J Phys Chem A [JOURNAL]
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200 papers
Gas-Phase Chemistry of Salt-Assisted MoS Growth.
Vadseth DS, Maruyama S, Page AJ
J Phys Chem A · 2026 May · PMID 42012138 · Publisher ↗
The gas-phase chemistry of salt-assisted MoS growth has been studied using quantum chemical molecular dynamics simulations, with the goal of understanding the effect of alkali metal chloride salts (LiCl, NaCl, KCl) on th...
The gas-phase chemistry of salt-assisted MoS growth has been studied using quantum chemical molecular dynamics simulations, with the goal of understanding the effect of alkali metal chloride salts (LiCl, NaCl, KCl) on the initial chemical pathways present during growth. We observe that a novel intermediate structural moiety, Cl-MoO-Z (Z = Li, Na, K), forms readily in all simulations with salt. This species persists throughout all simulations, as opposed to other species, such as S-MoO-S and S-MoO-Na, indicating that it may be a key driver of MoS formation and growth. Salt also significantly reduces sulfur oligomerization kinetics, suggesting the ability for improved control over MoS morphology. Most interestingly, NaCl disrupts MoO-MoO network formation and growth that occurs under high precursor densities, leading to higher populations of undercoordinated MoO and a tendency toward 2D networks morphologies, increasing opportunities for Mo sulfurization. These findings were found to be NaCl-concentration-dependent, suggesting another method for controlling the CVD synthesis of MoS via controlling salt concentration in the gas phase.
Ethylene-Oxygen Combustion: From Machine Learning Potential Function Construction to Molecular Dynamics Simulation.
Chen J, Liu S, Wu J … +3 more , Xie C, Hu Y, Ma J
J Phys Chem A · 2026 Apr · PMID 42009629 · Publisher ↗
Understanding and accurately modeling combustion processes of complex fuels remain challenging. In this study, we constructed a reactive machine learning potential function (MLP) for the CH-O system to investigate the co...
Understanding and accurately modeling combustion processes of complex fuels remain challenging. In this study, we constructed a reactive machine learning potential function (MLP) for the CH-O system to investigate the corresponding combustion behavior. The MLP was trained using DeePMD-kit with 890,682 configurations, achieving an average fitting error of 0.014 eV for ab initio points on the CH-O MLP. The training data set was mainly generated by random sampling configurations from molecular dynamics (MD) simulations performed with DPGen, complemented by representative structures extracted from key reactions and collisions, enabling an accurate description of the energetics relevant to CH-O combustion. The accuracy and transferability of the developed CH-O MLP were assessed in the NVT ensemble using MD simulations of a system initially composed of 100 CH and 300 O molecules at 3000 K. A total of 175 species and 633 reactions were identified, which were subsequently reduced to two simplified reaction networks leading to the formation of HO and CO. The predicted reaction rates and reaction network show good consistency with established combustion mechanisms. This work provides a basis for extending MLP to the simulation of combustion processes involving more complex fuels.
Synergetic Effect of Fluorine Substitution and Substitution Position on Two Competing ESIPT Pathways in BR through DFT/TD-DFT Investigation.
Ouyang X, Fang H
J Phys Chem A · 2026 Apr · PMID 42008641 · Publisher ↗
In this work, we systematically investigated the synergistic effect of fluorine (F) substitution and substitution position on the excited-state intramolecular proton transfer (ESIPT) mechanisms of 2,2'-(1-(4-bromophenyl)...
In this work, we systematically investigated the synergistic effect of fluorine (F) substitution and substitution position on the excited-state intramolecular proton transfer (ESIPT) mechanisms of 2,2'-(1-(4-bromophenyl)-1-1,2,4-triazole-3,5-diyl)diphenol (BR) with dual intramolecular hydrogen bonds (IHBs) using density functional theory (DFT) and time-dependent DFT (TD-DFT) methods. The geometric optimization of the enol (E) form and its single (SPT1, SPT2) and double proton-transfer (DPT) keto forms in the ground (S) and excited (S) states revealed that there is no stable DPT configuration in the S and S states. Structural changes, infrared vibration analysis, topological parameters, and core-valence bifurcation (CVB) indices collectively confirm that both IHBs are enhanced upon photoexcitation. Furthermore, the IHB of O-H···N (IHB2) in the S state is consistently stronger than the corresponding IHB of O-H···N (IHB1), which facilitates proton transfer along IHB2. The experimental absorption and fluorescence spectra of BR were reproduced at the TD-CAM-B3LYP/6-311+G(d,p) level. The potential energy curves revealed that the energy barrier of the ESIPT process occurring along with IHB2 is much lower than that along with IHB1, implying that the single ESIPT path from E to SPT2 (PT2 pathway) is preferred from the kinetic and thermodynamic viewpoints. The substituted position of the F atom has an effect on the ESIPT barrier of the PT2 pathway. It can be found that the F-substitution at the C/C/C/C position reduced the ESIPT barrier, while the F-substitution at other positions increased the ESIPT barrier.
Unraveling Cross-Ring Dissociation Mechanisms of Hexoses in Collision-Induced Dissociation.
Nguan HS, Lin YT, Ni CK
J Phys Chem A · 2026 Apr · PMID 42007683 · Full text
Understanding the fragmentation mechanisms of carbohydrates in mass spectrometry is essential for interpreting mass spectra and accurately identifying carbohydrate structures. In this study, we used β-glucose, methyl β-m...
Understanding the fragmentation mechanisms of carbohydrates in mass spectrometry is essential for interpreting mass spectra and accurately identifying carbohydrate structures. In this study, we used β-glucose, methyl β-mannose, and four disaccharides─Manβ-(1→2)-Manβ, Manβ-(1→3)-Manβ, Manβ-(1→4)-Manβ, and GlcNAcβ-(1→2)-Manα─as model systems. Combining high-level quantum chemistry calculations with collision-induced dissociation mass spectrometry experiments, we performed an extensive investigation of the cross-ring dissociation mechanisms of hexoses under collision-induced dissociation. In addition to the dissociation pathways proposed in previous studies, which account for the major cross-ring fragments, we identified new mechanisms that explain the minor cross-ring fragments. The newly proposed pathways begin with the same initial step as that of the previously reported mechanism: a ring-opening reaction initiated by hydrogen transfer from O1 to O5, followed by cleavage of the O5-C1 bond. The key distinction is that the established mechanism proceeds through a 1,2-hydrogen shift, whereas the newly identified pathways involve alternative hydrogen-shift processes. The low energy barrier associated with the 1,2-hydrogen shift explains the formation of major cross-ring fragments, while the higher energy barriers associated with the alternative hydrogen shifts account for minor fragments. Both the previously reported and newly proposed mechanisms occur only for hexose at the reducing end. The energy barriers for cross-ring dissociation of the hexose not at the reducing end are significantly higher, indicating that the hexose not at the reducing end contributes far less to cross-ring fragmentation. Applying these newly elucidated mechanisms to -glycans enables the interpretation of cross-ring fragments that would otherwise be misassigned as a mixture of different -glycan linkages in the sample.
Mechanistic Revelations: Surface Hydrogen-Mediated Selectivity Control in Aldol Condensation on TiO(101).
Guo Z, Geng Z, Qin L … +2 more , Gong H, Tao R
J Phys Chem A · 2026 Apr · PMID 42003105 · Publisher ↗
The aldol condensation of butyraldehyde to 2-ethyl-2-hexenal is a critical step in synthesizing 2-ethylhexanol and 2-ethylhexanoic acid. Although TiO is a promising replacement for traditional base catalysts, the reactio...
The aldol condensation of butyraldehyde to 2-ethyl-2-hexenal is a critical step in synthesizing 2-ethylhexanol and 2-ethylhexanoic acid. Although TiO is a promising replacement for traditional base catalysts, the reaction mechanisms of the main and side pathways and the selectivity factors remain elusive. To address this, the Density Functional Theory (DFT) was utilized to elucidate the reaction network and microscopic mechanisms of the aldol condensation on the anatase TiO(101) surface. The initial activation of butyraldehyde is dominated by the α-H dissociation pathway with a barrier of 0.45 eV rather than the direct enolization pathway that has a higher barrier of 2.69 eV. Following this step, the optimal pathway proceeds sequentially through C-C coupling, β-O hydrogenation, and dehydration. Among these, β-O hydrogenation is the rate-determining step, with an energy barrier of 1.00 eV. The dehydration step follows a stepwise pathway involving initial hydrogen elimination followed by OH removal with a barrier of 0.59 eV, lower than the 1.01 eV barrier of the concerted elimination pathway. A common feature in the side reactions is that the formations of both butyl butyrate and 4-heptanone are governed by hydrogen dissociation, with rate-determining barriers of 2.70 eV for the aldehyde-H dissociation in butyl butyrate formation and 1.04 eV for the β-H dissociation in 4-heptanone formation. Overall, the main reaction is limited by β-O hydrogenation, whereas the side reactions are controlled by H-dissociation. This mechanistic understanding suggests that tuning the surface hydrogen concentration is key to enhancing selectivity, providing a theoretical basis for developing advanced TiO catalytic processes.
Visualizing Size-Dependent Vibrational and Excited-State Evolution by Tip-Enhanced Raman Imaging.
Ma W, Dai M, Cao Y … +5 more , Chu D, Duan S, Song Y, Xie Z, Wang L
J Phys Chem A · 2026 Apr · PMID 41999328 · Publisher ↗
Tip-enhanced Raman scattering (TERS) enables real-space mapping of molecular vibrations and electronic excitations with subnanometer resolution, offering a direct route to track the molecular-size-dependent evolution of...
Tip-enhanced Raman scattering (TERS) enables real-space mapping of molecular vibrations and electronic excitations with subnanometer resolution, offering a direct route to track the molecular-size-dependent evolution of these properties. Here, using the hexagonal -coronene series as a model system, we show that vibrationally resolved nonresonant TERS images of the ring-breathing mode can characterize a pronounced size-dependent redistribution where the spatial vibration migrates outward and becomes progressively concentrated at the molecular periphery as the molecule grows. This vibrational evolution is quantitatively captured by an envelope-based model. In contrast, resonant TERS imaging identifies two low-lying excited states with size-independent and distinct spatial characters across the series, including a delocalized lowest excitation and a persistently edge-localized second excitation. These findings serve as good references for future TERS experiments on visualizing size-driven property evolution, deepening our understanding of the crossover from molecule-like to graphene-like nanodisk behavior as π-conjugation expands.
Fukui Functions, Bonding Fukui Functions, or Generalized Polarized Spin Fukui: Which Index Describes Radical Cyclizations?
Espinoza JM, González GB
J Phys Chem A · 2026 Apr · PMID 41999326 · Publisher ↗
In this work, the descriptive capacity of different local reactivity indices within the framework of conceptual density functional theory (cDFT) was systematically evaluated to rationalize the mechanism of Bergman, Azabe...
In this work, the descriptive capacity of different local reactivity indices within the framework of conceptual density functional theory (cDFT) was systematically evaluated to rationalize the mechanism of Bergman, Azabergman, and intramolecular hexadehydro-Diels-Alder (HDDA) radical cyclizations. The (FF), the (BFF), and its generalization in the (FFSP) were analyzed through a comparative study of energy profiles and local electronic redistribution. The main results show that the conventional Fukui function adequately describes the electronic charge predisposition and reproduces the symmetry or polarization of the reactive centers, whereas the bonding Fukui function characterizes the reactivity of existing π-bonds but does not identify the formation of the new σ-bond between the centers of interest. In contrast, the spin-polarized formalism reveals that the electronic reorganization associated with cyclization is dominated by spin density redistribution, with complementary contributions from the and functions at the reactive centers and their adjacent positions, respectively. These results indicate that intramolecular bond formation occurs through an electronic reorganization characterized by the generation and stabilization of a distributed biradical character. Consequently, the descriptors derived from the SP-DFT model provide the most appropriate representation of the electronic nature of these cyclizations.
Implications from Geometric Phase for Circulating Far Away Conical Intersection(s).
Nooijen M, Zeng T
J Phys Chem A · 2026 Apr · PMID 41996703 · Publisher ↗
People rarely associate a geometric phase with nuclear configurations that lie far away from a conical intersection, where the ground state is energetically well-separated from excited states. However, the geometric phas...
People rarely associate a geometric phase with nuclear configurations that lie far away from a conical intersection, where the ground state is energetically well-separated from excited states. However, the geometric phase is a nonlocal impact of a conical intersection that should emerge whenever a nuclear configuration travels on a closed loop trajectory that encloses the intersection in the branching plane, regardless of the distance from the intersection. In particular, if a trajectory starts at a structure with a stable closed-shell electronic configuration, how could the continuous closed-shell configuration possibly gain a sign change on finishing the loop? In this work, inspired by a recent paper by Kjønstad; ; Koch ( 2025, 163, 194104)., we performed full configuration interaction calculations and closed-shell single-reference calculations for the toy models of H and LiH to elucidate this problem. The investigation leads to the conjecture that restricted Hartree-Fock solutions necessarily encounter a point of degeneracy along closed loops that encircle a (or an odd number of) conical intersection(s). Single-reference wave functions need to change character close to such points and cusps or discontinuities in a potential energy surface and multireference characters are a likely result, even when the energy gap between ground and excited states is large.
Physical Origin for the Unusual -Values Observed for a Pb(I) Radical Complex: Quenching the Spin Angular Momentum Caused by Strong Spin-Orbit Coupling.
Miao Q, Ye S
J Phys Chem A · 2026 Apr · PMID 41996223 · Publisher ↗
Heavy main-group radical complexes likely exhibit unusual magnetic properties thanks to the intrinsically strong spin-orbit coupling (SOC) of the heavy elements. Herein, we elucidate the physical origin for the distinct...
Heavy main-group radical complexes likely exhibit unusual magnetic properties thanks to the intrinsically strong spin-orbit coupling (SOC) of the heavy elements. Herein, we elucidate the physical origin for the distinct magnetic anisotropy observed for group 14 Ge, Sn, and Pb radical anions (E = Ge, Sn, Pb) whose doublet ground states feature an (ns)(np) electron configuration. Complexes and display moderate magnetic anisotropy manifested by = 1.976, 1.976, 1.999 and = 1.879, 1.906, 1.982, respectively, ( , 61, e202201248), with all -factors close to the spin-only value, . In contrast, is distinguished by a highly anisotropic -tensor with = 1.335, 1.410, and 1.693, in particular, having an exceptionally low -factor. Effective Hamiltonian analyses based on wave function-based ab initio calculations reveal that and possess orbitally nondegenerate ground states, wherein the weak SOC between the ground state and the two low-lying excited states with dominant electron configurations of (ns)(np) and (ns)(np) partially restores the orbital angular momentum in the x- and -directions, resulting in ≈ < ≈ . However, the ground level of features a triple orbital near-degeneracy, and the ensuing strong SOC with the same excited states not only introduces the considerable orbital angular momentum in the - and -directions but also, more critically, substantially quenches the spin angular momentum in the -direction due to the conservation of the total angular momentum. As a consequence, all three -components of are significantly lower than , exhibiting a pattern of ≈ < < . This work, therefore, provides a general framework for correlating -matrices measured experimentally with electronic structures of = 1/2 main-group and transition-metal complexes.
Accelerating Density Fitting with Adaptive Precision and 8-Bit Integer on AI Accelerators.
Huang H, Shao W, Hammond J
J Phys Chem A · 2026 Apr · PMID 41995411 · Publisher ↗
The emergence of artificial intelligence (AI) accelerators like NVIDIA Tensor Cores offers new opportunities to speed up tensor-heavy scientific computations. However, applying them to quantum chemistry is challenging du...
The emergence of artificial intelligence (AI) accelerators like NVIDIA Tensor Cores offers new opportunities to speed up tensor-heavy scientific computations. However, applying them to quantum chemistry is challenging due to strict accuracy demands and irregular data patterns. We propose an adaptive precision algorithm to accelerate the density fitting (DF) method with Gaussian basis sets on AI accelerators using 8-bit integer (INT8) arithmetics. Implemented in the GPU-accelerated PySCF package, the algorithm is tested on more than 20 molecular systems with different NVIDIA GPUs. Compared to the standard FP64 code, our algorithm is up to 204% faster on an RTX 4090 gaming GPU and up to 364% faster on an RTX 6000 Ada workstation GPU without compromising the converged energy. This work demonstrates a practical approach to using AI hardware for reliable quantum chemistry simulations.
Second-Order Autocatalytic Acceleration in the Thermal Bleaching of Photochromes: Spectroscopic and Computational Analyses with an Isostructural Crystal Library.
Koibuchi R, Huang H, Yoshikawa I … +2 more , Shigemitsu Y, Houjou H
J Phys Chem A · 2026 Apr · PMID 41995247 · Publisher ↗
The photochromic behavior of molecular crystals is highly sensitive to local intermolecular interactions, which challenges quantitative structure-function correlation studies. Our approach, using an isostructural library...
The photochromic behavior of molecular crystals is highly sensitive to local intermolecular interactions, which challenges quantitative structure-function correlation studies. Our approach, using an isostructural library of salicylidenephenethylamines (SPAs), proposes a FW 2-step type mechanism in which substituent effects and the tautomeric state of neighboring molecules modulate the activation barrier of -to- thermal relaxation in the solid state. Two distinct types of crystals, Series I and II, showed different bleaching processes, namely simple first-order kinetics and autocatalytic second-order kinetics. Cluster model calculations revealed that Series-I crystals stabilized the transition state (TS) through electrostatic interactions between the NH moiety and the substituent on the salicylidene ring, modulating the activation barrier. By contrast, the Series-II crystals stabilize the transition state through an NH···O hydrogen bond, especially when a molecule is surrounded by the -Keto tautomer. This stabilization effect decreases as the bleaching reaction proceeds, increasing the activation barrier. These two stabilization modes link nonlinear kinetics and specific intermolecular contacts.
Theoretical Insights into the Ir-Catalyzed C(sp)-H Borylation Mechanism: Origin of Ligand-Controlled Regioselectivity and Identification of a Potentially Active Species.
Li X, Chong C, Wang H … +1 more , Zhang D
J Phys Chem A · 2026 Apr · PMID 41992763 · Publisher ↗
Comprehensive computational studies were carried out to elucidate the mechanistic basis and the origin of ligand-controlled regioselectivity in Ir-catalyzed C(sp)-H borylation. Both the (anionic)-type ligand L1 and the n...
Comprehensive computational studies were carried out to elucidate the mechanistic basis and the origin of ligand-controlled regioselectivity in Ir-catalyzed C(sp)-H borylation. Both the (anionic)-type ligand L1 and the neutral bipyridine ligand L2 operate via a classical Ir(III)/Ir(V) catalytic cycle, with regioselectivity determined at the C-H oxidative addition step. In the L1 system, the pronounced trans effect of the anionic carbon atom plays a decisive role in dictating the coordination geometry and reactivity. Therefore, during the regeneration of the active catalyst, the trans position relative to the anionic carbon center must be occupied by a substrate molecule. Additionally, computations identified an L1-chelated Ir(III)BpinH species as a plausible catalytically competent intermediate, capable of mediating C-H borylation using HBpin as the sole boron source. Critically, ligand-controlled regioselectivity originates from fundamental differences in the electronic nature of the C-N and N-N ligands, which leads to divergent coordinative unsaturation in the key Ir(III) intermediates: the four-coordinate L1-Ir(III)Bpin complex affords three accessible sites, allowing the acyl group to function as a directing chelator and thereby enabling selective -C-H activation, whereas the five-coordinate L2-Ir(III)Bpin complex possesses only two vacant coordination sites. This constrained coordination environment prevents effective chelation by the acyl group, causing it instead to behave as a steric hindrance and inducing a destabilizing lone-pair-π repulsion between the acyl carbonyl oxygen and the L2 ligand during -selective C-H activation, thereby leading to predominant - and -selectivity. Collectively, these insights establish a coherent mechanistic framework that provides guidance for the rational design of transition-metal-catalyzed C-H functionalization reactions with improved regiocontrol and enhanced synthetic efficiency.
Competing Reaction Mechanisms and Origin of Selectivity in Base-Controlled (4 + 1) versus (2 + 1)/(4 + 2) Annulations of -Aminochalcones with γ-Bromocrotonates.
Han P, Jiang Y, Yan Y … +4 more , Zhang S, Li D, Ge S, Liu C
J Phys Chem A · 2026 Apr · PMID 41991246 · Publisher ↗
Base-controlled reactions represent a cornerstone of modern organic synthesis. Despite significant advances, a comprehensive mechanistic understanding of the role of the base, particularly its influence on the reaction p...
Base-controlled reactions represent a cornerstone of modern organic synthesis. Despite significant advances, a comprehensive mechanistic understanding of the role of the base, particularly its influence on the reaction pathway selectivity, remains incomplete. In this study, we present a theoretical investigation of the competing mechanisms in CsCO-catalyzed (4 + 1) versus (2 + 1)/(4 + 2) annulations involving γ-bromocrotonates and -aminochalcones. Our calculations demonstrate that the (4 + 1) annulation is energetically favored over the (2 + 1)/(4 + 2) annulation. In the (4 + 1) annulation mechanism, the base catalyst CsCO deprotonates the relatively acidic N-H group of -aminochalcone, generating a resonance-stabilized amino anion, which undergoes nucleophilic attack on γ-bromocrotonate via an S2 mechanism to form a diene intermediate. This intermediate is subsequently deprotonated by CsCO to yield a carbanion that participates in an intramolecular vinylogous Michael addition, followed by protonation, to afford the -2,3-disubstituted indolines. In the overall pathway, the base CsCO acts as a non-nucleophilic strong base that deprotonates acidic substrates to generate reactive anionic intermediates for the subsequent Michael addition. To elucidate the origin of chemoselectivity, we employed the POCV method to evaluate the atomic reactivity vectors ⃗ for the hydrogen atoms at the N-H group f -aminochalcone and at the γ-carbon of γ-bromocrotonate. This analysis was complemented by p calculations to provide a quantitative thermodynamic perspective. To further probe the origin of diastereoselectivity, we performed noncovalent interaction (NCI), atoms in molecules (AIM), and natural bond orbital (NBO) second-order perturbation analyses. Collectively, these results offer mechanistic insights into the fundamental principles governing base-mediated reactions of γ-bromocrotonates, revealing key electronic and steric factors that dictate both chemoselectivity and diastereoselectivity.
Kinetics of the O Reactions with CHOCO and CHOCHO Formed from Methyl Formate.
Onel L, Shannon R, Robertson NCK … +3 more , Blitz MA, Stone D, Seakins PW
J Phys Chem A · 2026 Apr · PMID 41989862 · Full text
Methyl formate (CHOCHO, MF) is the simplest ester, a class of species that is of interest for combustion and atmospheric chemistry studies. H-abstraction reactions from the two sites of MF leads to radicals, R, that reac...
Methyl formate (CHOCHO, MF) is the simplest ester, a class of species that is of interest for combustion and atmospheric chemistry studies. H-abstraction reactions from the two sites of MF leads to radicals, R, that react with oxygen to form RO species that are important in the oxidation of MF under atmospheric and low temperature combustion conditions. This work reports the kinetics of the O reactions with R formed through the reaction of Cl with MF from 213 K to ∼420 K and in the range ∼5-100 Torr of N or Ar. The rate coefficients were determined by the analysis of the kinetic profiles of the OH radicals formed by the prompt dissociation of RO, which were measured using the pulsed laser flash photolysis-laser induced fluorescence technique. At 294 K in N (5-100 Torr), was pressure independent, within experimental error, with a value of (5.0 ± 0.4) × 10 cm molecule s. Isotopic studies using CHOCDO were used to differentiate between the kinetics of the CHOCO and CHOCHO associations with O. CHOCDO reacted faster than CHOCO by approximately 40% at 213 K, rising to 200% at 472 K. The enhanced reactivity of the CHOCHO with O can be explained by a more attractive potential energy surface and a looser transition state. It was also possible to determine the rate coefficients of the unimolecular decomposition of CHOCO, (348-470 K). The experimental values of were fitted with the master equation application, MESMER, with the literature (ANL0F″) barrier height of 57.3 kJ mol, and floating the average energy transfer parameter at 298 K, <Δ>, and the temperature exponent of <Δ>. A good fit to the data was obtained with: <Δ>(Ar) = (110 ± 30) × (/298 K) cm and <Δ>(He) = (34.4 ± 6.2) × (/298 K) cm.
Accurate Quantification of Single Aerosol Particle Microphysical Properties Using Broadband Light Scattering Spectroscopy.
Rafferty A, Orr-Ewing AJ, Reid JP … +1 more , Cotterell MI
J Phys Chem A · 2026 Apr · PMID 41989485 · Full text
The wavelength-dependent refractive indices of aerosol particles, (λ), are essential quantities for several areas of atmospheric science. Broadband light scattering (BLS) is a technique that has the potential to determin...
The wavelength-dependent refractive indices of aerosol particles, (λ), are essential quantities for several areas of atmospheric science. Broadband light scattering (BLS) is a technique that has the potential to determine (λ) and particle size at the single particle level by measuring variations in light scattering intensity with wavelength. However, a significant barrier to the use of BLS is the time-consuming analysis of measured spectra, caused primarily by the need to simulate large numbers of BLS spectra. We introduce a new approach to fitting BLS spectra for single, levitated, nonabsorbing aerosol particles that reduces the time required for analysis by minimizing the number of spectra that require calculation. The method is tested by comparing BLS measurements with concurrent cavity ring-down spectroscopy (CRDS) measurements of extinction cross section for two benchmark nonabsorbing aerosol species: (i) 1,2,6-hexanetriol (a semivolatile organic species) and (ii) aqueous particles containing the hygroscopic salt ammonium sulfate. The accuracy of the BLS-retrieved values for aerosol particle sizes and (λ) is verified by their use in simulations that reproduce the simultaneously measured BLS spectra and CRDS-derived extinction cross sections. For particles of radius 0.8-2.5 μm interrogated in our experiments, particle radii and the real component of the complex refractive index are retrieved with typical precisions of 1.4 nm and ∼10, respectively, across the 380-800 nm wavelength range of the measurements.
Simplifying the Chemical Design of Nonfused-Ring Electron Acceptors─Lessons Learned from Thienothiophene and Benzodithiophene Cores.
Tannir S, Murphy AL, Seban R … +5 more , Drochner D, Gish MK, Srinivasan S, Larson BW, Jeffries-El M
J Phys Chem A · 2026 Apr · PMID 41984533 · Publisher ↗
Nonfused-ring electron acceptors (NFREA)s have been proposed as alternatives to fused-ring acceptors in organic photovoltaics (OPV)s. The simpler molecular design of NFREAs results in a reduced synthetic complexity, pote...
Nonfused-ring electron acceptors (NFREA)s have been proposed as alternatives to fused-ring acceptors in organic photovoltaics (OPV)s. The simpler molecular design of NFREAs results in a reduced synthetic complexity, potentially lowering manufacturing costs, and easier access to desired optoelectronic properties by structural modifications. However, they have not seen the same rise in popularity as fused nonfullerene acceptors (NFA)s due to their lower performances in devices. In this work, we explore structure-property relationships of three NFREA molecules based on thieno[3,2-]thiophene (TT) and benzo[1,2-:4,5-']dithiophene (BDT) cores and malononitrile functionalized-isatin end group acceptors. We describe their synthetic routes, computational analysis, and photophysical and electronic properties. We investigated the effect of changing the core from TT to BDT on electronic properties of the molecules─a result of raising/lowering of the frontier molecular orbital (FMO) levels. We also explored the effect of branched vs nonbranched alkyl groups on the morphological and blend-capabilities in bulk heterojunction (BHJ) OPV devices. These effects were then reflected in the overall device performances, primarily due to favorable FMO energy alignment between the NFREA and polymer. To investigate the behavior of the excited states of the NFREAs within the active layer of the devices, we performed time-resolved microwave conductivity and transient absorption experiments, which confirmed that the TT molecules exhibited very low conductance while the BDT molecule showed moderate photoconductance. Our combined theoretical, synthetic, device, and charge carrier dynamics studies of these materials reveal the central role that structure-property relationships play in future molecular designs of NFREAs that can perform as well as their fused counterparts.
Assessing the Limits of the "Lego-Brick" Approach: Equilibrium Structures of Strained and Flexible Cyclic Molecules.
Alessandrini S, Savarese A, Melosso M … +2 more , Bizzocchi L, Puzzarini C
J Phys Chem A · 2026 Apr · PMID 41984471 · Full text
An accurate description of molecular structures is essential in several fields of chemistry and, in particular, in high-resolution molecular spectroscopy. The so-called "Lego-brick" approach has proven to provide near-sp...
An accurate description of molecular structures is essential in several fields of chemistry and, in particular, in high-resolution molecular spectroscopy. The so-called "Lego-brick" approach has proven to provide near-spectroscopic accuracy at a fraction of the computational cost of high-level composite schemes, but its applicability has so far been mainly assessed for rather rigid systems. In this work, we systematically investigate the performance of the "Lego-brick" approach for strained and conformationally flexible cyclic molecules. A chemically diverse benchmark set of three-, four-, and five-membered rings, including heterocycles and species with multiple conformers, is considered. By comparing template-molecule (TM) and full "Lego-brick" (TM+LR) rotational constants with the experimental counterparts, the accuracy of corresponding equilibrium structures is analyzed. The results show that the "Lego-brick" approach retains good accuracy for small cyclic systems, although the data set turned out to be a challenging test case. Linear-regression (LR) corrections are found to be fundamental to achieve the aimed precision. Interestingly, the TM+LR geometries are so accurate that can be employed in the framework of the semiexperimental approach, thus allowing one to obtain equilibrium structures of experimental quality also when there is a lack of isotopic data. Overall, this study delineates the applicability limits of the "Lego-brick" approach for flexible systems, pointing out the ability of significantly improving the initial density functional theory results.
Explainable Machine Learning for Efficient Cocrystal Prediction: Leveraging Morgan Fingerprints to Decode Local Structure-Cocrystal Formation Relationships.
Liu Y, Liu Y, Du Z … +3 more , Zheng H, Yang D, Gao Y
J Phys Chem A · 2026 Apr · PMID 41984199 · Full text
Cocrystallization is a pivotal strategy for optimizing the physicochemical properties of functional molecular materials, yet its development is bottlenecked by time-consuming and labor-intensive experimental screening. W...
Cocrystallization is a pivotal strategy for optimizing the physicochemical properties of functional molecular materials, yet its development is bottlenecked by time-consuming and labor-intensive experimental screening. While machine learning (ML) has emerged as a paradigm for high-throughput virtual screening, the black-box nature of existing models and their reliance on global molecular descriptors limit their utility in rational cocrystal design. Herein, we constructed a large-scale cocrystal data set encompassing 7700 samples. We innovatively adopted Morgan fingerprints which are capable of capturing fine-grained local chemical environment information to encode molecular structures into numerical vectors. These vectors retain key functional group and substructure features that are critical for cocrystal assembly. Five ML models (MF-KNN, MF-RF, MF-XGBoost, MF-SVM, and MF-ANN) were developed, and their optimal hyperparameter combinations were determined via systematic tuning. The MF-ANN model achieved state-of-the-art performance on the independent test set, with an accuracy of 97.16% and an F1-score of 98.35%, and exhibited excellent robustness through 10-fold, 5-fold, and 3-fold cross-validation. To address the black-box challenge, we pioneeringly applied the SHapley Additive exPlanations (SHAP) tool to cocrystal prediction: at the global level, we identified universal key substructures driving cocrystal formation, while at the local level, we correlated abstract model outputs with specific molecular interactions (e.g., hydrogen bonding, π-π stacking). This work not only provides a high-performance, interpretable ML framework for rapid cocrystal screening but also establishes a direct link between model predictions and chemical mechanisms, offering actionable guidance for the rational design of functional cocrystals in pharmaceuticals, energetic materials, and optoelectronics.
Si ← N Dative Tetrel Bonding in Anionic Bis(catecholato)silicates: Role of Local Electronic Anisotropy.
Shukla R
J Phys Chem A · 2026 Apr · PMID 41983611 · Publisher ↗
This study computationally investigates the formation of Si ← N dative tetrel bonds between anionic pentacoordinated bis(catecholato)silicate frameworks and a series of pyridine derivatives under aqueous conditions. Desp...
This study computationally investigates the formation of Si ← N dative tetrel bonds between anionic pentacoordinated bis(catecholato)silicate frameworks and a series of pyridine derivatives under aqueous conditions. Despite the silicon center being embedded within a globally anionic environment, it exhibits a pronounced local electronic anisotropy along the axial Si-O bond extension, giving rise to an electron-deficient σ-hole capable of interacting with nitrogen lone pairs. A systematic set of 27 dimers was examined by varying substituents on both the pyridine donor and the catecholate ligands. The calculated interaction energies span from -67.3 to -148.1 kJ mol, indicating the formation of energetically favorable donor-acceptor interactions that persist even after accounting for substantial monomer deformation. Analysis of the electron density redistribution accompanying complex formation reveals that the Si ← N contact occupies an intermediate regime between weak noncovalent interactions and classical covalent bonding, consistent with a closed-shell dative interaction dominated by directionality and orbital alignment. The interaction strength is found to be highly sensitive to remote electronic substitution, with stronger nitrogen donors and more electron-withdrawing catecholate substituents enhancing the electrophilic character of the silicon center. Overall, these results show that local electronic features can dominate over formal molecular charge, enabling tunable dative tetrel bonding in hypercoordinate anionic silicon systems.
Computational Study and Detailed Kinetic Model of C-C Aldehyde Formation from Cellulose-Based Anhydroglucose via Pyrolysis.
Xie X, Fujita M, Tonokura K
J Phys Chem A · 2026 Apr · PMID 41982171 · Full text
Cellulose-based carbohydrates are critical precursors of hazardous C-C aldehydes emitted during biomass combustion. Among these, 5,6-anhydroglucopyranose (AHGlu), a monomeric fragment of cellulose with a terminal methyle...
Cellulose-based carbohydrates are critical precursors of hazardous C-C aldehydes emitted during biomass combustion. Among these, 5,6-anhydroglucopyranose (AHGlu), a monomeric fragment of cellulose with a terminal methylene group, is expected to contribute significantly to the formation of formaldehyde, acetaldehyde, glyoxal, and methylglyoxal. This study aims to elucidate the elementary reaction pathways leading to C-C aldehyde formation from AHGlu during pyrolysis by using density functional theory (DFT) and transition state theory (TST). After excluding kinetically unfavorable pathways, AHGlu is predicted to convert into straight-chain terminal-methyl carbohydrates, forming formaldehyde through a trifurcated pathway with a rate-limiting activation barrier of 205.2 kJ/mol. Acetaldehyde formation proceeds via a bifurcated pathway with a rate-limiting activation barrier of 195.9 kJ/mol, while glyoxal and methylglyoxal are generated through a single-step isomerization-scission mechanism, with rate-limiting activation barriers of 189.8 and 177.2 kJ/mol, respectively. The uncertainty in calculating energy at the basis set level and the perturbation of the pressure dependence of the reaction on the final results were evaluated. Using reaction rates at 1 atm, comparative reactor simulations deviated from experimental references by less than 20%, indicating that the proposed mechanism is applicable to cellulose pyrolysis. According to sensitivity analysis, promoting the conversion of AHGlu toward LVG prior to the ring-opening step or conducting pyrolysis at pressures below 0.1 atm may substantially suppress aldehyde formation, particularly FMAD and ACAD. The formation mechanism of C-C aldehydes from AHGlu reported here provides a further solid foundation for the thermal decomposition of cellulose-based anhydroglucose, and considering the catalytic effect of water in relation to these research findings will lead to a deeper understanding.
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