Facile synthesis of AIEgens with wide color tunability for cellular imaging and therapy

Nonconjugated Biocompatible Macromolecular Luminogens for Sensing and Removals of Fe(III) and Cu(II): DFT Studies on Selective Coordination(s) and On-Off Sensing

This work reports the design and synthesis of two nonaromatic biocompatible macromolecular luminogens, i.e., 2-(dimethylamino)ethyl methacrylate-co-2-(dimethylamino)ethyl 3-(N-(methylol)acrylamido)-2-methylpropanoate-co-N-(methylol)acrylamide/DMAEMA-co-DMAENMAMP-co-NMA (P1) and methacrylic acid-co-3-(N-(methylol)acrylamido)-2-methylpropanoic acid-co-N-(methylol)acrylamide/MEA-co-NMAMPA-co-NMA (P2), prepared through in situ anchored acrylamido-ester/DMAENMAMP and acrylamido-acid/NMAMPA third comonomers, respectively, in a facile polymerization of two non-luminous monomers in water medium to circumvent the drawbacks related to aggregation-caused quenching of aromatic luminogens. The structures of P1/P2, in situ anchored comonomers, fluorophores, N-branching associated n-π* interactions, and hydrogen bonding assisted aggregation-enhanced emissions are comprehended by nuclear magnetic resonance, Fourier transform infrared (FTIR), X-ray photoelectron spectroscopy (XPS), ultraviolet-visible, thermogravimetric analysis (TGA), dynamic light scattering (DLS), transmission electron microscopy (TEM), fluorescence lifetime, and fluorescence imaging. P1 and P2 are appropriate for sensitive detections/exclusions of Fe(III)/Cu(II) and cell-imaging. The intrinsic fluorescence, on-off sensing, selective coordinations of Fe(III) and Cu(II) with fluorophores, emission quenching mechanisms, and removals of Fe(III) and Cu(II) are investigated by DFT/NTO analyses of P1/P2 and Fe(III)-P1 and Cu(II)-P2 complexes, XPS, and isotherms and kinetics parameters. The excellent biocompatibilities, comparable limit of detections, i.e., 1.70 × 10^-7 and 1.59 × 10^-7 [m], and higher adsorption capacities, i.e., 77.25 and 154.13 mg g^-1 , at low ppm; 303 K; and pH = 7 compel P1/P2 to be acceptable for multipurpose applications.

Rational construction of AIEgens with wide color tunability and their specific lipid droplet imaging applications

Organic light-emitting materials with aggregation-induced emission (AIE) character have experienced a rapid development in imaging, visualization and sensing. In this paper, by installing rotors to an aggregation-caused quenching (ACQ) compound, we constructed an AIE luminogen (AIEgens) system (A2-A4, B1-B3) with wide emission tunability, which covers almost all regions of visible light (400-780 nm). The calculated energy gap of the compounds is consistent with the value of the absorption transition. In the biological experiments, B3 showed excellent lipid droplet (LD) targeting ability in PC12 cells, and higher photostability compared with the commercial LDs bioprobe. Moreover, as a hydrophobic compound, B3 can distinguish blood from a hyperlipidemia patient and normal people. Thus, this study provides a strategy to construct red/NIR fluorescent materials with AIE character, and further apply it to identify the blood of people with hyperlipidemia.

Controllable and Diversiform Topological Morphologies of Self-Assembling Supra-Amphiphiles with Aggregation-Induced Emission Characteristics for Mimicking Light-Harvesting Antenna

Controllable construction of diversiform topological morphologies through supramolecular self-assembly on the basis of single building block is of vital importance, but still remains a big challenge. Herein, a bola-type supra-amphiphile, namely DAdDMA@2β-CD, is rationally designed and successfully prepared by typical host-guest binding β-cyclodextrin units with an aggregation-induced emission (AIE)-active scaffold DAdDMA. Self-assembling investigation reveals that several morphologies of self-assembled DAdDMA@2β-CD including leaf-like lamellar structure, nanoribbons, vesicles, nanofibers, helical nanofibers, and toroids, can be straightforwardly fabricated by simply manipulating the self-assembling solvent proportioning and/or temperature. To the best of knowledge, this presented protocol probably holds the most types of self-assembling morphology alterations using a single entity. Moreover, the developed leaf-like lamellar structure performs well in mimicking the light-harvesting antenna system by incorporating with a Förster resonance energy transfer acceptor, providing up to 94.2% of energy transfer efficiency.

Intracellular Ruthenium-Promoted (2+2+2) Cycloadditions

Metal-mediated intracellular reactions are becoming invaluable tools in chemical and cell biology, and hold promise for strongly impacting the field of biomedicine. Most of the reactions reported so far involve either uncaging or redox processes. Demonstrated here for the first time is the viability of performing multicomponent alkyne cycloaromatizations inside live mammalian cells using ruthenium catalysts. Both fully intramolecular and intermolecular cycloadditions of diynes with alkynes are feasible, the latter providing an intracellular synthesis of appealing anthraquinones. The power of the approach is further demonstrated by generating anthraquinone AIEgens (AIE=aggregation induced emission) that otherwise do not go inside cells, and by modifying the intracellular distribution of the products by simply varying the type of ruthenium complex.

Aggregation-Induced Emission Luminogens Married to 2D Black Phosphorus Nanosheets for Highly Efficient Multimodal Theranostics

Inspired by the respective advantages of aggregation-induced emission (AIE)-active photosensitizers and black phosphorus nanomaterials in cancer treatment, the facile construction of novel AIE photosensitizers married to 2D black phosphorus nanosheets and their application for multimodal theranostics are demonstrated. The developed nanomaterial simultaneously possesses distinctive properties and multiple functions including excellent stability, good biocompatibility, intensive fluorescence emission in the NIR region, high-performance reactive oxygen species generation, good photothermal conversion efficiency, outstanding cellular uptake, and effective accumulation at the tumor site. Both in vitro and in vivo evaluation show that the presented nanotheranostic system is an excellent candidate for NIR fluorescence-photothermal dual imaging-guided synergistic photodynamic-photothermal therapies. This study thus not only extends the applications scope of AIE and black phosphorus materials, but also offers useful insights into designing a new generation of cancer theranostic protocol for potential clinical applications.

Simultaneously boosting the conjugation, brightness and solubility of organic fluorophores by using AIEgens

Organic near-infrared (NIR) emitters hold great promise for biomedical applications. Yet, most organic NIR fluorophores face the limitations of short emission wavelengths, low brightness, unsatisfactory processability, and the aggregation-caused quenching effect. Therefore, development of effective molecular design strategies to improve these important properties at the same time is a highly pursued topic, but very challenging. Herein, aggregation-induced emission luminogens (AIEgens) are employed as substituents to simultaneously extend the conjugation length, boost the fluorescence quantum yield, and increase the solubility of organic NIR fluorophores, being favourable for biological applications. A series of donor-acceptor type compounds with different substituent groups (i.e., hydrogen, phenyl, and tetraphenylethene (TPE)) are synthesized and investigated. Compared to the other two analogs, MTPE-TP3 with TPE substituents exhibits the reddest fluorescence, highest brightness, and best solubility. Both the conjugated structure and twisted conformation of TPE groups endow the resulting compounds with improved fluorescence properties and processability for biomedical applications. The in vitro and in vivo applications reveal that the NIR nanoparticles function as a potent probe for tumour imaging. This study would provide new insights into the development of efficient building blocks for improving the performance of organic NIR emitters.

Development of A Thermo-Responsive Conjugated Polymer with Photobleaching-Resistance Property and Tunable Photosensitizing Performance

A thermo-responsive conjugated polymer, PFBT-gPA is synthesized by grafting the poly(N-isopropylacrylamide) (PNIPAAm) to the side chains of a conjugated polyfluorene derivative through atom transfer radical polymerization (ATRP). PFBT-gPA undergoes a reversible phase transition in water below and above the lower critical solution temperature (LCST) and the process is studied by differential scanning calorimetry (DSC) analysis and UV/vis absorption spectra. PFBT-gPA shows a good photostability under UV light irradiation especially above the LCST. Moreover, the photosensitizing performance of PFBT-gPA could be tuned simply by changing temperature. The unique properties of PFBT-gPA promise its potential applications in sensing and photodynamic therapy.

Supramolecular materials based on AIE luminogens (AIEgens): construction and applications

The emergence of aggregation-induced emission luminogens (AIEgens) has significantly stimulated the development of luminescent supramolecular materials because their strong emissions in the aggregated state have resolved the notorious obstacle of the aggregation-caused quenching (ACQ) effect, thereby enabling AIEgen-based supramolecular materials to have a promising prospect in the fields of luminescent materials, sensors, bioimaging, drug delivery, and theranostics. Moreover, in contrast to conventional fluorescent molecules, the configuration of AIEgens is highly twisted in space. Investigating AIEgens and the corresponding supramolecular materials provides fundamental insights into the self-assembly of nonplanar molecules, drastically expands the building blocks of supramolecular materials, and pushes forward the frontiers of supramolecular chemistry. In this review, we will summarize the basic concepts, seminal studies, recent trends, and perspectives in the construction and applications of AIEgen-based supramolecular materials with the hope to inspire more interest and additional ideas from researchers and further advance the development of supramolecular chemistry.

Aggregation-Induced Emission Photosensitizers: From Molecular Design to Photodynamic Therapy

Photodynamic therapy (PDT) has emerged as a promising noninvasive treatment option for cancers and other diseases. The key factor that determines the effectiveness of PDT is the photosensitizers (PSs). Upon light irradiation, the PSs would be activated, produce reactive oxygen species (ROS), and induce cell death. One of the challenges is that traditional PSs adopt a large flat disc-like structure, which tend to interact with the adjacent molecules through strong π-π stacking that reduces their ROS generation ability. Aggregation-induced emission (AIE) molecules with a twisted configuration to suppress strong intermolecular interactions represent a new class of PSs for image-guided PDT. In this Miniperspective, we summarize the recent progress on the design rationale of AIE-PSs and the strategies to achieve desirable theranostic applications in cancers. Subsequently, approaches of combining AIE-PS with other imaging and treatment modalities, challenges, and future directions are addressed.

N-Substitution of acridone with electron-donating groups: crystal packing, intramolecular charge transfer and tuneable aggregation induced emission

Acridone derivatives with electron-rich triphenylamine functionalized at the amino position were synthesized and their properties were experimentally and computationally investigated. The single crystal structure analysis revealed that the π–π interaction of acridone and the formation of hydrogen bonds of carbonyl and the hydrogen atoms of the pending phenyl ring were crucial in the determination of molecular packing in the crystalline state. An intramolecular charge transfer (ICT) process was observed between acridone and triphenylamine even with reduced conjugation by the nitrogen atom of acridone. Tuneable aggregation induced emissions with blue and green fluorescence were found due to the different aggregation state and particle size, which varied according to the water content in THF. Furthermore, the size of the spacer between acridone and the appended amine was also important in adjusting the property of aggregation induced emission or aggregation caused quenching in the solid state.

Triphenylamine functionalized acridone leads to a donor–acceptor system with intramolecular charge transfer process and tuneable aggregation induced enhanced emission.

Dual-Functional NIR AIEgens for High-Fidelity Imaging of Lysosomes in Cells and Photodynamic Therapy

Design and synthesis of water-soluble near-infrared (NIR) emissive fluorescent molecules with aggregation-induced emission (AIE) characteristics, perfect signal-to-noise ratio for imaging of organelle, and photodynamic therapy (PDT) functions has received enormous attention. However, the dual-functional NIR AIEgens of high-fidelity tracking lysosome and ablation cancer cells was rarely reported. Herein, a series of AIE luminogens (AIEgens) with a typical AIE effect, good biocompatibility, superior photostability, high brightness, and excellent reactive oxygen species (ROS) generation ability were developed, which had different electronic push-pull strength and conjugate system size in the molecular structure. These AIEgens could specifically "light up" and dynamically long-term track the lysosomes in living cells and zebrafish with ultrahigh colocalization imaging Pearson's correlation coefficients (Rr: 0.9687) and overlap coefficient (R: 0.9967). Additionally, the MPAT of NIR luminescence as a photosensitizer was used for photodynamic ablation of cancer cells, owing to prompt generation of the ROS under green light irradiation (495-530 nm, 10 mW cm^-2). Hence, this research not only expands the application range of NIR AIEgens but also provides useful insights into design of split-new method for the treatment of cancer.

A Fast-Response Red Shifted Fluorescent Probe for Detection of H2S in Living Cells

Near-infrared (NIR) fluorescent probes are attractive tools for bioimaging applications because of their low auto-fluorescence interference, minimal damage to living samples, and deep tissue penetration. H2S is a gaseous signaling molecule that is involved in redox homeostasis and numerous biological processes in vivo. To this end, we have developed a new red shifted fluorescent probe 1 to detect physiological H2S in live cells. The probe 1 is based on a rhodamine derivative as the red shifted fluorophore and the thiolysis of 7-nitro 1,2,3-benzoxadiazole (NBD) amine as the H2S receptor. The probe 1 displays fast fluorescent enhancement at 660 nm (about 10-fold turn-ons, k2 = 29.8 M-1s-1) after reacting with H2S in buffer (pH 7.4), and the fluorescence quantum yield of the activated red shifted product can reach 0.29. The probe 1 also exhibits high selectivity and sensitivity towards H2S. Moreover, 1 is cell-membrane-permeable and mitochondria-targeting, and can be used for imaging of endogenous H2S in living cells. We believe that this red shifted fluorescent probe can be a useful tool for studies of H2S biology.

Enhancement of the Aggregation-Induced Emission by Hydrogen Bond for Visualizing Hypochlorous Acid in an Inflammation Model and a Hepatocellular Carcinoma Model

As an important reactive oxygen species, hypochlorous acid (HClO) is produced in various physiological processes. The abnormal rise of the HClO level is associated with a large number of inflammatory diseases. In this work, we develop a simple, aqueous-soluble aggregration-induced emission (AIE) probe for sensing HClO with significant aggregation-induced fluorescence (>1000 times). Two probes, CH₃O-TPE-Py⁺-N⁺ (COTN) and OH-TPE-Py⁺-N⁺ (HOTN) (TPE, tetraphenylethylene), are synthesized for sensing HClO by the cleavage of the Py⁺-N⁺ group; the reaction products are CH₃O-TPE-CHO (COT) and OH-TPE-CHO (HOT), respectively. The hydrophobicity of the probes is changed with the increased aggregation-induced emission. During the process, HOTN shows significantly better response than COTN. The slightly different chemical structures of COTN and HOTN result in a significant response to HClO. The theoretical calculation data support the theory that the hydrogen bond contributes to the excellent sensitivity for HClO. On the basis of the good response to HClO in vitro, HOTN is used to image inflammation and hepatocellular carcinoma in vivo because these diseases always produce high HClO levels.

Azine based AIEgens with multi-stimuli response towards picric acid

Selective detection of picric acid using AIEgens via fluorescence enhancement and quenching in the monomer and aggregated from respectively.

Precise Molecular Design for High-Performance Luminogens with Aggregation-Induced Emission

Precise design of fluorescent molecules with desired properties has enabled the rapid development of many research fields. Among the different types of optically active materials, luminogens with aggregation-induced emission (AIEgens) have attracted significant interest over the past two decades. The negligible luminescence of AIEgens as a molecular species and high brightness in aggregate states distinguish them from conventional fluorescent dyes, which has galvanized efforts to bring AIEgens to a wide array of multidisciplinary applications. Herein, the useful principles and emerging structure-property relationships for precise molecular design toward AIEgens with desirable properties using concrete examples are revealed. The cutting-edge applications of AIEgens and their excellent performance in enabling new research directions in biomedical theranostics, optoelectronic devices, stimuli-responsive smart materials, and visualization of physical processes are also highlighted.

Thioarylmaleimides: accessible, tunable, and strongly emissive building blocks

A series of thioarylmaleimides was synthesized to investigate how variation of the thioaryl group can be used to control absorption and emission properties in solution and in the solid-state. Fine-tuning of the photochemical properties was found to be possible using this strategy, and a rainbow of colours and emission wavelengths are accessible in a single step from commercially available compounds.

Methyl-restricted rotor rotation on the stator produces high-efficiency fluorescence emission: a new strategy to achieve aggregation-induced emission

At present, we have realized that the aggregation-induced emission (AIE) achieves the purpose of fluorescence enhancement by restricting rotations to reduce intermolecular or intramolecular energy loss. Based on this idea, we synthesized a novel fluorene-based fluorescent compound with a restricted rotor rotation on the stator through the Suzuki coupling reaction. The luminescence effect was evaluated by comparing its fluorescence intensity with that of the control compound. Finally, theoretical calculations showed that the presence of methyl groups hindered the thermal rotation of the fluorenyl groups. Thus, the results indicated that the fluorescence of this compound was better than that of the control compound. A new synthetic pathway for high-efficiency AIE-based fluorescent luminogens has been developed.

At present, we have realized that the aggregation-induced emission (AIE) achieves the purpose of fluorescence enhancement by restricting rotations to reduce intermolecular or intramolecular energy loss.