AIE Properties Research Articles

An AIE-active fluorescent probe with near-infrared (NIR) emission for selectively monitoring and bioimaging Cys in living cells

Cysteine (Cys), as a kind of essential bio-thiols, plays a pivotal role in modulating cell metabolism, maintaining intracellular redox balance and facilitating protein synthesis. In order to investigate its role in these physiological processes, fluorescent probe was selected as an important method for selectively detecting Cys. However, most of the probes possess ACQ effect, which limits their applications in the field of biosensing and bioimaging. Herein, an AIE-active fluorescent probe TCF-TPA was synthesized for specifically detecting Cys in HeLa cells. TCF-TPA, consisted of a tricyanofuran (TCF) fluorophore, was modified with an acrylate group for distinguish Cys from other bio-thiols, and the incorporation of electron-donating triphenylamine endowed the probe with AIE property and strong intramolecular charge transfer effect, thereby enabling the probe to have near-infrared (NIR) emission length (666 nm). Meanwhile, TCF-TPA possessed low detection limit for Cys (73.0 nM) and was successfully performed bioimaging of Cys in HeLa cells.

Synthesis and Performance of Imide-Based Small Molecules Containing Carbazole Groups with AIE Properties.

Here, two novel naphthalimide derivatives SNI-Cz and SNI-DCz with AIE were designed and synthesized. The correctness of the two structures was characterized by NMR and HRMS. Their crystal structures, photophysical properties, electrochemical properties, thermal stabilities, fluorescence lifetime and yields have been characterized. Photoluminescence experiments revealed that SNI-DCz had superior properties due to the D-π-A-π-D structure and sliding away stacking of molecules. SNI-DCz exhibited weak fluorescence in pure DMF, with a significant AIE effect observed in the 40% water mixture and a sharp increase in fluorescence intensity was also observed. Cyclic voltammetry and thermogravimetric analysis indicated that SNI-DCz had good electron affinity and thermal stability. The excellent properties of SNI-DCz made it a promising emitter for optoelectronics.

Selective Visualization of Tumor Cell Membranes and Tumors with a Viscosity-Sensitive Plasma Membrane Probe.

Cancer is a worldwide health problem. Revealing the changes in the microenvironment after cell carcinogenesis is helpful to understand cancer and develop sensitive methods for cancer diagnosis. We developed herein a viscosity-responsive plasma membrane probe (TPA-S) that was successfully used to probe the viscosity difference between normal and tumor cell plasma membranes for the first time. The probe shows AIE properties with good water solubility, significant near-infrared (NIR) fluorescence responses to viscosity with high sensitivity, and excellent cell membrane location performance. With these features, our experiments showed that TPA-S could selectively visualize cancer cell plasma membranes, revealing that the plasma membrane of tumor cells is more viscous than that of normal cells. In addition, TPA-S was successfully applied to specifically light up tumors. Altogether, this work explored the changes of cell membrane viscosity after canceration, provided a new method for selective visualization of tumor cells, and opened up a new approach for cancer diagnosis.

Natural Coumarin Isomers with Dramatically Different AIE Properties: Mechanism and Application.

Aggregation-induced emission luminogens (AIEgens) are of great importance in optoelectronics and biomedical fields. However, the popular design philosophy by combining rotors with traditional fluorophores limits the imagination and structural diversity of AIEgens. Inspired by the fluorescent roots of the medicinal plant Toddalia asiatica, we discovered two unconventional rotor-free AIEgens, 5-methoxyseselin (5-MOS) and 6-methoxyseselin (6-MOS). Interestingly, a slight structural difference of the coumarin isomers leads to completely contrary fluorescent properties upon aggregation in aqueous media. Further mechanism investigation indicates that 5-MOS forms different extents of aggregates with the assistance of protonic solvents, leading to electron/energy transfer, which is responsible for its unique AIE feature, i.e., reduced emission in aqueous media but enhanced emission in crystal. Meanwhile, for 6-MOS, the conventional restriction of the intramolecular motion (RIM) mechanism is responsible for its AIE feature. More interestingly, the unique water-sensitive fluorescence property of 5-MOS enables its successful application for wash-free mitochondria imaging. This work not only demonstrates an ingenious tactic to seek new AIEgens from natural fluorescent species but also benefits the structure design and application exploration of next-generation AIEgens.

A unique AIE multi-responsive half-salamo-like fluorescence sensor for temperature, pH and Cu2+/S2- ions in aqueous media

A novel multi-stimulus responsive small molecule fluorescent sensor DHS was developed. DHS with solvent-dependent properties exhibited active AIE effects, which is rare in salamo-like compounds. DHS has an excellent reversible thermal response and pH fluorescence response under various external stimuli (temperature and acid-base conditions). The response mechanism is supported by relevant studies and theoretical calculations. In addition, DHS can be used as a highly selective and sensitive fluorescent probe for the sequential detection of Cu2+ and S2– in water. DHS exhibits very prominent detection limit (48.59 nM) for Cu2+, which is superior to most small molecule fluorescent sensors of the same type. The experiments showed that the sensor DHS can be used for the ions detection in portable test strips and actual water samples. This study reveals a new strategy for the construction of salamo-like compounds with AIE properties, which can be beneficial for research in the fields of temperature sensing, acidity detection and ion recognition.

Dansyl-labelled cellulose as dual-functional adsorbents for elimination and detection of mercury in aqueous solution via aggregation-induced emission

Dansyl chloride fluorophore exhibits typical aggregation induced fluorescence emission behavior in acetone/water solution. To realize the integration of detective and adsorptive functions, dansyl chloride is covalently immobilized on cellulose substrate to fabricate an efficient adsorbent for mercury ions in water. The as-prepared material exhibits excellent fluorescence sensing performance exclusively for Hg (II) with the presence of other metal ions. A sensitive and selective fluorescence quenching across the concentration range of 0.1–8.0 mg/L is observed with a detection limit of 8.33 × 10−9 M as a result of the inhibition of aggregation induced emission caused by the coordination between adsorbent and Hg (II). Besides, the adsorption properties for Hg (II) including the influence of initial concentration and contact time are investigated. Langmuir model and pseudo-second-order kinetics are demonstrated to fit well with the adsorption experiment for the uptake of Hg (II) by the functionalized adsorbent, also, intraparticle diffusion kinetic model is proved to aptly describe the Hg (II) removal in aqueous solution. In addition, the recognition mechanism is considered to originate from the Hg (II) triggered structural reversals of naphthalene ring units which are verified by the X-ray photoelectron spectroscopy and density functional theory calculation. Moreover, the synthesis method used in this work also provides a strategy for the sensing application of organic sensor molecules with AIE properties in which the aggregated behavior could be appropriately realized.

Design, synthesis and performance of novel fluorescent polymer microspheres tracers based on aggregation induced emission

AbstractIn this study, blue fluorescent polymer microspheres tracers are prepared by dispersion polymerization using aggregation induced emission monomers, styrene and sodium vinyl benzene sulfonate as raw materials. The properties of the microspheres are investigated by field emission scanning electron microscopy, fluorescence microscopy and fluorescence spectrum. The results show that N‐(4‐(4‐(1,2,2‐triphenylvinyl)phenoxy)butyl)acrylamide exhibits typical AIE properties in a mixture of water and tetrahydrofuran. The fluorescent polymer microspheres are smooth and monodisperse. Concentration‐dependent experiments indicate that the fluorescence intensity of the fluorescent polymer microspheres increases with the increasing of concentration. In addition, we explore the effects of temperature, pH, and some metal ions on the fluorescent polymer microspheres, and find that the fluorescence intensity is still good under these influencing conditions. We also investigate the stability of the polymer, the fluorescence intensity of the polymer hardly changed during the 30‐day monitoring period, indicating its good stability. Therefore, the above research results indicate that the fluorescent polymer microspheres can be used as potential oilfield tracers.

RAFT-synthesis and self-assembly-induced emission of pendant diphenylalanine-tetraphenylethylene copolymers.

Manipulation of the properties of aggregation-induced emission luminogens (AIEgens) by combining self-assembling motifs has attracted significant interest as a promising approach to developing various advanced materials. In this study, pendant diphenylalanine-tetraphenylethylene (TPE) copolymers exhibiting the ability for self-assembly and AIE properties were synthesized via reversible addition-fragmentation chain-transfer (RAFT) copolymerization. The resulting anionic and non-ionic amphiphilic copolymers with a carbon-carbon main chain bearing diphenylalanine-TPE through-space interactions self-assembled into nanorods and nanofibers, showing blue emissions originating from the aggregation of TPE side chains in the assembled structures. Suitable tuning of the comonomer composition, monomer structure, and environmental conditions (e.g., solvent polarity) enables manipulation of the self-assembled structures, AIE properties, and aggregation-induced circular dichroism by achiral TPE units via through-space interactions with diphenylalanine moieties.

Consecutive cross-dehydrogenative C–O and C–N construction for the synthesis of polyarene with AIE properties under electrochemical condition involving oxygen radical species

Regioselective C–H phenoxylation and azolation of phenol derivativesviaconsecutively O-radical participating pathway and subsequent electro-induced nucleophilic substitution (SNAr) between azoles and phenol derivatives was disclosed.

Construction of supramolecular dimer photosensitizers based on triphenylamine derivatives and cucurbit[8]uril for photocatalysis

We have designed and constructed supramolecular dimers between triphenylamine derivatives with AIE properties and CB[8] through host–guest interactions, which can be used as photosensitizers for photooxidation reactions of thioanisole.

Constructing spin crossover-fluorescence bifunctional iron(II) complexes based on tetraphenyl ethylene-decorated AIEgens.

Investigating spin crossover (SCO)-fluorescence bifunctional materials and establishing their structure-function relationships are attractive topics in chemistry and materials science. However, it remains challenging to preserve the fluorescence and SCO properties simultaneously in aggregated solid states. Herein, we design an (E)-2,6-bis(1H-pyrazol-1-yl)-4-(4-(1,2,2-triphenylvinyl)styryl)pyridine (tpe-bpp) ligand, which contains coordinated SCO and fluorescence units of an aggregation-induced emission luminogen (AIEgen). The coordination of the tpe-bpp ligand with different FeII salts generated three mononuclear complexes: [Fe(tpe-bpp)2](ClO4)2·5.75CH2Cl2 (1), [Fe(tpe-bpp)2](ClO4)2·CH2Cl2·3CH3OH (2) and [Fe(tpe-bpp)2](BF4)2·CH2Cl2·3CH3OH (3). Single-crystal X-ray diffraction studies showed that they shared a similar [Fe(tpe-bpp)2]2+ complex cation. Their counterions and co-crystallized solvents were different. Magnetic measurements revealed that 1, 2, and 3 exhibited a complete SCO behavior with the transition temperatures T1/2 of 375, 260, and 248 K, respectively. Fluorescence measurements confirmed the existence of the AIE property for both the tpe-bpp ligand and Fe(II) complexes. A monotonic decrease of the photoluminescence (PL) intensity upon increasing the temperature was behavior observed for all three complexes.

Effect of different substituents on the fluorescence properties of precursors of synthetic GFP analogues and a polarity-sensitive lipid droplet probe with AIE properties for imaging cells and zebrafish.

The green fluorescent protein (GFP) is a purely natural specialty protein that has been widely used to design synthetic fluorescent probes. In the present work we designed and synthesized a series of fluorescent compounds akin to GFP precursors by a one-step method, and investigated the luminescence properties of the fluorescent compounds by varying the substituents. We presented the first systematic summary of the photophysical data including extinction coefficients and fluorescence quantum yields for this class of fluorescent dyes. We also carried out density functional theory (DFT) calculations for these dyes to investigate the effect of electronic effects due to different substituents. These studied optical properties may provide a reference for later probe design. More interestingly, we have developed a polarity-sensitive lipid droplet probe T-LD with AIE properties on this basis. The probe exhibited not only favorable pH stability and kinetic stability in terms of optical properties, but also solvent discolouration and polarity-sensitive properties, and was able to label intracellular lipid droplets. We successfully applied the probe for intracellular lipid droplet level monitoring and zebrafish imaging.

Donor-acceptor cyanostilbene based nano-AIEgens: Synthesis and properties

Cyanostilbene‐based multiple donor–acceptor substituted compounds (6, 7 & 10a‐c) were synthesized utilizing Suzuki reaction and then characterized. The photophysical properties like absorption, fluorescence, fluorescence lifetime, thermal stability and electrochemical properties have been studied. All the synthesized molecules have shown blue to green light emission in solution phase with low quantum yield (Φfl ∼ 1‐3%), however in the aggregated state they display AIE property. The DLS and SEM studies confirmed the formation of nanostructure in the aggregated state with a particle size of ∼ 58‐395 nm. Biphenyl-based compounds (10a‐c) exhibit a high HOMO value (−5.15 eV for 10c) than TPE- based compounds (6 and 7) (−5.68 eV for 7). They are found to be thermally stable (Tg ∼ 95 °C).

Real-time visualization of the fluctuations in HOBr with AIE fluorescent probes during myocardial ischemia-reperfusion injury.

Two fluorescent probes (QM-S and QM-Se) featuring AIE properties were developed. The increased intracellular hypobromous acid (HOBr) in cardiomyocytes during MIRI was revealed with these probes. It was also observed that MIRI might be alleviated by combating oxidative stress, as well as inhibiting inflammation and ferroptosis, which could mediate oxidative stress.

The effect of substituents on the aggregation-induced emission of 9,10-phenanthraquinone-hydrazones

One-step synthesis of six hydrazone derivatives exhibiting red-shifted absorption is reported. The compounds are red-emissive in their solid state with moderate to high quantum efficiency and show AIE properties, supported by DLS and SEM studies.

A cyclopolymer incorporating tetraphenylethene groups in its cyclic repeating units

Although incorporating AIEgens in versatile polymer topological structures is of high interest, cyclopolymers incorporating AIEgens have rarely been reported yet. In this work, a cyclopolymer incorporating tetraphenylethene groups in its cyclic repeating units (pTPE-dMMA) is synthesized in comparison with a linear polymer with tetraphenylethene pendant side groups (pTPE-MMA). The PLQY of pTPE-dMMA in the solid state is 50.35%, higher than that of pTPE-MMA (32.06%) in the solid state. The AIE behaviors of both pTPE-dMMA and pTPE-MMA in solutions are investigated. Because of the ring-constraint, the PL color of AIE cyclopolymer is not dependent on aggregation, while the PL intensity increases as the increased cyclopolymer concentration or aggregation. Even in an ultra-dilute solution (0.002 mg/mL), pTPE-dMMA exhibits significant AIE performance as the water fraction is increased. The enhanced AIE properties of pTPE-dMMA are ascribed to the ring constraint in the side groups and dense intra-/inter-molecular stacking. This work is useful not only for the designing novel AIE materials or fluorescent dyes, but also for understanding the structure–property–function relationships of a cyclopolymer.

A series of AIE dyes derived from shikimic acid: The thermo/pressure dependent fluorescence and application in the sensing of arginine

Transformation of renewable bio-feedstock to fine chemicals and functional materials are much desirable in chemistry and chemical engineering. Herein, a series of AIE dyes (compounds a-o) with thermo/pressure dependent fluorescence were revealed. Fifteen compounds (a-o) with the ortho-carboxyl diarylamine key structure were obtained from the renewable biomass molecule shikimic acid and ten of them exhibited typical AIE behavior. By changing the substituent groups that might affect the AIE property, the fluorescent emission of the AIE dyes could be changed from white to green or blue. Thermo/pressure dependent fluorescence emission was observed for the tested AIE molecules and the fluorescent intensity changes could be used as a quantified signal for the surrounding temperature. Moreover, substituent moderating effect for the AIE property of compounds a-o was revealed by using DFT calculation. In addition, organic nanoparticle fluorescent probe (ONFP) was prepared based on compound o and used in the selective and sensitive detection of arginine in real water.

A Novel Bifunctional Nanoplatform with Aggregation-Induced Emission Property for Efficient Photodynamic Killing of Bacteria and Wound Healing.

Photodynamic antimicrobial therapy (PDAT) has been extensively studied because of its potential applications such as precise controllability, high spatiotemporal accuracy, and non-invasiveness. More importantly, it is difficult for bacteria to develop resistance to the aforementioned PDATs. However, the selectivity of traditional PDAT methods to bacteria is generally poor, so it has been proposed to introduce positively charged components such as quaternary ammonium salts to enhance the targeting of bacteria; however, they always possess high toxicity to normal cells. As a result, measures should be taken to enhance the targeting of bacteria and avoid side effects on normal cells. In our work, we creatively design a nanoplatform with high anti-bacterial efficiency, low side effects and its size is approximately 121 nm. BSA, as a nanocarrier, encapsulates the photosensitizer (E)-4-(4-(diphenylamino)styryl)-1-methylpyridin-1-ium with AIE properties named as BSA-Tpy, which increases its circulation time in vivo and improves the biocompatibility. Under acidic conditions (pH = 5.0), the surface positive charge of the BSA-Tpy is increased to +18.8 mV due to protonation of amine residues to achieve the targeting effect on bacteria. Besides, under the irradiation of white light, the BSA-Tpy will produce ROS to kill bacteria efficiently about 99.99% for both Gram-positive and Gram-negative bacteria, which shows the potential application value for the treatment of infected wounds. We have developed a feasible method for photodynamic antibacterial therapy, possessing excellent biocompatibility and high antibacterial efficiency with good fluorescence imaging property.

A novel strategy for constructing fluorescent liquid crystals with diphenylacrylonitrile groups derivatives based on Thiazolo[5,4-d]thiazole core

In this work, we reported a new series of multifunctional molecular columnar liquid crystalline phases with different terminal functional groups, MTM-1, MTM-2 and MTM-3. The macromolecule materials exhibited an ordered hexagonal columnar mesophase, high thermal stability, and excellent AIE properties in the THF-H2O system. Furthermore, it has been demonstrated that changing the terminal electronic affects the intermolecular forces and thus has a significant effect on the temperature range of the columnar mesophase. Specifically, the fluorescence quantum yield of MTM-1 in the solid state is as high as 45%. It is worth highlighting that the peripheral electron supply effect is favorable to enhance the fluorescence quantum yield. This work provides a new method for designing and synthesizing novel AIE liquid crystal materials.

A novel turn-on type fluorescent probe with a large red-shift based on TPE for detection of F−

A tetraphenylethylene derivative with AIE properties was successfully synthesized, displayed a large Stokes shift (Δλ = 123 nm) in THF. TBIP could also be used as a turn-on fluorescent probe for fluoride ion recognition, with a large red-shift (101 nm), rapid response, and excellent selectivity. The limit of detection (LOD) was calculated and derived as 0.006 μM in solvent, which was far lower than the maximum pollutant level of fluorine ion in drinking water, and fluorescence color changing from blue-purple to yellow. The application research indicated that the sensor could detect F− in natural water sensitively, and could prepare qualitative test strips for fluorine ion detection.