Pyridinium-Yne Click Polymerization: A Facile Strategy toward Functional Poly(Vinylpyridinium Salt)s with Multidrug-Resistant Bacteria Killing Ability.

Polymeric materials with antibacterial properties hold great promise for combating multidrug-resistant bacteria, which pose a significant threat to public health. However, the synthesis of most antibacterial polymers typically involves complicated and time-consuming procedures. In this study, we demonstrate a simple and efficient strategy for synthesizing functional poly(vinylpyridinium salt)s via pyridinium-yne click polymerization. This click polymerization could proceed with high atom economy under mild conditions without any external catalyst, yielding soluble and thermally stable poly(vinylpyridinium salt)s with satisfactory molecular weights and well-defined structures in excellent yields. Additionally, the incorporation of luminescent units such as fluorene, tetraphenylethylene, and triphenylamine into the polymer backbone confers excellent aggregation-enhanced emission properties upon the resulting polymers, rendering them suitable for bacterial staining. Moreover, the existence of pyridinium salt imparts intrinsic antibacterial activity against multidrug-resistant bacteria to the polymers, enabling them to effectively inhibit wound bacterial infection and significantly expedite the healing process. This work not only provides an efficient method to prepare antibacterial polymers, but also opens up the possibility of various applications of polymers in healthcare and other antibacterial fields.

Precise and long-term tracking of mitochondria in neurons using a bioconjugatable and photostable AIE luminogen.

Tracking mitochondrial movement in neurons is an attractive but challenging research field as dysregulation of mitochondrial motion is associated with multiple neurological diseases. To realize accurate and long-term tracking of mitochondria in neurons, we elaborately designed a novel aggregation-induced emission (AIE)-active luminogen, TPAP-C5-yne, where we selected a cationic pyridinium moiety to target mitochondria and employed an activated alkyne terminus to achieve long-term tracking through bioconjugation with amines on mitochondria. For the first time, we successfully achieved the accurate analysis of the motion of a single mitochondrion in live primary hippocampal neurons and the long-term tracking of mitochondria for up to a week in live neurons. Therefore, this new AIEgen can be used as a potential tool to study the transport of mitochondria in live neurons.

Novel Quinolizine AIE System: Visualization of Molecular Motion and Elaborate Tailoring for Biological Application.

Molecular motions are ubiquitous in nature and they immutably play intrinsic roles in all actions. However, exploring appropriate models to decipher molecular motions is an extremely important but very challenging task for researchers. Considering aggregation-induced emission (AIE) luminogens possess their unique merits to visualize molecular motions, it is particularly fascinating to construct new AIE systems as models to study molecular motion. Herein, a novel quinolizine (QLZ) AIE system was constructed based on the restriction intramolecular vibration (RIV) mechanism. It was demonstrated that QLZ could act as an ideal model to visualize single-molecule motion and macroscopic molecular motion via fluorescence change. Additionally, further elaborate tailoring of this impressive core achieved highly efficient reactive oxygen species production and realized fluorescence imaging-guided photodynamic therapy applications, which confirms the great application potential of this new AIE-active QLZ core. Therefore, this work not only provides an ideal model to visualize molecular motion but also opens a new way for the application of AIEgens.

Stimuli-Responsive AIEgens.

The unique advantages and the exciting application prospects of AIEgens have triggered booming developments in this area in recent years. Among them, stimuli-responsive AIEgens have received particular attention and impressive progress, and they have been demonstrated to show tremendous potential in many fields from physical chemistry to materials science and to biology and medicine. Here, the recent achievements of stimuli-responsive AIEgens in terms of seven most representative types of stimuli including force, light, polarity, temperature, electricity, ion, and pH, are summarized. Based on typical examples, it is illustrated how each type of systems realize the desired stimuli-responsive performance for various applications. The key work principles behind them are ultimately deciphered and figured out to offer new insights and guidelines for the design and engineering of the next-generation stimuli-responsive luminescent materials for more broad applications.

Making Aggregation-Induced Emission Luminogen More Valuable by Gold: Enhancing Anticancer Efficacy by Suppressing Thioredoxin Reductase Activity.

Gold complexes have been recognized as potential anticancer agents against various kinds of diseases due to their inherent suppressions of antioxidant thioredoxin reductase (TrxR) activity. Herein, a powerful aggregation-induced emission luminogen (AIEgen), TBP-Au, was designed and synthesized by integrating an anticancer Au(I) moiety with an AIE-active photosensitizer (TBP), in which both the production and consumption routes of reactive oxygen species (ROS) were elaborately considered simultaneously to boost the anticancer efficacy. It has been demonstrated that TBP-Au could realize superior two-photon fluorescence imaging in tumor tissues with high resolution and deep penetration as well as long-term imaging in live animals due to its AIE property. In addition, the introduction of a special Au(I) moiety could tune the organelle specificity and efficiently facilitate the ROS-determined photodynamic therapy (PDT). More impressively, TBP-Au could efficiently eliminate cancer cells under light irradiation through the preconceived synergetic approaches from the PDT and the effective suppression of TrxR, demonstrating that TBP-Au holds great potential for precise cancer theranostics.

Clusteroluminescence from Cluster Excitons in Small Heterocyclics Free of Aromatic Rings.

The study of nonconventional luminescence is important for revealing the luminescence of natural systems and has gradually drawn the attention of researchers in recent years. However, the underlying mechanism is still inexplicable. Herein, the luminescence behavior of two series of simple, heteroatom-containing small molecules without aromatic rings, i.e., maleimide and succinimide derivatives, are studied to gain further mechanistic insight into the nonconventional luminescence process. It has been unveiled that all the molecules exhibit bright and visible luminescence in concentrated solution and solid state and the formation of clusters is the root cause for such behaviors, which can effectively increase the possibility of both the nonradiative n-π* and favorable π-π* transitions and stabilize the excitons formed in the excited state. The distinctive luminescent phenomena and intriguing mechanism presented in this work will be significant for understanding the mechanism of clusteroluminescence and provide new strategies for the rational design of novel luminescent materials.

Functionalization of Silk by AIEgens through Facile Bioconjugation: Full-Color Fluorescence and Long-Term Bioimaging.

Silkworm silk is a promising natural biopolymer for textile and biomedical applications for its remarkable flexibility, excellent biocompatibility and controllable biodegradability. The functionalization of silks makes them more versatile for flexible displays and visible bioscaffolds. However, fluorescent silks are normally fabricated through unstable physical absorption or complicated chemical reactions under harsh conditions. Herein, we developed a simple strategy for preparing fluorescent silks. Five aggregation-induced emission luminogens (AIEgens) with activated alkynes were synthesized by rational molecular design, and then reacted with silk fibers through facile metal-free click bioconjugation. The resulting conjugates show bright full-color emissions and high stability. A white light-emitting silk was fabricated by simultaneous bioconjugation with red-, green- and blue-emissive AIEgens. The red-emissive AIEgen-functionalized silks were successfully applied for long-term cell tracking and two-photon bioimaging, demonstrating great potential for tissue engineering and bioscaffold monitoring.

Molecular Motions in AIEgen Crystals: Turning on Photoluminescence by Force-Induced Filament Sliding.

Life process is amazing, and it proceeds against the eternal law of entropy increase through molecular motion and takes energy from the environment to build high-order complexity from chaos to achieve evolution with more sophisticated architectures. Inspired from the elegance of life process and also to effectively exploit the undeveloped solid-state molecular motion, two unique chiral Au(I) complexes were elaborately developed in this study, in which their powders could realize a dramatic transformation from nonemissive isolated crystallites to emissive well-defined microcrystals under the stimulation of mechanical force. Such an unusual crystallization was presumed to be caused by molecular motions driven by the formation of strong aurophilic interactions as well as multiple C-H···F and π-π interactions. Such a prominent macroscopic off/on luminescent switching could also be achieved through extremely subtle molecular motions in the crystal state and presented a filament sliding that occurred in a layer-by-layer molecular stacking fashion with no involvement of any crystal phase transition. Additionally, it had been demonstrated that the manipulation of the solid-state molecular motions could result in the generation of circularly polarized luminescence.

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.

Multifunctional AuI -based AIEgens: Manipulating Molecular Structures and Boosting Specific Cancer Cell Imaging and Theranostics.

Gold(I) N-heterocyclic carbene (AuI -NHC) complexes have emerged as potential anticancer agents owing to their high cytotoxicity and stability. Integration of their above unique functions with customized aggregation-induced emission (AIE) luminogens to achieve specific bioimaging and efficient theranostics to cancer is highly desirable but is rarely studied. Now, a series of novel AuI -NHC compounds were developed with AIE characteristics. A complex with a PPh3 ligand was selected out as it could achieve both prominent specific imaging of various cancer cells and efficient inhibition of their growth with negligible toxic effects on normal cells due to the targeting binding and strong inhibition towards thioredoxin reductase. This complex could also act as a powerful radiosensitizer to boost the anticancer efficacy with performance superior to that of popularly used auranofin. It holds great potential as a specific and effective theranostic drug in cancer diagnosis and precise therapy.

Fast surface immobilization of native proteins through catalyst-free amino-yne click bioconjugation.

Surface immobilization provides a useful platform for biosensing, drug screening, tissue engineering and other chemical and biological applications. However, some of the used reactions are inefficient and/or complicated, limiting their applications in immobilization. Herein, we use a spontaneous and catalyst-free amino-yne click bioconjugation to generate activated ethynyl group functionalized surfaces for fast immobilization of native proteins and cells. Biomolecules, such as bovine serum albumin (BSA), human IgG and a peptide of C(RGDfK), could be covalently immobilized on the surfaces in as short as 30 min. Notably, the bioactivity of the anchored biomolecules remains intact, which is verified by efficiently capturing target antibodies and cells from the bulk solutions. This strategy represents an alternative for highly efficient surface biofunctionalization.

Real-Time Monitoring of Hierarchical Self-Assembly and Induction of Circularly Polarized Luminescence from Achiral Luminogens.

Constructing artificial helical structures through hierarchical self-assembly and exploring the underlying mechanism are important, and they help gain insight from the structures, processes, and functions from the biological helices and facilitate the development of material science and nanotechnology. Herein, the two enantiomers of chiral Au(I) complexes ( S)-1 and ( R)-1 were synthesized, and they exhibited impressive spontaneous hierarchical self-assembly transitions from vesicles to helical fibers. An impressive chirality inversion and amplification was accompanied by the assembly transition, as elucidated by the results of in situ and time-dependent circular dichroism spectroscopy and scanning electron microscope imaging. The two enantiomers could serve as ideal chiral templates to co-assemble with other achiral luminogens to efficiently induce the resulting co-assembly systems to show circularly polarized luminescence (CPL). Our work has provided a simple but efficient way to explore the sophisticated self-assembly process and presented a facile and effective strategy to fabricate architectures with CPL properties.

A Simple Approach to Bioconjugation at Diverse Levels: Metal-Free Click Reactions of Activated Alkynes with Native Groups of Biotargets without Prefunctionalization.

The efficient bioconjugation of functional groups/molecules to targeted matrix and bio-related species drives the great development of material science and biomedicine, while the dilemma of metal catalysis, uneasy premodification, and limited reaction efficiency in traditional bioconjugation has restricted the booming development to some extent. Here, we provide a strategy for metal-free click bioconjugation at diverse levels based on activated alkynes. As a proof-of-concept, the abundant native groups including amine, thiol, and hydroxyl groups can directly react with activated alkynes without any modification in the absence of metal catalysis. Through this strategy, high-efficient modification and potential functionalization can be achieved for natural polysaccharide, biocompatible polyethylene glycol (PEG), synthetic polymers, cell penetrating peptide, protein, fast whole-cell mapping, and even quick differentiation and staining of Gram-positive bacteria, etc. Therefore, current metal-free click bioconjugation strategy based on activated alkynes is promising for the development of quick fluorescence labeling and functional modification of many targets and can be widely applied towards the fabrication of complex biomaterials and future in vivo labeling and detection.

Functional Poly(dihalopentadiene)s: Stereoselective Synthesis, Aggregation-Enhanced Emission and Sensitive Detection of Explosives.

The development of polymeric materials with novel structures and unique properties and functionalities is of both academic and industrial significance. In this work, functional poly(dihalopentadiene)s were synthesized by boron trihalide-mediated multicomponent polymerization routes in a stereoselective manner. The polymerizations of tetraphenylethylene-containing diyne, BX3 (X = Cl, Br) and p-tolualdehyde proceed smoothly in dichloromethane under mild conditions to afford high molecular weight poly(dihalopentadiene)s with a predominant (Z,Z)-configuration in moderate to good yields. The reaction conditions and the boron trihalide used were found to have great effects on the stereochemistry of the resulting polymer structures. The obtained poly(1,5-dihalo-(Z,Z)-1,4-pentadiene)s possess high thermal stability and good film-forming ability. Their thin films show high refractive index of 1.9007⁻1.6462 in a wide wavelength region of 380⁻890 nm with low optical dispersion. The polymers are weakly emissive in dilute solutions but become highly emissive upon aggregated, demonstrating a unique phenomenon of aggregation-enhanced emission. Their nanoaggregates in aqueous media can serve as sensitive fluorescent chemosensors for the detection of explosives with a superamplification effect and a low detection limit.

Metal-Free Poly-Cycloaddition of Activated Azide and Alkynes toward Multifunctional Polytriazoles: Aggregation-Induced Emission, Explosive Detection, Fluorescent Patterning, and Light Refraction.

The metal-free click polymerization (MFCP) of activated alkynes and azides or activated azide and alkynes have been developed into powerful techniques for the construction of polytriazoles without the obsession of metallic catalyst residues problem. However, the MFCP of activated azides and alkynes is rarely applied in preparation of functional polytriazoles. In this paper, soluble multifunctional polytriazoles (PIa and PIb) with high weight-average molecular weights (Mw up to 32 000) are prepared via the developed metal-free poly-cycloaddition of activated azide and alkynes in high yields (up to 90%). The resultant PIa and PIb are thermally stable, and show aggregation-induced emission characteristics, enabling their aggregates to detect explosives with superamplification effect. Moreover, thanks to their containing aromatic rings and polar moieties, PIa and PIb exhibit high refractive indices. In addition, they can also be cross-linked upon UV irradiation to generate 2D fluorescent patterning due to their remaining azide groups and containing ester groups. Thus, these multifunctional polytriazoles are potentially applicable in the optoelectronic and sensing fields.

Spontaneous Amino-yne Click Polymerization: A Powerful Tool toward Regio- and Stereospecific Poly(ß-aminoacrylate)s.

Efficient synthesis of poly(enamine)s has been a great challenge because of their poor stability, poor solubility, and low molecular weights. In this work, a spontaneous amino-yne click polymerization for the efficient preparation of poly(enamine)s was established, which could proceed with 100% atom efficiency under very mild conditions without any external catalyst. Through systematic optimization of the reaction conditions, several soluble and thermally stable poly(ß-aminoacrylate)s with high molecular weights (Mw up to 64400) and well-defined structures were obtained in excellent yields (up to 99%). Moreover, the polymerization can perform in a regio- and stereospecific fashion. Nuclear magnetic resonance spectra analysis revealed that solely anti-Markovnikov additive products with 100% E-isomer were obtained. The reaction mechanism was well demonstrated with the assistance of density functional theory calculations. In addition, by introducing the tetraphenylethene moiety, the resulting polymers exhibit unique aggregation-induced emission characteristics and could be applied in explosives detection and bioimaging. This polyhydroamination is a new type of click polymerization and opens up enormous opportunities for preparing functional polymeric materials.

Efficient and Regioselectivity-Tunable Metal-Free Polycycloaddition of Activated Azide and Alkynes.

The transition-metal catalyzed and metal-free click polymerizations have been developed as powerful tools for the construction of functional polymers with linear and hyperbranched structures. The latter provides a thorough solution for the completely removing metallic residues from the products encountered in the former. Compared to the activated alkyne-azide metal-free click polymerization, the activated azide-alkyne one is rarely studied. In this Communication, a perfluorophenyl-activated azide of hexane-1,6-diyl-bis(4-azido-2,3,5,6-tetrafluorobenzoate) is rationally designed and facilely prepared. Through systematical optimization of the reaction conditions, an efficient metal-free perfluorophenylazide-alkyne polycycloaddition is established, and polytriazoles with high molecular weights (up to 166 000) and excellent solubility are obtained in excellent yields (up to 93%) under mild reaction conditions. Interestingly, the regioselectivity of the reaction could be fine-tuned by the solvents and diyne monomers. Therefore, this work provides not only a powerful tool for the preparation of functional polytriazoles, but also an attractive method for fine-tuning their regioregularity.

Multihydroxy dendritic upconversion nanoparticles with enhanced water dispersibility and surface functionality for bioimaging.

Upconversion nanoparticle (UCNP) as a new class of imaging agent is gaining prominence because of its unique optical properties. An ideal UCNP for bioimaging should simultaneously possess fine water dispersibility and favorable functional groups. In this paper, we present a simple but effective method to the synthesis of a UCNP-based nanohybrid bearing a multihydroxy hyperbranched polyglycerol (HPG) shell by the combination of a "grafting from" strategy with a ring-opening polymerization technique. The structure and morphology of the resulting UCNP-g-HPG nanohybrid were characterized in detail by Fourier transform infrared, (1)H NMR, thermogravimetric analysis, and transmission electron microscopy measurements. The results reveal that the amount of grafted HPG associated with the thickness of the HPG shell can be well tuned. UCNP-g-HPG shows high water dispersibility and strong and stable upconversion luminescence. On the basis of its numerous surface hydroxyl groups, UCNP-g-HPG can be tailored by a representative fluorescent dye rhodamine B to afford a UCNP-g-HPG-RB nanohybrid that simultaneously presents upconversion and downconversion luminescence. Preliminary biological studies demonstrate that UCNP-g-HPG shows low cytotoxicity, high luminescent contrast, and deep light penetration depth, posing promising potential for bioimaging applications.

Peach gum for efficient removal of methylene blue and methyl violet dyes from aqueous solution.

This study investigated the potential use of natural peach gum (PG) as alternative adsorbent for the removal of dyes from aqueous solutions. The PG showed high adsorption capacities and selectivity for cationic dyes (e.g., methylene blue (MB) and methyl violet (MV)) in the pH range 6-10. 98% of MB and MV could be adsorbed within 5 min, and both of the adsorptions reached equilibrium within 30 min. The dye uptake process followed the pseudo-second-order kinetic model. The intraparticle diffusion was not the sole rate controlling step. Equilibrium adsorption isotherm data indicated a good fit to the Langmuir isotherm model. Regeneration study revealed that PG could be well regenerated in acid solution. The recovered PG still exhibited high adsorption capacity even after five cycles of desorption-adsorption. On the basis of its excellent adsorption performance and facile availability, PG can be employed as an efficient low cost adsorbent for environmental cleanup.

Amphibious fluorescent carbon dots: one-step green synthesis and application for light-emitting polymer nanocomposites.

A facile and green approach for the synthesis of amphibious fluorescent carbon dots (CDs) from natural polysaccharide is reported. Light-emitting polymer nanocomposites with excellent optical performance can be easily prepared by incorporation of the amphibious CDs into the polymer matrix.