The Journal of Physical Chemistry Letters最新文献

Isotope-selective photodissociation is a promising route to laser-based separation, yet its efficiency remains constrained by fixed molecular cross sections. Here, we introduce an active optical-switching strategy that utilizes a nonresonant ultraviolet control pulse to generate and tailor isotopologue-specific Fano resonances. By coupling high-lying vibrational levels of the electronic ground state to a dissociative continuum, this pulse dynamically modulates photodissociation cross sections without direct electronic excitation. Using full quantum wave packet simulations of HF and DF isotopologues, we demonstrate that the photofragment yield ratio can be reversibly switched by orders of magnitude through tuning of the probe frequency across a light-induced resonance. This approach enables selective suppression or enhancement of dissociation for a target isotopologue with high spectral precision. Our work establishes a versatile and efficient mechanism for isotope-selective photochemistry and opens a pathway toward coherent optical control of molecular photodissociation.

The sudden polarization (SP) effect converts a resonant zwitterionic state into a polarized charge-separated (CS) state, yet its dynamics in stable diradicaloids remain insufficiently understood. Here we investigate a pair of C₂-symmetric sulfone-functionalized Chichibabin’s hydrocarbons with nearly degenerate zwitterionic states but differing in symmetric electron-withdrawing groups (EWGs). Femtosecond transient absorption spectroscopy directly captures subpicosecond SP processes in both systems and, together with quantum-chemical calculations, reveals the thermodynamic accessibility of the CS state governed by solvent polarity and excitonic coupling. Increasing solvent polarity facilitates the SP effect, which leads to full charge separation via the relaxation of polarized zwitterionic states. Additionally, weakening excitonic coupling through the substituent effect allows the CS state to be accessible across all polar media. These results establish the SP effect as the trigger for symmetry breaking and establish tunable substituents and dielectric environments as effective handles for directing SP relaxation dynamics in symmetric diradicaloids.

Artificial arrays of tin phthalocyanine molecules have been studied on Pb(100) using scanning tunneling microscopy (STM). The molecules adopt two azimuthal orientations with distinct spin states, which results in a checkerboard pattern in STM images. Upon converting the central molecule by current injection from its pristine state with the Sn ion above the molecular plane to a conformation with Sn between the macrocycle and the substrate, the orientations of all molecules are swapped. This cooperative rotation is modeled by combining the potential energies of the intermolecular and the molecule–substrate interactions.

The elasticity of adsorbates is relevant for many applications of porous materials. Theoretical studies predict a pronounced increase of elastic moduli for adsorbates under nanoconfinement, but an experimental confirmation is still missing. Here we present an ultrasonic study on the longitudinal modulus β_Ar,ads of liquid argon in porous glass samples with different pore radii between 1.8 and 12.8 nm. The analysis of the measured moduli of empty, β₀, and filled samples, β, reveals that the modulus of the adsorbate, β_Ar,ads, increases linearly with the inverse pore radius, 1/r_P, as predicted by theory.

We studied the interaction between salts and surfactants at the water surface using heterodyne-detected vibrational sum-frequency generation (HD-VSFG) spectroscopy. We used sodium dodecyl sulfate (SDS) as a prototype surfactant system at 75 μM bulk concentration in water, and measured the vibrational response of the OH band of near-surface oriented water molecules and the CH bands of the hydrophobic tails of the surfactant. We observed a dramatic enhancement of the surface density of the negatively charged SDS (DS^–) within a narrow range of added salt concentrations. We demonstrated this increase is strongly ion-specific and induced by the screening of the lateral Coulomb repulsion of the sulfate headgroups by the added cations, followed by strong hydrophobic interactions (hydrophobic collapse) when the DS^– surface density reaches a critical value. For a solution of 75 μM SDS, the required concentrations of CsCl, KCl, and NaCl for this transition are 2, 5, and 10 mM, respectively.

In this study, we use low-energy electron diffraction, X-ray photoelectron spectroscopy, temperature-programmed desorption, and density functional theory calculations to unveil that low-energy electron irradiation (140.8 eV) induces local reconstruction of the irradiated area on the anatase TiO₂(001)-(1 × 4) surface to the (1 × 1) domain, accompanied by the formation of Ti³⁺ species in the subsurface region and subsurface oxygen vacancies/surface hydroxyl groups, whereas the unirradiated regions retain the (1 × 4) periodicity. The low-energy electrons locally stimulate desorption of oxygen from the anatase TiO₂(001)-(1 × 4) surface probably via interatomic Auger processes, creating surface oxygen vacancies with associated Ti³⁺ species that consequently trigger the local (1 × 4) → (1 × 1) surface reconstruction. Such a local surface reconstruction process is facilitated by surface hydroxyl groups. The created surface oxygen vacancies and Ti³⁺ species tend to migrate into the bulk, leading to a recovery of the (1 × 4) surface structure. The anatase TiO₂(001)-(1 × 1) domain provides reactive Ti_5c surface sites with a much larger density than the reactive Ti_4c surface sites on the corresponding anatase TiO₂(001)-(1 × 4) surface. These results demonstrate the sensitivity of TiO₂ surface structures to the surface reduction, which commonly occurs for TiO₂-involved (photo/electro)catalysts.

Offshore oil spills and oily wastewater cause severe water pollution. Membrane separation offers a promising solution for efficient oil–water separation; however, conventional membranes often exhibit poor fouling resistance and face a trade-off between flux and separation efficiency due to mismatched pore sizes. To overcome these challenges, we developed a hydrolyzed polyacrylonitrile by tetraethyl orthosilicate modification (HPANT) nanofibrous membrane based on the synergistic mechanism of selective wettability and pore-size exclusion. And it achieves superhydrophilicity and underwater superoleophobicity, with the pore size regulated to ∼20 nm. This design achieves excellent fouling resistance and separation efficiencies of 98.29% for immiscible mixtures and 97.80% for surfactant-stabilized emulsions, with high fluxes of 6,941.5 L·L·m^–2·h^–1·bar^–1 and 8,379.6 L·m^–2·h^–1·bar^–1, respectively. Multiscale simulations (DFT, MD, FEM) further clarify the dual mechanism: the stable hydration layer resisting oil adhesion and tailored nanopores providing a physical barrier. This strategy provides guidance for the development of oil–water separation membranes.

Bowl-shaped polycyclic conjugated aromatic hydrocarbons have received tremendous attention because of their structural diversity and potential functionalization of their derivatives in fields such as spintronics, energy storage, etc. However, the topological electronic states of these organic buckybowl sumanenes have been less explored. Here we study the first- and higher-order topological states of a two-dimensional buckybowl supramolecular crystal of sumanene using density functional theory calculations and Wannier-based tight-binding models. A higher-order topological insulating state at the Fermi level is unveiled, which is demonstrated by the fractional corner charge and localized corner states in triangular nanodisks. The periodic arrangement of concave buckybowl sumanene yields a prototypical breathing Kagome lattice that hosts valley-contrasting Berry physics in its first conduction bands. The rationally designed one-dimensional atomic boundary, namely, sumanene zigzag edge, hosts the topologically protected kink states. This work establishes a typical example of coexisting first- and higher-order topology in an organic buckybowl sumanene, opening new avenues for engineering hierarchical topological phenomena through molecular curvature control in complex organic frameworks.

Metastable materials are attractive candidates for new catalysts, electrodes, and unconventional superconductors. Their unusual properties are rooted in nonstandard bonding, oxidation states, or coordination. However, potential applications of metastable materials are understudied, as it is difficult to obtain them via standard high-temperature solid-state synthesis methods, which result in the most thermodynamically stable products. Here, we computationally model a photochemical reaction that transforms synthetically available semiconducting crystals with a general formula K₂X₂ (X = S, Se, Te) into metastable materials with hypervalently bonded chains. The proposed reactions are an extension of well-documented ultrafast light-induced phase transitions, indicating the plausibility of these transformations under similar conditions.

Nuclear quantum effects of protons on electronic excitations in hydrogen-bonded organic materials remains underexplored. In theoretical studies, modeling excitons in these extended systems is particularly difficult, because they tend to have a large exciton binding energy and sometimes exhibit charge transfer character. We demonstrate how first-principles Green’s function theory combined with the nuclear-electronic orbital method enables us to examine the nature of excitons in a prototypical organic solid of eumelanin, for which extensive hydrogen bonds have been proposed to facilitate the formation of delocalized excitons. We investigate how the quantization of protons impacts electronic excitations. We discuss the extent to which the resulting proton quantum effects can be described as being derived from the structure and how they induce molecular-level anisotropy for the excitons in the organic solid.