Aggregation-induced Emission Materials Research Articles

Utilization of aggregation‐induced emission materials in urinary system diseases

AbstractWith the development of aggregation‐induced emission (AIE) materials, the drawbacks of conventional fluorescence materials subjected to aggregation‐caused quenching (ACQ) have been resolved. This has allowed for the improvement of novel AIE fluorescent materials that exhibit enhanced photostability, a higher signal‐to‐noise ratio, and better imaging quality. Meanwhile, the enhanced phototherapeutic effect of AIE materials has garnered widespread attention in the realm of tumor treatment. The distinct physiological and anatomical characteristics of the urinary system make it suitable for the use of AIE materials. Additionally, AIE‐based phototherapy provides a superior solution to deal with the weaknesses of conventional treatments for urologic neoplasms. In this review, the scientific advancement on the use of AIE materials in urinary system diseases since the emergence of the AIE concept is reviewed in detail. The review highlights the promise of AIE materials for biomarkers detection, fluorescence imaging (FLI) in vivo and in vitro, AIE‐based phototherapy, and synergistic therapy from both diagnostic and therapeutic viewpoints. It is firmly believed that AIE materials hold immense untapped potential for the diagnosis and treatment of urologic disease, as well as all diseases of the human body.

A Conjugated Carboranyl Main Chain Polymer with Aggregation-Induced Emission in the Near-Infrared.

Materials exhibiting aggregation-induced emission (AIE) are both highly emissive in the solid state and prompt a strongly red-shifted emission and should therefore pose as good candidates toward emerging near-infrared (NIR) applications of organic semiconductors (OSCs). Despite this, very few AIE materials have been reported with significant emissivity past 700 nm. In this work, we elucidate the potential of ortho-carborane as an AIE-active component in the design of NIR-emitting OSCs. By incorporating ortho-carborane in the backbone of a conjugated polymer, a remarkable solid-state photoluminescence quantum yield of 13.4% is achieved, with a photoluminescence maximum of 734 nm. In contrast, the corresponding para and meta isomers exhibited aggregation-caused quenching. The materials are demonstrated for electronic applications through the fabrication of nondoped polymer light-emitting diodes. Devices employing the ortho isomer achieved nearly pure NIR emission, with 86% of emission at wavelengths longer than 700 nm and an electroluminescence maximum at 761 nm, producing a significant light output of 1.37 W sr-1 m-2.

Machine Learning Prediction of Quantum Yields and Wavelengths of Aggregation-Induced Emission Molecules.

The aggregation-induced emission (AIE) effect exhibits a significant influence on the development of luminescent materials and has made remarkable progress over the past decades. The advancement of high-performance AIE materials requires fast and accurate predictions of their photophysical properties, which is impeded by the inherent limitations of quantum chemical calculations. In this work, we present an accurate machine learning approach for the fast predictions of quantum yields and wavelengths to screen out AIE molecules. A database of about 563 organic luminescent molecules with quantum yields and wavelengths in the monomeric/aggregated states was established. Individual/combined molecular fingerprints were selected and compared elaborately to attain appropriate molecular descriptors. Different machine learning algorithms combined with favorable molecular fingerprints were further screened to achieve more accurate prediction models. The simulation results indicate that combined molecular fingerprints yield more accurate predictions in the aggregated states, and random forest and gradient boosting regression algorithms show the best predictions in quantum yields and wavelengths, respectively. Given the successful applications of machine learning in quantum yields and wavelengths, it is reasonable to anticipate that machine learning can serve as a complementary strategy to traditional experimental/theoretical methods in the investigation of aggregation-induced luminescent molecules to facilitate the discovery of luminescent materials.

Application of AIE luminogen-loaded core–shell fibers in self-warning and self-healing polymer coatings with enhanced corrosion resistance

Aggregation-induced emission (AIE) materials have been used for non-destructive visual detection of cracks and damages to prevent the final structural failure and increase the service life of coatings. In this study, a self-warning and self-healing core–shell fiber is synthesized for developing AIE composite coatings. In these core–shell fibers, a mixture of hmethylene diisocyanate (HDI) and tetraphenylethylene (TPE) is used as core constituent, and polyacrylonitrile (PAN) is used for preparing the shell, which are continuously wrapped with a high loading rate through coaxial electrospinning technology. The parameters of electrospinning process are optimized to achieve core–shell fibers with smooth surface and average diameter of 100 ± 50 nm. The composite coating reveals effective fluorescence in case of cracks in a corrosive environment. The maximum self-healing efficiency of the fiber coating is 94.8 % after soaking for 120 h. The introduced composite coating paves the way for improving the safety and reliability of critical engineering components.

Rare earth-modified yellow carbon dots for long-term imaging in cells and zebrafish

Carbon dot (CDs) materials are typically hindered by aggregation-caused quenching (ACQ) effect. However, there are limitations in terms of their development and application. The introduction of aggregation-induced emission (AIE) characteristics into CDs has emerged as a viable solution to this challenge. In this work, we synthesized a novel yellow fluorescence (FL) rare earth-doped AIE CDs (named Y-CDs), which integrate the benefits of AIE materials, rare earth materials, and CDs. Y-CDs exhibit bright yellow FL, good temperature sensitivity and pH response properties. In cell imaging, Y-CDs showed excellent targeting capability towards the nuclear in HeLa cells. Y-CDs also showed excellent biocompatibility and safety in imaging of zebrafish embryos and zebrafish. Even on the 10th day following culture of zebrafish embryos, the digestive system and lens of zebrafish can be accurately located and imaged. The work presented here suggests the great potential of replacing commercial dyes with Y-CDs for highly specific nuclear labeling and bioimaging.

Bromine substituent position of tetraphenylethylene-based luminogens effect on enhanced AIE and reversible mechanofluorochromic properties by halogen bonding

The halogen atoms have been exploited for designing highly efficient aggregation-induced emission (AIE) materials in recent years, whereas the development of halogenated AIEgen has been greatly limited by the unclear inherent mechanism. In this paper, a series of 1,1,2,2-tetrakis (4-(phenyl ethynyl) phenyl) ethene (TPPE) derivatives with bromine (Br) substituents in different positions were synthesized and their unique photophysical behaviors based on the anti-heavy atom effect were investigated. The brominated TPPE derivatives possessed higher fluorescence quantum yield (ФF) than that of TPPE, resulting from the formation of intermolecular Br-based bonds. Single crystal analysis and theoretical calculations revealed that changing the positions of the Br substituents could induce the formation of different intermolecular interactions. The Br-based bonds efficiently restricted the intermolecular motion, in which the Br⋯Br bond made a decisive factor in determining the highly efficient fluorescence. TPPE derivatives displayed obvious mechanofluorochromic (MFC) properties. PXRD and SEM results demonstrated that the crystal-to-amorphous transition attributed to the reversibility of MFC properties. This work provides a straightforward and practical method to achieve highly efficient AIE-active materials with higher contrast MFC properties via introducing the halogen atoms.

Europium Metal-Organic Framework with a Tetraphenylethylene-Based Ligand: A Dual-Mechanism Quenching Immunosensor for Enhanced Electrochemiluminescence via the Coordination Trigger.

The effective applications of electrochemiluminescence (ECL) across various fields necessitate ongoing research into novel luminophores and ECL strategies. In this study, self-luminous flower-like nanocomposites (Eu-tcbpe-MOF) were prepared by coordination self-assembly using the aggregation-induced emission material 1,1,2,2-tetrakis(4-carboxyphenyl)ethylene (H4TCBPE) and Eu(III) ions as the precursors. Compared with the monomers and aggregates of H4TCBPE, Eu-tcbpe-MOF exhibits stronger ECL emission. Such enhanced electrochemiluminescence is due to coordination as the coordination-triggered electrochemiluminescence (CT-ECL) enhancement effect. In this study, a cubic-structured nanocomposite (Co9S8@Au@MoS2) was used as an efficient quencher, and a more sensitive ECL detection platform was achieved by two quenching mechanisms: resonance energy transfer and competitive consumption of coreactants. N,N-Diethylethanolamine (DBAE) was used as a coreactant, and DBAE has a faster electron transfer rate and stronger energy supply efficiency than the traditional anodoluminescent coreactant tripropylamine, which effectively improves the ECL signal intensity of Eu-tcbpe-MOF. Hence, a sandwich-type ECL immunosensor was prepared by employing a dual-quenching mechanism, utilizing Eu-tcbpe-MOF as the detection probe and Co9S8@Au@MoS2 as the quencher, achieving precise detection of carcinoembryonic antigen from 0.1 pg·mL-1 to 100 ng·mL-1 with a detection limit of 35.1 fg·mL-1.

A Holistic Perspective on Living Aggregate.

Aggregate is one of the most extensive existing modes of matters in the world. Besides the research objectives of inanimate systems in physical science, the entities in life science can be regarded as living aggregates, which are far from being thoroughly understood despite the great advances in molecular biology. Molecular biology follows the research philosophy of reductionism, which generally reduces the whole into parts to study. Although reductionism benefits the understanding of molecular behaviors, it encounters limitations when extending to the aggregate level. Holism is another epistemology comparable to reductionism, which studies objectives at the aggregate level, emphasizing the interactions and synergetic/antagonistic effects of a group of composed single entities in determining the characteristics of a whole. As a representative of holism, aggregation-induced emission (AIE) materials have made great achievements in the past two decades in both physical and life science. In particular, the unique properties of AIE materials endow them with in situ and real-time visual methods to investigate the inconsistency between microscopic molecules and macroscopic substances, offering researchers excellent toolkits to study living aggregates. The applications of AIE materials in life science are still in their infancy and worth expanding. In this Perspective, we summarize the research progress of AIE materials in unveiling some phenomena and processes of living systems, aiming to provide a general research approach from the viewpoint of holism. At last, insights into what we can do in the near future are also raised and discussed.

Multi-site isomerization of synergistically regulated stimuli-responsive AIE materials toward multi-level decryption

The utilization of multi-site modifications brings about the manipulation of excited-state processes and multi-stimuli responses of salicylaldehyde Schiff base isomers, which can be successfully applied in multi-level decryption.

Multi-Stimuli-Responsive and Cell Membrane Camouflaged Aggregation-Induced Emission Nanogels for Precise Chemo-photothermal Synergistic Therapy of Tumors.

Targeted and controllable drug release at lesion sites with the aid of visual navigation in real-time is of great significance for precise theranostics of cancers. Benefiting from the marvelous features (e.g., bright emission and phototheranostic effects in aggregates) of aggregation-induced emission (AIE) materials, constructing AIE-based multifunctional nanocarriers that act as all-arounders to integrate multimodalities for precise theranostics is highly desirable. Here, an intelligent nanoplatform (P-TN-Dox@CM) with homologous targeting, controllable drug release, and in vivo dual-modal imaging for precise chemo-photothermal synergistic therapy is proposed. AIE photothermic agent (TN) and anticancer drug (Dox) are encapsulated in thermo-/pH-responsive nanogels (PNA), and the tumor cell membranes are camouflaged onto the surface of nanogels. Active targeting can be realized through homologous effects derived from source tumor cell membranes, which advantageously elevates the specific drug delivery to tumor sites. After being engulfed into tumor cells, the nanogels exhibit a burst drug release at low pH. The near-infrared (NIR) photoinduced local hyperthermia can activate severe cytotoxicity and further accelerate drug release, thus generating enhanced synergistic chemo-photothermal therapy to thoroughly eradicate tumors. Moreover, P-TN-Dox@CM nanogels could achieve NIR-fluorescence/photothermal dual-modal imaging to monitor the dynamic distribution of therapeutics in real-time. This work highlights the great potential of smart P-TN-Dox@CM nanogels as a versatile nanoplatform to integrate multimodalities for precise chemo-photothermal synergistic therapy in combating cancers.

Improved aggregation-induced emission behavior in D-π-A architectures by modifying the donor units

With the development of aggregation-induced emission (AIE) in optoelectronic devices, stimulus-responsive sensors, optical storage and bioimaging, the design and synthesis of efficient AIE luminogens remains a challenge. Herein, a series of asymmetric pyrene derivatives were prepared by stepwise functionalization at the 1-, 3-positions using traditional reactions. The experimental results show that a promising white-light emitting material (Commission Internationale de L'Eclairage (CIE): x = 0.32, y = 0.31), namely TPxzPy, which has completely separated the highest occupied molecular orbital (HOMOs) and lowest unoccupied molecular orbital (LUMOs) distribution, was produced. Moreover, a new strategy was established to construct pyrene-based AIE luminogens along the short axis. All compounds exhibited higher emission efficiency in the solid or aggregated state versus in solution, especially for TTPaPy with a competitive photoluminescence quantum yield as high as 76.2 %. The present work provides a feasible strategy to construct pyrene-based AIE materials for optoelectronic devices.

High-efficient luminescence induced by the restriction of benzothiazole group torsion for the HBT-H-H molecule in the aggregate state

The aggregation-induced emission (AIE) effect has been demonstrated to have great potential application in different areas, from organic electronics to biomedical research and physical process monitoring. In general, molecules with AIE characteristic exhibit fluorescence enhancement in the aggregated state by restricting intramolecular motion consumption. The combination of AIE and excited-state intramolecular proton transfer (ESIPT) is meaningful for promoting luminescence. Recently, HBT-H-H molecule, as a derivative of 2-(2-Hydroxyphenyl)benzothiazole (HBT), has drawn extensive attention from researchers. The molecule possesses the intramolecular hydrogen bonding structure which has the potential for ESIPT. Moreover, the fluorescence quantum yield of HBT-H-H in the aggregation state is 35 times higher than that in Toluene. However, the interplay between excited state dynamics and the AIE effect for this molecule is not clear. Especially, how does AIE effect beat non-radiative transition channel by affecting motions of molecular structure. Herein, we investigated the excited state dynamics of HBT-H-H molecule by the spin-flip time-dependent density functional theory and QM/MM method. We found that the molecule relaxes to the conical intersection region through the twisting motion of the benzothiazole group in Toluene solvent. While the AIE effect effectively inhibits this process by preventing the torsion of benzothiazole group, which induces the emission enhancement. The interplay between the excited-state dynamics and AIE effect for the HBT-H-H molecule delineated in this work not only benefits the deep understanding of molecular behavior to the aggregate level, but also provides a guide for the synthesis of AIE materials with favorable performance.

Fabrication of AIE Polymer-Functionalized Reduced Graphene Oxide for Information Storage.

Reduced graphene oxide (RGO) has been extensively studied and applied in optoelectronic systems, but its unstable dispersion in organic solvents has limited its application. To overcome this problem, the newly designed and developed aggregation-induced emission (AIE) material poly[(9,9-bis(6-azidohexyl)-9H-fluorene)-alt-(9-(4-(1,2,2-triphenylvinyl)phenyl)-9H-carbazole)] (PAFTC) was covalently grafted onto RGO to produce (PFTC-g-RGO). The solubility of two-dimensional graphene was improved by incorporating it into the backbone of PAFTC to form new functional materials. In resistive random access memory (RRAM) devices, PFTC-g-RGO was used as the active layer material after it was characterized. The fabricated Al/PFTC-g-RGO/ITO device exhibited nonvolatile bistable resistive switching performances with a long retention time of over 104 s, excellent endurance of over 200 switching cycles, and an impressively low turn-ON voltage. This study provides important insights into the future development of AIE polymer-functionalized nanomaterials for information storage.

A novel AIE material for sensing of Erythromycin in pure water by hydrogen bond in portable test strips and cellular imaging applications

Erythromycin could be used to treat various bacterial infection, but it was harmful to the colonic microflora. Therefore, it is highly desirable to develop a fluorescence probe that could selectively and sensitively detect Erythromycin in pure water. In this work, a fluorescent probe named EHMC, which exhibited aggregation-induced emission (AIE) characteristic in solid state and water/EtOH binary solvent was developed for “turn on” sensing Erythromycin in pure water with high selectivity and sensitivity (detection limit: 1.78 × 10−8 M). Also, there are fewer interference from other antibiotics in the detection process of probe EHMC for Erythromycin. Moreover, probe EHMC could as a portable test strips for highly selective detection of Erythromycin and identification of different concentrations of Erythromycin. In addition, living cells imaging experiments displayed that probe EHMC could detect Erythromycin in A549 cells and BEAS-2B cells successfully. Combined with the theoretical calculation results The sensing mechanisms that the CO in Erythromycin and OH in EHMC formed intermolecular hydrogen bond and further formed new aggregates were confirmed by job’ plot, 1H NMR, FT-IR, ESI-MS, DLS and TEM and DFT calculation.

Unraveling the Mechanism of ACQ-to-AIE Transformation of Fluorescein Derivatives.

Although fluorescein derivatives have excellent properties and strong practicability, they are typical aggregation-induced quenching (ACQ) molecules, which are not conducive to working in the solid state. Recently, the fluorescein derivative Fl-Me with aggregation-induced emission (AIE) property was synthesized, which brought a new dawn for the research and development of fluorescein-based materials. In this study, the AIE mechanism of Fl-Me was investigated based on time-dependent density functional theory and the ONIOM method. The results revealed that an effective dark-state deactivation pathway leads to the fluorescence quenching of Fl-Me in a solution environment. Accordingly, the AIE phenomenon originates from the closure of the dark-state quenching channel. It is worth emphasizing that we found that the carbonyl group of molecular Fl-Me has intermolecular hydrogen bonding interaction with the adjacent molecules, which caused the increase of the dark-state energy in the crystalline state. Moreover, the restriction of the rotational motion and the nonexistence of the π-π stacking interaction are beneficial to the enhancement of fluorescence upon aggregation. Finally, the ACQ-to-AIE transformation mechanisms of fluorescein derivatives have been discussed. This work provides deeper insight into the photophysical mechanism for the fluorescein derivatives Fl-Me with AIE feature and eventually is expected to help researchers to develop more fluorescein-based AIE materials with remarkable properties for various fields.

Aggregation-induced Emission Materials for High-efficiency Perovskite Solar Cells.

The perovskite solar cells (PSCs) with high efficiency and stability are in great demand for commercial applications. Although the remarkable photovoltaic feature of perovskite layer plays a great role in improving the PCE of PSCs, the inevitable defects and poor stability of perovskite, etc. are the bottleneck and restrict the commercialization of PSCs. Herein, a review provides a strategy of applying aggregation-induced emission (AIE) molecules, containing passivation functional groups and distinct AIE character, which serves as the alternative materials for fabricating high-efficiency and high-stability PSCs. The methods of introducing AIE molecules to PSCs are also summarized, including additive engineering, interfacial engineering, hole transport materials and so on. In addition, the functions of AIE molecule are discussed, such as defects passivation, morphology modulation, well-matched energy level, enhanced stability, hole transport ability, carrier recombination suppression. Finally, the conclusions are offered and further research trend for high performance PSCs based on AIE materials is proposed.

Molecular Design and Biomedical Application of AIEgens with Photochemical Activity

Photochemical reaction is expected to become a promising type of green chemistry with merits of operational flexibility, excellent regioselectivity, high yield, and mild reaction condition. Recently, aggregation-induced emission (AIE)-based fluorescent molecules with photoresponsivity have been quickly developed and employed in the biomedical field. In this Review, photoresponsive AIE materials based on the inherent photochemical reactions are highlighted according to the photochemical pathways: photoisomerization, photocyclization, photodimerization, and multiple photoreactions. Following this, their biomedical applications are summarized and discussed, including photoactivatable bioimaging, diagnosis, and therapy. Finally, the challenges and future perspectives are presented.

Direct self-assembly of AIE-active tetraphenylethene derivative with cucurbit[7]uril as a fluorescence probe for metformin detection

A fast, simple, sensitive and stable “turn-on” fluorescent probe method by the self-assembly of aggregation-induced emission luminogen 1,1,2,2-tetra(biphenyl-4-yl)ethene and cucurbit[7]uril was developed for selective determination of metformin. Simultaneously the host–guest complex can improve the poor water solubility of traditional aggregation-induced emission material. The response mechanism of the supramolecular probe to metformin was studied by UV–visible absorption spectroscopy, Fourier transform infrared spectroscopy, nuclear magnetic resonance spectroscopy, dynamic light scattering technology, scanning electron microscope. The proposed method showed good sensitivity and accuracy for the detection of metformin. The relative fluorescence intensity was linearly correlated with the concentration of metformin in the range of 5 to 100 µM, with a detection limit of 1.5 µM. In addition, the aggregation-induced emission probe was successfully utilized to determine the metformin concentration in serum samples, and the recovery ranged from 90.80% to 104.0% with satisfactory results. Therefore, the established fluorescence assay provides a promising pathway for metformin analysis in biomedicine.

Specific discrimination and efficient elimination of gram-positive bacteria by an aggregation-induced emission-active ruthenium (II) photosensitizer.

The infections caused by Gram-positive bacteria (G+) have seriously endangered public heath due to their high morbidity and mortality. Therefore, it is urgent to develop a multifunctional system for selective recognition, imaging and efficient eradication of G+. Aggregation-induced emission materials have shown great promise for microbial detection and antimicrobial therapy. In this paper, a multifunctional ruthenium (II) polypyridine complex Ru2 with aggregation-induced emission (AIE) characteristic, was developed and used for selective discrimination and efficient extermination of G+ from other bacteria with unique selectivity. The selective G+ recognition benefited from the interaction between lipoteichoic acids (LTA) and Ru2. Accumulation of Ru2 on the G+ membrane turned on its AIE luminescence and allowed specific G+ staining. Meanwhile, Ru2 under light irradiation also possessed robust antibacterial activity for G+in vitro and in vivo antibacterial experiments. To the best of our knowledge, Ru2 is the first Ru-based AIEgen photosensitizer for simultaneous dual applications of G+ detection and treatment, and inspires the development of promising antibacterial agents in the future.

Debut of a novel AIE-based fluorescent probe as tyrosinase tracer to image skin pigmentary disorders

Tyrosinase (TYR) functions as the critical enzyme in biosynthesis of melanin, and its abnormality is an important hallmark for skin pigmentary disorders. This renders the visualization of tyrosinase dynamics a strategically vital way to facilitate clinical diagnostic and monitoring. However, the use of small molecule fluorescent probes to assess tyrosinase levels and evaluate related therapeutics and drugs has been limited. This is mainly due to the aggregation-induced quenching (ACQ) effects of existing fluorescent probes. In this study, we introduce the first aggregation-induced emission (AIE) small molecule fluorescent probe, BTFTYR, for simple, highly sensitive, and effective detection of tyrosinase activity. The specific fluorescence signal generated by tyrosinase catalytic reaction enables the imaging of pigment cells. We demonstrate its application in visualizing tyrosinase with high contrast in living vertebrates, benefiting from the inherent photobleaching resistance of AIE materials, large Stokes shift, and considerable tissue permeability. We also show the outstanding skin penetration capability of BTFTYR in a skin model. Moreover, we present the first comprehensive evaluation of relevant clinical therapeutic approaches or drugs, including ultraviolet B (UVB) irradiation, kojic acid, and α-MSH, by interpreting the tyrosinase variation with BTFTYR. Finally, our studies confirm that BTFTYR neither causes skin inflammation nor produces visceral toxicity, making it a promising chemical tool for medical diagnosis and drug screening. This tool may further help elucidate the pathomechanisms associated with tyrosinase.