Chemphyschem最新文献

Synthetic and natural carbons are widely used as carrier for electrodes in electrochemical applications. They need to have a controlled morphology in order to facilitate mass and charge transport, so the process of film formation is of uttermost importance. Here we show, how carbons (after proper preconditioning) can be codeposited with an ionomer by electrophoretic deposition, a method that does allow full control of deposition conditions during the process. In view of potential applications, we focus on the direct deposition on proton-conducting membranes. Ionomers and membranes applied are based on established per-fluorinated polyethylene with SO3H-terminated side chains (PFSA). Conditions for reproducible deposition are reported in terms of optimal charge on the carbon particles, field strength in the deposition cell and necessary deposition times for a given film thickness. Additionally, a horizontal cell arrangement is suggested to avoid gravitational effects.

We review an iconic class of chemical oscillators driven by phase transition instabilities, namely Gas Evolution Oscillators (GEOs). These systems show oscillatory dynamics in the delivery of gas sustained simple reactions yielding gaseous products in a liquid mixture, due to nucleation and supersaturation phenomena. After presenting the main fea- tures and properties of these systems, we deepen the underlying mechanism through a unified picture of the various models that have been proposed to describe this kind of oscillations. We finally discuss a concrete example of how such instabilities can impact chemical processes with applied relevance.

Systems with multiple photoswitchable units in one molecule have attracted considerable attention in the past years as they are useful for a broad variety of possible applications. Especially, linked azobenzenes sharing one benzene ring are of high interest since their direct linkage introduces an additional photoswitchable unit at only small increase in molecular weight. In this spirit, linear oligoazobenzenes had been synthesized, though their photochemical properties have only been investigated for short chain lengths. In this study, we use (time-dependent) density functional methodology for the evaluation of the excitations of meta- and para-connected oligo-azobenzenes to predict their switching ability. It becomes apparent, that the meta connection pattern enables each azobenzene subunit to act as an individual switchable unit, whereas they are strongly coupled and loose their individuality in para connection. Therefore, meta-oligo-azobenzenes are ideal candidates for future studies of azobenzene-based functional polymers, while para-oligo-azobenzenes are not.

The actinide-actinide bonding in tri-actinide clusters [An₃Cl₆]ᶻ (An = Ac-Pu, z = 1-6) and [An₃Cl₆Cp₃]ᶻ (z =-2-+3; Cp = (η5-C5H5)) is studied using density functional theory. We find 3-centre bonding similar to the tri-thorium cluster [{Th(η⁸-C₈H₈)(μ₃-Cl)₂}₃{K(THF)₂}₂]∞, as we previously reported (Nature 2021, 598, 72-75). The population of 3-centre molecular orbitals (3c-MOs) by zero, one or two electrons correlates with shortening of the An-An bond lengths, which also decrease with increasing actinide atomic number, consistent with the contraction of the actinide valence atomic orbitals. Mulliken analyses indicate that these 3c-MOs predominantly involve An 6d and 5f orbitals. Various methods evidence the presence of An-An bonding in most systems with populated 3c-MOs, including bond orders (Mayer and Wiberg), quantum theory of atoms in molecules metrics (ρ, ∇²ρ, -G/V, H, delocalization indices), electron localization function, and electron density assessments. Additionally, we explore the effect of Cp ligand substitution on uranium complexes, finding that bulkier Cp ligands can induce U-U bond distortions and result in slightly longer U-U bonds. Overall, this study advances our understanding of metal-metal bonding in tri-actinide clusters, highlighting its effects on geometric and electronic structures.

In this work, the stability and photoelectric properties of the MAI-terminated and PbI2-terminated of MAPbI3 (001) were thoroughly investigated using density functional theory calculation. To study the stability of exposed surface, adsorption energy of water molecules, ab initio molecular dynamics (AIMD), mean square displacement (MSD) and X-ray diffraction (XRD) were calculated. MSD of PbI2-terminated surface is greater by two orders of magnitude compared to MAI-terminated surface. For the photoelectric properties of MAPbI3, the bandgap, absorption coefficients, joint density of states (JDOS) and dielectric constants were investigated. The inhibitory effect of water on the photoelectric performance for PbI2-terminated surface is more significant than that of MAI-terminated surface. Although the photoelectric properties of water molecules adsorption on MAI-terminated surface is basically unchanged, the diffusion of water molecules reduces the photoelectric properties of MAPbI3. Overall, the stability and photoelectric properties of MAI-terminated surface are superior to PbI2-terminated surface. Therefore, we advocate paying attention to the exposed surface of MAPbI3 during the thin film production process and adjusting synthesis parameters to prepare MAI-terminated surface dominated thin film, which should substantially improve the performance of MAPbI3 in the application.

Phycobilisome (PBS) is a pigment-protein complex utilized by red algae and cyanobacteria in photosynthesis for light harvesting. A cyanobacterium Synechocystis sp. PCC 6803 contains PBS with a tricylindrical core built of allophycocyanin (APC) disks where six phycocyanin (PC) rods are attached. The top core cylinder is seemingly involved in attaching four PC rods and binding orange carotenoid protein (OCP) to quench excess of excitation energy. In this study, we have deleted the third linker domain (LD3) of ApcE subunit of PBS which assembles four APC discs into the top core cylinder. The mutation resulted in PBS with bicylindrical core, structurally comparable to the naturally existing PBS from Synechococcus 7942. Lack of LD3 and the top APC cylinder reduces the excitation energy transfer between PC and APC in the mutant. Moreover, these PBSs are more prone to light induced-photodamage and do not bind to the photoactivated orange carotenoid protein (OCP), a known PBS excitation quencher. These findings highlight the complex and elegant interplay between PBS architecture and functional efficiency, suggesting that in PBSs with naturally tri-cylindrical cores, the top cylinder has essential roles in recruiting the rods and proper binding of OCP and recruitment of the four PC rods.

Beryllium chemistry is typically governed by its electron deficient character, but in some compounds it can act as a base. In order to understand better the unusual basicity of Be, we have systematically explored the complexes of one such compound, Be(CO)₃, towards several hydrogen bond donors HX (X=F, Cl, Br, CN, NC, CCH, OH). For all complexes we find three different minima, two hydrogen bonded minima (to the Be or O atoms), and one weak beryllium bonded minimum. Further characterization of the interactions using a topological analysis of the electron density and Symmetry Adapted Perturbation Theory (SAPT) provide insight into the nature of these interactions. Overall these results highlight the capability of certain beryllium compounds to act as either a weak Lewis acid or, unconventionally, a Lewis base whose basicity towards hydrogen bonding is comparable to that of π systems.

This work investigates the influence of structural and electronic modification on the electrochemical performance of conversion and alloying materials. The CuSbSe2, a promising 2D layered conversion-and-alloying material is being investigated with references to parent pristine Sb2Se3 and a doped version of later Sn0.2Sb1.8Se3 for their sodium-ion battery performance. The CuSbSe2 with layered structure is well known to accommodate lattice distortions via inter-layer movement, potentially mitigating distortions brought about by the Alkali ion (Na in this case) insertion. In contrast, the parent conversion-cum-alloying material Sb2Se3 with its one-dimensional crystal structure leads to structural disintegration during battery operation. The Sn-doped analog, Sn0.2Sb1.8Se3, comparatively exhibits enhanced kinetics owing to the reduced long-range order. The 2D layered, CuSbSe2 despite exhibiting  2D long-range order exhibits superior electrochemical performance owing to the favorable electronic and structural features. The CuSbSe2 exhibits a reversible capacity of 881 mAh g-1 compared to 516 mAh g-1 for Sn0.2Sb1.8Se3 and 429 mAh g-1 for Sb2Se3, with an improved Coulombic efficiency as well. The transient electrochemical investigations of Electrochemical Impedance Spectroscopy (EIS) and Galvanostatic intermittent titration techniques (GITT) reveal that better performance exhibited by CuSbSe2 may well be attributed to kinetics owing to enhanced diffusion coefficients in the intercalation and conversion regime.

We present spectra of the first overtone vibration transition of C-H/ O-H stretch (2ν₁) in HCO⁺ and HOC⁺, recorded using a laser induced reaction action scheme inside a cryogenic 22 pole radio frequency trap. Band origins have been located at 6078.68411(19) and 6360.17630(26) cm^-1, respectively. We introduce a technique based on mass selective ejection from the ion trap for recording background free action spectra. Varying the number density of the neutral action scheme reactant (CO₂ and Ar, respectively) and collisional partner reactant inside the ion trap, permitted us to estimate the radiative lifetime of the state to be 1.53(34) and 1.22(34) ms, respectively, and the collisional quenching rates of HCO⁺(2ν₁) with He, H₂, and N₂.

A polymerizable diacetylene gelator, containing urea and urethane groups, that congeals various non-polar solvents was synthesized. The gelator molecules self-assemble forming non-covalent polymers through intermolecular hydrogen bonding, as evidenced from FT-IR and concentration-dependent 1H NMR spectroscopy. The self-assembly positions the diyne units of adjacent molecules at proximity and in a geometry suitable for their topochemical polymerization. UV irradiation of the gel resulted in topochemical polymerization, transforming the non-covalent polymer to a covalent polymer, in situ, in the gel state. The polymerization was confirmed by characterizing the polydiacetylene (PDA) using UV-Vis and Raman spectroscopy. Time-dependent rheological studies revealed gradual strengthening of the gel with the duration of irradiation, suggesting that the degree of polymerization increases with the duration of irradiation. The PDA formed is a semiconductor, which might be useful for various applications.