Aggregation-induced Emission Fluorescence Research Articles

The influence of multiple alkyl chains on mesomorphic and photophysical properties of diphenylacrylonitrile liquid crystals

ABSTRACT For the purpose of studying the influence of the number of alkyl chains on mesomorphic and photophysical properties of aggregation-induced emission liquid crystals, the novel diphenylacrylonitrile derivatives 6–9 with 2–5 alkyl chains were prepared in yields of 80%–86%. The studies suggested that the number of alkyl chains influenced greatly on both mesomorphic properties and aggregation-induced emission fluorescence. The four or five alkyl chains on diphenylacrylonitrile liquid crystals were favourable for the ordered hexagonal columnar mesophase. The three or four alkyl chains contributed to high fluorescence. The four alkyl chains on diphenylacrylonitrile derivatives were the optimised number for producing the ordered columnar liquid crystalline phase and high fluorescence.

The Nanoassembly of an Intrinsically Cytotoxic Near-Infrared Dye for Multifunctionally Synergistic Theranostics.

The combination of diagnostic and therapeutic functions in a single theranostic nanoagent generally requires the integration of multi-ingredients. Herein, a cytotoxic near-infrared (NIR) dye (IR-797) and its nanoassembly are reported for multifunctional cancer theranostics. The hydrophobic IR-797 molecules are self-assembled into nanoparticles, which are further modified with an amphiphilic polymer (C18PMH-PEG5000) on the surface. The prepared PEG-IR-797 nanoparticles (PEG-IR-797 NPs) possess inherent cytotoxicity from the IR-797 dye and work as a chemotherapeutic drug which induces apoptosis of cancer cells. The IR-797 NPs are found to have an ultrahigh mass extinction coefficient (444.3 L g-1 cm-1 at 797 nm and 385.9 L g-1 cm-1 at 808 nm) beyond all reported organic nanomaterials (<40 L g-1 cm-1 ) for superior photothermal therapy (PTT). In addition, IR-797 shows some aggregation-induced-emission (AIE) properties. Combining the merits of good NIR absorption, high photothermal energy conversion efficiency, and AIE, makes the PEG-IR-797 NPs useful for multimodal NIR AIE fluorescence, photoacoustic, and thermal imaging-guided therapy. The research exhibits the possibility of using a single ingredient and entity to perform multimodal NIR fluorescence, photoacoustic, and thermal imaging-guided chemo-/photothermal combination therapy, which may trigger wide interest from the fields of nanomedicine and medicinal chemistry to explore multifunctional theranostic organic molecules.

CO2‐Activated Reversible Transition between Polymersomes and Micelles with AIE Fluorescence

AbstractFluorescent polymersomes with both aggregation‐induced emission (AIE) and CO2‐responsive properties were developed from amphiphilic block copolymer PEG‐b‐P(DEAEMA‐co‐TPEMA) in which the hydrophobic block was a copolymer made of tetraphenylethene functionalized methacrylate (TPEMA) and 2‐(diethylamino)ethyl methacrylate (DEAEMA) with unspecified sequence arrangement. Four block copolymers with different DEAEMA/TPEMA and hydrophilic/hydrophobic ratios were synthesized, and bright AIE polymersomes were prepared by nanoprecipitation in THF/water and dioxane/water systems. Polymersomes of PEG45‐b‐P(DEAEMA36‐co‐TPEMA6) were chosen to study the CO2‐responsive property. Upon CO2 bubbling vesicles transformed to small spherical micelles, and upon Ar bubbling micelles returned to vesicles with the presence of a few intermediate morphologies. These polymersomes might have promising applications as sensors, nanoreactors, or controlled release systems.

CO2 -Activated Reversible Transition between Polymersomes and Micelles with AIE Fluorescence.

Fluorescent polymersomes with both aggregation-induced emission (AIE) and CO2 -responsive properties were developed from amphiphilic block copolymer PEG-b-P(DEAEMA-co-TPEMA) in which the hydrophobic block was a copolymer made of tetraphenylethene functionalized methacrylate (TPEMA) and 2-(diethylamino)ethyl methacrylate (DEAEMA) with unspecified sequence arrangement. Four block copolymers with different DEAEMA/TPEMA and hydrophilic/hydrophobic ratios were synthesized, and bright AIE polymersomes were prepared by nanoprecipitation in THF/water and dioxane/water systems. Polymersomes of PEG45 -b-P(DEAEMA36 -co-TPEMA6 ) were chosen to study the CO2 -responsive property. Upon CO2 bubbling vesicles transformed to small spherical micelles, and upon Ar bubbling micelles returned to vesicles with the presence of a few intermediate morphologies. These polymersomes might have promising applications as sensors, nanoreactors, or controlled release systems.

Synthesis, characterization and visible light activated fluorescence of azo caged aggregation-induced emission polymers

Tetraphenylethylene (TPE) based aggregation-induced emission (AIE) polymers containing different degrees of functionalization of photobleachable azo chromophores were developed and their photophysical properties were explored. The synthesized epoxy monomer derived from TPE core reacted with aniline to give the precursor polymer, which confirmed typical AIE characteristics. Then through a post-polymerization azo-coupling scheme, various contents of 2-phenylazo-4, 5-dicyanoimidazole groups were readily introduced into the TPE based epoxy precusor polymer. Experimental results suggested that only a small amount of such imidazole-type azo component could totally cage the intense AIE fluorescence of the whole polymer due to the fluorescence resonance energy transfer process. By exposure to visible light (450 nm), azo units could be photo bleached notably, thus resulting in dramatic recovery of the blue fluorescence. Depending on this, visible light induced fluorescent patterns were easily fabricated and erased, indicating that the prepared azo caged AIE Polymers could be promising candidates for anti-counterfeiting and optical information storage.

Amygdalin-Functionalized Carbon Quantum Dots for Probing β-Glucosidase Activity for Cancer Diagnosis and Therapeutics.

A fluorescence active nanosystem capable of targeting specific receptors of cancer cells with or without a biorecognition element is advantageous for biosensor studies. Herein, a naturally occurring anticancer drug, amygdalin (synthetic form: Laetrile, a misnomer: vitamin B17), has been modified on the surface of carbon quantum dots, prepared by a hydrothermal method, to probe β-glucosidase activity. Despite its cyanide toxicity, amygdalin is recently revived to be an anticancer molecule, and the risk factor can be optimized by understanding its binding efficiency with β-glucosidase in the cancer cells. In this study, an in vitro biorecognition pattern of amygdalin-functionalized carbon quantum dots (Amy@CQDs) toward β-glucosidase is typically evaluated by an aggregation-induced fluorescence emission mechanism. The optical functionality and structural integrity of CQDs before and after functionalization with amygdalin are comprehensively studied by spectroscopic and microscopic techniques. Our results demonstrate that Amy@CQDs is a stable hydrophilic graphitic carbon nanostructure exhibiting selective fluorescence quenching upon interaction with β-glucosidase, enabling the lowest detection limit of 134 nM. Hydrolysis products of amygdalin mediated by β-glucosidase were further confirmed by HPLC and colorimetric methods, indicating the selective binding of the prepared Amy@CQDs, which may find a useful application in cancer diagnosis and therapeutics.

Intracellular self-assembly of TPE-biotin nanoparticles enables aggregation-induced emission fluorescence for cancer-targeted imaging

Fluorogens with aggregation-induced emission (AIE) characteristics have recently been widely applied for studying biological events, and fluorogens with “smart” properties are especially desirable. Herein, we rationally designed and synthesized a biotinylated and reduction-activatable probe (Cys(StBu)-Lys(biotin)-Lys(TPE)-CBT (1)) with AIE properties for cancer-targeted imaging. The biotinylated probe 1 can be actively uptaken by the biotin receptor-overexpressing cancer cells, and then “smartly” self-assemble into nanoparticles inside cells and turn the fluorescence “On”. Employing this “smart” strategy, we successfully applied probe 1 for cancer-targeted imaging. We envision that this biotinylated intelligent probe 1 might be further developed for cancer-targeted imaging in routine clinical studies in the near future.

Ultrasensitive Detection of Formaldehyde in Gas and Solutions by a Catalyst Preplaced Sensor Based on a Pillar[5]arene Derivative

Abnormal formaldehyde (FA) is known to induce a variety of diseases. Herein, we report a novel and efficient method for ultrasensitive detection of formaldehyde in gas and solutions by a catalyst preplaced sensor based on the pillar[5]arene derivative (DP5J). By the catalyzation of (CF3SO3)2Bi, DP5J could selectively and sensitively sense formaldehyde through an aggregation-induced emission (AIE) “turn-on” response within 7.5 s, and the detection limits for formaldehyde is 3.27 × 10–9 M. Moreover, a FA test kit was prepared by loading the catalyst (CF3SO3)2Bi preplaced DP5J sensor (DP5J-Bi) on a silica gel plate. The test kit could conveniently and efficiently detect formaldehyde in gas or solution with ultrasensitivity. The catalysts preplaced method and FA reaction-induced AIE fluorescence “turn-on” mechanism is a novel approach to achieve ultrasensitive detection of FA. Importantly, it is also a novel approach for the efficient detection of other volatile organic compounds.

Sensing and intracellular imaging of Zn2+ based on affinity peptide using an aggregation induced emission fluorescence “switch-on” probe

Direct monitoring of Zn2+ in living system is extremely important to human health. In Zn2+ sensing, most chemical molecules with aggregation induced emission (AIE) effect were only used in vitro because of its potential biological toxicity. In this work, a biocompatible “turn-on” fluorescent probe for the determination of Zn2+ combined AIE fluorophore tetraphenylethene (TPE) molecule with peptide has been designed and synthesized based on Schiff base reaction. The TPE-Peptide probe exhibited strong emission in the presence of Zn2+ due to the formation of self-assembling complexes between Zn2+ and the three histidine residues in two strands of peptide, which triggered TPE moieties in an aggregated state. The TPE-Peptide probe displays a highly selective and sensitive fluorescence intensity with a relatively wide linear range from 0 to 100 μM and a detection limit of 18.56 nM. As designed, the probe can penetrate live HeLa cells and image intracellular Zn2+ by turn-on response with low cytotoxicity and good stability, implying that TPE-Peptide acts as a highly useful fluorescent biosensor for biological systems. Our strategy opens a new way for the investigation of other metal ions or bioactive molecules that can bind with special peptides and it may find wide applications in biological sensing.

A novel carbazole derivative containing fluorobenzene unit: aggregation-induced fluorescence emission, polymorphism, mechanochromism and non-reversible thermo-stimulus fluorescence

Different conformations and packing modes induce the compound with unique stimuli-responsive properties.

An ATP/ATPase responsive supramolecular fluorescent hydrogel constructed via electrostatic interactions between poly(sodium p-styrenesulfonate) and a tetraphenylethene derivative.

By electrostatic interactions between poly(sodium p-styrenesulfonate) 1 and the tetraphenylethene (TPE) derivative 2 containing two quaternary ammonium cations, a novel bioresponsive supramolecular fluorescent hydrogel 3 was constructed. This self-assembly process led to the aggregation of TPE, a typical chromophore with aggregation-induced emission (AIE) properties, thereby endowing this hydrogel with AIE fluorescence properties. Moreover, this supramolecular fluorescent hydrogel was responsive to biomolecules. When ATP was added to this system, it interacted with 2 more strongly than 1. Correspondingly, the network structure of the hydrogel was destroyed and the aggregation extent of 2 was decreased, which induced the transition from gel to sol and decreased the fluorescence intensity of the hydrogel at the same time. Subsequently, after phosphatase ATPase was added to the solution, ATP was decomposed and the electrostatic interactions between 1 and 2 were rebuilt, transforming sol into gel and recovering the fluorescence intensity of the hydrogel. Therefore, the fluorescent supramolecular hydrogel 3 was bioresponsive. Simultaneously, this fluorescent supramolecular hydrogel 3 could cross over the cell membrane and enter the cytoplasm, which could be applied in cell imaging.

Branched triphenylamine luminophores: Aggregation-induced fluorescence emission, and tunable near-infrared solid-state fluorescence characteristics via external mechanical stimuli

Three AIE-active branched luminophores (defined as 4a, 4b and 4c) containing triphenylamine and carbazole units forming intramolecular charge transfer (ICT) states have been developed. The studies of the mechanical stimuli effect on solid state showed that the branch number can affect effectively the performance of the tunable fluorescence in the solid state. Interestingly, only compound 4a displayed a distinct bathochromic shift of its fluorescence emission from the visible (λem = 598 nm) to the near-infrared section (λem = 643 nm) by mechanical stimuli. Moreover, 4a exhibited an obvious crystallization-induced emission enhancement (CIEE) effect. The crystal samples of 4a emit strong orange light with 49.8% solid-state fluorescence quantum yield (ФF) and the amorphous showed decreased red emission with 7.6% (ФF). Mechanical grinding and organic solvent stimuli can reversibly change the phase transition between crystalline and amorphous states. However, compounds 4b and 4c are not sensitive to the mechanical stimuli, because it is difficult for them to form crystalline structure due to bigger steric hindrance effect. The mechanism for their solid-state fluorescence behavior was investigated in detail by powder X-ray diffraction (PXRD), scanning electron microscopy (SEM) and differential scanning calorimetry (DSC) analysis.

Histone controlled aggregation of tetraphenylethene probe: A new method for the detection of protease activity

A novel fluorescence “turn-on” assay for protease activity based on controlled aggregation of a tetraphenylethene probe is reported. A tetraphenylethene derivative (TPE-2+) with two positive charges is used in this study. TPE-2+ has no emission in an aqueous solution. Heparin is an anionic polymer, which can induce aggregation of TPE-2+. Strong aggregation-induced fluorescence emission (AIE) is observed. Histone is a cationic protein, it binds with heparin via electrostatic attractive interactions, which hinders the binding of TPE-2+ to heparin. TPE-2+ is released, and a decreased emission signal is detected. Upon the addition of a protease, histone is hydrolyzed into small fragments, which weakens its competitive binding to heparin. Free heparin induces aggregation of TPE-2+. A turn-on emission signal is recorded. An efficient and convenient fluorescence assay for protease activity is therefore established.

A new aggregation-induced emission fluorescent probe for rapid detection of nitroreductase and its application in living cells

The biological activity of nitroreductase (NTR) is closely related to biological hypoxia status in organisms. The development of effective methods for monitoring the activity of NTR is of great significance for medical diagnosis and tumor research. Toward this goal, we have developed a new aggregation-induced emission (AIE) fluorescence NTR probe TPE-HY used the tetraphenylethene as the fluorophore, and used the nitro group as the NTR recognition site. The probe TPE-HY has many excellent properties, including rapid response, AIE characteristics, high sensitivity and selectivity, and low cytotoxicity. Importantly, the probe TPE-HY is successfully applied to monitor endogenous NTR in living HeLa cells.

Fluorescence Detection of Microcapsule-Type Self-Healing, Based on Aggregation-Induced Emission.

An extrinsic self-healing coating system containing tetraphenylethylene (TPE) in microcapsules was monitored by measuring aggregation-induced emission (AIE). The core healing agent comprised of methacryloxypropyl-terminated polydimethylsiloxane, styrene, benzoin isobutyl ether, and TPE was encapsulated in a urea-formaldehyde shell. The photoluminescence of the healing agent in the microcapsules was measured that the blue emission intensity dramatically increased and the storage modulus also increased up to 105 Pa after the photocuring. These results suggested that this formulation might be useful as a self-healing material and as an indicator of the self-healing process due to the dramatic change in fluorescence during photocuring. To examine the ability of the healing agent to repair damage to a coating, a self-healing coating containing embedded microcapsules was scribed with a razor. As the healing process proceeded, blue light fluorescence emission was observed at the scribed regions. This observation suggested that self-healing could be monitored using the AIE fluorescence.

Direct visualization and real-time monitoring of dissipative self-assembly by synchronously coupled aggregation-induced emission

Dissipative self-assembly was clearly visualized and real-time monitored throughin situintrinsic aggregation-induced emission fluorescence only in the assembly state.

T-shaped monopyridazinotetrathiafulvalene-amino acid diad based chiral organogels with aggregation-induced fluorescence emission.

A series of pyridazine coupled tetrathiafulvalene T-shaped derivatives with varying amino acid moieties have been synthesized and their gelation properties were studied in various organic solvents. Among these derivatives, two gelators bearing glycine or phenylalanine units display efficient gelation in aromatic and polar solvents. Interestingly, these gelators, except for the gelator containing two tryptophan units, are able to gel DMF via a solution-to-gel transformation when triggered with sonication for less than 20 s or cooled below zero. A number of experiments revealed that these gelator molecules self-assembled into elastically interpenetrating three-dimensional chiral fibrillar aggregates. Importantly, all of the resulting gels result in a dramatic enhancement of the fluorescence intensity compared with their hot solution in spite of the absence of a conventional fluorophore unit and the fluorescence was effectively quenched by the introduction of C60. Moreover, the gelators can be utilized for the removal of different types of toxic molecules, such as aromatic solvents and cationic dyes, from wastewater.

Fluorogenic Thorium Sensors Based on 2,6-Pyridinedicarboxylic Acid-Substituted Tetraphenylethenes with Aggregation-Induced Emission Characteristics.

A novel fluorescent sensor based on tetraphenylethene (TPE) modified with 2,6-pyridinedicarboxylic acid (PDA) that shows aggregation-induced emission (AIE) characteristics for thorium recognition with remarkable fluoresence enhancement response has been synthesized. This sensor is capable of visually distinguishing Th(4+) among lanthanides, transition metals, and alkali metals under UV light. Th(4+) can be detected by the naked eye at ppb levels owing to the AIE phenomenon. The sensor showed high selectivity for Th(4+) compared to all other metals tested, and this recognition displayed good anti-interference qualities. This study represents the first application of a AIE fluorescence sensor in actinide metal recognition and it has potential applications in environmental systems for thorium ion detection.

Ratiometric Biosensor for Aggregation-Induced Emission-Guided Precise Photodynamic Therapy

Photodynamic therapy faces the barrier of choosing the appropriate irradiation region and time. In this paper, a matrix metalloproteinase-2 (MMP-2) responsive ratiometric biosensor was designed and synthesized for aggregation-induced emission (AIE)-guided precise photodynamic therapy. It was found that the biosensor presented the MMP-2 responsive AIE behavior. Most importantly, it could accurately differentiate the tumor cells from the healthy cells by the fluorescence ratio between freed tetraphenylethylene and protoporphyrin IX (PpIX, internal reference). In vivo study demonstrated that the biosensor could preferentially accumulate in the tumor tissue with a relative long blood retention time. Note that the intrinsic fluorescence of PpIX and MMP-2-triggered AIE fluorescence provided a real-time feedback which guided precise photodynamic therapy in vivo efficiently. This strategy demonstrated here opens a window in the precise medicine, especially for phototherapy.

Aggregation-Induced Fluorescence Emission Properties of Dicyanomethylene-1,4-dihydropyridine Derivatives

A series of dicyanomethylene-1,4-dihydropyridine (DCMP) derivatives with aggregation-induced emission (AIE) were designed and synthesized. These target compounds emit low fluorescence in THF solutions because of the free rotation of the phenyl and dihydropyridine rings about the axes of the olefinic double bonds and the resultant nonradiative decay process, but they exhibit strong fluorescence in the aggregate state because of the restriction of intramolecular rotation (RIR), as confirmed by solution thickening and cooling experiments. Compared with the almost-planar dicyanomethylene-4H-pyran (DCM) derivative DCM-1 with aggregation-caused quenching (ACQ), DCMP-5 with AIE takes a highly twisted conformation by replacing the oxygen atom of the DCM skeleton with an N-ethyl group, as revealed by crystallographic data and theoretical calculations. Depending on the different electron-donating substituents, the solids of these compounds emit yellow or orange fluorescence. Moreover, the cyano group endows DCMP-5 with a strong self-assembly ability under proper conditions, and the obtained regular microparticles emit bright orange fluorescence. These materials will broaden the new family of AIE-exhibiting fluorophores.