Aggregation-Induced Emission Boosting the Study of Polymer Science.

The past one hundred years have witnessed the great development of polymer science. The advancement of polymer science is closely related with the development of characterization techniques and methods, from viscometry in molecular weight determination to advanced techniques including differential scanning calorimetry, nuclear magnetic resonance, and scanning electron microscopy. However, these techniques are normally constrained to tedious sample preparation, high costs, harsh experimental conditions, or ex situ characterization. Fluorescence technology has the merits of high sensitivity and direct visualization. Contrary to conventional aggregation-causing quenching fluorophores, those dyes with aggregation-induced emission (AIE) characteristics show high emission efficiency in aggregate states. Based on the restriction of intramolecular motions for AIE properties, the AIE materials are very sensitive to the surrounding microenvironments owing to the twisted propeller-like structures and therefore offer great potential in the study of polymers. The AIE concept has been successfully used in polymer science and provides a deeper understanding on polymer structure and properties. In this review, the applications of AIEgens in polymer science for visualizing polymerization, glass transition, dissolution, crystallization, gelation, self-assembly, phase separation, cracking, and self-healing are exemplified and summarized. Lastly, the challenges and perspectives in the study of polymer science using AIEgens are addressed.

Structural and theoretical insights into the AIE attributes of phosphindole oxide: the balance between rigidity and flexibility.

Multiple intramolecular motions consume the excited-state energy of luminogenic molecules upon photoexcitation and lower the emission efficiency. The low frequency rotational motion of aromatic rings can be facilely restricted by steric constraint in the condensed phase, but the high frequency bond stretching motion can hardly be suppressed by aggregation. In this work, three phosphorus-containing heterocycles, 1,2,3,4,5-pentaphenylphosphole-1-oxide (PPPO), 1,2,3-triphenylphosphindole-1-oxide (TPPIO), and 1,2,3-triphenylphosphindole (TPPI), were synthesized and characterized. Their optical properties, crystal-packing manners, electronic features, and fluorescence dynamics were systematically investigated, and theoretical calculations were performed to decipher structure-property relationships. The results reveal that these luminogens are weak emitters in solutions but show strong emission in aggregates, exhibiting obvious aggregation-induced emission (AIE) features. The aggregation-insensitive stretching motion, which is dominant in PPPO, is lowered in TPPIO, enabling TPPIO to fluoresce much more efficiently than PPPO in aggregates. The stretching motion is even more lowered in TPPI, but its relatively planar conformation suffers emission quenching due to strong π-π stacking interactions in aggregates. Therefore, a twisted molecular conformation consisting of a rigid stator and a rotatable periphery is demonstrated to be a rational design for more efficient AIE luminogens.

Aggregation-Induced-Emission-Active Macrocycle Exhibiting Analogous Triply and Singly Twisted Möbius Topologies.

Molecules with Möbius topology have drawn increasing attention from scientists in a variety of fields, such as organic chemistry, inorganic chemistry, and material science. However, synthetic difficulties and the lack of functionality impede their fundamental understanding and practical applications. Here, we report the facile synthesis of an aggregation-induced-emission (AIE)-active macrocycle (TPE-ET) and investigate its analogous triply and singly twisted Möbius topologies. Because of the twisted and flexible nature of the tetraphenylethene units, the macrocycle adjusts its conformations so as to accommodate different guest molecules in its crystals. Moreover, theoretical studies including topological and electronic calculations reveal the energetically favorable interconversion process between triply and singly twisted topologies.

Multienzyme cascades analysis of α-glucosidase by oxygen deficient MoO3-x.

BACKGROUND: Recently, the enzymatic cascade reactions during the cellular process are widely used for fabricating robust biosensors and they have attracted extensive attention in analyzing various clinical biomarkers. The enzymatic cascades analysis is commonly based on the peroxidase (POD)/oxidase coupled system. However, the requirement of harsh acidic environment, poor stability and interference from the oxidase further limit their analytical practicability. Herein, novel chromogenic nanomaterials with H2O2 sensitive features are urgently required to replace the POD nanozyme in enzymatic cascades based bioanalysis. RESULTS: Herein, oxygen deficient MoO3-x with H2O2 sensitive features and near-infrared (NIR) absorption band have been ultra-fast synthesized and utilized for the enzymatic cascades analysis of α-Glucosidase's activity, and inhibitors screening. With the addition of 4-nitrophenyl-α-d-glucopyranoside, the simultaneous presence of α-Glucosidase and glucose oxidase (GOx) would fade their dark blue color and decrease the NIR absorption. The α-Glucosidase's activity can be analyzed by the absorption at 770 nm, and their limit of detection is 8 × 10-5 U/mL, indicating the superior performance of the proposed colorimetric assay. Moreover, this proposed α-Glucosidase assay is further utilized for inhibitors screening. Moreover, the activity of α-Glucosidase can also be analyzed by the smartphone and microplate reader through the agarose-based colorimetric portable kit. SIGNIFICANCE: This MoO3-x involved enzymatic cascades assay would facilitate for the development of bio-analysis related to H2O2 generation or consumption. Moreover, this bio-analysis strategy will contribute to the development of other H2O2 sensitive chromogenic nanomaterials for the analysis of certain biomolecules and biological enzymes.

Carbon dots capped cerium oxide nanoparticles for highly efficient removal and sensitive detection of fluoride.

Since the excess exposure to F- may induce serious issues to human health, the effective adsorption and sensitive detection of F- is essential. Therefore, carbon dots (CDs) capped CeO2 (CeO2@CDs) was synthesized via hydrothermal treatment of tannic acid and CeCl3. Due to abundant phenolic hydroxyl are reserved and excellent hydrophilicity, CeO2@CDs possess high F- adsorption capacity. The partition coefficient parameters (PC) are determined to be 2.65 L/g, which is comparable with previous work. The kinetics results and adsorption isotherm are consistent with pseudo-second-order model and Freundlich model, respectively, indicating the chemisorption dominate the adsorption, mainly via the ion exchange between hydroxyl and F-. Since phenolic hydroxyl existed on the CeO2@CDs, synergetic effect of CDs and CeO2 contribute to superior ROS eliminating capacity, even at acidic conditions. Moreover, due to the ROS scavenging of CeO2 @CDs abilities can be potentiated by F-, colorimetric detection of F- can be realized via horseradish peroxidase as an indicator. The linear range is 0.3-2.1 mM with limit of detection is 0.13 mg/L. The current results imply that CeO2@CDs possess potential in both efficient removal and sensitive detection of F- related contamination issues and elucidation of development to address other anions related issues.

Simultaneously enhancing the photocatalytic and photothermal effect of NH2-MIL-125-GO-Pt ternary heterojunction for rapid therapy of bacteria-infected wounds.

Infections caused by bacteria threaten human health, so how to effectively kill bacteria is an urgent problem. We therefore synthesized a NH2-MIL-125-GO-Pt ternary composite heterojunction with graphene oxide (GO) and platinum (Pt) nanoparticles co-doped with metal-organic framework (NH2-MIL-125) for use in photocatalytic and photothermal synergistic disinfection under white light irradiation. Due to the good conductivity of GO and the Schottky junction between Pt and MOF, the doping of GO and Pt will effectively separate and transfer the photogenerated electron-hole pairs generated by NH2-MIL-125, thereby effectively improving the photocatalytic efficiency of NH2-MIL-125. Meanwhile, NH2-MIL-125-GO-Pt has good photothermal effect under white light irradiation. Therefore, the NH2-MIL-125-GO-Pt composite can be used for effective sterilization. The antibacterial efficiency of NH2-MIL-125-GO-Pt against Staphylococcus aureus and Escherichia coli were as high as 99.94% and 99.12%, respectively, within 20 min of white light irradiation. In vivo experiments showed that NH2-MIL-125-GO-Pt could effectively kill bacteria and promote wound healing. This work brings new insights into the use of NH2-MIL-125-based photocatalyst materials for rapid disinfection of environments with pathogenic microorganisms.

Nanowire crystals of a rigid rod conjugated polymer.

In this paper, we show that well-defined, highly crystalline nanowires of a rigid rod conjugated polymer, a poly(para-phenylene ethynylene)s derivative with thioacetate end groups (TA-PPE), can be obtained by self-assembling from a dilute solution. Structural analyses demonstrate the nanowires with an orthorhombic crystal unit cell wherein the lattice parameters are a approximately = 13.63 A, b approximately = 7.62 A, and c approximately = 5.12 A; in the nanowires the backbones of TA-PPE chains are parallel to the nanowire long axis with their side chains standing on the substrate. The transport properties of the nanowires examined by organic field-effect transistors (OFETs) suggest the highest charge carrier mobility approaches 0.1 cm(2)/(V s) with an average value at approximately 10(-2) cm(2)/(V s), which is 3-4 orders higher than that of thin film transistors made by the same polymer, indicating the high performance of the one-dimensional polymer nanowire crystals. These results are particular intriguing and valuable for both examining the intrinsic properties of PPEs polymer semiconductors and advancing their potential applications in electronic devices.

Molecular orientation and field-effect transistors of a rigid rod conjugated polymer thin films.

Molecular orientation in thin films of a rigid rod conjugated polymer, a derivative of poly(para-phenylene ethynylene)s with linear side chains and thioacetyl end groups, was investigated by reflection-absorption infrared spectroscopy and X-ray diffraction technique. The results indicated that TA-PPE molecules tended to align with their backbone planes perpendicular to substrates, that is, with an "edge-on" molecular orientation in the films. Such molecular orientation is favorable for the efficient carrier transport in two-dimensional direction in the polymer films (i.e., via both the intrachain and interchain), so that high performance organic field-effect transistors were fabricated with hole mobility at around approximately 4.3 x 10(-3) cm(2)/Vs.

Organic Single-Crystalline Ribbons of a Rigid "H"-type Anthracene Derivative and High-Performance, Short-Channel Field-Effect Transistors of Individual Micro/Nanometer-Sized Ribbons Fabricated by an "Organic Ribbon Mask" Technique.

The synthesis of a rigid, planar H-type anthracene derivative is described. Single-crystalline ribbons at micro- and nanometer sizes can be controllably produced and transistors based on an individual ribbon can be fabricated in situ through a newly developed "organic ribbon mask" method, in which the channel length of the transistors can be easily scaled down to sub-micrometer level.

Large π-Conjugated Porous Frameworks as Cathodes for Sodium-Ion Batteries.

Organic sodium-ion batteries (OSIBs) are promising alternatives of inorganic lithium-ion batteries. The cathodes of OSIBs still suffer from low capacity, poor rate performance, and low cyclability. For the first time, we demonstrate the large π-conjugated porous frameworks (CPFs) as cathodes for OSIBs, motivated by the speculation that the CPFs are capable of enhancing charge transport, facilitating ionic diffusion, inhibiting dissolution, as well as improving stability. The batteries based on the obtained CPFs indeed delivered much better electrochemical performance than the small molecular construction units without any complex post-treatments. The moderate BET surface area of CPFs and the detailed analyses suggested that the micropores and the lamellar structure should be responsible for the fast ionic diffusion. We believe that this work will provoke growing interest of CPFs for OSIBs with functional molecular design toward high performance and pave a venue to achieve OSIBs in large-scale applications.

An Aggregation-Induced Emission-Active Macrocycle: Illusory Topology of the Penrose Stairs.

The facile synthesis of a tetraphenylethene-based macrocycle having aggregation-induced emission characteristics and that expresses illusory topology of the Penrose stairs is presented. As a result of the twisted chirality (P or M) of the tetraphenylethene unit and the axial chirality of the macrocyclic linkage (R or S), the macrocycle exhibits two absolute configurations whose interconversion is energetically favorable as revealed by theoretical calculations.

Role of redox centre in charge transport investigated by novel self-assembled conjugated polymer molecular junctions.

Molecular electronics describes a field that seeks to implement electronic components made of molecular building blocks. To date, few studies have used conjugated polymers in molecular junctions despite the fact that they potentially transport charge more efficiently than the extensively investigated small-molecular systems. Here we report a novel type of molecular tunnelling junction exploring the use of conjugated polymers, which are self-assembled into ultrathin films in a distinguishable 'planar' manner from the traditional vertically oriented small-molecule monolayers. Electrical measurements on the junctions reveal molecular-specific characteristics of the polymeric molecules in comparison with less conjugated small molecules. More significantly, we decorate redox-active functionality into polymeric backbones, demonstrating a key role of redox centre in the modulation of charge transport behaviour via energy level engineering and external stimuli, and implying the potential of employing tailor-made polymeric components as alternatives to small molecules for future molecular-scale electronics.

A highly selective AIE fluorogen for lipid droplet imaging in live cells and green algae.

Lipid droplets (LDs) are subcellular organelles for energy storage and lipid metabolism regulation. Here we report an aggregation-induced emission-active fluorogen, TPE-AmAl, for specific LD imaging. TPE-AmAl is cell-permeable: upon entering the live cells, the dye molecules can selectively accumulate in the LDs and turn on the fluorescence. TPE-AmAl possesses twisted intramolecular charge transfer properties as well: the emission colour in the hydrophobic LDs is blue-shifted by >100 nm than that in aqueous buffers. Compared with the commercial lipid droplet dye, TPE-AmAl demonstrates the advantages of low background, short staining time, high selectivity, excellent biocompatibility, and good photostability. The utilization of TPE-AmAl for LD staining in green algae is also demonstrated, indicating their potential application in the high-throughput screening of high-value microalgae as a preferential biofuel source.

Ordering rigid rod conjugated polymer molecules for high performance photoswitchers.

Molecules of a rigid rod conjugated polymer, a derivative of poly(para-phenylene ethynylene)s with thioacetyl end groups (TA-PPE), were well aligned by drop-casting the polymer solution onto the friction-transferred poly(tetrafluoroethylene) substrates. TA-PPE molecules were found to be exactly oriented with their conjugated backbones along the PTFE sliding direction. Photoresponse characteristics based on the uniaxially ordered film were significantly improved compared to those of devices with the disordered film. For example, the switch on/off ratio of the photoswitchers with aligned molecules was as high as 330-400, while that of devices without alignment was only 8-12. It was due to the efficient carrier transport along the highly aligned polymer films, in which the molecules of TA-PPE oriented along the carrier transport direction of the devices.