The Journal of Physical Chemistry A最新文献

Singlet fission (SF) is attracting attention due to its potential applications in organic photovoltaics, quantum computing, and dynamic nuclear polarization. In this article, we have theoretically investigated the potential of 4,4′-diphenoquinone (1a) as a promising backbone for efficient SF chromophores. Single-reference ab initio correlated methods were employed to investigate the excited states of 1a. A strong photoabsorption is predicted for the S₀–S₃ transition, which is described by HOMO–LUMO excitation. Although the excitation energies of S₃ and T₁ states satisfy the exothermic energy matching condition of SF, internal conversion from the S₃ to a low-lying nπ* singlet excited state may suppress the efficient generation of ¹(T₁T₁) in the condensed phase. We have demonstrated that the obstacle of 1a can be overcome by introducing typical donors or halogen atoms and fusing aromatic six-membered ring(s) while retaining the advantages of the diphenoquinone backbone.

The composite of quantum dots (QDs) with graphene (GR) has significantly enhanced its potential for optoelectronic applications. Although existing research has experimentally confirmed the excellent optoelectronic properties of quantum dots-graphene (QD-GR) heterostructures, the underlying charge transfer mechanisms have not been fully elucidated. This study uses the Marcus theory to investigate the photoinduced charge transfer characteristics of QD-GR heterostructures under external electric field (F_ext) modulation. We first constructed a lead sulfide quantum dots-graphene (PbS QD-GR) heterojunction model using a minimal-sized lead sulfide quantum dots (PbS QDs) cluster and a single-layer flake graphene. Next, we systematically analyzed the electronic state distribution at the interface and elucidated the essential mechanism underlying the heterojunction’s structural stability. The excited state properties of the PbS QD-GR heterojunction under F_ext modulation were systematically investigated. Finally, based on Marcus theory, the reorganization energy (λ), Gibbs free energy (ΔG) and electron coupling matrix element (V_da) were quantitatively calculated to reasonably predict the charge transfer rate (K). The study revealed that the charge separation rate significantly exceeds the charge recombination rate (KCS ≫ KCR), demonstrating the heterostructure’s exceptional exciton dissociation capability. Our findings elucidate the trend of charge transfer parameters in specific PbS QD–graphene heterojunctions under external electric fields, thereby providing theoretical support for a deeper understanding of optoelectronic device performance.

A software implementation of analytic geometric derivatives of electron-repulsion integrals up to second order is presented for the modeling of vibrational spectroscopies at the level of first-principles Kohn–Sham density functional theory (DFT). In line with the general goals of the VeloxChem program, it targets efficient execution in high-performance computing environments with a hybrid MPI/OpenMP parallelization model and is based on the technique of automatic C++ code generation for high versatility. Gradient calculations scale identically with conventional Fock matrix constructions, and also with the prefactor taken into account, the computational cost of the gradient is significantly lower than that of the self-consistent field (SCF) optimization of the reference state. The Hessian calculation shows a scaling of N^3.5 with N being the number of contracted Gaussian basis functions. The computational bottleneck in the Hessian calculation is the solving of the coupled-perturbed Kohn–Sham equations that with VeloxChem can be offloaded to GPU-accelerated nodes. The large-scale virtues of the presented software module are demonstrated by the DFT/B3LYP calculation of the IR spectrum of the entire ubiquitin protein with 1,152 atoms in the quantum mechanical (QM) region and TIP3P water in the molecular mechanics (MM) region. The simulated amide I band shows to be in excellent agreement with experiment.

Carboxylic acids are ubiquitous in the atmosphere in both the gas and particle phase. One of their major degradation pathways is known to be their reaction with OH radicals. To enhance our understanding of carboxylic acid reactivity, we investigated the gas phase reactions of OH radicals with a series of these acids by performing quantum chemistry calculations at the ωB97X-V/def2-TZVPPD, ωB97M-V/def2-TZVPPD, CCSD(T)/6–311+G(2df,2p), and CCSD(T)/aug-cc-pVTZ level. Our calculations are mainly focused on the reactive decarboxylation pathway energetics that occur following the OH-driven abstraction of the carboxylic hydrogen of formic, acetic, malonic, fumaric, maleic, trifluoroacetic, and trichloro-acetic acids. All the reactions are exoergic, and in all cases, we find that a hydrogen-bonded complex with a 6-membered ring structure is formed between the acid group and the OH, followed by reactive decarboxylation with small or nonexistent barriers to both abstraction and decarboxylation steps. Finally, in the case of trifluoroacetic acid decarboxylation, we calculate the energetics of several pathways that may lead to stable oxidation product formation, and we compare our theoretical work to other experimental and theoretical studies.

We report a synchrotron radiation-based study of the simplest Polycyclic Aromatic Hydrocarbon (PAH) molecule, naphthalene, in the energy region 35,000–88,000 cm^–1 (4.4–10.9 eV). A complete spectral analysis of the VUV region is carried out for the first time, and several new bands are reported, while reassignments are made for many of the bands reported earlier. An extensive Rydberg series converging to the first seven ionization energies of naphthalene are observed, interspersed with several valence transitions. Rydberg series of ns, np, and nd types are assigned based on quantum defect analysis and correlated with theoretical calculations. Time-dependent density functional calculations performed using several functionals and basis set combinations helped in verifying and consolidating spectral assignments. From the absolute absorption cross-section data, the UV–VUV photolysis rates at different altitudes are estimated. It is found that the lower limit to the photolysis lifetime varies from ∼1 h at 20 km to ∼4 s at 50 km. Potential energy curves of the first few singlet and triplet excited states with respect to C–H bond length do not show any evidence of direct dissociation, thus implying that the H loss channel may not be very prominent in neutral naphthalene, in contrast to cationic naphthalene.

Halogen bonds (XBs) are a cornerstone of supramolecular chemistry, yet their response to external perturbations remains poorly investigated, particularly in systems with heavy elements where relativistic effects are significant. We benchmark two prototypical iodine-chloride X-bonded complexes, ClI···N(CH₃)₃ and ClI···NCH, under electric fields (EFs) using quantum chemical calculations up to CCSD and CCSD(T). Relativistic basis sets, including the all-electron jorge-TZP-DKH, are assessed against non-relativistic and pseudopotential-based alternatives (def2-TZVP, SDD, LANL2DZ) for their impact on XB geometries, binding energies, vibrational Stark shifts, and electron density redistribution. Explicit relativistic treatments substantially reduce the exaggerated field response otherwise observed. Benchmarking M06-2X and B3LYP with various basis sets against correlated methods confirms the accuracy of M06-2X, while showing that the relativistic effects included in the basis set influence the results more than the choice of functional itself. Symmetry-Adapted Perturbation Theory (SAPT) indicates that electrostatics dominate XB stabilization, with induction becoming more relevant under strong positive fields. Overall, XBs prove markedly more sensitive to external EFs than H-bonds across different field arrangements.

As a typical dielectric ceramic material, BaTiO₃ has attracted considerable interest owing to its high dielectric constant. Using a combination of high-pressure AC impedance spectroscopy, Raman spectroscopy, and theoretical calculations, this study investigated the structural and electrical properties of nanocrystalline BaTiO₃ at pressures of up to 30 GPa. The material underwent two phase transitions: from a mixed orthorhombic/tetragonal phase to a pure tetragonal phase and finally to a cubic phase. The superior dielectric constant of the tetragonal phase, compared to that of the other two phases, results from the rapid polarization switching of its 180° domains. The phase transition from the tetragonal phase to the cubic phase leads to a transformation from mixed ionic–electronic conduction to pure electronic conduction, as the high migration energy barrier in the cubic phase hinders ionic conduction. This work demonstrates that applying pressure is a feasible strategy to enhance the dielectric performance of BaTiO₃-type dielectrics.

Thermodynamic properties of real gases can be accurately described using realistic intermolecular potential energy surfaces. In this work, a first-order correction to the ideal gas equation of state is introduced through the computation of the classical second virial coefficient, B(T), derived from the configurational partition function, which explicitly depends on the intermolecular interaction potential. As a case study, the double many-body expansion (DMBE) potential energy surface for the ground electronic state of the N₂H₂ system was employed to derive pairwise interaction potentials for H₂···N₂ and NH···NH. These potentials were used to numerically evaluate the canonical partition function. Second virial coefficients, compressibility factors, and constant-volume heat capacities were computed in the temperature range 30–2000 K. The calculated B(T) values for H₂···N₂ are in good agreement with previous literature data, while the results for NH···NH lie within expected trends observed for similar systems.

Molecular-scale materials with bistable behavior and tunable properties are increasingly relevant for next-generation nanoscale electronic devices. Helical foldamers are promising candidates, but their structural and mechanical properties are highly sensitive to conformational stability and environmental conditions. A systematic methodology based on quantum-chemical calculations is proposed for assessing solvent-dependent mechanical behavior, combining analysis of π–π stacking interactions, conformational energetics, and environmental effects. Using this methodology we identified simple design principles for the rapid screening of new compounds, allowing evaluation of their conformational stability and effective mechanical rigidity. Applying these principles, we identify a modified helical aromatic foldamer that exhibits improved mechanical and stability characteristics compared to the initial reference compound.

In this study, we investigated the exceptional basicity of diazahelicenes through a comprehensive computational analysis using DFT calculations. Eighteen diazahelicene compounds were examined and compared with 1,8-bis(dimethylamino)naphthalene (DMAN), revealing that most exhibit stronger basicity than DMAN, qualifying them as proton sponges. The study employed the M06-2X functional with the def2tzvp basis set to analyze proton affinity, gas-phase basicity (GB), and structural changes upon protonation. We found that the basicity is significantly influenced by the interplanar angle, hydrogen bonding, conjugation, and aromaticity of the compounds. Most compounds demonstrated a decrease in interplanar angle upon protonation, with compounds containing nitrogen atoms in close proximity showing frustrated base behavior. Aromaticity analysis using HOMA (Harmonic Oscillator Model of Aromaticity) and Nucleus-independent Chemical Shift indices indicated enhanced electron delocalization after protonation. Further insights into electronic structure and bonding were obtained through AIM (atomic in molecules), MEP (molecule in electrostatic potential), NBO (Natural Bonding Orbital), ELF (electron localization function), and LOL (Localized Orbital Locator) analyses, providing a comprehensive understanding of the factors contributing to the exceptional basicity of these compounds.