Atomic Charge Densities Research Articles

The inductive effect does not explain electron density in haloacetates: are our textbooks wrong?

The inductive effect is a central concept in chemistry and is often exemplified by the pK a values of acetic acid derivatives. The reduction in pK a is canonically attributed to the reduction in the electron density of the carboxylate group through the inductive effect. However, wave functional theory calculations presented herein reveal that the charge density of the carboxylate group is not explained by the inductive effect. For a series of trihaloacetates (trichloro-, chlorodifluoro- and trifluoro-) we find that the trichloro group has the greatest reduction on the charge density of the carboxylate oxygen atoms; change in charge density is inversely related to substituent electronegativity. These puzzling results are experimentally supported by investigating three independent systems: literature gas phase acidities, specific ion effects in a model thermoresponsive polymer system, and nuclear magnetic resonance (NMR) spectroscopy of haloalkanes. Changes in the solubility of poly(N-isopropylacrylamide), PNIPAM, due to the presence of different (substituted) acetates allow ionic charge densities to be examined. These studies confirmed the unexpected charge density and substituent-electronegativity relationship. Further analysis of the literature showed anomalous charge densities for haloalkanes with 13C NMR spectroscopy and gas phase acidity of polyatomic acids. In summary, these independent results show that the induction effect does not explain pK a trends across the haloacetic acids.

Internal Electron-Donation Allocation Design for Intrinsic Solubilization of Lithium Nitrate in Ester Electrolyte for Stable Lithium Metal Batteries.

Lithium metal batteries (LMBs) have become a hot topic in the research of next-generation advanced battery technology due to their high specific energy. However, the high reaction activity between lithium metal and electrolyte is considered one of the key bottlenecks limiting large-scale applications of LMBs. As a classic electrolyte additive, lithium nitrate (LiNO3) significantly improves the stability of lithium metal in ether-based electrolytes. However, its solubility in carbonate-based electrolytes widely used in lithium-ion batteries is extremely low, causing limited protective capability on lithium metal, which has become a key obstacle to the commercial application of lithium metal batteries. Here, we enhanced the local negative charge density of carbonyl oxygen atoms in carbonate molecules by introducing electron donors, making it easier for them to coordinate with Li+, thereby weakening the interaction between Li+ and NO3 -, and significantly increasing the solubility of LiNO3 in ester electrolytes. The modified ester solvent promotes the derivatization and decomposition of salt anions, leading to the formation of a dense SEI layer rich in LiF and LiNxOy. This significantly improves the stability of lithium metal in ester-based electrolytes. The assembled Li||Li symmetric battery shows excellent cycling performance of over 4000 hours.

The Effect of Salinity on the Dielectric Permittivity of Nanoconfined Geofluids.

Nanoporosity is a characteristic feature of geological formations that provides potential pathways for geofluids to meander and interact with minerals. Confinement of water within nanopores leads to unique phenomena. The dielectric constant of water becomes anisotropic and adopts tensorial properties rather than remaining a scalar value. In such nanoconfinement, it has been found that the permittivity of water decreases perpendicularly and increases parallel to the interface. As geofluids are rarely pure water in nature, being a water-salt(-gas) mixture within the Earth, it becomes pivotal to examine how these additional constituents of water affect the permittivity of fluids confined within the nanopores of rocks. In this study, we present the calculation of the permittivity of saline water in calcite slit nanopores using molecular dynamics simulations under low-pressure-temperature conditions. The dielectric properties are weakly dependent on salinity for both the perpendicular and parallel dielectric permittivity components. We analyzed the atomic charge and polarization density of the fluid perpendicular to the nanochannel walls and the orientation of water molecules' dipole inside the nanochannel. From our analysis, most of these factors were generally not altered significantly in the presence of salinity. These findings are significant because they enable us to use well-studied pure water properties under nanoconfinement to determine the geochemical behavior of fluids within natural nanoporous systems.

Eley−Rideal path enhanced NH3-SCR: Central Fe atoms activation for electron transfer promotion

Manganese modified Fe2O3 catalyst is a promising candidate to replace the commercial NH3-SCR catalyst for controlling NOx emission due to its superior performance and N2 selectivity at low temperature. In order to elucidate the effects of different modification methods of Mn on physicochemical properties and reaction mechanism in Fe-Mn binary catalysts, two kinds of Mn modified Fe2O3 are prepared by co-precipitation and impregnation method, respectively. Compared with MnO2 loaded Fe2O3, Mn doped Fe2O3 achieves above 85 % of NOx conversion with 20 % increase in N2 selectivity within 100–200°C. Transient reaction experiments and DFT calculation results prove that doping Mn effectively increases the reaction rate of the main reaction and reduces the formation of N2O through Eley−Rideal path. The formation of multiple Fe-O-Mn structures after Mn doping facilities the formation of coordination bond between the central Fe atoms and NH3 via modulating local charge density of Fe atoms, effectively improving the adsorption of NH3 and preventing its excessive oxidation, which leads to high activity and N2 selectivity at low temperature. This mechanism provides theoretical support for increasing the activity and N2 selectivity of NH3-SCR catalysts at low temperature and gains clear insight on the interaction between binary metal oxides.

Dual Modulation of Bulk Electronic Structure and Surficial Active Sites in Sea Urchin‐Like MoO2 Nanoreactors Promoting Electrocatalytic Hydrogen Evolution

AbstractElectrocatalytic hydrogen evolution reaction (HER) is a promising strategy for realizing carbon neutralization as well as for the production of green hydrogen. Molybdenum dioxide (MoO2), possesses acid corrosion resistance and near‐metal‐level conductivity, endowing its widespread application in acidic HER. However, due to spatial barriers at the edge of sites and weak H* adsorption, the HER activity of MoO2 is greatly limited. Herein, a sea urchin‐like Pt@N‐MoO2 nanoreactor is designed, in which the bulk electronic structure and surface‐active sites are modulated by N doping and Pt single atoms anchoring, respectively. DFT calculations indicate that Mo─N coupling changes the charge density of Mo atoms, enhances the adsorption of H*, and thus optimizes the Gibbs free energy. The appearance of Pt‐O/N sites compensates for the lack of active sites exposed by MoO2, while promoting the desorption of H2 from the catalyst surface and accelerating the HER process. This work provides an effective strategy for activating inert electrocatalysts to promote energy conversion via a dual modulation strategy of bulk and surface engineering.

Fenton chemistry activation in metal-organic frameworks for synergistic bacteria eradication

The development of novel antibacterial strategies as alternatives to antibiotics is of great significance but remains considerable challenges due to the lack of safe, effective, and broad-spectrum agents. Here, we explored the potential of a biocompatible metal–organic framework Fe-MIL-53-NH2 (FM) for reactive oxygen species (ROS)-based antibacterial applications. However, FM was found to be catalytically inert due to the very weak reducibility of Fe3+ toward H2O2. To address this challenge, we incorporated a small amount of Co2+ (0.98 %) into FM (CFM), successfully activating Fenton chemistry and achieving a notable 5.5-fold improvement in Fenton activity. Density functional theory (DFT) calculations revealed that a very small amount of Co2+ doping significantly reduces the energy barrier of the Fenton reaction by shifting the d-band center to the Fermi level and optimizing the charge density of active Co atoms. We further enhanced the antibacterial properties of CFM by modifying it with the photothermal agent polydopamine (PDA), resulting in CFMP. Through the synergistic effects of ROS and photothermal properties, CFMP exhibited remarkable antibacterial activity, with bacterial eradication rates exceeding 99 % against both E. coli and S. aureus. Moreover, in vivo experiments demonstrated the exceptional efficacy of CFMP in sterilizing S. aureus-infected wounds, while causing negligible damage to other major organs. This study not only highlights the role of atom engineering in activating Fenton reaction, but also provides rational designs for a synergistic antibacterial strategy via powerful MOFs chemistry.

Atomic-scale insights into precipitates and their interfacial properties in CuCrZr alloys induced by cryogenic treatment

In this study, high-resolution TEM was utilized to provide a detailed characterization of the precipitates in CuCrZr alloys induced by cryogenic treatment. Building on these findings, first-principles computational models were developed to investigate the mechanical properties of various precipitates and their interfacial bonding characteristics with the matrix. The results demonstrated that cryogenic treatment generated two submicron-sized secondary phases in the matrix: pure Cr particles with a BCC structure and Cu5Zr particles with an FCC structure. Additionally, we observed that nano-sized pure Cr particles were dispersed throughout the matrix and exhibited an orientation relationship of (−111) Cu//(0–11) Cr and [0–11] Cu//[−1−1-1] Cr. First-principles calculations revealed that all the above precipitates exhibited higher modulus and hardness compared to the matrix, with Cr particles being particularly notable. Additionally, the adhesion strength of the Cr/Cu interface was exceptional, surpassing that of the fully coherent CuSlab and CuTwin. Furthermore, the analysis of the electronic properties of the interface revealed that the strengthening effect could be attributed to the higher charge density and localized nature of the Cr atoms near the interface. In summary, precipitates with high hardness and strong adhesion to the matrix can more effectively hinder dislocation movement, which is crucial for enhancing the mechanical properties of the alloys.

Influence of MXene Composition on Triboelectricity of MXene-Alginate Nanocomposites.

MXenes are highly versatile and conductive 2D materials that can significantly enhance the triboelectric properties of polymer nanocomposites. Despite the growing interest in the tunable chemistry of MXenes for energy applications, the effect of their chemical composition on triboelectric power generation has yet to be thoroughly studied. Here, we investigate the impact of the chemical composition of MXenes, specifically the Ti3CNTx carbonitride vs the most studied carbide, Ti3C2Tx, on their interactions with sodium alginate biopolymer and, ultimately, the performance of a triboelectric nanogenerator (TENG) device. Our results show that adding 2 wt % of Ti3CNTx to alginate produces a synergistic effect that generates a higher triboelectric output than the Ti3C2Tx system. Spectroscopic analyses suggest that a higher oxygen and fluorine content on the surface of Ti3CNTx enhances hydrogen bonding with the alginate matrix, thereby increasing the surface charge density of the alginate oxygen atoms. This was further supported by Kelvin probe force microscopy, which revealed a more negative surface potential on Ti3CNTx-alginate, facilitating high charge transfer between the TENG electrodes. The optimized Ti3CNTx-alginate nanogenerator delivered an output of 670 V, 15 μA, and 0.28 W/m2. Additionally, we demonstrate that plasma oxidation of the MXene surface further enhances triboelectric performance. Due to the diverse surface terminations of MXene, we show that Ti3CNTx-alginate can function as either tribopositive or tribonegative material, depending on the counter-contacting material. Our findings provide a deeper understanding of how MXene composition affects their interaction with biopolymers and resulting tunable triboelectrification behavior. This opens up new avenues for developing flexible and efficient MXene-based TENG devices.

Anti‐Coronavirus Activity of Certain Herbacetin Derivatives, A Theoretical Study

AbstractFlavonoids are natural products commonly found in the human diet with anti‐viral activity. The electrochemical activity of flavonoids is effective in their inhibitory properties. Herbacetin is an anti‐coronavirus drug from the flavonoid family. To understand structure‐electrochemical activity relations, ab initio calculations on some selected herbacetin derivatives were carried out using Gaussian 09 in B3LYP/6‐311G*. The effect of the position and type of the various substituents in the ring A of the flavone backbone are considered. The oxygen charge density of the hydroxyl group on C8 (O8) in the considered herbacetins was compared using nuclear quadrupole coupling constants (NQCC) calculations. Results showed that the presence of the amino group in the ortho position of O8 has the most significant effect on increasing the charge density of the O8 atom (O8‐NQCC=9.23 MHz). Based on the proposed mechanism of these drugs, ortho‐amino herbacetin is expected to show a significant anti‐coronavirus effect. Comparison of calculated O8‐NQCCs of tangeretin and nobiletin with herbacetin shows that with the replacement of OH with OCH3, the charge density of oxygen atoms decreases (about 2 MHz). Therefore tangeretin and nobiletin have a lower drug effect than herbacetin. Natural bond orbital (NBO) results are in agreement with calculated NQCCs.

Temperature-induced structure evolution in CoxBy liquids studied by ab initio molecular dynamics simulation

The relationship between the local structures and the thermodynamic properties of metallic liquids has been a fundamental issue, which significantly impacts the comprehensive performances of metallic materials. The temperature-induced structure evolution in CoxBy alloy liquids, involving CoB, Co2B, Co3B, and Co23B6, was investigated using ab initio molecular dynamics simulations. The results show that the clusters of icosahedral-like polyhedrons are found predominantly in all alloys at low temperature, while the heating induces the decrease in ideal icosahedral and the increase in defected icosahedral. At high temperature, the polyhedron clusters decrease significantly and the ideal icosahedra transforms into smaller short-range polyhedrons, signifying the temperature-induced chemical structure change from long-range to short-range ordering. The aggregation of B atoms at high temperature is confirmed by atomic configuration, charge density, and B-centered Voronoi polyhedrons, and the α-Co single phase is observed below 1600 K. This study is helpful for understanding the local structure variability in eutectic Co-B alloys and guiding solidification path in theory.

A Metal Coordination Number Determined Catalytic Performance in Manganese Borides for Ambient Electrolysis of Nitrogen to Ammonia.

A new strategy that can effectively increase the nitrogen reduction reaction performance of catalysts is proposed and verified by tuning the coordination number of metal atoms. It is found that the intrinsic activity of Mn atoms in the manganese borides (MnBx) increases in tandem with their coordination number with B atoms. Electron-deficient boron atoms are capable of accepting electrons from Mn atoms, which enhances the adsorption of N2 on the Mn catalytic sites (*) and the hydrogenation of N2 to form *NNH intermediates. Furthermore, the increase in coordination number reduces the charge density of Mn atoms at the Fermi level, which facilitates the desorption of ammonia from the catalyst surface. Notably, the MnB4 compound with a Mn coordination number of up to 12 exhibits a high ammonia yield rate (74.9 ± 2.1µg h-1 mgcat -1) and Faradaic efficiency (38.5 ± 2.7%) at -0.3V versus reversible hydrogen electrode (RHE) in a 0.1 m Li2SO4 electrolyte, exceeding those reported for other boron-related catalysts.

Development of Ti4O7 reactive electrochemical membrane and electrochemical oxidation of naphthols in aqueous solution

Naphthols (NAPs), commonly used phenolic compounds, have significant impact on environmental risk and human health, necessitating advanced treatment methods for their degradation. In this study, a Ti4O7 reactive electrochemical membrane (REM) was developed for the electrochemical oxidation of NAPs. The Ti4O7 REM presented a porosity of 42.18 ± 2.3% and a median pore diameter of 1.21 µm. High permeability (846 LMH bar−1) was achieved at relatively low transmembrane pressure and resulted in a convection-enhanced rate constant for Fe (CN)64- oxidation of 1.7 × 10−4 m/s. The increase in current density and decrease in plate spacing had a positive influence on NAPs degradation. The TOC removal efficiencies of 1-naphthol (1-NAP) and 2-naphthol (2-NAP) were 68.6% and 63.5%, respectively at the current density of 6 mA/cm2 and plate spacing of 10 mm. Additionally, quantum chemical calculation using density functional theory (DFT) was employed to identify the active sites of NAPs through atom charge and frontier electron density (FED) calculations. Results showed that C14 and C10 were identified as the active sites for 1-NAP, while C9 and C13 were the active sites for 2-NAP. Hydroxyl radical and sulfate radical produced on the electrode surface were the main oxidants for NAPs degradation during the electro-oxidation process. The degradation pathway included hydroxylation, oxygenation, decarbonylation, and ring-open processes, which was in agreement with the theoretical calculations. Furthermore, the quantitative structure-activity relationship (QSAR) predictive model was used to assess the toxicity changes during the electrochemical oxidation process of NAPs, suggesting that the toxicity of intermediates increased at the beginning and significantly reduced at the end. This comprehensive study provides practical and theoretical insights into the application of electrochemical oxidation technique for the reduction of refractory compounds in wastewater.

Theoretical insights into phosphate chains: Density functional theory study and Zinc ion insertion reaction

The present research delves into a theoretical examination of phosphate chains using the density functional theory method with the RB3LYP/6-311G model. The geometry of the studied chains was optimized and their atomic charge densities were evaluated. Various parameters, such as HOMO and LUMO energies, energy difference (ΔE), chemical hardness, chemical potential, softness, and global electrophilicity index were thoroughly investigated. Moreover, vibrational frequencies were explored, highlighting both symmetric and asymmetric vibrations in the chains based on the computed IR and Raman spectra. Subsequently, an investigation into the Zinc ion insertion reaction in the studied phosphate chains was carried out. Several parameters were calculated to determine the electrophilic/nucleophilic character of these two constituents. The outcomes revealed that the phosphate chains display nucleophilic behavior and tend to release electrons, while the Zinc ion exhibits electrophilic tendencies and retains electrons. Notably, electron transfer occurs from the chains to the Zinc ion, with the chains acting as electron donors and the Zinc ion as an electron acceptor. The smaller overall electrophilicity gap between chain III and Zn2+ indicates the weak polar character of this reaction. Furthermore, favorable nucleophilic sites for the attack of the Zinc ion (Zn2+) on chain III were identified using the FUKUI indexes.

A deep learning framework to emulate density functional theory

Density functional theory (DFT) has been a critical component of computational materials research and discovery for decades. However, the computational cost of solving the central Kohn–Sham equation remains a major obstacle for dynamical studies of complex phenomena at-scale. Here, we propose an end-to-end machine learning (ML) model that emulates the essence of DFT by mapping the atomic structure of the system to its electronic charge density, followed by the prediction of other properties such as density of states, potential energy, atomic forces, and stress tensor, by using the atomic structure and charge density as input. Our deep learning model successfully bypasses the explicit solution of the Kohn-Sham equation with orders of magnitude speedup (linear scaling with system size with a small prefactor), while maintaining chemical accuracy. We demonstrate the capability of this ML-DFT concept for an extensive database of organic molecules, polymer chains, and polymer crystals.

Structural, mechanical, electronic, optical and thermodynamic features of lead free oxide perovskites AMnO3 (A=Ca, Sr, Ba): DFT simulation based comparative study

Perovskite oxides with transition metals have been subjected to a lot of concern in the recent time having their exclusive physical and chemical property. Due to ferroelectric character these types of materials have huge technological applications in worldwide. In the existing project, the crystal structure stability, single and polycrystalline bulk properties, electron-charge density, photon and temperature related optical as well as thermal features of perovskite oxides AMnO3 (A = Ca, Sr, Ba) have been investigated through DFT simulation with CASTEP code. Very good accordance in the investigated and synthesized lattice parameters is found. Mechanical stabilities of phases AMnO3 (A = Ca, Sr, Ba) are ensured from the investigated elastic stiffness constants. Ductile nature of compounds AMnO3 (A = Ca, Sr, Ba) are ensured from the study of Pugh's and Poisson's ratios. Hardness calculations ensured that all the studied materials are hard in nature where SrMnO3 has little bit higher hardness nature compared to others. Very high machinability index of CaMnO3 confirmed its suitable industrial application compared to the rest two compounds. Anisotropic character of AMnO3 (A = Ca, Sr, Ba) is observed from the analysis of elastic anisotropy factor. Band structure calculations with up-spin and down-spin reveal the metallic and semi-metallic nature of AMnO3 (A = Ca, Sr, Ba) respectively. Ionic and covalent bonded nature of AMnO3 (A = Ca, Sr, Ba) are confirmed from the Mulliken atomic population and charge density calculations. Very high absorption and conductivity of AMnO3 (A = Ca, Sr, Ba) have been observed in the ultraviolet energy site which ensure their possible applications in optical devices operates at UV energy regions. The dielectric function make sure the metallic nature of AMnO3 (A = Ca, Sr, Ba) as the actual value approaches to zero from negative energy region. Comparatively high Debye temperature of AMnO3 (A = Ca, Sr, Ba) revealed that these compounds are thermally more conductive where CaMnO3 is more conductive than the rest two materials. Very low value of Kmin of material BaMnO3 ensured that this phase has more possibility to use in thermal barrier coating materials (TBC) than CaMnO3 and SrMnO3 materials.

Investigation of Temperature-Dependent Phonon Anharmonicity and Thermal Transport in SnS Single Crystals.

Tin sulfide has outstanding thermoelectric properties in the b-axis direction of crystallography as a IV-VI group layered compound, which arouses great attention. In this study, temperature-dependent Raman spectroscopy (TDRS) is used to quantify the phonon anharmonicity in SnS crystals from 77 to 475 K, where the three-phonon process dominates in this temperature region. Moreover, integration of the four-phonon process and lattice thermal expansion will better describe the temperature-dependent Raman experimental phenomenon. The good agreement between the calculated and experimental lattice thermal conductivity confirms the three-phonon scattering process is the dominant scattering mechanism at this temperature range. Further, combining the atomic thermal displacement and charge density through density functional theory calculation, the inherently low thermal conductivity of SnS is because of strong lattice anharmonicity, which is brought by the presence of asymmetric chemical bonding resulting from the Sn 5s2 lone pair electrons. These results provide key insights for studying thermal properties of other low-dimensional materials.

Reactivity of Acrylamides Causes Cytotoxicity and Activates Oxidative Stress Response.

Acrylamides are widely used industrial chemicals that cause adverse effects in humans or animals, such as carcinogenicity or neurotoxicity. The excess toxicity of these reactive electrophilic chemicals is especially interesting, as it is mostly triggered by covalent reactions with biological nucleophiles, such as DNA bases, proteins, or peptides. The cytotoxicity and activation of oxidative stress response of 10 (meth)acrylamides measured in three reporter gene cell lines occurred at similar concentrations. Most acrylamides exhibited high excess toxicity, while methacrylamides acted as baseline toxicants. The (meth)acrylamides showed no reactivity toward the hard biological nucleophile 2-deoxyguanosine (2DG) within 24 h, and only acrylamides reacted with the soft nucleophile glutathione (GSH). Second-order degradation rate constants (kGSH) were measured for all acrylamides with N,N'-methylenebis(acrylamide) (NMBA) showing the highest kGSH (134.800 M-1 h-1) and N,N-diethylacrylamide (NDA) the lowest kGSH (2.574 M-1 h-1). Liquid chromatography coupled to high-resolution mass spectrometry was used to confirm the GSH conjugates of the acrylamides with a double conjugate formed for NMBA. The differences in reactivity between acrylamides and methacrylamides could be explained by the charge density of the carbon atoms because the electron-donating inductive effect of the methyl group of the methacrylamides lowered their electrophilicity and thus their reactivity. The differences in reactivity within the group of acrylamides could be explained by the energy of the lowest unoccupied molecular orbital and steric hindrance. Cytotoxicity and activation of oxidative stress response were linearly correlated with the second-order reaction rate constants of the acrylamides with GSH. The reaction of the acrylamides with GSH is hence not only a detoxification mechanism but also leads to disturbances of the redox balance, making the cells more vulnerable to reactive oxygen species. The reactivity of acrylamides explained the oxidative stress response and cytotoxicity in the cells, and the lack of reactivity of the methacrylamides led to baseline toxicity.

Co modified N, P, B tri-doped porous yolk-shell biochar microspheres as catalyst for oxygen evolution reaction

Designing low-cost and high-activity electrocatalysts is crucial for improving the slow kinetic process of the oxygen evolution reaction (OER) and meeting global energy demands. This study focuses on the preparation of a novel OER catalyst, labelled Co@NPBC, which exhibits a porous yolk-shell configuration. The structure of Co@NPBC consists of N, P, B-doped carbon microspheres, amalgamated with the transition metal Co, and it is fabricated via a simple impregnation–carbonisation method. The doping of heteroatoms has the potential to modify both the charge and spin density of carbon atoms, while the presence of Co enhances the electrical conductivity of the material, which accelerates the electron transmission process. The porous structure provided numerous active sites for the reaction to occur, specifically at the catalytic interface. Furthermore, the yolk-shell structure serves a supportive function, ensuring the stability of the overall catalyst architecture. Upon testing in an alkaline environment, the Co@NPBC material demonstrated exceptional OER catalytic activity (η10: 355 mV, Tafel slope: 71.4 mV·dec−1). The results showed that the synergistic effect of carbon microspheres doped with heteroatoms and Co nanoparticles increased the OER catalytic activity and subsequently enhanced water splitting efficiency. For a comparative analysis, catalysts with either single (Co@NC, Co@BC, and Co@PC) or double doping (Co@NPC, Co@NBC, and Co@BPC) were also prepared. The results showed that Co@NPBC exhibited better OER catalytic activity than the other catalysts.

A BF2 Chelate Exhibiting Excimer-like Fluorescence with an Unusually Large Stokes Shift in the Crystalline Phase.

The target mono-BF2 complex is weakly emissive in fluid solution because radiationless decay of the excited-singlet state is promoted through an intramolecular N⋅⋅⋅H-N hydrogen bond. The lack of mirror symmetry for this compound is attributed to vibronic effects, as reported previously for the bis-BF2 complex (BOPHY). Red-shifted fluorescence is observed from single crystals, the emission quantum yield approaching 30 % with a fluorescence lifetime of 2 ns. The large Stokes shift of 5,700 cm-1 helps minimize self-absorption. Crystallography indicates that the internal fold and twist angles are increased substantially in the crystal, but the hydrogen bond is weakened relative to solution. The crystal structure is compiled from pairs of head-to-tail molecules having a shift of ca. 4.1 Å and closest approach of ca. 3.5 Å. These molecular pairs are arranged in columns, which, in turn, assemble into sheets. The proximity favors excitonic coupling between individual molecules, with the coupling strength obtained by analysis of the absorption spectrum reaching ca. 1,000 cm-1 . Both the ideal dipole approximation and the extended dipole methodology seriously overestimate the coupling strength, but the atomic transition charge density procedure leads to good agreement with experiment. Emission is attributed to the closely coupled molecular pair functioning in an excimer-like manner with the exciton trapped in a local minimum. Increasing temperature causes a slight blue shift and loss of fluorescence.

Interface Bonding Properties of CrAlSiN-Coated Cemented Carbides Doped with CeO2 and Y2O3 Rare Earth Oxides.

This study performed first-principle-based calculations of the interface adhesion work in interface models of three terminal systems: CrAlSiNSi/WC-Co, CrAlSiNN/WC-Co, and CrAlSiNAl/WC-Co. The results proved that the CrAlSiNSi/WC-Co and CrAlSiNAl/WC-Co interface models had the highest and lowest interface adhesion work values (4.312 and 2.536 J·m-2), respectively. Thus, the latter model had the weakest interface bonding property. On this basis, rare earth oxides CeO2 and Y2O3 were doped into the Al terminal model (CrAlSiNAl/WC-Co). Then, doping models of CeO2 and Y2O3 doped on the WC/WC, WC/Co, and CrAlSiNAl/WC-Co interfaces were established. The adhesion work value was calculated for the interfaces in each doping model. When CeO2 and Y2O3 were doped in the WC/WC and CrAlSiNAl/WC-Co interfaces, four doping models were constructed, each model contains interfaces withreduced adhesion work values, indicating deteriorated interface bonding properties. When the WC/Co interface was doped with CeO2 and Y2O3, the interface adhesion work values of the two doping models are both increased, and Y2O3 doping improved the bonding properties of the Al terminal model (CrAlSiNAl/WC-Co) more significantly than CeO2 doping. Next, the charge density difference and the average Mulliken bond population were estimated. The WC/WC and CrAlSiNAl/WC-Co interfaces doped with CeO2 or Y2O3, with decreased adhesion work, exhibited low electron cloud superposition and reduced values of charge transfer, average bond population, and interatomic interaction. When the WC/Co interface was doped with CeO2 or Y2O3, superposition of the atomic charge densities of electron clouds was consistently observed at the CrAlSiNAl/WC-Co interface in the CrAlSiNAl/WC/CeO2/Co and CrAlSiNAl/WC/Y2O3/Co models; the atomic interactions were strong, and the interface bonding strength increased. When the WC/Co interface was doped with Y2O3, the superposition of atomic charge densities and the atomic interactions were stronger than for CeO2 doping. In addition, the average Mulliken bond population and the atomic stability were also higher, and the doping effect was better.