Aromatic Bridges Research Articles

High Seebeck Coefficient Achieved by Multinuclear Organometallic Molecular Junctions.

This paper describes the thermoelectric properties of molecular junctions incorporating multinuclear ruthenium alkynyl complexes that comprise Ru(dppe)2 [dppe = 1,2-bis(diphenylphosphino)ethane] fragments and diethylnyl aromatic bridging ligands with thioether anchors. Using the liquid metal technique, the Seebeck coefficient was examined as a function of metal nuclearity, oxidation state, and substituent on the organic ligand backbone. High Seebeck coefficients up to 73 μV/K and appreciable thermal stability with thermovoltage up to ∼3.3 mV at a heating temperature of 423 K were observed. An unusually high proximity of the highest occupied molecular orbital (HOMO) energy level to the Fermi level was revealed to give the remarkable thermoelectric performance as suggested by combined experiments and calculations. This work offers important insights into the development of molecular-scale devices for efficient thermoregulation and heat-to-electricity conversion.

A Multifunctional Fluorinated Polymer Enabling Efficient MAPbI3-Based Inverted Perovskite Solar Cells.

Exploring polymeric hole-transporting materials (HTMs) with passivation functions represents a simplified and effective approach to minimize the perovskite defect density. To date, most of reported polymeric HTMs were applied to fabricate n-i-p regular perovskite solar cells (PSCs). The polymers compatible for p-i-n inverted PSCs were very limited. Moreover, the passivation polymers were devoted to passivate the uncoordinated Pb2+. However, the MA+ cation defect has profound unwanted effect on device efficiency and long-term stability. In order to synchronously passivate the Pb2+ and MA+ defects in p-i-n inverted PSCs, a new nonfused polymer was intentionally explored via mild polymerization. The aromatic bridge instead of long alkyl chains enabled polymer BN-12 to achieve excellent thermal stability and good wettability of perovskite precursor. Furthermore, the incorporation of chemical anchor sites ("C═O" and "F") strongly controlled the crystallization of perovskite and restrained the MA+ ion migration. As a result, a significant fill factor (FF) of 82.9% and an enhanced power conversion efficiency (PCE) of 20.28% were achieved for MAPbI3-based devices with the dopant-free BN-12, exceeding those with the commercial HTM PTAA (FF = 81.7%, PCE = 19.51%). More importantly, the unencapsulated devices based on BN-12 realized outstanding long-term stability, maintaining approximately 95% of its initial efficiency after stored for 85 days. By contrast, the PTAA-based device showed rapid decrease which retained only 50% of its initial value after 45 days.

Structural Model Construction and Optimal Characterization of High-Volatile Bituminous Coal Molecules

The structural characteristics of coal at the molecular level are important for its efficient use. Bituminous coal from the Baozigou Coal Mine is investigated, using elemental analysis, 13C nuclear magnetic resonance, X-ray photoelectron spectroscopy, and Fourier transform infrared. The molecular structure was determined. The aromatic compounds of bituminous coal molecules are primarily two- and three-ring structures, and the aliphatic structures are primarily in the form of methyl, ethyl side chains, and naphthenic hydrocarbons. The ratio of aromatic bridge carbon to peripheral carbon in the molecular structure is 0.279. Oxygen atoms in the form of carbonyl, phenolic hydroxyl and C–O, and nitrogen atoms in pyrroles. Thus, the average structure model of bituminous coal macromolecules was constructed; the molecular formula was C169H128O10N2S, and the molecular weight was 2378. The aromatic structural units in the macromolecular structure of coal include four naphthalenes, three anthracenes, two tetracenes, and heteroatoms in the form of three carbonyl groups, one phenolic hydroxyl group, one pyrrole, and one pyridine. The structure optimization and annealing kinetic simulation of a single macromolecular structure model were performed. Chemical bonds such as bridge bonds and aliphatic bonds were found to be twisted, and π–π interactions between the aromatic sheets in the molecule produced adjacent aromatic sheets. This arrangement tends to be approximately parallel, and the total energy decreases from 6713.401 to 2667.595 kJ/mol, among which the bond stretching energy and van der Waals energy dominate. We used 20 bituminous coal macromolecular models to construct aggregated structural models. After optimization by molecular dynamics simulation, the macromolecules were constrained by the surrounding molecules, and the sheet-like aromatic carbon structures that were originally approximately parallel were distorted. The macromolecular structure model of bituminous coal constructed in this study provides a theoretical model basis for the optimal surfactant.

Modulation of Electrochemical and Spectroscopic Properties in Ru(II)‐Terpyridyl End‐Capped Homobimetallic Organometallic Complexes by Varying π‐Conjugated Organic Spacers

AbstractA series of wire‐like binuclear Ru(II) complexes, 10–13, of general formula [(tpy‐C6H4‐Me)(PPh3)2Ru−C≡C−Ar‐C≡C−Ru(PPh3)2(tpy‐C6H4‐Me)]2+, (tpy‐C6H4‐Me=4′(4‐tolyl)‐2,2′‐6′,2′′‐terpyridyl; Ar=thienyl, phenyl, benzothiadiazolyl and fluorenyl respectively) have been judiciously designed, developed and characterized by various spectroscopic tools. The aromatic bridging moieties have been varied systematically to tune not only the chain length but also the electronic nature of the spacer units. To understand the intermetallic electronic properties, electrochemical and UV‐Vis‐NIR spectroscopic studies have been explored. Electrochemical studies reveal reversible redox waves for 10, and quasi‐reversible to irrreversible redox waves for 11–13 in the region of 0.30‐0.60 V and 0.55‐0.75 V (with respect to reference electrode of Ag/AgCl), presumably due to successive one electron oxidation of the Ru(II) conjugates. Interestingly, complexes 10 and 11 show promising NIR absorption (ϵ in order of 103 M−1cm−1). Electron transfer in the diruthenium wire‐like complexes can be perturbed to different extent by varying the spacer units. The computational studies (DFT and TDDFT) further support the structure property relationship, electrochemical and spectrsopic properties which is mediated through the participation of the bridging ligand in the corresponding mono‐oxidized organometallic wire‐like complexes.

Construction of Pingdingshan coal molecular model based on FT-IR and 13C-NMR

To construct a molecular model of coal and study the adsorption characteristics from the perspective of microscopic molecules, the microstructure of coal samples from Pingdingshan mining area in China was studied by means of Fourier transform infrared spectroscopy (FT-IR) and carbon-13 nuclear magnetic resonance spectroscopy (13C-NMR). The coal mainly possesses an aromatic molecular structure with fa (aromaticity), faH and XBP (the ratio of aromatic bridge carbon to surrounding carbon) being 0.86, 0.29 and 0.54, respectively. According to the results, the aromatic structure, with a high degree of condensation, is mainly dominated by pyrene and chrysene, while the aliphatic structure is mainly composed of methyl and methylene whose ratio is about 0.52. Furthermore, it contains a small amount of oxygen-containing functional groups such as carbonyl group, phenolic hydroxyl group and ether bond. In light of the above-mentioned molecular structure characteristics, the periodic structure model of Pingdingshan coal with the molecular formula C108H71O4N was constructed based on molecular mechanics and molecular dynamics by using the Materials Studio software. The model has a density of 1.3 g/cm3, a porosity of 4.1% and a specific surface area of 614.5 m2/g, faithfully reflecting the structural information of coal sample. Moreover, methane isothermal adsorption curves were simulated by the model at the temperatures of 318, 333 and 348 K. The experimentally measured and simulated isothermal methane adsorption curves both exhibit an error of smaller than 5% under high pressure. The results verify rationality and accuracy of the model structure. The study provides a model basis for further research on coal on the microscopic level.

Central-to-Folding Chirality Control: Asymmetric Synthesis of Multilayer 3D Targets With Electron-Deficient Bridges.

New multilayer 3D chiral molecules have been designed and synthesized asymmetrically through the strategy of center-to-multilayer folding chirality control and double Suzuki couplings. Individual diastereoisomers were readily obtained and separated via flash column chromatography. The key diastereoisomer was further converted into corresponding enantiomers. These enantiomers possess electron-deficient aromatic bridges layered with top and bottom aromatic scaffolds. X-ray structural analysis has unambiguously confirmed the configuration, and intermolecular packing results in regular planar patterns in solid crystals. The synthesis was achieved in a total of ten steps starting from commercially available starting materials.

A novel n-type organic semiconductor comprising a 1,5-naphthyridine-2,6-dione unit

The first examples of 1,5-naphthyridine-2,6-dione (NTD)-based n-type small molecules, NTDT-DCV and NTDP-DCV with an electron-withdrawing dicyanovinyl terminal unit and different aromatic bridging groups were synthesized and characterized.

Tuning iron-amine electronic coupling by different aromatic bridges based on ferrocene-ethynyl-triarylamine systems

The syntheses of a series of ferrocene (Fc)–ethynyl–triarylamine (TAA) inorganic–organic mixed-valence systems with different aromatic bridge linkers (Aryl = 1,4-phenyl [1], 1,4-naphthyl [2], 9,10-anthryl [3]) are reported in this study. These systems were accessible with good yields through the classical Sonogashira cross-coupling reactions of brominated intermediates, 1a, 2a, and 3a, with ethynylferrocene, respectively. Target compounds 1–3 were fully characterized by nuclear magnetic resonance, elemental analysis, and single-crystal X-ray diffraction analysis. Redox and electronic coupling properties were investigated by anodic voltammetry, UV–visible–near-infrared (NIR) spectroelectrochemistry, and density functional theory (DFT) calculations. Experimental results revealed that the first anodic steps of compounds 1–3 occur in ethynylferrocene units and the second redox process comes from triphenylamine moieties. This result is in accordance with the spin density distribution results. The Fe–N electronic coupling of singly oxidized species 1+–3+ observed by characteristic NIR bands proved the predicted electronic excitation of TAA to Fc from the time-dependent DFT calculations. The degree of electron coupling in 1+–3+ decrease with the increase in aromatic conjugation (phenyl, naphthyl, and anthryl).

Theoretical assessment of the influences of aromatic bridges on molecular second order nonlinear optical responses of Donor-Bridge-Acceptor types of molecular organic chromophores

Push-pull types Donor-Bridge-Acceptor (D-B-A) organic molecules have been reported as efficient functional materials for various technological applications. Often their interesting properties were reported to be directly linked to their nature of intramolecular charge transfers (ICT). Bridge that connects the D with A, plays the vital role in the ICT processes. A recent report of comparative experimental and computational nonlinear optical (NLO) study, shows many interesting behaviours exhibited by aromatic (diazine, thiophene and benzene rings) bridges. Many earlier studies also exist, where effects of one or more of aromatic bridges were investigated for NLO applications. But no systematic comparative study with well-known aromatic bridges at one place exist in literature. Inspired by those earlier works, this computational work reports the influences of a set of mono-aromatic ring bridges on NLO properties for a set of D-B-A types of organic molecules. This work can be expected to serve as a reference for many researchers working in the search of new and efficient functional materials.

Boosting the CO2 capture efficiency through aromatic bridged organosilica membranes

CO2 capture have attracted much attention due to serious environmental problems caused by excessive CO2 emission. Membrane-based technologies boasting of energy-saving and high-efficiency advantages exhibit much prospect in treating this issue. Benefited from excellent molecular sieving properties and high porosity, a wide variety of organosilica membranes were applied to the CO2 separation process. Nevertheless, most studies focused on the development of linear alkanes bridged organosilica membranes. Few researchers were dedicated to developing organosilica membranes with aromatic groups. In fact, the aromatic groups (e.g., such as benzene groups) functionalized organosilica precursors can endow derived membranes with robust network structures. Moreover, aromatic benzene groups can provide infinite possibilities of decoration. Herein, organosilica membranes fabricated using phenyltriethoxysilane (PhTES) with pendant benzene group, bis(triethoxysilyl)benzene (BTESB) with bridged benzene group and 4,4′-bis(triethoxysilyl)-1,1′-biphenyl (BTESBPh) with bridged biphenyl group, were used for CO2 capture separation. The effect of the location of aromatic benzene groups (bridged or pendant type) and the number of aromatic bridges (single benzene and biphenyl bridges) were evaluated in detail. For CO2/N2 mixtures separation at 50 °C, PhTES membranes displayed a CO2 permeance of 1087 GPU (1GPU = 3.348 ✕ 10−10 mol m−2 s−1 Pa−1) and CO2/N2 selectivity of 30. In contrast, BTESB membranes maintained a similar level of CO2/N2 selectivity of 34 but approximately 2.5 times enhanced CO2 permeance of 2600 GPU. BTESBPh membranes featured an unprecedentedly high CO2 permeance of 5465 GPU and CO2/N2 selectivity of 13. This clearly indicated that the aromatic functionalized organosilica membranes presented great potential in CO2 capture applications. Furthermore, the gas permeation properties of organosilica membranes can be finely tuned via the change of the location and the number of the benzene groups.

Cytotoxic activity and influence on acetylcholinesterase of series dinuclear platinum(II) complexes with aromatic nitrogen-containing heterocyclic bridging ligands: Insights in the mechanisms of action

Herein, the stability, lipophilicity, in vitro cytotoxicity, and influence on acetylcholinesterase of five dinuclear platinum(II) complexes with the general formula [{Pt(en)Cl}2(μ-L)]2+ (L is a different aromatic nitrogen-containing heterocyclic bridging ligands pyrazine (pz, Pt1), pyridazine (pydz, Pt2), quinoxaline (qx, Pt3), phthalazine (phtz, Pt4) and quinazoline (qz, Pt5), while en is bidentate coordinated ethylenediamine) were evaluated. The most active analyzed platinum complexes induced time-dependent growth inhibition of A375, HeLa, PANC-1, and MRC-5 cells. The best efficiency was achieved on HeLa and PANC-1 cells for Pt1, Pt2, and Pt3 at the highest concentration, while Pt1 was significantly more potent than cisplatin at a lower concentration. Additionally, a lower effect on normal cells was observed compared to cisplatin, which may indicate potentially fewer side effects of these complexes. Selected complexes induce reactive oxygen species and apoptosis on tumor cell lines. The most potent reversible acetylcholinesterase (AChE) inhibitors were Pt2, Pt4, and Pt5. Pt1 showed similar inhibitory potential toward AChE as cisplatin, but a different type of inhibition, which could contribute to lower neurotoxicity. Docking studies revealed that Pt2 and Pt4 were bound to the active gorge above the catalytic triad. In contrast, the other complexes were bound to the edge of the active gorge without impeding the approach to the catalytic triad. According to this, Pt1 represents a promising compound with potent anticancer properties, high selectivity, and low neurotoxicity.

Structural analysis of the boronic acid β-lactamase inhibitor vaborbactam binding to Pseudomonas aeruginosa penicillin-binding protein 3.

Antimicrobial resistance (AMR) mediated by β-lactamases is the major and leading cause of resistance to penicillins and cephalosporins among Gram-negative bacteria. β-Lactamases, periplasmic enzymes that are widely distributed in the bacterial world, protect penicillin-binding proteins (PBPs), the major cell wall synthesizing enzymes, from inactivation by β-lactam antibiotics. Developing novel PBP inhibitors with a non-β-lactam scaffold could potentially evade this resistance mechanism. Based on the structural similarities between the evolutionary related serine β-lactamases and PBPs, we investigated whether the potent β-lactamase inhibitor, vaborbactam, could also form an acyl-enzyme complex with Pseudomonas aeruginosa PBP3. We found that this cyclic boronate, vaborbactam, inhibited PBP3 (IC50 of 262 μM), and its binding to PBP3 increased the protein thermal stability by about 2°C. Crystallographic analysis of the PBP3:vaborbactam complex reveals that vaborbactam forms a covalent bond with the catalytic S294. The amide moiety of vaborbactam hydrogen bonds with N351 and the backbone oxygen of T487. The carboxyl group of vaborbactam hydrogen bonds with T487, S485, and S349. The thiophene ring and cyclic boronate ring of vaborbactam form hydrophobic interactions, including with V333 and Y503. The active site of the vaborbactam-bound PBP3 harbors the often observed ligand-induced formation of the aromatic wall and hydrophobic bridge, yet the residues involved in this wall and bridge display much higher temperature factors compared to PBP3 structures bound to high-affinity β-lactams. These insights could form the basis for developing more potent novel cyclic boronate-based PBP inhibitors to inhibit these targets and overcome β-lactamases-mediated resistance mechanisms.

Dynamic Spin-Spin Interaction Observed as Interconversion of Chemical Bonds in Stepwise Two-Photon Induced Photochromic Reaction.

Biradicaloids in π-conjugated organic molecules have been extensively studied in recent years because of the fundamental insights into the chemical bonds and unique optical, electrical, and magnetic properties. Several studies have reported that the spin-spin interactions of biradicaloids with flexible molecular frameworks dynamically evolve correlating with molecular structural changes. Although these dynamic behaviors will provide important insights into the relationship between molecular structures and spin properties, studies on such behaviors have been limited to two-spin systems. Here, we investigated the stepwise photochromic properties of biphotochromic molecules involving multiple spin interactions by double-pulse laser flash photolysis. The one-photon photochromic reaction generates the o-biradical form as the open-closed form, which thermally isomerizes to the o-quinoidal form and reaches the thermal equilibrium state between them. The additional absorption of a photon by the open-closed form leads to the photochromic reaction of the other photochromic unit, resulting in the generation of unpaired spins at the p-position of the central aromatic bridge of the biradical or quinoidal form. Under the situation, while the interaction between the unpaired spins and the o-biradical preferentially produces the p-quinoidal form in which the antiferromagnetic interaction at the p-position is dominant, that between the spins and the o-quinoidal form kinetically produces the bis(o-quinoidal) form followed by the thermal isomerization to the thermodynamically stable p-quinoidal form. These dynamic spin-spin interactions along with the rearrangement of chemical bonds will give a deeper understanding of the singlet biradicaloids and that to bridge organic multiradicals in molecular systems to cooperative spin behaviors in bulk materials.

Bridge Resonance Effects in Singlet Fission.

A major benefit of intramolecular singlet fission (iSF) materials, in which through-bond interactions mediate triplet pair formation, is the ability to control the triplet formation dynamics through molecular engineering. One common design strategy is the use of molecular bridges to mediate interchromophore interactions, decreasing electronic coupling by increasing chromophore-chromophore separation. Here, we report how the judicious choice of aromatic bridges can enhance chromophore-chromophore electronic coupling. This molecular engineering strategy takes advantage of "bridge resonance", in which the frontier orbital energies are nearly degenerate with those of the covalently linked singlet fission chromophores, resulting in fast iSF even at large interchromophore separations. Using transient absorption spectroscopy, we investigate this bridge resonance effect in a series of pentacene and tetracene-bridged dimers, and we find that the rate of triplet formation is enhanced as the bridge orbitals approach resonance. This work highlights the important role of molecular connectivity in controlling the rate of iSF through chemical bonds and establishes critical design principles for future use of iSF materials in optoelectronic devices.

Tuning the Topological Landscape of DNA-Cyclodextrin Nanocomplexes by Molecular Design.

Original molecular vectors that ensure broad flexibility to tune the shape and surface properties of plasmid DNA (pDNA) condensates are reported herein. The prototypic design involves a cyclodextrin (CD) platform bearing a polycationic cluster at the primary face and a doubly linked aromatic module bridging two consecutive monosaccharide units at the secondary face that behaves as a topology-encoding element. Subtle differences at the molecular level then translate into disparate morphologies at the nanoscale, including rods, worms, toroids, globules, ellipsoids, and spheroids. In vitro evaluation of the transfection capabilities revealed marked selectivity differences as a function of nanocomplex morphology. Remarkably high transfection efficiencies were associated with ellipsoidal or spherical shapes with a lamellar internal arrangement of pDNA chains and CD bilayers. Computational studies support that the stability of such supramolecular edifices is directly related to the tendency of the molecular vector to form noncovalent dimers upon DNA templating. Because the stability of the dimers depends on the protonation state of the polycationic clusters, the coaggregates display pH responsiveness, which facilitates endosomal escape and timely DNA release, a key step in successful transfection. The results provide a versatile strategy for the construction of fully synthetic and perfectly monodisperse nonviral gene delivery systems uniquely suited for optimization schemes.

Nonlinear Optical Pigments. Two-Photon Absorption in Crosslinked Conjugated Polymers and Prospects for Remote Nonlinear Optical Thermometry.

Nonlinear optical (NLO) pigments are compounds insoluble in solvents that exhibit phenomena related to nonlinear optical susceptibilities (χ(n) where n = 2,3,...), e.g., two-photon absorption (2PA) which is related to the imaginary part of χ(3). Determination of spectrally-resolved 2PA properties for NLO pigments of macromolecular nature, such as coordination polymers or crosslinked polymers, has long been a challenging issue due to their particulate form, precluding characterizations with standard techniques such as Z-scan. In this contribution, we investigate thus far unknown spectrally-resolved 2PA properties of a new subclass of NLO pigments—crosslinked conjugated polymers. The studied compounds are built up from electron-donating (triphenylamine) and electron-withdrawing (2,2’-bipyridine) structural fragments joined by vinylene (Pol1) or vinyl(4-ethynylphenyl) (Pol2) aromatic bridges. 2PA properties of these polymers have been characterized in broad spectral range by specially modified two-photon excited fluorescence (TPEF) techniques: solid state TPEF (SSTPEF) and internal standard TPEF (ISTPEF). The impact of self-aggregation of aromatic backbones on the 2PA properties of the polymers has been evaluated through extended comparisons of NLO parameters, i.e., 2PA cross sections (σ2) and molar-mass normalized 2PA merit factors (σ2/M) with those of small-molecular model compounds: Mod1 and Mod2. By doing this, we found that the 2PA response of Pol1 and Pol2 is improved 2–3 times versus respective model compounds in the solid state form. Further comparisons with 2PA results collected for diluted solutions of Mod1 and Mod2 supports the notion that self-aggregated structure contributes to the observed enhancement of 2PA response. On the other hand, it is clear that Pol1 and Pol2 suffer from aggregation-caused quenching phenomenon, well reflected in time-resolved fluorescence properties as well as in relatively low values of quantum yield of fluorescence. Accordingly, despite improved intrinsic 2PA response, the effective intensity of two-photon excited emission for Pol1 and Pol2 is slightly lower relative to Mod1 and Mod2. Finally, we explore temperature-resolved luminescence properties under one- (377 nm), two- (820 nm), and three-photon excitation (1020 nm) conditions of postsynthetically Eu3+-functionalized material, Pol1-Eu, and discuss its suitability for temperature sensing applications.

N/N Bridge Type and Substituent Effects on Chemical and Crystallographic Properties of Schiff-Base (Salen/Salphen) Niii Complexes

In total, 13 ligands R-salen (N,N’-bis(5-R-salicylidene)ethylenediamine (where R = MeO, Me, OH, H, Cl, Br, NO2) and R-salphen (N,N’-bis(5-R-salicylidene)-1,2-phenylenediamine (where R = MeO, Me, OH, H, Cl, Br) and their 13 nickel complexes NiRsalen and NiRsalphen were synthesized and characterized using IR (infrared) spectroscopy, mass spectrometry, elemental analysis, magnetic susceptibility, NMR (nuclear magnetic resonance), UV-vis (ultraviolet-visible) spectroscopy, cyclic voltammetry, and X-ray crystal diffraction. Previous studies have shown that all complexes have presented a square planar geometry in a solid state and as a solution (DMSO). In electrochemical studies, it was observed that in N/N aliphatic bridge complexes, the NiII underwent two redox reactions, which were quasi-reversible process, and the half-wave potential followed a trend depending on the ligand substituent in the 5,5’-R position. The electron-donor substituent—as -OH, and -CH3 decreased the E1/2 potential—favored the reductor ability of nickel. The crystals of the complexes NiMesalen, NiMeOsalen, NiMeOsalphen, and Nisalphen were obtained. It was shown that the crystal packaging corresponded to monoclinic systems in the first three cases, as well as the triclinic for Nisalphen. The Hirshfeld surface analysis showed that the packaging was favored by H∙∙∙H and C∙∙∙H/H∙∙∙C interactions, and C-H∙∙∙O hydrogen bridges when the substituent was -MeO and π-stacking was added to an aromatic bridge. Replacing the N/N bridge with an aromatic ring decreased distortion in square-planar geometry where the angles O-Ni-N formed a perfect square-planar.

Understanding the molecular structure of HSW coal at atomic level: A comprehensive characterization from combined experimental and computational study

In this work, the coal samples from Hongshiwan (HSW) mining area, Ningxia, northwest of China, are characterized by using several modern materials characterization techniques, such as proximate and ultimate analyses, solid state 13C nuclear magnetic resonance (13C NMR), X-ray photoelectron spectroscopy and Fourier transform infrared spectroscopy (FT-IR). Then the key information about elements, valence, and chemical bonding for coal molecular structural construction is obtained. The results reveal that the main structure of HSW coal has 75.96% aromatic skeleton in mass. The ratio of aromatic bridge carbon to aromatic peripheral carbon of HSW coal is 0.315, indicating more naphthalene than benzene and anthracene in coal structures. Oxygen predominantly presents in the forms of ether (C–O), carbonyl (CO) and carboxyl (–COO). Nitrogen presents in the forms of both pyridine and pyrrole. Methyl (–CH3) group is predominant in cyclic and aliphatic hydrocarbons. Based on obtained structural information and the approaches of average molecular structure, the single molecular formula of HSW coal is defined as C221H148O28N2, with a molecular weight of 3142.32. Also, the 2D and 3D molecular model of HSW coal are built with computer-aided modeling. The model is optimized and further verified by FT-IR and 13C NMR spectra simulation with quantum chemical calculations. Besides, a more complicated structure of complex model for HSW coal containing 10 single-molecules is also obtained. Therefore, molecular structure of HSW coal has been comprehensively depicted and understood at atomic level from both experimental and quantum chemical approaches in the current work.

Dynamic Covalent Synthesis of Crystalline Porous Graphitic Frameworks

Summary Porous graphitic framework (PGF) is a two-dimensional (2D) material that has emerging energy applications. An archetype contains stacked 2D layers, the structure of which features a fully annulated aromatic skeleton with embedded heteroatoms and periodic pores. Due to the lack of a rational approach in establishing in-plane order under mild synthetic conditions, the structural integrity of PGF has remained elusive and ultimately limited its material performance. Here, we report the discovery of the unusual dynamic character of the C=N bonds in the aromatic pyrazine ring system under basic aqueous conditions, which enables the successful synthesis of a crystalline porous nitrogenous graphitic framework with remarkable in-plane order, as evidenced by powder X-ray diffraction studies and direct visualization using high-resolution transmission electron microscopy. The crystalline framework displays superior performance as a cathode material for lithium-ion batteries, outperforming the amorphous counterparts in terms of capacity and cycle stability.

When Light and Acid Play Tic-Tac-Toe with a Nine-State Molecular Switch.

Combining different molecular switching functions in a single molecule is a simple strategy to develop commutable molecules featuring more than two commutation states. The present study reports on two molecular systems consisting of two indolino-oxazolidine (Box) moieties connected to an aromatic bridge (phenyl or bithiophene) by ethylenic junctions. Such systems, referenced as BiBox, are expected to show up multiaddressable and multiresponsive behaviors. On one hand, the oxazolidine ring opening/closure of Box moieties can be addressed by chemical stimuli, and on the other hand, the trans-to-cis isomerization of the ethylenic junctions is induced by visible light irradiation (with a thermal back conversion). NMR and UV-visible spectroscopies allowed to characterize up to nine out of the ten theoretically expected commutation states as well as to measure the kinetics of the interconversions. Also, steady state fluorescence spectroscopy measurements highlighted the strong influence of the open/closed states of the Box moieties on their emission properties.