Excellent Aggregation-induced Emission Research Articles

Coumarin-Based ACQ-AIE Conversion Photosensitizer for Mitochondrial Imaging and Synergistic Cancer Therapy.

Most of the traditional fluorescent molecules have the advantages of high fluorescence quantum yield, good stability, and excellent structural adjustability, but they exhibit the characteristics of fluorescence quenching caused by aggregation, which restricts their application in aqueous solutions or solids. The excellent luminescence properties and photosensitive potential of aggregation-induced emission (AIE) materials in a condensed state have made them widely concerned in the scientific research field, so it is very challenging to regulate the transformation of traditional aggregation-caused quenching (ACQ) fluorophores into AIE fluorophores. In this study, the traditional coumarin fluorophore was used as a matrix. After conjugating the triphenylamine AIE group, the triphenylphosphine cation was linked through the alkyl chain to obtain a molecular probe NCTPP with excellent AIE characteristic, water solubility, mitochondrial green light imaging, chemotherapy and photodynamic therapy capabilities. As far as we know, it was the first time that the photosensitivity of coumarin fluorescent molecules was imparted by the ACQ-AIE conversion method.

Synthesis and Aggregation-Induced Emission Properties of New Carbazole-Based Pyranones and their Ring-Transformed Derivatives

AbstractA new series of N-phenyl-carbazole (N-phCbz) appended pyranones were designed and synthesized using α-oxo-ketene-S,S-acetal under mild reaction conditions in good yields. The reactivity of donor-acceptor (D-A)-based 2H-pyranones was utilized to develop their ring-transformed benzene-cored N-phenyl-carbazole derivatives. All the synthesized carbazole-based pyranones showed aggregation-induced emission (AIE) characteristics in 80–99% water fraction (f w) in DMSO. Among all the synthesized compounds, 6-(4-(9H-carbazol-9-yl)phenyl)-4-(methylthio)-2-oxo-2H-pyran-3-carbonitrile exhibited excellent AIE behavior with ca. 70-fold increase in fluorescence in 80% fw at 550nm. Furthermore, this compound showed exceptionally high fluorescence in nonpolar solvent (THF) as compared to polar solvents such as DMSO (ca. 200-fold increase in fluorescence). The DFT, DSC, and TGA analyses of the synthesized D-π-A compounds suggested the strong electron-donor ability of N-phCbz, with good thermal stability in the range of 231–393 °C. These N-phenyl-carbazole-appended pyranones with interesting AIE properties have great potential as probes for bioimaging applications as well as for optoelectronic materials.

Tumor targeting pH-triggered fluorescence-switchable hyaluronic acid-based micelles with aggregation-induced emission activity for tracing drug release and intelligent drug delivery

In this study, an amphiphilic polymer (Bio-HA(TPE-CN)-mPEG) was designed and synthesized, which was fabricated by introducing hydrophobic aggregation-induced emission (AIE) fluorophore, acid-labile imine bond, methoxy poly (ethylene glycol) (mPEG) and tumor targeting ligand biotin to the backbone of hyaluronic acid. The polymer could self-assemble into micelles and solubilize hydrophobic anticancer drugs. In vitro drug release study indicated that the micelles could disassemble rapidly under acidic environment. The involvement of biotin and HA could enhance the cellular uptake of micelles by tumor cells. Modification of micelles by mPEG could minimize non-specific protein adsorption. Fluorescence studies indicated that the micelles exhibited excellent AIE features and emitted intense long-wavelength fluorescence. More excitingly, the micelles were red emissive in the normal physiological environment, but switched to blue fluorescence in the acidic tumor environment, which could be further applied for real-time monitoring and quantification of the drug release. The in vivo antitumor efficacy study demonstrated the superior antitumor activity of the PTX-loaded micelles. The Bio-HA(TPE-CN)-mPEG micelles were promising drug carriers for chemotherapy and bioimaging.

Novel triphenylamine-pyrene-based AIEgens: Specific detection and imaging of H2O2 in aqueous solution and cells

H2O2 plays a key regulatory role as a bioendogenous reactive oxygen species in cells and organisms. However, excessive production or accumulation of H2O2 during mitochondrial oxidative stress may lead to oxidative damage of cellular proteins and trigger rheumatic diseases, cancers, and a variety of neurodegenerative disorders such as Alzheimer's disease and Parkinson's disease. In addition, H2O2 is a very useful chemical widely employed in the textile and chemical industries, and its excessive emission not only pollutes the environment but also jeopardizes human health. Therefore, the sensitive and specific detection and removal of H2O2 is important for early diagnosis of diseases, treatment prognosis and environmental pollution monitoring. We have designed two novel triphenylamine-based AIEgens MOTPP and MOTPP-B, which each have a high solid-state fluorescence quantum yield and excellent aggregation-induced emission properties. MOTPP-B has high selectivity and anti-interference ability toward H2O2, a wide pH tolerance range, a sensing process that is complete in under 40 min, and a low detection limit of 120.77 nM. It has been successfully applied for the detection of low concentrations of H2O2 in the environment and to dual-channel imaging of low concentrations of exogenous H2O2 in living cells.

Novel biocompatible N-rich AIE fluorescent probe for live cell imaging and visual onsite detection of uranium.

A sensitive and biocompatible N-rich probe for rapid visualuranium detectionwas constructed by grafting two trianiline groups to 2,6-bis(aminomethyl)pyridine. Possessing excellent aggregation-induced emission (AIE) property and the advantages to form multidentate chelate with U selectively, the probe has been applied successfully to visualize uranium in complex environmental water samples and living cells, demonstrating outstanding anti-interference ability against large equivalent of different ions over a wide effective pH range. A large linear range (1.0 × 10-7-9.0 × 10-7mol/L) and low detection limit (72.6nmol/L, 17.28ppb) were achieved for the visual determination of uranium. The recognition mechanism, photophysical properties, analytical performance and cytotoxicity were systematically investigated, demonstrating highpotential for fast risk assessment of uranium pollution in field and in vivo.

GFP chromophore derived amphiphiles containing [12]aneN3 and biotin moieties as bio-imaging and targeting nonviral gene vectors

Gene therapy is a promising treatment, that brings the necessary opportunity to cure human genetic and major diseases, but it is hampered by the lack of safe and efficient gene delivery vectors. In this study, four amphiphiles were derived from GFP chromophore benzylimidazolidinone (G) through modifications with oxypropyl (1) or methylene (2) linked di(triazole-[12]aneN3) (M) in the presence or absence of tumor-targeting biotin (B) moiety, GMB-1/2 and GM-1/2. The four compounds showed excellent aggregation-induced emission (AIE) characteristics, strong DNA condensation abilities, and good biocompatibility. Among them, GMB-1, which containing targeting biotin moiety and a flexible propoxy linker, showed the highest transfection efficiency in three cell lines. The luciferase transfection efficiency of GMB-1 was as high as 15.2 times that of Lipofectamine 2000 (Lipo2000) without auxiliary lipid DOPE, and its gene therapy effect of delivering the p53 gene was also significantly better than that of Lipo2000 in HeLa cells due to its obvious targeting property. Fluorescence tracing experiments indicated that GMB-1 was able to quickly carry DNA into cells, to successfully escape from lysosomes, then to release DNA, and at last to smoothly deliver DNA into the nucleus. Moreover, its EGFP transfection efficiency in zebrafish reached 1.7 times that of Lipo2000. The excellent performance of GMB-1 demonstrated that the appreciative incorporation of GFP chromophore, di(triazole-[12]aneN3), and biotin moieties into the nonviral gene vectors provided a promising strategy for their clinical applications.

Donor-Acceptor Assembly of Amphiphilic Molecules Based on 9,10-Distyrylanthracene Derivatives with Terminal Naphthalene Groups.

Amphiphilic rod-coil compounds have excellent photophysical properties and can be assembled into supramolecular nanostructures of different sizes in water or polar solvents. Herein, we synthesized the amphiphilic compounds 2N-DSA, 4N-DSA, and 6N-DSA with 9,10-distyrylanthracene (DSA) as the core and a naphthalene unit as the terminal group that connected DSA through a tetraethylene glycol chain. These compounds have excellent aggregation-induced emission (AIE) properties in aqueous solution and are assembled into worm-like fragments or different sizes of spherical assemblies, defending the volume ratio of the rod to coil segments. Notably, the donor-acceptor interaction between DSA and electron- deficient compounds 2,4,6-trinitrophenol (TNP), 2,4,5,7-tetranitrofluorenone (TNF), and tetraethylene glycol dinitrobenzoate (TGDNB) forms a charge transfer complex, which can be used as a nanoreactor to improve the yield of the Suzuki coupling reaction about 8-10 times. The experimental results reveal that the synergy effect of the donor-acceptor, intermolecular π-π stacking, and hydrophobic-hydrophilic interactions significantly influences the morphology of aggregates and the efficiency of the nanoreactor.

Excimer emission from polycyclic arenes bearing triphenylmethyl group: Solid-state fluorescence, mechanofluorochromism, aggregation-induced emission and cell imaging application

The excimer emission based on discrete π-stacked dimers of polycyclic π-systems has generated significant interest in the structure-luminescence relationship of excimers owing to their ultra-large Stokes shift. Herein, a series of excimer emissive luminogens were obtained by conjugating different polycyclic aromatic aldehydes (anthraldehyde, pyrenealdehyde and perylenealdehyde) with triphenylmethylamine. In crystalline states, all the molecules were arranged in the form of π-stacked arene dimers which were spatially isolated from each other by the bulky triphenylmethyl groups, and thus emitted bright excimer emission. The anthracene and pyrene derivatives showed fluorescence enhancement responses to grinding and the enhanced fluorescence could recover to the original state upon heating. The aggregation-induced emission (AIE) properties of them were dependent on the shapes and sizes of the polycyclic aromatic groups. The pyrene derivative showed the most excellent excimer-based AIE behavior among them. All of them were more apt to exhibit the excimer emission when formed nanoparticles with pluronic F-127 than that without pluronic F-127. Furthermore, PETP was utilized for bioimaging of living Hela cells and the high-resolution image was observed.

Molecular engineering of AIE-active boron clustoluminogens for enhanced boron neutron capture therapy.

The development of boron delivery agents bearing an imaging capability is crucial for boron neutron capture therapy (BNCT), yet it has been rarely explored. Here we present a new type of boron delivery agent that integrates aggregation-induced emission (AIE)-active imaging and a carborane cluster for the first time. In doing so, the new boron delivery agents have been rationally designed by incorporating a high boron content unit of a carborane cluster, an erlotinib targeting unit towards lung cancer cells, and a donor-acceptor type AIE unit bearing naphthalimide. The new boron delivery agents demonstrate both excellent AIE properties for imaging purposes and highly selective accumulation in tumors. For example, at a boron delivery agent dose of 15 mg kg-1, the boron amount reaches over 20 μg g-1, and both tumor/blood (T/B) and tumor/normal cell (T/N) ratios reach 20-30 times higher than those required by BNCT. The neutron irradiation experiments demonstrate highly efficient tumor growth suppression without any observable physical tissue damage and abnormal behavior in vivo. This study not only expands the application scopes of both AIE-active molecules and boron clusters, but also provides a new molecular engineering strategy for a deep-penetrating cancer therapeutic protocol based on BNCT.

Kilogram-scale synthesis of carbon dots with high-efficiency full-color solid-state fluorescence using an aggregation-induced emission strategy

Carbon dots (CDs), one of the most promising luminescent nanomaterials, have attracted widespread concern due to their unique optoelectronic properties and widespread application. However, mass production of solid-state CDs with highly efficient full-color emission has rarely been reported, severely limiting their practical application in solid-state lighting and displays. Here, using an aggregation-induced emission (AIE) strategy, full-color solid-state fluorescent (SSF) CDs with quantum yields (QYs) of up to 55.3–27.9% have been prepared on a kilogram scale through one-step microwave-assisted pyrolysis of the same precursors. Detailed structure–property studies demonstrate that the SSF of CDs is derived from the suppression of surface carboxyl group motions and the decrease of the non-radiative rate in their aggregated state, and that their tunable emission is attributed to the excessive fluorescence resonance energy transfer (FRET) induced by the increasing number of aromatic rings on CD surfaces. Therefore, these CDs exhibit both the AIE enhancement and red shift throughout the entire visible spectrum in the solid state. Finally, because of their excellent AIE properties, these highly efficient SSF CDs have been applied to pattern encryption, large-area luminescent fibrous membranes (LFMs), light-emitting diodes (LEDs), and fingerprint detection.

3-Pyridylazoindole derivatives as photoswitches: Synthesis, photoswitching behavior research, and applied to “on–off” fluorescence sensor for Cu2+ combined with theoretical calculations

In order to exploit the compounds with excellent photoswitching properties, a series of 3-pyridylazoindole derivatives were designed and synthesized. The molecular structures were characterized via1H and 13C NMR, the structure of typical compound A6 was also confirmed via single crystal X-ray diffraction. This series of 3-pyridylazoindole derivatives had outstanding characteristics compared with traditional azo photoswitches, such as the red-shifted of maximum absorption wavelength, UV/vis light isomerization in both directions (PSScis: 45–78%; PSStrans: 47–98%) can be achieved easily and broad range of trans-isomer thermal half-lives from minutes to days (0.44–38.4 h). The relationship between structure and properties verified that the photoswiching behavior of azo photoswitches was closely related to the conjugation groups and electronic effects modifying groups. Besides, the frontier molecular orbital and differences of spatial structure calculated by density functional theory (DFT) further explained the performance characteristics of photoswitches. What more, the compound A7 exhibited excellent aggregation-induced emission (AIE) property and could also be used as selective “on–off” fluorescence sensor for Cu2+, which expanded the photochemical properties of 3-pyridylazoindole derivatives.

Multistimuli-responsive fluorescence behaviours of aggregation-induced emission small-molecule and electrospun nanofibre films for acid-base vapour sensing.

Multistimuli-responsive fluorescent materials have garnered great research interest benefited from their practical applications. Two twisted-structure compounds containing tetraphenylethylene (TPE) as the aggregation-induced emission (AIE) group and a pyridine unit as the acid reaction site to obtain new multistimuli-responsive fluorescent compounds (namely, TPECNPy: TPECNPy-2 and TPECNPy-3) were successfully synthesized through a one-step Knoevenagel condensation reaction. The multiple-stimuli response process of TPECNPy was investigated by means of photoluminescence (PL) spectra and emission colour. The results showed that both TPECNPy compounds with excellent AIE abilities displayed reversible emission wavelength and colour changes in response to multiple external stimuli, including grinding-fuming by CH2 Cl2 or annealing and HCl-NH3 vapour fuming. More importantly, fluorescent nanofibre films were prepared by electrospinning a solution of TPECNPy mixed with cellulose acetate (CA), and these exhibited reversible acid-induced discolouration, even with only 1wt% TPECNPy. The results of this study may inspire strategies for designing multistimuli-responsive materials and preparing fluorescent sensing nanofibre films.

Visible light-triggered acceptor-acceptor type dithienylethene with aggregation-induced emission for NIR photochromism in aqueous media

Photochromic dithienylethene (DTE) derivatives with aggregation-induced emission (AIE) performance are appealing for photoelectric functional materials and photopharmacology. However, they often have to be triggered by ultraviolet light to induce photoisomerization, severely limiting their potential applications in biological systems. Herein, a novel acceptor (A)-acceptor (A) type DTE derivative (CNSDTE) has been rationally designed and prepared, in which the cyanostilbene moieties as strong electron-withdrawing groups are incorporated into both sides of DTE skeleton. Its chemical structure is fully verified by 1H NMR, 13C NMR and HRMS. Upon alternating irradiation of visible and near-infrared light, CNSDTE shows excellent photochromic properties in toluene, chloroform and DMSO. Before irradiation with visible light, AIE properties and solid state luminescence behavior are observed. Furthermore, CNSDTE-loaded nanoparticles (CNSDTE NPs) are facilely fabricated by taking the amphiphilic Pluronic F127 as the encapsulating matrix. The as-prepared CNSDTE NPs display excellent photoswitching behavior in aqueous media. The experimental results of the excellent AIE properties and photoswitching behaviors in the various media is also confirmed by DFT calculations. In short, it may be employed in functional biomaterials as a novel visible light-triggered fluorescence switch with AIE features.

High solid-state CPL active materials based on chiral BINOL-dicyanodistyrylbenzene

Herein, we synthesized a pair of aggregation-induced emission (AIE) chiral fluorescence materials (R/S-BIN-Cyn enantiomers). The enantiomers were constructed by connecting a typical AIE molecule to a chiral 1,1′-bi-2-naphthol (BINOL) with ether linkages. The obtained enantiomers exhibited excellent AIE properties and unique state circularly polarized luminescence (CPL) behavior. Specifically, the enantiomers were CPL-active in the solid film with a high glum value of −1.1 × 10−1/+1.2 × 10−1. The CPL and circular dichroism (CD) spectra showed that chirality transfer was achieved from the chiral BINOL to the achiral AIE molecule. The present study is expected to provide a new perspective for preparing chiral luminescent devices with solid-state CPL active.

Controllable Aggregation-Induced Emission and Förster Resonance Energy Transfer Behaviors of Bistable [c2] Daisy Chain Rotaxanes for White-Light Emission and Temperature-Sensing Applications.

Bistable [c2] daisy chain rotaxanes with respective extended and contracted forms of [c2]A and [c2]B containing a blue-emissive anthracene (AN) donor and orange-emissive indandione-carbazole (IC) acceptor were successfully synthesized via click reaction. Tunable-emission bistable [c2] daisy chain rotaxanes with fluorescence changes from blue to orange, including bright-white-light emissions, could be modulated by the aggregation-induced emission (AIE) characteristics and Förster resonance energy transfer (FRET) processes through altering water fractions and shuttling processes (i.e., acid/base controls). Accordingly, as a result of excellent fine-tuning AIE (at 60% water content of H2O/THF) and FRET (with a compatible energy transfer of EFRET = 33.2%) behaviors after the shuttling process (by adding base), the brightest white-light emission at CIE (0.31, 0.37) with a quantum yield of Φ = 15.64% was obtained in contracted [c2]B with good control of molecular shuttling to possess higher photoluminescence (PL) quantum yields and better energy transfer efficiencies (i.e., the manipulation of reduced PET and enhanced FRET processes) due to their intramolecular aggregations of blue AN donors and orange IC acceptors with a proper water content of 60% H2O. Furthermore, dynamic light-scattering (DLS) and time-resolved photoluminescence (TRPL) measurements, along with theoretical calculations, were utilized to investigate and confirm AIE and FRET phenomena of bistable [c2] daisy chain rotaxanes. Especially, both bistable [c2] daisy chain rotaxanes [c2]A and [c2]B and noninterlocked monomer M could be exploited for the applications of ratiometric fluorescence temperature sensing due to the temperature effects on the AIE and FRET features. Based on these desirable bistable [c2] daisy chain rotaxane structures, this work provides a potential strategy for the future applications of tunable multicolor emission and ratiometric fluorescence temperature-sensing materials.

Rational Design of High-Performance Hemithioindigo-Based Photoswitchable AIE Photosensitizer and Enabling Reversible Control Singlet Oxygen Generation

A photosensitizer furnishing with reversible control singlet oxygen generation (1O2) is highly desirable for precise photodynamic therapy (PDT), lessening non-specific harm to healthy tissues. Here, a novel photoswitchable aggregation-induced emission (AIE) photosensitizer based on a triarylamine (TPA)-modified hemithioindigo (HTI), 6Br-HTI-TPA-OMe, was rationally designed. The triarylamine AIE photosensitizing moiety and HTI switch unit were covalently linked in one molecule, permitting reversible regulation of 1O2 production. The photophysical evaluations revealed that 6Br-HTI-TPA-OMe possessed excellent AIE properties and Z/E photoswitch performance in different solvents. Additionally, the amphiphilic phospholipid-fabricated nanoparticles (NPs) also exhibited photochromic behavior in water. The Z-NPs initiated the generation of 1O2 upon 520 nm light-emitting diode (LED) irradiation, but after switching to E-NPs, the generation of 1O2 was inhibited by the competitive energy transfer, suggesting that reversible Z/E isomerization could photocontrol 1O2 generation. The in vitro anti-tumor experiment verified that the 6Br-HTI-TPA-OMe can act as a photoswitchable AIE photosensitizer. This is the first report on the photoswitchable AIE photosensitizer of HTI-based molecules, to the best of our knowledge.

A supramolecular artificial light-harvesting system based on a luminescent platinum(II) metallacage.

A trigonal luminescent metallacage was constructed by the coordination-driven self-assembly of m-pyridine-modified tetraphenylene ligands with organic Pt(II) acceptors, which exhibited excellent Aggregation-Induced Emission (AIE) properties. An efficient artificial light-harvesting system was successfully constructed by selecting the metallacage as the donor and the hydrophobic fluorescent dye Nile Red (NiR) as the donor molecule in a system of acetone/water (1/9, v/v), The absorption spectra of NiR and the emission spectra of the metallacage showed considerable overlap, achieving energy transfer from the metallacage to NiR.

Tetrakis(4-pyridylphenyl)ethylene-based Zinc Metal-Organic Framework with Aggregation-Induced Chemiluminescence Emission on a Paper Platform for Formaldehyde Detection in Breath.

Volatile formaldehyde (FA) in exhaled breath (EB) is considered as a biomarker for lung cancer (LC). On-the-spot selective and sensitive detection of gaseous FA is rather important for LC screening and diagnosis. Herein, a tetrakis(4-pyridylphenyl)ethylene (Py-TPE)-based zinc metal-organic framework (MOF) with excellent aggregation-induced emission (AIE) property was utilized for absorption and selective detection of FA in EB. The porous Zn-Py-TPE served as a gaseous confinement cavity for the adsorption of FA in EB. Interestingly, Zn-Py-TPE was aggregated on paper, and then aggregation-induced chemiluminescence (CL) emission can be triggered by only adding bis(2,4,6-trichlorophenyl)oxalate (TCPO). Though without H2O2, the CL of Zn-Py-TPE-TCPO was enhanced greatly by FA. FA promoted the aggregation of Zn-Py-TPE on paper by forming halogen bonding between FA and Zn-Py-TPE, which contributed to the better selectivity. FA can also stimulate the production of more singlet oxygen (1O2) in the Zn-Py-TPE-TCPO CL system. Hence, FA could be detected via the proposed Zn-Py-TPE-TCPO system with a quantification linear range of 1.0-100.0 ppb and detection limit of 0.3 ppb. This portable, low-cost, and sensitive paper-based platform can achieve trace FA detection in EB and is expected to provide an on-the-spot screening platform for lung cancer.

Theoretical insights on the luminescent mechanism of a highly efficient green-activated delayed fluorescence emitter using the QM/MM method

The solid-state effect plays an important role in excited-state dynamics and luminescence properties of thermally activated delayed fluorescence (TADF) materials. Here, the luminescent mechanism of two novel TADF emitters, PPZTPI and PPZPPI, with aggregation-induced emission (AIE) features are theoretically studied based on the first-principles calculations. The polarisable continuum model (PCM) and the combined quantum mechanics and molecular mechanics (QM/MM) method are used to simulate the solvent environments in toluene and the solid-state effects, respectively. Our results show that both PPZTPI and PPZPPI exhibit excellent TADF and AIE properties with similar but not identical luminescence mechanisms. In the solid state, the delayed fluorescence emission of the two molecules mainly depends on the two-step reverse intersystem crossing process. The molecular radiation rates increase by 1–2 orders of magnitude due to the enhancement of intermolecular interactions in the aggregation. For PPZTPI, the solid-state environment exerts a greater influence on the molecular geometry and electronic structure, non-radiative transitions, excited state dynamics, and emission mechanism due to the substitution of tert-butyl groups and their induced steric hindrance effects. Our theoretical study reasonably elucidates the experimental results and provides valuable information for designing high-efficient AIE-TADF emitters.

An unexpected fluorescent emission of anthracene derivatives in the solid state

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