Aggregation-induced Emission Active Molecules Research Articles

Engineered Multifunctional Zinc-Organic Framework-Based Aggregation-Induced Emission Nanozyme for Accelerating Spinal Cord Injury Recovery.

Functional recovery following a spinal cord injury (SCI) is challenging. Traditional drug therapies focus on the suppression of immune responses; however, strategies for alleviating oxidative stress are lacking. Herein, we developed the zinc-organic framework (Zn@MOF)-based aggregation-induced emission-active nanozymes for accelerating recovery following SCI. A multifunctional Zn@MOF was modified with the aggregation-induced emission-active molecule 2-(4-azidobutyl)-6-(phenyl(4-(1,2,2-triphenylvinyl)phenyl)amino)-1H-phenalene-1,3-dione via a bioorthogonal reaction, and the resulting nanozymes were denoted as Zn@MOF-TPD. These nanozymes gradually released gallic acid and zinc ions (Zn2+) at the SCI site. The released gallic acid, a scavenger of reactive oxygen species (ROS), promoted antioxidation and alleviated inflammation, re-establishing the balance between ROS production and the antioxidant defense system. The released Zn2+ ions inhibited the activity of matrix metalloproteinase 9 (MMP-9) to facilitate the regeneration of neurons via the ROS-mediated NF-κB pathway following secondary SCI. In addition, Zn@MOF-TPD protected neurons and myelin sheaths against trauma, inhibited glial scar formation, and promoted the proliferation and differentiation of neural stem cells, thereby facilitating the repair of neurons and injured spinal cord tissue and promoting functional recovery in rats with contusive SCI. Altogether, this study suggests that Zn@MOF-TPD nanozymes possess a potential for alleviating oxidative stress-mediated pathophysiological damage and promoting motor recovery following SCI.

Recent Advances in Aggregation-Induced Emission Active Materials for Sensing of Biologically Important Molecules and Drug Delivery System.

The emergence and development of aggregation induced emission (AIE) have attracted worldwide attention due to its unique photophysical phenomenon and for removing the obstacle of aggregation-caused quenching (ACQ) which is the most detrimental process thereby making AIE an important and promising aspect in various fields of fluorescent material, sensing, bioimaging, optoelectronics, drug delivery system, and theranostics. In this review, we have discussed insights and explored recent advances that are being made in AIE active materials and their application in sensing, biological cell imaging, and drug delivery systems, and, furthermore, we explored AIE active fluorescent material as a building block in supramolecular chemistry. Herein, we focus on various AIE active molecules such as tetraphenylethylene, AIE-active polymer, quantum dots, AIE active metal-organic framework and triphenylamine, not only in terms of their synthetic routes but also we outline their applications. Finally, we summarize our view of the construction and application of AIE-active molecules, which thus inspiring young researchers to explore new ideas, innovations, and develop the field of supramolecular chemistry in years to come.

Discotic liquid crystals with aggregation-induced emission properties based on tetraphenylethylene and triphenylene derivatives

A novel aggregation-induced emission active molecules (TP-Cn-PETPE, n = 4 and 10) were synthesized, which contain a tetraphenylethene derivative as the emission active moiety, a pentahexyloxytriphenylene core as the mesogenic unit and an alkoxy spacer. Experimental results revealed that these two compounds both had AIE properties, even in the liquid state at room temperature. While only TP-C4-PETPE showed a monotropic liquid crystal phase upon heating. In addition, these two compounds were fully characterized by 1H and 13C NMR, IR, EA and MS.

Introduction to aggregation induced emission (AIE) materials.

Idea of introducing aggregation-induced emission (AIE) fundamentally altered the scientific community's perception of classical photophysical processes. Many exciting new possibilities have been coming into light due to the emergence of AIE, such as ability of rapid detection and in analyzing variety of bioactive substances required to monitor the complexed biological processes. This also became a handy tool in elucidating the essential physiological and pathological behaviors of organisms. AIE luminogens (AIEgens) are luminous substances that are either weakly or non-emissive in organic solvents or hydrophobic environment alone, but it gives strong emissive when aggregated along with transforming polarities upon aggregation. Owing to the their outstanding advantages such as rapid turn on/off of high brightness emission, big Stokes shift, excellent photostability, and strong biocompatibility AIEgens have become first choice among bio-inspired probes in biomedicine. In the view of providing basic information on AIE, this chapter give a brief overview of aggregation-caused quenching (ACQ) phenomenon, approaches to transform ACQ to AIE phenomenon, photo-physics of AIE phenomenon, followed by known and reportedly novel AIE active molecules and their biomedical applications.

AIE materials for nucleus imaging.

Emergence of a captivating phenomenon aggregation induced emission (AIE) in the early years of 21st century attracted worldwide researchers. In the last two decades various novel AIE active biocompatible small molecules, macromolecules and polymers have been developed for diverse biomedical applications. Imaging of specific organelle such as mitochondria, ribosomes, nuclei and many others play important in the controlling and successful treatment of various diseases. Conventional luminescent probe molecules used in the imaging at cellular or subcellular level exhibit very weak emission on dispersion or on aggregation in aqueous media. AIE luminogens development is indispensable to overcome the notorious aggregation-caused quenching (ACQ) issue inherited by conventional fluorophores. In the present chapter we mostly highlighted over one decade development of various AIE active luminogens utilized for imaging of cell nucleus, nucleon and nucleic acids. The development of those AIE luminogens exhibits promising results in the early diagnosis of cancer diseases.

Aggregation induced emission (AIE) molecules for measurement of intracellular temperature, pH, and viscosity sensing.

This book chapter presents insightful growth and progress in the field of sensing especially, temperature, pH, and viscosity sensing. We focus more on aggregation-induced emission (AIE)-active materials for measuring intracellular pH, viscosity, and temperature by means of fluorescence and absorption study. A special emphasis is given on AIE active fluorescent molecules, molecular rotors, polymeric nanomaterials which are considered as the important aspects of sense. It also gives the fundamental and brief understanding between these different AIE active material and its application in biological systems.

AIE active polymers for biological applications.

The discovery of aggregation-induced emission (AIE) phenomenon, significantly altered the understanding of the scientific world about the luminophore aggregation. Polymers with AIE features have recently emerged as promising materials with wide range of applications in optoelectronics devices, chemosensors, bioimaging, cancer theranostics and drug delivery. By introducing the AIE active molecule into the polymer structure, novel materials encompassing the characteristics properties of both the functional materials such as excellent brightness, versatile structure modification, high biocompatibility, exceptional stability and facile processability are achieved. This chapter presents the advances in synthetic design as well as potential biological applications of AIE active polymers, beginning with a brief introduction to the AIE phenomenon. The versatile synthetic route, easier functionalization, and light up feature of the AIE active polymers offer direct visualization of the physiological processes within or outside the living organisms. This chapter also precisely describes the photodynamic therapy/photothermal therapy (PDT/PTT) with up-to-date advancement of AIE active polymer and their emerging applications in biomedical field. The AIE active Photosensitizers (PSs) are much more efficient in singlet oxygen (1O2) production than their small molecule AIE active PSs due to their enhanced inter system crossing (ISC) process and improved light-harvesting ability. Additionally, the present chapter aims to focus on all recent AIE active polymers for drug screening and drug delivery. The AIE active polymer often shows decent drug loading capacity, high stability and good biocompatibility comprising image guided drug monitoring features. Lastly, the concluding discussion reveals the future prospective of the AIE active polymers.

Tuning Achiral to Chiral Supramolecular Helical Superstructures.

The design and synthesis of achiral organic functional molecules which can assemble into a chiral with selective handedness in the absence of chiral substances is an important in understanding the role chirality plays within these systems. In this review, we described general approaches towards supramolecular chiral molecules the synthesis and self-assembly of achiral molecule to active chiral molecules to investigate controlled supramolecular chiral nanostructures with their photoluminescent properties for rapid, sensitive and selective detection of analytes of choice. Various small molecules have been discussed for achiral to chiral along with induction of chirality and controlled chiral helical structures in detail. We discussed few examples where stimuli used to control the chirality such as temperature, pH etc. Finally, we will also explore on the photo responsive helicity properties of the aggregation induced emission active molecule such as tetraphenylethene conjugates.

Franck-Condon Blockade and Aggregation-Modulated Conductance in Molecular Devices Using Aggregation-Induced Emission-Active Molecules.

We report an effective modulation of the quantum transport in molecular junctions consisting of aggregation-induced-emission(AIE)-active molecules. Theoretical simulations based on combined density functional theory and rate-equation method calculations show that the low-bias conductance of the junction with a single tetraphenylethylene (TPE) molecule can be completely suppressed by strong electron-vibration couplings, that is, the Franck-Condon blockade effect. It is mainly associated with the low-energy vibration modes, which is also the origin of the fluorescence quenching of the AIE molecule in solution. We further found that the conductance of the junction can be lifted by restraining the internal motion of the TPE molecule by either methyl substitution on the phenyl group or by aggregation, a mechanism similar to the AIE process. The present work demonstrates the correlation between optical processes of molecules and quantum transport in their junction, and thus opens up a new avenue for the application of AIE-type molecules in molecular electronics and functional devices.

Galactose-Functionalized, Colloidal-Fluorescent Nanoparticle from Aggregation-Induced Emission Active Molecule via Polydopamine Coating for Cancer Cell Targeting

Aggregation-induced emission (AIE) active molecules emerge as new generation fluorescent probes, and their transformation to functional nanoparticle can greatly extend the application potential. Here we report an approach for transforming AIE active tetraphenylethene (TPE) molecule to galactose-functionalized colloidal nanoparticle that can be used for targeting/labeling of cancer cells. The approach involves polydopamine coating around aggregated TPE or TPE–chitosan conjugate followed by covalent linking with thiolated galactose. Resultant nanoparticles have 50–200 nm hydrodynamic size with good colloidal stability at physiological condition and 6–12% fluorescence quantum yield, and they selectively label cells with overexpressed galactose receptors. The unique advantage of this nanoprobe is that fluorescence remains intact in the presence of conventional quenchers. This approach may be extended for making AIE-active molecule-based various functional nanoprobes.

Rational Design of a Red-Emissive Fluorophore with AIE and ESIPT Characteristics and Its Application in Light-Up Sensing of Esterase.

The development of red fluorophores with efficient solid-state emission is still challenging. Herein, a red fluorophore 1 with aggregation-induced emission (AIE) and excited-state intramolecular proton transfer (ESIPT) characteristics is rationally designed and facilely synthesized by attaching an electron-donor diethylamine and an electron-acceptor maleonitrile group to salicyladazine. In contrast to many red fluorophores which undergo serious aggregation-caused quenching (ACQ), compound 1 emits bright red fluorescence (λem = 650 nm, ΦF = 24.3%) in the solid state with a large Stokes shift of 174 nm. Interestingly, control compounds 2 and 3, which have similar structures as 1, exhibit obvious aggregation-caused quenching (ACQ) characteristics. The difference in the crystal structures of 1, 2, and 3 reveals that the interplanar spacing among molecules plays a decisive role in realizing the AIE characteristics of 1. Moreover, when the hydroxyl group of 1 was substituted by an esterase reactive acetoxyl, a fluorescence light-up probe 4 was developed for sensing of esterase based on the selective reaction between 4 and esterase to generate the AIE and ESIPT active molecule 1. The linear range for in vitro quantification of esterase is 0.01-0.15 U/mL with a detection limit of 0.005 U/mL. Probe 4 was also successfully applied to image esterase in mitochondria of living cells.

Synthesis of an aggregation-induced emission (AIE) active salicylaldehyde based Schiff base: study of mechanoluminescence and sensitive Zn(ii) sensing

A simple AIE active organic molecule exhibits mechanoluminescence (ML) and turn-on Zn(ii) sensing and the causes behind such properties have been explored.

Probing the effects of external species on poly(acrylate acid) chain dynamics by using cationic AIE-active fluorophore

We report here our results on the investigation of the chain dynamics of poly(acrylic acid) in aqueous solution. The concentration of poly(acrylic acid) was approximately 3.8×10−4 mol/L, two orders of magnitude higher than that reported in the literature. The pH value of the solution was 3.9, and the hydrogen bonds between the intrinsic and ionized carboxylic acid groups formed dynamic networks, which captured aggregation-induced emission-active molecules (a tetra-quaternary ammonium modified tetraphenylethene derivative) inside the polymer coils and induced fluorescence emission. The hydrogen bonds can be classified as intra- or intermolecular; both can be probed based on the emission change of the tetra-quaternary ammonium modified tetraphenylethene probes. The effects of different external stimuli on the polymer chain dynamics were investigated using different metal cations (including Na+, Li+, Zn2+, Ni2+, Ca2+, and Co2+), different cation concentrations (1×10−6 to 4×10−4 mol/L), different poly(acrylic acid) molecular weights (5, 240, and 450 kDa), and different copolymers. The experimental results indicate that the long poly(acrylic acid) chains (high molecular weight) tend to form dense globular coils and exclude the probe molecules outside, which are robust and unsusceptible to water-soluble metal cations. However, the shorter poly(acrylic acid) chains tend to form intermolecular hydrogen bonds, which are helpful in capturing more probe molecules inside the networks, thus inducing stronger emission. Because of the dual functions of forming hydrogen bonds with carboxylic groups and acting as an acceptor of protons from the carboxylic acid group to form cationic species, copolymerization with acrylate amide [poly(acrylic acid)-co-poly(acrylamide)] can greatly affect the chain dynamics of poly(acrylic acid) segments, which is reflected by the drastically decreased emission intensity from the fluorescent probes.

STIMULUS RESPONSIVE LUMINESCENT MATERIALS: CRYSTALLIZATION-INDUCED EMISSION ENHANCEMENT

Crystallization of a luminogen normally red-shifts and weakens its emission. During investigation of some luminogens exhibiting aggregation-induced emission (AIE), we first noticed that some AIE active luminogens display higher photoluminescence (PL) intensity and bluer emission in the crystalline state than in their amorphous phase, which is termed as crystallization induced emission enhancement (CIEE). The twisted conformations of CIEE active molecules afford loose packing patterns and rule out any detrimental strong interaction. Molecular conformations are locked more tightly in crystals than those in amorphous solid due to the regular weak interactions in crystals, which affords the CIEE effect. The loose packing patterns facilitate emission switching through morphology modulation. Many AIE active molecules have been developed based on restriction of intramolecular rotation (RIR) mechanism, and we obtained many CIEE compounds from those AIE active luminogens and investigated their utilities as stimuli responsive functional materials, especially as chemosensors, thermosensor, mechanosensors and solid-state emitters. Thus, we provide a possible design strategy for the stimuli responsive solid luminescent materials.

聚集诱导发光分子在生物检测领域的应用

Aggregation-induced emission (AIE) refers to a unique photophysical phenomenon observed for some specific fluorophores, which are faintly or non-emissive in solution but become highly emissive in solid and aggregated states. In the cases of fluorescent probes, AIE active molecules possess some unparallel advantages over their classical counterparts. On one hand, it allows more AIE active molecules to bind to the target analyte, without worrying about the aggregation-induced fluorescence quenching; thus favors fluorescence detection. On the other hand, the feature of drastic enhancement in fluorescence intensity associating with an aggregation event can be used as a method of quantitative detection. In this paper, a series of representative AIE molecules are demonstrated; their applications as biological probes in sensing of protein, DNA, G4, and chiral amines are highlighted; their working principles and features of these molecules are described. Finally, a brief outlook on the design of new AIE-active molecules and the application of AIE-molecules in relevant fields is forwarded.