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Understanding Degradation Dynamics of Azomethine-containing Conjugated Polymers
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Imine-based semiconducting polymers based on thiophene-flanked diketopyrrolopyrrole (TDPP) are widely used to realize naturally disposable electronic devices. However, TDPP easily decomposes under mildly acidic conditions, limiting its potential for use in recyclable systems. Herein, we designed and synthesized two chemically recyclable thienoisoindigo (TII)-based polymers bearing an imine bond. These polymers were prepared from polycondensation reactions of the dialdehyde-functionalized monomer TII-(CHO)2 with p-phenylenediamine (PD) to produce p(TII-PD) and with 2,6-naphthalenediamine (2,6ND) to produce p(TII-2,6ND), respectively. Using ultraviolet-visible-near infrared spectroscopy, nuclear magnetic resonance, and mass spectroscopy, we examined the recyclability of both polymers. Under mildly acidic conditions, the imine-based polymers fully degrade into the original TII-(CHO)2 in as little as one day. Moreover, the recovered TII-(CHO)2 monomer is chemically stable for up to 6 months under acidic conditions, allowing us to isolate the monomer in high yield (>90%). Using the recovered TII-(CHO)2 monomer, we prepared recycled polymers, re-p(TII-PD) and re-p(TII-2,6ND). The recycled polymers displayed nearly the same electrical properties as the pristine polymers, with field-effect transistor mobilities in the order of 10⁻²–10⁻³ cm² V⁻¹ s⁻¹. These results demonstrate the versatility of the TII-based monomer unit for developing fully recyclable semiconducting polymers.
Conjugated copolymers containing electron donor and acceptor units in their main chain have emerged as promising materials for organic electronic devices due to their tunable optoelectronic properties.
The energies of CH2=CH−CH=N⁺R2+HNR*2→CH2=CH−CH=N⁺R*2+HNR2 reactions (exchange of propenal between two secondary amines) and of similar equilibria with cinnamaldehyde have been calculated and compared. Iminium ions from pyrrolidines with substituents that can help stabilize the positive charge are especially stable in the gas phase, as expected, whereas in very polar solvents the predicted order of stability (of their iminium ions) is: O‐tert‐butyldiphenylsilylprolinol>pyrrolidine>O‐methylprolinol>2‐tert‐butylpyrrolidine>Jørgensen‐Hayashi catalyst>2‐tritylpyrrolidine>N,N‐dimethylprolinamide>trimethylsilyl prolinate>3‐triflamidopyrrolidine>methyl prolinate≫MacMillan‐1 catalyst>MacMillan‐2 catalyst. When ion pairs such as iminium tetrafluoroborates, in CHCl3, are compared, the order is similar. These data can be used to predict which iminium salts may predominate when two or more secondary amines and appropriate acids are added to conjugated carbonyl compounds.
Per- and polyfluoroalkyl substances (PFASs) pose a significant health threat to humans at trace levels. Because of its ubiquity across the globe, there have been intense efforts to rapidly quantify PFASs in the environment while also mitigating their release. This work reports an electrochemical sensor with a selective perfluorinated anion exchange ionomer (PFAEI) coating for direct sensing of perfluorooctanoic acid (PFOA)-a type of PFAS. Notably, the sensor operates without the need of redox probes and has a limit of detection around 6.51 ± 0.2 ppb (15 nM) in buffered deionized water and drinking water. By testing the sensor with different ionomer electrode coatings, it was inferred that the PFAEI favors PFOA anions over other competing anions in solution through a combination of electrostatic and van der Waal interactions.
Degradable organic semiconductors have significant potential for transient and biomedical organic electronics, but there have been only a few studies on fully degradable conjugated polymers (CPs) that achieve high electrical performance. In addition, these examples are limited to p-type CPs. In this study, a series of fully degradable n-type CPs, naphthalene diimide (NDI)-based terpolymer (PNDIT2/IM-f) are developed. The incorporation of an imine linker (IM) into the CP backbone affords the capability of facile hydrolysis degradation while maintaining efficient π-conjugations and excellent electrical properties. An additional benefit of this molecular design is the systematic tunability of the degradation characteristics and electrical performance depending on the IM content (fIM). At the optimal point (fIM = 0.45) that enables complete degradation of the polymer under acidic conditions, the resulting PNDIT2/IM-0.45 film exhibits high electron mobility (μe) of 0.04 cm² V⁻¹ s⁻¹ in organic field-effect transistors (OFETs), demonstrating excellent potential as transient OFETs. The high μe value is mainly attributed to the enlarged edge-on orientations and tighter stacking of PNDIT2/IM-f crystallites as increasing fIM. Thus, this study provides useful guidelines for the design of fully degradable n-type CPs and establishes an important correlation between the molecular structure−electronic performance−transient properties.
Electronic e-waste (e-waste) is a growing problem worldwide. In 2019, total global production reached 53.6 million tons, and is estimated to increase to 74.7 million tons by 2030. This rapid increase is largely fuelled by higher consumption rates of electrical and electronic goods, shorter life cycles and fewer repair options. E-waste is classed as a hazardous substance, and if not collected and recycled properly, can have adverse environmental impacts. The recoverable material in e-waste represents significant economic value, with the total value of e-waste generated in 2019 estimated to be US $57 billion. Despite the inherent value of this waste, only 17.4% of e-waste was recycled globally in 2019, which highlights the need to establish proper recycling processes at a regional level. This review provides an overview of global e-waste production and current technologies for recycling e-waste and recovery of valuable material such as glass, plastic and metals. The paper also discusses the barriers and enablers influencing e-waste recycling with a specific focus on Oceania.
The tridentate ligand L and its complexes with transition-metal ions have been prepared and characterized. The polycondensation reactions of transition-metal complexes with different dialdehydes led to the formation of transition-metal-complex-based polyazomethines, which have been obtained by on-substrate polymerization, and their electrochemical and electrochromic performance have been investigated. The most interesting properties are exhibited by polymers of Fe(II) and Cu(II) ions obtained by the reaction of the appropriate complexes with a triphenylamine-based dialdehyde. Fe(II) polymer P1 undergoes a reversible oxidation/reduction process and a color change from orange to gray due to the oxidation of Fe(II) to Fe(III) ions concomitant with the oxidation of the triphenylamine group. Its electrochromic properties such as long-term stability, switching times, and coloration efficiencies have been investigated, providing evidence of the utility of the on-substrate polycondensation reaction in the formation of thin films of electrochromic metallopolymers.
Covalent organic frameworks (COFs) have emerged as an important class of organic semiconductors and photocatalysts for the hydrogen evolution reaction (HER)from water. To optimize their photocatalytic activity, typically the organic moieties constituting the frameworks are considered and the most suitable combinations of them are searched for. However, the effect of the covalent linkage between these moieties on the photocatalytic performance has rarely been studied. Herein, we demonstrate that donor‐acceptor (D‐A) type imine‐linked COFs can produce hydrogen with a rate as high as 20.7 mmol g⁻¹ h⁻¹ under visible light irradiation, upon protonation of their imine linkages. A significant red‐shift in light absorbance, largely improved charge separation efficiency, and an increase in hydrophilicity triggered by protonation of the Schiff‐base moieties in the imine‐linked COFs, are responsible for the improved photocatalytic performance.
Conjugated polymers are attractive for energy storage but typically require significant amounts of conductive additives to successfully operate with thin electrodes. Here, side‐chain engineering is used to improve the electrochemical performance of conjugated polymer electrodes. Naphthalene dicarboximide (NDI)‐based conjugated polymers with ion‐conducting ethylene glycol (EG) side chains (PNDI‐T2EG) and non‐ion‐conducting 2‐octyldodecyl side chains (PNDI‐T2) are synthesized, tested, and compared. For thick (20 µm, 1.28 mg cm−2) electrodes with a 60 wt% polymer, the PNDI‐T2EG electrodes exhibit 66% of the theoretical capacity at an ultrafast charge–discharge rate of 100C (72 s per cycle), while the PNDI‐T2 electrodes exhibit only 23% of the theoretical capacity. Electrochemical impedance spectroscopy measurements on thin (5 µm, 0.32 mg cm−2), high‐polymer‐content (80 wt%) electrodes reveal that PNDI‐T2EG exhibits much higher lithium‐ion diffusivity (DLi+ = 7.01 × 10−12 cm2 s−1) than PNDI‐T2 (DLi+ = 3.96 × 10−12 cm2 s−1). PNDI‐T2EG outperforms most previously reported materials in thick, high‐polymer‐content electrodes in terms of rate performance. The results demonstrate that the rate performance and capacity are significantly improved through the incorporation of EG side chains, and this work demonstrates a route for increasing the rate of ion transport in conjugated polymers and improving the performance and capacity of conjugated‐polymer‐based electrodes. Side‐chain engineering of naphthalene dicarboximide‐based conjugated polymer significantly enhances battery rate performance and storage capacity. By incorporating oligo‐ethylene glycol side chains, the nanocomposite electrodes demonstrate exceptional rate performance at high charge–discharge rates, high mass loadings, and high polymer contents. The improved performance is attributed to improved ionic and electronic conductivity in the side‐chain modified materials.
Per-and poly-fluoroalkyl substances (PFASs) have recently been labeled as toxic constituents that exist in many aqueous environments. However, traditional methods used to determine the level of PFASs are often not appropriate for continuous environmental monitoring and management. Based on the current state of research, PFAS-detecting sensors have surfaced as a promising method of determination. These sensors are an innovative solution with characteristics that allow for in situ, low-cost, and easy-to-use capabilities. This paper presents a comprehensive review of the recent developments in PFAS-detecting sensors, and why the literature on determination methods has shifted in this direction compared to the traditional methods used. PFAS-detecting sensors discussed herein are primarily categorized in terms of the detection mechanism used. The topics covered also include the current limitations, as well as insight on the future direction of PFAS analyses. This paper is expected to be useful for the smart sensing technology development of PFAS detection methods and the associated environmental management best practices in smart cities of the future.
Divanillin was synthesized in high yield and purity using Laccase from Trametes versicolor. It was then polymerized with benzene-1,4-diamine and 2,7-diaminocarbazole to form polyazomethines. Polymerizations were performed under microwave irradiation and without transition-metal-based catalysts. These biobased conjugated polyazomethines present a broad fluorescence spectrum ranging from 400 to 600 nm. Depending on the co-monomer used, polyazomethines with molar masses of around 10 kg·mol–1 and with electronic gaps ranging from 2.66 to 2.85 eV were obtained. Furthermore, time-dependent density functional theory (TD-DFT) calculations were performed to corroborate the experimental results.
The next materials challenge in organic stretchable electronics is the development of a fully degradable semiconductor that maintains stable electrical performance under strain. Herein, we decouple the design of stretchability and transience by harmonizing polymer physics principles and molecular design in order to demonstrate for the first time a material that simultaneously possesses three disparate attributes: semiconductivity, intrinsic stretchability, and full degradability. We show that we can design acid-labile semiconducting polymers to appropriately phase segregate within a biodegradable elastomer, yielding semiconducting nanofibers that concurrently enable controlled transience and strain-independent transistor mobilities. Along with the future development of suitable conductors and device integration advances, we anticipate that these materials could be used to build fully biodegradable diagnostic or therapeutic devices that reside inside the body temporarily, or environmental monitors that are placed in the field and break down when they are no longer needed. This fully degradable semiconductor represents a promising advance toward developing multifunctional materials for skin-inspired electronic devices that can address previously inaccessible challenges and in turn create new technologies.
A new category of thermally stable hybrid polyarylidene(azomethine-ether)s and copolyarylidene(azomethine-ether)s (PAAP) based on diarylidenecycloalkanones has been synthesized using solution polycondensation method. For potential cationic sensor development, a thin layer of PAAP onto a flat glassy carbon electrode (GCE, surface area: 0.0316 cm²) was prepared with conducting nafion (5%) coating agent to fabricate a sensitive and selective arsenic (III) [As³⁺] ion in short response time in neutral buffer system. The fabricated cationic sensor was measured the analytical performances such as higher sensitivity, linear dynamic range, detection limit, reproducibility, and long-term stability towards As³⁺ ions. The sensitivity and detection limit were calculated as 2.714 μAμM⁻¹cm⁻² and 6.8 ± 0.1 nM (SNR of 3; 3N/S) respectively from the calibration curve. This novel approach can be initiated a well-organized route of an efficient development of heavy selective arsenic sensor for hazardous pollutants in biological, environmental, and health care fields. Real sample analysis for various environmental sample was performed with PAAP-modified-GCE.
Sustainability has become the biggest concern of the semiconductor industry because of hundreds of high-purity organic and inorganic compounds involved in manufacturing semiconductors not being treated economically. The aim of this study was to understand how semiconductor companies manage their chemical wastes, by analyzing the U.S. Environmental Protection Agency's Toxics Release Inventory data for hydrogen fluoride, nitric acid, ammonia, N-methyl-2-pyrrolidone, hydrochloric acid, nitrate compounds, and sulfuric acid. Cluster analysis was adopted to classify the U.S. semiconductor companies into different performance groups according to their waste management approaches. On the basis of the results, twenty-seven companies were classified in the "best performance" category for the waste management of two or more chemicals. However, 15 companies were classified in the worst performance categories. The semiconductor companies can refer to our results to understand their performance and which companies they should benchmark regarding chemical waste management. City governments can also refer to our results to employ suitable policies to reduce the negative impacts of the chemical waste from regional semiconductor companies.
Biodegradable electronics have great potential to reduce the environmental footprint of devices and enable advanced health monitoring and therapeutic technologies. Complex biodegradable electronics require biodegradable substrates, insulators, conductors, and semiconductors, all of which comprise the fundamental building blocks of devices. This review will survey recent trends in the strategies used to fabricate biodegradable forms of each of these components. Polymers that can disintegrate without full chemical breakdown (type I), as well as those that can be recycled into monomeric and oligomeric building blocks (type II), will be discussed. Type I degradation is typically achieved with engineering and material science based strategies, whereas type II degradation often requires deliberate synthetic approaches. Notably, unconventional degradable linkages capable of maintaining long-range conjugation have been relatively unexplored, yet may enable fully biodegradable conductors and semiconductors with uncompromised electrical properties. While substantial progress has been made in developing degradable device components, the electrical and mechanical properties of these materials must be improved before fully degradable complex electronics can be realized.
Towards understanding the structural requirements for extending the anodic reversibility, a series of conjugated azomethine triads end-capped with amides were prepared.
Current understanding of molecular design principles for degradable imine-based polymer semiconductors is limited to semicrystalline polymer morphologies. Herein, we design and synthesize a new class of degradable, nanocrystalline semiconducting polymers...
Covalent adaptable networks, particularly imine vitrimers, have received considerable attention for the design of recyclable and reprocessable thermoset-like materials. However, the preparation of imine vitrimers often relies on solvent casting...
Conjugated polymers have received significant attention as potentially lightweight and highly tailorable alternatives to inorganic semiconductors, but their synthesis is often complex, produces toxic byproducts, and they are not typically designed to be degradable or recyclable. These drawbacks necessitate dedicated efforts to discover materials with design motifs that enable targeted and efficient degradation of conjugated polymers. In this vein, the synthetic simplicity of 1,4-dihydropyrrolo[3,2-b]pyrroles is exploited to access azomethine-containing copolymers via a benign acid-catalyzed polycondensation protocol. Polymerizations involve reacting a dialdehyde-functionalized dihydropyrrolopyrrole with p-phenylenediamine as the comonomer using p-toluenesulfonic acid as a catalyst. The inherent dynamic equilibrium of the azomethine bonds subsequently enabled the degradation of the polymers in solution in the presence of acid. Degradation of the polymers was monitored via NMR, UV-vis absorbance, and fluorescence spectroscopies, and the polymers are shown to be fully degradable. Notably, while absorbance measurements reveal a continued shift to higher energies with extended exposure to acid, fluorescence measurements show a substantial increase in the fluorescence response upon degradation. Results from this study encourage the continued development of environmentally-conscious polymerizations to attain polymeric materials with useful properties while simultaneously creating polymers with structural handles for end-of-life management or/and recyclability. This article is protected by copyright. All rights reserved.
Per- and poly(fluoroalkyl) substances (PFAS) are environmentally persistent pollutants that are of growing concern due to their detrimental effects at ultratrace concentrations (ng·L-1) in human and environmental health. Suitable technologies for on-site ultratrace detection of PFAS do not exist and current methods require complex and specialized equipment, making the monitoring of PFAS in distributed water infrastructures extremely challenging. Herein, we describe amplifying fluorescent polymers (AFPs) that can selectively detect perfluorooctanoic acid (PFOA) and perfluorooctane sulfonate (PFOS) at concentrations of ng·L-1. The AFPs are highly fluorinated and have poly(p-phenylene ethynylene) and polyfluorene backbones bearing pyridine-based selectors that react with acidic PFAS via a proton-transfer reaction. The fluorinated regions within the polymers partition PFAS into polymers, whereas the protonated pyridine units create lower-energy traps for the excitons, and emission from these pyridinium sites results in red-shifting of the fluorescence spectra. The AFPs are evaluated in thin-film and nanoparticle forms and can selectively detect PFAS concentrations of ∼1 ppb and ∼100 ppt, respectively. Both polymer films and nanoparticles are not affected by the type of water, and similar responses to PFAS were found in milliQ water, DI water, and well water. These results demonstrate a promising sensing approach for on-site detection of aqueous PFAS in the ng·L-1 range.
Carotenoids are a class of biobased conjugated molecules that bear a resemblance to the substructure of polyacetylene, a well-known conductive but insoluble polymer. Solubility is an important physical attribute for processing materials using different techniques. To impart solubility in polymers, alkyl side chains are often included in the molecular design. While these design strategies are well explored in conjugated systems, they have not been implemented with carotenoids as a building block in polymers. Here, we show a series of carotenoid-based polymers with varying side chain lengths to tune solubility. Using carotenoid and p-phenylenediamine-based monomers, degradable and biobased poly(azomethine)s were synthesized via imine polycondensation. Maximum solubilities corresponding to the varying alkyl chain lengths were quantitatively determined by ultraviolet-visible (UV-vis) absorption spectroscopy. Since carotenoids are biobased with known degradation products, the effect of acidic and artificial sunlight-promoted degradation was systematically investigated using UV-vis spectroscopy, 1H nuclear magnetic resonance (NMR) spectroscopy, infrared (IR) spectroscopy, gel permeation chromatography (GPC), and high-resolution mass spectroscopy (HRMS). Our polymer system was found to have two modes of on-demand degradation, with acid hydrolysis accelerating the rate of polymer degradation and artificial sunlight generating additional degradation products. This work highlights carotenoid monomers as viable candidates in the design of biobased, degradable, and conjugated polymers.
Understanding the impact of side chains on the aqueous redox properties of conjugated polymers is crucial to unlocking their potential in bioelectrochemical devices, such as organic electrochemical transistors (OECTs). Here, we report a series of polar propylenedioxythiophene-based copolymers functionalized with glyme side chains of varying lengths as well as an analogue with short hydroxyl side chains. We show that long polar side chains are not required for achieving high volumetric capacitance (C*), as short hydroxy substituents can afford facile doping and high C* in saline-based electrolytes. Furthermore, we demonstrate that varying the length of the polar glyme chains leads to subtle changes in material properties. Increasing the length of glyme side chain is generally associated with an enhancement in OECT performance, doping kinetics, and stability, with the polymer bearing the longest side chains exhibiting the highest performance ([μC*]OECT = 200 ± 8 F cm-1 V-1 s-1). The origin of this performance enhancement is investigated in different device configurations using in situ techniques (e.g., time-resolved spectroelectrochemistry and chronoamperometry). These studies suggest that the performance improvement is not due to significant changes in C* but rather due to variations in the inferred mobility. Through a thorough comparison of two different architectures, we demonstrate that device geometry can obfuscate the benchmarking of OECT active channel materials, likely due to contact resistance effects. By complementing all electrochemical and spectroscopic experiments with in situ measurements performed within a planar OECT device configuration, this work seeks to unambiguously assign material design principles to fine-tune the properties of poly(dioxythiophene)s relevant for application in OECTs.
Bioelectronics focuses on the establishment of the connection between the ion-driven biosystems and readable electronic signals. Organic electrochemical transistors (OECTs) offer a viable solution for this task. Organic mixed ionic/electronic conductors (OMIECs) rest at the heart of OECTs. The balance between the ionic and electronic conductivities of OMIECs is closely connected to the OECT device performance. While modification of the OMIECs' electronic properties is largely related to the development of conjugated scaffolds, properties such as ion permeability, solubility, flexibility, morphology, and sensitivity can be altered by side chain moieties. In this review, we uncover the influence of side chain molecular design on the properties and performance of OECTs. We summarise current understanding of OECT performance and focus specifically on the knowledge of ionic-electronic coupling, shedding light on the significance of side chain development of OMIECs. We show how the versatile synthetic toolbox of side chains can be successfully employed to tune OECT parameters via controlling the material properties. As the field continues to mature, more detailed investigations into the crucial role side chain engineering plays on the resultant OMIEC properties will allow for side chain alternatives to be developed and will ultimately lead to further enhancements within the field of OECT channel materials.
In this paper, we aimed to prepare poly(azomethine) and chitosan-based hydrogels for the controlled drug delivery applications. For this purpose, poly(azomethine)s were prepared by oxidative polymerization and they were characterized via using FT-IR, ¹H-NMR, ¹³C-NMR, and SEC analysis techniques. Then, poly(azomethine)s and chitosan-based hydrogels were prepared in the presence of 1,4-butanediol, and ammonium peroxodisulphate as chain extender, and initiator, respectively, and they were also characterized using FT-IR. The mechanical, thermal, morphological, swelling, biodegradability, antibacterial properties, and the controlled drug delivery application were carried out in the paper. The obtained results revealed that the fabricated hydrogels have consisted of a non-porous structure. The thermal stability of the hydrogels was decreased with the addition of chitosan into the hydrogel matrix. Moreover, poly(azomethine) and chitosan-based hydrogels were exhibited biodegradable, antibacterial, and pH-sensitive properties, and they have a potential application of the release of 5-FU.
We developed three types of film-type stimuli-responsive polymers based on aza-substituted conjugated polymers involving azobenzene, N_bith, N_fluo and Schiff base moieties, C_bith. All polymer films showed bathochromic shifts in absorption spectra followed by chromic behaviors by fuming trifluoroacetic acid (TFA). In particular, we disclosed that there were three significant differences on acid detecting ability between azobenzene and Schiff base derivatives in terms of absorption wavelengths, stability, and proton holding time. The azobenzene polymers exhibited real-time responses toward vapor fuming, meanwhile write and erase chromic behaviors were reversibly accomplished with the Schiff base polymer by exposing to acid and amine vapor. Theoretical calculation revealed that red-shifted absorption bands should be induced by protonation on nitrogen atoms in the aza-substituted positions. Diverse responses through dynamic regulation of electronic properties of main-chain conjugation can be accomplished by introducing the aza-substituents in polymers.
Abstract
Among the solution-based purification methods of as-produced single-walled carbon nanotubes (SWCNTs), conjugated polymer sorting is one of the most promising approaches to obtain semiconducting SWCNTs (s-SWCNTs) with high purity. In order to meet the demand for pure polymer-free s-SWCNTs after polymer wrapping, we synthesized several degradable fluorene- and carbazole-based copolymers for selective extraction of s-SWCNTs. The copolymers are interlinked by imine bonds, and thus, the cleavage can be easily accomplished by acid treatment. The polymer/SWCNT complex dispersions were prepared with as-produced HiPco SWCNTs in toluene and characterized with absorption, photoluminescence excitation and emission mapping, and Raman spectroscopy. Among the synthesized polyimines, fluorene-carbazole copolymers show extremely high separation yield toward s-SWCNTs and high separation purity, while the fluorene-fluorene and fluorene-p-phenylene copolymers show lower yield but higher selectivity to s-SWCNT with specific pairs of (n,m) indices. Quantitative removal of the polymer after acid-triggered degradation was confirmed by X-ray photoelectron spectroscopy. Moreover, the released dispersant-free s-SWCNTs can be further rewrapped by different polymers. Our results pave the way toward the use of dispersant-free semiconducting carbon nanotubes (CNTs) to develop the next generation of CNT devices.
Per- and polyfluoroalkyl substances (PFAS) make up a large group of persistent anthropogenic chemicals which are difficult to degrade and/or destroy. PFAS are an emerging class of contaminants, but little is known about the long-term health effects related to exposure. In addition, technologies to identify levels of contamination in the environment and to remediate contaminated sites are currently inadequate. In this opinion-type discussion paper, a team of researchers from the University of Connecticut and the University at Albany discuss the scientific challenges in their specific but intertwined PFAS research areas, including rapid and low-cost detection, energy-saving remediation, the role of T helper cells in immunotoxicity, and the biochemical and molecular effects of PFAS among community residents with measurable PFAS concentrations. Potential research directions that may be employed to address those challenges and improve the understanding of sensing, remediation, exposure to, and health effects of PFAS are then presented. We hope our account of emerging problems related to PFAS contamination will encourage a broad range of scientific experts to bring these research initiatives addressing PFAS into play on a national scale.
Organic photovoltaics have attracted much attention in the past few years, mainly due to their ability to be fully printed at low cost and large scale. However, the organic semiconductors utilized as the active layer are typically synthesized using Migita-Stille or Suzuki-Miyaura cross-coupling, which is not cost efficient and may bring toxicity concerns. In the search for atom-economical synthesis, direct (hetero)arylation polymerization (DHAP) enables the activation of aromatic C-H bonds, both reducing synthetic steps of monomers and toxic reaction byproducts. In this issue, we will discuss the recent contributions on direct (hetero)arylation synthesis toward mass production of photovoltaic materials. The impact of DHAP on material efficiency will be addressed and compared to conventional coupling methods. The ongoing improvements will be discussed, as DHAP becomes more sustainable at higher scale and materials are observed as having higher quality.
Per- and polyfluoroalkyl substances (PFAS) are an emerging class of pervasive and harmful micropollutant. Next-generation sensors are necessary to detect PFAS at sub-nanomolar levels. Electrochemistry can measure analyte concentrations at sub-10 nM levels and offers a deployable platform; however, the lack of chemical reactivity of PFAS species requires electrode surface functionalization with a molecularly imprinted polymer (MIP). Previously, such sensors have required a well-characterized one-electron mediator (i.e., ferrocene carboxylic acid or ferrocene methanol) for detection. Natural waterways do not have an abundance of ferrocenyl compounds for quantification, implying that these mediators limit sensor practicality, deployability, and cost. Here, we take advantage of ambient oxygen present in river water to quantify one of the more harmful PFAS molecules, perfluorooctanesulfonate (PFOS), from 0 to 0.5 nM on a MIP-modified carbon substrate. Differential pulse voltammetry (DPV) and electrochemical impedance spectroscopy (EIS) generated calibration curves for PFOS in river water using oxygen as the mediator. Importantly, we show that electrochemical impedance spectroscopy is superior to voltammetric techniques: like ultramicroelectrodes, this technique can be used in low-conductivity matrices like river water with high reproducibility. Further, impedance provides a PFOS limit of detection of 3.4 pM. We also demonstrate that the common interferents humic acid and chloride do not affect the sensor signal. These results are a necessary step forward in developing deployable sensors that act as a first line of defense for detecting PFAS contamination at its earliest onset.
The expansion of the field of organic electronics has hinged upon structural and fundamental developments in the field of conjugated polymers. Conjugated polymers allow for the manufacture of low-cost, light-weight, flexible organic electronic devices, with notable applications in organic photovoltaics (OPV), organic field effect transistors (OFET), and organic light emitting diodes (OLED). This extraordinary breadth of applications is due to the remarkable diversity of structure, an extensive understanding of structure-function relationships, and the relative ease of structural tuning. Important advancements and the development of such applications is largely due to the evolution of polymer structure, enabled by a broad range of synthetic methods for the tailoring of structures and the development of improved polymerization conditions to limit defects. This perspective provides background from the early days of concerted and focused conjugated polymer research (1970s-1990) to the present, and describes how the tailoring of conjugated polymer structure has now become closely tied to application. A significant focus is also directed to how polymerization methods have evolved from the aggressive, unselective conditions used for oxidative polymerizations to finely tuned transition-metal catalyzed polymerizations that can provide incredibly high structural-fidelity and can proceed through C–H activation. Areas for future work and emerging areas are also discussed, such as high-performing polymers without added structural and synthetic complexity, identifying polymer structures with improved environmental stability, flexible and transient or bioresorbable conjugated polymers, mixed-ion conductors, and photocatalytic and select biological applications.
Direct arylation polymerization (DArP) provides a more sustainable alternative to conventional methods for conjugated polymer synthesis, such as Stille–Migita or Suzuki–Miyura polymerizations. DArP proceeds through a C–H activation pathway, allowing for a reduction in the synthetic steps needed to access the monomer, since the installation of a transmetallating reagent, such as an organostannane or organoboron, is not required. However, compared to small-molecule synthesis, the prevalent conditions employed for DArP still require hazardous or unsustainably sourced reaction components, such as the solvent and transition-metal catalyst. This mini-review highlights recent work on the implementation of sustainable solvents, transition metal catalysts, and overall polymerization methods for DArP. The extension of small-molecule direct arylation conditions towards polymer synthesis is also discussed, along with the associated challenges, mechanistic considerations, and outlook for future work.
In this study, biodegradable and antibacterial poly(azomethine‐urethane) (PAMU)‐ and chitosan (CS)‐based hydrogels have been prepared for controlled drug delivery applications. Structural and morphological characterizations of the hydrogels were performed via Fourier transform‐infrared and scanning electron microscopy analyses. Thermal stability, hydrophilicity, swelling, mechanical, biodegradation, protein absorption properties, and drug delivery application of PAMU‐ and CS‐based hydrogels were also investigated. The swelling performance of the hydrogels was studied in acidic, neutral, and alkaline media. Swelling results showed that the hydrogels have higher swelling capacity in acidic and alkaline media than neutral medium. Biodegradation experiments of the hydrogels were also studied via hydrolytic and enzymatic experiments. The drug release property of the hydrogel was carried out using 5‐fluoro uracil (5‐FU), and 5‐FU release capacity of the hydrogels was found in the range from 40.10% to 58.40% after 3 days.
The aim of this paper was to prepare polyurethane-based hydrogels for the controlled release of 5-fluoro uracil. The polyurethane containing azomethine linkage in the main chain was prepared using different diisocyanates such as HDI, LDI or IPDI. A melamine-based amine compound has been used to synthesize polyurethane and this compound has wide range applications. The hydrogels were prepared by using polyurethanes and chitosan for the first time literature and the chemical structure and morphology were also investigated. Wettability, water uptake performance, in-vitro biodegradation, mechanical strength, thermal stability, protein absorption, and antibacterial properties were also evaluated. In the presence of LDI in the structure of the hydrogels, wettability, thermal stability, mechanical strength, in-vitro biodegradation rate and protein absorption performance of the hydrogels were enhanced. Moreover, drug loading and release application of the hydrogels were carried out and LDI containing hydrogels has higher 5-FU loading and release capacity than the other hydrogels.
Polymer multicomponent materials containing conjugated fragments (such as azo- or azomethine groups) have attracted significant attention due to their possible use in the efficient reversible stimuli-responsive, light-responsive devices. Light-responsive polyazomethines with azo groups in the backbone (Azo-Pams) are synthesized by polycondensation of tetrafluorobenzene- or octafluorobiphenylene-based bis-hydroxybenzaldehydes with hexamethylenediamine. The polymers feature the simultaneous combination of azo- and azomethine groups inside one conjugated block. The synthesized polymers can be solution cast into flexible solid films with tensile strength of about 24 MPa. We found that the obtained Azo-Pam polymers have an amorphous structure (Tg ~134 oC) and high thermal stability (up to 300 oC). Their optical spectra depend on the solvent type and its pH which influence the dynamical equilibrium between the tautomeric forms. It also determines the balance between the main (azo-form) and the ionized form in the solvent and allows to purposefully regulate the absorption maxima. We demonstrate the ability to record optical information using Azo-Pam films in the form of polarization gratings (holograms) with a regulated diffraction efficiency. A uniform orientation of liquid crystal is achieved by a polarized UV irradiation of glass substrates covered with the polymer Azo-Pam-ІІ. The obtained data show that the synthesis strategy of the Azo-Pam polymers is an effective instrument for designing a wide range of stimuli-responsive and optical active materials.
Electrochromic devices (ECDs) that modulate optical transmission or reflection in a controllable manner are attractive in energy-saving and colour-tuning applications. In this review, we discuss the key components, fundamental working principles and performance metrics of ECDs using layman's terms. We also highlight recent materials development of each component and illustrate how the structure–property relationships impact their processability, device performance and stability. We further introduce emerging materials that exhibit electrochromic properties, and discuss the transition from laboratory-scale, half-cell-based characterisations of electrochromic materials to the fabrication of solid-state electrochromic devices and evaluation of their performances. Finally, we lay out major challenges for fabricating large-scale and cost-effective ECDs, particularly the materials design and fabrication strategies for achieving chemically and electrochemically stable, high performance ECDs that can be produced by roll-to-roll techniques.
A method for preparing reprocessable epoxy thermoset is presented. The process is composed of synthesis of a bisphenol monomer bridged by an imine bond, glycidylation of the bisphenol, and cross-linking with a hardener to form thermoset. The resulting epoxy thermoset possesses comparable properties to conventional high-performance thermosets made from bisphenol A. However, when treated by a stimulus like acid, temperature, and/or water, the described thermoset exhibits reprocessability. Degradation and recycling involve hydrolysis and re-formation of imine bonds; reshaping and repairing of the thermoset are realized through imine exchange reactions. All the described processes require no metal catalyst, press heating, or additional monomer, which significantly widens thermoset reprocessing.
This work presents a soluble oligo(ether)‐functionalized propylenedioxythiophene (ProDOT)‐based copolymer as a versatile platform for a range of high‐performance electrochemical devices, including organic electrochemical transistors (OECTs), electrochromic displays, and energy‐storage devices. This polymer exhibits dual electroactivity in both aqueous and organic electrolyte systems, redox stability for thousands of redox cycles, and charge‐storage capacity exceeding 80 F g⁻¹. As an electrochrome, this material undergoes full colored‐to‐colorless optical transitions on rapid time scales (<2 s) and impressive electrochromic contrast (Δ%T > 70%). Incorporation of the polymer into OECTs yields accumulation‐mode devices with an ION/OFF current ratio of 10⁵, high transconductance without post‐treatments, as well as competitive hole mobility and volumetric capacitance, making it an attractive candidate for biosensing applications. In addition to being the first ProDOT‐based OECT active material reported to date, this is also the first reported OECT material synthesized via direct(hetero)arylation polymerization, which is a highly favorable polymerization method when compared to commonly used Stille cross‐coupling. This work provides a demonstration of how a single ProDOT‐based polymer, prepared using benign polymerization chemistry and functionalized with highly polar side chains, can be used to access a range of highly desirable properties and performance metrics relevant to electrochemical, optical, and bioelectronic applications.
Developing aqueous electrolyte compatible, redox-active polymers that can be processed from environmentally sustainable solvents is desirable because these traits will effectively reduce environmental impact and human health hazards during processing procedures and in the final device architecture. To achieve organic solvent solubility and aqueous compatibility, a poly(3,4-propylenedioxythiophene) containing four ester functionalities was synthesized via direct arylation polymerization. The resulting polymer was spray-cast into a thin film from the environmentally sustainable solvent 2-methyltetrahydrofuran, and the presence of multiple polar functionalities rendered the film aqueous electrolyte compatible. The multiester-functionalized polymer exhibits a relatively low onset of oxidation (∼0.4 V vs Ag/AgCl) and electrochromic character by transitioning from a colored neutral state to a colorless oxidized state with increasing potential in 0.1 M NaCl aqueous electrolyte. Additionally, the ester-functionalized polymer exhibits similar electrochromic properties in aqueous electrolytes when compared to traditional alkyl-substituted poly(3,4-propylenedioxythiophenes) in organic electrolytes, as evidenced by contrast values of ∼70% and switching speeds of ∼2 s. This work highlights the use of multipolar functionalities as a design strategy for synthesizing organic solvent processable, aqueous electrolyte compatible redox-active polymers without postpolymerization modifications or the sacrifice of electrochromic properties.
Incorporating labile bonds inside polymer backbone and side chains yields interesting polymer materials that are responsive to change of environmental stimuli. Drugs can be conjugated to various polymers through different conjugation linkages and spacers. One of the key factors influencing the release profile of conjugated drugs is the hydrolytic stability of the conjugated linkage. Generally, the hydrolysis of acid-labile linkages, including acetal, imine, hydrazone, and to some extent β-thiopropionate, are relatively fast and the conjugated drug can be completely released in the range of several hours to a few days. The cleavage of ester linkages are usually slow, which is beneficial for continuous and prolonged release. Another key structural factor is the water solubility of polymer–drug conjugates. Generally, the release rate from highly water-soluble prodrugs is fast. In prodrugs with large hydrophobic segments, the hydrophobic drugs are usually located in the hydrophobic core of micelles and nanoparticles, which limits the access to the water, hence lowering significantly the hydrolysis rate. Finally, self-immolative polymers are also an intriguing new class of materials. New synthetic pathways are needed to overcome the fact that much of the small molecules produced upon degradation are not active molecules useful for biomedical applications.
In this study, pentaerythritol tetra(3-mercaptopropionate)-allylurea-poly (ethylene glycol) (PETMP-AU-PEG), produced by the Schiff-base reaction between terminal-aldehyded PEG and PETMP-AU, was used to prepare doxorubicin (DOX)-loaded polymers for triggered release. The DOX-loaded PETMP-AU-PEG polymers had the sizes of about 200 nm, non-toxicity and high pH-sensitive properties. In vitro release study confirmed that the polymer could release DOX rapidly by cleavage of acid-labile imine bonds of the polymer. The release of DOX at neutral pH was very slow. However, in the weak acidic environment (pH 6.8 and pH 6.0), it released much faster within the first 2 h. Fluorescence microscopy further verified that DOX released from PETMP-AU-PEG polymers could be pH sensitive. According to the results of cytotoxicity determination and microscopic imaging of the U2OS cells (human osteosarcoma, tumor cells) and MC3T3 cells (normal tissue cells), it demonstrates that the DOX-loaded polymers could maintain high stability in the neutral environment while release DOX rapidly in responding to the very weak acidic environment. Moreover, it is more important that the U2OS could be inactivated in the micro-acidic environment produced by its own growth, even in a neutral environment, without any chemical reagents addition.
Organic π-conjugated small molecules and polymers, owing to their light-weight, solution-processibility, mechanical flexibility, and large synthetic variety for finely tunable structures and properties, are promising semiconducting materials for a new generation of optoelectronic devices such as light-emitting diodes (LEDs), field-effect transistors (FETs), photovoltaic devices and sensors. A vast library of π-conjugated systems have been synthesized through conventional tools of couplings (e.g. Suzuki coupling, Stille coupling) and have been used in the fabrication of organic optoelectronic devices. In recent years an emerging synthetic technique called direct C-H arylation has been extensively studied as a facile, atom-efficient and environmentally benign pathway for the synthesis of conjugated polymers and small molecules. C-C bond formation between two heteroaryls can be carried via the activation of C-H bonds in a transition-metal catalytic cycle, thereby overcoming additional pre-functionalization steps involving toxic reagents. Direct arylation has been applied to a broad range of monomers and its reaction conditions have been optimized to produce defect-free polymers as well as small molecules that exhibit performances comparable with those made from conventional reactions. In this review, we summarize the recent progress in synthesis of conjugated small molecules, linear polymers and porous polymers by direct C-H arylation. In particular, small molecules and linear polymers based on benzothiadiazole (BT), diketopyrrolopyrrole (DPP), napththalenediimide (NDI), isoindigo (IG), thienoisoindigo (TIIG) and thienothiadiazole (TTD) are discussed in detail. Device performances of some representative polymers synthesized via direct arylation polymerization (DAP) in FETs and bulk heterojunction solar cells are summarized. We finally discuss the present challenges and perspectives of DAP towards future “greener” and more industrially scalable synthesis of π-conjugated semiconducting polymers for a variety of applications.