The Journal of Physical Chemistry A最新文献

The crossed molecular beam technique was utilized to explore the reaction of dicarbon C₂ (X¹Σ_g⁺/a³Π_u) with 2-methyl-1,3-butadiene (isoprene, CH₂C(CH₃)CHCH₂; X¹A') at a collision energy of 28 ± 1 kJ mol^-1 using a supersonic dicarbon beam generated via photolysis (248 nm) of helium-seeded tetrachloroethylene (C₂Cl₄). Experimental data combined with previous ab initio calculations provide evidence of the detection of the hitherto elusive methyl elimination channels leading to acyclic resonantly stabilized hexatetraenyl radicals: 1,2,4,5-hexatetraen-3-yl (CH₂CC^•CHCCH₂) and/or 1,3,4,5-hexatetraen-3-yl (CH₂CHC^•CCCH₂). These pathways are exclusive to the singlet potential energy surface, with the reaction initiated by the barrierless addition of a dicarbon to one of the carbon-carbon double bonds in the diene. In combustion systems, both hexatetraenyl radicals can isomerize to the phenyl radical (C₆H₅) through a hydrogen atom-assisted isomerization─the crucial reaction intermediate and molecular mass growth species step toward the formation of polycyclic aromatic hydrocarbons and soot.

Spin-polarized magnetic systems, generated by the interaction of photoactive molecules with light, play a key role in a wide range of scientific applications. Representative examples are OLEDs, organic photovoltaics, and singlet fission. Further, they are important intermediates in certain biological processes including photosynthesis and, possibly, avian magnetoreception. Transient continuous-wave electron paramagnetic resonance (trEPR) spectroscopy is a powerful tool to reveal the temporal evolution of nonequilibrium spin states, which contains valuable information on any photoinduced dynamic processes occurring in these systems. For the analysis of the recorded trEPR data, simulations are essential. While the simulation of static trEPR spectra is supported well by tools like EasySpin, the simulation of time-resolved trEPR data is less developed. Here, we introduce teacups, a new freely available and well-documented Python-based routine for the simulation of the temporal evolution of trEPR spectra. The internal dynamics of different spin-polarized systems can be analyzed, thereby enhancing our mechanistic understanding. In this manuscript, we explain the theoretical background and provide a description of the features and setup of teacups. Further, a step-by-step example for data analysis is provided.

Exciplexes are pivotal in organic light-emitting diodes and photovoltaics. However, their formation and emission in nonpolar solvents remain unclear. Revisiting Weller's works on photoinduced electron transfer (PET) rates and exciplex emission based on electrochemical redox potentials, we investigate exciplex behavior in cyclohexane using anthracene (Ant) as an acceptor and N,N-dimethylaniline (DMA) derivatives as donors. Employing steady-state and time-resolved spectroscopy, electrochemistry, and density functional theory (DFT) calculations, we demonstrate that electrochemical redox potentials alone inadequately explain the exciplex behavior in nonpolar environments. Our DFT analysis reveals that the C-N rotational angle of the dimethylamine group of a donor influences the highest occupied molecular orbital (HOMO) energy levels, affecting quenching processes. Furthermore, time-dependent DFT simulations accurately reproduce experimental exciplex emission spectra, linking emission intensity to donor contribution in the exciplex HOMO. These findings deepen the understanding of exciplex behavior in nonpolar media and provide insights for designing and interpreting exciplex-based optoelectronic materials.

We have presented the theory, implementation, and benchmark results for the one-electronic variant of spin-free exact two-component (SFX2C1e) linear response coupled cluster (LRCCSD) theory for static and dynamic polarizabilities of atoms and molecules in the spin-summed formulation. The resolution of identity (RI) approximation for two-electron integrals has been used to reduce the computational cost of the calculation and has been shown to have a negligible effect on accuracy. The calculated static and dynamic polarizability values agree very well with the more expensive X2C-LRCCSD and the experimental results. Our calculated results show that accurate predictions of polarizabilities of atoms and molecules containing heavy atoms require the use of a large basis set containing an adequate number of diffuse functions, in addition to accounting for electron correlation and relativistic effects.

The oxy-fuel combustion of biochar connected with carbon capture, storage, and utilization technologies is an environmentally beneficial alternative for the replacement of fossil fuels. Biochar itself consists of porously stacked layers of hydrocarbons containing several heteroatoms, such as oxygen, nitrogen, and sulfur. At present, only limited information on the combustion mechanisms for oxygen and nitrogen functionalities is available in the literature; specific information on the combustion mechanisms of sulfur-containing groups (SFGs) is lacking. In this study, we present electronic structure calculations to uncover the mechanisms of the initial oxidation reactions of SFGs. Furthermore, it is examined if the reaction mechanisms remain similar or change with increasing system size. For this purpose, we apply an automatized workflow combining reactive molecular dynamics simulations with static electronic structure calculations at different levels of theory. The results show that terminal groups such as thiols, sulfonic acids, thioketones, and S,S-dioxides follow similar reaction pathways. These SFGs are all gradually oxidized before they eventually are eliminated as SO_x(H_y) species from the carbon framework. Embedded thiophenes follow somewhat different reaction pathways that lead to the elimination of HOS· radicals or carbonyl sulfide (COS), depending on the system size. For the found oxidation channels, we report reaction and activation energies and rate constants that can be used to improve comprehensive kinetic models for the combustion of sulfur-containing biochar as a biomass-based renewable energy source.

Nitreones are compounds with the general formula L → N⁺ ← L'. These compounds exhibit medicinal properties and have found applications in phase transfer catalysis. A few nitreones are cyclic; protonated cycloguanil (an antimalarial agent) is the most prominent example. Recently, a few more cyclic compounds were experimentally reported, in which the central N⁺ was shown to exhibit nitreone character. This led to attention being paid to the chemistry of neutral cyclic nitreones. A thorough literature search led to two sets of cyclic nitreones: C → N ← C type and P → N ← P type. In this work, we report quantum chemical analysis in exploring the electronic structure of neutral cyclic nitreones. Molecular orbital analysis, electron density analysis, charge, electron localization function (ELF), complexation energy values, and Tolman electronic parameter (TEP) all indicate that the studied compounds do carry nitrogen in the N(I) oxidation state and the two lone pairs are at the central nitrogen; thus, they qualify to be considered as cyclic nitreones.

Furfural is a typical representative molecule of furan compounds and an important intermediate species in the oxidation of furan derivatives. The rate constant of furfural with OH is calculated for the first time using a high-level quantum chemistry method combined with the Rice-Ramsperger-Kassel-Marcus theory/master equation method. The M06-2X/jun-cc-pVTZ method was used to construct the potential energy surface of the reaction path. The preliminary reactions can occur through three different pathways: H-abstraction from the furan ring, H-abstraction from the side chain, and a preliminary OH-addition. The pathways via the OH-addition mechanism of the furfural + OH system were superior to H-abstraction in the temperature range of 298-400 K. When the temperature exceeds 400 K, the H-abstraction will be faster. Moreover, with the increase of pressure, the competition of the pathway via the OH-addition mechanism in the low-temperature region will gradually weaken. Under low-temperature conditions, INT1 and INT4 are the main intermediate species. The formation of bimolecular products, the 2-furanol (P7) + aldehyde group and the (3E)-4-hydroxybuta-1,3-diene-1-one (P8) + aldehyde group at C(2) and C(5) sites, are the main reaction pathways via the OH-addition mechanism. The formation of (2-furanyl)(oxy) methyl (P4) + H₂O (i.e., R4) always dominates for the four H-abstraction reactions. For the initial H-abstraction reaction, there is no pressure dependence, but for the preliminary OH-addition reaction, there is a significant positive pressure dependence. This work not only provides the necessary rate constants for modeling development but also provides theoretical guidance for the practical application of furan-based fuel.

The formation of nitrogen- and sulfur-containing organic compounds (N-Org and S-Org) is important for atmospheric secondary organic aerosol (SOA) production, thereby influencing air quality and global climate. However, the mechanisms underlying N-Org and S-Org formation on aerosol particle surfaces are poorly understood due to the limited availability of surface-sensitive analytical techniques. This study investigates the surface interactions of glyoxal (GL), a known SOA precursor, with ammonium sulfate (NH₄)₂SO₄, under varying relative humidity (RH) conditions, using ambient-pressure X-ray photoelectron spectroscopy (APXPS), near-edge X-ray absorption fine structure (NEXAFS) spectroscopy, and molecular dynamics (MD) simulations. N-Org species, such as imines, a key intermediate in brown carbon (BrC) formation, are identified on the (NH₄)₂SO₄ surface at low RH (≤13.3%). The formed S-Org species cannot be specified due to the difficulties in distinguishing S-Org from inorganic sulfate in the XPS spectra. Elemental ratios on (NH₄)₂SO₄ surface across the entire probing depth show increased S/O and N/O ratios upon GL exposure, indicating the formation of N-Org and S-Org species. NEXAFS measurements further confirm the surface changes of (NH₄)₂SO₄ associated with the adsorption of GL and water. These findings provide compelling evidence of surface-driven N-Org and S-Org formation pathways, demonstrating that heterogeneous reactions on (NH₄)₂SO₄ particle surfaces could be an active source of atmospheric BrC and SOA.

Aliphatic hydroxyamino acids, namely, α-hydroxyglycine, α-hydroxyalanine, serine, threonine, and homoserine, were studied by quantum chemical calculations using two methods in water as a solvent. A hybrid variant of DFT-B3LYP was applied to optimize the geometry of neutral molecules, molecular cations, and anions for the canonical and zwitterionic form of amino acids. In the energy minimum, vibrational analysis was applied, enabling the evaluation of thermodynamic functions (internal energy, enthalpy, entropy, and Gibbs energy) of individual species and absolute oxidation and reduction potentials for redox couples. In the B3LYP preoptimized geometry, the advanced DLPNO-CCSD(T) method was applied to include the major part of the interelectron correlation energy. Calculated molecular descriptors were compared with previously studied molecules by the same method, and the whole set for 17 amino acids was processed by advanced statistical methods such as cluster analysis and principal component analysis. Calculated oxidation potentials correlate with the adiabatic ionization energies along a straight line, and analogously, the calculated reduction potential correlates with the electrophilicity index. The ionization energy in α-amino acids is systematically influenced (reduced) by the functional groups such as hydroxyl, methyl, ethyl, and iso-propyl; it decreases along a series of α-, β-, γ-, and δ-amino acids.

With the application of nonfullerene acceptors (NFAs) Y6 and its derivatives, the power conversion efficiencies (PCEs) of single-junction organic solar cells (OSCs) have exceeded 20%. Side-chain engineering has proven to be an important strategy for optimizing Y6-based NFAs. However, studies on the incorporation of conjugated side chains into Y6-based NFAs are still rare, and the corresponding underlying mechanisms are still not well understood. In this article, we systematically designed eight molecules based on modifications to the conjugated side chains of two reported Y6-based NFAs, involving alterations of branched alkyl chains at different positions on the thiophene, benzene, bithiophene, and benzene-thiophene moieties that serve as conjugated side chains. Using reliable density functional theory (DFT) and time-dependent DFT calculations, we obtained key photovoltaic parameters such as molecular planarity, dipole moments, electrostatic potential and corresponding fluctuations, frontier molecular orbitals, exciton binding energy (E_b), singlet-triplet energy differences (ΔE_ST), and UV-vis absorption spectra of these newly designed NFAs. The results show that the side conjugated rings and the positions of lateral alkyl chains attached to these rings exert noticeable influences on their photoelectric properties. Notably, compared to the prototype T3EH, 2T2EH, 2T3EH, PT2EH, PT3EH, and P2EH exhibit enhanced absorption (manifesting as increased total oscillator strength) and smaller E_b and ΔE_ST values, hinting at their promising potential as novel NFAs.