Chiral Layer Research Articles

Synthesis of Homochiral N-Heterocyclic Carbene-Based Nanosheets for Enhanced Asymmetric Catalysis.

Utilizing ultrathin 2D metal-organic framework nanosheets (2D MONs) as supports for incorporating chiral catalysts represents a highly promising avenue in the field of asymmetric catalysis. In this study, four pairs of isostructural chiral metal-organic layers (MOLs) adorned with N-Heterocyclic carbene (NHC) groups are successfully synthesized. Notably, the obtained bulky (S)-1-Zn crystals can be readily delaminated into ultrathin MONs consisting of 1-2 layers through an ion intercalation-assisted exfoliation process. Subsequent asymmetric catalysis studies revealed that the NHC sites can be effectively activated by a proton sponge while maintaining structural integrity for the subsequent benzoin condensation. Due to their well-exposed catalytic sites, ultrathin morphology, and porous structure, the (S)-1-Zn nanosheets exhibited significantly enhanced yield and enantioselectivity compared to their bulk counterparts and organic precursors. This research highlights an efficient strategy for incorporating chiral NHC species onto 2D MONs, thereby unlocking their immense potential for heterogeneous asymmetric catalysis.

Transmission of an optical wave through a multilayer structure with dispersive chiral layers

Background. The using of mirror asymmetric chemical compounds for doping quartz makes it possible to metamaterial creation that has the chirality property. In such a compositional structure, unusual effects may arise when interacting with an optical wave. Aim. We calculate the transmission and reflection of a linearly polarized optical wave through a multilayer structure consisting of two doped quartz glasses separated by two air gaps. Methods. Based on a homogeneous mathematical model of a chiral metamaterial, taking into account the dispersion of the dielectric constant and the chirality parameter based on the matrix method, a system of linear algebraic equations is obtained for the complex reflection and transmission coefficients of an electromagnetic wave of linear polarization. Results. An analysis of the frequency and angular characteristics of the modules of the reflection and transmission coefficients was carried out at various values of the quartz doping level. It is theoretically predicted that at some wavelengths, most of the incident optical energy can be concentrated in the air gaps of the multilayer structure. Conclusion. The data obtained as a result of calculations can be used in the development of planar structures for frequency-selective concentration of energy in the visible and infrared spectrum based on quartz glasses doped with chiral chemical compounds.

Tunable polarization-dependent defect modes and lateral shifts of one-dimensional photonic crystals containing Dirac semimetal-based hyperbolic metamaterials and chiral materials

The transmission and lateral shift properties of the one-dimensional photonic crystals containing Dirac semimetal-based hyperbolic metamaterials and chiral material defects are theoretically investigated by using the transfer matrix method in terahertz. It is found that the angle-independent omnidirectional photonic bandgaps (PBGs) for p-polarization can be realized in the photonic crystals made of dielectric and the Dirac semimetal-based hyperbolic metamaterials. However, the PBGs are blue-shifted with the incident angle for s-polarized wave. The omnidirectional PBGs can be tunable with the Fermi energy of the Dirac semimetal, the thickness ratio of the constitute layers and the structural parameters. When one or two isotropic chiral material layers are introduced in the photonic crystals, double or four polarization-dependent defect modes are found in the bandgap under oblique incidence due to the coupling and conversion between different polarized waves in the chiral defects. The frequency interval of the defect modes changes with the chirality parameter and the incident angle. It is also found that when a light is incident on the defective photonic crystals, the giant positive and negative Goos-Hänchen shifts of co-polarization reflected waves can be induced around the defect modes, which are sensitive to the polarization, the incident angle, the incident frequency and the chirality. The special optical properties of the proposed defective multiplayers provide possibilities for practical applications in designing polarization sensitive optical devices, such as filter and sensor.

Using the dispersion model of a chiral metamaterial to calculate the characteristics of homogeneous and heterogeneous reflective and waveguide structures

Currently, metamaterials are actively used in the creation of microwave and optic devices for various purposes. This is due to their non-traditional properties, compared to dielectric, conductive and other materials. One type of metamaterial is chiral media, which contain conductive microelements of mirror asymmetric shape. Such metamaterials have dispersion and, as a consequence, it is necessary to take it into account when developing various microwave structures. The work demonstrates taking into account the dispersion of the dielectric constant and the chirality parameter for calculating waveguide and reflecting structures with homogeneous and inhomogeneous chiral layers. The work carried out an electrodynamic analysis of the reflective properties of an inhomogeneous chiral layer and a rectangular waveguide, with a homogeneous layer of chiral metamaterial located in the transverse plane. The work has developed a method for calculating the reflection and transmission coefficients of an optical wave from the inhomogeneous chiral structure under consideration, which is based on the use of the differential sweep method. When constructing a mathematical model, we took into account the cross-polarization of the optical wave field, which consists in the appearance of orthogonal components during the interaction of the field with a chiral metamaterial. The solution to the problem was reduced to a matrix differential equation for the unknown reflection coefficients of the main and cross-polarized components of the optical field. The work examined chiral metamaterials with linear and parabolic inhomogeneity profiles. The results of the work can be applied in the design of new microwave and optics devices with layers of metamaterial, which can expand their functionality.

Exo-chirality of the α-helix

The structure of helical polymers is dictated by the molecular chirality of their monomer units. Particularly, macromolecular helices with monomer sequence control have the potential to generate chiral topologies. In α-helical folded peptides, the sequential repetition of amino acids generates a chiral layer defined by the amino acid side chains projected outside the amide backbone. Despite being closely related to peptides’ structural and functional properties, to the best of our knowledge, a general exo-helical symmetry model has not been yet described for the α-helix. Here, we perform the theoretical, computational, and spectroscopic elucidation of the α-helix principal exo-helical topologies. Non-canonical labeled amino acids are employed to spectroscopically characterize the different exo-helical topologies in solution, which precisely match the theorical prediction. Backbone-to-chromophore distance also shows the expected impact in the exo-helices’ geometry and spectroscopic fingerprint. Theoretical prediction and spectroscopic validation of this exo-helical topological model provides robust experimental evidence of the chiral potential on the surface of helical peptides and outlines an entirely new structural scenario for the α-helix.

Chiral Perovskite Heterostructure Films of CsPbBr3 Quantum Dots and 2D Chiral Perovskite with Circularly Polarized Luminescence Performance and Energy Transfer.

This work reports the synthesis of chiral perovskite heterostructure films by combining a two-dimensional (2D) chiral (R-/S-MBA)2PbI4 perovskite with CsPbBr3 quantum dots (QDs). The as-synthesized chiral heterostructure films exhibit obvious circularly polarized luminescence (CPL) properties, even though pure 2D chiral perovskite cannot present photoluminescence. It indicates that the chirality of the excited state of the QDs originates from the 2D chiral perovskite. The circular polarization-resolved transient absorption (TA) spectra further demonstrate that the CPL response of heterostructure films originates from the energy transfer between the chiral perovskite layer and QDs layer and the suppression of spin relaxation, which induces the imbalance of the spin population of excited states in QDs layer. In addition, the photoluminescence (PL), circular dichroism (CD), and CPL spectra of these heterostructure films can be controlled by varying the thickness and component of the chiral perovskite layer, which demonstrates that the anion exchange between chiral perovskite and CsPbBr3 QDs can tune the chemical composition and optoelectronic properties due to the low bonding energy difference between them and decrease the strain within the QDs layer to reduce the radiative recombination lifetime. This work provides guidance for the synthesis of chiral perovskites with a strong CPL response and further provides insight into the origination of CPL.

Correction to: Graphene‑Loaded Surface Plasmon Polariton (SPP) Waveguide Surrounded by Uniaxial Chiral (UAC) and Plasma Layers

Correction to: Graphene‑Loaded Surface Plasmon Polariton (SPP) Waveguide Surrounded by Uniaxial Chiral (UAC) and Plasma Layers

Unconventional superconductivity in chiral molecule-TaS2 hybrid superlattices.

Chiral superconductors, a unique class of unconventional superconductors in which the complex superconducting order parameter winds clockwise or anticlockwise in the momentum space1, represent a topologically non-trivial system with intrinsic time-reversal symmetry breaking (TRSB) and direct implications for topological quantum computing2,3. Intrinsic chiral superconductors are extremely rare, with only a few arguable examples, including UTe2, UPt3 and Sr2RuO4 (refs. 4-7). It has been suggested that chiral superconductivity may exist in non-centrosymmetric superconductors8,9, although such non-centrosymmetry is uncommon in typical solid-state superconductors. Alternatively, chiral molecules with neither mirror nor inversion symmetry have been widely investigated. We suggest that an incorporation of chiral molecules into conventional superconductor lattices could introduce non-centrosymmetry and help realize chiral superconductivity10. Here we explore unconventional superconductivity in chiral molecule intercalated TaS2 hybrid superlattices. Our studies reveal an exceptionally large in-plane upper critical field Bc2,|| well beyond the Pauli paramagnetic limit, a robust π-phase shift in Little-Parks measurements and a field-free superconducting diode effect (SDE). These experimental signatures of unconventional superconductivity suggest that the intriguing interplay between crystalline atomic layers and the self-assembled chiral molecular layers may lead to exotic topological materials. Our study highlights that the hybrid superlattices could lay a versatile path to artificial quantum materials by combining a vast library of layered crystals of rich physical properties with the nearly infinite variations of molecules of designable structural motifs and functional groups11.

Graphene-Loaded Surface Plasmon Polariton (SPP) Waveguide Surrounded by Uniaxial Chiral (UAC) and Plasma Layers

Graphene-Loaded Surface Plasmon Polariton (SPP) Waveguide Surrounded by Uniaxial Chiral (UAC) and Plasma Layers

Structural Regulations of Layered Borates: From Centric Layers to Chiral Porous Layers.

Three pentaborates were made by precise structural regulations under hydrothermal conditions, namely, K2Cs[B5O8(OH)]·0.5CO3 (1), KNa4Cs[B5O8(OH)]2·2OH (2), and NaBa[B5O8.5(OH)] (3). Compound 1 features the typical 2D layers constructed from the four-connected B5O10(OH) clusters. By adjustment of the reactants and pH values of the systems to remove interlayered CO3 2- groups, the centric layers in 1 were transformed to the chiral layers of 2. By further adjusting cationic templates based on host-guest charge matching, the B5O10(OH) cluster unit was transformed to B5O11(OH), which built the chiral porous layers of 3. The chiral compounds 2 and 3 exhibit moderate second harmonic generation (SHG) responses of 1.1 and 1.7 times that of KDP (KH2PO4). The structural regulations actualize the evolutions on both structural symmetries and dimensions.

Efficient Green Spin Light-Emitting Diodes Enabled by Ultrafast Energy- and Spin-Funneling in Chiral Perovskites.

Introducing molecular chirality into perovskite crystal structures has enabled the control of carrier spin states, giving rise to circularly polarized luminescence (CPL) in thin films and circularly polarized electroluminescence (CPEL) in LEDs. Spin-LEDs can be fabricated either through a spin-filtering layer enabled by chiral-induced spin selectivity or a chiral emissive layer. The former requires a high degree of spin polarization and a compatible spinterface for efficient spin injection, which might not be easily integrated into LEDs. Alternatively, a chiral emissive layer can also generate circularly polarized electroluminescence, but the efficiency remains low and the fundamental mechanism is elusive. In this work, we report an efficient green LED based on quasi-two-dimensional (quasi-2D) chiral perovskites as the emitting layer (EML), where CPEL is directly produced without separate carrier spin injection. The optimized chiral perovskite thin films exhibited strong CPL at 535 nm with a photoluminescence quantum yield (PLQY) of 91% and a photoluminescence dissymmetry factor (glum) of 8.6 × 10-2. Efficient green spin-LEDs were successfully demonstrated, with a large EL dissymmetry factor (gEL) of 7.8 × 10-2 and a maximum external quantum efficiency (EQE) of 13.5% at room temperature. Ultrafast transient absorption (TA) spectroscopic study shows that the CPEL is generated from a rapid energy transfer accompanied by spin transfer from 2D to 3D perovskites. Our study not only demonstrates a reliable approach to achieve high performance spin-LEDs but also reveals the fundamental mechanism of CPEL with an emissive layer of chiral perovskites.

Electro-optic characteristics of chiral nematic layers deformed by in-plane electric field

ABSTRACT Deformations of twisted and super-twisted layers composed of chiral and nonchiral nematic liquid crystals induced by in-plane electric field were studied numerically. The right-hand twisted structures with twist angles equal to 90°, 120°, 150°, 180°, 210°, 240° and 270° placed between crossed polarisers were considered. The optical transmission due to electro-optic effect which occurred in such systems was studied as a function of applied electric field strength. Steep and linear electro-optic characteristics were found in the case of nonchiral nematic confined in cells twisted by 90°. Such characteristics were favoured by large twist elastic constant, large dielectric anisotropy and weak azimuthal anchoring. In the case of super-twisted layers, useful characteristics were found for twist angles 210°, 240° and 270°, small twist elastic constant, strong azimuthal anchoring and large dielectric anisotropy.

Исследование отражения и прохождения волны через планарный слой кирального метаматериала, расположенного в прямоугольном волноводе с учетом материальной дисперсии

The work analyzes the diffraction of the fundamental wave of a rectangular waveguide on a planar layer of a chiral metamaterial located in a transverse plane. The mathematical model of the metamaterial takes into account its chirality and dispersion of material parameters. To connect the electromagnetic field vectors through the parameters of the chiral layer, two-sided approximate boundary conditions are used. Cross-polarization of the field is taken into account in the work. A system of linear algebraic equations for the reflection and transmission coefficients of the fundamental and cross-polarized waves was obtained in the work. It is shown that at the cutoff frequencies of the fundamental and cross-polarized waves are also excited in the waveguide. It is shown that at different levels of attenuation in the waveguide, situations arise when the degeneracy of resonant frequencies arises and disappears. It has been proven that the reflection and transmission of the fundamental wave at low attenuation values is of a frequency-selective resonant nature.

Defect Modes Generated in a Stack of Spin-Coated Chiral Liquid Crystal Layers

Nematic chiral liquid crystals (CLCs) are characterized by a helical arrangement of nematic LC molecules. A layer of CLC typically exhibits an optical reflection band due to Bragg reflection in the helical structure. When several layers of CLC are spin-coated and polymerized on top of each other without a barrier layer in between, defect modes can form in their reflection spectrum. By comparing experimental results and simulations, we investigate the origin of the defect modes, thereby revealing details on the behavior of the materials at the interfaces during deposition. Simulations show that these defect modes can originate from the migration of chiral dopant leading to a layer with a smaller pitch or from a discontinuity in the director orientation at the interface between two layers.

Enantioselective synthesis of a two-fold inherently chiral molecular nanographene

AbstractThe introduction and precise control of stereogenic elements in chemical structures is typically a challenging task. Most asymmetric methods require the presence of a heteroatom in the starting substrates acting as an anchor point for the successful transfer of chiral information. For this reason, compounds comprising only carbon atoms, such as optically active molecular nanographenes, are usually obtained as racemates, and isolated by chiral chromatographic separation. Here, we report an enantioselective strategy that uses three stereocontrolled synthetic steps to introduce and extend three different types of stereogenic elements, namely central, axial and helicoidal chirality, into a polycyclic aromatic structure. Thus, two chiral nanographene layers are covalently connected through a chiral triindane core. The final stereocontrolled graphitization Scholl reaction affords the formation of chiral nanographene units with remarkable enantiomeric excesses, high stereochemical stability and good chiroptical properties.

Chiral Diketopyrrolopyrrole-Based Conjugated Polymers with Intramolecular Rotation-Isomeric Conformation Asymmetry for Near-Infrared Circularly Polarized Light-Sensing Organic Phototransistors.

Recent advances in chiral nanomaterials interacting with circularly polarized (CP) light open new expectations for optoelectronics in various research fields such as quantum- and biology-related technology. To fully utilize the great potential of chiral optoelectronic devices, the development of chiral optoelectronic devices that function in the near-infrared (NIR) region is required. Herein, we demonstrate a NIR-absorbing, chiroptical, low-band-gap polymer semiconductor for high-performance NIR CP light phototransistors. A newly synthesized diketopyrrolopyrrole-based donor-acceptor-type chiral π-conjugated polymer with an asymmetric alkyl side chain exhibits strong chiroptical activity in a wavelength range of 700-1000 nm. We found that the attachment of an enantiomerically pure stereogenic alkyl substituent to the π-conjugated chromophore backbone led to strong chiroptical activity through symmetry breaking of the π-conjugation of the backbone in a molecular rotational motion while maintaining the coplanar backbone conformation for efficient charge transport. The NIR CP light-sensing phototransistors based on a chiral π-conjugated polymer photoactive single channel layer exhibit a high photoresponsivity of 26 A W-1 under NIR CP light irradiation at 920 nm, leading to excellent NIR CP light distinguishability. This study will provide a rationale and strategy for designing chiral π-conjugated polymers for high-performance NIR chiral optoelectronics.

Dielectric Tetramer Nanoresonators Supporting Strong Superchiral Fields for Vibrational Circular Dichroism Spectroscopy.

Chirality (C) is a fundamental property of objects, in terms of symmetry. It is extremely important to sense and distinguish chiral molecules in the fields of biochemistry, science, and medicine. Vibrational circular dichroism (VCD) spectroscopy, obtained from the differential absorption of left- and right- circularly polarized light (CPL) in the infrared range, is a promising technique for enantiomeric detection and separation. However, VCD signals are typically very weak for most small molecules. Dielectric metasurfaces are an emerging platform to enhance the sensitivity of VCD spectroscopy of chiral molecules via superchiral field manipulation. Here, we demonstrate a dielectric metasurface consisting of achiral germanium (Ge) tetramer nanoresonators that provide a proper and accessible high C enhancement (CE). We realize a maximum C enhancement (CE_max) with respect to the incident CPL (CE_max = Cmax/CRCP) of more than 750. The volume-averaged C enhancement (CE_ave = Cave/CRCP) is 148 in the 50 nm thick region above the sample surface and 215 in the central region of the structure. Especially, the corresponding CE_ave values are more than 89 and 183 even when a 50 nm thick chiral lossy molecular layer is coated on the metasurface. The metasurface benefits from geometrically achiral nanostructure design to eliminate intrinsic background chiral-optical signal from the substrate, which is useful in chiral sensing, enantioselectivity, and VCD spectroscopy applications in the mid-infrared range.

Active Control and Sensing Application of Ultra-Narrowband Circular Dichroism in Multilayer Chiral Nanorod Arrays.

Narrowband circular dichroism (CD) has attracted wide attention for its high sensitivity in detecting chiral molecules and catalysis. However, designing a chiral metasurface with excellent sensing performance that can be dynamically tuned still poses challenges. This paper introduces lithium niobate, an electrically tunable material, and a distributed Bragg reflector into chiral nanorod structures to form multilayer chiral nanorod arrays (MCNAs). Simulation results show that MCNAs can generate four strong ultra-narrowband (UNB) CD signals in the visible light spectrum. The UNB CD signal intensity was up to 0.86, and the minimum full width at half-maximum (FWHM) was up to 0.21 nm. The surface electric field and current distribution of MCNAs indicate that the four UNB CD signals mainly originate from the x and y direction Tamm resonances in the chiral nanorod layer. The refractive index of lithium niobate can be tuned by changing the electric field, allowing the active tuning of UNB CD signals. In addition, the sensing performance of MCNAs in the SARS-CoV-2 solution was analyzed, and the figure of merit (FOM) can reach an astonishing 2092. These findings not only assist with the design of UNB chiral devices but also offer new possibilities for the environmental monitoring and ultrasensitive detection of chiral molecules.

Formamidine Engineering the Lattice Distortion of Chiral Halide Perovskites for Efficient Blue Circularly Polarized Emission

AbstractChiral halide perovskites have emerged as promising circularly polarized light sources due to their great potential applications in 3D displays, optical data storage, and optical communication devices. However, to date, chiral halide perovskites with efficient blue circularly polarized luminescence (CPL) are scarcely unearthed. Herein, through formamidine engineering to decrease lattice distortion, the first new types of chiral corrugated 2D halide perovskites are presented (R/S)‐(BPEA)FAPbBr4·H2O (2‐R/S) (BPEA = 4‐bromophenylethylaminium, FA = formamidinium). Interestingly, driven by the incorporation of FA organic cations, the chiral perovskite layer realizes the transformation from (100)‐oriented (R/S)‐(BPEA)2PbBr4·H2O (1‐R/S) to (110)‐oriented 2‐R/S accompanying with reduced lattice distortion. More importantly, (110)‐oriented chiral perovskites 2‐R exhibit remarkable blue CPL with large asymmetry factors (glum =8.4 × 10−3). This work offers an exciting approach to realizing efficient blue CPL and promotes their further applications in photoelectronic devices.

Spin- and angle-resolved photoemission spectroscopy study of heptahelicene layers on Cu(111) surfaces.

It has been demonstrated previously that electrons interact differently with chiral molecules depending on their polarization. For enantiomeric pure monolayers of heptahelicene, opposite asymmetries in spin polarization were reported and attributed to the so-called chirality-induced spin selectivity effect. However, these promising proof-of-concept photoemission experiments lack the angular and energy resolution that could provide the necessary insights into the mechanism of this phenomenon. In order to fill in the missing gaps, we provide a detailed spin- and angle-resolved photoemission spectroscopy study of heptahelicene layers on a Cu(111) substrate. Throughout the large accessible energy and angle range, no chirality induced spin asymmetry in photoemission could be observed. Possible reasons for the absence of signatures of the spin-dependent electron transmission through the chiral molecular layer are briefly discussed.