The Journal of Physical Chemistry A最新文献

This work presents an innovative computational study of domain-based charge transfer that leverages the localized orbitals of pair coupled cluster doubles (pCCD). This method enables both directional monitoring and quantitative assessment of charge transfer among donor (D), bridge (B), and acceptor (A) moieties. We applied this approach to a series of newly designed carbazole-based prototypical organic dyes, doping the bridge at positions 1, 2, and 3 with nitrogen, oxygen, and sulfur atoms to generate mono-, di-, and tri-doped variants. Our results demonstrate a clear and progressive enhancement in charge transfer as the degree of nitrogen or oxygen doping increases from mono- to di- to tri-doped systems. For mono-doped dyes, the highest forward charge transfer from donor to bridge to acceptor (D → B → A) occurs when a heteroatom (N or O) is placed in the terminal ring of the bridge, closer to the acceptor. In di-doped dyes, the largest forward charge transfer is observed when heteroatoms occupy both terminal positions, with one atom (N or S) adjacent to the donor and the other (N) near the acceptor. Nitrogen-doped systems consistently outperform their oxygen and sulfur counterparts. Among all variants, the organic dye doped with three nitrogen atoms at the bridge exhibits the most efficient and highest directional donor-to-acceptor charge transfer (42.6%), making it the most promising candidate for potential applications in dye-sensitized solar cells. Finally, our calculations predict weak charge separation in all systems, indicating that charge transfer predominantly occurs from the bridge to the acceptor.

Internal contamination significantly degrades the performance and lifetime of optical components in high-power laser systems, making surface cleanliness a critical challenge. In this study, molecular dynamics simulations were employed to investigate the interfacial adsorption behavior and laser-induced removal efficiency of representative organic contaminants on fused silica surfaces, focusing on various molecular structures and surface coverages. The results reveal that molecular architecture is a decisive factor in adhesion and cleaning. Dibutyl phthalate demonstrates the highest affinity through polar and conjugated intermolecular interactions, leaving a residual surface density 3.3 times higher than benzene for an absorbed laser fluence of 10 J/cm². In contrast, benzene desorbs easily at low fluence, whereas long-chain alkanes and phthalates exhibit pronounced retention. Surface coverage further exerts a significant influence on cleaning performance. At low coverage, enhanced adsorption density and interfacial energy enable removal efficiencies exceeding 84%. However, once the fractional coverage above 1.17, multilayer adsorption causes the residual density to increase to roughly 4.0 times that under low-coverage conditions, impeding complete desorption even under high-energy irradiation. These findings highlight how contaminant structure and surface coverage govern laser cleaning performance, and lay the foundation for parametrized contaminant data sets to optimize optical component cleaning.

Radical–radical reactions play a crucial role in the molecular-weight growth that leads to the formation of polycyclic aromatic hydrocarbons (PAHs) and ultimately soot. In this study, we experimentally investigated the reaction between C₆H₅ (phenyl) and C₃H₃ (propargyl) at pressures around 30 Torr and combustion-relevant temperatures (∼1200 K). The reactants were generated through flash pyrolysis of nitrosobenzene and propargyl bromide in a resistively heated SiC tube. We identified the reaction intermediates and products using mass-selected threshold photoelectron spectroscopy (ms-TPES) with the photoelectron-photoion coincidence (PEPICO) instrument at the vacuum-ultraviolet (VUV) beamline of the Swiss Light Source at the Paul Scherrer Institute. Our findings indicate that C₆H₅ associates with C₃H₃ to form C₉H₈, which partially decomposes via hydrogen loss to yield C₉H₇ radicals. The C₆H₅ + C₃H₃ reaction is complex and yields more than just the most stable indene isomer. The experimental threshold photoelectron spectrum provides clear spectroscopic evidence of five isomers: indene, phenylallene, 1-phenyl-1-propyne, 1-phenyl-3-propyne, and cycloprop-2-en-1-ylbenzene. The inclusion of a sixth isomer, 3aH-indene, provides an even better fit to the experimental spectrum, although its presence should not be considered conclusive. All of these species correspond to minima on the known C₉H₈ potential energy surface [Selby et al., J. Phys. Chem. A, 2023, 127(11), 2577–2590 and Morozov et al., Phys. Chem. Chem. Phys. 2020, 22(13), 6868–6880]. Many of these isomers are not included in kinetic mechanisms that seek to describe the chemical pathways leading to PAHs.

Photodynamic therapy (PDT) still confronts substantial challenges in treating hypoxic tumors within deep-seated tissues, including the lack of oxygen-independent Type I photosensitizers and design principles. In this work, a series of two-photon photosensitizers of naphthalimide-based derivatives are designed by introducing furan/thiophene at the 4-position of NS (1S) and thio/selenocarbonyl modifications and synthesis routes are suggested. Theoretical studies by density functional theory (DFT) suggested that the compounds 1Se-furan2 and 1Se-furan3 exhibit exceptional photodynamic properties including large two-photon absorption cross sections (262.02/183.16 GM in the 650–900 nm therapeutic window), prolonged triplet state lifetimes (828/4487 μs), optimal lipophilicity (logP = 4.53/4.38), and exclusive superoxide anion radical generation via the Type I mechanism with low oxygen dependence. More importantly, the synergistic regulation mechanism of the two-photon response characteristics and type I/II reaction pathways of naphthalimide by heterocyclic substitution and thio/selenocarbonyl modifications is elucidated. A theoretical framework is also presented for the development of two-photon photosensitizers that preferentially undergo Type I reactions, thereby providing stronger tissue penetration and reducing the risk of photodamage.

We present the vibrational photodissociation spectrum of cryogenically prepared complexes of protonated nicotinamide with N₂ in the NH stretching region (3250 to 3600 cm^–1). We analyze the spectrum using quantum chemical methods and vibrational perturbation theory to capture anharmonic effects. The spectrum shows that only the protonation site on the pyridine ring is significantly populated. The calculations indicate that the N₂ tag is attached to the charged site and that it leads to a significant red-shift of the NH⁺ stretching frequency compared to protonated nicotinamide without the presence of the tag.

We perform laser spectroscopy of dysprosium monoxide (DyO) to determine the hyperfine structure of the ground X8 and excited [17.1]7 states in the ¹⁶¹Dy and ¹⁶³Dy isotopologues. These dysprosium nuclei have nonzero nuclear spin and dynamical octupole deformation, providing them high sensitivity to time-reversal-violating new physics via the nuclear Schiff moment (NSM). The DyO molecule was recently identified as being amenable to optical cycling─the basis for many laser cooling and quantum control techniques─which makes it a practical candidate for NSM searches. The measurements reported here are prerequisites to implementing optical cycling, designing precision measurement protocols, and benchmarking calculations of molecular sensitivity to symmetry-violating effects. The measured hyperfine parameters are interpreted using simple molecular orbital diagrams and show excellent agreement with relativistic quantum chemical calculations.

Aromatic polyamide thin film composite membranes have been extensively utilized in water treatment and desalination. However, unintended degradation of these membranes occurs when free chlorine is added to control biofouling. In this study, halogenation and degradation mechanisms of the polyamide monomer model compound, benzanilide (BA), during chlorination in the presence of halides Cl^–, Br^–, and I^– were systematically investigated by a quantum chemical computational method. The results indicate that the reactive amide N and ortho/para-C in the anilide ring of BA undergo the respective concerted and classic S_EAr mechanisms, and their reactivity depends on not only the chlorinating agents but also the speciation and tautomer of substrate BA, which could explain the experimental results observed at different pH. Comparing halogenation of BA by HOX (X = Cl/Br/I) at pH 7.0, notably, the kinetic reactivity order follows Br > I > Cl and I > Br > Cl for the amide N and C sites in the anilide ring, respectively, which can be explained by the “like–attracts–like” principle in the hard–soft-acid–base theory. The degradation of the membrane occurs in the hydrolysis of the chlorinated-BA with the C–N bond cleavage, in which N-halogenated products exhibit remarkably higher reactivity than BA and C-halogenated ones, and hydrolysis catalyzed by acid/base is definitely accelerated. Additionally, some modification strategies to improve the chlorine resistance of the polyamide membrane were proposed. The findings of this work are helpful in further understanding the degradation mechanisms and designing chlorine resistance of polyamide membrane during chlorination.

Trimethyl phosphite (TMPI) is an organophosphorus compound of growing interest in the contexts of fire safety and energetic materials. Yet, its gas-phase combustion kinetics remain largely underexplored. We develop a TMPI kinetic mechanism from first-principles quantum chemistry and master-equation (RRKM/MESS) calculations, supported by reactive molecular dynamics (ReaxFF-MD) to map early time bond activation and product growth. The potential-energy surfaces include C–O and P–O homolysis, hydrogen-atom abstraction (HAA) by Ḣ, ȮH, HȮ₂, ĊH₃, and CH₃Ȯ, and O₂, intramolecular H-transfer, and key association or isomerization steps. Thermochemistry (ΔHf°, S, c_p) and NASA polynomials are provided for all P-bearing intermediates. The model reproduces the expected Arrhenius behavior of ignition delay times (IDTs) for TMPI/air across a temperature range of 900–1500 K and pressures of 1 and 10 bar, with φ values ranging from 0.5 to 2.0. Increasing temperature and pressure shorten the IDT, with richer mixtures igniting faster. Sensitivity and flux analyses identify high-temperature chain branching (H + O₂ ⇌ O + OH) and control of the HO₂/OH pools as primary rate-controlling features, while TMPI–radical reactions that convert radicals to stable products inhibit ignition. Flux maps show HAA-initiated TMPI_R as the universal entry to the radical pool and reveal PO₂ as a central hub that feeds PO, HOPO/HOPO₂, and ultimately PO₃. Hybrid NVT+NVE MD trajectories further indicate an earlier onset of decomposition under adiabatic conditions, consistent with the rapid amplification of radicals once local hot spots are not thermostat-damped. The resulting mechanism and thermochemical set provide a consistent foundation for modeling phosphite oxidation and for comparing phosphite, phosphate, and phosphonate chemistries in fire-inhibition strategies.

Cyanide (CN^–), a highly toxic substance, is prevalent across industrial, agricultural, and natural environments, posing a grave threat to human health and ecosystems. Numerous fluorescent probes for cyanide detection have been developed based on mechanisms such as photoinduced electron transfer (PET) and intramolecular charge transfer (ICT). In this study, a theoretical approach was employed to investigate the sensing mechanism, photophysical properties, and reaction pathways of the TTB fluorescent probe in tetrahydrofuran (THF) solvent. This approach integrates the polarizable continuum model (PCM), time-dependent density functional theory (TD-DFT), and the thermal vibration correlation function formalism (TVCF) to provide a comprehensive understanding of the probe’s properties and behaviors. The photophysical and chemical properties of the fluorescent probe TTB and its cyanide adduct, TTB-CN, were systematically investigated. The results indicate that the TTB probe itself exhibits negligible fluorescence, whereas the product formed upon binding with cyanide demonstrates significant fluorescence emission. This difference is attributed to the substantially lower predicted radiative decay rate (k_r) of TTB compared to that of TTB-CN. Furthermore, the presence of a fluorine atom in TTB enhances the intersystem crossing rate (k_isc) by a factor of 7 relative to TTB-CN. Consequently, the calculated fluorescence quantum yield of TTB is only 0.042%, while that of TTB-CN exceeds 18.14%. These findings provide a scientific basis for the application of TTB as a fluorescent probe. Investigations into the reaction mechanism demonstrate that this reaction proceeds as a nucleophilic reaction featuring a relatively low energy barrier. Additionally, our calculations reveal that both TTB and TTB-CN exhibit two-photon absorption properties, suggesting their potential for two-photon-based detection in biological systems.