Chemphyschem最新文献

Attainment of quantum-confined materials with remarkable stoichiometric, geometric, and structural control has been made possible by advances in colloidal nanoparticle synthesis. The quantum states of these systems can be tailored by selective spatial confinement in one, two, or three dimensions. As a result, a multitude of prospects for controlling nanoscale energy transfer have emerged. An understanding of the electronic relaxation dynamics for quantum states of specific nanostructures is required to develop predictive models for controlling energy on the nanoscale. Variable-temperature, variable-magnetic field ( $VTV\overrightarrow{H}$ ) optical methods have emerged as powerful tools for characterizing transient excited states. For example, $VTV\overrightarrow{H}$ magnetic circular photoluminescence (MCPL) spectroscopy can be used to calculate electronic g factors, assign spectroscopic term symbols for transitions within metal nanoclusters, and quantify the energy gaps separating electronic fine-structure states. $VTV\overrightarrow{H}$ spectroscopic methods are effective for isolating the carrier dynamics of specific quantum fine-structure states, enabling determination of electronic relaxation mechanisms such as electron-phonon scattering and energy transfer between assembled nanoclusters. In particular $VTV\overrightarrow{H}$ -MCPL is especially effective for studying electronic spin-state dynamics and properties. This Review highlights specific examples that emphasize insights obtainable from these methods and discusses prospects for future research directions.

This paper discusses the use of the electrostatic potential in both recent and older literature, with an emphasis upon a 2022 Molecular Physics article by Politzer and Murray entitled "Atoms do exist in molecules: analysis using electrostatic potentials at nuclei". We discuss electrostatic potentials at nuclei and how they easily lead to atoms in molecules, without physically separating the individual atoms. We further summarize the work by the Politzer group on definitions of atomic radii by means of the electrostatic potential. The earlier studies began in the 1970's and continued through the 1990's. Unfortunately, access to these older publications is often limited, cfr. digital libraries often limit the authorized access until a certain publication year, and these papers are often not cited in current publications. Although still being highly interesting and relevant, this older literature is in danger of being lost. Digging into this older literature thus opens up new views. Our feeling is that Peter passed 'on' a vision that boundaries do not exist between atoms in molecules, but that some useful and meaningful radii can be obtained using the electrostatic potential between atoms in molecules.

This report investigates the synthesis, structural characterization, fundamental molecular photophysics, electrochemistry, UV-Vis spectroelectrochemistry, and time-resolved infrared spectroscopic properties of eight [fac-Re(dafR)(CO)₃L]^0/+ complexes, where R=ethyl [(dedaf); 1, 3, 5, 7] or H [(dafH); 2, 4, 6, 8] and L=Cl^- (1, 2), imidazole [(Im); 3, 4], 4-ethylpyridine [(4-Etpy); 5, 6], or pyridine [(py); 7, 8]. Universally, 1-8 yield higher energy photoluminescence (PL) emission bands and higher PL quantum yields (up to 53 %) than the classic 2,2'-bipyridine (bpy) and 1,10-phenanthroline (phen) ligated Re(I) tricarbonyl complexes. The excited state lifetimes of 1-8 lie between those corresponding to the bpy and phen derivatives, ranging from 120 and 1300 ns at room temperature. Combinations of reductive UV-Vis spectroelectrochemistry, transient absorption spectroscopy, and time-resolved infrared spectroscopy consistently assigned the lowest excited states in 1-8 being of metal-to-ligand charge transfer (MLCT) character. These new Re^I MLCT chromophores follow classic energy gap law behavior and possess the characteristics necessary for serving as valuable photosensitizers suitable to energize excited state electron and energy transfer photochemistry.

The prevailing overdependence on fossil fuels contributes to energy supply instability and pronounced price volatility. The combustion of these fuels emits considerable greenhouse gases and pollutants, further deteriorating the climate and environment. In response, Round-the-Clock Photocatalytic Systems (RTCPs) have emerged as a viable technological solution, attracting significant research interest due to their convenience, sustainability, and environmental benefits etc. which act as "photo-batteries" facilitate catalytic processes in the absence of light, offering continuous operation. Given the considerable potential of RTCPs, a timely examination of recent advancements is essential to optimize efforts. This review delineates the fundamental mechanisms of RTCPs, explores innovative strategies and current developments, and addresses the challenges of scaling up production. It aims to provide new insights and serve as a foundational reference for future research on RTCPs.

Oleylamine is widely used in the synthesis of colloidal nanoparticles, as a solvent, as a stabilizing agent, and sometimes as a reducing agent. For example, metallic nanoparticles are obtained through reduction when Ni(II) and Pd(II) precursors are used or through disproportionation in the case of Ni(I) or Co(I). A similar dichotomy is observed for Cu precursors, with an additional complexity due to the nature of the precursor salt. In the present article, we report a combined DFT evaluation of possible reduction paths for Cu(II) and Cu(I) reduction by oleylamine, including the competition with Cu(I) disproportionation, and X-ray Absorption Spectroscopy monitoring of the oxidation state of copper(II) acetylacetonate in oleylamine. We show that the reduction of copper(II) acetylacetonate goes through a two-steps process, with the intermediate formation of Cu(I) complexes. The role of phosphine ligands is demonstrated as well as the relevance of these findings in case alternative copper sources such as copper halogen salts.

Hydrolysis of NaBH₄ has garnered great concern in the production of hydrogen. Four different cobalt loadings (5 wt.%, 10 wt.%, 12.5 wt.% and 15 wt.%) were impregnated on SBA-15 molecular sieve. The effect of Co loading on the catalytic performance of the CoB/SBA-15 catalysts for NaBH₄ hydrolysis using the drainage method was studied. Characterizations using XRD, SEM, XPS, and N₂ adsorption-desorption were analytically conducted to examine the physiochemical properties of the CoB/SBA-15 catalyst. The catalytic activity test revealed that the optimum Co loading was 10 wt.% at which the maximum rate of hydrogen production was 153.0 mL/min⋅gcat, higher than the other samples. In addition, the effect of Co loaded, catalyst amount, and temperature were examined. Furthermore, the stability of the catalyst was maintained after five cycles. Cobalt-based catalysts are a promising catalytic system for hydrogen generation by hydrolysis of NaBH₄.

The increasing popularity of time-resolved X-ray absorption measurements for understanding dynamics in molecular and material systems has led to many advances in table-top sources for pulsed X-rays. We report on a table-top laser-produced plasma (LPP) source that can perform soft X-ray (SXR), near-edge X-ray absorption fine structure (NEXAFS) measurements using a laser source with 23 ps pulse duration. The spectrometer's key specifications, such as brilliance, resolution, and stability, are characterized against the more commonly used longer-pulse-duration LPP sources. The 23 ps laser produced approximately an order of magnitude weaker SXR flux than the 8 ns laser for a higher power density due to the smaller total energy absorbed by the plasma. The increased repetition rate, as well as the use of a high line-density X-grating, and a self-referencing scheme still allowed for NEXAFS measurements of Si₃N₄ and TiO₂ thin films with 2.5 minute acquisition times, a resolving power of E/ΔE=424, and a signal-to-noise ratio of 100. It was observed that degradation of the gas jet nozzle led to long-term instability of the source, which can be remediated using alternative nozzle designs. This work demonstrates the feasibility of achieving higher temporal resolution in future time-resolved X-ray absorption measurements using table-top LPP sources.

There are cases when a small change, such as capture of a simple particle, has a significant impact on the molecular properties. This indeed happens with the "proton sponges". It is shown how the substituent effect (SE) and the presence of an intramolecular hydrogen bond modulate the properties of 1,8-bis(dimethylamino)naphthalene (DMAN), its protonated form (DMANH⁺) and their 4-X substituted derivatives, based on the geometric, electronic structure and energetic parameters. For this purpose, the following substituents have been chosen: X=H, NO, NO₂, CN, CHO, Cl, F, CH₃, OCH₃, OH and NH₂, placed in the para position (C4 carbon atom) relative to the N(CH₃)₂ group, thus breaking the symmetry of the molecules. The study was performed using Density Functional Theory (DFT) at the B3LYP/6-311++G(d,p) level of theory. The Harmonic Oscillator Model of Aromaticity (HOMA) index was applied to study changes in the aromaticity of the naphthalene moiety. The strength of the intramolecular hydrogen bond (HB) was estimated by Espinosa-Molins-Lecomte (EML) equation. The Quantum Theory of Atoms in Molecules (QTAIM) and Interaction Region Indicator (IRI) were employed to investigate differences in electronic structure and non-covalent interactions caused by substitution. Finally, the Substituent Effect Stabilization Energy (SESE) and Charge of the Substituent Active Region (cSAR) were computed to evaluate the substituent effect characteristics. Natural Bond Orbital (NBO) analysis was carried out to evaluate the SE influence on the lone pair of nitrogen atoms (N1, N2). We have shown that the presence of a strong intramolecular HB significantly weakens the substituent effect. For electron-donating (ED) substituents, the SE effect was found to have a greater influence than hydrogen bonding in the DMANH⁺ series. The opposite result was obtained for electron-withdrawing (EW) substituents - the SE was estimated to be twice weaker than in the ED case.

We have performed DFT calculations to study the adsorption of single metal atoms (M=Ti, V, Cr, Mn, Fe, Co, Ni, Cu) on both BaO- and TaON-terminated surfaces of cis-BaTaO₂N (001). We have identified the most stable adsorption configuration of each case and explored the relative stability, structural deformations, charge transfer, work function, density of states and mechanism of photocatalytic HER. For BaO termination, all of the adatoms bind covalently on top of the surface oxygens. For TaON termination, the metal atoms are located at the fourfold hollow site. The single metal atoms tend to exist on TaON-termination while they are apt to aggregate on BaO-termination. The formation of impurity states in the band gap is mostly originated from the adatom. When electrons are transferred from the adatom to the surface, the conduction band of semiconductor becomes partially occupied. The charge gained from the BaO termination or transferred to the TaON termination reduces with the increase in electronegativity of metal adatoms. The attachment of metal atoms on the BaO termination is favorable to the improvement of HER activity. While the TaON termination adsorbed with Ti, V and Cr may have better or comparable performance of HER compared with the pure surface.

Recently, lithium-mediated nitrogen reduction reaction (Li-NRR) in nonaqueous electrolytes has proven to be an environmentally friendly and feasible route for ammonia electrosynthesis, revealing tremendous economic and social advantages over the industrial Haber-Bosch process which consumes enormous fossil fuels and generates massive carbon dioxide emissions, and direct electrocatalytic nitrogen reduction reaction (NRR) which suffers from sluggish kinetics and poor faradaic efficiencies. However, reaction mechanisms of Li-NRR and the role of solid electrolyte interface (SEI) layer in activating N₂ remain unclear, impeding its further development. Here, using electronic structure theory, we discover a nitridation-coupled reduction mechanism and a nitrogen cycling reduction mechanism on lithium and lithium nitride surfaces, respectively, which are major components of SEI in experimental characterization. Our work reveals divergent pathways in Li-NRR from conventional direct electrocatalytic NRR, highlights the role of surface reconstruction in improving reactivity, and sheds light on further enhancing efficiency of ammonia electrosynthesis.