Chemphyschem最新文献

Water is widely recognized as critical to the tunability and electrochemical stability of nonaqueous solvents such as deep eutectic solvents (DESs) and ionic liquids (ILs). Traditionally, the water content of these solvents has been controlled by either drying or adding small amounts of water to control their bulk properties to meet specific application requirements. The total water content by itself, does not provide sufficient information about the chemical reactivity and molecular interactions within DES- and IL-water mixtures. In this concept article, water activity is highlighted as a thermodynamically more rigorous descriptor to quantify the influence of the co-solvent water on DES- and IL-water mixtures. Water activity relates measurable physical properties, such as vapor pressure, density, viscosity, electrochemical stability, and conductivity of DESs and ILs to the underlying molecular interactions between their components. Furthermore, water activity of DESs and ILs correlates with changes in local solvent structures and thermodynamic excess properties, including excess molar volume, enthalpy, and Gibbs energy.

Benzazole derivatives exhibit distinctive photophysical behavior due to excited-state intramolecular proton transfer (ESIPT), making them promising candidates for optoelectronic applications such as organic light-emitting diodes (OLEDs) and fluorescent sensors. Understanding their sublimation energetics, phase behavior, and emissive properties is essential for both fundamental studies and materials design. This article reports an investigation on two benzazole derivatives-2-(2-hydroxyphenyl)benzothiazole and 2-(2-hydroxyphenyl)benzoxazole (HBO)-through studies of thermal analysis, vapor pressure measurements, and fluorescence spectroscopy to establish structure-property relationships. Thermal stability and phase transitions are characterized using simultaneous thermogravimetry-differential scanning calorimetry (TG-DSC) and heat-flux DSC. Vapor pressures are determined using both Knudsen effusion mass loss and mass spectrometry. The derived standard molar enthalpies of sublimation, vaporization, and fusion highlight the presence of heteroatom (S versus O) on intermolecular interactions. Solid-state fluorescence measurements reveal strong emission in both compounds, with a large Stokes shift-consistent with ESIPT-and complex spectra attributed to solid-state molecular packing. This comprehensive experimental strategy delivers benchmark thermodynamic and photophysical data, offering new insights into the interplay between molecular structure, thermal behavior, and fluorescence of benzazole derivatives. Such understanding is relevant for the development of advanced optoelectronic materials.

Chalcogen bond (ChB) catalysis is a significant strategy in organocatalysis due to its modifiable polarity, notable directionality, and the flexibility that aids both binding and dissociation. As an important benchmark reaction, the transfer hydrogenation of quinoline (QNL) is widely used to evaluate the catalytic performance and to explore the relationship between the structure and activity of catalysts. In this work, density functional theory calculations are employed to elucidate the mechanism of the ChB-catalyzed transfer hydrogenation of QNL using Hantzsch ester (HEH) as the hydrogen source. Analysis of the transition state properties in the rate-determining step reveals that the σ-hole of ChB catalysts interacts with the nitrogen lone pairs of HEH, accompanied by charge transfer and rearrangement processes occurring throughout the reaction. Energy decomposition analysis (EDA), together with Natural Bond Orbital (NBO) and quantum theory of atoms in molecules (QTAIM) analyses, reveals that polarization effects predominantly stabilize the chalcogen bond (ChB), thereby lowering the reaction energy barriers. This insight provides a foundation for the rational design of new ChB catalysts.

The pentaPod (P5) concept, combining tridentate and tripodal ligand fragments, is developed to obtain chemocatalytic Chatt-type complexes with greater stability than classical molybdenum and tungsten systems. In these pentaPod complexes, side reactions that usually inhibit catalysis in classic Chatt complexes are effectively suppressed. Using the original pentaPod ligand P5^Me, molybdenum and tungsten dinitrogen complexes [M(N₂)(P5^Me)] (M = Mo and W) are synthesized. Indeed, [Mo(N₂)(P5^Me)] generates 26 equivalents of ammonia with the PCET (proton coupled electron transfer) reagent SmI₂(THF)₂/H₂O as electron and proton source, whereas [W(N₂)(P5^Me)] affords 3 equivalents of ammonia, but primarily catalyzes the hydrogen evolution reaction (HER). Despite their different reactivities, both complexes exhibit similar redox potentials, and DFT calculations of the mechanisms of N₂-to-NH₃ reduction and HER show no differences between [Mo(N₂)(P5^Me)] and [W(N₂)(P5^Me)]. To improve the catalytic activity of the pentaPod complexes, the modified pentaPod ligand P5^Pln, containing two phospholane groups, is developed. The corresponding [M(N₂)(P5^Pln)] complexes (M = Mo and W) produce 22 (Mo) and 7 (W) equivalents of NH₃, respectively, rendering the latter the first tungsten complex to chemocatalytically generate ammonia. Surprisingly, spectroscopic and electrochemical data indicate lower Brønsted basicities of the tungsten dinitrogen complexes compared to their molybdenum analogs.

The construction of efficient Z-scheme heterojunctions is considered as a promising approach to improve the transfer and separation of photogenerated carries in the field of photocatalytic hydrogen evolution from water splitting. Herein, a novel CdS/UiO-66(Ce) with Z-scheme heterostructure is successfully fabricated from metal sulfide CdS and cerium-based UiO-66 metal-organic framework via a hydrothermal method. The Z-scheme CdS/UiO-66(Ce) heterojunctions can provide abundant active centers, broaden the response range to visible-light region, accelerate the transfer of interfacial charges, and suppress the recombination rate of photogenerated electron-hole pairs. As a result, CdS/UiO-66(Ce) (ω(CdS) = 30%) exhibits a hydrogen production rate of 1.975 mmol g^-1 h^-1, which is 19.1 times higher than that of UiO-66(Ce). Overall, this article may provide a new pathway for the rational design of efficient Z-scheme heterojunctions with photocatalytic hydrogen evolution.

The development of highly efficient and sustainable electrocatalytic technologies offers a significant solution to the growing global demand for energy, as well as to the achievement of carbon neutrality goals, where its success relies on the design and fabrication of electrocatalysts. Currently, carbon-based materials are promising alternative materials due to the tunable electronic structure, high conductivity, excellent stability, and abundant reserves; however, inherent inert structure significantly limits its catalytic activity. Herein, incorporating oxygen functional groups (OFGs) into carbon-based materials has been reviewed as a pivotal strategy to regulate electronic structure, charge transfer processes, and adsorption energy toward reaction intermediates, thereby enhancing electrocatalytic performance. The latest research progress of OFGs in crucial electrocatalytic reaction such as oxygen reduction reaction, CO₂ reduction reaction, and oxygen evolution reaction is systematically reviewed, deeply exploring core mechanisms of reaction kinetics regulation, while summarizing the precise structure–function relationships of different OFGs types in multireaction systems. Further, technical challenges and prospective opportunities in precise design and modulation of OFGs are discussed, offering a basis for research focusing on dynamic controllable strategies and optimal design of interfacial microenvironments. Finally, research insights and technical pathways of developing low-cost and high-performance oxygen-functionalized carbon-based materials for electrocatalytic applications are provided.

A key challenge of electrocatalytic water oxidation for H2 production remains in modulating structural and electronic features of transition metal complexes to enhance catalytic performance. Herein, inspired by previous experimental and computational studies on the macrocyclic catalyst [Cu(14-TMC)]²⁺ (1,4,8,11-tetramethyl-1,4,8,11-tetraazacyclotetradecane), we present a theoretical investigation based on Density Functional Theory (DFT) to examine the mechanistic impacts of its ring size reduction. To this end, we evaluated the water oxidation catalytic cycle mediated by [Cu(12-TMC)]²⁺, providing a comprehensive analysis of the electrochemical oxidation, OO bond formation, and O₂ evolution steps. Subsequently, we compare mechanistic features of [Cu(14-TMC)]²⁺ and [Cu(12-TMC)]²⁺ highlighting similarities and differences in the key reaction routes and intermediates, revealing that ligand ring size affects the electronics, steric hindrance and, consequently, the coordination numbers of these species. Notably, the rate-determining step of both catalytic cycles is the OO bond formation exhibiting significant differences in their mechanisms, especially regarding the structures of key intermediates. Despite that, both mechanisms have comparable energy barriers. For instance, the Gibbs free energy barriers are computed to be 18.96 and 19.26 kcal/mol for [Cu(12-TMC)]²⁺ and [Cu(14-TMC)]²⁺ catalysis, respectively. However, [Cu(12-TMC)]²⁺ provided more intricate mechanisms due to being more susceptible to ligand reorganization in the Cu coordination sphere.

Understanding the formation of lignin-carbohydrate complex (LCC) linkages in lignocellulosic biomass (LCB) is crucial because these interactions contribute to plant recalcitrance. Herein, a new mechanism for LCC linkage formation, based on the formation of the oxocarbenium intermediate, is explored. We applied density functional theory to monosaccharides and monolignol molecules serving as models for LCB. Mannopyranose, xylopyranose, arabinofuranose, and glucopyranuronic acid were used for hemicellulose; p-coumaryl alcohol, coniferyl alcohol, and sinapyl alcohol were employed for lignin. Computations without explicit water molecules predict the stable formation of glycosidic bonds between all lignin and sugar models, with some exceptions. Including explicit water molecules showed that, for all systems, the formation of LCC bonds is more thermodynamically favorable than in the absence of water or when using implicit solvent models. The explicit solvent models indicate that hydrogen bonds involving water and organic molecules promote the formation of stable LCC bonds. Transition states and intermediates associated with oxocarbenium ions were found for mannopyranose and xylopyranose, thus evaluating the kinetics of LCC linkage formation for major components of hemicellulose. These results suggest that glycosylation reactions via the oxocarbenium intermediate can occur in plant cell walls, further providing evidence for the formation of covalent LCC linkages in LCB.

To better understand the properties of carbene and biscarbene species derived from bisdiazo compounds with varied terminal groups, a density functional theory (DFT) study was conducted on bisdiazo compounds with four terminal groups (bisdiazo-X, where X=H, Me, NO₂ and NH₂) and their mono- and dicarbene derivatives. The studies included computation of their frontier molecular orbitals (FMOs), electronic structures, electrostatic potential (ESP) and polarity, as well as their IR and UV-vis spectra and their color in THF solutions. For bisdiazo compounds at both ground and excited states, the computational results matched well with published experimental data. The formation of carbene species from bisdiazo compounds was confirmed via a generalized IRC path calculation and IGMH analysis. The reaction sites and the lone pair electron locations were predicted using minimum ESP (i.e., ESPmin) and orbital-weighted Fukui dual descriptor for the possible intermediates in the transition state, along with spin density analysis through EPR/ESR predictions. Additionally, physisorption of bisdiazo and carbene species onto single-layer graphene was evaluated through geometry optimization, in which π-π stacking among the aromatic-ring likely determines surface packing via the simulated scanning tunnelling microscope (STM) images. The carbene species permit controlled growth of the patterned functional organic surfaces.

The Front Cover illustrates how encapsulating a calcium atom inside a carbon cage can be used as a tool to tune its reactivity. The Ca atom adopts an oxidation state of þ2, thus rendering the carbon frame work partially negatively charged. This charge transfer quenches the nucleophilic addition of pyridine, thus showcasing how metal encapsulation can modulate the chemistry of carbon nanostructures. More information can be found in the Research Article by U. Jacovella and co-workers (DOI: 10.1002/cphc.202500487).