We report the directed diastereoselective Simmons–Smith cyclopropanation and vanadium-catalyzed epoxidation reactions of alkenyl cyclopropyl carbinol derivatives. The reaction furnished densely substituted stereodefined bicyclopropanes and cyclopropyl oxiranes as a single diastereomer in each case. The remarkable selectivity is obtained thanks to the rigidity of the cyclopropyl core, allowing diastereoselective reactions on the alkenyl moiety. This emphasizes the uniqueness of the cyclopropyl ring as a central platform in stereoselective synthesis.

Fluorine atoms play an important role in all branches of chemistry and accordingly, it is very important to study their unique and varied effects systematically, in particular, the structure-physicochemical properties relationship. The present study describes exceptional physicochemical effects resulting from a H/F exchange at the methylene bridge of gem-difunctional compounds. The Δlog P (CF2-CH2) values, i.e. the change in lipophilicity, observed for the CH 2 /CF 2 replacement in various α,α-phenoxy- and thiophenoxy-esters/amides, diketones, benzodioxoles and more, fall in the range of 0.6-1.4 units, which for most cases, is far above the values expected for such a replacement. Moreover, for compounds holding more than one such gem-difunctional moiety, the effect is nearly additive, so one can switch from a hydrophilic compound to a lipophilic one in a limited number of H/F exchanges. DFT studies of some of these systems revealed that polarity, conformational prference as well as charge distributions are strongly affected by such hydrogen to fluorine atom substitution. The pronounced effects described, are a result of the interplay between changes in polarity, H-bond basicity and molecular volume, which were obtained with a very low ‘cost’ in terms of molecular weight or steric effects and may have a great potential for implementation in various fields of chemical sciences.

Exfoliated magnetic 2D materials provide access to a versatile tuning of magnetization properties, e.g., by gating and by proximity-induced exchange interactions with other types of 2D materials. However, the electronic band structure after exfoliation has not been probed for such materials yet, mostly due to their photochemical sensitivity. Here, we provide micron-scale angle-resolved photoelectron spectroscopy of the exfoliated intralayer antiferromagnet MnPS$_3$ above and below the N\'{e}el temperature in comparison with density functional theory calculations. We demonstrate a significant splitting of parts of the Mn 3d$_{z^2}$-bands induced by the antiferromagnetic ordering. Related changes of adjacent S 3p-bands indicate a competing contribution of a ferromagnetic superexchange. The novel access to the electronic band structure is likely transferable to other MPX$_3$ materials (M: transition metal, P: phosphorus, X: chalcogenide) that provide a multitude of antiferromagnetic arrangements.

We consider the dynamics of a quantum system immersed in a dilute gas at thermodynamics equilibrium using a quantum Markovian master equation derived by applying the low-density limit technique. It is shown that the Gibbs state at the bath temperature is always stationary while the detailed balance condition at this state can be violated beyond the Born approximation. This violation is generically related to the absence of time-reversal symmetry for the scattering T-matrix, which produces a thermalization mechanism that allows the presence of persistent probability and heat currents at thermal equilibrium. This phenomenon is illustrated by a model of an electron hopping between three quantum dots in an external magnetic field.

Solvent molecules are known to affect chemical reactions, especially if they interact with one or more of the reactants or catalysts. In ion microsolvation, i.e., solvent molecules in the first solvation sphere, strong electronic interactions are created, leading to significant changes in charge distribution and consequently on their nucleophilicity/electrophilicity and acidity/basicity. Despite a long history of research in the field, fundamental issues regarding the effects of ion microsolvation are still open, especially in the condensed phase. Using reactions between hydroxide and relatively stable quaternary ammonium salts as an example, we show that water microsolvation can change hydroxide’s chemoselectivity by differently affecting its basicity and nucleophilicity. In this example, the hydroxide reactivity as a nucleophile is less affected by water microsolvation than its reactivity as a base. These disparities are discussed by calculating and comparing oxidation potentials and polarizabilities of the different water–hydroxide clusters.

Qualitative aromaticity-based arguments are often used to explain singlet fission (SF) properties in polycyclic conjugated systems. It has been shown by Fowler and collaborators that magnetically induced ring currents are associated with transitions between occupied and unoccupied molecular orbitals (MOs). Since SF has to do with relative energies of electronic states, it was hypothesized that induced currents may indicate SF properties. The quantitative aromaticity of linear oligoacene and several doubly boron-doped anthracenes and phenanthrenes, in their closed-shell singlet, open-shell singlet (where applicable), and triplet electronic states, has been studied using nucleus-independent chemical shift (NICS)-XY scan methods. It is shown that quantitative magnetic aromaticity can be used to identify SF compounds, at least for initial screening. Thus, the induced current features that are indicative of singlet fission (SF) ability have been found to be global current and local current at each ring of the systems. This conclusion was verified for very different systems─a tetracyclic, nitrogen-containing quinone (6), diphenyl benzofurane (7), and cibalackrot (8), all reported to be SF systems. Finally, it is predicted that some isomers of the doubly boron-doped linear[4]phenylene should show SF properties.

The spectator exciton method follows stepwise changes in a nanocrystal’s absorption with the accumulated number of excitons. It involves comparison of pump–probe spectra in pristine samples with that from nanocrystals excited with a progressive number of cold excitons. Using this approach, 50% of hot electrons were shown to be blocked from cooling directly to the band edge in CdSe nanodots already excited with a single cold exciton due to electron spin orientation conflicts. Similar experiments which are reported here in quantum-confined PbS nanodots have not detected spin-related relaxation blockades. Instead, a progressive broadening of the 1S_e1S_h absorption band with loading of cold excitons is manifest in the difference spectra, demonstrating the inadequacy of any single-probe wavelength to quantify band-edge state filling. Comparing data for single and double spectator states proves that the sub band gap induced absorption characteristic of hot exciton states in all quantum dots is not the low-energy half of biexciton shifting to the 1S_e1S_h absorption band. Instead, it is part of a broad induced absorption characteristic of hot excitons regardless of the spectator count. Finally, the unique capability of spectator excitons (SXs) to detect contributions of stimulated emission to pump–probe signals is demonstrated in singly excited PbS nanocrystals. Contrary to recent literature reports of such contributions, none are observed. These outcomes call for revisions to the conventional interpretation of excited state spectroscopy in quantum confined nanocrystals.

Pore structure is a critical material property of carbon materials, determining their surface area, active site accessibility, wettability, and efficiency of bubble removal. In the self-templating approach to pore design, inorganic particles form inside a carbon during pyrolysis, templating meso- and macropores. This strategy is simple and economic, yet limited by choice of templating elements and by incomplete understanding of carbon-template interactions. We followed the self-templating process of eight lanthanoid coordination compounds (the iminodiacetates of La³⁺, Nd³⁺, Sm³⁺, Eu³⁺, Gd³⁺, Tb³⁺, Er³⁺, and Yb³⁺), shedding light on the pore structure and the processes that form it. The resulting carbons showed high BET specific surface areas (up to 2700 m² g⁻¹), hierarchical micro-, meso- and macro-porosity, and lanthanoid-imprinted nitrogen moieties that could be transmetalated to yield atomically dispersed Fe–N_x sites. Some of the resulting Fe–N–C materials showed excellent activity towards hydrazine oxidation electrocatalysis, helping to identify several key links between porosity and electrocatalysis, especially the removal of electrode-blocking N₂(g) bubbles. Overall, this detailed investigation expands the toolbox of rational design methods towards rich and useful electrocatalyst porosities.

Natural processes continuously degrade a material’s performance throughout its life cycle. An emerging class of synthetic self-healing polymers and composites possess property-retaining functions with the promise of longer lifetimes. But sustained in-service repair of structural fiber-reinforced composites remains unfulfilled due to material heterogeneity and thermodynamic barriers in commonly cross-linked polymer-matrix constituents. Overcoming these inherent challenges for mechanical self-recovery is vital to extend in-service operation and attain widespread adoption of such bioinspired structural materials. Here we transcend existing obstacles and report a fiber-composite capable of minute-scale and prolonged in situ healing — 100 cycles: an order of magnitude higher than prior studies. By 3D printing a mendable thermoplastic onto woven glass/carbon fiber reinforcement and co-laminating with electrically resistive heater interlayers, we achieve in situ thermal remending of internal delamination via dynamic bond re-association. Full fracture recovery occurs below the glass-transition temperature of the thermoset epoxy-matrix composite, thus preserving stiffness during and after repair. A discovery of chemically driven improvement in thermal remending of glass- over carbon-fiber composites is also revealed. The marked lifetime extension offered by this self-healing strategy mitigates costly maintenance, facilitates repair of difficult-to-access structures (e.g., wind-turbine blades), and reduces part replacement, thereby benefiting economy and environment.

One-dimensional (1D) semiconductor heterojunctions with asymmetric or symmetric metal cocatalysts are promising systems for high-performance photocatalytic reactions such as solar-to-fuel conversion as the heterostructure junction enables improved charge separation. However, synthesizing such unique heterostructures with well-designed non-noble-metal cocatalysts in an affordable and scalable manner remains a challenging task. Herein, we report the sequential selective growth of ternary dumbbells composed of IrSe₂@MoSe₂-CdS nanowires (TDNWs), in which clusters of an IrSe₂ core coated with a MoSe₂ shell are selectively grown on both ends of CdS nanowires (NWs). This special configuration contributes to efficient charge separation. With this unique structure, the TDNWs exhibit a photocatalytic H₂ production rate of as high as 137 mmol/g h and an apparent quantum efficiency (AQE) of ∼14.5% within 1 h, which is far superior to those of non-tipped CdS NWs and asymmetrical MoSe₂-tipped CdS NWs (ANWs). Our facile synthetic strategy extends spatial anisotropic nanorod growth and enables the construction of advanced multifunctional nano-heterostructures, paving the path for new applications.