Peripheral carbazole units-decorated MR emitter containing B−N covalent bond for highly efficient green OLEDs with low roll-off

Boron−nitrogen doped multiple resonance(BN-MR)emitters,characterized by B−N covalent bonds,offer distinctive advantages as pivotal building blocks for facile access to novel MR emitters featuring narrowband spectra and high efficiency.However,there remains a scarcity of exploration concerning synthetic methods and structural derivations to expand the library of novel BN-MR emitters.Herein,we present the synthesis of a BN-MR emitter,tCz[B−N]N,through a one-pot borylation reaction directed by the amine group,achieving an impressive yield of 94%.The emitter is decorated by incorporating two 3,6-di-tbutylcarbazole(tCz)units into a B−N covalent bond doped BN-MR parent molecule via para-C−π−D and para-N−π−D conjugations.This peripheral decoration strategy enhances the reverse intersystem crossing process and shifts the emission band towards the pure green region,peaking at 526 nm with a narrowband full-width at half maximum(FWHM)of 41 nm.Consequently,organic light emitting diodes(OLEDs)employing this emitter achieved a maximum external quantum efficiency(EQEmax)value of 27.7%,with minimal efficiency roll-off.Even at a practical luminance of 1000 cd·m^(−2),the device maintains a high EQE value of 24.6%.

The Even-Odd and the Isoelectronicity Rules Applied to Single Covalent Bonds in Ionic, Double-Face-Centered Cubic and Diamond-Like Crystals

Although atom configuration in crystals is precisely known thanks to imaging techniques, there is no experimental way to know the exact location of bonds or charges. Many different representations have been proposed, yet no theory to unify conceptions. The present paper describes methods to derive bonds and charge location in double-face-centered cubic crystals with 4 and 6 atoms per unit cell using two novel rules introduced in earlier works: the even-odd and the isoelectronicity rules. Both of these rules were previously applied to ions, molecules and some solids, and the even-odd rule was also tested on two covalent crystal structures: centered-cubic and single-face-centered cubic crystals. In the present study, the diamond-like structure was subjected to the isoelectronicity rule in order to derive Zinc-blende structures. Rock-salt-like crystals were derived from each other using both rules. These structures represent together more than 230 different crystals. Findings for these structures are threefold: both rules describe a very sure method to obtain valid single covalent-bonded structures;single covalent structures can be used in every case instead of the classical ionic model;covalent bonds and charges positions do not have any relation with the valence number given in the periodic table.

Introducing an Extended Covalent Bond between Oxygen Atoms with an OXO-Shape in Ions and Molecules: Compatibility with the Even-Odd and the Isoelectronicity Rules

Building on the recent success of the even-odd rule, the present paper explores its implications by studying the very specific case of OXO compounds. These compounds are usually represented with double bonds linking two oxygen atoms to a central atom—as in carbon dioxyde—yet can sometimes be drawn in a triangular structure, such as in calcium dioxyde. Measurement data moreover indicate that most OXO compounds have an angle around 120° between oxygen atoms, although that seems incompatible with triangular representations. The aim here is to unify these commonly admitted representations by linking oxygen atoms through a single bond that is longer than usual covalent bonds: an “elongated bond”. This elongated bond has the interesting effect of suppressing the need for double bonds between oxygen and the central atom. The elongated bond concept is applied to about a hundred of molecules and ions and methodically compared to classical representations. It is shown that this new representation, associated to the even-odd rule, is compatible with all studied compounds and can be used in place of their classical drawings. Its usage greatly simplifies complex concepts like resonance and separated charges in gases. Elongated bonds are also shown to be practicable with the isoelectronic rule as well as isomers, and throughout chemical reactions. This study of an especially long and wide angle bond confirms the versatility of the even-odd rule: it is not limited to compounds with short covalent bonds and can include OO covalent bond lengths of more than 200 pm and with OXO angles above 90°.

Covalent bonding and J–J mixing effects on the EPR parameters of Er^(3+) ions in GaN crystal

The EPR parameters of trivalent Er（3＋） ions doped in hexagonal Ga N crystal have been studied by diagonalizing the 364×364 complete energy matrices. The results indicate that the resonance ground states may be derived from the Kramers doublet Γ6. The EPR g-factors may be ascribed to the stronger covalent bonding and nephelauxetic effects compared with other rare-earth doped complexes, as a result of the mismatch of ionic radii of the impurity Er（3＋）ion and the replaced Ga（3＋） ion apart from the intrinsic covalency of host Ga N. Furthermore, the J–J mixing effects on the EPR parameters from the high-lying manifolds have been evaluated. It is found that the dominant J–J mixing contribution is from the manifold 2K（15/2）, which accounts for about 2.5%. The next important J–J contribution arises from the crystal–field mixture between the ground state 4I（15/2） and the first excited state4I（13/2）, and is usually less than 0.2%. The contributions from the rest states may be ignored.

Development of the Orbital-Free Density Functional Approach: The Problem of Angles between Covalent Bonds

The Paulie’s principle is used for development of the orbital-free (OF) version of the density functional theory. On the example of the three-atomic clusters, Al3, Si3, and C3, it is shown that the OF approach may lead to equilibrium configurations of atomic systems with both the metallic and covalent bonding. The equilibrium interatomic distances, interbonding angles and binding energies are found in good accordance with the known data. Results will be useful for developing of theoretical study of huge molecules and nanoparticles.

Regulating Actuations and Shapes of Liquid Crystal Elastomers through Combining Dynamic Covalent Bonds with Cooling-Rate-Mediated Control

Realizing multiple locked shapes in pre-oriented liquid crystal elastomers(LCEs)is highly desired for diversifying deformations and enhancing multi-functionality.However,conventional LCEs only deform between two shapes for each actuation cycle upon liquid crystal-isotropic phase transitions induced by external stimuli.Here,we propose to regulate the actuation modes and the locked shapes of a pre-orientated epoxy LCE by combining dynamic covalent bonds with cooling-rate-mediated control.The actuation modes can be adjusted on demand by exchange reactions of dynamic covalent bonds.Derived from the established actuation modes,such as elongation,bending,and spiraling,the epoxy LCE displays varied locked shapes at room temperature under different cooling rates.Various mediums are utilized to control the cooling rate,including water,silicone oil,and copper plates.This approach provides a novel way for regulating the actuation modes and locked shapes of cuttingedge intelligent devices.

Carbon dots-enhanced pH-responsive lubricating hydrogel based on reversible dynamic covalent bondings

Due to the various pH liquid environment in nature,the pH-responsive lubricating hydrogel is widely investigated and developed for tissue interface substitute.However,the applied liquid environment will lead to poor mechanical property and weaken the pH-responsive capability.In this work,a carbon dotsenhanced pH-responsive lubricating hydrogel is developed by combining a pH-responsive section of dynamic PVA-borax network into a PAAm covalent polymer network.The formed hydrogel presents a partial gel-sol transition under controlled pH environments.At low pH environments(<6.0),the formed lubricating layer originated from dynamic disassembly of PVA-borax hydrogel,and brings the lubricating properties on the hydrogel surface.Moreover,the mechanical strength and lubrication properties are well promoted by introducing the carbon dots into the hydrogel,the blue sol layer can be observed more visually under the fluorescence microscope.The pH-response also exhibits well reversibility.The prepared hydrogel broadens the idea for designing pH-responsive soft materials for soft lubricating actuator or robot.

A Dynamic Covalent Bonding-based Nanoplatform for Intracellular Co-Delivery of Protein Drugs and Chemotherapeutics with Enhanced Anti-Cancer Effect

Efficient intracellular delivery of protein drugs is critical for protein therapy.The combination of protein drugs with chemotherapeutics represents a promising strategy in enhancing anti-cancer effect.However,co-delivery systems for efficient delivery of these two kinds of drugs are still lacking because of their different properties.Herein,we show a well-designed delivery system based on dynamic covalent bond for efficient intracellular co-delivery of ribonuclease A(RNase A)and doxorubicin(DOX).Two polymers,PEG-b-P(Asp-co-AspDA)and PAE-b-P(Asp-co-AspPBA),and two 2-acetylphenylboronic acid(2-APBA)-functionalized drugs,2-APBA-RNase A and 2-APBA-DOX,self-assemble into mixed-shell nanoparticles(RNase A/DOX@MNPs)via dynamic phenylboronic acid(PBA)-catechol bond between PBA and dopamine(DA)moieties.The PBA-catechol bond endows the nanoparticles with high stability and excellent stimulus-responsive drug release behavior.Under the slight acidic environment at tumor tissue,RNase A/DOX@MNPs are positively charged,promoting their endocytosis.Upon cellular uptake into endosome,further protonation of PAE chains leads to the rupture of endosomes because of the proton sponge effect and the cleavage of PBA-catechol bond promotes the release of two drugs.In cytoplasm,the high level of GSH removed the modification of 2-APBA on drugs.The restored RNase A and DOX show a synergistic and enhanced antic-cancer effect.This system may be a promising platform for intracellular co-delivery of protein drugs and chemotherapeutics.

Tuning Lithiophilicity and Stability of 3D Conductive Scaffold via Covalent Ag-S Bond for High-Performance Lithium Metal Anode

Li metal anode holds great promise to realize high-energy battery systems.However,the safety issue and limited lifetime caused by the uncontrollable growth of Li dendrites hinder its commercial application.Herein,an interlayer-bridged 3D lithiophilic rGO-Ag-S-CNT composite is proposed to guide uniform and stable Li plating/stripping.The 3D lithiophilic rGO-Ag-S-CNT host is fabricated by incorporating Ag-modified reduced graphene oxide(rGO)with S-doped carbon nanotube(CNT),where the rGO and CNT are closely connected via robust Ag-S covalent bond.This strong Ag-S bond could enhance the structural stability and electrical connection between rGO and CNT,significantly improving the electrochemical kinetics and uniformity of current distribution.Moreover,density functional theory calculation indicates that the introduction of Ag-S bond could further boost the binding energy between Ag and Li,which promotes homogeneous Li nucleation and growth.Consequently,the rGO-Ag-S-CNT-based anode achieves a lower overpotential(7.3 mV at 0.5 mA cm^(−2)),higher Coulombic efficiency(98.1%at 0.5 mA cm^(−2)),and superior long cycling performance(over 500 cycles at 2 mA cm−2)as compared with the rGO-Ag-CNT-and rGO-CNT-based anodes.This work provides a universal avenue and guidance to build a robust Li metal host via constructing a strong covalent bond,effectively suppressing the Li dendrites growth to prompt the development of Li metal battery.

Metal-free two-dimensional phosphorene-based electrocatalyst with covalent P-N heterointerfacial reconstruction for electrolyte-lean lithium-sulfur batteries

The use of lithium-sulfur batteries under high sulfur loading and low electrolyte concentrations is severely restricted by the detrimental shuttling behavior of polysulfides and the sluggish kinetics in redox processes.Two-dimensional(2D)few layered black phosphorus with fully exposed atoms and high sulfur affinity can be potential lithium-sulfur battery electrocatalysts,which,however,have limitations of restricted catalytic activity and poor electrochemical/chemical stability.To resolve these issues,we developed a multifunctional metal-free catalyst by covalently bonding few layered black phosphorus nanosheets with nitrogen-doped carbon-coated multiwalled carbon nanotubes(denoted c-FBP-NC).The experimental characterizations and theoretical calculations show that the formed polarized P-N covalent bonds in c-FBP-NC can efficiently regulate electron transfer from NC to FBP and significantly promote the capture and catalysis of lithium polysulfides,thus alleviating the shuttle effect.Meanwhile,the robust 1D-2D interwoven structure with large surface area and high porosity allows strong physical confinement and fast mass transfer.Impressively,with c-FBP-NC as the sulfur host,the battery shows a high areal capacity of 7.69 mAh cm^(−2) under high sulfur loading of 8.74 mg cm^(−2) and a low electrolyte/sulfur ratio of 5.7μL mg^(−1).Moreover,the assembled pouch cell with sulfur loading of 4 mg cm^(−2) and an electrolyte/sulfur ratio of 3.5μL mg^(−1) shows good rate capability and outstanding cyclability.This work proposes an interfacial and electronic structure engineering strategy for fast and durable sulfur electrochemistry,demonstrating great potential in lithium-sulfur batteries.

Effect of interlayer bonded bilayer graphene on friction

We study the friction properties of interlayer bonded bilayer graphene by simulating the movement of a slider on the surface of bilayer graphene using molecular dynamics.The results show that the presence of the interlayer covalent bonds due to the local sp^(3) hybridization of carbon atoms in the bilayer graphene seriously reduces the frictional coefficient of the bilayer graphene surface to 30%,depending on the coverage of interlayer sp^(3) bonds and normal loads.For a certain coverage of interlayer sp3bonds,when the normal load of the slider reaches a certain value,the surface of this interlayer bonded bilayer graphene will lose the friction reduction effect on the slider.Our findings provide guidance for the regulation and manipulation of the frictional properties of bilayer graphene surfaces through interlayer covalent bonds,which may be useful for applications of friction related graphene based nanodevices.

An efficient visible-light photocatalyst for CO2 reduction fabricated by cobalt porphyrin and graphitic carbon nitride via covalent bonding

Nanoparticle photosensitizers possess technical advantages for photocatalytic reactions due to enhanced light harvesting and efficient charge transport.Here we report synthesis of semiconductor nanoparticles through covalent coupling and assembly of metalloporphyrin with condensed carbon nitride.The resultant nanoparticles consist of light harvesting component from the condensed carbon nitride and photocatalytic sites from the metalloporphyrins.This synergetic particle system effectively initiates efficient charge separation and transport and exhibits excellent photocatalytic activity for CO2 reduction.The CO production rate can reach up to 57μmol/(g·h)with a selectivity of 79%over competing H2 evolution.Controlled experiments demonstrate that the combination of light harvesting with photocatalytic activity via covalent assembly is crucial for the high photocatalytic activity.Due to effective charge separation and transfer,the resultant nanoparticle photocatalysts show exceptional photo stability against photo-corrosion under light irradiation,enabling for long-term utilization.This research opens a new way for the development of stable,effective nanoparticle photocatalysts using naturally abundant porphyrin pigments.

Biodegradation,hemocompatibility and covalent bonding mechanism of electrografting polyethylacrylate coating on Mg alloy for cardiovascular stent

Organic coatings are the most widely employed approach for the promotion of corrosion resistance of magnesium(Mg)alloys.Unfortunately,traditional organic coatings are weakly bonded to Mg substrates due to physical adsorption.Herein,a polyethylacrylate(PEA)coating was fabricated on Mg-Zn-YNd alloy via electro-grafting.The surface structure and chemical composition were characterized by means of scanning electron microscope(SEM),energy dispersive X-ray spectroscopy(EDS),atomic force microscope(AFM)and Fourier transform infrared(FTIR)as well as time of flight-secondary ion mass spectrometer(To F-SIMS).The results showed that the surface roughness of PEA coating was dominated by scan rate;while the coverage and integrity of PEA coating were mainly affected by the monomer concentration and sweep circles.To F-SIMS results indicated that PEA coating was wholly covered on Mg alloy,and the presence of C2H3Mg-fragment confirmed the covalent bond between PEA coating and Mg alloy.In addition,DFT calculation results of the adsorption of EA molecules with Mg substrate agree well with the experimental phenomena and observation,suggesting that the electrons in 3s orbit of Mg atoms and 2pz orbit of C1 atom participated in the formation of covalent bond between PEA coating and Mg substrate.Potentiodynamic polarization curves and immersion test demonstrated that the PEA coatings could effectively enhance the corrosion resistance of Mg alloy.The platelet adhesion results designated that platelets were barely visible on PEA coating,which implied that PEA coating could effectively prevent the thrombosis and coagulation of platelets.PEA coating might be a promising candidate coating of Mg alloy for cardiovascular stent.

Analyte-responsive fluorescent probes with AIE characteristic based on the change of covalent bond

It is important for the determination of biologically and/or environmentally relevant species by utilization of fluorescent probes. Conventional fluorescent probes are subjected to the influence of aggregation-caused quenching that is limiting their application due to low selectivity as well as photobleaching. Additionally, quencher pairs are usually introduced in the design of these probes, which lead to the complex synthetic procedure. A novel class of fluorogens with aggregation-induced emission (AIE) characteristic provide a solution to address the dilemma. By taking advantage of the unique characteristic of AIE fluorogens, specific turn-on probes have been developed via combination with recognition components, exhibiting low background, good selectivity and outstanding photostability. This review focuses on the development of fluorescent probes with AIE characteristics via the bond cleavage as well as formation strategy.

Covalent and Ionic Bonding between Tannin and Collagen in Leather Making and Shrinking:A MALDI-ToF Study

Collagen powder hydrolysates were reacted with a solution of commercial mimosa bark tannin extract.The mixture was prepared at ambient temperature and prepared at 80°C to determine what reactions,if any,did occur between the collagen protein through its amino acids and the polyphenolic condensed tannin.The reaction products obtained were analyzed by matrix assisted laser desorption ionization time-of-flight(MALDI ToF)mass spectrometry.Reactions between the two materials did appear to occur,with the formation of a relatively small proportion of covalent and ionic linkages at ambient temperature but a considerable proportion of covalent linkages tannin-protein amino acids and the disappearance of ionic bonds.The linkages between the two materials appeared to be by amination of the phenolic–OHs of the tannin by the amino groups of the non-skeletal side chains of arginine,and by esterification by the–COOH groups of glutamic and aspartic acid of the aliphatic alcohol-OH on the C3 site of the flavonoid units heterocycle of the tannin.The proportion of covalent linkages increases markedly and predominate with increasing temperatures.This tightening of the tannin-protein covalent network formed may be an additional contributing factor both to leather wear resistance and performance as well to leather shrinking when this is subjected to excessive temperatures.

Strong and stiff Ag nanowire-chitosan composite films reinforced by Ag-S covalent bonds

High-performance composites containing various kinds of nanofibers as reinforcing building blocks have recently received considerable attention, owing to their superior mechanical properties. One of the effective strategies to reinforce these composites involves strengthening interfacial interactions via covalent bonds. However, in contrast to nanosheets, covalent bonds have been rarely used in nanofiber-reinforced composites. Herein, we report the macroscale fabrication of a series of Ag nanowire （NW）-thiolated chitosan （TCS） composite films via spray induced self-assembly. The obtained films were significantly strengthened by Ag-S covalent bonds formed between the Ag NWs and the thiol groups of TCS. The tensile strength of the optimized Ag NW-TCS film was up to 3.9 and 1.5 times higher compared with that of pure TCS and Ag NW-chitosan （CS） films, respectively.

Cancer Therapy by Targeting Thioredoxin Reductase Based on Selenium-Containing Dynamic Covalent Bond

Thioredoxin Reductase(TrxR)plays a pivotal role in defending cells against reactive oxygen species(ROS)and maintaining a reduced intracellular environment.It has been discovered that TrxR is elevated significantly in human cancer,evidenced by its association with the promotion of tumor cell proliferation,inhibiting tumor cell apoptosis,as well as enhancing tumor drug resistance.Hence,finding highly selective inhibitors of TrxR is urgently needed.Herein,we developed a selenium-containing small molecule(EbD),which had two Se–N bonds.Under reduction conditions,the two Se–N bonds reacted with Se–H bond and S–H bond in TrxR to form new Se–Se bond and Se–S bonds,respectively.Subsequently,the newly formed bonds were able to disrupt the thioredoxin(Trx)reduction catalytic cycle,and thus,inhibited the TrxR activity irreversibly,which resulted in the collapse of the antioxidant system.As a consequence,ROS levels elevated that triggered cancer cell apoptosis.This strategy,based on selenium-containing dynamic covalent bonds,provides a new avenue for cancer therapy via targeting TrxR.

Self-assembly of supra-amphiphile of azobenzene-galactopyranoside based on dynamic covalent bond and its dual responses

In this paper, dynamic covalent bond has been employed to construct supra-amphiphile of carbohydrate for the first time. In neutral environment, the molecule was fabricated by reacting a hydrophobic building block bearing benzoic aldehyde with a hydrophilic building block bearing hydrazine to form a sugar-containing supra-amphiphile based on acylhydrazone bond, The obtained azobenzene- galactopyranoside （Azo-Gal） supra-amphiphile self-assembled to fibrillar structure in water, which showed dual responses to UV light and pH.

Synthesis and Luminescence Properties of SBA-15 Functionalized with Covalently Bonded Terbium-Benzoic Acid Complex

Novel hybrid materials containing covalently bonded Terbium-benzoic acid complex in mesoporous silicaSBA-15 (denoted as Tb-SBA-15 ) were prepared via co-condensation of tetrethoxysilane (TEOS) and N-(4-benzoicacid-yl), N'-(propyltriethoxysilyl) urea (denoted as PABI).XRD, FTIR and luminescence spectroscopy were employed to characterize Tb-SBA-15.When monitored by the ligand absorption wavelength (270 nm), Tb-SBA-15 displays the emission of Tb3+ (5D4→7Fj (j = 6, 5, 4, 3 ) transition) due to the energy transfer from the ligands to Tb3+.

Creep-Resistant Covalent Adaptable Networks with Excellent SelfHealing and Reprocessing Performance via Phase-Locked Dynamic Covalent Benzopyrazole-Urea Bonds

Covalent adaptive networks(CANs)are capable of undergoing segment rearrangement after being heated,which endows the materials with excellent self-healing and reprocessing performance,providing an efficient solution to the environment pollution caused by the plastic wastes.The main challenge remains in developing CANs with both excellent reprocessing performance and creep-resistance property.In this study,a series of CANs containing dynamic covalent benzopyrazole-urea bonds were developed based on the addition reaction between benzopyrazole and isocyanate groups.DFT calculation confirmed that relatively low dissociation energy is obtained through undergoing a five-member ring transition state,confirming excellent dynamic property of the benzopyrazole-urea bonds.As verified by the FTIR results,this nice dynamic property can be well maintained after incorporating the benzopyrazole-urea bonds into polymer networks.Excellent self-healing and reprocessing performance is observed by the 3-ABP/PDMS elastomers owing to the dynamic benzopyrazole-urea bonds.Phase separation induced by the aggregation of the hard segments locked the benzopyrazole-urea bonds,which also makes the elastomers display excellent creep-resistance performance.This hard phase locking strategy provides an efficient approach to design CANs materials with both excellent reprocessing and creep-resistance performance.