Chemphyschem最新文献

We applied ab initio methods, including the GW approximation, the Koopmans functionals, range-separated hybrid functionals, and time-dependent density functional theory (TDDFT) to investigate the energy gap and optical gap of perylene-3,4,9,10-tetracarboxylic dianhydride (PTCDA) and perylene diimide (PDI) derivatives. A detailed comparison of our calculated results from all the methods with experimental values was made, with particular focus on the properties of single molecules versus molecular crystals. Single-molecule TDDFT with the polarizable continuum model (PCM) shows reasonable accuracy for the energy and optical gaps in molecular crystals but is less accurate in predicting ionization energy (IE) and electron affinity (EA) compared to GW calculations. These findings provide guidance for selecting reliable computational approaches for evaluating key electronic and optical properties of organic semiconductor systems.

This study investigates the reactivity of a novel intermolecular phosphine/borane (P/B) frustrated Lewis pair in the activation of CO₂ via a push-pull mechanism. Detailed computational analyses, particularly intrinsic reaction coordinate calculations, reveal a single-step and concerted mechanism for CO₂ activation. The reaction is characterized as exergonic, with notable efficiency in bromobenzene solvent. Furthermore, natural bond orbital analysis provides critical insights into the electron transfer processes, elucidating the roles of key donor–acceptor interactions in facilitating the reaction. These findings enhance the understanding of frustrated Lewis pair-mediated CO₂ activation and highlight the potential of this system for catalytic applications.

Coupling investigations of the photochemistry of ambient samples with the detection of photoproduced radicals is a field of ongoing interest. Herein, we investigated the use of chemical actinometers to account for the photon flux in in situ electron paramagnetic resonance (EPR) spectroscopy experiments (I_EPR) and correct it for solar light exposure. The developed method is based on the production of singlet oxygen (¹O₂) and its detection in spin-trapping with TEMP-OH in the photosensitization of Protoporphyrin IX (PPIX) and rose bengal (RB). Similar I_EPR values were achieved in both PPIX and RB systems, with values ranging from (1.3 ± 0.2) × 10⁻⁸ ≤ I_EPR ≤ (1.6 ± 0.3) × 10⁻⁸ mol photons L⁻¹ s⁻¹. TEMP-OH protonation was shown to interfere with the results at pH < 2. The aggregation effects of PPIX were investigated, and solutions were shown to be stabilized by the presence of TEMP-OH. The photochemical activity of the sea-surface microlayer (SML) samples was subsequently probed in in situ EPR experiments for the first time and corrected for the equivalent solar photochemical activity. The average results of the sunlight-induced oxidant formation rate were (3.8 ± 0.5) 10⁻⁸ M s⁻¹, demonstrating the pronounced photochemical activity present in SML samples.

A robust coherent control strategy for enantioselective excitation in chiral molecules is presented. This approach employs a cyclic three-state rotational manifold, driven by three linearly polarized microwave fields, enabling analytical determination of the amplitude and phase requirements for enantioselective state transfer. To further enhance resilience against pulse-area errors, a composite pulse is introduced at a critical stage of the excitation process. This composite pulse minimizes pulse-area errors while maintaining enantioselectivity by precisely optimizing the subpulses’ phases. As a demonstration, the scheme is applied to cyclohexylmethanol, a model chiral molecule. Numerical simulations reveal that the tailored microwave fields reliably steer the two enantiomers into distinct target states, and that the composite pulse markedly improves robustness. Importantly, the population of the enantiomer-specific target state remains above 0.99 even for pulse-area deviations of up to ±30%, representing a substantial improvement over single pulse protocols. These results highlight the potential of this method to achieve high fidelity enantioselective control, even in the presence of practical uncertainties in the control field.

In this study, six activated carbons were synthesised using low-rank coal from Labin and Spitsbergen through single- and two-step KOH activation methods. The materials were evaluated for their ability to adsorb rhodamine B from aqueous solutions. The method of activation and impregnation ratio significantly affected the structural and sorption properties of the carbons. BET surface areas ranged from 602 to 855 m²/g. Surface functional groups varied depending on the precursor used. Adsorption experiments explored the effects of initial dye concentration, contact time, adsorbent mass, shaking speed and pH. Kinetic and isotherm models were applied to understand the adsorption mechanism. The linear Langmuir isotherm best fit the data, indicating uniform adsorption sites, while the process followed a pseudo-second-order kinetic model. Maximum adsorption capacities ranged from 100 to 294 mg/g. One adsorbent demonstrated excellent reusability, achieving up to 90% desorption efficiency after three cycles. These results highlight the material's strong potential for removing organic pollutants from water.

The precise positioning and manipulation of individual nanoclusters in ordered arrangements are essential prerequisites for both comprehensive understanding and mathematical formulation to generalize the intrinsic optical characteristics for the advent of nanoscale applications. In analogy with our long-standing understanding of molecular polymers, linear chains of metallic nanostructures have been coined as plasmonic polymers, where the individual particles can be considered as the monomeric building units. The possibility of plasmonic waveguiding in these well-defined strongly coupled plasmonic nanostructures has motivated their investigation as prototypical model systems to fulfill the modern demand of applications in photonics miniaturized at the nanoscale dimensions. 1D chain-like assemblies of nanostructures, because of their high symmetry, represent particular spatial arrangements for propagating surface plasmon polaritons that can venture directed energy transfer along the chain and to unravel short- and long-range electromagnetic coupling mechanisms in these oriented assemblies. The optical properties of these plasmonic polymers are dependent upon the structural characteristics, such as the aggregation number, interparticle distances, and mutual orientations that explicitly correlate with the degree of polymerization, bond lengths, and bond angles, respectively, in these lattice architectures. Moreover, the morphological characteristics, such as size, and geometry of the individual building blocks, are of paramount significance to the critical condensation of the intriguing optical features in these polymeric configurations. The cumulative effect of all these intrinsic physical observables associated with the polymeric configurations can reckon the complete story towards the observed plasmonic properties. As to the first initiative to distill this complex relationship, a theoretical formulation has been devised in simple intuitive terminologies to correlate the chain length dependence on the plasmonic characteristics and electric field distribution patterns in 1D aggregation of size-selective gold nanostructures. The complementarity of theoretical, experimental, and numerical simulation approaches has been adopted in bridging the interrelation between the associated physical parameters and optical characteristics of the periodic assemblies with varying chain lengths comprised of size-selective gold nanoparticles. The unique ability of plasmonic waveguiding and coherent exchange of near electric fields along these 1D chain-like assemblies can endow newer perspectives towards their potential applications in light-trapping in photovoltaic devices, nanoscale photonics, optical circuitry, chemical and biological sensing, and surface enhanced spectroscopies.

In this study, first-principles calculations were employed to systematically explore the stability and structural evolution of all-inorganic lead-free perovskites RbGeX₃ (X = I, Br, Cl) in three optically active phases: Pm$$m, R3m, and Pna2₁. Total energy and phonon spectra indicate that Pna2₁ is the most stable phase, followed by R3m and Pm$$m. Ab initio molecular dynamics (AIMD) simulations at 300 and 500 K further confirm the thermal robustness of RbGeX₃. The distortion parameters (D, σ², ψ) indicate that the R3m and Pna2₁ phases exhibit varying degrees of symmetry breaking compared to the Pm$$m phase. Analysis of the soft phonon modes reveals that instability in Pm$$m originates from off-center displacements of Ge atoms coupled with halide vibrations, whereas in R3m it is driven by X-site-induced tilting of GeX₆ octahedra. After AIMD simulations, the structures of both Pm$$m and R3m exhibit significant octahedral tilting, while the Pna2₁ phase shows minimal structural change, indicating greater thermal robustness. Finally, band structure calculations using the Heyd–Scuseria–Ernzerhof hybrid functional show a progressive bandgap increase with decreasing symmetry, offering theoretical guidance for the development of efficient lead-free perovskites.

Heavy-metal fluoride (HMF) glasses exhibit a combination of broad infrared transparency, low phonon energy, and potential fluoride-ion conductivity, rendering them promising candidates for optical and electrochemical applications. However, the atomic-scale environment of La³⁺ ions, which governs these properties, remains inadequately characterized. In this work, we systematically examine NaF–LaF₃ and LiF–LaF₃ binary mixtures as model systems using a suite of solid-state nuclear magnetic resonance (NMR) techniques. Our findings reveal markedly distinct behaviors of the alkali cations. NaF readily reacts with LaF₃ to form a crystalline NaLaF₄ phase, as unambiguously confirmed by ¹⁹F and ²³Na NMR, along with 2D ¹⁹F–²³Na HETCOR and CP/MAS experiments. In contrast, LiF exhibits no evidence of forming Li–La–F coordination structures, instead persisting as a phase-separated LiF/ LaF₃ composite. This divergence is attributed to the stronger Li–F bonding and the limited coordination flexibility of Li⁺, which hinders disruption of the LaF₃ lattice. These mechanistic insights highlight the critical influence of alkali cation identity on the structural evolution in mixed fluoride systems and offer valuable design principles for ZBLAN and related HMF glasses.

The conformational behavior of SH···S H-bonded ethanethiol (EtSH) dimer and trimer has been experimentally studied in cold and solid argon (Ar) and nitrogen (N₂) matrices via analysis of the $$ spectral region. Over 20 spectral bands were observed in both matrices exhibiting a wide range of $$ spectral shifts (4.8–87.5 cm⁻¹). Their spectral assignment was supported by normal mode frequencies calculated at the ωB97X-D/aug-cc-pV(D + d)Z level of theory, which displayed close match. Calculations predicted 24 (EtSH)₂ conformers belonging to four classes (GG, GG′, GA, and AA) and 45 (EtSH)₃ conformers from seven classes (GGG, GGG′, GG′G′, GGA, GG′A, GAA, and AAA) formed by gauche (G and G’) and anti (A) monomers. Experimentally, 16 dimers and 9 trimers were identified as the relative stability showed small variation; only 1.42 and 2.77 kcal mol⁻¹ for dimer and trimer. However, no AA dimer as well as GAA and AAA trimer could be identified in any matrix, due to the presence of multiple lesser stable A monomers. The most stable conformers were found to possess weaker and longer SH···S H-bonds, while the lesser stable conformers possessed stronger and shorter SH···S H-bonds. When compared against SH···S H-bonds in H₂S clusters, the ones in EtSH clusters showed markedly greater contribution of dispersion interaction.

The magic-angle spinning NMR technique, Centerband-Only Detection of EXchange (CODEX), can be used to determine the oligomerization state of molecules when combined with site-specific labeling. Calibrated with amino acid crystals, the method is successfully applied to proteins, primarily combined with ¹⁹F labeling. The use of ¹³C spins for CODEX-based oligomer determination in proteins is hampered by limited sensitivity of ¹³C spins due to the low gyromagnetic ratio of ¹³C and the presence of natural abundance background spins which contribute to the observed CODEX decay. The use of CODEX is proposed in conjunction with dynamic nuclear polarization (DNP) at low temperature to increase sensitivity. It is necessary to correct for effects of ¹³C present at natural abundance. A (PDSD) proton driven spin diffusion-based correction is demonstrated to be effective when the isotropic chemical shifts of the natural abundance background are distinct from the labeled site. Using a ¹³C-ζ-phenylalanine-labeled GB1 sample, it is demonstrated that the autocorrelation peak decay observed in a series of PDSD spectra can be utilized to correct for the additional dephasing and recover the expected CODEX decay curve. With ¹³C-γ-phenylalanine labeling and ¹³C-depleted background, mixing times up to 1500 s are demonstrated.