Aggregation-induced Emission Molecules Research Articles

Construction of aggregation-induced emission monolayer at the air/water interface

Construction of aggregation-induced emission monolayer at the air/water interface Kohei Iritani, Department of Applied Chemistry, School of Engineering, Tokyo University of Technology. Organic fluorescent materials using a molecule with aggregation-induced emission (AIE) effect have intense interest due to their potential utilities such as flexible display devices and photovoltaics. For the applications to two-dimensional devices, we purposed the construction of a monolayer formed by a tetraphenylethylene (TPE) derivative as an AIE molecule at the air/water interface. To this end, we synthesized amphiphilic TPE derivatives. We found that the TPE derivative formed a thin film with blue- green emission on the water surface. Moreover, from AFM observations, we confirmed that the transferred film had monolayer thickness.

Self-assembled super-small AIEgen nanoprobe for highly sensitive and selective detection of protamine and trypsin.

Amphiphilic aggregation-induced emission (AIE) molecules show superior potential for fabricating novel ultrasmall nanoprobes. Here, an anionic dipyridyl tetraphenylethene (TPE) derivative is rationally designed and a super-small self-assembled AIEgen nanoprobe (TPE-2Py-SO3NaNPs, ca. 2.48 nm) is thus conveniently constructed for the supersensitive detection of protamine and trypsin. In HEPES/DMSO solution (8 : 2, v/v, pH = 7.4), negatively charged TPE-2Py-SO3NaNPs exhibited an AIE effect in the presence of positively charged protamine, presenting a fluorescence enhancement at 498 nm together with a large Stokes shift of 150 nm and a low detection limit of 8.0 ng mL-1. In addition, the in situ formed TPE-2Py-SO3Na/protamine nanocomposite can be dissociated by trypsin due to the highly selective degradation of protamine via enzymatic hydrolysis, achieving a detection limit for trypsin as low as 5.0 ng mL-1.

Restriction of photoinduced electron transfer as a mechanism for the aggregation-induced emission of a trityl-functionalised maleimide fluorophore.

The restriction of intramolecular motion (RIM) and restricted access to a conical intersection (RACI) have been accepted as general working mechanisms for aggregation-induced emission (AIE) phenomena. However, as the family of AIE molecules grows, the RIM and RACl mechanisms cannot be used to fully understand some AIE phenomena. Herein, the restriction of the photoinduced electron transfer (RPET) state is proposed to rationalize the AIE phenomena of trityl-functionalised maleimide molecule based on density functional theory calculations. The "state-crossing from a locally excited to an electron transfer state" (SLEET) model was employed to predict the ON/OFF molecular PET in solution and solid states. According to the SLEET model, we showed that a non-emissive electron transfer excited state leads to the fluorescence quenching of trityl-functionalised maleimide in solution. However, due to the reduced polarity of the environment in aggregates, the electron transfer state is thermodynamically inaccessible, and a low-lying locally excited state exhibits intense emission. These findings provide a theoretical foundation to understand the working mechanisms of AIE molecules and the design of new AIEgens. We expect that the RPET mechanism can be used to screen potential AIEgens using the SLEET model.

A biodegradable injectable fluorescent polyurethane-oxidized dextran hydrogel for non-invasive monitoring.

Hydrogels have been extensively used in the field of biomedical engineering. In order to achieve non-invasive and real-time visualization of the in vivo status of hydrogels, we designed a fluorescent polyurethane-oxidized dextran (PU-OD) hydrogel with good injectability and self-healing properties, which was cross-linked from a tetraphenyl ethylene (TPE)-containing fluorescent polyurethane emulsion with oxidized dextran by dynamic acylhydrazone bonds. The hydrogel can be used as a visual platform for drug delivery as well as monitoring its own degradation. The network structure of the hydrogel gave it drug-loading capability, and the acylhydrazone bond enabled its pH-responsive drug release. Meanwhile, the PU-OD hydrogel could undergo fluorescence resonance transfer with doxorubicin hydrochloride, showing its potential application in monitoring drug release. In addition, fluorometric and weighing methods were performed to monitor the degradation behavior of the hydrogels in vivo and in vitro, respectively, showing that the non-invasive fluorometric method can be consistent with the invasive weighing method. This work highlights that the introduction of aggregation-induced emission molecules into polyurethanes provides a visual platform that allows for non-invasive monitoring of the material without affecting its own function, which is convenient and less damaging to the body or animals. Consequently, it possesses excellent and promising potential in biomedical materials technologies.

Modulating the electron-donating ability of aggregation-induced emission molecules for improved photo-responsive properties

Multifunctional photoresponsive materials with aggregation-induced emission properties were constructed and modulated by electron-donating ability variation and favorable packing mode.

The preparation of novel AIE fluorescent microspheres by dispersion polymerization

ABSTRACT An approach to prepare monodisperse polystyrene microspheres with aggregation-induced emission (AIE) characteristics has been developed which shows promising applications in fluorescence-encoding. The micron-sized, monodisperse polystyrene microspheres with AIE molecules were perfectly synthesized by two-stage dispersion polymerization. Fluorescent AIE monomer was synthesized by Suzuki reaction, confirmed by nuclear magnetic resonance (NMR). These AIE fluorogens (AIEgens) exhibited unique properties such as bright green emission in solid state and increased emission in tetrahydrofuran (THF) solution with the increase of water content. The influence of the AIE molecules concentration to microspheres synthesis was well investigated. The reaction conditions were optimized to obtain the functional polystyrene microspheres with a size distribution around 3%. The novel microspheres were characterized by scanning electron microscopy (SEM), confocal fluorescence microscope and flow cytometry. According to these results, two-stage dispersion polymerization was proved to be an efficient pathway for the preparation of AIE fluorescent and functionalized microspheres, which could be used in many biomedical industries.

Precisely Confined AIEgens in Giant Imidazolium–Terpyridinyl Cuboctahedra with Enhanced Fluorescence for Single Supramolecule

AbstractTo study the fluorescent behavior of quantitatively confined aggregation‐induced emission (AIE) molecules in a giant cavity, herein a new type of coordination‐driven cuboctahedron cage is presented, with 12 AIE molecules anchored endohedrally linked with different‐length alkyl chains. The cage with confined tetraphenylethylene molecules shows strong fluorescence in highly diluted conditions (4 × 10−7 m). The fluorescence quantum yield can be altered from 3.23% up to 81.37%, upon prolonging the length of alkyl chains to C16. The study shows a great potential application in biology mimic and fluorescent microscopes utilizing confined or isolated fluorescent methods.

An unexpected fluorescent emission of anthracene derivatives in the solid state

Luminescent small molecules in the solid states are of significant importance for organic light-emitting diodes, cell images, fluorescent probes and sensors, owing to the low cost, low toxicity and chemical stability. Herein, two anthracene-based molecules with the same skeleton, but differing in the end group namely M-MMA and M-4VB (methyl methacrylate for M-MMA, 4-vinylbenzeyl for M-4VB) were successfully designed and synthesized. M-4VB exhibits strong green fluorescence with high quantum yield (37%) in the solid state and excellent aggregation-induced emission (AIE) behavior in DMF/water mixtures, while M-MMA shows relatively weak emission. The crystal structures of both M-MMA and M-4VB were successfully obtained in THF/ethanol mixtures. The more rigid environment and stronger intermolecular hydrogen bonding interactions contribute to the enhanced emission behavior of M-4VB at both solid state and aggregation state. The novel and simple synthesis strategy in this work provides a new approach to the transformation from aggregation-caused quenching to AIE molecules with enhanced emission behavior in the solid state.

Insights into Self-Assembly of Nonplanar Molecules with Aggregation-Induced Emission Characteristics.

Utilizing nonplanar conjugated molecules as building blocks facilitates the development of self-assembly but is fundamentally challenging. To study the self-assembly behavior, we herein demonstrate the self-assembly process of a nonplanar conjugated molecule with aggregation-induced emission (AIE) feature from an isolated molecule to an irregular cluster to a well-defined vesicle driven by amphiphiles. The superhigh aggregation-sensitive emission affords more precise and detailed information about the self-assembly process than traditional dyes. Meanwhile, the arrangements of the AIE-active molecule change from disordered to well-organized forms by reducing the twisted configuration during the transformation process, and the strong hydrophobicity of amphiphiles is crucial for such configuration and morphology transformations. Owing to the thermophilic bacteria-mimetic membranes, the obtained vesicles exhibit a property of superhigh thermal stability. They also display promising light-harvesting applications. This work not only deciphers the self-assembly of AIE molecules but also provides a strategy for nonplanar molecules to build well-organized self-assemblies.

Bio-inspired polymer array vapor sensor with dual signals of fluorescence intensity and wavelength shift

Organic vapor sensors based on polymer owing to their tunable molecular structures and designable functions have attracted considerable research interest. However, detecting multiple organic vapors with high accuracy and a low detection limit is still challenging. Herein, inspired by the mammalian olfactory recognition system, organic vapor sensors based on one-dimensional microfilament array structures with a wide range of sensing gases are demonstrated. By introducing aggregation-induced emission (AIE) molecules, sensors possess dual-optical sensing mechanisms of variation in fluorescence intensity and wavelength. By virtue of the synergistic effects of dual signals, superb accuracy and incredibly low detection limit are achieved for identifying analytes. In particular, the polymer/AIE microfilament array can detect acetone vapor down to 0.03% of saturated vapor pressure. In the saturated vapor of acetone, the fluorescence intensity of the sensor arrays was reduced by 53.7%, while the fluorescence wavelength was red-shifted by 21nm. Combined with the principal component analysis (PCA) algorithm, the polymer/AIE molecular sensor arrays accomplished the classification and identification of acetone, ethanol, methylene chloride, toluene, and benzene. This bioinspired approach with dual sensing signals may broaden practical applications to high-performance gas sensors for precise molecular detection.

Solution-processed electroluminescent white-light-emitting devices based on AIE molecules and Cu-In-Zn-S nanocrystals

Solution process is a key technique for the manufacture of large-area and low-cost semiconducting devices and, thus, attracts a lot of attention from both academia and industry. Herein, we realized solution-processed light-emitting diodes (excluding a cathode) based on aggregation-induced emission (AIE) molecules of tetraphenylethylene-4Cl (TPE-4Cl) and cadimum-free semiconductor nanocrystals (NCs) for the first time. By mixing Cu-In-Zn-S NCs and TPE-4Cl as an emissive layer, a new type of environmentally friendly white-light-emitting diodes (WLEDs) was prepared through a solution-processed technique. After systematical optimization of the as-prepared WLEDs, the corresponding color rendering index can reach up to 87 with a maximum luminance of 262 cd/ m 2 . This study may pave a new road to realize AIE-based WLEDs through a solution-processed technique.

NIR-Driven White Light Diode Formed with UCNP@AIEgen Nanocomposites

Upconversion nanoparticles (UCNPs) and polymerizable molecules of aggregation-induced emission (AIE) were combined to produce white light emission. Blue and ultraviolet light-emitting doped lanthanide UCNPs (LiYF4:Yb3+/Tm3+@LiYF4:Yb3+), polymerizable red light-emitting 1,4-bis(piperidinyl-1-propenyl bromide)anthracene (1,4-BPPA), and green light-emitting 9,10-BPPA AIE molecules were mixed with photopolymerizable acrylate oligomers for photopolymerization to form a luminescent film. The fluorescence spectrum, obtained by exciting the LiYF4:Yb3+/Tm3+@LiYF4:Yb3+ UCNPs with 980 nm near-infrared light, exhibited visible light emission, and high-energy emission included ultraviolet light at 365 nm and blue light at 450 and 475 nm. The high-energy light produced through the transfer of energy from the UCNPs excited 1,4-BPPA and 9,10-BPPA molecules to emit red and green light, thus producing a hybrid of red, blue, and green light emission that resulted in white light. X-ray diffractometry, scanning electron microscopy, ultraviolet–visible spectrometry, and fluorescence spectrometry were used to analyze the materials. The CIE coordinates of the white light-emitting film were (0.3358, 0.3536), corresponding to a correlated color temperature of 5370 K. The results demonstrate that upconversion particles and polymerizable AIE molecules can be combined to fabricate a white light-emitting diode film.

Insights into AIE materials: A focus on biomedical applications of fluorescence.

Aggregation-induced emission (AIE) molecules have garnered considerable interest since its first appearance in 2001. Recent studies on AIE materials in biological and medical areas have demonstrated that they show their promise as biomaterials for bioimaging and other biomedical applications. Benefiting from significant advantages of their high sensitivity, excellent photostability, and good biocompatibility, AIE-based materials provide dramatically improved analytical capacities for in vivo detection and demonstration of vital biological processes. Herein, we introduce the development history of AIE molecules and recent progress in areas of biotesting and bioimaging. Additionally, this review also offers an outlook for the potential applications of versatile AIE materials for tracing and treating pathological tissues, including overcoming challenges and feasible solutions.

Synthesis and properties of AIE-active Triazaborolopyridiniums toward fluorescent nanoparticles for cellular imaging and their biodistribution in vivo and ex vivo

Three new aggregation-induced emission (AIE) molecules have been prepared by incorporation of the tetraphenylethylene (TPE) unit to the triazaborolopyridinium (TBP). The compounds exhibit broad absorption from 470 to 510 nm and emission from 530 to 600 nm in various solvents. The TPE-linked TBP, TT-1, and the compound with a phenylene bridge, TT-2, demonstrated high fluorescence quantum yields and solvent-sensitive behaviors due to twisted intramolecular charge transfer (TICT). In contrast, the derivative with a thiophene bridge, TT-3, showed less solvent dependence and low fluorescence quantum yield. The presence of a thiophene moiety led to redshift in the absorption and emission spectra due to a lower energy gap, confirmed by cyclic voltammetry (CV) and density functional theory (DFT) calculations. All derivatives displayed AIE in THF-water mixtures at water contents higher than 80% v/v. TT-1 was encapsulated within phospholipid-connected polyethylene glycol (DSPE-PEG) by nanoprecipitation, yielding fluorescent nanoparticles with the average sizes of 80.7–83.7 nm. In cell imaging experiments, the resulting TT-1@DSPE-PEG nanoparticles (NPs) showed no toxicity to H1299 lung carcinoma cells at concentrations up to 50 μM and were successfully internalized by the cells after 2 h incubation. Finally, the biodistribution of TT-1@DSPE-PEG NPs was studied in a bladder cancer murine model. In vivo and ex vivo images indicated that the NPs were highly localized in the stomach of the mouse after 2 h post-injection and showed a small uptake by the tumor after 4 h post-injection.

Recent advances in chiral aggregation-induced emission fluorogens

• Chiral AIEgens can identify chiral molecules visually based on color change and precipitation reaction, quantitatively analyze chiral molecules, demonstrating its high selectivity, sensitivity and accuracy in chiral identification. • The CPL asymmetry factor (glum) of chiral AIE fluorogens (AIEgens) can reach 1.42, which is very close to the theoretical value of 2. • The combination of chiral elements and luminescent groups promotes their adoption in the field of organic CPL materials. • We have summarized the recent advances of chiral AIEgens in both chiral molecule recognition and circularly polarized organic light-emitting diode. As a flourishing research field, we believe that a detailed and timely literature collection of this field is highly desirable for the chemistry and material community. Over the past decade, aggregation-induced emission (AIE) molecules have played a pivotal role in bioimaging, anti-microbial, and photodynamic therapy, and have been at the forefront of several disciplines worldwide. When combined with chiral moieties, they can easily collide with dazzling sparks and exhibit exceptional and unique advantages. In the application of chiral recognition and measurement of enantiomeric excess, it can identify chiral molecules visually based on color change and precipitation reaction, quantitatively analyze chiral molecules while determining the enantiomeric composition based on the fluorescence intensity change at different wavelengths, and obtain two parameters about chiral molecules from one measurement, thereby demonstrating its high selectivity, sensitivity and accuracy in chiral identification. In the field of organic circularly polarized luminescent (CPL) materials, the asymmetry (g lum ) of common organic light emitting elements is usually between 10 −5 and 10 −2 , whereas the CPL asymmetry factor (g lum ) of chiral AIE fluorogens (AIEgens) can reach 1.42, which is very close to the theoretical value of 2. Therefore, the combination of chiral elements and luminescent groups promotes their adoption in the field of organic CPL materials. Herein we have summarized the recent applications of chiral AIEgens in both chiral molecule recognition and circularly polarized organic light-emitting diode (CP-OLED) in order to provide future researchers with a more comprehensive and detailed understanding of chiral AIEgens and to encourage more scientists to contribute to the development of AIEgens.

Triphenylethene-carbazole-based molecules for the realization of blue and white aggregation-induced emission OLEDs with high luminance

Molecules that use triphenylethene-carbazole moieties decorated with different substitutions were designed and synthesized, harvesting wide energy bandgaps and aggregation-induced emission (AIE) characteristics. The photophysical, thermal, and electroluminescence (EL) characteristics of the designed emitters were investigated to clarify the molecular structure-property-performance relationship. The photoluminescence spectra of the synthesized molecules measured using tetrahydrofuran-water solution presented strong blue emissions, confirming their AIE property. The doped blue-emitting organic light-emitting diodes (OLEDs) with compound 2 exhibited satisfactory peak efficiency of 8.7 cd/A and high maximum luminance of 18474 cd/m2. In comparison, the peak efficiency of the 2-based sky-blue OLEDs with a non-doped emitting layer was 10.2 cd/A with an even superior peak luminance of 39661 cd/m2. Blue-emitting AIE OLEDs have rarely presented such high luminance values, and this improvement can facilitate the development of white-emitting OLEDs (WOLEDs) for lighting applications. The fabricated WOLEDs with 2 achieved a maximum efficiency of 5.6% (8.0 cd/A and 7.5 lm/W), stable EL spectra, and high luminance of 29319 cd/m2. These results indicate that the triphenylethene-carbazole structure designs for AIE molecules could simultaneously harvest wide energy bandgap and high luminance, demonstrating their high potential for EL applications.

Combined Skeleton and Spatial Rigidification of AIEgens in 2D Covalent Organic Frameworks for Boosted Fluorescence Emission and Sensing of Antibiotics.

AIEgens show relatively weak fluorescence performance owing to the existence of π-π interlayer accumulation, molecular layer planarization, and intramolecular rotation in aggregation-induced emission (AIE) molecules, which limit its application scope. Herein, we put forward a combined skeleton and spatial rigidification method to boost the fluorescence emission efficiency of AIEgens. As a proof-of-concept experiment, two highly fluorescent covalent organic frameworks (COFs) were designed and constructed by the Knoevenagel condensation reaction. The experimental results show that the combined skeleton and spatial rigidification endowed excellent fluorescence emission for the resulting F-COF-2 by destruction of the π-π interlayer accumulation, interference of the molecular layer planarization, and restriction of the intramolecular rotation of the AIEgen unit. F-COF-2 displayed highly sensitive and selective NFT and NZF detection. Particularly, the Ksv value and limit of detection of F-COF-2 toward NFT were estimated to be 9.12 × 105 M-1 and 3.35 ppb, respectively, which surpassed all the reported crystalline porous fluorescent materials. The mechanism study proved that its outstanding fluorescence detection property was ascribed to the formation of a nonfluorescent complex induced by hydrogen bond interactions and electron transfer between F-COF-2 and NFT and NZF. This work not only proposes a combined skeleton and spatial rigidification strategy to improve the fluorescence efficiency of AIE molecules but also develops a sensor with high fluorescence efficiency, high chemical stability, and highly efficient detection of antibiotics.

Visualization of Mitochondria During Embryogenesis in Zebrafish by Aggregation-Induced Emission Molecules.

Aggregation-induced emission (AIE) molecules have been widely utilized for fluorescence imaging in many biomedical applications, benefited from large Stokes shift, high quantum yield, good biocompatibility, and resistance to photobleaching. And visualization of mitochondria is almost investigated in vitro and ex vivo, but in vivo study of mitochondria is more essential for systematic biological research, especially during embryogenesis. Therefore, suitable and time-saving alternatives with simple operation based on AIE molecules are urgently needed compared with traditional transgenic approach. Five tetraphenylethylene isoquinolinium (TPE-IQ)-based molecules with AIE characteristics and their ability of mitochondrial visualization in vitro and in vivo and mitochondrial tracking during embryogenesis on zebrafish model were investigated. The biosafety of these AIE molecules was also evaluated systematically in vitro and in vivo. All these five AIE molecules could image mitochondria in vitro with good biocompatibility. In them, TPE-IQ1 exhibited excellent imaging quality for in vivo visualization and tracking of mitochondria during the 4-day embryogenesis in zebrafish, in comparison with the conventional transgenic fluorescent protein. Furthermore, TPE-IQ1 could visualize mitochondrial damage induced by chemicals in real time on 24-h post fertilization (hpf) embryos. This study indicated TPE-IQ-based AIE molecules had the potential for mitochondrial imaging and tracking during embryogenesis and mitochondrial damage visualization in vivo.

AIE Molecules UV‐Filtering Effect Improves the Photostability of Organic Solar Cells

AbstractDue to the poor stability of organic solar cells (OSCs), especially ultraviolet light (UV) stability, they are not yet up to the standard for commercial applications. Inverted devices based on the ZnO electron transport layer (ETL) are relatively thermal‐ and air‐stable, while their UV light stability is poor. Moreover, the active layer materials undergo severe degradation under UV light, which also causes the degradation of the device. Here, aggregation‐induced emission (AIE) molecules as an optical barrier layer are coated between ZnO‐ETL and active layer to fabricate efficient OSCs with excellent UV photostability. AIE molecules can avoid direct photodegradation of the active layer materials by absorbing UV light. At the same time, they can passivate the oxygen defects on the ZnO surface and prevent photocatalytic degradation of the active layer materials. Therefore, the ZnO/TPIZ‐based devices maintain 84% of the original power conversion efficiency (PCE) with continuous irradiation by 5 mW cm–2 UV light (365 nm) for 1500 h, and similarly T80 for more than 700 h under 20 mW cm–2 UV light exposure. Moreover, the ZnO/TPIZ‐based devices also preserve excellent thermal stability accompanying the upgrading of PCE.

Fabrication of monolayer with aggregation-induced emission at the air/water interface

Existing methods for producing transparent fluorescent materials are adequate for small scale production but unsuitable for larger scales. Assistant Professor Kohei Iritani and his team at the Department of Applied Chemistry, School of Engineering, Tokyo University of Technology, Japan, are working to develop 2D monolayers to overcome this. These monolayers are formed by the self-assembly of organic molecules at the solid/liquid or air/water interface and monolayers with the aggregation-induced emission (AIE) effect have the potential to be used as transparent fluorescent materials. The researchers have been successful in synthesising various AIE molecules and have made attempts to form a monolayer using the Langmuir-Blodgett (LB) trough. The team established a method whereby if a monolayer could not be obtained, feedback was given to the molecular design and a process of trial and error was repeatedly performed while new molecules were synthesised. This led to the construction of a fluorescence monolayer that can be transferred to a glass substrate while maintaining fluorescence emission. In their work to construct a monolayer with AIE effect at the air/water interface the researchers are seeking to suppress intramolecular motion using a flat surface of water as a substrate and make it emit fluorescence by forming a monolayer.