A Borinic Acid Polymer with Fluoride Ion- and Thermo-responsive Properties that are Tunable over a Wide Temperature Range

Anion-Responsive Colorimetric and Fluorometric Red-Shift in Triarylborane Derivatives: Dual Role of Phenazaborine as Lewis Acid and Electron Donor

Photophysical modulation of triarylboranes (TABs) through Lewis acid-base interactions is a fundamental approach for sensing anions. Yet, design principles for anion-responsive TABs displaying significant red-shift in absorption and photoluminescence (PL) have remained elusive. Herein, a new strategy for modulating the photophysical properties of TABs in a red-shift mode has been presented, by using a nitrogen-bridged triarylborane (1,4-phenazaborine: PAzB) with a contradictory dual role as a Lewis acid and an electron donor. Following the strategy, PAzB derivatives connected with an electron-deficient azaaromatic have been developed, and these compounds display a distinct red-shift in their absorption and PL in response to an anion. Spectroscopic analyses and quantum chemical calculations have revealed the formation of a tetracoordinate borate upon the addition of fluoride, narrowing the HOMO-LUMO gap and enhancing the charge-transfer character in the excited state. This approach has also been demonstrated in modulating the photophysical properties of solid-state films.

Synthesis of New Glycine-Based Polymers and their Thermoresponsive Behavior in Water

In this work, new glycine-derived polymers are developed that exhibit thermoresponsive properties in water. Therefore, a series of monomers containing one, two, or three amide functional groups and one terminal cyanomethyl group is synthesized. The resulting homopolymers, obtained by free radical polymerization (FRP) and reversible addition fragmentation chain transfer (RAFT) polymerization, display a sharp and reversible upper critical solution temperature (UCST)-type phase transition in water. Additionally, it is shown that the cloud point (TCP) can be adjusted over more than 60 °C by the number of glycyl groups present in the monomer structure and by the polymer's molar mass. These novel thermoresponsive polymers based on cyanomethylglycinamide enrich the range of nonionic UCST polymers and are promising to find applications in various fields.

Recent Advances in the Synthesis of Borinic Acid Derivatives

Borinic acids [R2B(OH)] and their chelate derivatives are a subclass of organoborane compounds used in cross-coupling reactions, catalysis, medicinal chemistry, polymer or optoelectronics materials. In this paper, we review the recent advances in the synthesis of diarylborinic acids and their four-coordinated analogs. The main strategies to build up borinic acids rely either on the addition of organometallic reagents to boranes (B(OR)3, BX3, aminoborane, arylboronic esters) or the reaction of triarylboranes with a ligand (diol, amino alcohol, etc.). After general practical considerations of borinic acids, an overview of the main synthetic methods, their scope and limitations is provided. We also discuss some mechanistic aspects.

One-Pot Synthesis of Stimuli-Responsive Fluorescent Polymers through Polymerization-Induced Emission

Stimuli-responsive opposite emission (A)/absorption (B) polymer material (A∪B = Ω and A∩B = Ø) represents a novel polymer material that is difficult to prepare. Here, we demonstrate a one-pot strategy for the molecular design of stimuli-responsive opposite emission/absorption polymer material with intriguing properties of opposite emission/absorption and aggregation-induced emission (AIE) type nontraditional intrinsic luminescence (NTIL) in the visible region, through reversible addition-fragmentation chain transfer polymerization-induced emission (PIE) of the N,N-dimethyl-triphenylmethanol moiety. Investigations reveal that NTIL is due to the through-space conjugation effect caused by polymer chain entanglement, when increasing the repeating unit number. The corresponding stimuli-responsive opposite emission/absorption properties are derived from the carbocation-quinoid mechanism, which enables the fluorescence encryption capability. This work therefore demonstrates the proof of concept of a novel opposite emission/absorption polymer material that might cause inspiration in different fields.

Molecular bases for temperature sensitivity in supramolecular assemblies and their applications as thermoresponsive soft materials

Thermoresponsive supramolecular assemblies have been extensively explored in diverse formats, from injectable hydrogels to nanoscale carriers, for a variety of applications including drug delivery, tissue engineering and thermo-controlled catalysis. Understanding the molecular bases behind thermal sensitivity of materials is fundamentally important for the rational design of assemblies with optimal combination of properties and predictable tunability for specific applications. In this review, we summarize the recent advances in this area with a specific focus on the parameters and factors that influence thermoresponsive properties of soft materials. We summarize and analyze the effects of structures and architectures of molecules, hydrophilic and lipophilic balance, concentration, components and external additives upon the thermoresponsiveness of the corresponding molecular assemblies.

Barbier single-atom polymerization induced emission as a one-pot approach towards stimuli-responsive luminescent polymers

A one-pot strategy for the design of stimuli-responsive luminescent polymers has been demonstrated through Barbier PIE, where the N,N-dimethyl moiety endows the polymers with both stimuli-responsive and red-shifted nonconjugated emission properties.

Mo2 C/Reduced Graphene Oxide Composites with Enhanced Electrocatalytic Activity and Biocompatibility for Microbial Fuel Cells

A simple, cost-effective strategy was developed to effectively improve the electron transfer efficiency as well as the power output of microbial fuel cells (MFCs) by decorating the commercial carbon paper (CP) anode with an advanced Mo₂ C/reduced graphene oxide (Mo₂ C/RGO) composite. Benefiting from the synergistic effects of the superior electrocatalytic activity of Mo₂ C, the high surface area, and prominent conductivity of RGO, the MFC equipped with this Mo₂ C/RGO composite yielded a remarkable output power density of 1747±37.6 mW m^-2 , which was considerably higher than that of CP-MFC (926.8±6.3 mW m^-2 ). Importantly, the composite also facilitated the formation of 3D hybrid biofilm and could effectively improve the bacteria-electrode interaction. These features resulted in an enhanced coulombic efficiency up 13.2 %, nearly one order of magnitude higher than that of the CP (1.2 %).

The Introduction of the Radical Cascade Reaction into Polymer Chemistry: A One-Step Strategy for Synchronized Polymerization and Modification

Polymerization and modification play central roles in polymer chemistry and are generally implemented in two steps, which suffer from the time-consuming two-step strategy and present considerable challenge for complete modification. By introducing the radical cascade reaction (RCR) into polymer chemistry, a one-step strategy is demonstrated to achieve synchronized polymerization and complete modification in situ. Attributed to the cascade feature of iron-catalyzed three-component alkene carboazidation RCR exhibiting carbon-carbon bond formation and carbon-azide bond formation with extremely high efficiency and selectivity in one step, radical cascade polymerization therefore enables the in situ synchronized polymerization through continuous carbon-carbon bond formation and complete modification through carbon-azide bond formation simultaneously. This results in a series of α, β, and γ poly(amino acid) precursors. This result not only expands the methodology library of polymerization, but also the possibility for polymer science to achieve functional polymers with tailored chemical functionality from in situ polymerization.

Well-controlled polymerization of tri-vinyl dynamic covalent boroxine monomer: one dynamic covalent boroxine moiety toward a tunable penta-responsive polymer

Attributed to dynamic characteristics of dynamic covalent boroxine, well-controlled polymerization of tri-vinyl monomer and molecular design of penta-responsive polymer with only one functional moiety are achieved.

Ion specific fluorescence modulation of polyvinyl alcohol-boronate matrices

Borylated polymers are emerging as valuable chemosensors that can report analyte binding through an array of responses. Condensing aryl boronic acids onto polyvinyl alcohol affords fluorescent polymers that can detect and extract borophilic anions.

Exploring Organic Metal Halides with Reversible Temperature-Responsive Dual-Emissive Photoluminescence

The exceptional structural tunability of organic metal halides endows them with fascinating electronic and photophysical properties, providing much scope for applications. In this work, single crystals of the organic metal halide (C₄ H₉ NH₃ )₂ MnI₄ are found to show reversible thermo-induced luminescent chromism within a wide temperature range. The (C₄ H₉ NH₃ )₂ MnI₄ single crystal exhibits two emission peaks at 550 and 672 nm, which are assigned to a d-d transition of Mn²⁺ -centered tetrahedra and self-trapped excitons, respectively. The temperature-dependent emission color change is attributed to the thermo-induced trapping and detrapping process of the self-trapped exciton. (C₄ H₉ NH₃ )₂ MnI₄ exhibits a maximum photoluminescence quantum efficiency of up to 68 % at 70 °C. The disclosed interacted photoluminescence decay mechanisms may prove useful for the further design of organic metal halides for optical thermometry.

Tunable Hydrogen Release from Amine-Boranes via their Insertion into Functional Polystyrenes

Polystyrene-g-boramine random copolymers are dihydrogen reservoirs with tunable dehydrogenation temperatures, which can be adjusted by selecting the boramine content in the copolymers. They display a unique dihydrogen thermal release profile, which is a direct consequence of the insertion of the amine-boranes in a polymeric scaffold, and not from a direct modification of the electronics or sterics of the amine-borane function. Finally, the mixture of polystyrene-g-boramines with conventional NH₃ -BH₃ (borazane) allows for a direct access to organic/inorganic hybrid dihydrogen reservoirs with a maximal H₂ loading of 8 wt %. These exhibit a dehydrogenation temperature lower than that of either the borazane or the polystyrene-g-boramines taken separately.

Promoting water dissociation performance by borinic acid for the strong-acid/base-free hydrogen evolution reaction

Borinic acid is reported as a new proton donor with promoted water dissociation performance for the strong-acid/base-free hydrogen evolution reaction.

Let There be Light: Polymeric Micelles with Upper Critical Solution Temperature as Light-Triggered Heat Nanogenerators for Combating Drug-Resistant Cancer

Complete drug release and efficient drug retention are two critical factors in reversing drug resistance in cancer therapy. In this regard, polymeric micelles with an upper critical solution temperature (UCST) are designed as a new exploration to reverse drug resistance. The amphiphilic UCST-type block copolymers are used to encapsulate photothermal agent IR780 and doxorubicin (DOX) simultaneously. The integrated UCST-type drug nanocarriers show light-triggered multiple synergistic effects to reverse drug resistance and are expected to kill three birds with one stone: First, owing to the photothermal effect of IR780, the nanocarriers will be dissociated upon exposure to laser irradiation, leading to complete drug release. Second, the photothermal effect-induced hyperthermia is expected to avoid the efflux of DOX and realize efficient drug retention. Last but not least, photothermal ablation of cancer cells can be achieved after laser irradiation. Therefore, the UCST-type drug nanocarriers provide a new strategy in reversing drug resistance in cancer therapy.

Anion Specificity in Dimethyl Sulfoxide-Water Mixtures Exemplified by a Thermosensitive Polymer

In the present work, we have investigated the anion-specific upper critical solution temperature (UCST) behavior of polymer-supported borinic acid (PBA) in dimethyl sulfoxide-water (DMSO-H₂O) mixtures. An inverted V-shaped series CH₃COO^- < Cl^- < salt-free > NO₃^- > ClO₄^- > SCN^- is observed in terms of the anion-specific UCST of PBA in the DMSO-H₂O mixtures. Both direct anion-polymer interactions and indirect solvent-mediated anion-polymer interactions are involved in the specific anion effect on the UCST behavior of PBA. The direct binding of anions to the PBA surface generates a salting-in effect on PBA, causing the UCST for the different types of anions to increase from chaotropic to kosmotropic anions due to the stronger binding of the more chaotropic anions. On the other hand, the indirect anionic polarization of hydrogen bonding between PBA and DMSO molecules also produces a salting-in effect on PBA, leading the UCST for the different types of anions to increase from kosmotropic to chaotropic anions because of the stronger capability of the more kosmotropic anions to polarize the hydrogen bonding. Thus, the dominating anion-PBA interactions change from the direct anion binding to the indirect anionic polarization of hydrogen bonding as the anions change from chaotropes to kosmotropes. The observed inverted V-shaped series suggests that the specific anion effect on the UCST behavior of PBA in the DMSO-H₂O mixtures is determined by the combined effects of the binding of anions to the PBA surface and the anionic polarization of hydrogen bonding between PBA and DMSO molecules.

Preparation of lactic acid- and glucose-responsive poly(ε-caprolactone)-b-poly(ethylene oxide) block copolymer micelles using phenylboronic ester as a sensitive block linkage

The present study describes the synthesis, self-assembly and responsiveness to glucose and lactic acid of biocompatible and biodegradable block copolymer micelles using phenylboronic ester as the linkage between hydrophobic poly(ε-caprolactone) (PCL) and hydrophilic poly(ethylene oxide) (PEO). The PCL block with pendant phenylboronic acid (PCLBA) was synthesized by combining ε-caprolactone (ε-CL) ring-opening polymerisation (ROP), using 4-hydroxymethyl(phenylboronic) acid pinacolate as the initiator, and pinacol deprotection. The glucose-terminated PEO (PEOGlc) was prepared by 1,3-dipolar, Cu(i)-catalysed, alkyne-azide cycloaddition of α-methoxy-ω-propargyl poly(ethylene oxide) and 1-azido-1-deoxy-d-glucopyranose. All new compounds were evaluated by 1H NMR spectroscopy and by SEC analysis. PCLBA and PEOGlc blocks were linked in NaOH acetone solution, which was indirectly confirmed by Alizarin Red S fluorescence and directly by 1H NMR spectroscopy. Dialysis against Milli-Q water induced the self-assembly of PCLBA-b-PEOGlc nanoparticles, which were characterised by static (SLS) and dynamic (DLS) light scattering and by cryogenic transmission electron microscopy (cryo-TEM). Furthermore, the microscopic properties of the charged interface between the hydrophobic PCLBA core and the hydrophilic PEOGlc shell were examined by electrophoretic light scattering (zeta potential) and by fluorescence spectroscopy using the fluorescent probe 5-(N-dodecanoyl)aminofluorescein (DAF) as a pH indicator. Subsequently, the nanoparticles were transferred to a phosphate buffer saline (PBS) solution supplemented with different concentrations of glucose to simulate the physiological conditions in blood or lactic acid to simulate acidic cytosolic or endosomal conditions in tumour cells. Adding a surplus of glucose or lactic acid, which competitively binds to PBA, removes the stabilising hydrophilic PEOGlc blocks, thereby triggering marked nanoparticle aggregation. However, the rate of aggregation induced by lactic acid is considerably faster than that induced by glucose, as confirmed by light scattering. Thus, this novel block copolymer may contribute to the field of selective, lactic acid- and/or glucose-responsive drug delivery vehicle design under both pathological and physiological conditions.

Discrimination of saturated alkanes and relevant volatile compounds via the utilization of a conceptual fluorescent sensor array based on organoboron-containing polymers

A conceptual sensor array for the efficient discrimination and fast detection of saturated alkanes and commonly found volatile solvents is reported.

This work reports a conceptual sensor array for the highly discriminative analysis of 20 clinically and environmentally relevant volatile small organic molecules (VSOMs), including saturated alkanes and common solvents, in the air at room temperature. For the construction of the sensor array, a four coordinated, non-planar mono-boron complex and four relevant polymers are synthesized. Based on the polymers and the use of different substrates, 8 fluorescent films have been fabricated. Integration of the film-based sensors results in the sensor array, which demonstrates unprecedented discriminating capability toward the VSOMs. Moreover, for the signal molecule of lung cancer, n-pentane, the response time is less than 1 s, the experimental detection limit is lower than 3.7 ppm, and after repeating the tests over 50 times no observable degradation was observed. The superior sensing performance is partially ascribed to the tetrahedral structure of the boron centers in the polymers as it may produce molecular channels in the films, which are a necessity for fast and reversible sensing. In addition, the polarity of the micro-channels may endow the films with additional selectivity towards the analytes. The design as demonstrated provides an effective strategy to improve the sensing performance of fluorescent films to very challenging analytes, such as saturated alkanes.

The introduction of the Barbier reaction into polymer chemistry

The Barbier reaction, a widely utilized reaction for carbon-carbon bond formation, has played important roles in modern organic chemistry for more than a century. Here, we show its successful introduction to polymer chemistry. Through one-pot Barbier polyaddition (both A₂+B₂ type and AB type) of monomers containing an organic halide and a benzoyl group, a series of phenylmethanol group containing polymers, including polymonophenylmethanol (PMPM), polydiphenylmethanol (PDPM), and polytriphenylmethanol (PTPM), have been synthesized. Para-PTPM exhibits interesting aggregation-induced emission, tunable thermo-responsive over a wide temperature range, sensory, luminescence enhancement of fluorescent dye in solid-state and processing properties. This significantly expands the libraries of monomer and polymer, and opens up an avenue for the design and application of functional polymer materials.

Pincushion of Tubule Discovery and Tubular Morphology Landscape Establishment of Block Copolymer Self-Assemblies

Block copolymer (BCP) self-assembly is a versatile technique in the preparation of polymeric aggregates with varieties of morphologies. However, its morphology library is limited. Here, the discovery of pincushion of tubules is reported for the first time, via BCP self-assembly of poly(4-vinylpyridine)-b-polystyrene (P4VP-b-PS) with very high molecular weight (500 kDa) and asymmetry (2 mol% P4VP). The investigation confirms the importance of core-forming block length on morphology control of BCP self-assemblies, especially with respect to tubular structures. The morphology landscape of tubular structures is successfully established, where dumbbell of tubule, tubule, loose clew of tubules, tight clew of tubules, and pincushion of tubules can be prepared by adjusting the core-forming block length. This work therefore expands the structure library of BCP self-assemblies and opens up a new avenue for the further applications of these tubular materials.

Catalytic B-C Coupling by Si/B Exchange: A Versatile Route to π-Conjugated Organoborane Molecules, Oligomers, and Polymers

Conjugated organoboranes have emerged as attractive hybrid materials for optoelectronic applications. Herein, a highly efficient, environmentally benign catalytic B-C bond formation method is presented that uses organosilicon compounds, dibromoboranes, and the metal-free organocatalyst Me₃SiNTf₂. This Si/B exchange approach has been successfully applied to the synthesis of arylborane molecules 4a-c, oligomers 8a,b, and polymers 8a',b'. Photophysical investigations, supported by TD-DFT calculations, reveal highly effective π-conjugation in thienyl- and furylborane species; the latter are also highly emissive.

Double Recognition and Selective Extraction of Glycoprotein Based on the Molecular Imprinted Graphene Oxide and Boronate Affinity

Specific recognition and separation of glycoproteins from complex biological solutions is very important in clinical diagnostics considering the close relationship between glycoproteins with the occurrence of diverse diseases, but the lack of materials with high selectivity and superior capture capacity still makes it a challenge. In this work, graphene oxide (GO) based molecularly imprinted polymers (MIPs) possessing double recognition abilities have been synthesized and applied as highly efficient adsorbents for glycoprotein recognition and separation. Boronic acid functionalized graphene oxide (GO-APBA) was first prepared and a template glycoprotein (ovalbumin, OVA) was then immobilized onto the surface of GO-APBA through boronate affinity. An imprinting layer was subsequently deposited onto GO-APBA surface by a sol-gel polymerization of organic silanes in aqueous solution. After the removal of the template glycoprotein, 3D cavities with double recognition abilities toward OVA were obtained in the as-prepared imprinted materials (GO-APBA/MIPs) because of the combination of boronate affinity and molecularly imprinted spatial matched cavities. The obtained GO-APBA/MIPs exhibited superior specific recognition toward OVA with imprinted factor (α) as high as 9.5, significantly higher than the corresponding value (4.0) of GO/MIPs without the introduction of boronic acid groups. Meanwhile, because of the synergetic effect of large surface area of graphene and surface imprinting, high binding capacity and fast adsorption/elution rate of GO-APBA/MIPs toward OVA were demonstrated and the saturation binding capacity of GO-APBA/MIPs could reach 278 mg/g within 40 min. The outstanding recognizing behavior (high adsorption capacity, highly specific recognition, and rapid binding rate) coupled to the facile and environmentally friendly preparation procedure makes GO-APBA/MIPs promising in the recognition, separation, and analysis of glycoproteins in clinics in the future.

Borinic Acid Polymer: Simplified Synthesis and Enzymatic Biofuel Cell Application

A simplified one-pot and less harmful method has been introduced for the synthesis of borinic acid monomer. The corresponding borinic acid polymer (PBA) has been prepared by reversible addition-fragmentation chain transfer polymerization. Property investigations confirm the characteristics of PBA as a new type of "smart material" in the field of thermo-responsive polymer. The potential application of PBA in the field of enzymatic biofuel cell has been illustrated with a wide open circuit potential of 0.92 V.

Recent developments in and perspectives on three-coordinate boron materials: a bright future

The empty p z -orbital of a three-coordinate organoboron compound leads to its electron-deficient properties, which make it an excellent π-acceptor in conjugated organic chromophores. The empty p-orbital in such Lewis acids can be attacked by nucleophiles, so bulky groups are often employed to provide air-stable materials. However, many of these can still bind fluoride and cyanide anions leading to applications as anion-selective sensors. One electron reduction generates radical anions. The π-acceptor strength can be easily tuned by varying the organic substituents. Many of these compounds show strong two-photon absorption (TPA) and two-photon excited fluorescence (TPEF) behaviour, which can be applied for e.g. biological imaging. Furthermore, these chromophores can be used as emitters and electron transporters in OLEDs, and examples have recently been found to exhibit efficient thermally activated delayed fluorescence (TADF). The three-coordinate organoboron unit can also be incorporated into polycyclic aromatic hydrocarbons. Such boron-doped compounds exhibit very interesting properties, distinct from their all-carbon analogues. Significant developments have been made in all of these areas in recent years and new applications are rapidly emerging for this class of boron compounds.

Thermoresponsive functional polymers based on 2,6-diaminopyridine motif with tunable UCST behaviour in water/alcohol mixtures

Two thermoresponsive polyacrylamides based on the 2,6-diaminopyridine motif were synthesized and their UCST-type reversible thermoresponsive behaviour was studied in water/alcohol mixtures.

RAFT polymerization to form stimuli-responsive polymers

Stimuli-responsive polymers respond to a variety of external stimuli, which include optical, electrical, thermal, mechanical, redox, pH, chemical, environmental and biological signals. This paper is concerned with the process of forming such polymers by RAFT polymerization.

Expanding the morphology library of block copolymer self-assemblies with clews of tubules

Clews of tubules are reported via block copolymer self-assembly of P4VP-b-PS with both high asymmetry and very high molecular weight.

Versatile Method to Expand the Morphology Library of Block Copolymer Solution Self-Assemblies with Tubular Structures

Self-assembly of block copolymers (BCPs) in solution is a powerful technology to achieve a broad range of structures, such as spheres, cylinders, vesicles, and other hierarchical structures. However, the BCP self-assembly library is limited, especially with respect to tubular structures. Here we show a versatile strategy to expand the morphology library of block copolymer solution self-assemblies with tubular structures (including tubular dumbbells and tubules) via self-assembly of the most common diblock copolymers P4VP-b-PS BCPs in methanol. No special chemistry is needed in this strategy, which proves the universality of this method. The novelty of the strategy is to keep the BCPs both highly asymmetric and with very high molecular weight. The underlying formation mechanism and kinetics of these tubular structures were elucidated. The prepared tubular structures expand the structure library of BCP solution self-assemblies and open up a new avenue for the further applications of a variety of tubular materials.

Control of Polymer Phase Separation by Roughness Transfer Printing for 2D Microlens Arrays

Great efforts have been devoted to the control of phase separation between blended polymers in terms of the advantages for engineering functional topologies. A simple and straightforward pathway through roughness transfer printing (RTP) is proposed to realize the control of polymer phase separation. The additional roughness difference, which is introduced by trace agarose transferred from a hydrogel stamp, offers a great effect on the rate of nucleation and coalescence orientation of polymethylmethacrylate (PMMA) protrusions grown from a polydimethylsiloxane (PDMS) network. Using a particular topography of agarose stamp and a proper growth time in toluene atmosphere, a 2D microlens array with high uniformity is obtained that shows great potential for optical applications. Moreover, the control of polymer phase separation was successfully extended to the collection and identification of fingerprints with a high degree of replication.