AIE Mechanism Research Articles

Aggregation-induced emission luminogens for intracellular bacteria imaging and elimination

Intracellular bacterial infections are a serious threat to human health due to their ability to escape immunity and develop drug resistance. Recent attention has been devoted to identifying and ablating intracellular bacteria with fluorescence probes. Aggregation-induced emission luminogens (AIEgens) photosensitizers as fluorescence probes possess excellent photostability and rapid response, which have emerged as powerful fluorescent tools for intracellular bacterial detection and antibacterial therapy. This review is intended to highlight the current advances in AIEgens on intracellular bacteria imaging and elimination, which covers topics from intracellular AIE mechanism, intracellular bacteria imaging of AIEgens to the elimination of intracellular bacteria with AIEgens. AIEgens utilized different interactions to detect intracellular bacteria, emitting bright light due to restricted intramolecular movement to visualize intracellular bacteria. Photosensitive AIEgens generate reactive oxygen species (ROS) in the aggregate state to elimate intracellular bacteria. Moreover, the prospects and application of AIEgens in intracellular bacteria imaging and elimination are also discussed, which provides insights for the development of AIE-based diagnostic and therapeutic materials and technologies.

An easily accessible probe for H2S based on AIE mechanism and its application in cell imaging

Hydrogen sulfide (H2S) is a crucial endogenous gas transmitter, maintaining the redox homeostasis in biological systems. Thus, a real-time and specific H2S detection approach is urgently necessary to study the attack and management of disorders linked to H2S. In this paper, a novel fluorescent probe HMP based on AIE property for the detection of H2S was elaborately conducted. In PBS buffer solution HMP exhibited high photostability, low detection limit (0.82 μM), significant anti-interference ability and fast response time and specificity to H2S. What’s more, it could be employed for the monitoring and luminescent imaging of H2S with Hela cells, thereby broadening the prospective capacity for diagnosing associated diseases.

β-Galactosidase-activated near-infrared AIEgen for ovarian cancer imaging in vivo

Near-infrared (NIR) aggregation induced-emission luminogens (AIEgens) circumvent the noisome aggregation-caused quenching (ACQ) effect in physiological milieu, thus holding high promise for real-time and sensitive imaging of biomarkers in vivo. β-Galactosidase (β-Gal) is a biomarker for primary ovarian carcinoma, but current AIEgens for β-Gal sensing display emissions in the visible region and have not been applied in vivo. We herein propose an NIR AIEgen QM-TPA-Gal and applied it for imaging β-Gal activity in vitro and in ovarian tumor model. After being internalized by ovarian cancer cells (e.g., SKOV3), the hydrophilic nonfluorescent QM-TPA-Gal undergoes hydrolyzation by β-Gal to yield hydrophobic QM-TPA-OH, which subsequently aggregates into nanoparticles to turn NIR fluorescence “on” through the AIE mechanism. In vitro experimental results indicate that QM-TPA-Gal has a sensitive and selective response to β-Gal with a limit of detection (LOD) of 0.21 U/mL. Molecular docking simulation confirms that QM-TPA-Gal has a good binding ability with β-Gal to allow efficient hydrolysis. Furthermore, QM-TPA-Gal is successfully applied for β-Gal imaging in SKOV3 cell and SKOV3-bearing living mouse models. It is anticipated that QM-TPA-Gal could be applied for early diagnosis of ovarian cancers or other β-Gal-associated diseases in near future.

Theoretical insights into the AIE mechanism of assembles

AbstractFluorophores in aggregated state are commonly used in optoelectronic devices, and the molecular packing are complex and diverse, including crystal, amorphous aggregate in solution, thin film, ordered supramolecular assemblies, and highly ordered cell membrane. In addition, the luminous behavior of the aggregated state can be precisely regulated by external stimuli such as hydrostatic pressure. In this review, we summarize the representative progress on the application of multiscale modeling protocol to illustrate the underlying mechanism of fluorescent emission of organic dyes in different assembles. The aim is to obtain the molecular packing in different forms of assembles and then to understand their underlying mechanism of stimuli‐responsive fluorescent behavior at the molecular level. This is essential for the rational design, synthesis, and efficient application of fluorescent dyes.

Phenazine functionalized pillar[5]arene: Synthesis, host-guest property and application in the fluorescence sensing of biogenic amine in solution, gel and air

The development of selective sensing materials for biogenic amine detection has attracted tremendous interest because amines have high toxicity and exist widely. In this paper, phenazine-bridged pillar[5]arene monomers PA and a naphthalene diimide containing neutral guest-bearing alkyl chain binding sites NDI were designed and synthesized. They could self-assemble by host–guest interactions to form a microsphere structure in dilute solution. A series of biogenic amines can selectively quench the microsphere fluorescence. The microsphere structure transformed into the supramolecular polymer gel at relatively high concentrations. More interestingly, the supramolecular polymerization process induced fluorescence emission enhancement based on an AIE mechanism in the gel state. The supramolecular polymer gel material exhibited sensitive stimulus–response behavior owing to stimuli-induced reversible electron transfer in the presence of various amines. The gel soft material collapse could be achieved by fuming under a series of amines vapors. Besides, our results demonstrate an effective material design strategy that may be extended to fluorescence sensing of biogenic amine in solution, gel, and air and applications to detect food spoilage. It is envisaged that this important method would pave the way for overcoming the sensor's application constraints in the solution state.

Tandem detection of aluminum ion and norfloxacin by Au-doped copper nanoclusters based on AIE and coordination reaction

Herein, we proposed a method for dual detection of Al3+ and norfloxacin (NOR) by Au-doped N-acetyl-L-cysteine capped copper nanoclusters (NAC-Cu@AuNCs) following a tandem process. The non-luminescent NAC-Cu@AuNCs was fabricated via a bottom-up reduction method. Under neutral solutions, Al3+ was detected sensitively and selectively based on AIE mechanism. The sensing achieved satisfactory results, displaying a broad linear range from 0.1 µM to 90 µM and a low LOD of 0.15 µM, which is significantly lower than the World Health Organization criterion (7.41 µM). Subsequently, ratiometric sensing of NOR was further successfully realized by Al3+/NAC-Cu@AuNCs via coordination reaction between NOR and Al3+. A good linear relationship was obtained in the range of 0.02–16 µM, with LOD as low as 38.3 nM. This work shows great potential in constructing MNCs as sensors for multifunctional detection by combinatorial principles.

Internal acylation-induced AIE/AIEE switch of pyrimido[2,1-b][1,3]benzothiazoles (PBTs): Restriction of access to dark state caused by distortion of 4H-pyrimidine ring

As atypical propeller-shaped AIEgens, pyrimido[2,1-b][1,3]benzothiazoles (PBTs) exhibit good to excellent solid-state fluorescence quantum yields and full-color tunability. However, the working mechanism of PBT AIEgens still remains elusive. In this article, three internally acylated PBTs (PBT-B7−B9) were synthesized. In agreement with our previous report, locking the exocyclic ester resulted in the emergence of solution-phase fluorescence, i.e. AIE/AIEE switch. Theoretical calculation results indicated that the 4H-pyrimidine ring experiences the most significant electronic structure alterations upon excitation. Comparative analysis of potential energy curves (PECs) and optimized excited-state geometries of both locked and unlocked PBTs revealed that as a cumulative result of bond length/angle changes in 4H-pyrimidine, the distortion of the ring is the direct cause for decoupling of π-conjugated MOs and major driving force for access to the resulting dark state. On the other hand, the restriction of rotation of exocyclic ester or carbonyl in locked PBTs maintains the conformation of 4H-pyrimidine, thereby avoiding the generation of dark state and making them emissive in solution. This AIE mechanism well explained the drastically decreased fluorescence quantum yields of unlocked PBTs in PMMA films, and indicated that locking the exocyclic ester or carbonyl could be an effective strategy to improve their PL performance in polymer matrix.

Design and Synthesis of New Bithiophene Based Planar AIE Red Light Emitters: A Detailed Theoretical and Experimental Analysis**

AbstractBithiophene core with −CN substituted pyrazole and imidazole side chains yielding B1, B2, and B3 have been designed and synthesized viz Schiff's base condensation reaction. Molecules, at their solid‐state exhibited red‐light emission supporting AIE mechanism. The series exhibited the highest relative quantum yield of value 18.66 % by B1 with the lowest recorded for B3 exhibiting 2.4 %. DFT results reveal the synthesized molecules at their optimized ground state adopt a planar structure. Theoretical calculation further validates the molecules to adopt a slip‐stacking type of molecular packing arrangement at its condensed state, conducive for AIE. A large π‐π stacking distance between the lattice plane of 3.4 Å, 3.6 Å and 3.5 Å possessed by B1, B2, and B3 respectively, favors AIE. Computational calculation on electron and hole reorganization energy reveals the effective role of two −CN groups in altering the hole mobility in comparison with the other molecules in the series.

Precise Probe Design Based Esipt Coupled Aie Mechanism Toward Endogenous Cyanide in Food Detection and Bioimaging

Precise Probe Design Based Esipt Coupled Aie Mechanism Toward Endogenous Cyanide in Food Detection and Bioimaging

Facile ACQ-to-AIE transformation via diphenylphosphine (DPP) modification with versatile properties

Diphenylphosphine (DPP) was incorporated facilely into a typical aggregation-caused quenching (ACQ) luminophore to facilitate ACQ-to-AIE transformation. The rapid intersystem crossing process was explored as the DPP-based AIE mechanism.

Aggregation-induced barrier to oxygen-a new AIE mechanism for metal clusters with phosphorescence.

ABSTRACTMetal clusters are useful phosphors, but highly luminescent examples are quite rare. Usually, the phosphorescence of metal clusters is hindered by ambient O2 molecules. Transforming this disadvantage into an advantage for meaningful applications of metal clusters presents a formidable challenge. In this work, we used ligand engineering to judiciously prepare colour-tuneable and brightly emitting Cu(I) clusters that are ultrasensitive to O2 upon dispersion in a fluid solution or in a solid matrix. When the O2 scavenger dimethyl sulfoxide (DMSO) was used as the solvent, joint photo- and oxygen-controlled multicolour switches were achieved for the first time for metal cluster-based photopatterning and photo-anticounterfeiting. More importantly, an aggregation-induced barrier to oxygen, a new aggregation-induced emission mechanism for metal clusters, was proposed, providing a new pathway to realizing the intense emission of metal clusters in the aggregated state. These results are expected to promote the application of metal clusters and enrich the luminescence theory of metal cluster aggregates.

Two-phase activated colorimetric and ratiometric fluorescent sensor for visual detection of phosgene via AIE coupled TICT processes

In this paper, we specifically designed and synthesized an excellent colorimetric and ratiometric fluorescent sensor DPA-CI for rapid and convenient detection of the highly toxic phosgene. DPA-CI was developed by incorporated a diphenylamine (DPA) and a 2-imine-3-benzo[d]imidazole as the enhanced push–pull electronic structure into the coumarin fluorophore matrix. The sensor DPA-CI towards phosgene sensing exhibited both visible colorimetric and ratiometric fluorescent color change in solution and in gaseous conditions with TICT and AIE mechanism respectively, which can be easily distinguished by using the naked eye. Also, the sensor DPA-CI showed splendid sensing performance such as excellent selectivity, rapid response (less than 8 s in THF and 2 min in gaseous condition), and fair sensitivity (limit of detection less than 0.11 ppm in gaseous condition and 0.27 μM in solution). The design strategy based on enhanced push–pull electronic structure with AIE and TICT properties will be helpful to construct a solid optical sensor with excellent potential application prospects for portable and visual sensing of gaseous phosgene through distinct color and ratiometric fluorescence change by the naked eyes.

Bio-inspired AIE pillar[5]arene probe with multiple binding sites to discriminate alkanediamines.

Two functionalized pillar[5]arenes (H1 and H2) with significant AIE properties were synthesized. H2 is an excellent probe to selectively detect specific alkanediamines owing to its multiple binding sites, which result in the enhancement of emission based on the AIE mechanism and the induced-fit mechanism, and provides a new strategy to develop probes with high selectivity and sensitivity.

“Turn-on” fluorescent sensor for Th4+ in aqueous media based on a combination of PET-AIE effect

Previously reported fluorescent sensors for Th4+ experienced emission quenching or generated false positive signal upon aggregate formation in aqueous media. Herein, a simple and novel thorium sensor (CDB-BA) based on cyanodistyrene structure was designed and synthesized, which integrated the highly emitting characteristic of AIE effect and off-on response of PET modulation for the first time to construct the “turn-on” fluorescent probe for Th4+. Besides excellent selectivity, CDB-BA exhibited remarkable fluorescent enhancement which was linearly related to the concentration of Th4+ in the range of 0.25–8 μM. The detection limit was attained 0.074 μM, which was lower than that of most previously reported sensors. The mechanism of tris-chelate complex of CDB-BA with Th4+ was confirmed by mass spectra, IR spectra and DFT calculation. The excellent Th4+ sensing ability of CDB-BA was successfully applied to detecting Th4+ on TLC plates, in real water samples and living-cell imaging. This work suggested that the combination of AIE and PET photophysical mechanism could offer the merits of minimized background and enhanced signal fidelity to develop novel “turn-on” fluorescent probe in complicated aqueous environment and biological research.

Sugar-Based Aggregation-Induced Emission Luminogens: Design, Structures, and Applications.

Sugars are abundant natural sources existing in biological systems, and bioactive saccharides have attracted much more attention in the field of biochemistry and biomaterials. For better understanding of the sugar-based biomaterials and biological sciences, aggregation-induced emission luminogens (AIE-gens) have been widely employed for detection, tracing, and imaging. This review covers the applications of AIE molecules on sugar-based biomaterials by three parts, polysaccharide, oligosaccharide, and monosaccharide, mainly focusing on saccharide detection, stimuli response materials preparation, bioimaging, and study of the AIE mechanism. These excellent works suggest the promising future of the sugar-based AIE bioconjugates, considering that the naturally designed and elaborately functionalized saccharides play discriminate roles in biological processes and AIE-tagged species may work as an indicator in each case. However, there are a lot of sugar-based biological species that have not been touched, such as mucopolysaccharides and glycoproteins on the cell surface and in the cell plasma. Based on these features, we enthusiastically look forward to more glorious developments in this bright research area.

Discrimination of Pd0 and Pd2+ in solution and in live cells by novel light-up fluorescent probe with AIE and ESIPT characteristics

A novel and simple light-up fluorescent probe (PASPy-al) with a D-π-A structure based on AIE as well as ESIPT processes was designed for highly selective discrimination of Pd2+ and Pd0. PASPy-al displayed a large Stokes shift (95 nm), a high light-up ratio (116 fold) and a low limit of detection (LOD: 96 nM) toward Pd0. Moreover, the practical applications of PASPy-al for detection of Pd0 in environmental, human urine and pharmaceutical samples were realized, indicating the unique advantages of designing anti-ACQ fluorescent probes based on AIE and ESIPT mechanism. Fluorescence imaging of Pd0 in live cells was realized by using PASPy-al. Furthermore, imaging of Pd0 generation in live cells was also realized by in situ reduction of Pd2+ to Pd0 in the presence of reducing agent like CO, indicating the potential ability of this probe for further fluorescent imaging of cellular reducing agent. The easy preparation of probe PASPy-al plus their excellent parameters would make it a simple to handle probe for detection of Pd0 both in practical samples and in live cells. Elsevier B.V. All rights reserved.

Recent Advances in the Z/E Isomers of Tetraphenylethene Derivatives: Stereoselective Synthesis, AIE Mechanism, Photophysical Properties, and Application as Chemical Probes.

Focused research on the Z/E isomers of tetraphenylethene (TPE) derivatives is scarce in comparison with the thousands of luminogens with AIE properties (AIEgens) that have been synthesized based on the TPE moiety. The similar chemical and physical properties of the Z/E isomers make them difficult to separate by using conventional chromatographic techniques. However, they can be isolated by introducing polar groups and the pure isomers exhibit very different photophysical properties, mechanochromism, and host-guest coordination, as well as assisting in deciphering the AIE mechanism. In this Minireview, we present an overview of the disagreement regarding the AIE mechanism between the restriction of intramolecular vibration and photoinduced Z/E isomerization. Then, we discuss the development of (Z)-/(E)-TPE derivatives, their use in host-guest detection, and their mechanoluminescence properties, with a focus on their photophysical characteristics. Finally, we explore the stereoselective synthesis of pure (Z)-/(E)-TPE derivatives.

Exceptional aggregation-induced emission from one totally planar molecule

Planar molecules usually display aggregation-caused quenching (ACQ). Here, it was found that a completely planar organic compound, 5,7,12,14-tetraoxapentacene A-D-A triad with carbon-oxygen bonds, had no fluorescence in high polar solvents but emitted strong light in suspension and in solid state, showed typical AIE effect. One novel AIE mechanism was disclosed by molecular packing in crystal state. In addition, its exceptional AIE effect showed great potential applications in fluorescent thermometer and highly sensitive sensor for selective detection of nitrophenolic compounds. The detection limit for 2,4,6-trinitrophenol was low to 0.168 nM.

A nitro-capped tetraaniline derivative with AIE features for BSA detection and the selective imaging of Gram-positive bacteria

A nitro-capped tetraaniline derivative (NO2-B3-Ani4-NO2) with AIE feature was synthesized and characterized, which presented an ultrasensitive turn-on response towards bovine serum albumin and selective imaging of Gram-positive bacteria based on AIE mechanism.

Novel Hydrogen-Bonding Cross-Linking Aggregation-Induced Emission: Water as a Fluorescent “Ribbon” Detected in a Wide Range

The development of efficient sensors for detection of the water content in a wide detection range is highly desirable for balance in many industrial processes and products. Presented herein are six novel different substituted Schiff base Zn(II) complexes, which exhibit the remarkable capability to detect traces of water in a wide linear range (most can reach 0-94%, v/v), low detection limit of 0.2% (v/v), and rapid response time of 8 s in various organic solvents by virtue of an unusual water-activated hydrogen-bonding cross-linking AIE (WHCAIE) mechanism. As a proof-of-concept, the WHCAIE mechanism is explained well by single X-ray diffraction, absorption spectra, fluorescence spectra, dynamic light scattering, 1H NMR spectra, and theoretical calculations. In addition, the molecules demonstrated their application for the detection of humidity (42-80%). These Schiff base Zn(II) complexes become one of the most powerful water sensors known due to their extraordinary sensitivity, fast response, and wide detection range for water.