Dipolar Repulsion Research Articles

Electricity-Driven Strain-Release Cascade Cyclization of Bicyclo[1.1.0]butane (BCB): Stereoselective Synthesis of Functionalized Spirocyclobutyl Oxindoles.

Spirocyclobutyl oxindoles, characterized by their unique three-dimensional structures, are valuable building blocks for many pharmacophores and drug units. However, stereoselective synthetic strategies for these scaffolds remain underdeveloped, with most existing methods relying on transition metal catalysts and stoichiometric redox reagents. In this work, we introduce an electrochemical strain-release driven cascade spirocyclization of bicyclo[1.1.0]butane (BCB) derivatives for the stereoselective synthesis of functionalized spirocyclobutyl oxindoles. Tetrabutylammonium bromide serves a dual purpose as both a supporting electrolyte and brominating agent. The method offers a broad substrate scope, high atom economy, and excellent diastereoselectivity. The stereoselectivity of the product is controlled by minimizing the dipolar repulsion between the amide C=O and the C-Br bonds. We also explored the methodology's versatility by applying it to various functionalizations and demonstrated its scalability for practical use. The efficient derivatization of the products allowed for the rapid creation of a diverse library of functionalized spirocyclobutyl oxindoles.

Lattice Strain Engineering Boosts CO2 Electroreduction to C2+ Products

AbstractRegulating the binding effect between the surface of an electrode material and reaction intermediates is essential in highly efficient CO2 electro‐reduction to produce high‐value multicarbon (C2+) compounds. Theoretical study reveals that lattice tensile strain in single‐component Cu catalysts can reduce the dipole–dipole repulsion between *CO intermediates and promotes *OH adsorption, and the high *CO and *OH coverage decreases the energy barrier for C−C coupling. In this work, Cu catalysts with varying lattice tensile strain were fabricated by electro‐reducing CuO precursors with different crystallinity, without adding any extra components. The as‐prepared single‐component Cu catalysts were used for CO2 electro‐reduction, and it is discovered that the lattice tensile strain in Cu could enhance the Faradaic efficiency (FE) of C2+ products effectively. Especially, the as‐prepared CuTPA catalyst with high lattice tensile strain achieves a FEC2+ of 90.9 % at −1.25 V vs. RHE with a partial current density of 486.1 mA cm−2.

Exciton-Exciton Interactions in Van der Waals Heterobilayers

Exciton-exciton interactions are key to understanding nonlinear optical and transport phenomena in van der Waals heterobilayers, which emerged as versatile platforms to study correlated electronic states. We present a combined theory-experiment study of excitonic many-body effects based on first-principle band structures and Coulomb interaction matrix elements. Key to our approach is the explicit treatment of the fermionic substructure of excitons and dynamical screening effects for density-induced energy renormalization and dissipation. We demonstrate that dipolar blueshifts are almost perfectly compensated by many-body effects, mainly by screening-induced self-energy corrections. Moreover, we identify a crossover between attractive and repulsive behavior at elevated exciton densities. Theoretical findings are supported by experimental studies of spectrally narrow, mobile interlayer excitons in atomically reconstructed, h-BN-encapsulated MoSe2/WSe2 heterobilayers. Both theory and experiment show energy renormalization on a scale of a few meV even for high injection densities in the vicinity of the Mott transition. Our results revise the established picture of dipolar repulsion dominating exciton-exciton interactions in van der Waals heterostructures and open up opportunities for their external design. Published by the American Physical Society 2024

Unraveling the C–C coupling mechanism on Ni–O–Fe asymmetric sites for photocatalytic nonoxidative coupling of methane

Photocatalytic non-oxidative coupling of methane is an attractive strategy for CH4 to C2 conversion, how to facilitate the photogenerated charge separation and accelerate the C–C coupling to promote the reaction kinetics remains a great challenge. Herein, a symbiotic r-Fe2O3/NiO heterostructure with robust interfaces is constructed in situ. The coherent interface not only provides unique Ni–O–Fe asymmetric sites, but also achieves the separation and transport of photogenerated charge. The unbalanced charge density distribution of two adjacent methyl or methylene at the Ni–O–Fe asymmetric site alleviates the dipole repulsion of the C–C coupling, and promotes C–C coupling to form C2 hydrocarbons. Under visible light irradiation, the optimal r-Fe2O3/NiO performs a brilliant C2 activity up to 71.00 μmol g−1h−1, and the C2H4 yield can reach a high value of 40.46 μmol g−1h−1 and the selectivity of 56.98 %. This work provides new insights into the coupling of C–C to generate C2 hydrocarbons.

Reconfigurable Assembly of Planar Colloidal Molecules via Chemical Reaction and Electric Polarization.

Colloidal molecules, ordered structures assembled from micro- and nanoparticles, serve as a valuable model for understanding the behavior of real molecules and for constructing materials with tunable properties. In this work, we introduce a universal strategy for assembling colloidal molecules consisting of a central active particle surrounded by several passive particles as ligands. During the assembly process, active particles attract the surrounding passive particles through phoresis and osmosis resulting from the chemical reactions on the surface of the active particles, while passive particles repel each other due to the electric polarization induced by an alternating current (AC) electric field. By carefully selecting particles of varying structures and sizes, we have assembled colloidal molecules of symmetric and asymmetric dimers, trimers, and multimers. Furthermore, the coordination number of these colloidal molecules can be regulated in real time and insitu by tuning the interaction forces between the constituent particles. Brownian dynamics simulations reproduced the formation of the colloidal molecules and validated that the self-assembly arises from chemically induced attraction and electrical dipolar repulsion. This strategy for reconfigurable colloidal assemblies poses the potential for designing adaptive micro-nanomachines.

Constructing asymmetric dual active sites through symbiotic effect for achieving efficient and selective photoreduction of CO2 to C2H4

Asymmetric dual active sites are constructed through symbiotic effect. Owing to the differences in electron density, adsorption capacity and dipole–dipole repulsion, the energy barriers are reduced, leading to selective C2H4 production.

Breaking Radial Dipole Symmetry in Planar Macrocycles Modulates Edge-to-Edge Packing and Disrupts Cofacial Stacking.

Dipolar interactions are ever-present in supramolecular architectures, though their impact is typically revealed by making dipoles stronger. While it is also possible to assess the role of dipoles by altering their orientations by using synthetic design, doing so without altering the molecular shape is not straightforward. We have now done this by flipping one triazole unit in a rigid macrocycle, tricarb. The macrocycle is composed of three carbazoles (2 Debye) and three triazoles (5 Debye) defining an array of dipoles aligned radially but organized alternately in and out. These dipoles are believed to dictate edge-to-edge tiling and face-to-face stacking. We modified our synthesis to prepare isosteric macrocycles with the orientation of one triazole dipole rotated 40°. The new dipole orientation guides edge-to-edge contacts to reorder the stability of two surface-bound 2D polymorphs. The impact on dipole-enhanced π stacking, however, was unexpected. Our stacking model identified an unchanged set of short-range (3.4 Å) anti-parallel dipole contacts. Despite this situation, the reduction in self-association was attributed to long-range (~6.4 Å) dipolar repulsions between π-stacked macrocycles. This work highlights our ability to control the build-up and symmetry of macrocyclic skeletons by synthetic design, and the work needed to further our understanding of how dipoles control self-assembly.

Ultrastable Super-Tonks-Girardeau Gases under Weak Dipolar Interactions.

The highly excited super-Tonks-Girardeau (sTG) gas was recently observed to be extremely stable in the presence of a weak dipolar repulsion. Here we reveal the underlying reason for this mysterious phenomenon. By exactly solving the trapped small clusters with both contact and dipolar interactions, we show that the reason lies in the distinct spectral responses between sTG gas and its decaying channel (bound state) when a weak dipolar interaction is present. Specifically, a tiny dipolar force can produce a visible energy shift for the localized bound state, but can hardly affect the extended sTG branch. As a result, the avoided level crossing between two branches is greatly modified in both location and width in the parameter axis of coupling strength, leading to a more (less) stable sTG gas for a repulsive (attractive) dipolar force. These results, consistent with experimental observations, are found to robustly apply to both bosonic and fermionic systems.

Vortex dynamics of a three-dimensional dipolar Bose–Einstein condensate

By numerically solving the Gross–Pitaevskii equation with phenomenological dissipation term, we study the vortex formation properties of a three-dimensional dipolar Bose–Einstein condensate of 164Dy atoms. We studied the influence of the contact interaction between atoms on the formation mechanism of vortices. We also study how the dipole orientation affects the vortex formation properties and the number of vortices. We find that enhancing the interaction of short-range repulsion interaction or dipolar repulsion interaction can shorten the time to form a stable vortex structure and increase the number of vortices.

Strong Dipolar Repulsion of One-Dimensional Interfacial Excitons in Monolayer Lateral Heterojunctions.

Repulsive and long-range exciton-exciton interactions are crucial for the exploration of one-dimensional (1D) correlated quantum phases in the solid state. However, the experimental realization of nanoscale confinement of a 1D dipolar exciton has thus far been limited. Here, we demonstrate atomically precise lateral heterojunctions based at transitional-metal dichalcogenides (TMDCs) as a platform for 1D dipolar excitons. The dynamics and transport of the interfacial charge transfer excitons in a type II WSe2-WS1.16Se0.84 lateral heterostructure were spatially and temporally imaged using ultrafast transient reflection microscopy. The expansion of the exciton cloud driven by dipolar repulsion was found to be strongly density dependent and highly anisotropic. The interaction strength between the 1D excitons was determined to be ∼3.9 × 10-14 eV cm-2, corresponding to a dipolar length of 310 nm, which is a factor of 2-3 larger than the interlayer excitons at two-dimensional van der Waals vertical interfaces. These results suggest 1D dipolar excitons with large static in-plane dipole moments in lateral TMDC heterojunctions as an exciting system for investigating quantum many-body physics.

Harmonic to anharmonic tuning of moiré potential leading to unconventional Stark effect and giant dipolar repulsion in WS2/WSe2 heterobilayer

Excitonic states trapped in harmonic moiré wells of twisted heterobilayers is an intriguing testbed for exploring many-body physics. However, the moiré potential is primarily governed by the twist angle, and its dynamic tuning remains a challenge. Here we demonstrate anharmonic tuning of moiré potential in a WS2/WSe2 heterobilayer through gate voltage and optical power. A gate voltage can result in a local in-plane perturbing field with odd parity around the high-symmetry points. This allows us to simultaneously observe the first (linear) and second (parabolic) order Stark shift for the ground state and first excited state, respectively, of the moiré trapped exciton - an effect opposite to conventional quantum-confined Stark shift. Depending on the degree of confinement, these excitons exhibit up to twenty-fold gate-tunability in the lifetime (100 to 5 ns). Also, exciton localization dependent dipolar repulsion leads to an optical power-induced blueshift of ~ 1 meV/μW - a five-fold enhancement over previous reports.

Small changes in lipid backbone linkages can lead to big changes in liquid-liquid phase separation in model membranes.

Cells can dynamically alter the spatial organization of lipids and proteins in the plasma membrane (PM) to regulate processes including cell signaling. The size and morphology of membrane domains, and how these depend on lipid composition, have drawn attention as potentially important variables in these processes. Model membrane studies have proven invaluable for elucidating the influence of phospholipid chains and headgroups, as well as cholesterol concentration, on membrane phase behavior. Following this approach, we have investigated simplified three- and four-component models for the PM outer leaflet to understand the role of the lipid backbone. Specifically, we replaced ester-linked DPPC and DOPC with their ether-linked counterparts to selectively change the membrane dipole potential of coexisting liquid-disordered (Ld) and liquid-ordered (Lo) phases, while titrating DOPC with POPC to control the line tension. Fluorescence imaging of GUVs gave insight into the macroscopic phase behavior, while FRET and cryo-EM of LUVs allowed us to probe nanoscale heterogeneity. Our results can be understood in terms of a model in which the tendency to minimize line tension is counteracted by dipole repulsion, which can in some cases result in stable arrays of small domains or modulated phases. These findings suggest that relatively small changes in the structure of the lipid backbone can influence domain formation and morphology in biomimetic membranes.

Extended Bose-Hubbard model with dipolar excitons.

The Hubbard model constitutes one of the most celebrated theoretical frameworks of condensed-matter physics. It describes strongly correlated phases of interacting quantum particles confined in lattice potentials1,2. For bosons, the Hubbard Hamiltonian has been deeply scrutinized for short-range on-site interactions3-6. However, accessing longer-range couplings has remained elusive experimentally7. This marks the frontier towards the extended Bose-Hubbard Hamiltonian, which enables insulating ordered phases at fractional lattice fillings8-12. Here we implement this Hamiltonian by confining semiconductor dipolar excitons in an artificial two-dimensional square lattice. Strong dipolar repulsions between nearest-neighbour lattice sites then stabilize an insulating state at half filling. This characteristic feature of the extended Bose-Hubbard model exhibits the signatures theoretically expected for a chequerboard spatial order. Our work thus highlights that dipolar excitons enable controlled implementations of boson-like arrays with strong off-site interactions, in lattices with programmable geometries and more than 100 sites.

Quantum phases of bosonic chiral molecules in helicity lattices

We reveal the existence of polarizing quantum phases for the enantiomers of cold, interacting chiral molecules in an optical helicity lattice by means of an extended Bose-Hubbard model. These recently proposed lattices have sites with alternating helicity which exert a discriminatory force on chiral molecules with different handedness. In our study of the phase diagram we find that a strong dipolar repulsion between molecules results in the separation of left and right enantiomers.

Correction to: A Nonlocal Isoperimetric Problem with Dipolar Repulsion

Correction to: A Nonlocal Isoperimetric Problem with Dipolar Repulsion

Carbene Ligands Enabled C–N Coupling for Methylamine Electrosynthesis: A Computational Study

Electrocatalytic conversion of carbon monoxide (CO) and nitric oxide (NO) into methylamine (MMA, CH3NH2) could convert excessive renewable energy and environmental pollutants into valuable chemicals. The main hurdle, however, is the inefficient C–N coupling as a result of the repulsive dipole–dipole interaction between adjacent coupling precursors. Herein, we report a simple strategy to weaken the repulsive dipole–dipole interaction using N-heterocyclic carbene to modify the pristine catalyst surface. The pristine catalyst for our study is MXene-doped with two Cu atoms using the O vacancy site of Mo2NO2 (Cu2@v-Mo2NO2). Our molecular modeling work based on density functional theory calculation discovered that surface-functionalized carbene ligands perturb the electronic configuration of chelated Cu sites, hence causing charge redistribution on the adsorbed reaction intermediates. Such charge redistribution successfully weakens the CO/NO dipole–dipole repulsion, effectively optimizes the binding strength of precursors, and leads to an effective C–N bond formation. Consequently, a pathway that selectively converts CO and NO to MMA with a facile C–N coupling step and low limiting potential is identified on the catalyst surface. Our work suggests a facile electrocatalyst surface functionalization strategy for the improved coupling between small-molecule precursors featuring dipole–dipole repulsion, with the potential to generalize to the sustainable synthesis of multi-carbon/nitrogen chemicals.

Dual nature of magnetic nanoparticle dispersions enables control over short-range attraction and long-range repulsion interactions

Competition between attractive and repulsive interactions drives the formation of complex phases in colloidal suspensions. A major experimental challenge lies in decoupling independent roles of attractive and repulsive forces in governing the equilibrium morphology and long-range spatial distribution of assemblies. Here, we uncover the ‘dual nature’ of magnetic nanoparticle dispersions, particulate and continuous, enabling control of the short-range attraction and long-range repulsion (SALR) between suspended microparticles. We show that non-magnetic microparticles suspended in an aqueous magnetic nanoparticle dispersion simultaneously experience a short-range depletion attraction due to the particulate nature of the fluid in competition with an in situ tunable long-range magnetic dipolar repulsion attributed to the continuous nature of the fluid. The study presents an experimental platform for achieving in situ control over SALR between colloids leading to the formation of reconfigurable structures of unusual morphologies, which are not obtained using external fields or depletion interactions alone.

The Optical Absorption Force Allows Controlling Colloidal Assembly Morphology at an Interface

AbstractGaining control on particle–particle interactions and in this way on their (self)‐assembled structures is essentialfor colloidal and material sciences. Currently, different strategies are described to achieve such control, however, all of them lack the spatiotemporal resolution required at the microscale. In this work, the potential of combining optical trapping and resonant photoexcitation for modifying particle–particle interactions and subsequent assembling of dye‐doped particles at the solution interface is demonstrated. The particle assemblies prepared by nonresonant 1064 nm optical trapping undergo morphology changes after resonant photoexcitation of the embedded dye molecules. Depending on the physicochemical properties of interface, quick hexagonal close packing (HCP)‐rearrangement or explosive dispersion of assemblies is observed at air/solution (A/S) and glass/solution interfaces, respectively. By contrast, by resonant photoexcitation only, the dispersed dye‐doped particles are pushed toward the A/S interface, followed by association to yield HCP‐structured assemblies. The results are rationalized by considering the optical absorption force coupled with other nonoptical forces (e.g., capillary force, dipole–dipole or electrostatic repulsion) at the solution interface. Due to the inherent spatiotemporal properties of light and electronic transition of materials, absorption force is a unique element to control and modify the structural order of particle assemblies at interfaces.

Investigating the role of membrane dipole potential in liquid-liquid phase separation: ether lipids influence domain size

Lateral lipid heterogeneity is thought to play an important role in the functioning of cell membranes. Parameters such as the shape, size, and composition of domains are not well-understood in biological membranes, in part because of their chemical complexity. Factors including line tension, dipole repulsions, and thermal fluctuations contribute to these parameters. To elucidate the impact of these factors, we use simple three- or four- component model membranes. Liquid-liquid phase separation in these systems have provided numerous insights into the behavior of domains in biological membranes.

Oxidation of Sn at the Cluster–Support Interface: Sn and Pt–Sn Clusters on TiO2(110)

The growth of Sn and Pt–Sn clusters on TiO2(110) has been studied by scanning tunneling microscopy, X-ray photoelectron spectroscopy (XPS), low energy ion scattering (LEIS), and density functional theory (DFT). At low Sn coverages (0.02 ML), single-layer high clusters of SnOx are formed with a narrow size distribution and uniform spatial distribution. XPS experiments indicate that these clusters consist of oxidized Sn, and the corresponding reduction in the TiO2 substrate is observed. At higher Sn coverages, the surface is still dominated by two-dimensional clusters of SnOx, but larger three-dimensional clusters of metallic Sn also appear. As the Sn coverage is increased, the number of three-dimensional clusters increases, and the ratio of Sn/SnOx increases, suggesting that SnOx and reduced TiOx form at the cluster–support interface. When Pt is deposited on top of the Sn/SnOx clusters, the relatively mobile Pt atoms diffuse across the TiO2 surface and become incorporated into existing Sn/SnOx clusters. Furthermore, the addition of Pt to the Sn/SnOx clusters causes the reduction of SnOx to metallic Sn and the oxidation of Ti3+ to Ti4+; this behavior is attributed to the formation of Pt–Sn alloy clusters, which results in the diffusion of Sn away from the interface with the TiO2 support. In contrast, when Sn is deposited on an equal coverage of Pt clusters, new Sn/SnOx clusters are formed that coexist with Pt–Sn clusters. However, the surfaces of both Pt on Sn and Sn on Pt clusters are Sn-rich due to the lower surface free energy of Sn compared to Pt. DFT calculations demonstrate that M–TiO2 bonding is favored over M–M bonding for M = Sn, unlike for transition metals such as M = Pt, Au, Ni, and Co. Furthermore, the substantial charge transfer from Sn to TiO2 leads to dipole–dipole repulsion of Sn atoms that prevents agglomeration into the larger clusters that are observed for the mid-late transition metals. DFT studies also confirm that the addition of Pt to a Sn cluster results in strong Pt–Sn bond formation and diminished Sn–O interactions.