Search

International audience; Alcohols and epoxides are arguably ideal electrophiles for the Friedel-Crafts alkylation, since they are widely available, require no pre-activation, and produce no stoichiometric waste beyond water. However, neither primary aliphatic alcohols nor most classes of terminal epoxides are compatible with existing intermolecular Friedel-Crafts methodologies, and sequential Friedel-Crafts reactions starting from epoxides consequently remain underexplored. Here, we report that these limitations are easily overcome using Brønsted acid catalysis in hexafluoroisopropanol (HFIP) as a solvent. Electron-poor aromatic epoxides and aliphatic epoxides undergo stereospecific arylation to give an alcohol which, depending on the reaction conditions, can partake in a second nucleophilic substitution with a different arene in one pot. Phenyl ethanols react through a phenonium intermediate, whereas simple aliphatic alcohols participate in a rare intermolecular SN2 Friedel-Crafts process, delivering linear products exclusively. This work provides an alternative to metal-catalyzed cross-couplings for accessing important scaffolds, widening the range of applications of the Friedel-Crafts reaction

Boronic acid catalysis has emerged as a mild method for promoting a wide variety of reactions. It has been proposed that the mode of catalysis involves Lewis acid or covalent activation of hydroxyl groups by boron, but limited mechanistic evidence exists. In this work, representative boronic acid catalyzed reactions of alcohols and oximes have been reinvestigated. A series of control experiments with boronic and Bronsted acids were interpreted along with correlations between their reactivity and their acidity measured by the Gutmann-Beckett method. Overall, it was concluded that the major modes of catalysis involve either dual H-bond catalysis or Bronsted acid catalysis. Strong Bronsted acids were shown to be generated in situ from covalent assembly of the boronic acids with hexafluoroisopropanol, explaining why the solvent had such a major impact on the reactivity. This new insight should guide the future development of boronic acid catalysis, where the diverse and solvent-specific nature of catalytic modes has been overlooked.

Intestinal farnesoid X receptor (FXR) signaling is involved in the development of obesity, fatty liver disease, and type 2 diabetes. However, the role of intestinal FXR in atherosclerosis and its potential as a target for clinical treatment have not been explored. The serum levels of fibroblast growth factor 19 (FGF19), which is encoded by an FXR target gene, were much higher in patients with hypercholesterolemia than in control subjects and were positively related to circulating ceramide levels, indicating a link between intestinal FXR, ceramide metabolism, and atherosclerosis. Among ApoE(–/–) mice fed a high-cholesterol diet (HCD), intestinal FXR deficiency (in Fxr(ΔIE) ApoE(–/–) mice) or direct FXR inhibition (via treatment with the FXR antagonist glycoursodeoxycholic acid [GUDCA]) decreased atherosclerosis and reduced the levels of circulating ceramides and cholesterol. Sphingomyelin phosphodiesterase 3 (SMPD3), which is involved in ceramide synthesis in the intestine, was identified as an FXR target gene. SMPD3 overexpression or C16:0 ceramide supplementation eliminated the improvements in atherosclerosis in Fxr(ΔIE) ApoE(–/–) mice. Administration of GUDCA or GW4869, an SMPD3 inhibitor, elicited therapeutic effects on established atherosclerosis in ApoE(–/–) mice by decreasing circulating ceramide levels. This study identified an intestinal FXR/SMPD3 axis that is a potential target for atherosclerosis therapy.

Metal oxide anode material is one of promising candidates for the next-generation LIBs, due to its high theoretical capacity and low cost. The poor conductivity and huge volume change during charge/discharge, however, restrict the commercialization of metal oxide anode material. In this work, we design a novel Cu-SnO2 composite derived from Cu6Sn5 alloy with three dimensional (3D) metal cluster conducting architecture. The novel Cu structure penetrates in the composite particles inducing high conductivity and space-confined SnO2, which restrict the pulverization of SnO2 during lithiation/delithiation process. The optimized Cu-SnO2 composite anode delivers an initial discharge capacity of 933.7 mA h/g and retains a capacity of 536.1 mA h/g after 200 cycles, at 25 °C and a rate of 100 mA/g. Even at the high rate of 300 mA/g, the anode still exhibits a capacity of more than 29% of that tested at 50 mA/g. Combining with the phase and morphology analysis, the novel Cu-SnO2 composite not only has good electrical conductivity, but also possesses high theoretical capacity (995 mAh/g), which may pave a new way for the design and construction of next-generation metal oxide anode materials with high power and cycling stability.

The enzymatic Pictet-Spengler (PS) reaction, catalyzed by Pictet-Spenglerase (PSase), is the feature of β-carboline (βC) alkaloid biosynthesis. NscbB is a rare microbial PSase discovered from a cryptic β-carboline alkaloid biosynthetic gene cluster (BGC) in the Nocardiopsis synnemataformans DSM 44143 (kidney transplant patient derived) by homologous alignment with its well-characterized counterpart McbB. The biochemical analysis showed that NscbB could catalyze l -tryptophan (KM = 89.64 ± 8.69 μM) and methylglyoxal (KM = 147.70 ± 16.38 μM), without cofactors, to form the two βC skeletons 1-acetyl-3-carboxy-β-carboline and 1-acetyl-β-carboline in vitro. Additionally, the heterologous expression of nscbB in E. coli BL21 (DE3) revealed the efficient bioproductivity of NscbB to bioproduce two βC skeletons, 1-acetyl-3-carboxy-β-carboline (5.5 mg/L) and 1-acetyl-β-carboline (3.1 mg/L), within 16 h fermentation. These results demonstrate NscbB is a novel and practical microbial PSase, which is useful for future bioactive βC alkaloid exploitation and development.

Covering: up to 2018 Chlorophylls, bacteriochlorophylls and related hydroporphyrins constitute invaluable natural products but have largely remained outside the scope of viable syntheses. The campaign toward chlorophyll a by Woodward and coworkers is a deservedly celebrated landmark in organic synthesis yet the route entailed 49 steps, relied on semisynthetic replenishment of advanced intermediates, and then pointed to (but did not implement) uncertain literature procedures for the final transformations. Indeed, the full synthesis at any scale of any (bacterio)chlorophylls - conversion of small-molecule starting materials to the product - has never been accomplished. Herein, the reported syntheses of (±)-bonellin dimethyl ester (0.93 mg) and tolyporphin A O,O-diacetate (0.38 mg), as well as the never-fully traversed route to chlorophyll a, have been evaluated in a quantitative manner. Bonellin and tolyporphin A are naturally occurring chlorin and bacteriochlorin macrocycles, respectively, that lack the characteristic fifth ring of (bacterio)chlorophylls. A practical assessment is provided by the cumulative reaction mass efficiency (cRME) of the entire synthetic process. The cRME for the route to chlorophyll a would be 4.3 × 10-9 (230 kg of all reactants and reagents in total would yield 1.0 mg of chlorophyll a), whereas that for (±)-bonellin dimethyl ester or tolyporphin A O,O-diacetate is approximately 6.4 × 10-4 or 3.6 × 10-5, respectively. Comparison of the three syntheses reveals insights for designing hydroporphyrin syntheses. Development of syntheses with cRME > 10-5 (if not 10-4), as required to obtain 10 mg quantities of hydroporphyrin for diverse physicochemical, biochemical and medicinal chemistry studies, necessitates significant further advances in tetrapyrrole chemistry.

Carbon quantum dots (CQDs) have attracted considerable interest because of their advantages of low cost, nontoxicity, easy preparation, and diverse optical properties. Photophysical properties and stability are two key issues that affect the further use of CQDs, especially for solid-state applications. Here, we report a facile and effective method to enhance the fluorescence and moisture-resistance of CQDs. CQDs were synthesized by the thermolysis of citric acid on a multigram scale and were readily used to react with zinc powder in an aqueous solution to produce zinc-reduced CQDs (Zn-CQDs). The process was operated under mild conditions and completed in 10 min. The fluorescence intensity of the CQDs increased more than three times after reacting with zinc. In contrast to the pristine CQD solids, which easily absorbed moisture and turned into viscous liquids, the as-prepared Zn-CQD blocks possessed an ordered porous structure and were immune to moisture in the air. They remained stable under ambient condi...

The chemistry of reduced tetrapyrroles is less developed than that of the fully unsaturated (porphyrin) analogues, yet is of comparable importance given the natural roles of hydroporphyrins (e.g., chlorophylls, bacteriochlorophylls) and contracted hydroporphyrins (cobalamin). The self-condensation of a 1-(dimethoxymethyl)-2,3-dihydro-3,3-dimethyldipyrrin (termed a dihydrodipyrrin-acetal) affords the corresponding bacteriochlorin or tetradehydrocorrin with the outcome potentially controllable by choice of the catalysis conditions. The ability to install distinct patterns of substituents about the perimeter of the synthetic macrocycles is essential for biomimetic studies. Here, 18 new target (and 9 intermediate) hydrodipyrrins encompassing a range of dipyrrin saturation levels (dihydro, tetrahydro, hexahydro) and equipped with diverse α-pyrrole (-H, -SMe, -SPh, -Br, -Me, -CO2R, dioxaborolanyl) and α-pyrroline (methyl, formyl, dimethoxymethyl, oxo, methoxy, methylthio, iminomethyl, ethoxycarbonylvinyl, dicyanovinyl) substituents have been prepared and examined in the directed synthesis of bacteriochlorins. The routes – inspired by a directed route to chlorins – rely on condensation of two hydrodipyrrins to produce a hydrobilin followed by ring closure to form the macrocycle. Four new unsymmetrically substituted bacteriochlorins were obtained in very low yields; as an offshoot, efficient routes to three new tetradehydrocorrins (nickel chelates) were discovered, including two B,D-tetradehydrocorrins (pyrroline–pyrrole A–D ring junction) and one B,C-tetradehydrocorrin (pyrroline–pyrroline A–D ring junction). Taken together, this study deepens our understanding of the chemistry of hydrodipyrrins and hydrobilins as precursors to hydroporphyrins.

Thick nanoporous electrode design with pore size in several nanometers can substantially improve the active sites to achieve high energy density. However, the sluggish ion/charge kinetics and mechanical instability limit their rate and long-term cycling capability. To address these obstacles, herein, a thick vacancy-riched nanoporous NiCoMn@oxides (Vo-3DNCM@oxides) core-shell structure as pseudocapacitive electrode in alkaline electrolyte was prepared by polarizing a nanoporous NiCoMn alloy and subsequently mild annealing in Ar atmosphere. As a result, a large number of coordination unsaturated sites can be exposed on active oxide layer by mild annealing. Meanwhile, the nanopores can be coarsened to tens of nanometers. The coordination unsaturated sites synergy with coarsened nanopores can not only endow high-efficient ion/electrons transport channels but also hold the structure stable during fast charge/discharge process. Electrochemical performance characterization illustrates that the 4Vo-3DNCM@oxides electrode annealed at 400 °C shows high capacity retention of about 69.7% at current rates from 1 A cm−3 to upward of 10 A cm−3 (1464 C cm−3 at 1 A cm−3 and 908 C cm−3 at 10 A cm−3) and high energy density of 90.7 mWh cm−3, demonstrating a potential application in pseudocapacitors. More importantly, the novel structural design exhibits promising prospects toward the practical application of integrated thick electrodes.

Development of transition-metal-oxides (TMO) based high-energy density aqueous pseudocapacitors requires simultaneously high charge storage capacity, high electronic conductivity and large redox potential window. Engineering the interfacial electronic structure among electrolyte, oxides and current collectors and thus modifying the corresponding multi-redox reactions displays a great potential to address the above challenges. Herein, a series of nanoporous alloy@oxide composite electrodes are prepared by self-oxidation of the nanoporous NiMMn alloys, where various dopants of 3d transition metal elements (M = Ti, V, Cr, Fe, Co, Cu) are introduced to tune the electronic structures prior to oxidation of the alloys. Within the alloy-core and oxide-shell structure, it is found that all the dopants effectively suppress the hydrogen production to ensure the high operation voltage. Additionally, Co dopant displays the largest energy density (145 mWh cm−3) comparing to others. The hydrogen suppression stems from the tuning of the work function of NiMn via doping different 3d elements so that the out-layer oxide electronic structures downshift accordingly. Further DFT calculation on the doped active surfaces (0 0 1) and (1 1 1) illustrates that Co dopant results in the large amounts of density of states within the external scan voltage −0.9 V ~ 0.6 V (vs. Ag/AgCl electrode), yielding the high capacitance to accommodate the electrons. This work provides insights into the design of the promising capacitive materials with a high energy density via interface engineering of the core alloy and the out-layer oxides.

A bis-nitrobenzoxadiazole (NBD) derivative of calix[4]arene (L1) and a control compound (L2), mono-NBD derivative of the calixarene were designed and prepared via click chemistry. Fluorescence studies demonstrated that L1 as created can function as a switch with the presence of Ag+ in THF, of which the free state of L1 emits at ∼527 nm, but the binding state at 576 nm. Based upon this discovery, L1 was studied as a chemo-sensor of Ag+ in a mixture solvent of THF and H2O with a detection limit (DL) of ∼6.2 × 10−7 mol/L. Presence of other commonly found metal ions shows little effect upon the determination. Moreover, the L1 in the Ag+-L1 complex could be fully released with introduction of HCHO, a bases for the sensitive and selective detection of the toxic chemical. The DL of this test is 6.6 × 10−7 mol/L. Interestingly, binding and releasing of the fluorescent ligand could be repeated for at least 5 times. Furthermore, both sensing could be performed in a visualized manner. It is believed that the fluorescent compound as created should have a potential to find real-life applications.

Bacteriochlorins absorb strongly in the near-infrared spectral region and hence are of great interest across the field of photochemistry. The established de novo self-condensation of a dihydrodipyrrin-acetal has afforded stable bacteriochlorins bearing a variety of β-pyrrolic substituents, but the route was incompatible with the presence of two alkyl groups. The lacuna stemmed from the instability of the dialkyl-substituted dihydrodipyrrin-acetal. Here, two dihydrodipyrrin-carboxaldehydes, each bearing a tert-butoxycarbonyl group at the pyrrole α-position, were prepared and found to be stable to routine handling. Each ester-substituted dihydrodipyrrin-carboxaldehyde in acid underwent in situ ester cleavage and ensuing self-condensation to provide the corresponding 2,3,12,13-tetraalkylbacteriochlorin. The alkyl groups examined include methyl and methyl acetate. Such synthetic bacteriochlorins, while previously unknown, provide valuable models of the natural chromophores. The absorption and fluorescence characteristics of the tetraalkylbacteriochlorins are generally typical for this genre of macrocycle. The X-ray structure of the tetramethylbacteriochlorin reveals that the pyrrolinic (reduced) rings are modestly more twisted out-of-plane (torsional angle ∼11°) than those of the nearly planar (torsional angle ∼1°) parent bacteriochlorin that lacks pyrrolic tetraalkyl groups. The resonance Raman spectrum of the tetramethylbacteriochlorin is also far richer in the low- to mid-frequency region than that of the unsubstituted analogue, but like the unsubstituted counterpart, is far sparser in the high-frequency region than that of native bacteriochlorophyll. Access to tetraalkylbacteriochlorins constitutes one step on the path from the most simple, fully unsubstituted bacteriochlorin to the fully decorated, natural bacteriochlorophylls.

Nanostructured transition metal oxides (TMOs) have shown extraordinary promise as anode materials for Lithium ion battery but still been challenging for practical applications due to their low conductivity and activity with high loading mass. Herein, we prepare an integrated high-loading-mass TMOs based anode with 3D nanoporous structure and metallurgical bonding interface between oxide and current collector by self-combustion and subsequently mild annealing of the nanoporous NiCuMn (np-NiCuMn). Self-combustion, caused by the high surface energy of np-NiCuMn, induces ligament coarsening and deep surface oxidation of the alloy, which consumes all the energy quickly and form metal core and oxide shell structure with loading mass up to 7.3 mg cm−2. Mild annealing in H2 at 250 °C creates robust vacancies in oxide layers (6.9 mg cm−2 of oxide retention) with some precipitated Cu doping, which not only provides more Li+ storage sites but also further enhance the electron/ion transportation in the anode. Consequently, the flexible integrated electrode demonstrates an ultrahigh area capacity of up to 9.48 mAh cm−2 at a current density of 0.5 mA cm−2, as well as excellent rate performance and cycle stability. This work is expected to open a cost-effective and large-scale route to prepare high-capacity electrodes for next-generation energy storage devices.

Janus membranes with asymmetric wettability have attracted intense attention in oil/water separation, membrane distillation, liquid/fog collection, liquid diode, etc. Facile manipulation of the paradoxical wetting/antiwetting property on opposite surfaces of a 2D membrane is challenging. Different from most postmodification methods, herein, we propose one single-step unidirectional segregation strategy to fabricate a polymeric Janus membrane with extremely opposite wetting surfaces showing almost a 150° contact angle difference for the first time. We achieved the unidirectional segregation of the hydrophilic copolymer poly(vinylpyrrolidone-vinyltriethoxysilane) in a polyvinylidene fluoride (PVDF) membrane during phase separation. A glycerol coating on the nonwoven fabric support locally limited the phase separation on the bottom surface, blocked the segregation of hydrophilic copolymer, and promoted the segregation to the top surface. Working collaboratively with the asymmetric micro-/nanostructure on both surfaces, the resulting Janus membrane exhibited a superhydrophilic top surface and a superhydrophobic bottom surface. The Janus PVDF membrane showed switchable separation performance and high separation efficiency for both oil-in-water emulsions and water-in-oil emulsions because of its anisotropic wettability compared with solely hydrophobic or hydrophilic PVDF membranes.

A calix[4]arene-based dimeric-cholesteryl derivative with naphthalene in the linkers (C2N2C) was designed and synthesized. The gelation behaviors of the compound in 36 liquids were evaluated. It was demonstrated that C2N2C could gel 16 of the liquids tested, which include both polar and apolar liquids. SEM and AFM studies revealed that the morphologies of the gel networks are dependent on the concentrations of C2N2C and the nature of the liquids under study. Importantly, rheological studies revealed that the gel of the compound in benzene possesses sensitive, fast and fully reversible thixotropic property. More importantly, the Tgel of the C2N2C/benzene gel could be at least more than 60 degrees higher than the boiling point of benzene when the gelator concentration is greater than 6% (w/v), a result never reported before. CD measurements revealed the chiral nature of the assemblies of the gel networks. Further investigation by AFM measurements confirmed the right-hand helical structures of the gel networks of C2N2C/benzene gel. As anticipated, hydrogen bonding and π–π stacking are the two main driving forces for the formation of the gels.

Synthetic bacteriochlorins—analogues of bacteriochlorophylls, Nature’s near-infrared absorbers—are attractive for diverse photochemical studies. meso-Arylbacteriochlorins have been prepared by the self-condensation of a dihydrodipyrrin–carbinol or dihydrodipyrrin–acetal following an Eastern-Western (E-W) or Northern-Southern (N-S) joining process. The bacteriochlorins bear a gem-dimethyl group in each pyrroline ring to ensure stability toward oxidation. The two routes differ in the location of the gem-dimethyl group at the respective 3- or 2-position in the dihydrodipyrrin, and the method of synthesis of the dihydrodipyrrin. Treatment of a known 3,3-dimethyldihydrodipyrrin-1-carboxaldehyde with an aryl Grignard reagent afforded the dihydrodipyrrin-1-(aryl)carbinol, and upon subsequent acetylation, the corresponding dihydrodipyrrin-1-methyl acetate (dihydrodipyrrin–acetate). Self-condensation of the dihydrodipyrrin–acetate gave a meso-diarylbacteriochlorin (E-W route). A 2,2-dimethyl-5-aryldihydrodipyrrin-1-(aryl)carbinol underwent self-condensation to give a trans-A2B2-type meso-tetraarylbacteriochlorin (N-S route). In each case, the aromatization process entails a 2e−/2H+ (aerobic) dehydrogenative oxidation following the dihydrodipyrrin self-condensation. Comparison of a tetrahydrodipyrrin–acetal (0%) versus a dihydrodipyrrin–acetal (41%) in bacteriochlorin formation and results with various 1-substituted dihydrodipyrrins revealed the importance of resonance stabilization of the reactive hydrodipyrrin intermediate. Altogether 10 new dihydrodipyrrins and five new bacteriochlorins have been prepared. The bacteriochlorins exhibit characteristic bacteriochlorophyll-like absorption spectra, including a Qy band in the region 726–743 nm.

Bacteriochlorophylls contain a bacteriochlorin macrocycle bearing an annulated fifth ring. The fifth ring, termed the isocyclic ring or ring E, is equipped with 131-oxo and 132-carbomethoxy substituents. Herein, a general route to stable, synthetic bacteriochlorophyll analogues is described. Knoevenagel condensation (∼40 mM, rt, CH2Cl2, piperidine/AcOH/molecular sieves) of a dihydrodipyrrin–carboxaldehyde (AD half) and a dihydrodipyrrin substituted with a β-ketoester (BC half) forms a propenone bearing the two halves (a hydrobilin analogue). Subsequent treatment (0.2 mM) with acid (Yb(OTf)3, CH3CN, 80 °C) promotes a double ring-closure process: (i) condensation between the α-position of pyrrole ring A and the α-acetal unit attached to pyrroline ring B forms the bacteriochlorin macrocycle, and (ii) Nazarov cyclization of the β-(propenoyl)-substituted ring C forms the isocyclic ring (E). Five new bacteriochlorins bearing various substituents (alkyl/alkyl, aryl, and alkyl/ester) at positions 2 and 3 (β-pyrro...

We have investigated the impact of surface recombination on the effective carrier injection efficiency and the Joule heating of axial InGaN/GaN nanowire light-emitting diodes (LEDs). The results reveal that the carrier injection efficiency of such devices is extremely low $({ , due to the severe carrier loss through nonradiative surface recombination. It is further observed that the thermal resistance of typical nanowire LEDs is comparable with, or lower than that of their planar counterparts, in spite of the reduced thermal conductivity of nanowires. The poor carrier injection efficiency, however, leads to significantly elevated junction temperatures for nanowire LEDs. We have further demonstrated, both theoretically and experimentally, that the carrier injection efficiency can be significantly improved in p-doped nanowires, due to the downward surface band bending, and in InGaN/GaN/AlGaN dot-in-a-wire core-shell nanoscale heterostructures, due to the superior carrier confinement offered by the large bandgap AlGaN shell. This paper offers important insight for the design and epitaxial growth of high-performance nanowire LEDs.

In response to the severe blocks of the large volume change and sluggish capacity decay originating from the Lithium ion insertion/extraction in the anodes of Lithium ion batteries, transition metal oxides with high cycle stability are desirable yet extremely challenging for achieving high energy density anodes. Here, we report that a double-shelled NiO nanocrystal-doped MnO layer with robust defects, epitaxially grown on a nanoporous Ni network by simultaneously dealloying and oxidising NiMn alloy, can overcome these challenges to deliver a large capacity with excellent cycle stability. The interconnected core-shell nanoporous structure with robust defects possesses ultrahigh efficient electron/ion transport and a volume buffer. Consequently, the free-standing electrode as a whole delivers a highly reversible capacity of 1172 mAh cm−3 (960 mAh g−1) with a remarkable cycle life (105% retention after 200 cycles at 100 mA g−1). Furthermore, the electrode achieves a high capacity of 831.5 mAh cm−3 (681 mAh g−1) even at 1000 mA g−1, demonstrating a high rate capability. The proposed synthetic strategy can be further explored for the construction of other three-dimensional metal@metal oxide electrodes for application in next-generation energy storage systems.

The authors have investigated the impact of nanowire geometry on the carrier transport in axial indium gallium nitride and gallium nitride (InGaN/GaN) nanowire light-emitting diodes (LEDs). The results reveal that hole transport depends critically on the nanowire geometry. With identical material parameters, the carrier transport process can be varied with different nanowire geometry designs, which lead to different overall device performance. This study offers important insight into the design and epitaxial growth of high-performance nanowire LEDs.

A gold-catalyzed intermolecular carboalkoxylation of ­alkenes has been developed. Readily available and inexpensive ­dimethyl acetals have been employed as a facile reagent to achieve the carboalkoxylation of alkenes.

A binuclear heteroligated titanium(IV) catalyst based on phenoxyimine ligands (FI2-Ti2) with its crystal structure elucidated has been developed for the first time for olefin (co)polymerization. In ethylene polymerization, the activity of the binuclear catalyst FI2-Ti2 can reach 3.0 × 106 g mol–1 h–1, and the polydispersity of the resulting polymers is narrow. In copolymerization of ethylene and other olefins, similar incorporation ratios for monoenes are obtained for FI2-Ti2 and FI-Ti1. However, the incorporation ratio of 1,5-hexadiene increases from 3.2% using FI-Ti1 to 8.8% with FI2-Ti2. In comparison, the binuclear monophenoxyimine catalyst, [FI2-Ti2(THF)2], exhibits higher catalytic activity and incorporates more α-olefins than its mononuclear analogue [FI-Ti1(THF)] in the copolymerization. These results are interpreted as consequences of two effects. First, the cooperativity between the two metal centers facilitates the coordination of olefin. Second, the substitutions near the active sites exert a ...

Full-color, catalyst-free InGaN/GaN dot-in-a-wire light-emitting diodes (LEDs) were monolithically grown on Si(111) by molecular beam epitaxy, with the emission characteristics controlled by the dot properties in a single epitaxial growth step. With the use of p-type modulation doping in the dot-in-a-wire heterostructures, we have demonstrated the most efficient phosphor-free white LEDs ever reported, which exhibit an internal quantum efficiency of ∼56.8%, nearly unaltered CIE chromaticity coordinates with increasing injection current, and virtually zero efficiency droop at current densities up to ∼640 A/cm(2). The remarkable performance is attributed to the superior three-dimensional carrier confinement provided by the electronically coupled dot-in-a-wire heterostructures, the nearly defect- and strain-free GaN nanowires, and the significantly enhanced hole transport due to the p-type modulation doping.

DFT/B3LYP/6-311G+(d,p) basis set including solvent effect was first used to calculate a set of molecular descriptors of 55 phenylalkylamine and 20 tryptamine compounds with hallucinogenic activity. Four quantitative structure-activity relationship (QSAR) models of the hallucinogenic activity for phenylalkylamines and tryptamines were obtained by employing multiple linear regression (MLR) method. The QSAR analysis indicated that electron-related descriptors were major contributors to the hallucinogenic activities of phenylalkylamines and tryptamines. In addition, electron-unrelated descriptors have some impact on the hallucinogenic activities of phenylalkylamines. Based on the results of QSAR study, a novel Conformation Complementary Judgement, Transformation and Induction (CCJTI) model had been proposed to explain different action mechanisms of phenylalkylamines and tryptamines with their target receptors. It was concluded that phenylalkylamines might combine with receptor by electronic effect, but steric factor could affect it also, whereas tryptamines could act only through the electronic effect.

Herein, the report on a new class of self-healing and pH/temperature responsive mixed solvent (ethanol and water) gels shows unusual mechanical properties to resist slicing, sustain high compression, and withstand stretching as evidenced by the cutting breaking stress, the fracture compressive stress, and the stretching ratio of one of the gels as obtained can reach or exceed 26.4 MPa, 9.2 MPa, and ≈5 times, respectively. The gels are designed by introducing dynamic covalent bond, acylhydrazone, which is believed to combine the merits of conventional chemical bonds and those of supramolecular interactions. Specifically, a hydrazide-modified calix[4]arene derivative and linear benzaldehyde-terminated poly(ethylene glycol)s are synthesized and used as reactive components to build gel networks. Interestingly, acid-degradable hydrogel can be obtained via natural drying of the mixed solvent gel first and then swelling in pure water.

We report on the achievement of high-performance InGaN/GaN dot-in-a-wire red light-emitting diodes on Si(111) substrates. Owing to the superior 3-D carrier confinement offered by the self-organized dot-in-a-wire heterostructures, the devices exhibit relatively high (~18%-32%) internal quantum efficiency at room temperature. Moreover, no efficiency droop was observed for injection current up to ~480A/cm2 under pulsed biasing conditions. We have also demonstrated that, by controlling the inhomogeneous broadening of the dot-in-a-wire heterostructures, the devices can exhibit relatively stable emission characteristics with increasing current.

We have developed phosphor-free InGaN/GaN/AlGaN dot-in-a-wire core-shell white light emitting diodes, which can break the carrier injection efficiency bottleneck of conventional nanowire white light emitting diodes, leading to a dramatic enhancement of the output power. Additionally, such phosphor-free nanowire white light emitting diodes can deliver a very high color rendering index (CRI) of ~92-98.

We show that the performance of InGaN/GaN axial nanowire LEDs is largely limited by the poor carrier injection efficiency. We have further demonstrated high performance phosphor-free white LEDs using InGaN/GaN/AlGaN dot-in-a-wire core-shell heterostructures.

We report on the achievement of InGaN/GaN dot-in-a-wire phosphor-free white light-emitting diodes, which can exhibit a record internal quantum efficiency of ∼57% and virtually zero efficiency droop for injection currents up to ∼2,200 A/cm2.

We report on the achievement of a record high internal quantum efficiency in InGaN/GaN dot-in-a-wire light emitting diodes by significantly reducing the electron overflow and enhancing the hole transport in the device active regions.

A record high internal quantum efficiency of 36.7% was achieved for nanowire LEDs by using InGaN/GaN dot-in-a-wire heterostructures. The devices can exhibit strong green, red, and white emission, depending on the dot sizes and compositions.

We report on the epitaxial growth, fabrication, and characterization of full-color InGaN/GaN dot-in-a-wire nanoscale LEDs on Si(111), which can exhibit an internal quantum efficiency of ∼ 45% and negligible saturation up to ∼ 300 A/cm2.

We report on the molecular beam epitaxial growth and characterization of In(Ga)N nanowires on Si(111) substrates. We also describe the growth and optical properties of InGaN/GaN dot-in-a-wire heterostructures on Si(111) substrates with emission in the green, yellow, and red wavelength range. The design, fabrication, and characterization of In(Ga)N nanowire solar cells and LEDs are discussed. InN p-i-n axial nanowire homojunction solar cells exhibit a promising short-circuit current density of ~ 14.4 mA/cm2 and an energy conversion efficiency of ~ 0.68% under 1-sun, AM1.5G illumination. Strong green, yellow, and amber emission has also been achieved from InGaN/GaN dot-in-a-wire LEDs at room temperature.