Aggregation-induced Emission Polymers Research Articles

Application of hyperbranched polysiloxanes in biomedical materials based on AIE polymer properties

Application of hyperbranched polysiloxanes in biomedical materials based on AIE polymer properties

Regulation of Photophysical Behaviors in Hyperbranched Aggregation-Induced Emission Polymers for Reactive Oxygen Species Scavenging.

Developing nonconjugated materials with large Stokes shifts is highly desired. In this work, three kinds of hyperbranched aggregation-induced emission (AIE) polymers with tunable n/π electronic effects were synthesized. HBPSi-CBD contains alkenyl groups in the backbone and possesses a promoted n-π* transition and red-shifted emission wavelength with a large Stokes shift of 186 nm. Experiments and theoretical simulations confirmed that the planar π electrons in the backbone are responsible for the red-shifted emission due to the strong through-space n···π interactions and restricted backbone motions. Additionally, the designed HBPSi-CBD could be utilized as an ROS scavenger after coupling with l-methionine. The HBPSi-Met exhibits remarkable ROS scavenging properties with a scavenging capacity of 77%. This work not only gains further insight into the structure-property relationship of nonconjugated hyperbranched AIE polymers but also provides a promising ROS-scavenging biomaterial for the treatment of ROS-related diseases.

Multi-functional fluorescent silicon elastomer cross-linked with AIE polymer by dynamic imine bond and its application in anti-counterfeiting

Fluorescent elastomer materials have received extensive attention due to their excellent optical performance, flexibility, and chemical stability in recent years, and demonstrate great application potentials in intelligent sensors, optoelectronic devices, medical equipment and other fields. Although the traditional method for constructing fluorescent elastomers by doping fluorescent small molecules is facile and universal, it also has limitations such as low luminous efficiency, uneven dispersion, poor stability and single function. In this work, an aggregation-induced emission (AIE) fluorescent polymer with aldehyde groups in side chain was synthesized and crosslinked with aminopropyl double capped polydimethylsiloxane (NH2-PDMS-NH2) through mild Schiff base reaction to construct a fluorescent elastomer. Compared with fluorescent small molecules, AIE polymers have superior fluorescence performance and can be flexibly designed according to demands. The dynamic imine bonds endow the as-obtained elastomers with self-healing and recycling properties, enabling rapid repair and remodeling at room temperature. Besides, the tensile and swelling properties of PDMS enable them to adjust the concentration of fluorescent units in the matrix under corresponding stimulus, thereby achieving tunable fluorescence emission. Taking advantage of the fluorescent elastomers, we prepared fluorescent anti-counterfeiting patterns that were hidden in daylight and visible under UV light, demonstrating the potential applications of the fluorescent elastomers in the fields of anti-counterfeiting and information encryption. This study also provides an alternative strategy for developing multifunctional fluorescent elastomers.

High-Performance Fluorescent Microspheres Based on Fluorescence Resonance Energy Transfer Mode for Lateral Flow Immunoassays.

The label with a large Stokes shift and strong fluorescence properties could improve the sensitivity of the lateral flow immunoassay (LFIA). Herein, two aggregation-induced emission (AIE) luminogens with spectral overlap were encapsulated in polymers by using the microemulsion method as a label, and the construction of a fluorescence resonance energy transfer mode was further verified via theoretical calculation and spectral analysis. Satisfactorily, the doped AIE polymer microspheres (DAIEPMs) exhibited a large Stokes shift of 285 nm and a 10.8-fold fluorescence enhancement compared to those of the AIEPMs loaded with acceptors. Benefiting from the excellent optical performance, DAIEPMs were applied to the LFIA for sensitive detection of chlorothalonil, which is an organochlorine pesticide. The limit of detection of the proposed DAIEPMs-LFIA was 1.2 pg/mL, which was 4.8-fold and 11.6-fold lower than those of quantum dot bead LFIA and gold nanoparticle LFIA, respectively. This work provides a new strategy to improve the optical properties of fluorescent materials and construct a sensitive and reliable detection platform.

Color-Shifting Fluorescent System Based on an AIE Polymer with an Upper Critical Solution Temperature

The design of thermoresponsive luminescent polymers with both a tunable upper critical solution temperature (UCST) and a tunable color is of great challenge. Herein, a series of thermoresponsive copolymers with UCST and aggregation-induced emission (AIE) behaviors are prepared, and a color-shifting fluorescent system based on the energy conversion between the AIE polymers and fluorescent dyes is constructed. The copolymers are prepared from acrylamide and 6-(4-vinylphenyl)-2,4-diamino-1,3,5-triazine (VPhDT). Benefitting from VPhDT, an AIE-active monomer that can provide multiple hydrogen bonds and enhance association of the polymer chains, the obtained copolymers exhibit both UCST and AIE behaviors in aqueous solutions. Utilizing the AIE copolymers as the donor and fluorescent dyes as the acceptors, color-shifting fluorescent systems that can emit blue, green, and red lights are established. The color-shifting fluorescent systems also exhibit tunable luminescent intensities and colors with the stimuli of temperature and pH. Such a color-shifting fluorescent system may have promising applications in the fields of temperature sensors and information displays.

Tuning the Emission of a Nonconventional Aggregation-Induced Emission Polymer via Silicon-Bridged Twisted Intramolecular Charge Transfer for Targeted Delivery and Visualized Drug Release.

The design of tunable luminescent biomaterials with large Stokes shifts is usually pursued by a twisted intramolecular charge transfer (TICT) effect with switchable emission colors in response to various external stimuli. However, such a strategy is usually realized in conjugated molecules containing benzene or its derivatives and consequently suffers from poor biocompatibility. In this work, a hyperbranched polysiloxane (HBPSi)-based non-conjugated fluorescent polymer with TICT and aggregation-induced emission (AIE) features is developed, and its luminescent properties, fluorescence mechanism, and potential applications are investigated. Initially, the non-conjugated HBPSi exhibits remarkable AIE characteristics due to the formation of through-space conjugation. With the introduction of the sulfur atom, a non-conjugated D-A type AIE material, HBPSi-Cys, that exhibits a dual-state emission with a large Stokes shift of 213 nm, is obtained. The correlation of the lower-energy emission band with solvent polarity suggests the existence of the TICT state. TICT and AIE characteristics direct different properties of HBPSi-Cys, with TICT regulating solvatochromic emission wavelengths and AIE manipulating the emission intensity with a compensation effect. Density functional theory calculations reveal that the non-conjugated D-A structure in HBPSi-Cys was formed across the silicon bridge, with auxochromic sulfhydryl groups and adjacent amide groups as acceptor units and amine and hydroxyl groups as donor units. Additionally, the AIE-active HBPSi could be utilized as a fluorescent probe for the analysis of metal ions. After grafting the AS1411 aptamer to HBPSi-Cys as the recognition motif, HBPSi-Apt possesses excellent targeted bioimaging, drug loading, pH/GSH dual-responsive drug release, and visualized drug delivery performance. This work provides a new way to design functional AIE polymers with tunable optical properties, and the synthesized HBPSi-Cys shows great potential as a smart fluorescent biomaterial.

Smart aggregation‐induced emission polymers: Preparation, properties and bio‐applications

AbstractOwing to the outstanding photophysical properties, organic luminescent materials featuring aggregation‐induced emission (AIE) characteristics have attracted wide attention in various fields. Numerous researches focused on low‐mass AIE luminogens, and relatively less attention has been paid on AIE polymers and the related applications, in spite of the fact that AIE polymers exhibit excellent advantages of processability, multifunctional integration and synergistic effects. In this review, we briefly summarize and discuss the superiorities of AIE polymers in preparation, properties and bio‐applications, and the considerable progress in these aspects are introduced as well. Finally, the structure‐property relationship, challenges and opportunities are also discussed. Hopefully, this review will be a trigger for smart AIE polymer research and further broaden their applications.

Aggregation‐induced emission polymer systems with circularly polarized luminescence

AbstractFunctional materials with circularly polarized luminescence (CPL) have attracted tremendous attention due to their promising applications in three‐dimensional displays, chiral recognition and catalysis, photoelectronic devices, contrast imaging, information encryption, and other fields. Among various CPL‐active materials, polymeric systems with aggregation‐induced emission (AIE) have emerged as excellent candidates because of their efficient aggregate‐state fluorescence, large solid‐state dissymmetry factor, excellent processibility, diversified self‐assembly behaviors, and readily switchable CPL properties. This review summarizes and discusses the recent progress as well as future perspective of diverse AIE polymer systems with CPL, including CPL‐active covalent AIE polymers, CPL‐active supramolecular AIE polymers, and AIEgen/polymer composites with CPL. According to the location or introduction method of AIEgen in polymer structures, this review further divides CPL‐active covalent AIE polymers into three categories, including polymers with AIEgen in main chains, polymers with AIEgen in side chains, and CPL‐active polymers with clusterization‐triggered emission. CPL‐active supramolecular AIE polymers are discussed based on the driving force for the formation of supramolecular polymers, including host–guest interactions, metal coordination, and other non‐covalent interactions. Moreover, examples on the construction of CPL‐active AIEgen/polymer composites by physically mixing AIEgens with chiral (supra)polymers are also presented. This review is anticipated to provide readers with an overall view on the design strategies of CPL‐active AIE polymers, and facilitate further research on the development of CPL materials and AIE polymers with advanced applications.

Facile Assembly Strategy for Luminescent Lanthanide Nanoparticles with Antibacterial Activity Using Aggregation-Inducing Emission Polymers

Aggregation-induced emission (AIE) polymers that permit both outstanding biocompatibility and excellent bioimaging properties are a highly appealing means by which to meet the demands of new-generation biosensors. However, dozens of problems puzzling researchers include the poor water solubility, lack of self-assembling ability, and a luminescence quenching phenomenon cannot be solved thoroughly until now, which limits the further application of AIE polymers. Herein, we developed new polymers with terminal-functionalized 2,6-dipiclinic acid (DPA) groups. The biocompatible polymers with intrinsic AIE properties can form supramolecular aggregates. Furthermore, the polymers can coordinate with Eu3+ to contribute dynamic complexing networks to remain luminescent in water solution. More importantly, all the supramolecular polymers and luminescent lanthanide nanoparticles are demonstrated with satisfying antifouling and antibacterial properties, which provides a bright prospect for medical antifouling coatings and biosensors.

Controlling the Fluorescence Performance of AIE Polymers by Controlling the Polymer Microstructure.

Aggregation-induced emission (AIE) polymers with expected emission wavelength/color and fluorescence efficiency are valuable in applications. However, most AIE polymers exhibit irregular emission wavelength/color changes compared to the original AIE monomers. Here, we report the synthesis of AIE polymers with unchanged emission wavelength by ring-opening (co)polymerizations of 4-(triphenylethenyl)phenoxymethyloxirane (TPEO) and other epoxides or phthalic anhydride. The chemical structures/physical properties of all (co)polymers were characterized by NMR, SEC, MALDI-TOF, and DSC. The co-polyether microstructures were revealed by calculating the reactivity ratios and visualized by Monte Carlo simulation. The photoluminescence quantum yields of all the (co)polymers were determined in the solid state. We systematically correlated the fluorescence performance with molecular weights, crystallinity, monomer compositions, glass transition temperatures, side lengths, and flexibility/rigidity.

Theranostic FRET Gate to Visualize and Quantify Bacterial Membrane Breaching.

Designing new antimicrobial-cum-probes to study real-time bacterial membrane breaching and concurrently developing inquisitorial image-based analytical tools is essential for the treatment of infectious diseases. An array of aggregation-induced emission (AIE) polymers (donor) consisting of neutral, anionic, and cationic charges were designed and employed as antimicrobial theranostic gatekeepers for the permeabilization of the peptidoglycan layer-adherable crystal violet (CV, acceptor). An AIE-active tetraphenylethylene (TPE)-tagged polycaprolactone biodegradable platform was chosen, and their self-assembled tiny amphiphilic nanoparticles were employed as a gatekeeper in the construction of bacterial membrane-reinforced fluorescent resonance energy transfer (FRET) probes. Electrostatic adhering of the cationic AIE polymer and subsequent gate opening aided fluorescent FRET probe activation on the membrane of Gram-negative bacteria, Escherichia coli. The selective photoexcitation energy transfer process in confocal microscopy experiments facilitated the building of a visualization-based FRET assay for the quantification of bactericidal activity. Nonantimicrobial AIE polymers (neutral and anionic) did not breach the bacterial membrane, resulting in no FRET signal. Detailed photophysical studies were done to establish the FRET probe mechanism, and a proof of concept was established.

Controlling AIE and ACQ properties of conjugated carbazole-tetraphenylethene copolymers by ethynylene spacer

Aggregation-induced emission (AIE) and aggregation-caused quenching (ACQ) are controlled by ethynylene spacers between the carbazole and tetraphenylethene. AIE polymers are applied to polymer dots with good emission and water dispersion stability.

A Cationic Amphiphilic AIE Polymer for Mitochondrial Targeting and Imaging.

Mitochondria are important organelles that play key roles in generating the energy needed for life and in pathways such as apoptosis. Direct targeting of antitumor drugs, such as doxorubicin (DOX), to mitochondria into cells is an effective approach for cancer therapy and inducing cancer cell death. To achieve targeted and effective delivery of antitumor drugs to tumor cells, to enhance the therapeutic effect, and to reduce the side effects during the treatment, we prepared a cationic amphiphilic polymer with aggregation-induced emission (AIE) characteristic. The polymer could be localized to mitochondria with excellent organelle targeting, and it showed good mitochondrial targeting with low toxicity. The polymer could also self-assemble into doxorubicin-loaded micelles in phosphate buffer, with a particle size of about 4.3 nm, an encapsulation rate of 11.03%, and micelle drug loading that reached 0.49%. The results of in vitro cytotoxicity experiments showed that the optimal dosage was 2.0 μg/mL, which had better inhibitory effect on tumor cells and less biological toxicity on heathy cells. Therefore, the cationic amphiphilic polymer can partially replace expensive commercial mitochondrial targeting reagents, and it can be also used as a drug loading tool to directly target mitochondria in cells for corresponding therapeutic research.

AIE Polymer Micelle/Vesicle Photocatalysts Combined with Native Enzymes for Aerobic Photobiocatalysis

Biocatalytic transformation has attracted increasing attention in the green synthesis of chemicals due to the diversity of enzymes, their high catalytic activities and specificities, and environmentally benign conditions. Most redox enzymes in nature are dependent on nicotinamide cofactors like β-nicotinamide adenine dinucleotide (NAD+)/reduced nicotinamide adenine dinucleotide (NADH). The use of solar energy, especially visible light, in the regeneration of cofactors through the combination of photocatalysis and biocatalysis provides an extraordinary opportunity to make complete green processes. However, the combination of photocatalysts and enzymes has been challenged by the rapid degradation and deactivation of the enzymatic material by photogenerated reactive oxygen species (ROS). Here, we design core-shell structured polymer micelles and vesicles with aggregation-induced emission (AIE) as visible-light-mediated photocatalysts for highly stable and recyclable photobiocatalysis under aerobic conditions. NAD+ from NADH can be efficiently regenerated by the photoactive hydrophobic core of polymer micelles and the hydrophobic membrane of polymer vesicles, while the enzymatic material (glucose 1-dehydrogenase) is screened from the attack of photogenerated ROS by the hydrophilic surface layer of polymer colloids. After at least 10 regeneration cycles, the enzyme keeps its active state; meanwhile, polymer micelles and vesicles maintain their photocatalytic activity. These polymer colloids show the potential to be developed for the implementation of industrially relevant photobiocatalytic systems.

Multi-stimuli responsive fluorescence switching behaviours of AIE polymers for acid-base vapour sensing and highly sensitive ferric ion detection

Novel aggregation-induced emission (AIE) polymers, i.e., P1-SP and P2-SP, consisting of AIEgenic tetraphenylethylene (TPE) and photochromic spiropyran (SP) units are reported. Both P1-SP and P2-SP exhibit excellent AIE behaviours of TPE moieties in near-aqueous solutions THF/H2O (95% water) and solid states with strong cyan and blue emissions at 494 and 477 nm, respectively. Upon acidification, the close forms of P1-SP and P2-SP can be opened and switched to open P1-MCH+ and P2-MCH+ structures of protonated merocyanine (MCH+), resulting in fluorescence quenching of TPE units through corresponding intramolecular charge transfer (ICT) and Förster resonance energy transfer (FRET) processes. The fluorescence recovery of TPE can be monitored by the neutralization of P1-MCH+ and P2-MCH+ with base solutions under ambient/visible light attributed to the re-close P1-SP and P2-SP structures, which led to respective turn-off ICT and FRET phenomena. Distinct fluorescence quenching behaviours of P1-SP and P2-SP can be observed under various stimuli, including acid conditions and ferric ion interactions, which are also confirmed by theoretical studies. Moreover, P1-SP and P2-SP can be utilized as fluorescence quenching sensors for nanomolar level detections of ferric ion (LOD = 166 and 110 nM for corresponding P1-SP and P2-SP) with excellent selectivities in near-aqueous solutions and paper test strips. Additionally, the interesting visible and fluorescence colour changes of coated cellulosic papers, blended PMMA films and powder forms based on P1-SP and P2-SP under multi-external stimuli (acid-base vapour and visible light/heating processes) are also explored in this report.

Aggregation-induced emission nanoparticles with improved optical absorption for boosting fluorescence signal of tumors in vivo

Nanomaterial development has been extensively investigated for several decades to realize sensitive and accurate imaging of tumors in vivo. The manufacturing of nanoparticles with highly efficient tumor targeting and excellent optical properties is still an important research topic. The structure and composition ratio of materials that decisively contribute to the brightness and size of nanoparticles have a great influence on image sensitivity and tumor targeting efficiency. In this study, we developed aggregation-induced emission (AIE) nanoparticles with a widened light absorption window (nanoPMeOCN/BDP) to enable sensitive in vivo tumor imaging. The signal of nanoparticles is enhanced by integrating a high-density AIE polymer (PMeOCN) and light-absorbing fluorescent dye (BDP) in a nanoscopic space. BDP not only improves the light absorption of particles but also enhances the fluorescence signal of particles by effectively transferring absorbed energy to PMeOCN. The physically blended nanoPMeOCN/BDP show strong light absorption and improved sensitivity for the imaging of biological tissues because of their excellent optical performance compared to nanoPMeOCN of similar nanosizes (∼19 nm in size). In vivo imaging results further confirm that nanoPMeOCN/BDP can provide amplified signals with the successful accumulation of tumor tissue through the enhanced permeability and retention effect. We expect that the design strategy of nanoparticles with improved light absorption will provide a simple and general method for improving the accuracy of disease diagnosis.

Fluorescent Polymers Conspectus.

The development of luminescent materials is critical to humankind. The Nobel Prizes awarded in 2008 and 2010 for research on the development of green fluorescent proteins and super-resolved fluorescence imaging are proof of this (2014). Fluorescent probes, smart polymer machines, fluorescent chemosensors, fluorescence molecular thermometers, fluorescent imaging, drug delivery carriers, and other applications make fluorescent polymers (FPs) exciting materials. Two major branches can be distinguished in the field: (1) macromolecules with fluorophores in their structure and (2) aggregation-induced emission (AIE) FPs. In the first, the polymer (which may be conjugated) contains a fluorophore, conferring photoluminescent properties to the final material, offering tunable structures, robust mechanical properties, and low detection limits in sensing applications when compared to small-molecule or inorganic luminescent materials. In the latter, AIE FPs use a novel mode of fluorescence dependent on the aggregation state. AIE FP intra- and intermolecular interactions confer synergistic effects, improving their properties and performance over small molecules aggregation-induced, emission-based fluorescent materials (AIEgens). Despite their outstanding advantages (over classic polymers) of high emission efficiency, signal amplification, good processability, and multiple functionalization, AIE polymers have received less attention. This review examines some of the most significant advances in the broad field of FPs over the last six years, concluding with a general outlook and discussion of future challenges to promote advancements in these promising materials that can serve as a springboard for future innovation in the field.

In vivo photodynamic therapy based on Near-Infrared AIE cationic polymers

• Cationic AIE polymers synthesized from AIEgen monomers with D-A-D structures. • Quaternary ammonium groups in our AIE-polymers enhance the biocompatibility for PDT. • AIE polymers with absorption maximum near 520 nm and activation by white LED light. • AIE polymers with NIR fluorescence imaging capacity and effective 1 O 2 production. • A metal-free and high atomic-efficiency polymerization method for our AIE polymers. New near-infrared (NIR) photo-responsive polymers with the merits of highly biocompatibility, penetrability and biostability, are highly desirable for cancer photodynamic therapy. Herein, a near-infrared cationic polymers (DCPN-2) featuring aggregation-induced emission (AIE) is synthesized via a ring-opening polymerization to achieve the forceful restriction of intramolecular motion, yielding nanoparticles (NPs) with diameter of about ∼ 200 nm. DCPN-2 exhibits the bright emissions in the NIR region (>650 nm) covering most of visible-light range and effectively generates reactive oxygen species (ROS) under light irradiation. Importantly, the inhibition of tumor growth upon DCPN-2 treatment under light irradiation was demonstrated both in vitro and in vivo. Collectively, this study not only provides potential NIR AIE-polymers for cancer phototheranostics, but also presents a novel strategy of the design of biocompatible photo-responsive polymers for future biomedical applications.

Aggregation-induced emission-active fluorescent polymer sensors for the detection of water in organic solvents, Cu2+ and hemolysis

The hydrophobic polymer HDDA-EDT-SADA with aggregation-induced emission (AIE) property was synthesized via the thiol-ene click copolymerization of salicylaldehyde azine (SA) derivative diacrylate monomer SADA and commercially available 1,2-ethanedithiol (EDT) and 1,6-hexanediol diacrylate (HDDA). HDDA-EDT-SADA was found to display unexpected intense fluorescence in acetone and DMSO compared to that in other good solvents, which dramatically decreased by adding small amount of water. We demonstrate that HDDA-EDT-SADA can be used as a fluorescent sensor for water detection in acetone and DMSO. To improve the water solubility of the AIE-active polymer, SADA was copolymerized with dithiothreitol (DTT) and poly(ethylene glycol) diacrylate (PEGDA) to give an amphiphilic AIE polymer PEGDA-DTT-SADA. Similar fluorescence phenomenon was also found in DMF, suggesting that PEGDA-DTT-SADA could serve as an indicator for water detection in DMF. Thanks to the PEG segments and DTT units, the PEGDA-DTT-SADA was able to well-disperse in water via the formation of stable micelles. The PEGDA-DTT-SADA selectively complexed with Cu2+ and thus could be used as a fluorescent sensor for Cu2+ detection in aqueous media. Moreover, the PEGDA-DTT-SADA could be utilized as a fluorescent sensor for hemolysis ratio detection of red blood cells (RBCs) due to the inner filter effect.

Fused Heterocyclic Polymers with Aggregation-Induced Emission: Synthesis and Applications

Fused heterocyclic polymers with aggregation-induced emission (AIE) have attracted much attention due to their unique photoelectric properties, efficient aggregate-state fluorescence, high thermal stability, and superamplification effect as fluorescence sensors as well as multiple functionalities. Among various synthetic methodologies toward fused heterocyclic AIE polymers, polymerization based on triple bond-containing monomers such as alkynes and (iso)cyanides is a powerful synthesis tool that can in situ generate fused heterocyclic units in polymer backbones in high efficiency. In this Review, we summarize the recent progress in the synthesis of nitrogen-, oxygen-, and multiple heteroatom-containing fused cyclic polymers with AIE features based on polymerizations of triple bond-containing monomers. Furthermore, the high-tech applications of the corresponding fused heterocyclic AIE polymers in the visualization of morphological structures, fluorescence chemo-sensors, stimuli-responsive materials, and photodynamic therapy are illustrated. Finally, perspectives on the challenges and future development directions of this field are discussed.