conducting pathways and how they interact with each other in molecules with a secondary structure is an indispensable foundation to achieve this goal. Herein, we elucidate the synergistic effect from through-space and through-bond conducting pathways in foldamers derived from

Two organic luminogens with aggregation-induced emission properties have been developed and their emission colors are switchable under external stimuli. In addition, they can selectively image lipid droplets and mitochondria, respectively.

Conjugation, as an essential chemical term used to describe electron delocalization, can be roughly grouped into two categories, through-bond conjugation (TBC) and through-space conjugation (TSC). ...

Fluorescence and magnetic resonance imaging (FL/MRI) has received much attention from their complementary characteristics. However, the simultaneous enhancement of fluorescence and MR signals plus the efficacy of the treatment is still a major challenge. To solve this problem, we put forward a strategy of aggregation and de-aggregation based on aggregation-induced emission (AIE). NIR II photosensitizer TQ-TPA with Type I reactive oxygen species (ROS) generation ability and an amphiphilic 2TPE-Gd were firstly synthesized, and both of them showed the AIE property. Depending on the hydrophilic properties, hydrophobic TQ-TPA spontaneously aggregated into the core of nanomicelles formed by DSPE-PEG. Meanwhile, the aggregated 2TPE-Gd in aqueous solution could de-aggregate and insert in the interface, and formed TGdTT NMs. Based on this strategy and AIE property, TGdTT NMs exhibited strong NIR II fluorescence emission and Type I ROS generation ability, and enhanced T1 relaxivity (r1). Moreover, in vitro, in vivo, and pharmacokinetics results demonstrated these nanomicelles had good biosafety and long blood circulation time. Finally, they successfully realized complementary MR/NIR II fluorescence dual-modal imaging guided photodynamic therapy (PDT) to inhibit tumor growth. This work demonstrated that aggregation and de-aggregation strategy of AIEgens in the core-shell nanomicelle exudes infinite charm for constructing the multifunctional theranostic probes.

Through-space charge transfer (TSCT) is adopted in the design of thermally activated delayed fluorescence (TADF) emitters owing to the facile separation of frontier orbitals. However, the advantages of TSCT in the creation of TADF emitters has not been fully resolved. To address this issue, we design and synthesize a series of V-shaped molecules with TSCT and linear molecules with through-bond charge transfer (TBCT), consisting of a 1,3,5-triazine acceptor, a phenoxazine or phenothiazine donor, and an o- or p-terphenyl bridge. A comparative study is conducted to demonstrate their differences in photoluminescence (PL) and electroluminescence (EL) properties. Both kinds of molecules have apparently separated frontier orbitals and prominent aggregation-induced delayed fluorescence properties. Owing to the through-space edge-to-face alignment, the V-shaped molecules with TSCT exhibit higher solid-state PL quantum yields and faster reverse intersystem crossing processes than the linear molecules with TBCT. The V-shaped molecules hold better EL performances with higher EL efficiencies and smaller efficiency roll-offs than linear molecules, regardless of whether they are in nondoped or doped organic light-emitting diodes (OLEDs). These results indicate that TSCT could be a good choice for the creation of TADF emitters, particularly for those with long conjugation molecular backbones.

Developing effective therapies to fight against biofilm-associated infection is extremely urgent. The complex environment of biofilm forces the bacteria to evade the elimination of antibiotics, resulting in recalcitrant chronic infections. To address this issue, a cationic antibacterial agent based on phosphindole oxide (β-PM-PIO) is designed and prepared. The unique molecular structure endows β-PM-PIO with aggregation-induced emission feature and efficient singlet oxygen generation ability. β-PM-PIO shows excellent visual diagnostic function to planktonic bacteria and biofilm. In addition, owing to the synergistic effect of phototoxicity and dark toxicity, β-PM-PIO can achieve superb antibacterial and antibiofilm performance against Gram-positive bacteria with less potential of developing drug resistance. Notably, β-PM-PIO also holds excellent anti-infection capacity against drug-resistant bacteria in vivo with negligible side effects. This work offers a promising platform to develop advanced antibacterial agents against multidrug-resistant bacterial infection.

Robust photosensitizers with strong red/NIR fluorescence, efficient reactive oxygen species (ROS) generation and high photostability are highly desired for photodynamic therapy (PDT). Herein, three novel red conjugated polyelectrolytes (CPEs) with tetraphenylethene and 2,1,3-benzothiadiazole on the main chains and triphenylphosphonium on the side chains are developed. These CPEs display apparent aggregation-induced emission feature and high fluorescence quantum yields in the aggregated state. They can target lysosome in HeLa cells for fluorescence bioimaging. By virtue of the good retention effect and high photostability, these CPEs show ultralong-term tracing performance of subcutaneous tumors, and the tumor site can still be visualized for 20 days after injection. Owing to their good biocompatibility and strong ROS generation ability, the image-guided PDT based on these CPEs can effectively inhibit the growth of subcutaneous tumor and significantly prolong the survival of tumor bearing mice. The H&E and IHC staining reveal that the PDT of these CPEs depress the proliferation of tumor cells, and promote apoptosis and necrosis process. These new CPEs may be employed both as fluorescent probes for in vitro and in vivo long-term tracing and as photosensitizers for image-guided PDT of tumors.

Aggregation-induced emission (AIE) has attracted widespread attention of late in academic and industrial circles owing to its diverse applications. Developing AIE-active materials for application in organic light-emitting diodes (OLEDs) has become an effective method of improving device efficiency and stability. In this work, two novel luminogens (PIO-α-DMAc and PIO-β-DMAc) consisting of 9,9-dimethyl-9,10-dihydroacridine and phosphoindole oxide were synthesized and systemically characterized. Their crystal structures, thermal stabilities, electronic structures, and electrochemical behaviors were studied. They showed apparent AIE properties and emitted strongly in the aggregated state. Non-doped and doped green OLEDs were fabricated using these luminogens as light-emitting layers, and exhibited high brightness, good electroluminescence efficiencies, and low turn-on voltages.

Photodynamic therapy (PDT) is considered a pioneering and effective modality for cancer treatment, but it is still facing challenges of hypoxic tumors. Recently, Type I PDT, as an effective strategy to address this issue, has drawn considerable attention. Few reports are available on the capability for Type I reactive oxygen species (ROS) generation of purely organic photosensitizers (PSs). Herein, we report two new Type I PSs, α-TPA-PIO and β-TPA-PIO, from phosphindole oxide-based isomers with efficient Type I ROS generation abilities. A detailed study on photophysical and photochemical mechanisms is conducted to shed light on the molecular design of PSs based on the Type I mechanism. The in vitro results demonstrate that these two PSs can selectively accumulate in a neutral lipid region, particularly in the endoplasmic reticulum (ER), of cells and efficiently induce ER-stress mediated apoptosis and autophagy in PDT. In vivo models indicate that β-TPA-PIO successfully achieves remarkable tumor ablation. The ROS-based ER stress triggered by β-TPA-PIO-mediated PDT has high potential as a precursor of the immunostimulatory effect for immunotherapy. This work presents a comprehensive protocol for Type I-based purely organic PSs and highlights the significance of considering the working mechanism in the design of PSs for the optimization of cancer treatment protocols., Phosphindole oxide-based photosensitizers with Type I reactive oxygen species generation ability are developed and used for endoplasmic reticulum stress-mediated photodynamic therapy of tumors.

Immunogenic cell death (ICD) is considered an effective death mode to trigger immune response. However, the currently available efficient ICD inducers are quite limited. Endoplasmic reticulum (ER) stress is known as the precursor of ICD, which can be directly triggered by reactive oxygen species in situ. Herein, a novel photosensitizer (α-Th-TPA-PIO) based on phosphindole oxide, featuring aggregation-induced emission (AIE) is designed and prepared, which possesses good ability of hydroxyl radicals (HO

Simultaneous in situ monitoring critical organelles upon oxidative stress and implementing therapeutics utilizing oxidative stress are of vital importance and remain challenging task. Herein, we rationally design and facilely synthesized a photoactivatable fluorescent probe bearing 1,4-dihydropyridine moiety with aggregation-induced emission (AIE) tendency, namely TPA-DHPy, which can rapidly transform into its pyridine counterpart TPA-Py via photo-oxidative dehydrogenation showing strong polarity sensitivity and largely red-shifted emission. TPA-DHPy- and TPA-Py-based type I/type II photosensitization is able to effectively generate reactive oxygen species to induce in situ oxidative stress under white light irradiation. TPA-DHPy can be taken up by cancer cells, and gradually light up lipid droplets (LDs) and endoplasmic reticulum (ER) during photoactivatable process, as well as in situ monitoring difference and alteration of their microenvironment upon oxidative stress by means of multi-color fluorescence imaging in lambda mode. Furthermore, the in situ generated TPA-Py is capable of further destroying the functions of LDs and ER with prolonging the irradiation time, and remarkably inhibiting tumor growth under white light irradiation by the way of photodynamic therapy. This study thus offers useful insights into designing a new generation of theranostic agents towards imaging-guided precise cancer therapy.

Attitude control of Hypersonic Aircraft is a very challenging subject due to the uncertainties and various noises of the system. In this paper, we propose a new methodology to solve this problem. Firstly, the attitude control of Hypersonic Aircraft is reformulated as a system of Forward-Backward Stochastic Differential Equations. Deep Neural Networks (DNNs) are used to get optimal solution of the equations. We have studied several deep neural networks, including FC-based architecture and LSTM-based architecture and proposed a new FC-based architecture that shares the weights between different time steps, which performed satisfactorily in this problem. The performance and universality of the algorithm are tested in both unconstrained and control-constrained cases. Simulation and experimental results verify the superiority of the algorithm.

A novel strategy has been established to assemble a series of single (Z)- or (E)-1H-isoindole derivatives through selectively and sequentially activating carbon-nitrogen triple bonds in a multicomponent system containing various nucleophilic and electrophilic sites. The reaction provides efficient access to structurally unique fluorophores with aggregation-induced emission characteristics. These new fluorophores show fluorescence wavelengths and efficiencies that can be modulated and have excellent potential to specifically light up lipid droplets (LDs) in living cells with bright fluorescence, low cytotoxicity and better photostability than commercially available LD-specific dyes.

Surface modification with bioactive groups is critical to the advanced bio-application of fluorescent nanoparticles (NPs), because it may offer specific interaction between the NPs and tissues, cells, as well as organelles. In this work, amino-functionalized aggregation-induced emission (AIE) polymeric NPs (AIE-PNPs) were efficiently synthesized through a one-pot miniemulsion copolymerization of methyl methacrylate and an amino-containing functional comonomer. The AIE-PNPs displayed a well-defined spherical morphology with a sub-100 nm particle size, and narrow particle size distribution. The surface of AIE-PNPs was further modified with maleimide groups and HIV-1 Tat peptides through a sequential carbodiimde reaction and a thiol-maleimide click reaction. The peptide-modified AIE-PNPs displayed good photostability and colloidal stability under continuous light irradiation or under various pH values, as well as good storage stability in aqueous media. The cell uptake efficiency of AIE-PNPs was significantly improved by the surface modification of HIV-1 Tat peptides, achieving good cell fluorescence imaging quality at a relatively low AIE-PNP concentration.

A series of new conjugated polyelectrolytes (CPEs) with emissive tetraphenylethene-containing backbones and specific targeting pendants are synthesized and characterized. These new CPEs exhibit prominent aggregation-induced emission (AIE) properties, high photostability and low cytotoxicity, and can efficiently detect heparin and stain lysosomes in living cells.

Serious hypoxia in solid tumor as well as vicious aggregation-caused fluorescence quenching (ACQ) of conventional photosensitizers (PSs) limit the progress of the fluorescence imaging-guided photodynamic (PDT) although it has obvious advantages in precise spatial-temporal control and noninvasive treatment. The photosensitizers featuring Type I reactive oxygen species (ROS) based on free radical and novel aggregation-induced emission (AIE) characteristic (AIE-PSs) could offer precious opportunity to resolve above problems, but there was rare feasible molecular engineering in previous reports. Herein, we proposed that the strategy of fabricating stronger intermolecular charge transfer (ICT) effect in electron-rich anion-π+ AIE-active luminogens (AIEgens) aimed to help suppressing nonradiative internal conversion (IC) as well as promote radiative and intersystem crossing (ISC) processes for boosting more free radical generation. Systematic and detailed experimental and theoretical calculations proved our ideas when the electron-donating abilities enhanced in collaborative donors, and the AIE-PSs exhibited higher performance in near-infrared red (NIR) fluorescence image-guided cancer PDT in vitro/vivo. This work would become an important reference to the design of AIE-active free radical generators for overcoming ACQ effect and tumor hypoxia in future PDT.

Photodynamic therapy (PDT) strategy has been widely used in tumor treatment, and the reagents for reactive oxygen species (ROS) play a crucial role. Herein, we develop a fluorogen (TTB) containing an electron-accepting benzo[1,2-b:4,5-b']dithiophene 1,1,5,5-tetraoxide core and electron-donating 4,4'-(2,2-diphenylethene-1,1-diyl)bis(N,N-diphenylaniline) groups for image-guided targeting PDT application. TTB exhibits a prominent aggregation-induced emission (AIE) property with strong near-infrared (NIR) fluorescence in aggregates and is capable of efficiently generating ROS of O2•- and 1O2 under white light irradiation. The nanoparticles (RGD-4R-MPD/TTB NPs) with NIR emission (∼730 nm), high photostability, and low dark cytotoxicity are fabricated by encapsulating TTB within polymeric matrix and then modified with RGD-4R peptide. They show excellent performance in targeting PDT treatment of PC3, HeLa, and SKOV-3 cancer cells in vitro. The investigations on pharmacokinetics, biodistribution, and long-term tracing in vivo reveal that RGD-4R-MPD/TTB NPs can selectively accumulate in tumors for real-time, long-term image-guided PDT treatment. The RGD-4R-MPD/TTB NPs-mediated PDT in multiple xenograft tumor models disclose that the growth of cervical, prostate, and ovarian cancers in mice can be effectively inhibited. These results demonstrate that the reagents employing NIR fluorogen TTB as a photosensitizer could be promising candidates for in vivo image-guided PDT treatments of tumors.

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.

Aggregation-induced emission (AIE) is an intriguing and significant photophysical phenomenon currently attracting intense research interest. Different from conventional luminophores suffering from the commonly acknowledged aggregation-caused quenching problem, luminogens with AIE characteristics (AIEgens) are more promising to be applied to various research fronts. In the family of AIEgens, those created based on main group heterocycles are diverse in functionality owing to their unique electronic structures and thus distinctive optoelectronic processes. In this review article, the newly emerging AIEgens based on heterocycles of silicon, sulphur, oxygen, phosphorus, nitrogen, boron, etc., are introduced, and their intrinsic working mechanism and substituent effect are elucidated in detail. These insights and systematical elucidation of the correlation between structure and function are of great significance for fundamental understanding, and are surely conducive to the design of new AIEgens and the exploration of efficient AIE-active functional materials with specific applications.

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.

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.

Faraday Discussion 196: aggregation-induced emission brought together around 100 researchers to discuss recent progress, current challenges and potential breakthroughs in the design of new AIE luminogens, the understanding of AIE mechanisms and the exploration of advanced technological applications.

Aggregation-induced emission (AIE) is currently receiving intense interest because of its important implications in photophysics. The structure-property relationship decipherment of AIE luminogens is of crucial importance for the fundamental understanding and application exploration. In this research, a series of novel luminogens based on phosphindole oxide (PIO), including a peculiar one with a folded conformation and apparent through-space conjugation, were synthesized and studied as models to elucidate the AIE mechanism. The significant impacts of steric, conjugation and electronic effects on the AIE property are presented based on the results of crystallography analysis, optical spectra measurements and theoretical computation. Non-doped yellow organic light-emitting diodes were fabricated with the new PIO-based luminogens, and they exhibited high brightness, good electroluminescence efficiencies and low efficiency roll-off.

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.

Intramolecular charge transfer (ICT) has significant impacts on organic optoelectronic materials, photochemistry, biotechnology, and so on. However, it is hard to stabilize the ICT state because of the rapid nonradiative charge recombination process, which often quenches light emission. In this work, we use new foldamers of the protonated pyridine-modified tetraphenylethene derivatives that possess through-space conjugation (TSC) characters as the models to study the impact of TSC on the ICT state. Steady and transient spectroscopies illustrate that the lifetime of the ICT state in the molecule with strong TSC can be much longer than those of molecules without TSC, giving rise to a higher fluorescence quantum yield. By combining the theoretical calculations, we demonstrate that the strong TSC can stabilize the ICT state and slow the charge recombination rate by more efficiently dispersing charges. This is a conceptually new design strategy for functional optoelectronic materials that require more stable ICT states.

A method of selectively activating carbon–nitrogen triple bonds has been developed to access 1H-isoindole AIE fluorophores for lipid droplet imaging., A novel strategy has been established to assemble a series of single (Z)- or (E)-1H-isoindole derivatives through selectively and sequentially activating carbon–nitrogen triple bonds in a multicomponent system containing various nucleophilic and electrophilic sites. The reaction provides efficient access to structurally unique fluorophores with aggregation-induced emission characteristics. These new fluorophores show fluorescence wavelengths and efficiencies that can be modulated and have excellent potential to specifically light up lipid droplets (LDs) in living cells with bright fluorescence, low cytotoxicity and better photostability than commercially available LD-specific dyes.

We successfully synthesized solid and hollow ZnO microspheres by a template-free hydrothermal method on the substrate of porous alumina membranes. The morphology of prepared sample was characterized by scanning electron microscopy and transmission electron microscopy. The growth mechanism of the synthesized ZnO microspheres is discussed in detail. At step 1, solid ZnO microspheres were prepared by the thermal decomposition of the Zn(OH)2 microspheres synthesized under the mixture of Zn(NO3)2·6H2O, C6H12N4, and C6H5Na3O7·2H2O solution. The quantity of C6H5Na3O7·2H2O dopant will greatly affect the morphology of the prepared sample by controlling ZnO nucleation and growth rate. At step 2, hollow ZnO microspheres were prepared by removing the Zn(OH)2 cores in an alkaline solution. The proper pH value also plays a key role in preparing hollow ZnO microspheres with high quality. Compared with hollow nanostructure, the solid ZnO microsphere shows the relatively strong Raman peaks at 437 cm-1, which suggests that the prepared solid spheres should have the better crystal quality. Photoluminescence spectra show that the solid ZnO microspheres have the relatively strong ultraviolet (UV) peak at ~ 380 nm attributed to the recombination of free exciton, and the weak green peak owing to the low surface-to-volume ratio. DOI: http://dx.doi.org/10.5755/j01.ms.24.4.19141

A series of neutral conjugated polymers (NCPs) and conjugated polyelectrolytes (CPEs) containing tetraphenylethene (TPE) were synthesized and characterized. Due to the presence of TPE units, NCPs exhibit aggregation-induced emission characteristics and strong fluorescence in the aggregated state. NCPs can function as fluorescent probes to detect 2,4,6-trinitrophenol in aqueous media with extremely high sensitivity, low detection limit and good anti-photobleaching properties. The value of quenching constants (Ksv) is by up to 1.72 × 107 M−1 and the detection limit is as low as 5 nM. NCPs can also be made into the fluorescence test strips for the detection of 2,4,6-trinitrophenol in a practical application. The corresponding CPEs are obtained from the facile reaction of the NCPs with pyridines. The CPEs exhibit low cytotoxicity and can be used to track lysosomes in HeLa cells, which is meaningful in visualizing and understanding intracellular metabolism and various physiological processes. Based on the identical polymer skeleton, these conjugated polymers could be employed as fluorescent probes for multipurpose application.

Through-space conjugated molecules are interesting building blocks for the construction of functional materials that allow multi-dimensional transport of carrier and energy. However, the well explored through-space conjugated molecules are quite limited, which defers their structure-property correlation establishment and wide-scale application. In this review, we introduce a kind of newly-emerging folded tetraphenylethene derivatives featuring through-space conjugation. Their synthesis, crystal and electronic structures, and optical properties are described, and their representative applications as bipolar charge-transporting materials in organic light-emitting diodes and as single-molecule wires in molecular devices are presented, which are anticipated to provide guidance for the further expansion of through-space conjugated systems.

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.

A series of new folded tetraphenylethene derivatives with different substituents are stereoselectively synthesized, which exhibit interesting through-space conjugation, aggregation-enhanced emission, polymorphism and piezochromism properties.