The Journal of Physical Chemistry A最新文献

Fully nonfused ring electron acceptors (NFREAs) have attracted growing attention as cost-effective alternatives to fused-ring electron acceptors (FREAs) in organic solar cells (OSCs). However, their molecular frameworks, linked entirely by single bonds, typically result in wider bandgaps, limited near-infrared (NIR) absorption, and poor electron mobility, leading to inferior performance compared to FREAs. In this work, we propose a molecular engineering strategy to design olefin-bridged NFREAs (OB-NFREAs) by introducing olefin bridges into the fully nonfused backbone of TBT-26. Theoretical calculations indicate that all OB-NFREAs, namely D-O1, D-O2, and D-O3, demonstrate a significant enhancement in optoelectronic performance. The olefin double bonds extend π-conjugation, reduce the bandgap, and improve molecular planarity. Consequently, the absorption edge of the absorption range of OB-NFREAs expands from 300 to 900 nm (TBT-26) to 300–1200 nm (D-O3), with a significant redshift of the absorption peak to 895 nm and 1.8-fold increase in integrated absorption intensity. Moreover, electron mobility is substantially enhanced, with D-O1 reaching 1.14 × 10^–3 cm² V^–1 s^–1, which is more than an order of magnitude higher than that of TBT-26. These results indicate that rational olefin bridge design can enhance π–π stacking, facilitate more efficient charge transfer, improve electron mobility, and redshift the absorption spectrum. Fine-tuning olefin bridges is thus a powerful strategy for constructing NFREAs with high mobility and strong NIR absorption, paving the way for next-generation organic photovoltaic materials.

A transparent, data-driven route to improve approximate density functionals by learning only the position dependence of an exact-exchange admixture in local hybrid functionals is discussed. Motivated by the scarcity of exact constraints for valence regions and by gauge ambiguity issues of exchange-energy densities, we replace hand-crafted inhomogeneity measures by neural-network local mixing functions (n-LMFs) evaluated on rung-3 or rung-4 descriptors while keeping the overall structure of the functional transparent and explainable. This limited use of machine learning (ML) has already provided a number of practical outcomes. The LH24n-B95 and LH24n functionals achieve broad main-group accuracy and, strikingly, suppress gauge artifacts without use of so-called calibration functions. The reasons for the latter observation can be visualized and analyzed directly in real space. Extending the idea to rung-5 functionals leads to the first local double hybrids in which a position-dependent exact-exchange admixture is paired with an SCS-PT2 correlation, delivering consistent gains over constant-mixing analogues. To escape the zero-sum game between delocalization errors and static-correlation errors, an n-LMF has subsequently been trained in the presence of an explicit strong-correlation factor. The resulting LH25nP functional combines the so far best rung-4 performance for main-group energetics with improved spin-restricted bond-dissociation curves, fractional-spin behavior, and reduction of spin-contamination artifacts, while remaining numerically robust. The limited ML approach preserves explainability and facilitates the transfer of insights back to rational designs.

Formamide (HCONH₂), the simplest organic molecule with a peptide bond, has been detected in various interstellar environments and is regarded as a potential precursor to essential biomolecules, such as amino acids and nucleic acids. Many of the proposed synthetic routes involve its ionized and protonated forms in the interstellar medium, where ion–molecule gas-phase reactions are predominant. However, spectroscopic data on cationic and protonated formamide is limited. In this work, we report the first bare-ion and Ne-tagged broadband vibrational spectra of isomeric forms of the formamide cation [HCONH₂]⁺ (m/z 45) and protonated formamide [HCONH₂]H⁺ (m/z 46). The vibrational spectra were obtained using two techniques, leak-out spectroscopy and Ne-tagging infrared predissociation spectroscopy, in a cryogenic 22-pole ion trap at the infrared free-electron laser facility HFML-FELIX. The measured spectra within the fingerprint region 650–1800 cm^–1 are compared to anharmonic vibrational frequency calculations at the B2PLYP-D3/aug-cc-pVTZ level of theory for structural identification and band assignments. For the formamide cation, spectral signatures of both the low-energy aminohydroxycarbene isomer (NH₂–C^•+–OH) and the higher-energy canonical cation (HCONH₂^•+) were detected, while protonated formamide was observed exclusively as the more stable O-protonated isomer with no indication of N-protonation. Additionally, a comparative analysis of the two spectroscopic techniques, supported by potential energy surface and vibrational frequency calculations, highlights how the weakly bound Ne tag subtly affects the vibrational signatures of the ions.

Optical emission spectroscopy was used to spatially resolve excited OH (OH*) emission as a function of height along the flame for nitromethane (NM) combusting in both inert and oxidative environments at 34 bar. Emission spectra from OH A²Σ⁺ → X²Π relaxation show that electronically excited OH* emission persists over the length of a nitromethane flame in air, but emission diminishes abruptly within several millimeters of nitromethane flames burning in inert atmospheres (N₂). These findings mark the first reported instances of spatially resolved spectral images of NM combustion at elevated pressures and provide important benchmarks for monopropellant combustion models, where number densities of products and intermediates are often reported as a function of distance from a nominal flame front. Vibrational and rotational temperatures calculated as a function of distance along the flame are compared to Cantera-simulated adiabatic flame temperatures. OH* rotational temperatures appear thermalized, although vibrational temperatures suggest that the radical possesses excess vibrational energy. Additionally, vibrational temperatures are used to infer the formation pathway─chemical vs thermal─of OH* as a function of height within the flame.

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.