Curvature and self-assembly of semi-conducting nanoplatelets

Semi-conducting nanoplatelets are two-dimensional nanoparticles whose thickness is in the nanometer range and controlled at the atomic level. They have come up as a new category of nanomaterial with promising optical properties due to the efficient confinement of the exciton in the thickness direction. In this perspective, we first describe the various conformations of these 2D nanoparticles which display a variety of bent and curved geometries and present experimental evidences linking their curvature to the ligand-induced surface stress. We then focus on the assembly of nanoplatelets into superlattices to harness the particularly efficient energy transfer between them, and discuss different approaches that allow for directional control and positioning in large scale assemblies. We emphasize on the fundamental aspects of the assembly at the colloidal scale in which ligand-induced forces and kinetic effects play a dominant role. Finally, we highlight the collective properties that can be studied when a fine control over the assembly of nanoplatelets is achieved.

Thermal synthesis of conversion-type bismuth fluoride cathodes for high-energy-density Li-ion batteries

Towards enhancement of the energy density of Li-ion batteries, BiF3 has recently attracted considerable attention as a compelling conversion-type cathode material due to its high theoretical capacity of 302 mAh g−1, average discharge voltage of ca. 3.0 V vs. Li+/Li, the low theoretical volume change of ca. 1.7% upon lithiation, and an intrinsically high oxidative stability. Here we report a facile and scalable synthesis of phase-pure and highly crystalline orthorhombic BiF3via thermal decomposition of bismuth(III) trifluoroacetate at T = 300 °C under inert atmosphere. The electrochemical measurements of BiF3 in both carbonate (LiPF6-EC/DMC)- and ionic liquid-based (LiFSI-Pyr1,4TFSI) Li-ion electrolytes demonstrated that ionic liquids improve the cyclic stability of BiF3. In particular, BiF3 in 4.3 M LiFSI-Pyr1,4TFSI shows a high initial capacity of 208 mA g−1 and capacity retention of ca. 50% over at least 80 cycles at a current density of 30 mA g−1.

Structural insights into the potency and selectivity of covalent pan-FGFR inhibitors

FIIN-2, TAS-120 (Futibatinib) and PRN1371 are highly potent pan-FGFR covalent inhibitors targeting the p-loop cysteine of FGFR proteins, of which TAS-120 and PRN1371 are currently in clinical trials. It is critical to analyze their target selectivity and their abilities to overcome gatekeeper mutations. In this study, we demonstrate that FIIN-2 and TAS-120 form covalent adducts with SRC, while PRN1371 does not. FIIN-2 and TAS-120 inhibit SRC and YES activities, while PRN1371 does not. Moreover, FIIN-2, TAS-120 and PRN1371 exhibit different potencies against different FGFR gatekeeper mutants. In addition, the co-crystal structures of SRC/FIIN-2, SRC/TAS-120 and FGFR4/PRN1371 complexes reveal structural basis for kinase targeting and gatekeeper mutations. Taken together, our study not only provides insight into the potency and selectivity of covalent pan-FGFR inhibitors, but also sheds light on the development of next-generation FGFR covalent inhibitors with high potency, high selectivity, and stronger ability to overcome gatekeeper mutations.

Ordering a rhenium catalyst on Ag(001) through molecule-surface step interaction

Atomic scale studies of the anchoring of catalytically active complexes to surfaces may provide valuable insights for the design of new catalytically active hybrid systems. In this work, the self-assembly of 1D, 2D and 3D structures of the complex fac-Re(bpy)(CO)3Cl (bpy = 2,2′-bipyridine), a CO2 reduction catalyst, on the Ag(001) surface are studied by a combination of low-temperature scanning tunneling microscopy and density functional theory calculations. Infrared and sum frequency generation spectroscopy confirm that the complex remains chemically intact under sublimation. Deposition of the complexes onto the silver surface at 300 K leads to strong local variations in the resulting surface coverage on the nanometer scale, indicating that in the initial phase of deposition a large fraction of the molecules is desorbing from the surface. Low coverage regions show a decoration of step edges aligned along the crystal’s symmetry axes <110>. These crystallographic directions are found to be of major importance to the binding of the complexes to the surface. Moreover, the interaction between the molecules and the substrate promotes the restructuring of surface steps along these directions. Well-aligned and decorated steps are found to act as nucleation point for monolayer growth (2D) before 3D growth starts.

Superelasticity of a photo-actuating chiral salicylideneamine crystal

Superelasticity is a type of elastic response to an applied external force, caused by a phase transformation. Actuation of materials is also an elastic response to external stimuli such as light and heat. Although both superelasticity and actuation are deformations resulting from stimulus-induced stress, there is a phenomenological difference between the two with respect to whether force is an input or an output. Here, we report that a molecular crystal manifests superelasticity during photo-actuation under light irradiation. The crystal exhibits stepwise twisted actuation due to two effects, photoisomerization and photo-triggered phase transition, and the actuation behavior is simulated based on a dynamic multi-layer model. The simulation, in turn, reveals how the photoisomerization and phase transition progress in the crystal, indicating superelasticity induced by modest stress due to the formation of photoproducts. This work provides not only a successful simulation of stepwise twisted actuation, but also to the best of our knowledge the first indication of superelasticity induced by light.

Prediction of heptagonal bipyramidal nonacoordination in highly viable [OB-M©B7O7-BO]− (M = Fe, Ru, Os) complexes

Non-spherical distributions of ligand atoms in coordination complexes are generally unfavorable due to higher repulsion than for spherical distributions. To the best of our knowledge, non-spherical heptagonal bipyramidal nonacoordination is hitherto unreported, because of extremely high repulsion among seven equatorial ligand atoms. Herein, we report the computational prediction of such nonacoordination, which is constructed by the synergetic coordination of an equatorial hepta-dentate centripetal ligand (B7O7) and two axial mono-dentate ligands (-BO) in the gear-like mono-anionic complexes [OB-M©B7O7-BO]– (M = Fe, Ru, Os). The high repulsion among seven equatorial ligand B atoms has been compensated by the strong B–O bonding. These complexes are the dynamically stable (up to 1500 K) global energy minima with the HOMO-LUMO gaps of 7.15 to 7.42 eV and first vertical detachment energies of 6.14 to 6.66 eV (being very high for anions), suggesting their high probability for experimental realization in both gas-phase and condensed phases. The high stability stems geometrically from the surrounded outer-shell oxygen atoms and electronically from meeting the 18e rule as well as possessing the σ + π + δ triple aromaticity. Remarkably, the ligand-metal interactions are governed not by the familiar donation and backdonation interactions, but by the electrostatic interactions and electron-sharing bonding.

Interactions between atomically dispersed copper and phosphorous species are key for the hydrochlorination of acetylene

Vinyl chloride, the monomer of polyvinyl chloride (PVC), is industrially synthesized via acetylene hydrochlorination. Thereby, easy to sublimate but toxic mercury chloride catalysts are widely used. It is imperative to find environmentally friendly non-mercury catalysts to promote the green production of PVC. Low-cost copper-based catalysts are promising candidates. In this study, phosphorus-doped Cu-based catalysts are prepared. It is shown that the type of phosphorus configuration and the distribution on the surface of the carrier can be adjusted by changing the calcination temperature. Among the different phosphorus species, the formed P-C bond plays a key role. The coordination structure formed by the interaction between P-C bonds and atomically dispersed Cu2+ species results in effective and stable active sites. Insights on how P-C bonds activate the substrate may provide ideas for the design and optimization of phosphorus-doped catalysts for acetylene hydrochlorination.

Mechanochemistry of phosphate esters confined between sliding iron surfaces

The molecular structure of lubricant additives controls not only their adsorption and dissociation behaviour at the nanoscale, but also their ability to reduce friction and wear at the macroscale. Here, we show using nonequilibrium molecular dynamics simulations with a reactive force field that tri(s-butyl)phosphate dissociates much faster than tri(n-butyl)phosphate when heated and compressed between sliding iron surfaces. For both molecules, dissociative chemisorption proceeds through cleavage of carbon−oxygen bonds. The dissociation rate increases exponentially with temperature and stress. When the rate−temperature−stress data are fitted with the Bell model, both molecules have similar activation energies and activation volumes and the higher reactivity of tri(s-butyl)phosphate is due to a larger pre-exponential factor. These observations are consistent with experiments using the antiwear additive zinc dialkyldithiophosphate. This study represents a crucial step towards the virtual screening of lubricant additives with different substituents to optimise tribological performance.

Environment-sensitive emission of anionic hydrogen-bonded urea-derivative–acetate-ion complexes and their aggregation-induced emission enhancement

Anions often quench fluorescence (FL). However, strong ionic hydrogen bonding between fluorescent dyes and anion molecules has the potential to control the electronic state of FL dyes, creating new functions via non-covalent interactions. Here, we propose an approach, utilising ionic hydrogen bonding between urea groups and anions, to control the electronic states of fluorophores and develop an aggregation-induced emission enhancement (AIEE) system. The AIEE ionic hydrogen-bonded complex (IHBC) formed between 1,8-diphenylnaphthalene (p-2Urea), with aryl urea groups at the para-positions on the peri-phenyl rings, and acetate ions exhibits high environmental sensitivities in solution phases, and the FL quantum yield (QY) in ion-pair assemblies of the IHBC and tetrabutylammonium cations is more than five times higher than that of the IHBC in solution. Our versatile and simple approach for the design of AIEE dye facilitates the future development of environment-sensitive probes and solid-state emitting materials.