Physical Chemistry Chemical Physics

doi: 10.1039/d6cp90115hpmid: N/A

doi: 10.1039/d6cp90116fpmid: N/A

doi: 10.1039/d6cp90117dpmid: N/A

Dong, Bowen; Mi, Xiaoyu; Zhang, Ming; Zhao, Leshi; Guo, Zhaoheng; Li, Sizhe; Bokarev, Sergey; Bostedt, Christoph; Xu, Haitan; Li, Zheng

doi: 10.1039/d6cp00599cpmid: 42189576

The emergence of X-ray free-electron lasers (XFELs) with attosecond capabilities has opened unprecedented opportunities for probing ultrafast spin dynamics in molecules. Magnetic X-ray scattering (MXS), while well-established in condensed matter physics, remains nascent for isolated molecules. Here we review the theoretical framework and computational methodology for molecular MXS on femtosecond and attosecond timescales. Using circular dichroism to separate spin-dependent contributions from dominant charge scattering, MXS enables direct probing of spin-dependent dynamics during ultrafast processes. We demonstrate these capabilities through three paradigmatic examples: femtosecond spin–orbit beating in NO molecules, sub-femtosecond singlet–triplet oscillations in core-excited TiCl4, and Berry phase detection during CH2OH photodissociation. We connect this molecular framework to established condensed-matter magnetic X-ray techniques and compare with the recent proposal of time-resolved XMCD for molecular photodynamics. Together, these theoretical and computational developments position molecular MXS as a powerful tool for understanding spin-resolved electron dynamics inaccessible by other ultrafast techniques.

Upadhyay, Shrish Nath; Joshi, Himani; Sharma, Naveen; Pakhira, Srimanta

doi: 10.1039/d6cp00222fpmid: 42207562

Two-dimensional (2D) materials have emerged as a versatile platform for high-performance electrocatalysts in sustainable energy conversion and storage technologies, including fuel cells, water splitting, and metal–air batteries (MABs). The central part of the electrochemical reactions, such as the H2 evolution reaction (HER), O2 reduction reaction (ORR), and O2 evolution reaction (OER), determines the efficiency, performance, and stability of these 2D materials. While noble metals like Pt, Ir, and Ru exhibit superior activity, their high cost and limited durability hinder large-scale applications. 2D materials, including transition metal dichalcogenides, MXenes, doped graphene, and single-atom 2D catalysts, offer tunable electronic structures, high surface area, abundant active sites, and defect-rich architectures, enabling efficient and durable catalysis. Combined with advanced computational approaches, such as density functional theory (DFT) calculations and machine learning (ML), these materials provide a pathway for rational design and high-throughput screening of next-generation electrocatalysts. This review critically summarizes recent progress in 2D material-based electrocatalysts for the HER, ORR, and OER, highlighting design strategies, synthesis techniques, stability challenges, and emerging trends toward scalable and practical energy conversion technologies.

Koots, Rian; Mirahmadi, Marjan; Pérez-Ríos, Jesús

doi: 10.1039/d6cp01349jpmid: 42132775

For over a century, termolecular (third-order) chemical reactions have been explained by the Lindemann–Hinshelwood mechanism, assuming sequential stabilization via bimolecular encounters. Here, we demonstrate that barrierless termolecular reactions are fundamentally governed by direct three-body dynamics. Using classical trajectory calculations in hyperspherical coordinates, we quantitatively reproduce ion-atom recombination kinetics across a wide temperature range without invoking intermediate complexes or steady-state assumptions. Our results not only resolve longstanding discrepancies between theory and experiment, but also establish a general mechanistic framework for barrierless termolecular reactions, with implications spanning atmospheric chemistry, plasma physics, and ultracold chemistry.

Kinugawa, Yuuki; Kawagoe, Yoshiaki; Matsumoto, Keigo; Ohno, Masashi; Mishima, Shoko; Kawai, Takahiko; Okabe, Tomonaga

doi: 10.1039/d6cp01039cpmid: 42148944

Epoxy resins are widely used in electronic and structural applications. However, their use at high temperatures is limited by their glass transition temperature (Tg). Although the addition of multifunctional resins increases Tgvia crosslink density, the molecular-scale contribution of specific intermolecular interactions, such as π–π stacking, remains poorly understood in multicomponent systems. Here, we investigated the molecular-level mechanism of Tg enhancement in a multicomponent epoxy resin system incorporating a triazine-based epoxy resin, tris(2-epoxypropyl)isocyanurate (TEPIC), into a conventional epoxy resin. The experimental results revealed a non-monotonic dependence of Tg on TEPIC content, with an initial decrease at low concentration followed by a pronounced increase at higher concentration, which cannot be explained solely by changes in crosslink density. Structural analysis using wide-angle X-ray scattering and molecular dynamics (MD) simulations showed that the amorphous halo originating from intermolecular packing splits into two peaks, suggesting that one of these peaks includes a contribution from π–π stacking interactions. MD simulations showed that ring pairs with centre-of-mass distances of 3.4–5.8 Å form stable π–π stacking structures, and that the population of these interactions correlates strongly with the observed variation in Tg. Quantum chemical calculations further demonstrated that benzene–triazine stacking interactions introduced by TEPIC are significantly stronger than benzene–benzene stacking. These results indicate that the enhancement of Tg arises not only from an increase in crosslink density but also from localized intermolecular constraints induced by strong stacking interactions, providing a molecular-level design guideline for high-performance epoxy resins.

Zhang, Yanpeng; Sun, Xuehong; Qin, Guoche; Liu, Liping; Liu, Hongshun; Wang, Xingyu

doi: 10.1039/d6cp00004epmid: 42300052

Terahertz (THz) absorbers are attractive for emerging 6G links, imaging, sensing and electromagnetic protection; however, practical devices often face coupled trade-offs among absorption bandwidth, structural complexity, polarization/angle robustness and active tunability. Here, a dual-functional-layer metamaterial absorber is proposed. Unlike conventional single-layered designs, the synergy between a periodically patterned VO2 layer and a continuous VO2 film forms an asymmetric Fabry–Pérot (F–P) cavity that reconfigures the internal field distribution across different phase states. This design allows a continuous VO2 film and a periodically patterned c layer to form an asymmetric F–P cavity, while a metallic backplane eliminates transmission. Finite-element simulations are carried out from 0.1 to 20 THz, and the conductivity evolution across the VO2 insulator-to-metal transition is described with a Drude model. When both VO2 layers are in the metallic state, the absorber provides ultrabroadband near-perfect absorption, exhibiting absorptance above 90% from 3.25–16.56 THz with an average absorptance of approximately 96.4%. By programming the phase states of the two VO2 layers, the response can be switched among an ultrabroadband mode, a dual-band mode (2.15–6.17 THz and 11.75–16.52 THz), and a narrowband mode with a peak absorptance of about 99.98%. The design is essentially polarization-insensitive for rotation angles from 0° to 90° and preserves high absorption up to 60° incidence under both TE and TM polarizations. These results demonstrate a compact route to multifunctional THz absorbers combining ultrabroad bandwidth, wide-angle robustness and reconfigurable control for adaptive THz systems.

Negi, Saurabh Singh; Gupta, Puneet

doi: 10.1039/d5cp04363hpmid: 42046928

N-heterocyclic carbenes (NHCs) are very versatile ligands known for their strong σ-donating ability and stability, making them suitable for forming complexes with alkaline earth metals (AEMs). In this study, we designed a machine learning (ML) based approach for high-throughput screening of NHC–AEM complexes based on their binding energies (BEs), obtained from density functional theory (DFT) optimized structures and single-point domain-based local pair-natural orbital based singles and doubles coupled cluster (DLPNO-CCSD(T)) calculations. The ML models were trained on descriptors derived from fundamental metal properties, RDKit and Sterimol parameters, which were refined through recursive feature refinement steps. The ML workflow involved successive feature refinement steps, beginning with principle component analysis (PCA) filtering (r > 0.9), feature engineering (only in the case of Sterimol parameters), sure independence screening (SIS) based on distance correlation, and stepwise feature elimination. Seven different ML models were trained on the different datasets mentioned above, with the best one achieving a mean square error (MSE) of 0.10 eV2. Furthermore, Shapley additive explanations (SHAP) analysis was employed to identify the most influential descriptor governing BE.

Bütikofer, Matthias; Sonnefeld, Anna; Stadler, Gabriela R.; Torres, Felix; Bodenhausen, Geoffrey; Sheberstov, Kirill F.; Riek, Roland

doi: 10.1039/d6cp00658bpmid: 42212435

Photo chemically induced dynamic nuclear polarization (photo-CIDNP) and long-lived spin states (LLS) are two nuclear magnetic resonance (NMR) techniques that can be combined to achieve large signal enhancements and extended lifetimes of spin order, respectively, and their combination is useful for detecting biomolecular interactions. Here, we demonstrate that integrating photo-CIDNP hyperpolarization with LLS excitation through spin-lock induced crossing (SLIC) enables the highly sensitive detection of signals of ligands at micromolar concentrations. Using indole-3-propionic acid (IPA), we show that two of its CH2 protons are simultaneously suitable for efficient photo-CIDNP polarization and for SLIC-based singlet excitation, thus allowing the conversion of hyperpolarized Zeeman order into long-lived singlet order. The resulting CIDNP-LLS approach provides a signal-to-noise enhancement of up to 30-fold over conventional LLS, enabling the detection of 25 µM IPA in a 3 mm tube within two scans. In the presence of the enzyme arylalkylamine N-acetyltransferase (AANAT) at a 100 nM concentration, CIDNP-LLS offers superior binding contrast compared to conventional CIDNP or CIDNP combined with perfect echo refocusing (CIDNP-PEARLScreen), making it a powerful method for monitoring weak protein–ligand interactions.