Non‐alternant non‐benzenoid π‐conjugated polycyclic hydrocarbons (PHs) are expected to exhibit very different electronic properties from the all‐benzenoid PHs. Herein, we report the synthesis and ...physical properties of three azulene‐fused acene molecules (1, 2 and 3), which are isoelectronic to the pentacene, hexacene and heptacene, respectively. X‐ray crystallographic analysis, NMR spectra, and theoretical calculations reveal a localised aromatic backbone comprising all the six‐ and five‐membered rings while the seven‐membered ring remains non‐aromatic. They display properties of both azulene and acenes and are much more stable than the respective acenes. The dications of 1, 2 and 3 were formed by chemical oxidation. Notably, 32+ exhibited an open‐shell diradical character (y0=30.2 %) as confirmed by variable‐temperature NMR and ESR measurements, which can be explained by recovery of aromaticity of an 2,6‐anthraquinodimethane unit annulated with two aromatic tropylium rings.
Fusion of azulene to acenes of various length led to unexpected properties such as aromaticity and photophysical properties, and they are more stable than the respective isoelectronic acenes. Their dications showed aromaticity shift and one of them exhibited open‐shell diradical character.
Freshwater flux and energy consumption are two important benchmarks for the membrane desalination process. Here, we show that nanoporous carbon composite membranes, which comprise a layer of porous ...carbon fibre structures grown on a porous ceramic substrate, can exhibit 100% desalination and a freshwater flux that is 3-20 times higher than existing polymeric membranes. Thermal accounting experiments demonstrated that the carbon composite membrane saved over 80% of the latent heat consumption. Theoretical calculations combined with molecular dynamics simulations revealed the unique microscopic process occurring in the membrane. When the salt solution is stopped at the openings to the nanoscale porous channels and forms a meniscus, the vapour can rapidly transport across the nanoscale gap to condense on the permeate side. This process is driven by the chemical potential gradient and aided by the unique smoothness of the carbon surface. The high thermal conductivity of the carbon composite membrane ensures that most of the latent heat is recovered.
Solar‐driven reduction of CO2 to value‐added products represents a sustainable strategy for mitigating the greenhouse effect and addressing the related green‐energy crisis. Herein, it is demonstrated ...that modifying the surface coordination sphere can significantly enhance the reaction kinetics and overall efficiency of CO2 reduction. More specifically, the decoration of isolated Mn atoms over the multi‐edged TiO2 nano‐pompons (Mn/TONP) upshifts the d‐band center that allows favorable CO2 adsorption. Ultrafast spectroscopy demonstrates the greatly accelerated charge transfer between photoexcited multi‐edged TONP and the newly implanted Mn reactive centers, supplying long‐lifetime electrons to reduce absorbed CO2 molecules. By integrating adsorption and activation functions into the newly decorated Mn sites, the developed photocatalyst demonstrate impressive capacity for CO2 reduction (80.51 mmol g−1 h−1). The surface modulation strategy at the atomic level not only opens new avenues for regulating the reaction kinetics toward photocatalytic CO2 reduction, but also paves the way for the rational design of highly efficient and selective photocatalysts for clean energy conversion.
This study develops an efficient CO2 reduction photocatalyst by modifying isolated Mn sites on the TiO2 surface. The Mn site is proven to be a unified site for the adsorption and activation of CO2 molecules both experimentally and theoretically. Furthermore, this work explicitly reveals the influence of Mn species on the energy transfer process in photocatalytic CO2 reduction.
Axially chiral molecules are among the most valuable substrates in organic synthesis. They are typically used as chiral ligands or catalysts in asymmetric reactions. Recent progress for the ...construction of these chiral molecules is mainly focused on the transition-metal-catalyzed transformations. Here, we report the enantioselective NHC-catalyzed (NHC: N-heterocyclic carbenes) atroposelective annulation of cyclic 1,3-diones with ynals. In the presence of NHC precatalyst, base, Lewis acid and oxidant, a catalytic C-C bond formation occurs, providing axially chiral α-pyrone-aryls in moderate to good yields and with high enantioselectivities. Control experiments indicated that alkynyl acyl azoliums, acting as active intermediates, are employed to atroposelectively assemble chiral biaryls and such a methodology may be creatively applied to other useful NHC-catalyzed asymmetric transformations.
Boundary conformal field theories have several additional terms in the trace anomaly of the stress tensor associated purely with the boundary. We constrain the corresponding boundary central charges ...in three- and four-dimensional conformal field theories in terms of two- and three-point correlation functions of the displacement operator. We provide a general derivation by comparing the trace anomaly with scale dependent contact terms in the correlation functions. We conjecture a relation between the a-type boundary charge in three dimensions and the stress tensor two-point function near the boundary. We check our results for several free theories.
Defect engineering of metal-organic frameworks (MOFs) offers promising opportunities for tailoring their properties to specific functions and applications. However, determining the structures of ...defects in MOFs-either point defects or extended ones-has proved challenging owing to the difficulty of directly probing local structures in these typically fragile crystals. Here we report the real-space observation, with sub-unit-cell resolution, of structural defects in the catalytic MOF UiO-66 using a combination of low-dose transmission electron microscopy and electron crystallography. Ordered 'missing linker' and 'missing cluster' defects were found to coexist. The missing-linker defects, reconstructed three-dimensionally with high precision, were attributed to terminating formate groups. The crystallization of the MOF was found to undergo an Ostwald ripening process, during which the defects also evolve: on prolonged crystallization, only the missing-linker defects remained. These observations were rationalized through density functional theory calculations. Finally, the missing-cluster defects were shown to be more catalytically active than their missing-linker counterparts for the isomerization of glucose to fructose.
Achieving site selectivity in carbon-hydrogen (C-H) functionalization reactions is a formidable challenge in organic chemistry. Herein, we report a novel approach to activating remote C-H bonds at ...the C5 position of 8-aminoquinoline through copper-catalyzed sulfonylation under mild conditions. Our strategy shows high conversion efficiency, a broad substrate scope, and good toleration with different functional groups. Furthermore, our mechanistic investigations suggest that a single-electron-transfer process plays a vital role in generating sulfonyl radicals and subsequently initiating C-S cross-coupling. Importantly, our copper-catalyzed remote functionalization protocol can be expanded for the construction of a variety of chemical bonds, including C-O, C-Br, C-N, C-C, and C-I. These findings provide a fundamental insight into the activation of remote C-H bonds, while offering new possibilities for rational design of drug molecules and optoelectronic materials requiring specific modification of functional groups.
Two-dimensional (2D) covalent organic framework (COF) materials have the most suitable microstructure for membrane applications in order to achieve both high flux and high selectivity. Here, we ...report the synthesis of a crystalline TFP-DHF 2D COF membrane constructed from two precursors of 1,3,5-triformylphloroglucinol (TFP) and 9,9-dihexylfluorene-2,7-diamine (DHF) through the Langmuir–Blodgett (LB) method, for the first timed. A single COF layer is precisely four unit cells thick and can be transferred to different support surfaces layer by layer. The TFP-DHF 2D COF membrane supported on an anodic aluminum oxide (AAO) porous support displayed remarkable permeabilities for both polar and nonpolar organic solvents, which were approximately 100 times higher than that of the amorphous membranes prepared by the same procedure and similar to that for the best of the reported polymer membranes. The transport mechanism through the TFP-DHF 2D COF membrane was found to be a viscous flow coupled with a strong slip boundary enhancement, which was also different from those of the amorphous polymer membranes. The membrane exhibited a steep molecular sieving with a molecular weight retention onset (MWRO) of approximately 600 Da and a molecular weight cutoff (MWCO) of approximately 900 Da. The substantial performance enhancement was attributed to the structural change from an amorphous structure to a well-defined ordered porous structure, which clearly demonstrated the high potential for the application of 2D COFs as the next generation of membrane materials.
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