Aggregation-induced Emission Polymers Research Articles

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.

Unexpected Fluorescence Emission Behaviors of Tetraphenylethylene-Functionalized Polysiloxane and Highly Reversible Sensor for Nitrobenzene

Tetraphenylethylene (TPE), a typical luminogen with aggregation-induced emission (AIE) features, has been widely used to prepare AIE fluorescent materials. In this study, TPE-functionalized polydimethylsiloxane (n-TPE-AP-PDMS) was successfully synthesized by attaching TPE to polydimethylsiloxane via aza-Michael addition. The introduction of polydimethylsiloxane to TPE had no obvious effect on photophysical properties. Intriguingly, n-TPE-AP-PDMS exhibited two opposite fluorescence emission behaviors in different systems: aggregation-induced quenching (ACQ) behavior in a tetrahydrofuran/water mixture and typical AIE phenomenon in a tetrahydrofuran/hexane mixture. This unexpected transition from ACQ to AIE can be attributed to a twisted intramolecular charge-transfer effect and flexible aminopropyl polydimethylsiloxane. n-TPE-AP-PDMS was further used as a fluorescent probe to detect nitrobenzene and it showed high quenching efficiency. Moreover, the n-TPE-AP-PDMS film showed high reversibility so that the quenching efficiency remained constant after five cycles. This work can provide a deeper understanding of AIE behavior and guidance to develop a new AIE polymer for chemosensors with high performance.

Modulation of Aggregation-Caused Quenching to Aggregation-Induced Emission: Finding a Biocompatible Polymeric Theranostics Platform for Cancer Therapy.

Dual intramolecular FRET polymers are synthesized via Suzuki coupling and their luminescence characteristics from aggregation-caused quenching (ACQ) to aggregation-induced emission (AIE) is modulated conveniently by adjusting the charged ratios. The finally obtained AIE polymer is further employed to construct doxorubicin loaded nanoparticles as a promising theranostics platform for cancer therapy.

Photoresponsive aggregation-induced emission polymer film for anti-counterfeiting

The development of solid-state smart materials, in particular those showing photoresponsive luminescence, is highly desirable for their cutting edge applications in displays, sensors, data-storage, and anti-counterfeiting. However, to achieve both excellent photoresponsive performance and bright luminescence in solid state remains challenge. Herein, we integrate a novel photochromic fluorophore YL into flexible polymer chains, thereby enabling the resultant polymer PYL with reversible photoisomerization upon aggregation. Remarkably, the polymer PYL possesses excellent photochromic properties and aggregation-induced emission (AIE) activity, which can be attributed to the photoactive YL moiety. Upon light exposure, its film exhibits reversibly off-to-on fluorescent modulation with quick response, high emission efficiency and signal contrast, sharply different from the weak emission in solution. The novel photoresponsive AIE polymer with invisible/visible color and fluorescence transformation allows for advanced anti-counterfeiting applications. This work provides an efficient platform for constructing solid-state photocontrollable luminescent materials.

Novel Authentic and Ultrafast Organic Photorecorders Enhanced by AIE‐Active Polymer Electrets via Interlayer Charge Recombination

AbstractOrganic photonic memory, featuring a variety of glamorously light‐driven characteristics, is rapidly growing into an indispensable building block for next‐generation optical communication systems. However, the ambiguity of their operating mechanism associated with the limitation of photoadaptive materials as an electronics promoter results in the slow development of photonic transistor‐based devices. In this study, the conjugated polymers composed of donor–acceptor motifs with typical aggregation‐induced emission (AIE) behaviors are designed and successfully discover high‐performance photoprogrammable memory. Moreover, the mechanism of photoboosted recording behavior, attributed to the recombination of the formed interlayer excitons right after simultaneous excitation without applying vertical and parallel electric‐field at the interface in‐between active semiconductor and AIE polymers, is cautiously corroborated by steady‐state PL and pulse PL measurements. The AIE‐polymer memory devices perform ultrafast photoresponse time of 0.1 ms, an outstanding current switch ratio up to 106, and retention stability over 40 000 s without significant dissipation. Furthermore, photoresponsive AIE‐polymer electrets not only modulate the memory performance through the emission wavelength but easily switch storage behavior of nonvolatile memory from flash to WORM by adjusting the torsion‐angle through the motif of the donor and acceptor moieties. These findings open an avenue for designing conjugated polymer electret for ultrafast optical storage devices.

Amphiphilic polymers for aggregation-induced emission at air/liquid interfaces

Polymersomes and related self-assembled nanostructures displaying Aggregation-Induced Emission (AIE) are highly relevant for plenty of applications in imaging, biology and functional devices. Experimentally simple, scalable and universal strategies for on-demand self-assembly of polymers rendering well-defined nanostructures are highly desirable. A purposefully designed combination of amphiphilic block copolymers including tunable lengths of hydrophilic polyethylene glycol (PEGm) and hydrophobic AIE polymer poly(tetraphenylethylene-trimethylenecarbonate) (P(TPE-TMC)n) has been studied at the air/liquid interface. The unique 2D assembly properties have been analyzed by thermodynamic measurements, UV–vis reflection spectroscopy and photoluminescence in combination with molecular dynamics simulations. The (PEG)m-b-P(TPE-TMC)n monolayers formed tunable 2D nanostructures self-assembled on demand by adjusting the available surface area. Tuning of the PEG length allows to modification of the area per polymer molecule at the air/liquid interface. Molecular detail on the arrangement of the polymer molecules and relevant molecular interactions has been convincingly described. AIE fluorescence at the air/liquid interface has been successfully achieved by the (PEG)m-b-P(TPE-TMC)n nanostructures. An experimentally simple 2D to 3D transition allowed to obtain 3D polymersomes in solution. This work suggests that engineered amphiphilic polymers for AIE may be suitable for selective 2D and 3D self-assembly for imaging and technological applications

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.

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.

One-Step Multicomponent Polymerizations for the Synthesis of Multifunctional AIE Polymers.

As a new class of functional luminescent materials, polymers with aggregation-induced emission (AIE) feature attract much attention because of their advantages of efficient solid-state fluorescence, excellent processability, structural diversity, and multifunctionalities. Among all polymerization methods toward AIE polymers, multicomponent polymerizations (MCPs) exhibit the merits of simple operation, good atom economy, high polymerization efficiency, broad functional-group tolerance, etc. In this feature article, the recent progress on the development of one-step MCPs for the synthesis of AIE polymers is highlighted. The representative functionalities of the resulting AIE polymers are illustrated. Perspectives on the challenges and future development directions of this field are also discussed.

An AIE polymer prepared via aldehyde-hydrazine step polymerization and the application in Cu2+ and S2− detection

Herein we reported the synthesis of a novel amphiphilic AIE (aggregation-induced emission) polymer with salicylaldehyde azine (SA) moieties and PEG segments in the backbone via the aldehyde-hydrazine step polymerization. The polymer can self-assemble into stable micelles in water at ambient temperature and display intense orange fluorescence because of the aggregation of SA moieties in the core. Moreover, the polymer was found to be thermoresponsive with a relatively high LCST (lower critical solution temperature) and the LCST can be tuned via the chain length of PEG segments. The polymer micelles formed at ambient temperature can serve as a turn-off fluorescent probe for the selective detection of Cu2+ in aqueous media with a low detection limit of 53 nM. The fluorescence of polymer can be completely quenched by Cu2+ and the formed polymer-Cu2+ complex can be used as a turn-on fluorescent probe for the selective detection of S2− with a detection limit of 0.24 μM. The polymer is expected as a useful fluorescent probe for the selective detection of Cu2+ and S2− in environmental field.

Aggregation-induced emission polymers for high performance PLEDs with low efficiency roll-off

AIE polymers pTPE-DPA-Cz and pTPE-DPA-Flu are synthesized and used as emitting layers in doped and non-doped polymeric LEDs through a solution process, and show maximum EQE of 3.26% in the doped PLEDs and CE of 3.69 cd A−1 for the non-doped PLEDs and low efficiency roll-off.

Near-Infrared Polymer Dots with Aggregation-Induced Emission for Tumor Imaging

Semiconducting polymer dots (Pdots) have been applied in various biological fields owing to their tunable fluorescence, high brightness, and facile functionalization. However, most Pdots emit in the visible region, wherein fluorescence imaging would suffer from significant photon scattering and autofluorescence in biological tissues. Furthermore, Pdots typically exhibit a reduced fluorescence compared to the corresponding original polymers in organic solvents as a result of aggregation-caused quenching effect. These drawbacks make it difficult to develop Pdots that exhibit bright emission in the near-infrared (NIR) wavelength range. Herein, based on an aggregation-induced emission (AIE) polymer, we report Pdots exhibiting NIR emission along with high fluorescence quantum yield. After fabricating the AIE polymer into Pdots, the fluorescence intensity was enhanced by 2.5-times, yielding NIR emission with a quantum yield of ∼23%. The Pdots also possess outstanding optical properties and biocompatibility, mak...

Synthesis of AIE polyethylene glycol-block-polypeptide bioconjugates and cell uptake assessments of their self-assembled nanoparticles

A synthetic polypeptide-based bioconjugate bearing tetraphenylethylene (TPE) at the polypeptide side chains, named mPEG-PPLGgTPE, was synthesized by ring-opening polymerization (ROP) of α-amino acid-N-carboxyanhydride (NCA) along with post-polymerization modification method. Interestingly, the bioconjugate enabled both the aggregation induced emission (AIE) effect at 469 nm and the aggregation caused quenching (ACQ) effect around 365 nm depending on water fraction in the tetrahydrofuran/water (THF/H2O) mixed solution, and this feature was very different from the commonly used TPE-based AIE polymers. The strong emission at the 365 nm was a rarely seen monomeric emission for the TPE units. Further studies on the fluorescence spectra indicated that the monomeric emission was not related with the secondary structure of polypeptides, but caused by the TPE unit itself. The mPEG-PPLGgTPE could self-assemble to AIE nanoparticles (NPs) in water in a mean size of 253 nm with polyethylene glycol (PEG) as the shells in surface. In addition, HeLa cell uptake level of the NPs was unsatisfactory according to the cell imaging results, which was independent of the polypeptides conformation, the PEG length and the size of NPs.

Synthesis, characterization and visible light activated fluorescence of azo caged aggregation-induced emission polymers

Tetraphenylethylene (TPE) based aggregation-induced emission (AIE) polymers containing different degrees of functionalization of photobleachable azo chromophores were developed and their photophysical properties were explored. The synthesized epoxy monomer derived from TPE core reacted with aniline to give the precursor polymer, which confirmed typical AIE characteristics. Then through a post-polymerization azo-coupling scheme, various contents of 2-phenylazo-4, 5-dicyanoimidazole groups were readily introduced into the TPE based epoxy precusor polymer. Experimental results suggested that only a small amount of such imidazole-type azo component could totally cage the intense AIE fluorescence of the whole polymer due to the fluorescence resonance energy transfer process. By exposure to visible light (450 nm), azo units could be photo bleached notably, thus resulting in dramatic recovery of the blue fluorescence. Depending on this, visible light induced fluorescent patterns were easily fabricated and erased, indicating that the prepared azo caged AIE Polymers could be promising candidates for anti-counterfeiting and optical information storage.

AIEgens-lightened Functional Polymers: Synthesis, Properties and Applications

Recently, polymers with aggregation-induced emission (AIE) effects have attracted significant attention due to their broad applications in luminescence sensors, stimuli responsive materials, electroluminescence devices, etc. In this review, we summarize recent advances concerning AIE polymers. Four types of AIE polymers including end-functionalized polymers, side-chain polymers, main-chain polymers, and other polymers according to the location of AIEgens, are described. Their synthetic preparation, optical property, AIE effects, and applications are also illustrated in this review.

Geminal Cross Coupling (GCC) Reaction for AIE Materials

Tetraphenylethylene (TPE) derivatives are typical aggregation-induced emission (AIE) molecules, which have been widely investigated and applicated. The Rathore’s procedures and McMurry reaction are the two frequently used methods for synthesizing the TPE derivatives. The complex processes and low tolerance of active function groups make the TPE with limited structures and properties in some degree. Very recently, a novel strategy, named geminal cross coupling (GCC) reaction, is developed for designing and synthesizing various topological small molecules and polymers with rich optical properties beyond simple TPE compounds, and becomes a powerful synthesis method to AIE materials. This review overviews the current progresses of AIE molecules and polymers prepared by GCC as well as their applications. We believe that GCC reaction will have a bright future in the development of the next generation of tetraarylethylene (TAE)-kind AIE materials.

A versatile method for preparing well-defined polymers with aggregation-induced emission property

The living ring-opening metathesis polymerization (ROMP) was demonstrated as a versatile method for preparing the well-defined polymers with aggregation-induced emission (AIE) property. In this approach, the norbornene-based monomers were prepared containing side groups of varied typical AIE fluorogens such as distyrenneanthracene (M1), 1,2,3,4,5-pentaphenylsiole (M2), and tetraphenylethene derivative (M3). Initiating by the Grubbs third generation catalyst (G3), ROMP could consume all of the exemplified monomers in less than 30 min and produce the corresponding well-defined AIE polymers of poly(M1), poly(M2), and poly(M3) with controlled molecular weight and narrow polydispersity. By copolymerizing with the norbornene-based monomer (M4) having poly(ethylene glycol) (PEG) side chain, ROMP could also produce the well-defined amphiphilic AIE block copolymers such as poly(M1)-b-poly(M4) and poly(M2)-b-poly(M4). Compared to norbornene-based AIE monomers, the resultant polymers showed enhanced AIE property, in which the same fluorescence intensity was obtained from the lower molar concentration of AIE fluorogen inside polymers than that inside monomers. In addition, the self-assembly of amphiphilic AIE block copolymers in selective solvents produced the fluorescent nanoparticles with varied morphologies and structures including spherical micelles, cylindrical micelles, and vesicles.

The Marriage of Aggregation-Induced Emission with Polymer Science.

Aggregation-induced emission (AIE) is a novel photophysical phenomenon coined in 2001 by our group and describes the enhanced light emission of some luminogens in the aggregate or solid state. The combination of AIE research and polymer science is a smart approach to produce functional luminescent materials with mechanical strength and excellent processability for real-world applications. In this feature article, recent progress in AIE polymeric systems, including chemical synthesis and physical blending strategies, is summarized. Through chemical synthesis, various AIE-active polymers, such as covalently bonded polymers, supramolecular polymers, and nonconjugated luminescent polymers, can be obtained. Serving as environmentally sensitive probes, AIE luminogens can also be physically doped into polymers to generate interesting systems. Finally, outlooks and perspectives on the future direction of AIE polymeric systems are discussed.

Indication of Mechanical Damage through Piezochromic Materials

Piezochromic materials have attracted a great deal of attentions for decades by the virtue of detecting mechanical damage in advance and avoid dangerous failure. However, several vital issues, such as the structure-properties relationship of aggregation-induced emission (AIE), still remain unclear, which impede the discovery of novel piezochromic luminescent materials with excellent properties. Here, the research on the mechanism of AIE polymers will be deeply reviewed, and other types of piezochromic systems will be introduced in order to suggest the future design of novel piezochromic device

A Comparison of ACQ, AIE and AEE-Based Polymers Loaded on Polyurethane Foams as Sensors for Explosives Detection.

An aggregation-caused quenching (ACQ)-active polymer (PF), an aggregation-induced emission (AIE)-active polymer (PFTPE) and an aggregation-enhanced emission (AEE)-active polymer (PTTPE) were synthesized by tetraphenylethane (TPE), fluorene and thiophene moieties. Polyurethane (PU) foams modified by PF, PFTPE and PTTPE, namely PU-PF, PU-PFTPE and PU-PTTPE, using ultrasonication-assisted method have been prepared. A comparative study of PU-PF, PU-PFTPE and PU-PTTPE for detection explosives had been performed, and significant fluorescence quenching was observed with the introduction of PA solutions. The as-prepared PU-PF, PU-PFTPE and PU-PTTPE sensors exhibited a superior sensitivity for PA solutions with different concentrations. Remarkably, PU-PF gave a quenching efficiency of 96.2%, higher than 93.5% for PU-PFTPE and 86.7% for PU-PTTPE at a PA concentration of 180 µg·mL−1 in methanol, which was attributed to the effective energy transfer from the fluorophore (PF) to the nitro explosive (PA). This suggested that some ACQ polymers, applied to detect explosives, could afford better performances than AIE or AEE polymers through modification of structures and selection of adequate carriers. At the same time, these chemical sensors can be recycled many times.