Abstract For insight into photochemical processes, it is required to observe structures and spectra with the corresponding thermodynamic functions and electronic states. We have compared the photochemical processes between MV[NiL2]2 (L = 1,3-dithole-2-selone-4,5-dithiolate, the selone derivative, or L = 1,3-dithiole-2-thione-4,5-dithiolate, the thione derivative), which exhibited sufficiently slow photochemical changes to observe them by various methods, to study heavy-atom effects on photoluminescence. X-ray single-crystal structural analyses, first-principles calculations, and Raman spectra indicated that, in both derivatives after cessation of photoirradiation, their molecular orbitals, charge distributions, and thermodynamic quantities remained changing for weeks to months. Triggered by a 532 nm laser, the selone derivative more efficiently emitted infrared light than did the thione derivative. Comparison between the two derivatives revealed structural and thermodynamic aspects of heavy-atom effects. The findings bridge macroscopic and microscopic viewpoints of photoinduced phenomena in materials, providing experimental grounds for theories.
Abstract Grain boundaries (GBs) in monolayer 1H-MoS2 can provide favorable hydrogen-adsorption sites relevant to the hydrogen evolution reaction (HER), but the atomistic origin of this behavior remains unclear for experimentally realized boundary structures. Here, spin-polarized density functional theory calculations are performed to investigate an experimentally observed ∼18° MoS2 GB containing an apparently periodic sequence of five-, seven-, and four-membered rings, i.e., 5–7–4 GB motif. Four local configurations (α1, α2, β1, and β2) are examined as candidate structures of the 5–7–4 GB motif. The β-oriented supercell exhibits a lower average GB formation energy (11.02 eV nm–1) than the α-oriented supercell (12.86 eV nm–1), while β1 most closely reproduces the experimentally inferred bond connectivity. GB reconstruction generates boundary-localized Mo 4d and S 3p states near the Fermi level. Among six distinct sulfur environments, the undercoordinated h2 (α1) and h4 (β1) sites exhibit near-thermoneutral hydrogen adsorption free energies of −0.20 and −0.05 eV, respectively. Occupied nonbonding states localized on these sulfur sites provide a plausible electronic origin for their favorable hydrogen adsorption thermodynamics.
Abstract Surface-enhanced Raman scattering (SERS) on single-atom platforms offers a reproducible, hotspot-free sensing paradigm, yet its fundamental mechanism remains elusive. Herein, we present a comprehensive density functional theory (DFT) investigation into the “Single-Atom-Intermediated Raman Activation (SAIRA)” mechanism using a pyridine-adsorbed Au/g-C3N4 model. Ground-state electronic structure analyses reveal that the cavity-confined Au single atom acts as an indispensable polarization center that triggers strong orbital hybridization and interfacial charge transfer upon molecular adsorption. Consequently, the simulated static Raman activity yields a chemical enhancement factor about 1 order of magnitude higher than that of conventional Au20 clusters. Based on a model chemistry established through systematic benchmark evaluations of DFT functionals and basis sets, this protocol successfully captured experimental observations across various probe molecules. Importantly, extending this validated protocol to a two-dimensional descriptor map based on energetic and electronic parameters for 30 d-block elements reveals that the systems segregate into three distinct mechanistic domains, exhibiting pronounced interdomain variations in Raman enhancement. Furthermore, this 2D descriptor mapping demonstrates high robustness against alternative model chemistries. Ultimately, this work establishes electronic-level design principles not only for next-generation single-atom-based SERS technologies but also for the rational design of functional single-atom catalysts.
Abstract The pursuit of atomic-scale magnetic storage has driven intense research into lanthanide-based single-atom magnets (SAMs), where magnetic bistability and long magnetic relaxation times are essential for practical applications. However, a fundamental challenge is to achieve strong uniaxial magnetic anisotropy while simultaneously suppressing quantum tunneling of magnetization (QTM), since the former stabilizes the magnetization whereas the latter enables rapid relaxation and undermines magnetic memory. Here, we systematically investigate the magnetic stability and relaxation dynamics of Ho (4f10, J = 8) and Tb (4f8, J = 6) adatoms adsorbed on defective hexagonal boron nitride (Dh-BN) with C3v symmetry, using an integrated approach combining density functional theory (DFT+U+SOC) and model Hamiltonian analysis. Our results reveal that the interplay between total angular momentum J and crystal field symmetry dictates the intrinsic magnetic stability. For Ho@Dh-BN, C3v symmetry protects the degenerate |J = 8, mJ ≈ ±8⟩ ground states from QTM, as transverse crystal field terms (ΔmJ = ±3) cannot mix the |±8⟩ states. This yields a substantial effective reversal barrier of Urev = 28.72 meV and an Arrhenius magnetic lifetime of 1150 s at 12 K, demonstrating robust zero-field stability. In stark contrast, Tb@Dh-BN exhibits strong mixing of its |J = 6, mJ ≈ ±6⟩ ground states via QTM channels, resulting in a vanishing reversal barrier and no magnetic stability at zero field. Remarkably, applying an external magnetic field (B = 8 T) along the easy axis can restore the stability in the Tb system: the magnetic field lifts the ground-state degeneracy to suppress QTM by purifying the wave functions and forces magnetization reversal to proceed via multistep spin-flip pathways. This raises an effective barrier to Urev = 42.10 meV and extends the Arrhenius magnetic lifetime to 791 s at 18 K. Our work establishes two complementary design principles for achieving long spin lifetimes in lanthanide SAMs: intrinsic protection through favorable combinations of J and crystal field symmetry that inherently forbid QTM, and active field-induced stabilization that dynamically suppresses QTM in otherwise unstable systems. The findings provide a comprehensive microscopic understanding of magnetic relaxation in surface-supported lanthanide atoms and offer a clear theoretical roadmap for engineering electrically or magnetically addressable atomic-scale memory devices.
Abstract Efficient charge transfer at near-zero frontier-orbital offset is established; whether a fast transfer rate guarantees a high charge-generation yield is not. We examine this in PTO2:IT-4F (PCE 14.7%), whose HOMO (∼0.07 eV) and LUMO (∼0.52 eV) offsets are strongly asymmetric: 720 nm excitation opens only the near-zero-offset hole channel, whereas 530 nm excitation also opens the conventional-offset electron channel at the same junction. At 720 nm, a PTO2 hole-polaron bleach at 550 nm, free of acceptor features, reports hole transfer directly. Global target analysis in which all IT-4F excitons share one spectrum, requiring no extinction coefficients, shows that only about 45% of the excitons transfer in 0.57 ps; the rest transfer in 4.5 ps after diffusing to an interface, for a total injection yield of at least 60%. The yield is limited downstream: about 42% of the bound pairs recombine geminately (τ ≈ 140 ps). At 530 nm, energy transfer and direct electron-transfer quench PTO2 excitons within the instrument response in similar proportions (energy transfer ≈0.5, electron transfer ≈0.5). A delayed rise assigned to long-range separation persists in PTO2:IT-4F but is nearly absent in PTO2:PC71BM despite its larger HOMO offset, pointing to the donor/acceptor pair rather than energetic alignment as the origin of the high efficiency.
