J Phys Chem A [JOURNAL]
Sun
200 papers
Exploring the Copper(I)-Catalyzed Azide-Alkyne Cycloaddition: A Unified Reaction Valley Approach and Local Vibrational Mode Study.
McKenna L, Sexton TM, Freindorf M … +1 more , Kraka E
J Phys Chem A · 2026 Jul · PMID 42301271 · Publisher ↗
The mechanism of the copper(I)-catalyzed azide-alkyne cycloaddition (CuAAC), an adaptable, regioselective, and high-yielding click reaction, was investigated using the Unified Reaction Valley Approach (URVA) and Local Mo...
The mechanism of the copper(I)-catalyzed azide-alkyne cycloaddition (CuAAC), an adaptable, regioselective, and high-yielding click reaction, was investigated using the Unified Reaction Valley Approach (URVA) and Local Mode Analysis (LMA). The cycloaddition and ring contraction steps of catalysis via both mononuclear and dinuclear catalysts, in the form of Cu(I)-acetylides forming 1,4- and 1,5-products, were explored at the B3LYP/cc-pVTZ level of theory as well as at the CCDT(T) level. The dinuclear mechanism for 1,4-addition was found to have the lowest activation energy and was identified as the most effective catalytic pathway. With the first cycloaddition step presenting the highest energy barrier, single-point energy calculations showed that this barrier is lowest for the dinuclear catalyst, while LMA suggests that regioselectivity may arise from catalyst dissociation and stronger stabilization of the final product. URVA analysis indicated that the transition state of the first step occurs prior to any C-N bond formation, signifying that the energy barrier originates from initial electronic structural changes. These mechanistic insights provide a basis for the design of more efficient CuAAC catalysts.
Photochemistry of Sodium Pyruvate Clusters.
Madlener SJ, Reimann M, Hartmann JC … +3 more , van der Linde C, Ončák M, Beyer MK
J Phys Chem A · 2026 Jul · PMID 42300025 · Publisher ↗
Pyruvate is frequently found in aged sea salt aerosols. To test the influence of the salt environment on the photochemistry of pyruvate, small model clusters were generated from sodium pyruvate salt using electrospray io...
Pyruvate is frequently found in aged sea salt aerosols. To test the influence of the salt environment on the photochemistry of pyruvate, small model clusters were generated from sodium pyruvate salt using electrospray ionization. These clusters were studied using Fourier-Transform Ion Cyclotron Resonance mass spectrometry (FT-ICR MS). UV/vis spectra were recorded using a tunable optical parametric oscillator (OPO) system. Additionally, photokinetics as well as sustained off-resonance irradiation (SORI) collision-induced dissociation (CID) experiments help to further understand the mechanisms responsible for the fragmentation of the studied systems. Quantum chemical calculations allow assignment of the transitions responsible for the absorptions. The clusters mainly fragment by losing sodium pyruvate units, NaPyr, resulting in NaPyr fragments. Photodissociation cross sections for nonstoichiometric fragmentation are around 2 orders of magnitude lower. We found that the formation of these fragments starts with the C-C bond photolysis of a pyruvate anion and can lead to several secondary fragments. For the two larger cluster sizes, neutral CHCOCOO is lost, presumably in the form of a CHCO radical, followed by CO elimination. The electron is transferred to a second pyruvate molecule in the cluster, resulting in a radical dianion, CHCOCOO. For the smallest cluster size, a variety of secondary fragments was observed, including CO stabilized by two Na ions in the cluster.
Methyl Cation Affinity and Methyl Anion Affinity Prediction Using Uni-Mol-Based Models.
Iwasaki Y, Sato A, Miyao T
J Phys Chem A · 2026 Jul · PMID 42299900 · Publisher ↗
Predicting nucleophilicity and electrophilicity at atomic sites in organic compounds is crucial for the design of polar reactions. Methyl cation affinity (MCA) and methyl anion affinity (MAA), calculated using quantum-ch...
Predicting nucleophilicity and electrophilicity at atomic sites in organic compounds is crucial for the design of polar reactions. Methyl cation affinity (MCA) and methyl anion affinity (MAA), calculated using quantum-chemistry-based simulations, are good indicators of nucleophilicity and electrophilicity, respectively. Machine learning surrogate models have been developed to accelerate inference for MCA and MAA. However, their prediction accuracy, even for state-of-the-art models, remains inadequate for practical use. We present accurate machine-learning surrogate models for MCA and MAA, achieving root-mean-square errors of 8.90 [kJ/mol] for MCA and 10.02 [kJ/mol] for MAA. The model architecture comprises a pretrained Uni-Mol encoder block and a feed-forward neural network. Without pretraining on massive conformers, models with the proposed architecture still perform comparably, suggesting its architectural superiority to a molecular graph-based neural network model. The conformation used to calculate MCA and MAA as the model input is found to slightly improve prediction accuracy. Furthermore, the proposed models are robust to underlying MCA/MAA calculation protocols. The inference time of the proposed MCA and MAA surrogate models is less than 0.1 s per compound on a single GPU, and data scarcity arising from expensive MCA/MAA calculation protocol can be overcome by a simple fine-tuning approach, enabling fast and accurate reactivity prediction for synthetic chemistry.
Structural Insights into the Cyclic Peptide Antibiotic Thiostrepton via NMR Spectroscopy.
Pradhan BL, Sen P, Ghosh P … +2 more , Dey KK, Ghosh M
J Phys Chem A · 2026 Jul · PMID 42299055 · Publisher ↗
A complex cyclic polypeptide antibiotic, thiostrepton, is made by two large macrocyclic rings: a 26-membered ring associated with a thiazoline moiety and a 27-membered ring accompanied by a quinaldic acid unit, a dehydro...
A complex cyclic polypeptide antibiotic, thiostrepton, is made by two large macrocyclic rings: a 26-membered ring associated with a thiazoline moiety and a 27-membered ring accompanied by a quinaldic acid unit, a dehydropiperidine ring, and a flexible bis-dehydroalanine tail. The site-specific local structure and nuclear-spin dynamics of this polypeptide antibiotic is determined by using 2D solution NMR (H-C HSQC, H-C HMBC, H-H COSY, H-H TOCSY, and H-H NOESY) and solid-state NMR methods (C CP-MAS 2D PASS, H-C HETCOR, and site-specific C spin-lattice relaxation measurements). The combined H-C HETCOR and H-H NOESY data demonstrate that the quinaldic acid residue is positioned in close spatial proximity to multiple structural elements, including the thiazoline and piperidine rings, isoleucine-valine chain, butyrine, thiostreptin residue, dehydroalanine units, threonine, and thiazole. These interactions generate a compact hydrophobic core that stabilizes the conformation of the bis-dehydroalanine tail. The flexible side chains of both macrocyclic rings, together with the tail region, accommodate themselves within the interface of ribosomal protein L11 and the 23S rRNA, thereby perturbing the 70S ribosomal subunit. The dynamics of these flexible segments are quantified by employing NMR relaxometry. Therefore, although functional activity is not examined directly, the integrated solution- and solid-state NMR results deliver site-specific structural information and local nuclear spin dynamics at individual carbon sites of this cyclic polypeptide antibiotic. These characteristics are associated with the functional state of thiostrepton and offer a foundation for the rational design of next-generation polypeptide antibiotics.
The CP-PAW Code Package for First-Principles Calculations from a User's Perspective.
Blöchl PE, Schade R, Allen-Rump L … +5 more , Rajpurohit S, Rathnakaran A, Tamoev K, Lokamani M, Kühne TD
J Phys Chem A · 2026 Jun · PMID 42296305 · Publisher ↗
CP-PAW is a combined electronic structure and molecular dynamics code to perform mixed quantum and classical simulations of atomistic condensed phase systems, such as solids, liquids, and molecular systems. As the name...
CP-PAW is a combined electronic structure and molecular dynamics code to perform mixed quantum and classical simulations of atomistic condensed phase systems, such as solids, liquids, and molecular systems. As the name suggests, the CP-PAW code unifies the all-electron projector augmented-wave (PAW) method with the Car-Parrinello (CP) approach to determine not only the electronic and nuclear ground states of condensed matter but also to study their properties and dynamics. In addition to briefly outlining the underlying theory, the focus will be on the unique aspects of CP-PAW and how to correctly employ them as a user. How to install CP-PAW using the new build system will also be briefly mentioned.
Simulation Framework for the Chemical Degradation in Polymeric Solids.
Steiakakis K, Vogiatzis GG, van Breemen LCA … +1 more , Hütter M
J Phys Chem A · 2026 Jul · PMID 42294983 · Publisher ↗
The kinetics of chemical aging in most commercial plastics have remained long debated, since the nature of dense polymeric solids inhibits the in situ experimental investigation of complex degradation paths, while tradit...
The kinetics of chemical aging in most commercial plastics have remained long debated, since the nature of dense polymeric solids inhibits the in situ experimental investigation of complex degradation paths, while traditional computational techniques fail to reach the time scales associated with slow-progressing degradative reactions. In this work, a novel mechanistic framework is introduced in which the infrequent reaction events that govern the long-time-scale evolution of the chemistry of any amorphous solid are described as successive elementary transitions of the atomistic configuration between local minima on its energy landscape. For each elementary reaction event, the corresponding transition state is identified, allowing the estimation of the free-energy barrier and, thereby, of the transition rate constant by means of transition state theory. The result is a network of states populated by the stationary states that are visited by the system along chemical paths. We demonstrate the applicability of the presented approach for the study of complex reaction schemes by applying it to the study of the autoxidation of glassy polystyrene. The introduction of an appropriately trained reactive force field, ReaxFF-lg/CHOpox, tailored for the accurate description of the reactions propagating polymer oxidation, i.e., peroxy radical and hydroperoxide formation, in the glassy state, allows the large-scale sampling of potential reaction paths in situ. From the created network of states, we extracted the energetics and rates of the elementary reactions in the glassy state. For both reactions, the broad distribution of free-energy barriers, spanning over many orders of magnitude, is indicative of the significant impact that the local dense environment has on reaction kinetics and highlights the importance of studying solid-state reactions in situ.
Spectroscopic Studies of 1,2-Dibromobenzene Using Synchrotron Radiation in the UV-VUV Region.
Gorai KK, Das AK, Shastri A
J Phys Chem A · 2026 Jul · PMID 42294930 · Publisher ↗
The electronic absorption spectrum of the brominated benzene derivative 1,2-dibromobenzene (1,2-DBB) is studied using synchrotron radiation. Absolute absorption cross sections are measured in the ultraviolet (UV) and vac...
The electronic absorption spectrum of the brominated benzene derivative 1,2-dibromobenzene (1,2-DBB) is studied using synchrotron radiation. Absolute absorption cross sections are measured in the ultraviolet (UV) and vacuum ultraviolet (VUV) regions 1200-2900 Å (34,500-83,300 cm); the VUV spectrum in the 1200-1700 Å (∼58,800-83,300 cm) region is reported for the first time. A detailed spectral analysis is performed, supported by time-dependent density functional theory (TDDFT) calculations. The S-S transition in the UV region shows extensive vibrational structure, typical of benzene derivatives, tentatively assigned to ring deformation modes using calculated excited-state vibrational frequencies. The intensity profile of this band, simulated using Franck-Condon Herzberg-Teller simulations, shows a good agreement with the experimental spectrum. The VUV absorption spectrum is dominated by strong valence bands with weak and diffuse Rydberg transitions superimposed on the intensity profiles of the valence bands. Rydberg series converging to the first three ionization potentials of 1,2-DBB are assigned using quantum defect analysis. Vertical excitation energies calculated at the TDDFT/CAM-B3LYP/aug-cc-pVTZ level of theory help in corroborating the Rydberg assignments and assigning valence transitions and charge transfer transitions. Simulations of excited-state potential energy curves along the CBr bond provide some insights into the photodissociation dynamics of 1,2-DBB. The measured UV absorption cross-section data helps in estimating photolysis lifetimes of 1,2- and 1,3-DBB with respect to CBr bond breaking at different altitudes from the Earth's surface, thus providing valuable inputs toward modeling the ozone depletion processes in the upper atmosphere.
Threshold Photoelectron Spectroscopy, Dissociative Photoionization, and Pyrolysis of Aziridine.
Cardwell H, Schleier D, Petersen J … +7 more , Wenzel M, McClish R, Kamer J, Hemberger P, Bodi A, Mitrić R, Bouwman J
J Phys Chem A · 2026 Jul · PMID 42294905 · Publisher ↗
The threshold photoelectron spectrum, dissociative photoionization, and pyrolysis of aziridine, a nitrogen-bearing hydrocarbon of c-CHNH composition, were studied by double-imaging photoelectron photoion coincidence spec...
The threshold photoelectron spectrum, dissociative photoionization, and pyrolysis of aziridine, a nitrogen-bearing hydrocarbon of c-CHNH composition, were studied by double-imaging photoelectron photoion coincidence spectroscopy at the Swiss Light Source. The aziridine adiabatic ionization energy (AIE) was measured at (9.30 ± 0.03) eV. The full ground-state band of the threshold photoelectron spectrum, exhibiting strong anharmonicity, was simulated using the Thawed Gaussian Approximation (TGA) method. At higher photon energies, dissociative photoionization products corresponding to hydrogen loss and methyl loss were identified with respective appearance energies of (10.59 ± 0.05) eV and (10.53 ± 0.05) eV obtained by fitting a statistical model to the dissociative ionization data. Aziridine pyrolysis was also studied at a temperature of 1360 K. Isomerization plays an important role with multiple CHN isomers contributing to the thermal decomposition of neutral aziridine. Ethenamine, methyl radical, and radicals of HCN composition were detected as pyrolysis products. The AIE for ethenamine was measured at (8.16 ± 0.03) eV. Isomerization to (/)-ethanimine and -methylmethanimine was also implicated in the pyrolysis data.
Understanding the Mechanism of Low-Temperature NH-SCR Half-Cycle on Cu-CHA Using Automated Reaction Path Search.
Morimoto R, Sugiyama K, Higashi M … +1 more , Sato H
J Phys Chem A · 2026 Jun · PMID 42290079 · Publisher ↗
Nitrogen oxides (NO) emitted from diesel engines are major air pollutants. Copper-exchanged chabazite (Cu-CHA) can efficiently remove NO via ammonia-assisted selective catalytic reduction (NH-SCR), yet its molecular mech...
Nitrogen oxides (NO) emitted from diesel engines are major air pollutants. Copper-exchanged chabazite (Cu-CHA) can efficiently remove NO via ammonia-assisted selective catalytic reduction (NH-SCR), yet its molecular mechanism remains unclear. In this study, the low-temperature NH-SCR half-cycle on Cu-CHA was analyzed using density-functional theory (DFT) calculations combined with an automated reaction path search, and the reaction path networks consisting of many local minima and connecting paths were obtained. The results show that the side-on dimer [CuO(NH)] reacts with two adsorbed NO molecules and exergonically cleaves into two mononuclear [Cu(NH)(ON)] complexes. Each monomer then reacts with one NO and one NH to produce HONO, NHNO, and the reduced [Cu(NH)]. Intracomplex N-N bond formation (Δ = 102.2 kJ/mol) emerges as the rate-determining step of the reduction half-cycle, simultaneously reducing Cu to Cu. Orbital-level analyses indicate that Cu-mediated ligand-ligand coupling is significant in N-N bond formation.
Theoretical Studies on Photodissociation and Isomerization Dynamics of Diazines Following Ultraviolet Excitation.
Chin CH, Chou SL, Wang BC … +1 more , Wu YJ
J Phys Chem A · 2026 Jun · PMID 42283694 · Publisher ↗
Photodissociation of diazines following UV excitation provides a prototypical system for examining unimolecular reaction dynamics on vibrationally excited ground-state potential energy surfaces. In this work, we present...
Photodissociation of diazines following UV excitation provides a prototypical system for examining unimolecular reaction dynamics on vibrationally excited ground-state potential energy surfaces. In this work, we present a comprehensive theoretical study of the isomerization and dissociation dynamics of the isomers of diazines (CHN), with particular emphasis on pyrazine, after rapid internal conversion to the ground electronic state. A unified ground-state potential energy surface is constructed using CCSD(T)/CBS energies, and microcanonical rate constants and product branching ratios are evaluated using Rice-Ramsperger-Kassel-Marcus theory in combination with microcanonical variational transition-state theory. The results reveal a strong energy dependence of the photodissociation dynamics arising from the interplay between isomerization and competing fragmentation pathways. At lower excitation energies (248 nm), rapid isomerization funnels population into pyrimidine, and dissociation proceeds predominantly through pyrimidine-centered channels. At intermediate energies (193 nm), direct dissociation of pyrazine becomes competitive, with concerted three-body fragmentation producing acetylene and hydrogen cyanide accounting for approximately 36% of the total product yield. At higher energies (157 nm), the dynamics approach a statistical limit dominated by concerted three-body dissociation. These results demonstrate that product branching in diazine photodissociation is governed by a coupled isomerization-dissociation network and cannot be inferred from isolated reaction pathways.
Bond Dissociation Energies of the Actinide Halides AnX, An = Ac-Lr and X = F-I, Utilizing Relativistic Composite Coupled Cluster Approaches.
Bonar BO, Peterson KA
J Phys Chem A · 2026 Jun · PMID 42283454 · Publisher ↗
Bond dissociation energies (BDEs) have been calculated for the set of actinide halides AnX with An = Ac, Pa, and Np-Lr and X = F-I. Two composite thermochemistry methods based on the Feller-Peterson-Dixon (FPD) approach...
Bond dissociation energies (BDEs) have been calculated for the set of actinide halides AnX with An = Ac, Pa, and Np-Lr and X = F-I. Two composite thermochemistry methods based on the Feller-Peterson-Dixon (FPD) approach have been utilized, one involving spinor-based relativistic CCSD(T) calculations where spin-orbit (SO) was included at the orbital level and another using scalar relativistic CCSD(T) with SO contributions based on 2-component multireference configuration interaction calculations. The method that was chosen for a given actinide halide was based on which representation yielded the best single determinant reference determinant for the coupled cluster calculation. The spinor-based method was chosen for all cases except for AmX, CmX, and BkX. Both composite approaches included contributions accounting for basis set truncation, outer-core correlation, the Gaunt interaction, and QED. The scalar FPD results, as well as the spinor-based calculations for AcF, also included higher order electron correlation up through CCSDT(Q). In addition to BDEs, CCSD(T) equilibrium bond lengths, harmonic frequencies, and vibrational anharmonicity constants are reported for all species. Last, the FPD BDEs for the fluorides were used to confirm the trend across the actinide series previously predicted by Gibson using bonding models based atomic promotion energies that provide a single 6d electron for bonding. In particular the local minimum in the BDEs at AmF is confirmed in the present calculations. The BDEs for LrX are predicted to be slightly larger than those of AcX, making them the largest in the actinide halide series.
Directed Gas-Phase Formation of The Propargyl Family of Resonance-Stabilized Radicals in The Reactions of Ground-State Carbon Atoms (C; P) with Butene Isomers (CH): Dimethylpropargyl and Ethylpropargyl.
Nikolayev AA, Medvedkov IA, Metya S … +3 more , Goettl SJ, Mebel AM, Kaiser RI
J Phys Chem A · 2026 Jun · PMID 42283213 · Publisher ↗
The propargyl radical (CH) is the simplest resonance-stabilized free radical (RSFR), but how does stepwise methyl substitution in the alkene reactant affect its dynamics of their formation? We report a crossed molecular...
The propargyl radical (CH) is the simplest resonance-stabilized free radical (RSFR), but how does stepwise methyl substitution in the alkene reactant affect its dynamics of their formation? We report a crossed molecular beam study of the reactions of atomic carbon (C, P) with four butene isomers (CH) under single-collision conditions at a collision energy of 28 ± 2 kJ mol. Barrierless addition of atomic carbon to the alkene C═C bond triggers ring opening to substituted triplet allenes─a insertion mechanism─followed by unimolecular decomposition via atomic hydrogen (H), methyl (CH), or ethyl (CH) loss, yielding a family of propargyl-type RSFRs. RRKM calculations reveal that the branching ratios are highly sensitive to the alkene structure. While the methyl loss channel, affording 1-methylpropargyl, dominates for 2-butenes (80-90%), the predicted hydrogen-atom loss channel (≈10%), leading to 1,3-dimethylpropargyl is identified experimentally by comparison with theoretical energetics. For isobutene, near-equal competition is observed, with the reaction producing 3-methylpropargyl (≈50%) and 1,1-dimethylpropargyl (≈40%), along with 2-vinylallyl (≈5%), whose formation is supported by experimental data. Most notably, the reaction with 1-butene uniquely favors an enthalpically driven hydrogen shift, eventually producing 1-vinylallyl (≈38%), which is assigned based on the excellent agreement between the measured and calculated reaction exothermicity. Rapid entropically favored fragmentation channels yield ≈40% of propargyl-type species (propargyl, 1- and 3-ethylpropargyls), slightly outcompeting the allyl-type product. These results establish a systematic progression from CH via CH to CH, where the increasing alkyl substitution unlocks new fragmentation channels, providing a versatile gas-phase route to alkylated RSFRs─key intermediates in the growth of methylated and ethylated PAHs and aliphatic chains in combustion and cold interstellar environments (molecular clouds).
Liquid-Microjet Photoelectron Spectroscopy of the Photoactive Yellow Protein Chromophore in Aqueous Solution.
Simonetti E, Boichenko AN, Rademacher J … +8 more , Henley A, Robertson K, Kaur H, Malerz S, Wilkinson I, Winter B, Bochenkova AV, Fielding HH
J Phys Chem A · 2026 Jun · PMID 42281141 · Full text
Photoactive yellow protein (PYP), a prototypical photoreceptor responsible for the photophobic response of the bacterium to harmful ultraviolet (UV) radiation, is known to undergo photooxidation in aqueous solution. How...
Photoactive yellow protein (PYP), a prototypical photoreceptor responsible for the photophobic response of the bacterium to harmful ultraviolet (UV) radiation, is known to undergo photooxidation in aqueous solution. However, the vertical detachment energy and electronic structure of the deprotonated chromophore that lies at the heart of PYP have not been measured in aqueous solution. Here, we use X-ray, extreme ultraviolet (EUV), and multiphoton UV liquid-microjet photoelectron spectroscopy, supported by high-level quantum chemistry calculations, to map out the electronic structure of the deprotonated PYP chromophore in aqueous solution. The vertical and adiabatic electron detachment energies are found to be 6.8 ± 0.1 eV and around 5.9 eV, respectively. Multiphoton UV photoelectron spectroscopy measurements confirm the existence of a high-lying two-photon resonance close to the detachment threshold that could be responsible for UV photooxidation, and they reveal the existence of a three-photon resonance in the detachment continuum. This work demonstrates the power of combining X-ray, EUV, and UV liquid-microjet photoelectron spectroscopy to unravel the electronic structure of weakly soluble organic chromophores, paving the way for deeper insights into their roles in photobiological processes.
Atomic-Level Composition Engineering in M Nanoclusters for Photocatalytic Degradation of Methylene Blue: From Homometallic Au, Ag, and Cu to Heterometallic AuCu.
Wu Z, Liu K, Zhao J … +4 more , Ma A, Xu J, Guo X, Wang S
J Phys Chem A · 2026 Jun · PMID 42275245 · Publisher ↗
Atomically precise metal nanoclusters provide an ideal platform for elucidating composition-activity relationships in photocatalysis. Herein, four structurally defined M nanoclusters, Au, Ag, Cu, and AuCu, were supported...
Atomically precise metal nanoclusters provide an ideal platform for elucidating composition-activity relationships in photocatalysis. Herein, four structurally defined M nanoclusters, Au, Ag, Cu, and AuCu, were supported on g-CN to establish an atomic-level composition-engineering model for photocatalytic methylene blue (MB) degradation. Among the homometallic clusters, Au exhibited the highest activity, followed by Ag, whereas Cu showed the lowest performance. Remarkably, substitution of a single Au atom into Cu to form AuCu markedly enhanced the photocatalytic activity to a level comparable to that of Au. AuCu/g-CN achieved over 95% MB degradation within 120 min, a TOC removal efficiency of 71.6%, and retained above 88% degradation efficiency after five cycles. Photoelectrochemical measurements indicate that the improved performance of AuCu is associated with more efficient interfacial charge transfer and suppressed charge-carrier recombination relative to the Cu-based system. These results demonstrate that single-atom heterometal incorporation can effectively regulate photocatalytic function and provide a practical strategy for designing efficient and economical nanocluster-based photocatalysts.
Why Are Verdazyl Radicals Nonemissive?
Malinge A, Thériault PL, Kéna-Cohen S
J Phys Chem A · 2026 Jun · PMID 42267683 · Publisher ↗
Verdazyl radicals are a versatile class of air-stable organic radicals used in various applications. Yet, despite the development of a wide range of verdazyl derivatives, they are all nonemissive. To investigate the reas...
Verdazyl radicals are a versatile class of air-stable organic radicals used in various applications. Yet, despite the development of a wide range of verdazyl derivatives, they are all nonemissive. To investigate the reasons behind this and to understand the excited-state dynamics of verdazyls, we combine steady-state and femtosecond pump-probe spectroscopy with quantum chemical calculations. In the carbazole-substituted 2,4,6-triphenylverdazyl (TPV-Cz), we observe ultrafast internal conversion of the first excited state on a time scale of 0.5 ± 0.1 ps, followed by vibrational relaxation with a lifetime of 3.7 ± 0.4 ps. Spin-flip time-dependent density functional theory calculations reveal that the subpicosecond nonradiative decay comes from a low-energy conical intersection between the D and D states, driven by an out-of-plane distortion of the verdazyl ring (VR). This distortion is observed and remains energetically accessible in the isolated VR, in 2,4,6-triphenylverdazyl, and in TPV-Cz. This shows that the conical-intersection geometry is a recurring feature across different types of verdazyl derivatives and explains why all verdazyls are nonemissive despite different functionalization. Our results provide a mechanistic understanding of the photophysical properties of verdazyl radicals and offer a pathway for the future design of emissive verdazyl derivatives.
An Efficient Framework for Simulating Optical Responses of Dynamically Evolving Periodic Nanoarrays.
You Y, Song Y, Zhang S … +2 more , Wang C, Jiang Y
J Phys Chem A · 2026 Jun · PMID 42265845 · Publisher ↗
Predicting and controlling the optical response of dynamically evolving nanoarrays are crucial for advancing applications in sensing, photonics, and optoelectronics. Discrete dipole approximation (DDA) under periodic bou...
Predicting and controlling the optical response of dynamically evolving nanoarrays are crucial for advancing applications in sensing, photonics, and optoelectronics. Discrete dipole approximation (DDA) under periodic boundary conditions (PBCs) has been widely used, but it becomes prohibitively expensive for structurally evolving systems, as each structural or compositional change requires resolving a large electromagnetic problem. Recently, we introduced the rank-one decomposition DDA (RD-DDA) to accelerate the simulation for isolated nanostructures, and here, it is extended to periodic boundary conditions, establishing an efficient and accurate framework for modeling the optical behavior of nanoarrays with dynamically evolving lattice units. Using this RD-DDA-PBC framework, we continuously tracked the spectral evolution of plasmonic nanoarrays during etching and coating, capturing simulated intermediate configurations and associated transient spectral features that are difficult to sample efficiently with repeated full DDA-PBC calculations. By coupling RD-DDA-PBC with kinetic Monte Carlo (KMC) simulations, we investigated the etching kinetics of nanoarray structures under a localized electric field enhancement. Furthermore, integration with reinforcement learning (RL) enables inverse optical geometry design, allowing the autonomous generation of nanoarray structures with prescribed spectral features. Overall, this work establishes an efficient framework for updating periodic DDA calculations during lattice evolution and demonstrates its use in forward spectral tracking, coarse-grained field-biased KMC simulations, and the proof-of-concept inverse design of periodic nanoarrays.
Universal Rapid Machine Learning Models for Predicting Unconvoluted and Convoluted X-ray Absorption Spectra.
Zhan F, Geng Z
J Phys Chem A · 2026 Jun · PMID 42263236 · Publisher ↗
X-ray absorption near-edge structure (XANES) serves as a powerful analytical technique for probing the local three-dimensional (3D) atomic structure in materials and molecules. Rapid computation of XANES based on 3D stru...
X-ray absorption near-edge structure (XANES) serves as a powerful analytical technique for probing the local three-dimensional (3D) atomic structure in materials and molecules. Rapid computation of XANES based on 3D structures of materials or molecules constitutes the cornerstone and a vital element of quantitative XANES analysis. Here, we introduce an XANES prediction model that accepts 3D structures as input and generates either XANES or unconvoluted XANES as output, demonstrating excellent generalizability across diverse broadening. The model's predictive accuracy is validated for both hard X-ray XAS (exemplified by K-edge spectroscopy of 3d/4d transition metals) and soft X-ray XAS (demonstrated via sulfur K-edge spectroscopy). By adopting the model, researchers can predict XANES of multiple elements using a single unified model, eliminating the need for element-specific models. Remarkably, even with sparse 3D structural data for target elements, the model reliably predicts the corresponding XANES spectra. This model empowers researchers to perform real-time validation of hypothesized 3D structures during XAS beamline experiments.
The Threshold Photoelectron Spectrum of the Vinylcyclopentadienyl Radical, a CH Resonance-Stabilized Radical.
McClish R, Bentley MR, Muse M … +8 more , Jones GH, Franke PR, Schleier D, Hemberger P, Bodi A, Ellison GB, Stanton JF, Bouwman J
J Phys Chem A · 2026 Jun · PMID 42263181 · Full text
We generated the aromatic resonance-stabilized vinylcyclopentadienyl radical, CH-CH=CH, in the gas phase via flash pyrolysis of -vinylanisole, CHO-CH-CH=CH. Double-imaging photoelectron photoion coincidence spectroscopy...
We generated the aromatic resonance-stabilized vinylcyclopentadienyl radical, CH-CH=CH, in the gas phase via flash pyrolysis of -vinylanisole, CHO-CH-CH=CH. Double-imaging photoelectron photoion coincidence spectroscopy was used to measure the photoion mass-selected threshold photoelectron spectrum of the vinylcyclopentadienyl radical. Spectral assignments were enabled by independent, high-level coupled cluster calculations of adiabatic ionization energies originating from the ground electronic state of the doublet neutral, X̃ A″, to both the ground state of the cation, X̃A', and the lowest triplet state, ãA'. The experimentally determined band origin energies are found to be (7.81 ± 0.02) eV (X̃A' ← X̃ A″) and (8.08 ± 0.02) eV (ãA' ← X̃ A″), in agreement with the respective calculated values of (7.83 ± 0.01) eV and (8.09 ± 0.01) eV. The combined experimental and theoretical characterization presented here provides a foundation to identify important resonance-stabilized radicals in complex gas-phase environments.
Exploitation of Complex Abelian Point Groups in Quantum-Chemical Calculations.
Kitsaras MP, Stopkowicz S
J Phys Chem A · 2026 Jun · PMID 42262182 · Full text
Quantum-chemical calculations often make use of point-group theory to exploit molecular symmetry, resulting in a reduction of the computational cost and in insights into the electronic structure. This exploitation is oft...
Quantum-chemical calculations often make use of point-group theory to exploit molecular symmetry, resulting in a reduction of the computational cost and in insights into the electronic structure. This exploitation is often limited to subgroups of that are Abelian with real characters. Here, we extend the symmetry exploitation to Abelian point groups with complex characters. Such point groups are often encountered in calculations that involve finite magnetic fields, though their occurrence is not limited to these cases alone. We present the evaluation of integrals over symmetry-adapted orbitals using the double-coset decomposition, as well as the use of these symmetries in the contractions needed within post-Hartree-Fock calculations in the context of block tensors. Efficiency gains are discussed for four simple hydrocarbons that exhibit a complex Abelian point group in the presence of a magnetic field.
Kinetics of Submerged Intersystem Crossings in Strongly Coupled Ion-Molecule Reactions: I + CHX (X = F, Cl, Br, I).
Lewis TWR, Viggiano AA, Ard SG … +1 more , Shuman NS
J Phys Chem A · 2026 Jun · PMID 42261963 · Full text
The kinetics of the reaction between I and the methyl halides CHX (X = F, Cl, Br, I) are measured at temperatures ranging from 300 to 600 K using a selected-ion flow tube apparatus. Exothermic product channels for X = F,...
The kinetics of the reaction between I and the methyl halides CHX (X = F, Cl, Br, I) are measured at temperatures ranging from 300 to 600 K using a selected-ion flow tube apparatus. Exothermic product channels for X = F, Cl, Br forming CHI + HX or CHX + HI require an intersystem crossing, making the series a model system for the kinetics involving consistently large spin-orbit coupling. The reaction efficiencies relative to capture rates increase steeply along the series (X = F: 0.07, Cl: 0.22, Br: 0.67, I: 0.95); however, this is shown not to be a function of the halide mass or increasing coupling. Nonadiabatic transition state theory was applied to reaction coordinates calculated using density functional theory by treating minimum energy crossing points between singlet and triplet surfaces as proxies for the adiabatic transition states. This quantitatively reproduced both the magnitude and temperature dependence of the X = F, Cl, and Br reactions. The reaction efficiencies are controlled by the energy of the adiabatic transition state as the incident I approaches a hydrogen atom, leading to abstraction. The energies of those transition states are, in turn, a function of the entrance well depth of the triplet I(HCX) complexes, which are electrostatically bound and scale with the polarizabilities of the methyl halides. Charge transfer processes (dominating the X = I reaction and a minor product for X = Br) behave nonstatistically.
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