Three geometrically constrained, Lewis acidic magnesium diamides [Mg(RNONAr)] (RNONAr = 4,5-bis(ArN)-2,7-dialkyl-9,9-dimethyl-xanthene; R = Et, Ar = 2,4,6-tricyclohexylphenyl (TCHP) 1; R = tBu, Ar = TCHP 2; R = Et, Ar = 2,6-di(3-pentyl)phenyl (Dipep) 3) have been synthesized. X-ray crystal structures of 1 and 2 reveal them to be dimeric, with Mg centers intermolecularly coordinated by a cyclohexyl-CH2 fragment from an opposing monomer unit. Treating 1 with n-pentane, n-hexane, or tetramethylsilane (TMS) gave the first examples of group 2 metal-alkane/TMS complexes, [Mg(EtNONTCHP)(κ2-H,H-pentane)] 4, [Mg(EtNONTCHP)(κ2-H,H-hexane)] 5 and [Mg(EtNONTCHP)(κ3-H,H,H-TMS)] 6. While the coordinated alkane in 4 and 5 is displaced in cycloalkane solutions, compound 6 was spectroscopically observed to remain intact at low temperatures. Neutron and/or X-ray crystal structures of 4-6 confirm their formulations in the solid state. DFT analyses of 4-6 reveal the bonding between the alkane/TMS and Mg(EtNONTCHP) fragment to be weak (ΔG°298K = -2.9 to -5.6 kcal mol-1) but comparable to related values for transition metal σ-alkane complexes. ETS-NOCV and NBO analyses of the bonding in 4-6 indicate that electrostatic interactions between the alkane/TMS and Mg(EtNONTCHP) fragments dominate (ca. 65%), but dispersion (ca. 20%) and orbital (ca. 15%) interactions are significant. Dispersion forces predominantly result from interaction of the alkane/TMS unit with the TCHP flanked lipophilic coordination pocket of Mg(EtNONTCHP). Approximately, 40-60% of the orbital interactions between the alkane/TMS and Mg(EtNONTCHP) units in 4-6 result from charge flow from the alkane/TMS CH2 or CH3 fragment to the magnesium center. This is supported by NCI and QTAIM analyses of the compounds.

The development of heterocyclic compounds with significant biological activity remains a priority in modern medicinal chemistry. The use of cascade domino reactions, such as Knoevenagel condensation combined with hetero-Diels-Alder cyclization, enables the efficient construction of complex structures with potential anticancer properties. The aim of the study. To synthesize a series of thiopyrano[2,3-d]thiazole derivatives via a cascade Knoevenagel–hetero-Diels–Alder reaction followed by N3-alkylation and evaluate their in vitro antitumor activity in the NCI-60 human cancer cell line panel. Materials and methods. Structural identification of the compounds was carried out using NMR spectroscopy in DMSO-d₆ with tetramethylsilane (TMS) as the internal standard, and LC-MS analysis with an APCI mass-selective detector. Biological activity was assessed using the NCI-60 screening program, which includes a panel of 60 human cancer cell lines of various origins. Key parameters such as growth inhibition (GI₅₀), lethal concentration (LC₅₀), and cytotoxicity at micromolar concentrations were determined. Results. A series of thiopyrano[2,3-d]thiazole derivatives were synthesized through a two-step domino Knoevenagel condensation and intramolecular hetero-Diels–Alder cyclization between 4-thioxo-2-oxothiazolidinone and O-alkylated salicylaldehyde derivatives bearing allylic or propargyl substituents. Subsequent N3-alkylation yielded compounds 3.1 (60.0%), 3.2 (67.0%), and 4 (58.0%). Introduction of a piperidine moiety enabled the synthesis of water-soluble methanesulfonate salt 5 (70.0%). Reaction with 2,5-(2-propynyloxy)benzaldehyde led to in situ aromatization and the formation of a stable compound 8. Four compounds were tested for anticancer activity. Compound 8 showed the highest efficacy, causing complete cell death in OVCAR-4 (Ovarian Cancer, LC₅₀ = 29.5 μM) and strong growth inhibition in SR (Leukemia, GI₅₀ = 0.676 μM), 786-0 (Renal Cancer, GI₅₀ = 0.696 μM), A498 (Renal Cancer, GI₅₀ = 0.528 μM), and BT-549 (Breast Cancer, GI₅₀ = 0.666 μM) cells. Conclusions. The proposed synthetic methodology enables efficient preparation of structurally diverse thiopyrano[2,3-d]thiazole derivatives in high yields. N3-alkylation and incorporation of a piperidine fragment allowed for the synthesis of a water-soluble methanesulfonate salt 5. Among the tested compounds, compound 8 exhibited the most promising cytotoxicity and selectivity towards several cancer cell lines, suggesting its potential as a lead compound for further preclinical development of novel anticancer agents

An indium-sulfide tetramer ([InMe2(SSiMe3)]4), which contains reactive silyl and methyl groups, is shown to be an isolable intermediate in cluster synthesis. The reactive groups allow it to act as a synthon in the formation of multinuclear indium-sulfide architectures, evidenced by the crystallization of a coordination polymer ([In20S14Me32(4,4'-bpy)5·5CH2Cl2]n) utilizing In10S7 clusters as nodes. The reaction between trimethylindium (InMe3) and bis(trimethylsilyl)sulfide (S(SiMe3)2) is explored with and without the presence of a ligating bipyridine. In both cases, a sulfide-indium adduct is formed, which slowly converts into a multimetallic complex. The ligand 2,2'-bipyridine (2,2'-bpy) is coordinated to InMe3 to form the adduct InMe3(bpy), which upon addition of sulfide, eliminates tetramethylsilane (TMS) and binds two additional InMe3 moieties (InMe2(bpy)(μ3-SSiMe3)(InMe3)2). When reacted neatly without bipyridine, InMe3 and S(SiMe3)2 form the adduct InMe3(S(SiMe3)2), which subsequently eliminates TMS and intermolecularly associates to yield [InMe2(SSiMe3)]4. Although stable in an inert atmosphere, [InMe2(SSiMe3)]4 undergoes facile hydrolysis to yield [InMeS]n when exposed to air. The effect of ligand addition (4,4'-bipyridine (4,4'-bpy)) to [InMe2(SSiMe3)]4 is then examined. In every case, it is shown that the presence of the bpy ligand has a profound influence on the resulting structure, as shown by the unexpected formation of a trimer and In10S7 cluster network.

Abstract By using tetramethylsilane (TMSi) as a Si dopant source, thick intentionally Si-doped β-Ga2O3 homoepitaxial layers were grown by low-pressure hot-wall metalorganic vapor phase epitaxy. The Si concentration was linearly controlled by varying the TMSi supply, and a RT electron density nearly equal to the Si concentration was achieved in the range from 1.8 × 1016 to 1.3 × 1019 cm–3. For the layer with a Si concentration and RT electron density of 1.8 × 1016 cm–3, the RT electron mobility of 136 cm2​​​​​ V–1 s–1 was found to be limited by polar optical phonon scattering.

Effects of Tetramethyl Silane Concentration on Amorphous SiCN Films Deposited by Microwave Sheath-Voltage Combination Plasma at High Substrate Temperatures

Tetrakis(trimethylsilyl)silane as a standard compound for fast spinning Solid-State NMR experiments

Hydrogenated amorphous carbon (a-C:H) is a type of coating vastly applied on steel alloys due to its low friction coefficient, high hardness, and chemical inertness. Also, its characteristic brilliant black color like onyx stone is desirable for decorative applications. Despite the beneficial properties conferred to ferrous substrates, the adhesion of a-C:H films is weakened by its residual stress. In order to improve the adhesion of a-C:H films/steel alloy structures, one adopted strategy is the addition of an interlayer. This research investigated the influence of the bias voltage applied on the deposition of hydrogenated amorphous silicon carbide (a-SiCx:H) interlayers, with tetramethylsilane (TMS) as the precursor, to promote adhesion in a-C:H/a-SiCx:H/ferrous alloy structures for decorative applications. The thicker interlayer was achieved at −600 V. Two regimes were proposed to explain this behavior considering ionization rates and resputtering rates and chemical reactions in plasma. The chemical structure in different regions of the a-SiCx:H interlayer was analyzed in detail. An increase in the applied bias voltage leads to oxygen incorporation at the a-C:H/a-SiCx:H interface. Higher bias voltages result in lower silicon content at the a-SiCx:H/steel interface, which is correlated to the −800 V sample’s poor adhesion. Finally, we have included a discussion about a new range of loads when a decorative piece is held by the hand where the critical loads for delamination of a-C:H coatings measured here are good enough for decorative applications.

Poor thermal conductivity in the through-thickness direction is a critical limitation in the performance of carbon fiber-reinforced polymer (CFRP) composites over a broad range of applications in the aviation industry, where heat dissipation is required (e.g., battery packs, electronic housing, and heat spreaders). In this work, it is demonstrated for the first time that a hierarchical network of vertically oriented graphene nanoflakes (GNFs), with nanoconfined silicon carbide (SiC) nanocrystals, self-assembled on carbon fibers (CFs) can provide significant improvement to the thermal conductivity (TC) of CFRPs in the through-thickness direction. The vertically aligned SiC/GNF heterostructures were grown directly on CFs for the first time by single-step plasma-enhanced chemical vapor deposition (PECVD) employing tetramethylsilane (TMS) and methane (CH4) gases at temperatures of 800 and 950 °C. At the deposition temperature of 950 °C, the controlled introduction of SiC/GNF heterostructures induced a 56% improvement in through-thickness TC over the bare CFRP counterparts while simultaneously preserving the tensile strength. The increase in thermal conductivity is accomplished by SiC nanocrystals, which serve as linkage thermal conducting paths between the vertical graphene layers, further enhancing the smooth transmission of phonons in the vertical direction. The work demonstrates for the first time the unique potential of novel SiC/GNF heterostructures for attaining strong and thermally conductive multifunctional CFRPs.

Revisiting the initial reaction rates for TMS combustion and a new evidence for metastable silica nanoparticles in the gas-phase synthesis

PECVD SiC:H (SiCN:H) films were produced using tetramethylsilane (TMS) as a precursor in a mixture with inert helium or ammonia as a source of nitrogen. Mild plasma conditions were chosen in order to prevent the complete decomposition of the precursor molecules and promote the incorporation of the fragments of precursor into the film structure. The effect of deposition temperature and composition of gas mixture on the chemical bonding structure, elemental composition, deposition rate, and optical properties (transmittance, optical bandgap, and refractive index) of films have been examined. Use of the chosen deposition conditions allowed them to reach a relatively high deposition rate (up to 33 nm/min), compared with films produced in high plasma power conditions. Use of ammonia as an additional gas led to effective incorporation of N atoms in the films. The composition of the films moved from SiC:H to SiN:H with increasing of ammonia content to P(NH3)/P(TMS) = 1. The refractive index and optical bandgap of the films varied in the range of 1.55–2.08 and 3.0–5.2 eV, correspondingly, depending on the film composition and chemical bonding structure. The effect of treatment of SiCN films deposited at 400 °C by plasma of He, O2 or NH3 were studied by X-ray photoelectron spectroscopy, atomic force microscopy, and contact angle measurements. It was shown that plasma treatment significantly changes the surface characteristics. The water contact angle of the film was changed from 71 to 37° after exposure in the plasma conditions.

An efficient nuclear magnetic resonance (NMR)-based method was developed to detect and quantify the presence of phthalates in plastic fragments obtained from a children’s toy and cosmetic product containers. Bis-2-ethyl hexyl phthalate (BEHP) was present at a concentration of 8.5% w/w in the plastic toy residue. This indicates levels of phthalates above the permitted threshold (e.g., <0.1% w/w) imposed by EU and USA regulations restricting the use of plasticizers in plastic toys for children aged 0 to 3 years. An added value of this method is that the tetramethylsilane (TMS) internal standard present at a concentration of 2.2 mmol/L in commercially available CDCl3 solvents may be conveniently used for the quantitative nuclear magnetic resonance (qNMR) analysis. The protocol described here is highly reproducible and may be easily applied to large scale investigations of plasticizers content into polyvinyl chloride (PVC) polymers.

Synthesis, vibrational spectra, Hirshfeld surface analysis, DFT calculations, and in silico ADMET study of 3-(2-chloroethyl)-2,6-bis(4-fluorophenyl)piperidin-4-one: A potent anti-Alzheimer agent

Silicon-carbide (SiC) nanocrystals (NCs) of controlled 2–4 nm size are produced in low-pressure nonthermal plasma from the simple alkylsilane precursor tetramethylsilane (TMS). Generating material on the slightly carbon-rich side of 50/50 Si/C, we establish a process for thermally removing residual carbon, which in turn promotes a degree of intrinsic solubility in polar solvents such as isopropanol (IPA). Using the size-dependent Tauc gap of luminescent silicon NCs (Si NCs) as a point of reference, we demonstrate quantum confinement in nanocrystalline β-SiC but without measurable luminescence. Surface-sensitive spectroscopic techniques reveal an oxide shell surrounding a nanocrystalline SiC core, where negative surface charge groups promote solubility while likely acting as efficient trap states for nonradiative recombination. An analytical model is presented that combines electrostatic repulsion with van der Waals attraction to explain experimental observations of concentration-dependent cluster formation and reversible NC aggregation. We anticipate that these materials will be of interest for use as nanofillers in polymer composites and in specialty coatings, while providing a foundation for exploring routes to band gap emission from nanocrystalline SiC.

Determination of drug release profile of doxorubicin encapsulated in SLN with NMR spectroscopy

Supramolecular Nanohelix Fabricated by Pillararene-Based Host–Guest System for Chirality Amplification, Transfer, and Circularly Polarized Luminescence in Water

Comparative investigation on tetramethylsilane and neopentane combustion: Jet-stirred reactor pyrolysis and kinetic modeling

Open AccessCCS ChemistryRESEARCH ARTICLE5 Aug 2022Diradicals or Zwitterions: The Chemical States of m-Benzoquinone and Structural Variation after Storage of Li Ions Chenyang Zhang†, Yong Zhang†, Kun Fan†, Qian Zou, Yuan Chen, Yanchao Wu, Songsong Bao, Limin Zheng, Jing Ma and Chengliang Wang Chenyang Zhang† School of Optical and Electronic Information, Wuhan National Laboratory for Optoelectronics (WNLO), Optics Valley Laboratory, Huazhong University of Science and Technology, Wuhan 430074, Hubei , Yong Zhang† School of Chemistry and Chemical Engineering, Nanjing University, Nanjing 210093, Jiangsu , Kun Fan† School of Optical and Electronic Information, Wuhan National Laboratory for Optoelectronics (WNLO), Optics Valley Laboratory, Huazhong University of Science and Technology, Wuhan 430074, Hubei , Qian Zou School of Chemistry and Chemical Engineering, Nanjing University, Nanjing 210093, Jiangsu , Yuan Chen School of Optical and Electronic Information, Wuhan National Laboratory for Optoelectronics (WNLO), Optics Valley Laboratory, Huazhong University of Science and Technology, Wuhan 430074, Hubei , Yanchao Wu School of Optical and Electronic Information, Wuhan National Laboratory for Optoelectronics (WNLO), Optics Valley Laboratory, Huazhong University of Science and Technology, Wuhan 430074, Hubei , Songsong Bao School of Chemistry and Chemical Engineering, Nanjing University, Nanjing 210093, Jiangsu , Limin Zheng School of Chemistry and Chemical Engineering, Nanjing University, Nanjing 210093, Jiangsu , Jing Ma *Corresponding authors: E-mail Address: [email protected] E-mail Address: [email protected] School of Chemistry and Chemical Engineering, Nanjing University, Nanjing 210093, Jiangsu and Chengliang Wang *Corresponding authors: E-mail Address: [email protected] E-mail Address: [email protected] School of Optical and Electronic Information, Wuhan National Laboratory for Optoelectronics (WNLO), Optics Valley Laboratory, Huazhong University of Science and Technology, Wuhan 430074, Hubei https://doi.org/10.31635/ccschem.021.202101333 SectionsSupplemental MaterialAboutAbstractPDF ToolsAdd to favoritesDownload CitationsTrack Citations ShareFacebookTwitterLinked InEmail m-Benzoquinones are often regarded as unstable materials in the form of radicals. Herein, an air-stable small molecular m-benzoquinone [4,6-diamino-1,3-benzoquinone (4,6DA1,3BQ)] without bulky groups or large conjugated systems is reported, and its chemical structure and state are profoundly elucidated by a series of substantial investigations that indicate their presence as zwitterions rather than as diradicals. This deep study indicated that the m-benzoquinone structure of 4,6DA1,3BQ was stabilized through the combination of hydrogen bonding and electron delocalization. Due to the presence of hydrogen bonding and zwitterions, the solubility and electrochemical performance hence were strongly dependent on the intermolecular interactions between the materials and the electrolyte compositions (Li salt, solvent, and concentration). The 4,6DA1,3BQ underwent the reversible transformation from more zwitterion structures to more conjugated benzene nature after storage of Li ions. These results provide insights into the chemistry of 4,6DA1,3BQ and promote the further development of new materials of m-benzoquinone for various applications. Download figure Download PowerPoint Introduction Organic materials have attracted a lot of attention for their applications in metal-ion batteries due to their flexibility, structural designability, recyclability, and potentially low cost and availability from vast natural resources.1–7 Hence, various organic materials have been reported as electrodes for batteries.8–12 Among them, carbonyl-based materials are the most significant because of their high capacity and stable charge/discharge voltage, which stimulate the revival of organic batteries. However, the reported carbonyl materials were mainly based on o- or p-benzoquinones, o-imides or p-carboxylates.13–19 It is well accepted that the m-benzoquinones are not stable materials and typically occur in the form of radicals. Hence, bulky groups or large π-conjugated systems are normally necessary to stabilize the m-benzoquinone analogues.20,21 On the basis of these findings and our previous works on conjugated coordination polymers (CCPs),22–24 in which m-benzoquinone structures or analogues might be stabilized by the π-d conjugation ( Supporting Information Figure S1), herein, we report an air-stable small molecular m-benzoquinone [4,6-diamino-1,3-benzoquinone (4,6DA1,3BQ), Figure 1a] without bulky groups or large conjugated systems. Basically, the small molecule should be unstable. However, through controlling the growth of single crystals, various characterizations of the chemical structures as well as the magnetic characterizations and theoretical calculations, we concluded that the chemical states of 4,6DA1,3BQ were mainly in the form of zwitterions, and the easily observed electron paramagnetic resonance (EPR) signals in 4,6DA1,3BQ samples were probably from the presence of minor diradicals and the defects of single crystals (Figure 1b). Compared with its analogues, that is, the oxidation states of m-dihydroxybenzene (m-DHB, Figure 1a), the m-benzoquinone structure of 4,6DA1,3BQ was stabilized through the combination of hydrogen bonding and electron delocalization (Figure 1c). Due to the presence of hydrogen bonding and zwitterions, the solubility and electrochemical performance were strongly dependent on the intermolecular interactions between the materials and the electrolyte composition (Li salt, solvent, and concentration). The 4,6DA1,3BQ underwent the reversible transformation from more zwitterion structures to more conjugated benzene nature after storage of Li ions. These results provide insights into the chemistry of 4,6DA1,3BQ and would promote the further development of new materials of m-benzoquinone for various applications. Figure 1 | Design of stable small molecular m-benzoquinone. (a) Diagram of the deprotonation and oxidation of m-DHB and 4,6DA1,3DHB. (b) The possible resonant chemical states of 4,6DA1,3BQ. (c) The proposed strategy of the combination of hydrogen bonding and electron delocalization for achieving stable small molecular m-benzoquinone (Orange dotted lines, possible intramolecular hydrogen bonds; cyan dotted lines, possible intermolecular hydrogen bonds). Download figure Download PowerPoint Experimental Methods Synthesis of 4,6DA1,3BQ powders All commercially available reagents and solvents were purchased from Energy Chemical (Shanghai, China) or Sinopharm Chemical Reagent Co., Ltd. (Shanghai, China) and used as received without further purification. First, 42.6 mg (0.2 mmol) of 4,6-diamino-1,3-dihydroxybenzene dihydrochloride (4,6DA1,3DHB•2HCl) was dissolved in 20 mL of deionized water. Subsequently, ammonium hydroxide (10 equiv to 4,6DA1,3DHB•2HCl) was slowly dropped into the solution as a proton scavenger. The mixture was stirred for 12 h at room temperature. The resulting dark purple suspension was filtered and washed several times with deionized water and methanol, and dried under vacuum at 80 °C for 10 h. Finally, the 4,6DA1,3BQ powder was obtained with a yield of 93%. 1H NMR (300 MHz, dimethyl sulfoxide (DMSO), δ): 4.91 (s, 1H) 5.62 (s, 1H) 8.44 (s, 2H) 9.19 (s, 2H). High-resolution mass spectrometry (HR-MS) (m/z): [M + H]+ calcd for C6H7N2O2+, 139.05; found, 139.05016. Synthesis of 4,6DA1,3BQ crystals 213 mg (1 mmol) of 4,6DA1,3DHB•2HCl was dissolved in 24 mL of deionized water. Subsequently, the as-obtained solution was transferred to a 12-well culture plate, and excess ammonium hydroxide was added to the interval of culture plate. This culture plate was maintained at room temperature without shock for 10 h. Finally, large-scale filiform 4,6DA1,3BQ crystals were collected by filtration. Materials characterizations 1H NMR spectra were recorded on a Bruker Avance 400 (400 MHz) spectrometer (Bruker, Switzerland), using DMSO-d6 as solvent and tetramethylsilane (TMS) as internal standard. MS spectra were acquired from a orbitrap liquid chromatography-mass spectrometry (LC/MS) (Q Exactive) spectrometer (Agilent, United States). The Fourier transformed infrared (FT-IR) spectra were recorded by a Bruker ALPHA spectrometer (KBr pellets; Bruker, Germany). A Pyris1 thermogravimetric analyzer (PerkinElmer Instruments, United States) was used to perform thermogravimetric analysis (TGA) tests at Ar atmosphere with a heating rate of 10 °C min−1. The morphology characterizations were carried out on a scanning electron microscope (ZEISS Gemini 300, Carl Zeiss, Germany). X-ray photoelectron spectroscopy (XPS) was collected on a Thermo Fisher ESCALAB 250Xi (Thermofisher, United States) using a monochromic Al X-ray source (hν = 1486.6 eV). The single-crystal X-ray diffraction (XRD) study of as-obtained 4,6DA1,3BQ was carried out using XtaLAB PRO MM007HF (Rigaku, Japan). UV–vis absorption spectra were recorded using SolidSpec-3700 (Shimadzu, Japan). The saturated solutions of 4,6DA1,3BQ in different electrolytes were collected by carefully filtering supersaturated solution through filters. These saturated solutions were properly diluted for further measurement. Furthermore, these standard solutions of 4,6DA1,3BQ were prepared with various concentrations. The solubility of 4,6DA1,3BQ in different electrolytes was determined according to the calibration curve obtained by linking the maximum absorbance of the standard solutions to their concentration. EPR spectra were carried out on a Bruker A300 spectrometer (Bruker, Germany). Microwave frequency was set at 9.854 GHz with a power of 20.23 mW. Magnetic measurements were performed using a Quantum Design SQUID VSM magnetometer (Quantum Design, United States) with a field of 0.1 T. Electrochemical measurements To prepare the working electrodes, the 4,6DA1,3BQ powder was blended with super P (conductive additive) and sodium salt of carboxyl methyl cellulose (binder) in a mass ratio of 5∶4∶1, using deionized water as solvent. The resulting slurry was coated on Cu or Al foil and dried at 80 °C for overnight under vacuum, giving areal loading of 4,6DA1,3BQ active material of 1.0∼2.0 mg cm−2. The electrochemical performance of 4,6DA1,3BQ electrode was evaluated using 2032 type coin cells with Li foil as the counter electrode. Glass fiber membrane (Whatman, GF/B) was used as separator. Various electrolytes formulations were homemade. These cells were assembled in an Ar-filled glove box with a low level of H2O (<0.1 ppm) and O2 (<1.0 ppm). The battery performance was evaluated on the Landt CT2001A battery testing system (Wuhan, China) at room temperature. The cyclic voltammetry (CV) measurements were performed on the BioLogic VMP3 potentiostat. The ex situ measurements were carried out by disassembling the batteries in the Ar-filled glove box. The electrodes were washed by 1,2-dimethoxyethane (DME), dried in vacuum, and then sealed in bottles for further tests. Theoretical capacity calculation The 4,6DA1,3BQ small molecule can undergo reversible redox reaction and gain or lose one electron. According to the calculation equation: C capacity = ( n × 26 , 801 ) / M where n is the number of electrons gained or lost, and M is the relative molecular mass the 4,6DA1,3BQ molecule. Therefore, the theoretical specific capacity is 194.2 mAh g−1. Electronic structure calculation To better understand the fundamental electronic structures of 4,6DA1,3BQ, we used density functional theory (DFT) to obtain the electronic-spin structures, which were performed with Guassian 16 package suite. The UB3LYP functional was used for the geometry optimization, and the def2svp level basis set was selected for all atoms.25–27 Frequency calculations were also performed to identify that all the optimized structures were local minima. As illustrated below, there are three different singlet electronic states of 4,6DA1,3BQ. Calculations showed that the lowest singlet state of 4,6DA1,3BQ is the close-shell singlet (S0) state, which was 10.38 kcal/mol lower than that of the open-shell singlet (S0′) state and 31.38 kcal/mol lower than that of the S0(TS) state. However, the diradical signal can only be detected in S0′ state and the main part of the spin density is located on the C=O fragment in the unit cell. The reason why the energy of S0′ is lower than that of S0(TS) is easy to understand. In the S0′ state, the two nonbonding electrons are largely localized on the exocyclic carbonyl groups, leaving the six-membered ring with an aromatic, benzenoid π system. In contrast, in the S0(TS) state, there is substantial π bonding to the exocyclic carbonyl groups at the expense of the aromaticity of the π system of the six-membered ring in 4,6DA1,3BQ. On the basis structure of S0, open-shell triplet state (T1) was also calculated. Compared to the S0 state, a significant difference exists: there is a stronger radical signal in T1 and the electrons are located on the whole system. However, the electronic energy is calculated to be 23.99 kcal/mol higher than that of the S0 ground state, which means that the T1 state is less stable than S0. The electrostatic potential surfaces (EPS) of 4,6DA1,3BQ at the UB3LYP/def2svp level were calculated using Multiwfn program.28 The S0 state is a typical zwitterion structure whose negative charges are delocalized between the oxygen atoms of 4,6DA1,3BQ, but the positive charges are delocalized between the nitrogen atoms of 4,6DA1,3BQ, which means no radical exists in the system and hence could lower the energy of the system. However, for T1 state, there is no clear boundary between positive and negative charges, which leads to the instability of the T1 state. We also considered resonance structures and their electronic structures. Both the S2 and T2 state can be detected with a radical signal. However, the electronic energy of S2 and T2 is calculated to be 58.57 and 67.89 the kcal/mol higher than that of the S0 state, respectively, which leads to the instability of the resonance structures at room temperature. Theoretical calculation on the electron transfer number (ETN) To investigate why only one rather than two electrons were accepted, DFT calculations were performed with the CASTEP module in Materials Studio software.29 The generalized gradient approximation (GGA) and the Perdew–Burke–Ernzerhof (PBE) functional were employed in geometry optimizations with Grimme's correction, and the ultrasoft pseudopotential was carried out.30 The cutoff energy for the plane wave expansion was 500 eV. The Brillouin zone (BZ) was sampled with a 4 × 2 × 2 k-point. In every supercell, four molecules were present. The geometry optimization was carried out until the total energy was <2.0 × 10−5 eV/atom, max force: 0.05 eV/Å, max stress: 0.1 GPa, max displacement: 0.002 Å. The binding energy per Li ion, Eb, of the 4,6DA-1,3BQ was calculated by using the following equation: E b = E A − n Li − E n Li − E A 4 n where EA−nLi and EA are the energies of the reduction states and pristine 4,6DA1,3BQ, respectively; EnLi is the energy of Li atom. Results and Discussion Synthesis and characterizations of the stable small molecular m-benzoquinone (4,6DA1,3BQ) As shown in Figure 1a, m-DHB underwent a one-pot deprotonation and oxidation reaction and then transformed into a radical intermediate state that bears two free lone electrons within the single molecule of benzene ring. Given the fact that the radical intermediate state of m-DHB was extremely unstable,31–33 amino groups were hence introduced to construct intra- and inter-molecular hydrogen bonding,34 which resembled the coordination bonds in our previously reported CCPs,22,35 forming a cross-linking network (Figure 1c). Simultaneously, the electron delocalization (Figure 1b) further enhanced the stability through resonance.36 The stable 4,6DA1,3BQ was then synthesized via one-pot in situ deprotonation and oxidation of 4,6DA1,3DHB in a basic environment ( Supporting Information Figures S2 and S3). Large crystals were obtained through controlling the temperature and reaction speed and selected for single-crystal X-ray analysis. The results strongly confirmed the proposed chemical structure of 4,6DA1,3BQ (Figure 2a). The reactant was deprotonated and oxidized, leading to deprotonated phenoxyl structure. No water molecules were observed in the crystal structure, which was different from the previous reports (4,6DA1,3BQ•H2O).37 The length of four C–C bonds (C1–C2 and C3–C4) was about 1.38∼1.39 Å, which was slightly longer than the typical C=C double bonds; while the other two (C2–C3) were about 1.52 Å, slightly shorter than the typical C–C single bonds. Besides, the length of C–O bonds was about 1.25 Å, which was between the values of typical single and double C–O bonds ( Supporting Information Table S1). Furthermore, only one hydrogen atom was connected to the C1 and C4; and no hydrogen atoms were connected to the oxygen atoms. The whole molecule was planar. Intramolecular hydrogen bonds (2.276 Å, Figure 2b and Supporting Information Table S2) could be observed between O1 and H1B. All of these results indicated the conjugated nature of the small molecule 4,6DA1,3BQ. The single-crystal structure of 4,6DA1,3BQ belonged to an orthorhombic space group Pbcn with a = 5.3320 (1) Å, b = 11.0053 (2) Å, c = 10.2294 (2) Å, and V = 600.26 (2) Å3 ( Supporting Information Table S3). It displayed a layer-by-layer packing motif along the b axis through intermolecular hydrogen bonds (N1-H1A···O1, 2.037 Å, Figure 2b). The molecules in every layer packed in the same orientation with two kinds of π–π interfacial spacing of 3.23 and 4.13 Å, respectively. Another type of intermolecular hydrogen bond (N1-H1B···O1, 2.166 Å, Figures 2b and 2c) was present within the layer, forming one-dimensional molecular chains. The molecules in the adjacent layers showed different orientations, leading to a herringbone structure with a dihedral angle of 78.38° (Figure 2d). The intermolecular hydrogen bonds and the π–π interactions resulted in the three-dimensional cross-linking networks. Figure 2 | The solved single-crystal structure of 4,6DA1,3BQ. (a) The solved molecular structure of 4,6DA1,3BQ. (b) View of inter- and intra-molecular hydrogen bond of 4,6DA1,3BQ. (c and d) Molecular stacking of 4,6DA1,3BQ: single layer (c) and double layer (d). Download figure Download PowerPoint As expected, the XRD patterns of 4,6DA1,3BQ powders with mass production were consistent well with the simulated XRD results using the single-crystal structure (Figure 3a), indicating that all of the resultant materials were of the same molecular arrangement with the single crystals of 4,6DA1,3BQ. The chemical structure of 4,6DA1,3BQ was further confirmed by energy-dispersive spectroscopy (EDS), elemental analyses (EA), mass spectrum (MS), 1H NMR spectra, FT-IR spectroscopy, and TGA. The EDS spectrum indicated the presence of C, N, and O elements and the elemental mapping revealed their homogeneous distribution of them in the as-prepared products ( Supporting Information Figures S4 and S5). EA results proved that the contents of C, H, N, and O were extremely close to theoretical values in the proposed formula ( Supporting Information Table S4). Additionally, the MS spectrum (Figure 3b) clearly demonstrated that the material was deprotonated with accurate molecular weight with the proposed structure. The material was not easily soluble in DMSO, probably due to the strong intermolecular interactions (hydrogen bonding and π–π interactions). Nevertheless, the 1H NMR spectra of 4,6DA1,3BQ in DMSO clearly reconfirmed that no hydrogen atoms were connected to oxygen atoms. Furthermore, due to the conjugation in the whole molecule and the stronger electronegativity of oxygen, the chemical shift of H4 shifted down-field (high chemical shift) compared with H1. On the other hand, because of the intramolecular hydrogen bonds, the chemical shift of H1B shifted down-field compared with H1A (Figure 3c, Supporting Information Figure S6). Figure 3 | Characterization of 4,6DA1,3BQ powders. (a) XRD patterns of 4,6DA1,3BQ and 4,6DA1,3DHB•2HCl powders, the simulated XRD patterns based on the single-crystal structure of 4,6DA1,3BQ and 4,6DA1,3BQ•H2O.37 (b) MS spectrum of 4,6DA1,3BQ. (c) 1H NMR spectrum of as-prepared 4,6DA1,3BQ in DMSO. (d) TGA curves of 1,4-benzoquinone (BQ), m-PDA and 4,6DA1,3BQ. (e) The variable-temperature EPR spectra of 4,6DA1,3BQ powders. (f) The variable-temperature 1H NMR spectrum of 4,6DA1,3BQ in DMSO. Download figure Download PowerPoint To further confirm the chemical structure of 4,6DA1,3BQ, the FT-IR spectra of the products as well as 4,6DA1,3DHB•2HCl and the m-phenylenediamine (m-PDA) were conducted. The characteristic vibrations of primary amine salt (–NH3+) at 3155 cm−1 disappeared, and the vibrations of N–H bonds at 3282 cm−1 could be obviously observed in 4,6DA1,3BQ, indicating that the hydrochloride was thoroughly eliminated, and the amino groups remained stable ( Supporting Information Figure S7). As expected, significant attenuation of C–O stretching vibration around 1209 cm−1 along with the clear signal of C=O stretching vibration at 1575 cm−1 in 4,6DA1,3BQ compared to 4,6DA1,3DHB were observed, which indicated the conjugated nature of the products.38 We also noted that the stretching vibration peak of proton acceptor (C=O) underwent a bathochromic shift compared with the typical carbonyl while the stretching vibration peak and the vibration peak of the proton a bathochromic and respectively, compared with of These the of intermolecular hydrogen bonds between the and C=O In single and double of and bonds All of these results indicated the resonant structure of the obtained 4,6DA1,3BQ. The TGA results also the of strong intermolecular hydrogen bonds. Compared with without intermolecular hydrogen bonds, as and the stability of 4,6DA1,3BQ was The of weight to °C for 4,6DA1,3BQ, which was higher than of and m-PDA (Figure In the weight remained as high as after which was with the materials with intermolecular hydrogen The of 4,6DA1,3BQ after at °C was further by scanning electron and XRD ( Supporting Information Figure The morphology remained to the pristine 4,6DA1,3BQ. However, the XRD indicated the could be to These results demonstrated that strong intermolecular hydrogen bonds enhanced the stability of 4,6DA1,3BQ and its rather than Chemical states of 4,6DA1,3BQ: the possible of diradicals after deprotonation and oxidation of we further the chemical states of 4,6DA1,3BQ using EPR the powders of 4,6DA1,3BQ strong EPR signal with a of the possible presence of electrons ( Supporting Information Figure as EPR signal was observed for the reactant (4,6DA1,3DHB•2HCl) and the analogues and signal was stable that could be detected after in for more than These results indicated the possible chemical states of 4,6DA1,3BQ in its diradical states (Figure 1b). The variable-temperature EPR and 1H NMR spectroscopy were as of the presence of We the EPR and 1H NMR measurements of 4,6DA1,3BQ at different The EPR signal of 4,6DA1,3BQ powders with temperature (Figure which was often regarded as the triplet states at as shown in Figure with the of the of H1A and H1B in 1H NMR spectra and which were also often used to the presence of All of these results indicated that 4,6DA1,3BQ to be present in the diradical Chemical states of 4,6DA1,3BQ: However, was proposed about that the 4,6DA1,3BQ be in the form of of was Therefore, we further the magnetic measurements of 4,6DA1,3BQ powders to their chemical The measurements indicated that the magnetic of 4,6DA1,3BQ powders was indicating its (Figure is the curves reconfirmed that the diradicals were not the states in the less than of the molecules might be in the diradical states (Figure to the high of EPR the EPR signal might from the presence of minor diradical states of 4,6DA1,3BQ or defects in the crystal powders. These results indicated that the states of 4,6DA1,3BQ should be the In the stronger of the EPR signals of 4,6DA1,3BQ powders at higher should be to the of the (Figure On the other hand, the in the 1H NMR spectra at higher should to the vibration of atoms and the of intermolecular interactions of hydrogen bonds (Figure The of molecules in the solvents at higher the hydrogen could also be by of the chemical the chemical of H1A and H1B shifted while the chemical of and H4 shifted which could be to the attenuation of hydrogen bond Figure 4 | Magnetic measurements and theoretical (a) of for 4,6DA1,3BQ powders from 2 to in the SQUID (b) curves of 4,6DA1,3BQ powders at 2 (c) The EPR signals of 4,6DA1,3BQ powders and (d) possible electron states of 4,6DA1,3BQ and the electron single state, triplet state, state. (e) The structure of states and the selected bond are in Å. (f) The spin surfaces of states = are as and The calculated of 4,6DA1,3BQ at the UB3LYP/def2svp level = positive and negative Download figure Download PowerPoint Chemical states of 4,6DA1,3BQ: DFT calculations DFT calculations were then performed to further the electronic structures of 4,6DA1,3BQ. The crystal structure of 4,6DA1,3BQ was used as the geometry for optimization of the possible electronic electronic states were obtained at the UB3LYP/def2svp level = the open-shell open-shell close-shell and three other states with higher energy states Among them, the chemical state of S0 the indicating that S0 was the most stable chemical state of 4,6DA1,3BQ ( Supporting Information Figure On the other hand, also could be transformed into T1 states through the intermediate which the same chemical structure as These results were consistent with the magnetic measurements and reconfirmed that the states of 4,6DA1,3BQ were

Silicon carbide (SiC) has been widely used in many applications, which require high mechanical endurance or high electrical resistance. It also serves as a basic material for light emitting diodes. Here, we present an in-liquid plasma method to produce SiC nanoparticles. A sustained spark-discharge in a dielectric liquid, which is energized by a nanosecond pulsed power supply, is established for the synthesis. To provide Si and C, we employed graphite and silicon as electrodes and cyclohexane (CHX) and tetramethylsilane (TMS) as dielectric liquids. For a reasonable comparison, we tested various combinations of electrode and liquid, namely Si-to-C in CHX, Si-to-Si in CHX, and C-to-C in TMS. We found that discharges in CHX produce Si particles encapsulated in C-shell and Si nanoparticles in C-matrix. Meanwhile, discharges in TMS consistently produce SiC nanoparticles with an average size of ~ 10 nm, regardless of the electrode material.

Abstract The optically active silicon‐vacancy (SiV) center in diamonds is an excellent candidate for quantum photonics and sensing applications. To date, optimizing the photoluminescence (PL) collection efficiency of SiV centers has proven difficult. To address this issue, the current study presents a simple two‐step method for preparing single‐crystalline diamond nanoneedle arrays. In the first step, silicon‐doped (001) textured diamond films are deposited with a mixture of microcrystalline and nanocrystalline grains in a microwave plasma CVD (MPCVD) system, using tetramethylsilane (TMS) gas as the dopant source. Subsequently, air annealing is used to selectively etch nanocrystalline diamond and sp2 amorphous carbon phases, while retaining the [001]‐oriented diamond nanoneedles with a curved top surface. In comparison to the as‐deposited films, the PL emission of SiV centers in these diamond nanoneedles is enhanced by a factor of up to 12.1. The finite‐difference time‐domain simulations further demonstrate that removing the nanocrystalline diamond and sp2 carbon from the sidewall of the diamond nanoneedles results in a remarkable increase in photoluminescence collection. Therefore, the findings have established for the first time the constraint effect of sp2 carbon on the optical collection of color centers at the sidewall rather than the top surface.

An Aggregation-Induced Emission Optical Highlighter for the Studies of Endoplasmic Reticulum-Lipid Droplet Content Dynamics