Directional dipole dice enabled by anisotropic chirality.

Directional radiation and scattering play an essential role in light manipulation for various applications in integrated nanophotonics, antenna and metasurface designs, quantum optics, etc. The most elemental system with this property is the class of directional dipoles, including the circular dipole, Huygens dipole, and Janus dipole. A unified realization of all three dipole types and a mechanism to freely switch among them are previously unreported, yet highly desirable for developing compact and multifunctional directional sources. Here, we theoretically and experimentally demonstrate that the synergy of chirality and anisotropy can give rise to all three directional dipoles in one structure at the same frequency under linearly polarized plane wave excitations. This mechanism enables a simple helix particle to serve as a directional dipole dice (DDD), achieving selective manipulation of optical directionality via different "faces" of the particle. We employ three "faces" of the DDD to realize face-multiplexed routing of guided waves in three orthogonal directions with the directionality determined by spin, power flow, and reactive power, respectively. This construction of the complete directionality space can enable high-dimensional control of both near-field and far-field directionality with broad applications in photonic integrated circuits, quantum information processing, and subwavelength-resolution imaging.

Mie Magnetic Structural Colors from Short Chains of TiO2 Nanospheres.

We demonstrate distinctive structural colors within a small footprint by using a short chain of nanospheres. Rather than using high-index materials like Si (n ∼ 4), which ensure strong modal confinement, TiO2 is employed. TiO2 has an intermediate index (n ∼ 2), promoting stronger modal coupling between the magnetic dipoles of each particle. This approach enables selective engineering of the magnetic response and yields larger spectral changes compared to that of Si. Despite the lower refractive index, the absence of absorption in TiO2 also produces higher scattering intensities than Si. We develop a quasistatic analytical model that describes the dipolar modal coupling in a trimer and use it to reveal distinct magnetic field strengths in the outer or central particle depending on the polarization of incident light. These results suggest pathways to manipulate the magnetic field in chains of particles and create vibrant structural colors with simple configurations.

High-Performance Up-Conversion Photodetectors with Zero-Barrier Interconnection via Self-Assembled Surface Dipoles.

The performance of lead sulfide (PbS) quantum-dot-based up-conversion photodetectors is greatly limited owing to a large potential barrier at the interconnection layer between the photodetecting (PD) unit and light-emitting (LED) unit. Thus, very high driving voltage is required, rendering high energy consumption and poor working stability. By introducing azetidinium iodide (AzI) at the PD/LED interface, zero-barrier interconnection was achieved for the PbS-based infrared up-conversion photodetectors. The turn-on voltage under infrared illumination was greatly reduced to 1.2 V and a high photon-to-photon conversion efficiency (ηpp) of ∼3% was obtained at 3 V, showing a 10-fold enhancement compared to those previously reported devices. The mechanism for the regulation of interface energy level alignments was related to the self-assembly of the AzI dipole molecules, resulting from the van der Waals force between the S atoms in the ligands of PbS and the protonated H atoms around N atoms in AzI.

Achieving Ideal Magnetic Light Emission with Electric-Type Emitters.

Optical magnetic dipole (MD) emission predominantly relies on emitters with significant MD transitions, which, however, rarely exist in nature. Here, we propose a strategy to transform electric dipole (ED) emission to a magnetic one by elegantly coupling an ED emitter to a silicon nanoparticle exhibiting a strong MD resonance. This emission mode transformation enables an artificially ideal magnetic dipole source with an MD purity factor of up to 99%. The far-field emission patterns of such artificial MD sources were experimentally measured, which unambiguously resolved their magnetic-type emission origin. This study opens the path to achieving ideal magnetic dipole emission with nonmagnetic emitters, largely extending the availability of magnetic light emitters conventionally limited by nature. Beyond the fundamental significance in science, we anticipate that this study will also facilitate the development of magnetic optical nanosource and enable potential photonic applications relying on magnetic light emission.

Enhancement of the Piezocatalytic Response of La-Doped BiFeO3 Nanoparticles by Defects Synergy.

Because of their intrinsic polarization and related properties, ferroelectrics attract significant attention to address energy transformation and environmental protection. Here, by using trivalent-ion-lanthanum doping of BiFeO3 nanoparticles (NPs), it is shown that defects and piezoelectric potential are synergized to achieve a high piezocatalytic effect for decomposing the model Rhodamine B (RhB) pollutant, reaching a record-high piezocatalytic rate of 21 360 L mol-1 min-1 (i.e., 100% RhB degradation within 20 min) that exceeds most state-of-the art ferroelectrics. The piezocatalytic Bi0.99La0.01FeO3 NPs are also demonstrated to be versatile toward various pharmaceutical pollutants with over 90% removal efficiency, making them extremely efficient piezocatalysts for water purification. It is also shown that 1% La-doping introduces oxygen vacancies and Fe2+ defects. It is thus suggested that oxygen vacancies act as both active sites and charge providers, permitting more surface adsorption sites for the piezocatalysis process, and additional charges and better energy transfer between the NPs and surrounding molecules. Furthermore, the oxygen vacancies are proposed to couple to Fe2+ to form defect dipoles, which in turn introduces an internal field, resulting in more efficient charge de-trapping and separation when added to the piezopotential. This synergistic mechanism is believed to provide a new perspective for designing future piezocatalysts with high performance.

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.

Ferroelectric Dipoles Tailoring Solid-Electrolyte-Interphase Chemistry to Enable Reversible Lithium Metal Batteries.

Solid-electrolyte interphase (SEI) plays a decisive role in building reliable Li metal batteries. However, the scarcity of anions in Helmholtz layer (HL) caused by electrostatic repulsion usually leads to the inferior SEI derived from solvents, resulting in dendrites and 'dead' Li. Therefore, regulating the distribution of anions in electric double layer (EDL) and continuously introducing more anions into HL to tailor anions-derived SEI is crucial for achieving stable Li plating/stripping. Herein, by jointly utilizing the controlled defects of reduced graphene oxide (rGO) and the oriented dipoles of ferroelectric BaTiO3 (BTO), the rGO-BTO composite layer sustainedly brings more TFSI- and NO3 - into anion-defecient HL, promoting favorable decomposition of anions and guiding the generation of robust and fast-Li+-transport SEI containing more inorganics LiF and Li3N species. Thus, the resulting Li deposit shows smooth and dense morphologies without dendrites, leading to high average Coulombic efficiency. The Li//Cu@rGO-BTO (10 mAh cm-2 plated Li) cell exhibits an enhanced Li plating/stripping stability (2700 h) and a higher rate capability. The LiFePO4 full cell (N/P≈6.3) using rGO-BTO displays an enhanced capacity retention (82.0 % @ 430 cycles). This work provides a new insight on the construction of robust SEI by regulating the distribution of anions within EDL.

Photoinduced Bartoli Indole Synthesis by the Oxidative Cleavage of Alkenes with Nitro(hetero)arenes.

Given the unique charm of dipole chemistry, intercepting N-O=C dipoles precisely generated by designed processes to develop novel reactivity has become a seminal challenge. The polar fragmentation of 1,3,2-dioxazolidine species generated through the radical addition of excited nitro(hetero)arenes to alkenes represents a significantly underappreciated mechanism for generating N-O=C dipoles. Herein, we present a photoinduced Bartoli indole synthesis by the oxidative cleavage of alkenes with nitro(hetero)arenes. Various indoles and azaindoles are constructed through the multi-step spontaneous rearrangement of carbonyl imine intermediates generated by the polar fragmentation of 1,3,2-dioxazolidine species. Mechanism studies and DFT calculations support that the reaction involves radical cycloaddition, ozonolysis-type cycloreversion, intramolecular H-shift of carbonyl imines, and 3,3-sigmatropic shift of O-Alkenyl hydroxylamines, etc. The implementation of continuous- flow photochemistry, in particular, significantly enhances efficiency, thereby overcoming obstacles to the commercialization process.

Dielectric Matching by the Unique Dynamic Dipoles in Hybrid Organic/Inorganic Superlattices toward Ultrathin Microwave Absorber.

There is an urgent demand of ultrathin high-performance microwave absorbing materials (MAMs) in the electromagnetic protection field. However, minimizing thickness is challenging mainly due to dielectric mismatch at high permittivity from excessive dielectric loss, leading to strong reflection at 2-18 GHz. Here, a hybrid TaS2 /Co(Cp)2 superlattice is fabricated with alternating [TaS2 ] inorganic layers and [Co(Cp)2 ] organic layers. Dynamic Ta─Co dipoles offer a unique interfacial polarization relaxation mechanism involving the inversion and rotation of dynamic Ta─Co dipoles. The prolonged relaxation time of limited dynamic Ta─Co dipoles contributes to enhanced dielectric matching at high permittivity, which is essential for ultrathin high-performance MAMs. Furthermore, the confinement of paramagnetic Co(Cp)2 molecules in the interlayer space of the diamagnetic TaS2 sublattice triggers unexpected ferromagnetism via interfacial magnetic coupling conducive to the improved microwave-absorbing performance at reduced thickness. Therefore, it presents a 1.271-mm thick ultrathin absorber that can attenuate up to 99.99% of electromagnetic wave energy with a broad effective absorption bandwidth of 4.05 GHz, thus pushing the limits of thickness of 2D-based high-performance MAMs. This paper demonstrates a new strategy toward ultrathin MAMs with tunable and decent electromagnetic loss derived from electrical and magnetic coupling at the atomic scale.

A Single-Fed Wideband Circularly Polarized Cross-Fed Cavity-Less Magneto-Electric Dipole Antenna.

In this paper, we proposed a new wideband circularly polarized cross-fed magneto-electric dipole antenna. Different from conventional cross-dipole or magneto-electric dipole antennas, the proposed simple geometry realizes a pair of complementary magnetic dipole modes by utilizing the two open slots formed between the four cross-fed microstrip patches for achieving circular polarization and high stable gain across a wide frequency band. No parasitic elements are required for extending the bandwidths; therefore, both the radiation patterns and in-band gain are stable. The simulated field distributions demonstrated the phase complementarity of the two pairs of magnetic and electric dipole modes. A parametric study was also performed to demonstrate the radiation mechanism between the electric and magnetic dipole modes. The radiating elements are realized on a piece of double-sided dielectric substrate fed and mechanically supported by a low-cost commercial semirigid cable. The overall thickness of the antenna is about 0.22λo at the center frequency of axial ratio bandwidth. The measured results show a wide impedance bandwidth (|S11| < -10 dB) of 70.2% from 2.45 to 5.10 GHz. The in-band 3-dB axial ratio bandwidth is 51.5% from 3.0 to 5.08 GHz. More importantly, the gain of the antenna is 9.25 ± 0.56 dBic across the 3-dB axial ratio bandwidth.

Copper-Catalyzed Enantioselective C1,N-Dipolar (3+2) Cycloadditions of 2-Aminoallyl Cations with Indoles.

2-Aminoallyl cations are versatile 1,3-dipoles that could potentially be used for diverse (3+n) cycloaddition reactions. Despite some preliminary studies, the asymmetric catalytic transformation of these species is still underdeveloped. We herein report a binuclear copper-catalyzed generation of 2-aminoallyl cations from ethynyl methylene cyclic carbamates and their enantioselective (3+2) cycloaddition reaction with indoles to construct chiral pyrroloindolines. This transformation features a novel C1,N-dipolar reactivity for 2-aminoallyl cations.

Temperature-Resistant Intrinsic High Dielectric Constant Polyimides: More Flexibility of the Dipoles, Larger Permittivity of the Materials.

High dielectric constant polymers have been widely studied and concerned in modern industry, and the induction of polar groups has been confirmed to be effective for high permittivity. However, the way of connection of polar groups with the polymer backbone and the mechanism of their effect on the dielectric properties are unclear and rarely reported. In this study, three polyimides (C0-SPI, C1-SPI, and C2-SPI) with the same rigid backbone and different linking groups to the dipoles were designed and synthesized. With their rigid structure, all of the polyimides show excellent thermal stability. With the increase in the flexibility of linking groups, the dielectric constant of C0-SPI, C1-SPI, and C2-SPI enhanced in turn, showing values of 5.6, 6.0, and 6.5 at 100 Hz, respectively. Further studies have shown that the flexibility of polar groups affected the dipole polarization, which was positively related to the dielectric constant. Based on their high permittivity and high temperature resistance, the polyimides exhibited outstanding energy storage capacity even at 200 °C. This discovery reveals the behavior of the dipoles in polymers, providing an effective strategy for the design of high dielectric constant materials.

An N-Trifluoromethylation/Cyclization Strategy for Accessing Diverse N-Trifluoromethyl Azoles from Nitriles and 1,3-Dipoles.

N-Trifluoromethyl azoles are valuable targets in medicinal chemistry, but their synthesis is challenging. Classical preparation of N-CF3 azoles relies on the functional group interconversions but suffers from tedious N-pre-functionalization and unfriendly agents. Introduction of the CF3 onto the nitrogen of heterocycles provides a direct route to such motifs, but the N-trifluoromethylation remains underdeveloped. Reported here is an alternative and scalable cyclization strategy based on NCF3 -containing synthons for constructing N-CF3 azoles. The approach involves the N-trifluoromethylation of nitriles followed by a [3+2] cyclization between resulting N-CF3 nitrilium derivatives and 1,3-dipoles. PhICF3 Cl was an effective CF3 source for the transformation. As a result, a generic platform is established to divergently synthesize N-trifluoromethylated tetrazoles, imidazoles, and 1,2,3-triazoles by using sodium azide, activated methylene isocyanides, and diazo compounds as dipoles.

Unshielded bent folded-end dipole 9.4 T human head transceiver array decoupled using modified passive dipoles.

PURPOSE: To develop an unshielded dipole transceiver array for human head imaging at 9.4 Tesla and to improve decoupling of adjacent dipole elements, a novel array design with modified passive dipole antennas was developed, evaluated, and tested. METHODS: The new array consisted of 8 bent folded-end dipole elements placed in a single row and surrounding the head. Adjacent elements of RF transceiver arrays are usually decoupled by introducing circuits electrically connected to elements. These methods are difficult to use for dipole arrays because of the distant location of the adjacent antennas. A recently developed decoupling technique using passive dipoles is simple and does not require any electrical connection. However, common parallel passive dipoles can produce destructive interference with the RF field of the array itself. To minimize this interference, we placed the passive dipoles perpendicularly to the active dipoles and positioned them at the ends of the array. We also evaluated the effect of different passive dipoles on the array transmit performance. Finally, we optimized the array transmit performance by varying the length of the dipole folded portion. RESULTS: By rotating the passive dipoles 90º and moving them toward the ends of the array, we minimized the destructive interference to an acceptable level without compromising decoupling and the transmit efficiency. CONCLUSION: While keeping the benefits of the passive dipole decoupling method, the new modified dipoles produce substantially less destructive interference with the RF field of the array than the common design. The constructed transceiver array demonstrated good decoupling and whole-brain coverage.

Transition-Metal-Free Coupling of 1,3-Dipoles and Boronic Acids as a Sustainable Approach to C-C Bond Formation.

The need for alternative, complementary approaches to enable C-C bond formation within organic chemistry is an on-going challenge in the area. Of particular relevance are transformations that proceed in the absence of transition-metal reagents. In the current study, we report a comprehensive investigation of the coupling of nitrile imines and aryl boronic acids as an approach towards sustainable C-C bond formation. In situ generation of the highly reactive 1,3-dipole facilitates a Petasis-Mannich-type coupling via a nucleophilic boronate complex. The introduction of hydrazonyl chlorides as a complementary nitrile imine source to the 2,5-tetrazoles previously reported by our laboratory further broadens the scope of the approach. Additionally, we exemplify for the first time the extension of this protocol into another 1,3-dipole, through the synthesis of aryl ketone oximes from aryl boronic acids and nitrile N-oxides.

Modeling Superlattices of Dipolar and Polarizable Semiconducting Nanoparticles.

We present an analytical model to describe the stability of arbitrary semiconducting nanoparticle (NP) superlattices as a function of the dipole and polarizability of their constituents. We first validate our model by comparison with density functional theory calculations of simple cubic superlattices of small CdSe NPs, and we show the existence of a regime, relevant to experiments, where NP interactions are predominantly dipole-like. We then apply our model to binary superlattices and find striking differences between the stable geometries of lattices composed of polarizable and nonpolarizable NPs. Finally, we discuss the interplay of dipolar and ligand-ligand interactions in determining the stability of NP superlattices.

Electric Double Layer and Orientational Ordering of Water Dipoles in Narrow Channels within a Modified Langevin Poisson-Boltzmann Model.

The electric double layer (EDL) is an important phenomenon that arises in systems where a charged surface comes into contact with an electrolyte solution. In this work we describe the generalization of classic Poisson-Boltzmann (PB) theory for point-like ions by taking into account orientational ordering of water molecules. The modified Langevin Poisson-Boltzmann (LPB) model of EDL is derived by minimizing the corresponding Helmholtz free energy functional, which includes also orientational entropy contribution of water dipoles. The formation of EDL is important in many artificial and biological systems bound by a cylindrical geometry. We therefore numerically solve the modified LPB equation in cylindrical coordinates, determining the spatial dependencies of electric potential, relative permittivity and average orientations of water dipoles within charged tubes of different radii. Results show that for tubes of a large radius, macroscopic (net) volume charge density of coions and counterions is zero at the geometrical axis. This is attributed to effective electrolyte charge screening in the vicinity of the inner charged surface of the tube. For tubes of small radii, the screening region extends into the whole inner space of the tube, leading to non-zero net volume charge density and non-zero orientational ordering of water dipoles near the axis.

Naphthalene-Diimide-Based Ionenes as Universal Interlayers for Efficient Organic Solar Cells.

Self-doping ionene polymers were efficiently synthesized by reacting functional naphthalene diimide (NDI) with 1,3-dibromopropane (NDI-NI) or trans-1,4-dibromo-2-butene (NDI-CI) via quaternization polymerization. These NDI-based ionene polymers are universal interlayers with random molecular orientation, boosting the efficiencies of fullerene-based, non-fullerene-based, and ternary organic solar cells (OSCs) over a wide range of interlayer thicknesses, with a maximum efficiency of 16.9 %. NDI-NI showed a higher interfacial dipole (Δ), conductivity, and electron mobility than NDI-CI, affording solar cells with higher efficiencies. These polymers proved to efficiently lower the work function (WF) of air-stable metals and optimize the contact between metal electrode and organic semiconductor, highlighting their power to overcome energy barriers of electron injection and extraction processes for efficient organic electronics.

Long-Range Chirality Recognition of a Polar Molecule on Au(111).

Chiral molecular self-assemblies were usually achieved using short-range intermolecular interactions, such as hydrogen-, metal-organic, and covalent bonding. However, unavoidable surface defects, such as step edges, surface reconstructions, or site dislocations may limit the applicability of short-range chirality recognition. Long-range chirality recognition on surfaces would be an appealing but challenging strategy for chiral reservation across surface defects at long distances. Now, long-range chirality recognition is presented between neighboring 3-bromo-naphthalen-2-ol (BNOL) stripes on an inert Au(111) surface across the herringbone reconstruction as investigated by STM and DFT calculations. The key to achieving such recognition is the herringbone reconstruction-induced local dipole accumulation at the edges of the BNOL stripes. The neighboring stripes are then forced to adopt the same chirality to create the opposite edged dipoles and neutralize the neighbored dipole moments.

A combined 32-channel receive-loops/8-channel transmit-dipoles coil array for whole-brain MR imaging at 7T.

PURPOSE: Multichannel receive arrays provide high SNR and parallel-imaging capabilities, while transmit-only dipole arrays have been shown to achieve a large coverage of the whole-brain including the cerebellum. The aim of this study was to develop and characterize the performances of a 32-channel receive-only loop array combined with an 8-channel dipole coil array at 7T for the first time. METHODS: The 8Tx-dipoles/32Rx-loops coil array was characterized by the SNR, g-factors, noise correlation matrix, accelerated image quality, and B1+ maps, and compared with a commercial 1Tx-birdcage/32Rx-loops array. Simulated and measured B1+ maps were shown for the 8Tx-dipoles/32Rx-loops coil array and compared with the 8Tx/Rx dipole array. RESULTS: The in-house built 32-channel receive coil demonstrated a large longitudinal coverage of the brain, particularly the upper neck area. G-factors and accelerated MR acquisitions demonstrated robust performances up to R = 4 in 2D, and R = 8 (4 × 2) in 3D. A 83% increase in SNR was measured over the cerebellum with the in-house built 8Tx/32Rx coil array compared to the commercial 1Tx/32Rx, while similar performances were obtained in the cerebral cortex. CONCLUSIONS: The combined 32-channel receive/8-channel transmit coil array demonstrated high transmit-receive performances compared to the commercial receive array at 7T, notably in the cerebellum. We conclude that in combination with parallel transmit capabilities, this coil is particularly suitable for whole-brain MR studies at 7T.