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A series of exo -7-thiabicyclo[2.2.1]hept-5-ene-2,3-dicarboximides were synthesized and polymerized using Schrock's catalyst, 2,6-diisopropylphenylimidoneophylidene molybdenum(VI) bis(hexafluoro- tert -butoxide). The ring-opening metathesis polymerization (ROMP) reactions were found to proceed in a controlled manner, enabling chain extensions and tuning of polymer molecular weight. The polymers were characterized using size exclusion chromatography (SEC) as well as spectroscopic (NMR, FT-IR), thermal (TGA, DSC), and optical techniques. The physical, chemical, and optical properties of the polymers were found to be affected by the embedded sulfur atoms and the pendant substituents. Copolymers with norbornene were also synthesized and characterized. Treatment of a poly(thianorbornene) with potassium hydroxide led to ring-opening hydrolysis and afforded a derivative that was soluble in aqueous media.

The catalytic activities displayed by single-atom catalysts (SACs) depend on the coordination structure. SACs supported on carbon materials often adopt saturated coordination structures with uneven distributions because they require high-temperature conditions during synthesis. Herein, bisnitrogen-chelated Co SACs that are coordinatively unsaturated are prepared by integrating a Co complex into a conjugated microporous polymer (CMP-CoN 2 ). Compared with saturated analogues, i.e., tetranitrogen-chelated Co SACs (denoted as CMP-CoN 4 ), CMP-CoN 2 exhibits higher electrocatalytic activity in polysulfide conversions due to an enhanced hybridization between the 3d orbitals of the Co atoms and the 3p orbitals of the S atoms in the polysulfide. As a result, sulfur cathodes prepared with CoN 2 deliver outstanding performance metrics, including a high specific capacity (1393 mA h g -1 at 0.1 C), a superior rate capacity (673.2 mA h g -1 at 6 C), and a low capacity decay rate (of only 0.045% per cycle at 2 C over 1000 cycles). They also outperform sulfur cathodes that contain CMP-CoN 4 or CMPs that are devoid of Co SACs. This work reveals how the catalytic activity displayed by SACs is affected by their coordination structures, and the rules that underpin the structure-activity relationship may be extended to designing electrocatalysts for use in other applications.

High-quality solid electrolyte interphase (SEI) layers can effectively suppress the growth of Li dendrites and improve the cycling stability of lithium metal batteries. Herein, 1-(6-bromohexanoyl)-3-butylurea is used to construct an organic/inorganic hybrid (designated as LiBr-HBU) SEI layer that features a uniform and compact structure. The LiBr-HBU SEI layer exhibits superior electrolyte wettability and air stability as well as strong attachment to Li foils. The LiBr-HBU SEI layer achieves a Li + conductivity of 2.75 × 10 -4 S cm -1 , which is ≈50-fold higher than the value measured for a native SEI layer. A Li//Li symmetric cell containing the LiBr-HBU SEI layer exhibits markedly improved cyclability when compared with the cell containing a native SEI layer, especially at a high current density (e.g., cycling life up to 1333 h at 15 mA cm -2 ). The LiBr-HBU SEI layer also improves the performance of lithium-sulfur cells, particularly the rate capability (548 mAh g -1 at 10 C) and cycling stability (513 mAh g -1 at 0.5 C after 500 cycles). The methodology described can be extended to the commercial processing of Li metal anodes as the artificial SEI layer also protects Li metal against corrosion., (© 2024 Wiley‐VCH GmbH.)

In an effort to target polypeptides at nonterminal sites, we screened the binding of the synthetic receptor cucurbit[8]uril (Q8) to a small library of tetrapeptides, each containing a nonterminal dipeptide binding site. The resulting leads were characterized in detail using a combination of isothermal titration calorimetry, 1 H NMR spectroscopy, electrospray ionization time-of-flight mass spectrometry (ESI-TOF-MS), and X-ray crystallography. The equilibrium dissociation constant values determined for the binding of Q8 to nonterminal dipeptide sites Lys-Phe (KF) and Phe-Lys (FK) were 60 and 86 nm, respectively. These are to the best of our knowledge the highest affinities reported to date for any synthetic receptor targeting a nonterminal site on an unmodified peptide. A 0.79 Å resolution crystal structure was obtained for the complex of Q8 with the peptide Gly-Gly-Leu-Tyr-Gly-Gly-Gly (GGLYGGG) and reveals structural details of the pair-inclusion motif. The molecular basis for recognition is established to be the inclusion of the side chains of Leu and Tyr residues, as well as an extensive network of hydrogen bonds between the peptide backbone, the carbonyl oxygens of Q8, and proximal water molecules. In addition, the crystal structure reveals that Q8 induces a type II β-turn. The sequence-selectivity, high affinity, reversibility, and detailed structural characterization of this system should facilitate the development of applications involving ligand-induced polypeptide folding.

While transition metal nitrides (TMNs) are promising electrocatalysts, their widespread use is challenged by the complex synthetic methodology and a limited understanding of the underlying electrocatalytic mechanisms. Herein, we describe a novel synthesis of TMNs (including Mo 2 N, NbN, and ZrN) and explore their potential as electrocatalysts to affect sulfur cathode reactions. The TMNs were prepared in-situ using a process that simultaneously infuses nitrogen-doped porous graphitic carbon (designated as TMN@N-PGC). The methodology avoids the use of ammonia, which poses safety risks due to its flammability and toxicity. Analysis of the d-p hybridized orbitals formed between the transition metal ions and sulfur species revealed that the antibonding orbitals are empty. Thus, TMNs with more negative d-band centers exhibit stronger affinities towards polysulfides. NbN facilitated polysulfide conversion as well as Li 2 S detachment, and thus featured a high electrocatalytic capability for promoting cathode kinetics. Lithium-sulfur (Li-S) batteries containing NbN@N-PGC exhibited the highest performance metrics in terms of specific capacity (1488 mA h g -1 at 0.1 C), rate capacity (521 mA h g -1 at 6 C), and cycling stability (603 mA h g -1 at 0.5 C after 1300 cycles, corresponding a capacity decay of 0.030% per cycle). Li-S cells with high sulfur loadings also exhibit outstanding performance., Competing Interests: Declaration of Competing Interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (Copyright © 2023 Elsevier Inc. All rights reserved.)

Lithium-sulfur (Li-S) batteries hold great promise for widespread application on account of their high theoretical energy density (2600 Wh kg -1 ) and the advantages of sulfur. Practical use, however, is impeded by the shuttle effect of polysulfides along with sluggish cathode kinetics. it is reported that such deleterious issues can be overcome by using a composite film (denoted as V-CMP@MWNT) that consists of a conjugated microporous polymer (CMP) embedded with vanadium single-atom catalysts (V SACs) and a network of multi-walled carbon nanotubes (MWNTs). V-CMP@MWNT films are fabricated by first electropolymerizing a bidentate ligand designed to coordinate to V metals on self-standing MWNT films followed by treating the CMP with a solution containing V ions. Li-S cells containing a V-CMP@MWNT film as interlayer exhibit outstanding performance metrics including a high cycling stability (616 mA h g -1 at 0.5 C after 1000 cycles) and rate capability (804 mA h g -1 at 10 C). An extraordinary area-specific capacity of 13.2 mA h cm -2 is also measured at a high sulfur loading of 12.2 mg cm -2 . The underlying mechanism that enables the V SACs to promote cathode kinetics and suppress the shuttle effect is elucidated through a series of electrochemical and spectroscopic techniques., (© 2023 Wiley-VCH GmbH.)

Nonstoichiometric compounds are widely used in contemporary energy technologies due to their high surface polarity, tailored electronic structure, high electrical conductivity, and other enhanced properties. However, the preparation of such nonstoichiometric compounds can be complicated and, in some cases, uncontrollable and dangerous. Here, we report a "one-pot" strategy for synthesizing N-doped porous graphitic carbon that is hybridized with nonstoichiometric scandium oxide (denoted as ScO 0.95 @N-PGC) and show that the composite significantly promotes sulfur cathode kinetics in lithium-sulfur (Li-S) batteries. The synthesis of the ScO 0.95 @N-PGC composite entails heating a porous dry gel that consists of a C source (glucose), a N source (dicyandiamide), and a Sc source (Sc(NO 3 ) 3 ·H 2 O). Thermally decomposing the dicyandiamide creates a highly reductive atmosphere that simultaneously affords the hypoxic state of the ScO 0.95 and dopes the carbon matrix with nitrogen. Density functional theory reveals the presence of oxygen vacancies that enable the ScO 0.95 crystals to function as excellent electrical conductors, exhibit enhanced adsorption toward polysulfides, and accelerate the cathode reactions by lowering the corresponding activation energies. Moreover, Li-S cells prepared from the ScO 0.95 @N-PGC composite display a high specific capacity (1046 mA h g -1 at 0.5 C), an outstanding cycling stability (641 mA h g -1 after 1000 charge-discharge cycles at 0.5 C, a capacity decay of 0.038% per cycle), and a particularly outstanding rate capability (438 mA h g -1 at 8 C). The methodology described establishes a sustainable approach for synthesizing nonstoichiometric compounds while broadening their potential utility in a broad range of energy technologies.

Despite significant progress in the preparation and characterization of two-dimensional (2D) materials, the synthesis of 2D organic materials remains challenging. Here, we report a novel space-confined polymerization method that enables the large-scale synthesis of 2D sheets of a functional conjugated polymer, namely, poly(3,4-ethylenedioxythiophene) (PEDOT). A key step in this method is the confinement of monomer to the boundaries of ice crystals using micelles. This spatial confinement directs the polymerization to form 2D PEDOT sheets with high crystallinity and controlled morphology. Supercapacitors prepared from the 2D PEDOT sheets exhibit outstanding performance metrics. In aqueous electrolyte, a high areal specific capacitance of 898 mF cm -2 at 0.2 mA cm -2 along with an excellent rate capability is achieved (e.g., capacitance retention of 67.6 % at a 50-fold higher current). Moreover, the 2D PEDOT-based supercapacitors exhibit outstanding cycling stability (capacitance retention of 98.5 % after 30,000 cycles). Device performance is further improved when an organic electrolyte is used., (© 2023 Wiley-VCH GmbH.)

Red phosphorus (RP) is a promising anode material for use in lithium-ion batteries (LIBs) due to its high theoretical specific capacity (2596 mA h g -1 ). However, the practical use of RP-based anodes has been challenged by the material's low intrinsic electrical conductivity and poor structural stability during lithiation. Here, we describe a phosphorus-doped porous carbon (P-PC) and disclose how the dopant improves the Li storage performance of RP that was incorporated into the P-PC (designated as RP@P-PC). P-doping porous carbon was achieved using an in situ method wherein the heteroatom was added as the porous carbon was being formed. The phosphorus dopant effectively improves the interfacial properties of the carbon matrix as subsequent RP infusion results in high loadings, small particle sizes, and uniform distribution. In half-cells, an RP@P-PC composite was found to exhibit outstanding performance in terms of the ability to store and utilize Li. The device delivered a high specific capacitance and rate capability (1848 and 1111 mA h g -1 at 0.1 and 10.0 A g -1 , respectively) as well as excellent cycling stability (1022 mA h g -1 after 800 cycles at 2.0 A g -1 ). Exceptional performance metrics were also measured when the RP@P-PC was used as an anode material in full cells that contained lithium iron phosphate as the cathode material. The methodology described can be extended to the preparation of other P-doped carbon materials that are employed in contemporary energy storage applications.

Lithium (Li) metal has attracted significant attention in areas that range from basic research to various commercial applications due to its high theoretical specific capacity (3860 mA h g -1 ) and low electrochemical potential (-3.04 vs. standard hydrogen electrode). However, dendrites often form on the surfaces of Li metal anodes during cycling and thus lead to battery failure and, in some cases, raise safety concerns. To overcome this problem, a variety of approaches that vary the electrolyte, membrane, and/or anode have been proposed. Among these efforts, the use of three-dimensional frameworks as Li hosts, which can homogenize and minimize the current density at the anode surface, is an effective approach to suppress the formation of Li dendrites. Herein, we describe the development of using carbon-based materials as Li hosts. While these materials can be fabricated into a variety of porous structures, they have a number of intrinsic advantages including low costs, high specific surface areas, high electrical conductivities, and wide electrochemical stabilities. After briefly summarizing the formation mechanisms of Li dendrites, various methods for controlling structural and surface chemistry will be described for different types of carbon-based materials from the viewpoint of improving their performance as Li hosts. Finally, we provide perspective on the future development of Li host materials needed to meet the requirements for their use in flexible and wearable devices and other contemporary energy storage techniques., (© 2022 Wiley-VCH GmbH.)

A novel 2 : 1 host-guest complex forms between 8- tert -butyl-6 b 2 -azapenta-benzo[ bc , ef , hi , kl , no ]corannulene (1) and C 60 with positive cooperativity ( α = 2.56) and high affinity ( K 1 × K 2 = 2.8 × 10 6 M -2 ) at 25 °C. The C 60 undergoes increasing shape complementarity toward 1 throughout the binding process.

A library of fluorinated aryl diazomethanes were polymerized using BF 3 ·OEt 2 as a catalyst. The polymerization of 2,3,4,5,6-pentafluorophenyl diazomethane was found to be controlled, permitted chain extensions, and facilitated access to a series of block copolymers. Moreover, the polymer chains grew in one carbon increments (so-called "C1 polymerizations") and, as such, afforded highly substituted polymers that featured aryl units pendant to every carbon atom of the backbone. The polymers were characterized using size exclusion chromatography, various spectroscopic techniques, and a series of static and dynamic contact angle measurements. Compared to less-substituted analogues that were prepared using typical C2 polymerization methodologies, the C1 fluorinated polymers were found to be more hydrophobic while maintaining a sufficient solubility to be processed into robust films.

Electrocatalysis is critical to the performance displayed by sulfur cathodes. However, the constituent electrocatalysts and the sulfur reactants have vastly different molecular sizes, which ultimately restrict electrocatalysis efficiency and hamper device performance. Herein, the authors report that aggregates of cobalt single-atom catalysts (SACs) attached to graphene via porphyrins can overcome the challenges associated with the catalyst/reactant size mismatch. Atomic-resolution transmission electron microscopy and X-ray absorption spectroscopy measurements show that the Co atoms present in the SAC aggregates exist as single atoms with spatially resolved dimensions that are commensurate the sulfur species found in sulfur cathodes and thus fully accessible to enable 100% atomic utilization efficiency in electrocatalysis. Density functional theory calculations demonstrate that the Co SAC aggregates can interact with the sulfur species in a synergistic manner that enhances the electrocatalytic effect and promote the performance of sulfur cathodes. For example, Li-S cells prepared from the Co SAC aggregates exhibit outstanding capacity retention (i.e., 505 mA h g -1 at 0.5 C after 600 cycles) and excellent rate capability (i.e., 648 mA h g -1 at 6 C). An ultrahigh area specific capacity of 12.52 mA h cm -2 is achieved at a high sulfur loading of 11.8 mg cm -2 ., (© 2021 The Authors. Advanced Science published by Wiley-VCH GmbH.)

Lithium (Li) metal is regarded as the ultimate anode material for use in Li batteries due to its high theoretical capacity (3860 mA h g -1 ). However, the Li dendrites that are generated during iterative Li plating/stripping cycles cause poor cycling stability and even present safety risks, and thus severely handicap the commercial utility of Li metal anodes. Herein, we describe a graphene and carbon nanotube (CNT)-based Li host material that features vertically aligned channels with attached ZnO particles (designated ZnO@G-CNT-C) and show that the material effectively regulates Li plating and stripping. ZnO@G-CNT-C is prepared from an aqueous suspension of Zn(OAc) 2 , CNTs, and graphene oxide by using ice to template channel growth. ZnO@G-CNT-C was found to be mechanically robust and capable of guiding Li deposition on the inner walls of the channels without the formation of Li dendrites. When used as an electrode, the material exhibits relatively low polarization for Li plating, fast Li-ion diffusion, and high Coulombic efficiency, even over hundreds of Li plating/stripping cycles. Moreover, full cells prepared with ZnO@G-CNT-C as Li host and LiFePO 4 as cathode exhibit outstanding performance in terms of specific capacity (155.9 mA h g -1 at 0.5 C), rate performance (91.8 mA h g -1 at 4 C), cycling stability (109.4 mA h g -1 at 0.5 C after 800 cycles). The methodology described can be readily adapted to enable the use of carbon-based electrodes with well-defined channels in a wide range of contemporary applications that pertain to energy storage and delivery., (© 2021 Wiley-VCH GmbH.)

The aim of this research project is to analyze support panels that are based on aramid fabrics which are reinforced with polybenzoxazine/urethane (poly(BA-a/PU)) composites and contain multiwalled carbon nanotubes (MWCNTs). Through the measurement of mechanical properties and a series of ballistic-impact tests that used 7.62 × 51 mm 2 projectiles (National Institute of Justice (NIJ), level III), the incorporated MWCNTs were found to enhance the energy-absorption ( E Abs ) property of the composites, improve ballistic performance, and reduce damage. The perforation process and the ballistic limit ( V 50 ) of the composite were also studied via numerical simulation, and the calculated damage patterns were correlated with the experimental results. The result indicated hard armor based on polybenzoxazine nanocomposites could completely protect the perforation of a 7.62 × 51 mm 2 projectile at impact velocity range of 847 ± 9.1 m/s. The results revealed the potential for using the poly(BA-a/PU) nanocomposites as energy-absorption panels for hard armor.

Two-dimensional (2D) organic materials hold great promise for use in a multitude of contemporary applications due to their outstanding chemical and physical properties. Herein, 2D sheets of poly(3,4-ethylenedioxythiophene):poly(4-styrenesulfonate) (PEDOT:PSS) are prepared from a commercially available PEDOT:PSS suspension using ice as a template. The 2D PEDOT:PSS sheets grow in the boundaries of ice crystals as the polymers are "squeezed" out of the suspension when the water solidifies. The mechanical robustness of the sheets can be enhanced by incorporating WO 3 nanowires, and the PSS component can be conveniently removed with a concentrated solution of H 2 SO 4 to afford stable suspensions of PEDOT or WO 3 @PEDOT sheets, either of which can be converted into flexible films with tunable thicknesses via filtration. Swagelok- or pouch-type supercapacitor devices prepared from the WO 3 @PEDOT films exhibit outstanding energy-storage characteristics, including high rate capability, thickness-independent energy storage ( e . g ., 701 mF cm -2 is achieved with a 1-mm-thick film), high resistance toward mechanical deformation, and good cycling stability. Additionally, a high energy density of 0.083 mWh cm -2 is measured for a device prepared using a 1-mm-thick film at a high power density of 10 mW cm -2 . The methodology described establishes an efficient and readily scalable approach for accessing 2D organic sheets.

A series of substituted polybenzoxazines was synthesized and studied as binders in non-asbestos friction composite materials. The structures of the polybenzoxazines were varied in a systemic fashion by increasing the number and position of pendant alkyl (methyl) groups and was accomplished using the respective aromatic amines during the polymer synthesis step. By investigating the key thermomechanical and tribological characteristics displayed by the composite materials, the underlying structure-properties relationships were deconvoluted. Composite friction materials with higher thermomechanical and wear resistance properties were obtained from polybenzoxazines with relatively high crosslink densities. In contrast, polybenzoxazines with relatively low crosslink densities afforded composite friction materials with an improved coefficient of friction values and specific wear rates.

Using high-resolution transmission electron microscopy and electron energy-loss spectroscopy, we show that beryllium oxide crystallizes in the planar hexagonal structure in a graphene liquid cell by a wet-chemistry approach. These liquid cells can feature van-der-Waals pressures up to 1 GPa, producing a miniaturized high-pressure container for the crystallization in solution. The thickness of as-received crystals is beyond the thermodynamic ultra-thin limit above which the wurtzite phase is energetically more favorable according to the theoretical prediction. The crystallization of the planar phase is ascribed to the near-free-standing condition afforded by the graphene surface. Our calculations show that the energy barrier of the phase transition is responsible for the observed thickness beyond the previously predicted limit. These findings open a new door for exploring aqueous-solution approaches of more metal-oxide semiconductors with exotic phase structures and properties in graphene-encapsulated confined cells., (© 2020 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim.)

Poly(2-vinylnaphthalene) was synthesized in the solid-state by ball milling a mixture of the corresponding monomer, a Cu-based catalyst, and an activated haloalkane as the polymerization initiator. Various reaction conditions, including milling time, milling frequency and added reductant to accelerate the polymerization were optimized. Monomer conversion and the evolution of polymer molecular weight were monitored over time using 1 H NMR spectroscopy and size exclusion chromatography, respectively, and linear correlations were observed. While the polymer molecular weight was effectively tuned by changing the initial monomer-to-initiator ratio, the experimentally measured values were found to be lower than their theoretical values. The difference was attributed to premature mechanical decomposition and modeled to accurately account for the decrement. Random copolymers of two monomers with orthogonal solubilities, sodium styrene sulfonate and 2-vinylnaphthalene, were also synthesized in the solid-state. Inspection of the data revealed that the solid-state polymerization reaction was controlled, followed a mechanism similar to that described for solution-state atom transfer radical polymerizations, and may be used to prepare polymers that are inaccessible via solution-state methods., (© 2020 The Authors. Published by Wiley-VCH Verlag GmbH & Co. KGaA.)

A straightforward and environmentally friendly method for synthesizing agar-reduced graphene oxide (ArGO) was devised. The topological features and emergent physical properties displayed by the novel carbon material were controlled by varying its water content. Dehydrated films of ArGO were found to be stable in water due to the π-π stacking interactions that formed between the aromatic components of its constituent sheets. In contrast, porous variants of ArGO afforded hydrogels that exhibited high swelling capacities. The intrinsic mechanical strength, elasticity and chemical stability of the hydrogels were further enhanced through adaption into double-network analogues. Such hydrogels, which were prepared using a facile and efficient one-pot methodology, exhibited a high fracture stress upon compression, and retained their shape in basic aqueous environments. These features can be expected to enable water purification and tissue engineering applications, among others., Competing Interests: There are no conflicts to declare., (This journal is © The Royal Society of Chemistry.)

Carbocatalysts, materials which are predominantly composed of carbon and catalyze the synthesis of organic or inorganic compounds, are promising alternatives to metal-based analogues. Even though current carbocatalysts have been successfully employed in a broad range of synthetic transformations, they suffer from a number of drawbacks in part due to their heterogeneous nature. For example, the insolubility of prototypical carbocatalysts, such as graphene oxide (GO), may restrict access to catalytically-active sites in a manner that limits performance and/or challenges optimization. Herein we describe the preparation and utilization of soluble asphaltene oxide (sAO), which is a novel material that is composed of oxidized polycyclic aromatic hydrocarbons and is soluble in a wide range of organic solvents as well as in aqueous media. sAO promotes an array of synthetically useful transformations, including esterifications, cyclizations, multicomponent reactions, and cationic polymerizations. In many cases, sAO was found to exhibit higher catalytic activities than its heterogeneous analogues and was repeatedly and conveniently recycled, features that were attributed to its ability to form homogeneous phases., Competing Interests: There are no conflicts to declare., (This journal is © The Royal Society of Chemistry.)

The synthesis and study of a library of cyclic (aryl)(amido)carbenes (CArAmCs), which represent a class of electrophilic NHCs that feature low calculated singlet-triplet gaps (ΔE ST =19.9 kcal mol -1 ; B3LYP/def2-TZVP) and exhibit reactivity profiles expected from triplet carbenes, are described. The electrophilic properties of the CArAmCs were quantified by analyzing their respective selenium adducts, which exhibited the largest downfield 77 Se NMR chemical shifts (up to 1645 ppm) measured for any NHC derivative known to date, as well as their Ir carbonyl complexes, from which large Tolman electronic parameter (TEP) values (up to 2064 cm -1 ) were ascertained. The CArAmCs were found to engage in reactions that are typically observed with triplet carbenes, including C-H insertions, [2+1] cycloadditions with alkenes as well as alkynes, and spontaneous oxidation upon exposure to oxygen., (© 2019 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim.)

Adamantyl vinyl ketone (AVK) and its copolymers are synthesized using reversible addition fragmentation chain-transfer (RAFT) methodology and then degraded using UV light. The polymerization of AVK is found to be controlled as indicated by a linear correlation between the molecular weights of the polymers produced and monomer conversion as well as a series of chain extensions. The RAFT method is also used to synthesize random and block copolymers of AVK and methyl methacrylate. Irradiating poly(adamantyl vinyl ketone) (PAVK) with UV light affords a polyolefin and adamantane as the major products. Similar products are obtained, along with poly(methyl methacrylate) (PMMA), when the block copolymer is subjected to UV light. The random copolymer undergoes complete degradation under similar conditions. A mechanism wherein stereoelectronic effects channel photodegradation through Norrish I Type pathways in a manner that preserves the main chain of the polymer during the decomposition process is proposed., (© 2019 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.)

Treating iminoxyl species with oxygen acceptors such as PPh 3 resulted in oxygen atom transfer and afforded the corresponding iminyl radicals. DFT and other calculations revealed that association between the oxygen atom acceptors and the iminoxyl species results in the formation of key intermediates during the reaction. Subsequent dissociation is accompanied with homolytic cleavage of the N-O bond and generates iminyl radicals with spin densities that are localized on exocyclic nitrogen atoms.

Switchable catalysts respond to various types of stimuli in a manner that results in distinct structural or electronic changes. When each state exhibits a different activity, selectivity, or solubility, the corresponding catalyst may be used to control chemical reactions in a temporally- or spatially-resolved fashion. N-Heterocyclic carbenes (NHCs) are versatile scaffolds for building switchable catalysts and many examples that respond to changes in electrochemical potential or light have been introduced. Such types of switchable NHCs will be described in this Feature Article. The accompanying discussions include design considerations, characterization methodology, quantification of the underlying switching phenomena, and utility in catalytic applications. Challenges for the field as well as perspectives on potential opportunities for future development are also provided.

Lithium-sulfur (Li-S) batteries have received significant attention due to the high theoretical specific capacity of sulfur (1675 mA h g -1 ). However, the practical applications are often handicapped by sluggish electrochemical kinetics and the "shuttle effect" of electrochemical intermediate polysulfides. Herein, we propose an in-situ copolymerization strategy for covalently confining a sulfur-containing copolymer onto reduced graphene oxide (RGO) to overcome the aforementioned challenges. The copolymerization was performed by heating elemental sulfur and isopropenylphenyl-functionalized RGO to afford a sulfur-containing copolymer, that is, RGO- g-poly(S- r-IDBI), which is featured by a high sulfur content and uniform distribution of the poly(S- r-IDBI) on RGO sheets. The covalent confinement of poly(S- r-IDBI) onto RGO sheets not only enhances the Li + diffusion coefficients by nearly 1 order of magnitude, but also improves the mechanical properties of the cathodes and suppresses the shuttle effect of polysulfides. As a result, the RGO- g-poly(S- r-IDBI) cathode exhibits an enhanced sulfur utilization rate (10% higher than that of an elemental sulfur cathode at 0.1C), an improved rate capacity (688 mA h g -1 for the RGO- g-poly(S- r-IDBI) cathode vs 400 mA h g -1 for an elemental sulfur cathode at 1C), and a high cycling stability (a capacity decay of 0.021% per cycle, less than one-tenth of that measured for an elemental sulfur cathode).

A 4,5-dithienylimidazolium salt outfitted with pendant styrenyl groups was synthesized and studied. The salt was found to undergo reversible electrocyclization upon UV irradiation; subsequent exposure to visible light reversed the reaction. Acyclic diene metathesis (ADMET) polymerization of the salt afforded a novel fluorescent polyelectrolyte.

A novel carbazole-based probe was synthesized and found to exhibit fluorescence upon introduction to potassium permanganate in aqueous media. Guided by a series of experimental studies and DFT calculations, the underlying mechanism is proposed to proceed through a series of tandem proton and electron transfer processes.

The use of sulfur as a cathode material for lithium-sulfur (Li-S) batteries has attracted significant attention due to its high theoretical specific capacity (1675 mA h g -1 ); however, practicality is hindered by a number of obstacles, including the shuttling effect of polysulfides and the low electrical conductivity of sulfur. Herein, ball milling sulfur with unzipped multiwalled carbon nanotubes (UMWNTs) was found to covalently immobilize sulfur nanoparticles to the UMWNTs and resulted in composites (designated as S@UMWNTs) with high electrical conductivity. The unzipping degree of MWNTs was first controlled to optimize the immobilization of sulfur nanoparticles to UMWNTs and the electrochemical performance of the resulting Li-S batteries. The presence of C-S covalent bonds between the UMWNTs and sulfur nanoparticles was verified using x-ray photoelectron spectroscopy and Fourier transform infrared spectroscopy, and the formation of C-S bonds was ascribed to the reactions between the mechanically-induced sulfur radicals and the functional groups of UMWNTs. As a result, when used as a cathode material for Li-S batteries, the S@UMWNTs exhibited excellent electrochemical performance, including a good long-term cycling stability and low capacity decay (e.g., ca. 0.09% per cycle over 500 charge/discharge cycles at 1 C) due to the suppression of the shuttling effect by the C-S covalent bonds.

This Article describes the molecular recognition of peptides containing an N-terminal methionine (Met) by the synthetic receptor cucurbit[8]uril (Q8) in aqueous solution and with submicromolar affinity. Prior work established that Q8 binds with high affinity to peptides containing aromatic amino acids, either by simultaneous binding of two aromatic residues, one from each of two different peptides, or by simultaneous binding of an aromatic residue and its immediate neighbor on the same peptide. The additional binding interface of two neighboring residues suggested the possibility of targeting nonaromatic peptides, which have thus far bound only weakly to synthetic receptors. A peptide library designed to test this hypothesis was synthesized and screened qualitatively for Q8 binding using a fluorescent indicator displacement assay. The large fluorescence response observed for several Met-terminated peptides suggested strong binding, which was confirmed quantitatively by the determination of submicromolar equilibrium dissociation constant values for Q8 binding to MLA, MYA, and MFA using isothermal titration calorimetry (ITC). This discovery of high affinity binding to Met-terminated peptides and, more generally, to nonaromatic peptides prompted a detailed investigation of the determinants of binding in this system using ITC, electrospray ionization mass spectrometry, and 1 H NMR spectroscopy for 25 purified peptides. The studies establish the sequence determinants required for high-affinity binding of Met-terminated peptides and demonstrate that cucurbit[ n]uril-mediated peptide recognition does not require an aromatic residue for high affinity. These results, combined with the known ability of cucurbit[ n]urils to target N-termini and disordered loops in folded proteins, suggest that Q8 could be used to target unmodified, Met-terminated proteins.

Although dicyanamide (i.e., [N(CN) 2 ] - ) has been commonly used to obtain low-viscosity, halogen-free, room-temperature ionic liquids, liquid-crystalline salts containing such anions have remained virtually unexplored. Here we report a series of amphiphilic dicyanamide salts that, depending on their structures and compositions, adopt smectic, columnar, or bicontinuous cubic thermotropic liquid-crystalline mesophases, even at room temperature in some cases. Their thermal properties were explored by polarized light optical microscopy, differential scanning calorimetry, thermogravimetric analysis (including evolved gas analysis), and variable-temperature synchrotron X-ray diffraction. Comparison of the thermal phase characteristics of these new liquid-crystalline salts featuring "V-shaped" [N(CN) 2 ] - anions with those of structural analogues containing [SCN] - , [BF 4 ] - , [PF 6 ] - , or [CF 3 SO 3 ] - anions indicated that not only the size of the counterion but also its shape should be considered in the development of mesomorphic salts. Collectively, these discoveries may be expected to facilitate the design of thermotropic ionic liquid crystals that form inverted-type bicontinuous cubic and other sophisticated liquid-crystalline phases., (© 2018 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim.)

We have grown a single-crystal beryllium oxide (BeO) thin film on a gallium nitride (GaN) substrate by atomic-layer deposition (ALD) for the first time. BeO has a higher thermal conductivity, bandgap energy, and dielectric constant than SiO 2 . As an electrical insulator, diamond is the only material on earth whose thermal conductivity exceeds that of BeO. Despite these advantages, there is no chemical-vapor-deposition technique for BeO-thin-film deposition, and thus, it is not used in nanoscale-semiconductor-device processing. In this study, the BeO thin films grown on a GaN substrate with a single crystal showed excellent interface and thermal stability. Transmission electron microscopy showed clear diffraction patterns, and the Raman shifts associated with soft phonon modes verified the high thermal conductivity. The X-ray scan confirmed the out-of-plane single-crystal growth direction and the in-plane, 6-fold, symmetrical wurtzite structure. Single-crystalline BeO was grown on GaN despite the large lattice mismatch, which suggested a model that accommodated the strain of hexagonal-on-hexagonal epitaxy with 5/6 and 6/7 domain matching. BeO has a good dielectric constant and good thermal conductivity, bandgap energy, and single-crystal characteristics, so it is suitable for the gate dielectric of power semiconductor devices. The capacitance-voltage (C-V) results of BeO on a GaN-metal-oxide semiconductor exhibited low frequency dispersion, hysteresis, and interface-defect density.

Silicon-on-insulator (SOI) technology improves the performance of devices by reducing parasitic capacitance. Devices based on SOI or silicon-on-sapphire technology are primarily used in high-performance radio frequency (RF) and radiation sensitive applications as well as for reducing the short channel effects in microelectronic devices. Despite their advantages, the high substrate cost and overheating problems associated with complexities in substrate fabrication as well as the low thermal conductivity of silicon oxide prevent broad applications of this technology. To overcome these challenges, we describe a new approach of using beryllium oxide (BeO). The use of atomic layer deposition (ALD) for producing this material results in lowering the SOI wafer production cost. Furthermore, the use of BeO exhibiting a high thermal conductivity might minimize the self-heating issues. We show that crystalline Si can be grown on ALD BeO and the resultant devices exhibit potential for use in advanced SOI technology applications.

High-performance flame-retardant materials are urgently needed to address outstanding issues that pertain to safety. Traditional flame retardants are toxic to the environment and/or lack the physical properties required for use in many contemporary applications. Here, we show that isocyanate-based polyimide (PI) foam, a flammable material, can exhibit unusually superior flame retardancy as well as other excellent properties, such as being lightweight and displaying high mechanical strength, by incorporating red phosphorus (RP)-hybridized graphene. The covalent bonds formed between the graphene platelets and the PI matrix provide the resultant PI foam with a specific Young's modulus (83 kNm kg -1 ) that is comparable to or even higher than those displayed by state-of-the-art foams, including silica aerogels, polystyrene foams, and polyurethane foams. In addition, even a low content of the RP-hybridized graphene (2.2 wt %) results in an exceptionally higher limiting oxygen index (39.4) than those of traditional flame-retardant polymer-based materials (typically 20-30). The resultant PI foam also exhibits thermal insulation properties that are similar to that of air. Moreover, the RP-hybridized graphene is prepared using a one-step ball milling process in 100% yield, and does not require solvent or produce waste. The preparation of the flame-retardant PI foams can be scaled as the starting materials are commercially available and the techniques employed are industrially compatible.

We report the preparation of polymer nanofibers with enhanced flame retardancy by coaxial electrospinning polyamide 66 (PA 66) and nanoscale graphene hybridized with red phosphorus (NG-RP). Transmission electron microscopy and energy-dispersive X-ray spectroscopy revealed that the nanofibers contained a NG-RP-based core surrounded by a PA 66 shell. The flame-retardant characteristics of the nanofibers were investigated by thermal gravimetric analysis, micro combustion calorimetry, and a series of vertical flame tests. The encapsulation of the NG-RP not only enhanced the flame-retardant characteristics of the nanofibers, but also improved their mechanical properties while maintaining the color and luster of the polymer, making the resultant nanofibers appropriate for use in a wide range of applications., Competing Interests: The authors declare no competing financial interest.

A ring-opening metathesis polymerization catalyst supported by a redox-active N-heterocyclic carbene was synthesized and found to undergo reversible reduction. In its neutral form, the catalyst polymerized 1,5-cis,cis-cyclooctadiene at a higher rate than that of a norbornene derivative; however, upon reduction, the selectivity was found to reverse. Utilizing this oxidation state dependent selectivity, a series of copolymers with controlled compositions, microstructures, and physical properties were prepared by redox-switching the catalyst over the course of a series of polymerization reactions., (© 2017 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim.)

Polymeric membranes are an energy-efficient means of purifying water, but they suffer from fouling during filtration. Modification of the membrane surface is one route to mitigating membrane fouling, as it helps to maintain high levels of water productivity. Here, a series of common techniques for modification of the membrane surface are reviewed, including surface coating, grafting, and various treatment techniques such as chemical treatment, UV irradiation, and plasma treatment. Historical background on membrane development and surface modification is also provided. Finally, polydopamine, an emerging material that can be easily deposited onto a wide variety of substrates, is discussed within the context of membrane modification. A brief summary of the chemistry of polydopamine, particularly as it may pertain to membrane development, is also described., (© 2017 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim.)

The covalent functionalization of single and bilayer graphene on SiO 2 (300 nm)/Si was effected through sequential treatment with the alkalide reductant [K(15-crown-5) 2 ]Na and electrophilic aryl or alkyl halides, of which the iodides proved to be the most reactive. The condensation reactions proceeded at room temperature and afforded the corresponding aryl- or alkyl-appended graphenes. For each sample, Raman and X-ray photoelectron spectroscopies were used to evaluate the degrees and uniformities of functionalization. Statistical analyses of the Raman data revealed that the introduction of the organic moieties was accompanied by sp 3 -rehybridization of the basal plane atoms. When bilayers consisting of 13 C and 12 C layers were treated, both the top and bottom sheets were decorated with organic groups. The reaction was followed using Raman spectroscopy, and the mechanism was studied by theoretical calculations. Indicative of its structure and reactivity, 4-pyridyl-decorated single-layer graphene was readily benzylated and appears to be an ideal platform to develop functional materials.

Here, we describe an in situ approach for growing polyepoxides from the surfaces of graphene oxide (GO) using a surface-initiated polymerization reaction. The polymerization methodology is facile and general as a broad range of epoxides carrying various functional groups have been successfully polymerized by simply adding GO powders in the epoxide monomers. The resultant polyepoxide grafted GO are found to show enhanced dispersibility in various common solvents and to exhibit increased d-spacing between the basal planes. In particular, grafting poly(2,3-epoxy-1-propanol) (PEP) to GO results in a composite (i.e., GO-g-PEP) that is dispersible in water and miscible with polyether block amide, i.e., Pebax MH 1657. Preliminary studies have indicated the membranes prepared using Pebax/GO-g-PEP composites exhibit enhanced CO 2 permeabilities and selectivities in comparison to H 2 , O 2 , or N 2 . The excellent performance in gas separation is attributed to the layered structure of the GO-g-PEP sheets with enlarged d-spacing and the functional groups present on the PEP chains grafted to the surfaces of GO sheets.

The Burgess reagent ([methoxycarbonylsulfamoyl]triethylammonium hydroxide) has historically found utility as a dehydrating agent. Herein we show that, in the presence of dimethyl sulfoxide, the Burgess reagent efficiently and rapidly facilitates the oxidation of a broad range of primary and secondary alcohols to their corresponding aldehydes and ketones in excellent yields and under mild conditions, and can be combined with other transformations (e.g., Wittig olefinations). A mechanism similar to those described for the Pfitzner-Moffatt and Swern oxidations is proposed.

Few-layer graphenes, supported on Si with a superficial oxide layer, were subjected to a Birch-type reduction using Li and H 2 O as the electron and proton donors, respectively. The extent of hydrogenation for bilayer graphene was estimated at 1.6-24.1% according to Raman and X-ray photoelectron spectroscopic data. While single-layer graphene reacts uniformly, few-layer graphenes were hydrogenated inward from the edges and/or defects. The role of these reactive sites was reflected in the inertness of pristine few-layer graphenes whose edges were sealed. Hydrogenation of labeled bilayer ( 12 C/ 13 C) and trilayer ( 12 C/ 13 C/ 12 C) graphenes afforded products whose sheets were hydrogenated to the same extent, implicating passage of reagents between the graphene layers and equal decoration of each graphene face. The reduction of few-layer graphenes introduces strain, allows tuning of optical transmission and fluorescence, and opens synthetic routes to long sought-after films containing sp 3 -hybridized carbon.

To enhance the limited degradability of poly(ethylene glycol) (PEG), a straightforward method of synthesizing poly[(ethylene glycol)-co-(glycolic acid)] (P(EG-co-GA)) via a ruthenium-catalyzed, post-polymerization oxyfunctionalization of various PEGs is developed. Using this method, a set of copolymers with GA compositions of up to 8 mol% are prepared with minimal reduction in molecular weight (<10%) when compared to their commercially available starting materials. The P(EG-co-GA) copolymers are shown to undergo hydrolysis under mild conditions., (© 2016 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.)

The structural and electronic properties of graphene coated on a Cu(111) surface can be strongly influenced by the arrangement of adsorbates at the graphene edges. Oxygen and water intercalation at the graphene edges could lead to oxidation and hydrolysis at the graphene/Cu(111) interface, eventually causing decoupling of graphene from the Cu substrate. However, the reaction pathways for oxygen or water (or both) intercalation at the graphene edges are not well understood at the molecular level. Using ab initio density functional theory calculations, we observed a strong hybridization of π orbitals at a zigzag edge of a graphene nanoribbon (GNR) on a bare Cu(111) surface, whereas such hybridization was absent for the corresponding armchair edge under otherwise identical conditions. These results indicate that the edge type influences the oxidation chemistry beneath the GNR. Moreover, we demonstrate that the presence of oxygen species, as well as GNR, facilitates the propagation of H2O. The following decoupling mechanisms are discussed: (i) GNRs with armchair edge configurations on Cu(111) can be decoupled via a sequential reaction that involves O2 dissociation followed by H2O intercalation, whereas (ii) GNRs with zigzag edge configurations on Cu(111) can be decoupled by oxygen intercalation.

Since the first reported isolation of a carbene just over a quarter century ago, the study of such compounds-including stable derivatives-has flourished. Indeed, N-heterocyclic carbenes (NHCs), of which imidazolylidenes and their derivatives are the most pervasive subclass, feature prominently in organocatalysis, as ligands for transition metal catalysts, and as stabilizers of reactive species. However, imidazolylidenes (and many other NHCs) typically lack the reactivity characteristic of electrophilic carbenes, including insertion into unactivated C-H bonds, participation in [2 + 1] cycloadditions, and reaction with carbon monoxide. This has led to debates over whether NHCs are truly carbenic in nature or perhaps better regarded as ylides. The fundamental and synthetic utility of transformations that involve electrophilic carbenes has motivated our group and others to expand the reactivity of NHCs and other stable carbenes to encompass electrophilic carbene chemistry. These efforts have led to the development of the diamidocarbenes (DACs), a stable and unique subset of the NHCs that feature carbonyl groups inserted into the N-heterocyclic scaffold. To date, crystalline five-, six-, and seven-membered DACs have been prepared and studied. Unlike imidazolylidenes, which are often designated as prototypical NHCs, the DACs exhibit a reactivity profile similar to that of bona fide carbenes, reactive species that are less "tamed" by heteroatom π conjugation. The DACs engage in [2 + 1] cycloadditions with electron-rich or -poor alkenes, aldehydes, alkynes, and nitriles, and doing so in a reversible manner in some cases. They also react with isonitriles, reversibly couple to CO, and mediate the dehydrogenation of hydrocarbons. Such rich chemistry may be rationalized in terms of their ambiphilicity: DACs are nucleophilic, as required for some of the reactions above, yet also have electrophilic character, as evidenced by their insertions into unactivated N-H and C-H bonds, including nonacidic derivatives. As will become clear, such reactivity is unique among isolable carbenes. DAC chemistry is expected to find applications in synthesis, dynamic covalent chemistry, and catalysis. For example, the hydrolysis of DAC-derived diamidocyclopropanes and -propenes affords carboxylic acids and cyclopropenones, respectively. These new hydrocarboxylation and carbonylation methodologies are significant in that they represent alternatives to processes that typically involve precious metals and gaseous carbon monoxide. Future efforts in this area may involve modifications that transform the stoichiometric conversions facilitated by DACs into catalytic variants. In this context, the reversible binding of CO to DACs is an indication that the latter may serve as a blueprint for the development of more electrophilic, stable carbenes with the capacity to activate other challenging small molecules.

Since the aliphatic C-H···anion interaction is relatively weak, anion binding using hydrophobic aliphatic C-H (Cali-H) groups has generally been considered not possible without the presence of additional binding sites that contain stronger interactions to the anion. Herein, we report X-ray structures of organic crystals that feature a chloride anion bound exclusively by hydrophobic Cali-H groups. An X-ray structure of imidazolium-based scaffolds using Cali-H···A(-) interactions (A(-) = anion) shows that a halide anion is directly interacting with fifteen Cali-H groups (involving eleven hydrogen bonds, two bidentate hydrogen-bond-type binding interactions and two weakly hydrogen-bonding-like binding interactions). Additional supporting interactions and/or other binding sites are not observed. We note that such types of complexes may not be rare since such high numbers of binding sites for an anion are also found in analogous tetraalkylammonium complexes. The Cali-H···A(-) interactions are driven by the formation of a near-spherical dipole layer shell structure around the anion. The alternating layers of electrostatic charge around the anion arise because the repulsions between weakly positively charged H atoms are reduced by the presence of the weakly negatively charged C atoms connected to H atoms.

The installation of heterojunctions on the surfaces of carbon nanotubes (CNTs) is an effective method for promoting the charge separation processes needed for CNT-based electronics and optoelectronics applications. Conjugated polymers are proven state-of-the-art candidates for modifying the surfaces of CNTs. However, all previous attempts to incorporate conjugated polymers to CNTs resulted in unordered interfaces. Herein we show that well-defined chains of regioregular poly(3-hexylthiophene) (P3HT) were successfully grown from the surfaces of multiwalled CNTs (MWNTs) using surface-initiated Kumada catalyst-transfer polycondensation. The polymerization was found to proceed in a controlled manner as chains of tunable lengths were prepared through variation of the initial monomer-to-initiator ratio. Moreover, it was determined that large-diameter MWNTs afforded highly ordered P3HT aggregates, which exhibited a markedly bathochromically shifted optical absorption due to a high grafting density induced planarization of the polymer chains. Using ultrafast spectroscopy, the heterojunctions formed between the MWNTs and P3HT were shown to effectively overcome the binding energy of excitons, leading to photoinduced electron transfer from P3HT to MWNTs. Finally, when used as prototype devices, the individual MWNT-g-P3HT core-shell structures exhibited excellent photoresponses under a low illumination density.

This Review covers the recent developments (2005-2015) in the design, synthesis, characterization, and application of thermotropic ionic liquid crystals. It was designed to give a comprehensive overview of the "state-of-the-art" in the field. The discussion is focused on low molar mass and dendrimeric thermotropic ionic mesogens, as well as selected metal-containing compounds (metallomesogens), but some references to polymeric and/or lyotropic ionic liquid crystals and particularly to ionic liquids will also be provided. Although zwitterionic and mesoionic mesogens are also treated to some extent, emphasis will be directed toward liquid-crystalline materials consisting of organic cations and organic/inorganic anions that are not covalently bound but interact via electrostatic and other noncovalent interactions.

The synthesis and study of a cyclic (alkyl)(amido)carbene is described. The carbene was found to undergo C-H insertion at low temperatures, formed cyclopropenes upon exposure to alkynes, and facilitated desulfurization reactions. Spectroscopic studies revealed that the carbene is strongly π-accepting but retains a complimentary degree of σ-donating properties.

Ferrocene containing N -heterocyclic carbene (NHC) ligated gold(I) complexes of the type [Au(NHC) 2 ] + were prepared and found to be capable of regulating the formation of reactive oxygen species (ROS) via multiple mechanisms. Single crystal X-ray analysis of bis(1-(ferrocenylmethyl)-3-mesitylimidazol-2-ylidene)-gold(I) chloride ( 5 ) and bis(1,3-di(ferrocenylmethyl)imidazol-2-ylidene)-gold(I) chloride ( 6 ) revealed a quasi-liner geometry around the gold(I) centers, (i.e., the C - Au - C bond angle were measured to be ~177° and all the Au - C carbene bonds distances were in the range of 2.00 (7) - 2.03 (1) Å). A series of cell studies indicated that cell proliferation inhibition and ROS generation were directly proportional to amount of ferrocene contained within the [Au(NHC) 2 ] + complexes (IC 50 of 6 < 5 < bis(1-benzyl-3-mesitylimidazol-2-ylidene)-gold(I) chloride ( 4 )). Complexes 4 - 6 were also confirmed to inhibit thioredoxin reductase as inferred from lipoate reduction assays and increase chelatable intracellular zinc concentrations. RNA microarray gene expression assays revealed that 6 induces endoplasmic reticulum stress response pathways as a result of ROS increase.