Chemphyschem最新文献

Zinc tin oxide (ZTO) is investigated as a photoluminescent sensor for oxygen (O₂); chemisorbed oxygen quenches the luminescence intensity. At the same time, ZTO is also studied as a resistive sensor; being an n-type semiconductor, its electrical conductance decreases by adsorption of oxygen. Both phenomena can be exploited for quantitative O₂ sensing. The respective sensor responses can be described by the same modified Stern-Volmer model that distinguishes between accessible and non-accessible luminescence centers or charge carriers, respectively. The impact of the temperature is studied in the range from room temperature up to 150 °C.

We have used grazing incidence X-ray absorption near edge spectroscopy (XANES) to investigate the behavior of monolayer FeO ${}_x$ films on Pt(111) under near ambient pressure CO oxidation conditions with a total gas pressure of 1 bar. Spectra indicate reversible changes during oxidation and reduction by O ${}_2$ and CO at 150 °C, attributed to a transformation between FeO bilayer and FeO ${}_2$ trilayer phases. The trilayer phase is also reduced upon heating in CO+O ${}_2$ , consistent with a Mars-van-Krevelen type mechanism for CO oxidation. At higher temperatures, the monolayer film dewets the surface, resulting in a loss of the observed reducibility. A similar iron oxide film prepared on Au(111) shows little sign of reduction or oxidation under the same conditions. The results highlight the unique properties of monolayer FeO and the importance of the Pt support in this reaction. The study furthermore demonstrates the power of grazing-incidence XAFS for in situ studies of these model catalysts under realistic conditions.

Molecular photoswitches have demonstrated potential for storing solar energy at the molecular level, with power densities comparable to commercial batteries and hydroelectric energy storage. However, development of efficient photoswitches is hindered by limitations in cyclability and optical properties of existing materials. We here demonstrate that certain limitations in photoswitches based on electrocyclizations stem from the issue of controlling competition between Woodward-Hoffmann allowed and forbidden pathways. Our approach moves beyond the traditional view of activation barriers and reveals that second-order saddle points are crucial in dictating the competition between disrotatory and conrotatory pathways. These insights suggest new opportunities to manipulate the competition between these pathways through geometric constraints, fundamentally altering the connectivity of the potential energy surface. Our study also emphasizes the necessity of multi-reference methods and the need to conduct higher-dimensional explorations for competing pathways beyond photoswitch design.

The adsorption of the radical α,ɣ-bisdiphenylene-β-phenylallyl (BDPA) molecule to the Cu(100) surface was studied using scanning tunnelling microscopy (STM), scanning tunnelling spectroscopy (STS), and density functional theory (DFT) calculations accounting for dispersion forces. BDPA on Cu(100) was observed to align preferentially along $⟨01\bar{1}⟩$ directions due to weak Cu-C chemisorption between fluorenyl carbons with the underlying copper atoms. The curved shape of the BDPA molecule on Cu(100) can be ascribed to the lack of molecular orbital character on the phenyl substituent. A Kondo-like feature from differential conductance (dI/dV) measurements centered close to the Fermi energy ( $E_F$ ) suggests the retention of an electron spin-1/2 state, which is corroborated by hybrid DFT calculations that place the SOMO (singly occupied molecular orbital) below and SUMO (singly unoccupied molecular orbital) above $E_F$ for BDPA adsorbed to Cu(100).

Pyrolysis of carbonaceous waste material has become an attractive method of recycling to generate value added products. Alongside pyrolytic oil and gas fractions, the thermal degradation forms solid pyrolytic char, which can be further processed. Local waste materials, including birch wood residue (BW), Reynoutria japonica stems (KW), spent coffee grounds (CG), tire rubber (TR), and lobster shells (LS) we assessed to form pyrolytic char. Using a simple acid treatment step on the chars, this study has shown successfully incorporate many of them into the low-temperature synthesis of plasmonic TiC NPs. Each char was shown to display distinctive physical and chemical characteristics, which was exploited to synthesize TiC NPs with unique properties. To study the plasmonic behaviour of each TiC sample, solar driven desalination experiments were conducted. TiC formed from TR char achieved broadband absorbance of ~95 % of the solar spectrum, reaching a near-perfect solar-to-vapor generation efficiency of 95 %, or a water generation rate of 1.40±0.01 kg m^-2 h^-1 under one-sun illumination. This makes it the best performing of all chars tested, and among the top performers reported in the literature to date. The evaporators maintain activity over time and under strongly hypersaline conditions.

The rotational spectrum of diphenylsilane was investigated using chirped-pulse Fourier transform microwave spectroscopy in the frequency range of 2-8 GHz. The lowest energy structure of diphenylsilane has C ${}_2$ point group symmetry with the C ${}_2$ symmetry axis coinciding with the $b$ -inertial axis of the molecule. Through the assignment of the main isotopologue as well as singly substituted heavy-atom isotopologues, including ${}^{13}$ C, ${}^{29}$ Si, and ${}^{30}$ Si, we were able to obtain a comprehensive gas-phase structure of diphenylsilane. The structure of diphenylsilane was compared with its oxygen analogue, diphenylether, including a discussion of the barrier height to the large-amplitude motion of the phenyl rings. Furthermore, the structural comparison was extended to include a range of C-Si bond lengths and bond angles from other organosilicon molecules where the silicon atom is bonded to aliphatic and/or aromatic moieties.

The major challenges in enhancing the cycle life of lithium-sulfur (Li-S) batteries are polysulfide (PS) shuttling and sluggish reaction kinetics (S to Li₂S, Li₂S to S). To alleviate the above issues, the use of heteroatom-doped carbon as a cathode host matrix is a low-cost and efficient approach, as it works as a dual-functional framework for PS anchoring as well as an electrocatalyst for faster redox kinetics. Here, the dual role of heteroatom-doped carbon sheets (CS) in the chemisorption of Li₂S₆ and catalysis of its faster conversion to Li₂S is established. To substantiate the catalytic effect, composite cathodes were prepared by encapsulating sulfur in CS which is further blended with carbon nanotubes (CNTs) to form a free-standing cathode. The electrochemical performances of the three cathodes (S@Fe-N-CS-CNT, S@Fe-S-CS-CNT, and S@Fe-NS-CS-CNT) were evaluated by constructing Li-S cells. The S@Fe-NS-CS-CNT delivers a high initial discharge capacity of 1017 mAh g^-1 at 0.5 C rate and sustains a capacity of 751 mAh g^-1 after 260 cycles with a capacity retention of 73.8 %. Even at a high S loading (12 mg cm^-2), it delivers an initial discharge capacity of 892 mAh g^-1 and retained 575 mAh g^-1 after 200 cycles.

With the rapid advancement of information technology, the need to achieve ultra-high-density data storage has become a pressing necessity. This study synthesized three hyperbranched polyimides (HBPI-TAPP, HBPI-(Zn)TAPP, and HBPI-(Cu)TAPP) by polymerizing 5,10,15,20-tetrakis(4-aminophenyl)porphyrin (TAPP), which features a cavity for metal ion coordination, with 4,4'-(hexafluoroisopropylidene)diphthalic anhydride (6FDA), to systematically investigate the effect of metal ion species on storage performance. According to the results, memory devices based on HBPI-(Zn)TAPP exhibit volatile SRAM (static random-access memory) characteristics, whereas devices employing HBPI-TAPP and HBPI-(Cu)TAPP demonstrate non-volatile WORM (write-once, read-many) characteristics. Molecular simulations based on density functional theory (DFT) reveal that the storage behaviors of these polymers are governed by a charge-transfer mechanism, wherein electrons transfer from the porphyrin donor segment to the 6FDA acceptor segment, forming charge-transfer complexes that are not easily dissociated. The larger dipole moments of HBPI-TAPP and HBPI-(Cu)TAPP render the complexes difficult to dissociate, resulting in WORM-type memory behavior. In contrast, HBPI-(Zn)TAPP has the lowest threshold voltage, with a stronger electron binding that hinders the dissociation of the charge transfer complex, thereby enabling SRAM-type memory behavior.

Small gas-phase metal clusters serve as model systems for complex catalytic reactions, enabling the exploration of the impacts of the size, doping, charge state and other factors under clean conditions. Although the mechanisms of reactions involving metal clusters are known in many cases, they are not always sufficient to interpret the experimental results, as those can be strongly influenced by the chemical kinetics under specific conditions. Therefore, our objective here is to develop a model that utilizes quantum chemical computations to comprehend and predict the precise kinetics of gas-phase cluster reactions, particularly under low-pressure conditions. In this study, we demonstrate that master equation simulations, utilizing reaction paths computed through quantum chemistry, can effectively elucidate the findings of previous experiments. Furthermore, these simulations can accurately predict the kinetics spanning from low-pressure conditions (typically observed in gas-phase cluster experiments) to atmospheric or higher pressures (typical for catalytic experiments). The models are tested for simple elementary steps (Cu₄+H₂). We highlight the importance of the reaction mechanism simplification in Cu₄ ⁺+H₂ and provide an interpretation for the previously observed product branching in Pt⁺+CH₄.

The red/green cyanobacteriochrome (CBCR) slr1393g3 exhibits a quantum yield of only 8 % for its forward photoconversion, significantly lower than other species from the same CBCR subfamily. The cause for this reduced photoconversion is not yet clear, although in the related NpR6012g4 dark-state structural heterogeneity of a paramount Trp residue has been proposed to cause the formation of nonproductive subpopulation. However, there is no such information on the equivalent residue in slr1393g3, W496. Here we use solid-state NMR to explore all possible sidechain rotamers of this Trp residue and their local interactions at the atomic level. The indole nitrogen (Nϵ1) is used as an NMR probe, achieved by site-specific ¹⁵N-indole labeling of a quadruply Trp-deleted variant and trehalose vitrification technique. The data reveal a set of seven indole rotamers of W496 with four distinct environments for the Nϵ1-H group. Only a minority population of 20 % is found to retain the π-stacking and hydrogen-bonding interactions with the chromophore in the dark state that has been assigned to account for complete forward photoconversion. Our results demonstrate the direct role of W496 in modulating the forward quantum yield of slr1393g3 via rearrangement of its sidechain rotameric conformations.