Chemphyschem最新文献

Stronger molecule-electrode coupling is associated with higher conductance in single-molecule junctions. This has been taken to imply that more coordination-what will be referred to here as higher denticity-between the molecule and the electrode is expected to impart higher conductance to the overall junction. Herein, this assumption using a single molecule construct, a rigid N-heterohexacene molecule with tetradentate ethyl sulfide (-SEt) anchors, is examined. Thus, rather than comparing a series of molecules with different anchoring groups, it is investigated how variations in effective denticity arise naturally within one molecule. Using the nonequilibrium Green's function technique in conjunction with density functional theory and mechanically controlled break-junction (MCBJ) experiments, it is found that increasing the denticity between the molecule and the electrode does not yield the expected higher conductance. Instead, simulated break-junction traces reveal a strong correlation between conductance and the dihedral angle between the electrode and the molecular core, with changes to dihedral angles providing far more variation in conductance values than denticity alone. In fact, it is shown that counter to naïve expectations, different denticities cannot be distinguished by conductance, merging instead into a single conductance feature. This is supported by MCBJ experiments on this molecule, where only a single conductance state is identified, suggesting that the expected denticity-dependent multistate conductance behavior is dominated by the effect of dihedral angles. By restricting dihedral angles to more favorable values by molecular design, the calculations show that significantly higher conductance values can still be achieved despite the limitations imposed by dihedral-denticity coupling. The work demonstrates that mere denticity may not be sufficient to design highly conductive molecular junctions, and that the association of conductance features with different denticities should be treated with caution.

In this work, a computational protocol has been developed to predict the ligand-based low-lying excited-state energies of Eu³⁺ coordination compounds with antenna ligands. A computational strategy, based on density functional theory (DFT) and time-dependent density functional theory (TD-DFT), has been developed using compounds with reliable structural and spectroscopic experimental data as a reference set. This approach aims to predict both the geometry and energy of the lowest-excited triplet state, critical factors influencing the efficiency of the antenna effect and energy transfer to the Eu³⁺ ion. The model not only shows the ability to replicate available experimental data at a relatively low computational cost, but also accurately predicts triplet-state energies for compounds that have not been included in the training set. This work is a first step toward the development of an affordable method for accurate predictions of the quantum yield of lanthanide-based complexes to assess their potential application as down-shifting spectral converters in solar cells.

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 feasibility of the C₁₀₀ fullerene as a nanocontainer for glycine, alanine, and serine has been investigated using density functional theory (B3LYP-D3), second-order Møller-Plesset perturbation theory, and the domain-based local pair natural orbital-coupled cluster singles doubles and perturbative triples (DLPNO-CCSD(T)) method. The interaction energies for glycine@C₁₀₀, alanine@C₁₀₀, and serine@C₁₀₀ are calculated to be -47.8, -45.5, and -43.8 kcal mol^-1, respectively, for their most stable conformers, at the DLPNO-CCSD(T) level, indicating favorable host-guest interactions. Furthermore, encapsulation leads to substantial stabilization of both the intramolecular hydrogen-bonded and nonhydrogen-bonded conformers of the amino acids. Vibrational frequency analysis shows a blueshift for most of the vibrational modes, indicative of restricted motion due to the confined space. However, the OH-stretch mode, especially for the intramolecular hydrogen-bonded conformers, exhibits a large redshift upon encapsulation, suggesting a strengthening of the hydrogen bond due to confinement. The results of the dipole moment calculations reveal a significant reduction in the dipole moment after encapsulation, indicating an effective screening of the dipole by the C₁₀₀ cage. ¹H NMR chemical shift calculations reveal a large downfield shift, consistent with the deshielding effects experienced by the encapsulated molecules due to the unique electronic environment within the fullerene cavity.

Gaussian process (GP) regression provides a strategy for accelerating saddle point searches on high-dimensional energy surfaces by reducing the number of times the energy and its derivatives with respect to atomic coordinates need to be evaluated. The computational overhead in the hyperparameter optimization can, however, be large and make the approach inefficient. Failures can also occur if the search ventures too far into regions that are not represented well enough by the GP model. Here, these challenges are resolved by using geometry-aware optimal transport measures and an active pruning strategy using a summation over Wasserstein-1 distances for each atom-type in farthest-point sampling, selecting a fixed-size subset of geometrically diverse configurations to avoid rapidly increasing cost of GP updates as more observations are made. Stability is enhanced by a permutation-invariant metric that provides a reliable trust radius for early-stopping and a logarithmic barrier penalty for the growth of the signal variance. These physically motivated algorithmic changes prove their efficacy by reducing to less than a half the mean computational time on a set of 238 challenging configurations from a previously published data set of chemical reactions. With these improvements, the GP approach is established as a robust and scalable algorithm for accelerating saddle point searches when the evaluation of the energy and atomic forces requires significant computational effort.

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.

Owing to their high safety and energy density, all-solid-state batteries (ASSBs) are regarded as one of the most promising next-generation energy storage systems and have attracted significant attention. However, their large-scale deployment remains hindered by technical challenges, including interfacial issues between solid electrolytes and electrodes, dendrite growth, and poor cycling and rate performance. In particular, the limited ionic conductivity of solid electrolytes is widely regarded as one of the key factors constraining battery performance. Among them, NASICON-type solid electrolytes stand out as multifunctional oxide materials with rigid frameworks and excellent thermal stability, making them suitable for applications such as lithium-ion ASSBs. Nevertheless, they also face challenges of insufficient ionic conductivity and poor interfacial stability. This work reviews recent strategies to address these issues, conduct an in-depth analysis of its mechanism of action and effect, and evaluate its advantages, disadvantages, and development potential. To improve ionic conductivity, we discuss element doping, synthesis and fabrication methods, sintering additives, and densification strategies. To mitigate interfacial instability, we summarize approaches such as inorganic protective layers, composite electrolytes, and hot-pressing or hot-forming techniques. These insights provide both theoretical guidance and practical references for designing and developing high-performance, stable NASICON-type solid electrolytes.

Isolated monolayer graphene can be coupled with silica (SiO₂) as graphene-based nanoelectronic devices. The fabricated heterojunction composites in moist environments have been involved in environmental monitoring, optical detection, and health sensors. However, the corresponding interfacial stability and structures between graphene and silica substrates remain unexplored. Herein, molecular simulations were applied to investigate the adhesion of graphene/SiO₂ composite interfaces in water media. Different SiO₂ surface types and varied SiO₂ hydrophilicity degrees were considered. The thermodynamic free energy was simulated to characterize the interfacial interaction. The required energetic barriers associated with the graphene detachment can be determined. SiO₂ substrates possess differential surface affinity toward graphene. The connection between the adhesion strength and the substrate types was established. Under higher hydrophilic conditions, the attached graphene sheet can easily be separated from the silica substrates. This behavior cannot be observed in dry conditions, which is attributed to competitive actions between the interfacial hydration force and the substrate interaction. The morphologic transformations and hydration structures of the graphene-silica interface with intervening water layers were also characterized, which is critical in modulating the interface stability. Our simulation results provide new microscopic insights into the interfacial states and structures of graphene-SiO₂ systems in an aqueous environment.

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.

The outstanding alkaline hydrogen evolution reaction (HER) performance of MoP₂-NiCoP heterostructure has been reported. However, the mechanism behind its catalytic activity remains unclear, and the underlying synergistic catalysis has not been revealed at the atomic scale. Based on these research gaps, the theoretical investigation on the MoP₂-NiCoP heterostructure is conducted, revealing that the MoP₂-NiCoP heterostructure exhibits superior HER activity ( $\Delta G_H$  = -0.016 eV) but limited oxygen evolution reaction (OER) performance ( $\Delta G_{\text{OOH}}-\Delta G_O$  = 2.589 eV). Electronic structure analysis demonstrates that interfacial charge redistribution optimizes the adsorption strength of the H* intermediate, significantly lowering the HER energy barrier while restricting the O* → OOH* transition, thus hindering OER processes. Doping strategies (e.g., W, Ta) further enhance HER performance and a linear scaling relationship between the d-band center ( ${\epsilon }_d$ ) and HER activity descriptor ( $\Delta G_H$ ) shows strong correlation (R² = 0.993). This work reveals the origin of the high intrinsic HER activity and the interfacial synergistic mechanism in the MoP₂-NiCoP catalyst, verifying its lack of effective OER activity. It further identifies a novel strategy for directional enhancement of catalytic performance through electronic structure modulation, establishing a theoretical framework for designing bifunctional electrocatalysts on experiments.