Recent Advances and Future Prospects of Aggregation-induced Emission Carbohydrate Polymers

Synthesis of an aggregation-induced emission (AIE) dye with pH-sensitivity based on tetraphenylethylene-pyridine for fluorescent nanoparticles and its applications in bioimaging and in vitro anti-tumor effect

In this contribution, a novel AIE monomers 2-(4-styrylphenyl)- 1,2-diphenylvinyl)styryl)pyridine (SDVPY) with smart fluorescent pH-sensitivity basing on tetraphenylethylene-pyridine were successfully synthesized for the first time, subsequently, a series of amphiphilic copolymers PEG-PY were achieved by reversible addition-fragmentation chain transfer (RAFT) polymerization of SDVPY and poly(ethylene glycol) methacrylate (PEGMA), which would self-assemble in water solution to form core-shell nanoparticles (PEG-PY FONs) with about 150 nm diameter. The PEG-PY FONs showed obvious fluorescence response to Fe3+, HCO3- and CO32- ions in aqueous solution owing to their smart pH-sensitivity and AIE characteristics, and their maximum emission wavelength could reversibly change from 525 nm to 624 nm. The as-prepared PEG-PY FONs showed also prospective application in cells imaging with the variable fluorescence for different pH cells micro-environment. When PEG-PY copolymers self-assembled with the anti-tumor drug paclitaxel (PTX), the obtained PY-PTX FONs could effectively deliver and release PTX with pH-sensitivity, and could be easily internalized by A549 cells and located at the cytoplasm with high cytotoxicity, which was further confirmed by the Calcein-AM/PI staining of dead and alive A549 cells. Moreover, the flow cytometry results indicated that the PY-PTX FONs could obviously induce the apoptosis of A549 cells, which further showed the great potential of PY-PTX FONs in the application of tumors therapy.

Aggregation-Induced Emission-Active Fluorescent Polymer: Multi-Targeted Sensor and ROS Scavenger

A multi-functional polymer with aggregation-induced emission (AIE)-active salicylaldehyde azine (SA) functionality and reactive oxygen species (ROS)-responsive thioether groups is readily prepared via thiol-ene click polymerization of SA derivative diacrylate monomer, poly(ethylene glycol) diacrylate, and 3,6-dioxa-1,8-octanedithiol. The obtained AIE-active polymer exhibited an unexpected strong emission in amide solvents compared to that in other common organic solvents that was dramatically decreased by adding a trace amount of water, suggesting that the polymer could be utilized as a water trace indicator in amide solvents. In the backbone, the PEG segments make the polymer well dispersed in water and the ROS-responsive thioether groups enable this polymer as a promising ROS scavenger, with embedded SA moieties as a fluorescent indicator for the hemolysis determination. Due to the ability of SA moieties to complex with Cu²⁺, this AIE polymer can also be utilized as a fluorescent sensor for selective Cu²⁺ detection in real-world water samples. Thus, this multi-functional polymer is anticipated to be well applied in biological and environmental applications.

Synthesis and Fluorescent Thermoresponsive Properties of Tetraphenylethylene-Labeled Methylcellulose

Functional polymer, especially the one based on renewable and sustainable materials, has attracted increasing attention to satisfy the growing demand for the design of stimuli-responsive devices. Methylcellulose (MC) is a water-soluble derivative of cellulose, which has been widely used in many fields for its biocompatibility and biological inertness. In this work, MC is labeled by tetraphenylethylene (TPE) via azide-alkyne click reaction to obtain a fluorescent cellulose-based derivative of MC-TPE. The degree of substitution of MC-TPE is determined to be 0.074, which can be self-assembled into micelles in water with the size of 42 ± 6 nm. MC-TPE shows thermoresponsivity and thermoreversibility in size, transmittance, and fluorescence, enabling it to work as a fluorescent thermosensor. Moreover, MC-TPE exhibits nontoxicity and biocompatibility, allowing its application in MCF-7 cell imaging. Therefore, this newly functional natural polymer shows promising potentials in the fields of sensing and bioimaging.

Synthesis, characterization, aggregation-induced enhanced emission and solvatochromic behavior of dimethyl 4′-(diphenylamino)biphenyl-3,5-dicarboxylate: experimental and theoretical studies

Red shift in the emission wavelength by 149 nm as a result of increased solvent polarity.

Aggregation-Induced Emission (AIE)-Labeled Cellulose Nanocrystals for the Detection of Nitrophenolic Explosives in Aqueous Solutions

Aggregation-induced emission (AIE) active cellulose nanocrystals (TPE-CNCs) were synthesized by attaching tetraphenylethylene (TPE) to cellulose nanocrystals (CNCs). The structure and morphology of TPE-CNCs were characterized by FT-IR, XRD, ζ-potential measurements, elemental analysis, TEM, atomic force microscopy (AFM), and dynamic laser light scattering (DLS). Fluorescent properties of TPE-CNCs were also further studied. Unlike aggregation-caused quenching (ACQ), TPE-CNCs emitted weak fluorescence in the dilute suspensions, while emitting efficiently in the aggregated states. The AIE mechanism of TPE-CNCs was attributed to the restriction of an intramolecular rotation (RIR) process in the aggregated states. TPE-CNCs displayed good dispersity in water and stable fluorescence, which was reported through the specific detection of nitrophenolic explosives in aqueous solutions by a fluorescence quenching assay. The fluorescence emissions of TPE-CNCs showed quantitative and sensitive responses to picric acid (PA), 2,4-dinitro-phenol (DNP), and 4-nitrophenol (NP), and the detection limits were 220, 250, and 520 nM, respectively. Fluorescence quenching occurred through a static mechanism via the formation of a nonfluorescent complex between TPE-CNCs and nitrophenolic analytes. A fluorescence lifetime measurement revealed that the quenching was a static process. The results demonstrated that TPE-CNCs were excellent sensors for the detection of nitrophenolic explosives in aqueous systems, which has great potential applications in chemosensing and bioimaging.

Organic Fluorescent Dye-based Nanomaterials: Advances in the Rational Design for Imaging and Sensing Applications

Self-assembled fluorescent nanomaterials based on small-molecule organic dyes are gaining increasing popularity in imaging and sensing applications over the past decade. This is primarily due to their ability to combine spectral properties tunability and biocompatibility of small molecule organic fluorophores with brightness, chemical and colloidal stability of inorganic materials. Such a unique combination of features comes with rich versatility of dye-based nanomaterials: from aggregates of small molecules to sophisticated core-shell nanoarchitectures involving hyperbranched polymers. Along with the ongoing discovery of new materials and better ways of their synthesis, it is very important to continue systematic studies of fundamental factors that regulate the key properties of fluorescent nanomaterials: their size, polydispersity, colloidal stability, chemical stability, absorption and emission maxima, biocompatibility, and interactions with biological interfaces. In this review, we focus on the systematic description of various types of organic fluorescent nanomaterials, approaches to their synthesis, and ways to optimize and control their characteristics. The discussion is built on examples from reports on recent advances in the design and applications of such materials. Conclusions made from this analysis allow a perspective on future development of fluorescent nanomaterials design for biomedical and related applications.

Construction of Functional Hyperbranched Poly(phenyltriazolylcarboxylate)s by Metal-Free Phenylpropiolate-Azide Polycycloaddition

The 1,3-dipolar cycloaddition of activated internal alkynes with azides has been developed into an efficient polymerization reaction for constructing functional linear 1,4,5-trisubstitued polytriazoles. However, it is rarely employed for the synthesis of hyperbranched polymers. In this work, metal-free polycycloadditions of tris(3-phenylpropiolate)s (1) and tetraphenylethene-containing diazides (2) are performed in dimethylformamide at 100 °C for 7 and 12 h, producing hyperbranched poly(phenyltriazolylcarboxylate)s (hb-PPTCs) with high molecular weights and satisfactory regioregularities in good yields. The hb-PPTCs have good solubility in common organic solvents and high thermal stability. They are non-emissive in solutions, but emit intensively upon aggregation, showing an aggregation-induced emission effect. Their aggregates can work as fluorescent sensors for explosive detection with high sensitivity. Furthermore, the polymers can be utilized for the fabrication of 2D fluorescent patterns with high resolution by UV irradiation through copper grid masks.

Color-tunable AIE-active conjugated polymer nanoparticles as drug carriers for self-indicating cancer therapy via intramolecular FRET mechanism

In this paper, two novel AIE-active conjugated polymers were synthesized by Pd-catalyzed Suzuki coupling polymerization reaction.

Synthesis, characterization, aggregation-induced emission, solvatochromism and mechanochromism of fluorinated benzothiadiazole bonded to tetraphenylethenes

Compounds consisting of unsubstituted, monofluoro and difluoro substituted benzothiadiazole bonded to two tetraphenylethenes were successfully prepared by palladium catalyzed Suzuki–Miyaura cross-coupling reaction of their corresponding co-monomers. All compounds exhibited aggregation-induced emission characteristics when the water fraction was higher than 60% in the THF/water mixtures. The emission maximum for the three compounds was blue-shifted when the water content reached 90% compared to that in THF solution. The intensity of emission maximum of difluorinated benzothiadiazole linked with two tetraphenylethenes was 2.5 times higher in 90% water compared to those in THF solution. Surprisingly, two liquid crystal phases with two distinct emission colors were observed only for the compound containing difluorinated benzothiadiazole bonded to two tetraphenylethene. All compounds showed remarkable solvatochromic properties in selected solvents with different polarities. The powder XRD results and mechanochromism of the compounds suggested that the solid state structures can change from one form to another by grinding, fuming or annealing processes.

Fluorinated benzothiadiazole bonded to two tetraphenylethenes were synthesized. The compounds exhibited remarkable aggregation-induced emission, solvatochromism and mechanochromism.

Luminescent color tuning with polymer films composed of boron diiminate conjugated copolymers by changing the connection points to comonomers

The boron diiminate polymers with variable connection points and optical properties were synthesized.

Metal-free phenylpropiolate–azide polycycloaddition: efficient synthesis of functional poly(phenyltriazolylcarboxylate)s

Metal-free polycycloaddition of phenylpropiolates and azide is developed to afford multifunctional triazole-containing polyesters.

Ca2+ Induced Crosslinking of AIE-Active Polyarylene Ether Nitrile into Fluorescent Polymeric Nanoparticles for Cellular Bioimaging

Biocompatible fluorescent polymeric nanoparticles (FPNs) are promising luminescent probes in cellular bioimaging, while the fabrication of high-quantum-yield FPN using nonconjugated heterochain polymers derived from step-growth polymerization is still in its infancy. Herein, the nonconjugated polyarylene ether nitrile (PEN) is endowed with aggregation-induced emission (AIE) feature by incorporation of an AIEgen named of 1,2-di(4-hydroxyphenyl)-1,2-diphenylethene into macromolecular backbone. Furthermore, the AIE-active PEN is crosslinked into water soluble fluorescent nanospheres showing good biocompatibility and strong emission ≈480 nm with a quantum yield of 21% in the presence of Ca²⁺ , which allows the successful bioimaging of cancer cells. Due to the facile fabrication of FPNs and their effective bioimaging performance, the current work will open the way for the biomedical applications of various high performance polyarylene ethers.

Nano-Star-Shaped Polymers for Drug Delivery Applications

With the advancement of polymer engineering, complex star-shaped polymer architectures can be synthesized with ease, bringing about a host of unique properties and applications. The polymer arms can be functionalized with different chemical groups to fine-tune the response behavior or be endowed with targeting ligands or stimuli responsive moieties to control its physicochemical behavior and self-organization in solution. Rheological properties of these solutions can be modulated, which also facilitates the control of the diffusion of the drug from these star-based nanocarriers. However, these star-shaped polymers designed for drug delivery are still in a very early stage of development. Due to the sheer diversity of macromolecules that can take on the star architectures and the various combinations of functional groups that can be cross-linked together, there remain many structure-property relationships which have yet to be fully established. This review aims to provide an introductory perspective on the basic synthetic methods of star-shaped polymers, the properties which can be controlled by the unique architecture, and also recent advances in drug delivery applications related to these star candidates.