Chiral-induced Spin Selectivity Effect Research Articles

Structural Asymmetry and Chiral-Induced Spin Selectivity in Chiral Palladium-Halide Semiconductors.

Chiral Pb-free metal-halide semiconductors (MHSs) have attracted considerable attention in the field of spintronics due to various interesting spin-related properties and chiral-induced spin selectivity (CISS) effect. Despite their excellent chemical and structural tunability, the material scope and crystal structure of Pb-free chiral MHSs exhibiting the CISS effect are still limited; chiral MHSs that have metal-halide structures of octahedra and tetrahedra are only reported. Here, we report a new class of chiral MHSs, of which palladium (Pd)-halides are formed in 1D square-pyramidal structures or 0D square-planar structures, with a general formula of ((R/S-MBA)2PdBr4)1-x((R/S-MBA)2PdCl4)x (MBA = methylbenzylammonium; x = 0, 0.25, 0.5, 0.75, and 1) for the first time. The crystals adopt the 1D helical chain of Pd-halide square-pyramid (for x = 0, 0.25, 0.5, and 0.75) and 0D structure of Pd-halide square-plane (for x = 1). All the Pd-halides are distorted by the interaction between the halide and the chiral organic ammonium and arranged in a noncentrosymmetric position. Circular dichroism (CD) for ((R/S-MBA)2PdBr4)1-x((R/S-MBA)2PdCl4)x indicates that chirality was transferred from chiral organic ammonium to Pd-halide inorganics. ((R-MBA)2PdBr4)1-x((R-MBA)2PdCl4)x (x = 0, 0.25, 0.5, and 0.75) shows a distortion index of 0.127-0.128, which is the highest value among the previously reported chiral MHSs to the best of our knowledge. We also find that (R/S-MBA)2Pd(Br1-xClx)4 crystals grow along the out-of-plane direction during spin coating and have high c-axis orientation and crystallinity, and (R/S-MBA)2Pd(Br1-xClx)4 (x = 0 and 0.5) crystals exhibit a CISS effect in polycrystalline bulk films. These results demonstrate the possibility of a new metal-halide series with square-planar structures or square-pyramidal structures for future spintronic applications.

The Importance of Spin-Polarized Charge Reorganization in the Catalytic Activity of D-Glucose Oxidase.

The front cover artwork is provided by Prof. Ron Naaman's group at the Weizmann Institute of Science. The image shows that direct electron transfer through GOx is governed by electron spins, which result from the chiral-induced spin selectivity (CISS) effect. Read the full text of the Research Article at 10.1002/cphc.202400033.

Unveiling the electronic origin of lanthanide based Metal Organic Framework with ideal spin filtering capacity

Recently, a three dimensional metal-organic framework (MOF) based on Dy(III) and the L-tartrate ligand was experimentally shown to exhibit a spin polarization (SP) power of 100% at room temperature. The material’s spin filtering ability was ascribed to the chiral-induced spin selectivity (CISS) effect. In this work, we computationally characterize the electronic structure of this MOF, revealing that the high SP of the material is linked to the asymmetric arrangement, around the Fermi level, of the alpha- and beta-spin electron states arising from the 4f-states of the lanthanide Dy atom, which results in two different conduction channels (band gaps) for each spin state. Based on the understanding gathered in this work, we propose that the substitution of the hydroxyl groups of the ligand by mercaptan groups should boost the electrical conductivity, while retaining the spin filtering power of the material.

Dimensional and Doping Engineering of Chiral Perovskites with Enhanced Spin Selectivity for Green Emissive Spin Light-Emitting Diodes.

Chiral perovskites play a pivotal role in spintronics and optoelectronic systems attributed to their chiral-induced spin selectivity (CISS) effect. Specifically, they allow for spin-polarized charge transport in spin light-emitting diodes (LEDs), yielding circularly polarized electroluminescence at room temperature without external magnetic fields. However, chiral lead bromide-based perovskites have yet to achieve high-performance green emissive spin-LEDs, owing to limited CISS effects and charge transport. Herein, we employ dimensional regulation and Sn2+-doping to optimize chiral bromide-based perovskite architecture for green emissive spin-LEDs. The optimized (PEA)x(S/R-PRDA)2-xSn0.1Pb0.9Br4 chiral perovskite film exhibits an enhanced CISS effect, higher hole mobility, and better energy level alignment with the emissive layer. These improvements allow us to fabricate green emissive spin-LEDs with an external quantum efficiency (EQE) of 5.7% and an asymmetry factor |gCP-EL| of 1.1 × 10-3. This work highlights the importance of tailored perovskite architectures and doping strategies in advancing spintronics for optoelectronic applications.

Persistent Chirality-Induced Spin-Selectivity Effect in Circular Helix Molecules.

The spin-orbit coupling (SOC), the dynamics of the nonequilibrium transport process, and the breaking of time-reversal and space-inversion symmetries have been regarded as key factors for the emergence of chirality-induced spin selectivity (CISS) and chirality-dependent spin currents in helix molecules. In this work, we demonstrated the generation of persistent CISS currents in various circular single-stranded DNAs and 310-helix proteins for the first time, regardless of whether an external magnetic flux is applied or not. This new CISS effect presents only in equilibrium transport processes, distinct from the traditional CISS observed in nonequilibrium transport processes and linear helix molecules; we term it as the PCISS effect. Notably, PCISS manifests irrespective of whether the SOC is chirality-driven or stems from heavy-metal substrates, making it an efficient way to generate chirality-locked pure spin currents. Our research establishes a novel paradigm for examining the underlying physics of the CISS effect.

Co@CoO chiral nanostructures enabling efficient oxygen electrocatalysis by modulated spin-polarization

The sluggish kinetics of the oxygen evolution reaction (OER) and oxygen reduction reaction (ORR) frequently hinder advances in Zn-air battery-dependent technologies. In this study, the chiral-induced spin selectivity (CISS) effect was employed to achieve spin alignment, resulting in a reduction in the reaction overpotential for chiral nanocatalysts compared to their compositionally similar achiral counterparts. Moreover, we demonstrated that chiral L-type Co@CoO catalysts (Co@CoO-L) could achieve outstanding oxygen electrocatalytic performances, overcoming thermodynamic limitations, by manipulating the spin alignment of the reaction intermediates during the catalytic reaction. Zn-air batteries assembled with Co@CoO-L exhibited excellent performances, including a high specific capacity (839.5 mA h g−1 @ 10 mA cm−2), large open-circuit voltage (1.47 V), and long-term cycling stability (800 h). This work provides new insights into the construction excellent catalysts by exploiting chiral-induced spin selectivity.

The Importance of Spin-Polarized Charge Reorganization in the Catalytic Activity of D-Glucose Oxidase.

The reaction of D-glucose oxidase (GOx) with D- and L-glucose was investigated using confocal fluorescence microscopy and Hall voltage measurements, after the enzyme was adsorbed as a monolayer. By adsorbing the enzyme on a ferromagnetic substrate, we verified that the reaction is spin dependent. This conclusion was supported by monitoring the reaction when the enzyme is adsorbed on a Hall device that does not contain any magnetic elements. The spin dependence is consistent with the chiral-induced spin selectivity (CISS) effect; it can be explained by the improved fidelity of the electron transfer process through the chiral enzyme due to the coupling of the linear momentum of the electrons and their spin. Since the reaction studied often serve as a model system for enzymatic activity, the results may suggest the general importance of the spin-dependent electron transfer in bio-chemical processes.

Hybrid mesoporous electrodes evidence CISS effect on water oxidation.

Controlling product selectivity is essential for improving the efficiency of multi-product reactions. Electrochemical water oxidation is a reaction of main importance in different applications, e.g., renewable energy schemes and environmental protection, where H2O2 and O2 are the two principal products. In this Communication, the product selectivity of electrochemical water oxidation was controlled by making use of the chiral induced spin selectivity (CISS) effect at mesoporous-TiO2 on the molecule-modified Au substrate. Our results show a decrease in H2O2 formation when using chiral hetero-helicene molecules adsorbed on the Au substrate. We propose a mechanism for this kinetic effect based on the onset of CISS-induced spin polarization on the Au-helicene chiral interface. We also present a new tunable substrate to investigate the CISS mechanism.

Spin-Dependent Stereochemistry: A Nonadiabatic Quantum Dynamics Case Study of S + H2 → SH + H Reaction.

We study the spin-dependent stereodynamics of the S + H2 → SH + H reaction by using full-dimensional quantum dynamics calculations with zero total nuclear angular momentum along the triplet 3A″ states and singlet 1A' states. We find that the interplay between the electronic spin direction and the molecular geometry has a measurable influence on the singlet-triplet intersystem crossing reaction probabilities. Our results show that for some incident scattering angles in the body-fixed frame, the relative difference in intersystem crossing reaction probabilities (as determined between spin up and spin down initial states) can be as large as 15%. Our findings are an ab initio demonstration of spin-dependent nonadiabatic dynamics, which we hope will shine light as far as understanding the chiral-induced spin selectivity effect.

Inducing Circularly Polarized Single-Photon Emission via Chiral-Induced Spin Selectivity.

One of the central aims of the field of spintronics is the control of individual electron spins to effectively manage the transmission of quantized data. One well-known mechanism for controlling electronic spin transport is the chiral-induced spin-selectivity (CISS) effect in which a helical nanostructure imparts a preferential spin orientation on the electronic transport. One potential application of the CISS effect is as a transduction pathway between electronic spin and circularly polarized light within nonreciprocal photonic devices. In this work, we identify and quantify the degree of chiral-induced spin-selective electronic transport in helical polyaniline films using magnetoconductive atomic force microscopy (mcAFM). We then induce circularly polarized quantum light emission from CdSe/CdS core/shell quantum dots placed on these films, demonstrating a degree of circular polarization of up to ∼21%. Utilizing time-resolved photoluminescence microscopy, we measure the radiative lifetime difference associated with left- and right-handed circular polarizations of single emitters. These lifetime differences, in combination with Kelvin probe mapping of the variation of surface potential with magnetization of the substrate, help establish an energy level diagram describing the spin-dependent transport pathways that enable the circularly polarized photoluminescence.

Covalent Organic Frameworks with Tunable Chirality for Chiral-Induced Spin Selectivity.

Chiral covalent organic frameworks (CCOFs) have attracted extensive interest for their potential applications in various enantioselective processes. However, the exploitation of chirality-induced spin selectivity (CISS) that enables a new technology for the injection of spin polarized current without the need for a permanent magnetic layer within CCOFs remains a largely untapped area of research. Here, we demonstrate that, for the first time, COFs can be an attractive platform to develop spin filter materials with efficient CISS. This facilitates the design and synthesis of a new family of Zn(salen)-based 2D CCOFs, namely, CCOFs-9-12, by imine condensation of chiral 1,2-diaminocyclohexane and tri- or tetra(salicylaldehyde) derivatives. CCOF-9, distinguished by its unique C2 symmetric "armchair" tetrasubstituted pyrene conformation, exhibits the most pronounced chirality among these materials and serves as a solid-state host, enabling the enantioselective adsorption of racemic drugs with an enantiomeric excess (ee) of up to 97%. After substituting diamagnetic zinc(II) ions for paramagnetic cobalt(II), the resulting CCOF-9-Co not only retains its high crystallinity, porosity, and exceptional chirality but also exhibits enhanced conductivity, a crucial factor for the effective observation of CISS. Magnetic conductive atomic force microscopy showed that CCOF-9-Co exhibited a remarkable CISS effect with up to an 88-94% spin polarization ratio. This phenomenon is further confirmed by the increased intensity in the magnetic circular dichroism (MCD) when CCOF-9-Co is under an external magnetic field. This work therefore shows the tremendous potential of CCOFs for controlling spin selectivity and will stimulate the creation of new types of crystalline polymers with strong CISS effects for spin filters.

Chiral-Induced Spin Selectivity Modulated Time-Correlated Single-Photon Counting for DNA Hybridization Detection.

The chiral-induced spin selectivity (CISS) effect can distinguish between the spin of electrons as they pass through chiral molecules by backscattering one of the spin components. Herein, we explore the role of the CISS effect in time-correlated single-photon counting measurements to detect DNA hybridization. We observe that the average lifetime of optical excited states of quantum dots attached to double-stranded DNA (dsDNA) varies with directions of the applied magnetic field. Specifically, the difference in the nonradiative average decay lifetime for the two orientations of the applied magnetic field is 2.21 ns in the case of hybridized strands, which is 130 times higher than that observed with quantum dots attached to single-strand DNA. Additionally, we investigate the application of Fourier transform infrared (FTIR) spectroscopy for detecting double-stranded DNA in the presence of a magnetic field, establishing a theoretical framework to substantiate the experimental evidence of magnetic field-dependent FTIR spectroscopy for dsDNA.

Chiral Induced Spin Selectivity.

Since the initial landmark study on the chiral induced spin selectivity (CISS) effect in 1999, considerable experimental and theoretical efforts have been made to understand the physical underpinnings and mechanistic features of this interesting phenomenon. As first formulated, the CISS effect refers to the innate ability of chiral materials to act as spin filters for electron transport; however, more recent experiments demonstrate that displacement currents arising from charge polarization of chiral molecules lead to spin polarization without the need for net charge flow. With its identification of a fundamental connection between chiral symmetry and electron spin in molecules and materials, CISS promises profound and ubiquitous implications for existing technologies and new approaches to answering age old questions, such as the homochiral nature of life. This review begins with a discussion of the different methods for measuring CISS and then provides a comprehensive overview of molecules and materials known to exhibit CISS-based phenomena before proceeding to identify structure-property relations and to delineate the leading theoretical models for the CISS effect. Next, it identifies some implications of CISS in physics, chemistry, and biology. The discussion ends with a critical assessment of the CISS field and some comments on its future outlook.

Dual-ligand quasi-2D perovskites with chiral-induced spin selectivity for room temperature spin-LEDs.

Spin-LEDs have been a central topic in semiconductor spintronics research and represent a promising avenue for advanced optoelectronic devices and applications. The future advancements of spin-LEDs will undoubtedly hinge on the generation and manipulation of spin-polarized population at room temperature. In this research, we elucidate the development of room-temperature spin-LEDs using quasi-2D perovskites, based on the chiral-induced spin selectivity (CISS) effect. During the carrier transfer from the chiral n2 phase to the randomly oriented high-n phase caused by the bandgap gradient distribution, CISS works to generate non-equilibrium spin population, leading to room-temperature spin-polarized fluorescence. A spin-polarization of ∼93% is observed for the films. Finally, we realize spin-LEDs at room temperature, exhibiting a |gCP-EL| value of 0.05 and an EQE of 3.8%. This work highlights the potential of integrating dual ligands to optimize the phase distribution and crystalline orientation in quasi-2D films to achieve efficient CISS for spin-LED applications.

Electronic and spin states at edges of finite p-orbital helical atomic chain.

In connection to the chiral-induced spin selectivity effect, we theoretically analyze the electronic and spin states of edges of a finite p-orbital helical atomic chain with the intra-atomic spin-orbit interaction. This model can host the spin-filtering state in which two up-spins propagate in one direction and two down-spins propagate in the opposite direction without breaking the time-reversal symmetry (TRS). The enhancement of charge modulations concentrated at the edges due to the evanescent states is induced, although the spin density is absent because of the TRS. A Zeeman field at an edge of the atomic chain, which breaks the TRS, yields a finite spin polarization, whose direction depends on the chirality of the molecule. The chirality change induces a reasonable amount of the energy difference, which may provide an insight into the enantioselective adsorption of chiral molecules on the ferromagnetic surface.

Spin Quantum Dot Light-Emitting Diodes Enabled by 2D Chiral Perovskite with Spin-Dependent Carrier Transport.

Chiral-induced spin selectivity (CISS) effect provides innovative approach to spintronics and quantum-based devices for chiral materials. Different from the conventional ferromagnetic devices, the application of CISS effect is potential to operate under room temperature and zero applied magnetic field. Low dimensional chiral perovskites by introducing chiral amines are beginning to show significant CISS effect for spin injection, but research on chiral perovskites is still in its infancy, especially on spin-light emitting diode (spin-LED) construction. Here, the spin-QLEDs enabled by 2D chiral perovskites as CISS layer for spin-dependent carrier injection and CdSe/ZnS quantum dots (QDs) as light emitting layer are reported. The regulation pattern of the chirality and thickness of chiral perovskites, which affects the circularly polarized electroluminescence (CP-EL) emission of spin-QLED, is discovered. Notably, the spin injection polarization of 2D chiral perovskites is higher than 80% and the CP-EL asymmetric factor (gCP-EL ) achieves up to 1.6×10-2 . Consequently, this work opens up a new and effective approach for high-performance spin-LEDs.

Spin-Dependent Destructive and Constructive Quantum Interference Associated with Chirality-Induced Spin Selectivity in Single Circular Helix Molecules.

Chirality-induced spin selectivity (CISS) effect in straight helical molecules has received intense studies in past decade; however, the CISS effect in circular helical molecules (CHMs) has still rarely been explored. Here, we have constructed single CHMs having chirality-induced spin-orbit coupling (SOC) and connected by two nonmagnetic leads and successfully gained the required conditions for CISS effect occurring in CHMs for the first time. Our results uncover that only when the CHMs form a closed loop and when the lattice positions are coupled asymmetrically with both leads does the CISS effect occur. More importantly, the CISS-associated spin-dependent destructive and constructive quantum interference (QI) together with their phase transition appears in CHMs. The combination of CISS effect and spin-dependent QI phenomena opens up a new door to understand the underlying physics of the CISS effect in helical molecules.

Coherent spin transport in an Fe-S protein

Spin transport in a molecule was recently examined to discuss the chiral-induced spin selectivity (CISS) effect. This effect has been particularly reported in metalloproteins because the presence of transition metals improves spin polarization in a helical peptide structure. Among metalloproteins, iron-sulfur proteins have ubiquitous redox properties in photosynthesis and respiration. Iron can enhance spin polarization. In this study, the coherent spin transport in an Fe-S protein was investigated using first-principles calculations based on the Landauer formula. Proteins containing the [4Fe-4S] cluster were used for the calculations. The results of the spin transmission pathway revealed spin flow via Fe-S clusters.

Spin-dependent electrochemistry and electrochemical enantioselective recognition with chiral methylated bis(ethylenedithio)-tetrathiafulvalenes.

Enantio-discrimination and spin-dependent electrochemistry (SDE), as a manifestation of the chirality-induced spin selectivity (CISS) effect, are important phenomena that can be probed by "chiral" electrochemistry. Here, we prepared chiralized surfaces of gold and nickel, to serve as working electrodes, through effective chemisorption of enantiopure dimethyl-bis(ethylenedithio)-tetrathiafulvalene (DM-BEDT-TTF) 1, tetramethyl-bis(ethylenedithio)-tetrathiafulvalene (TM-BEDT-TTF) 2, and their capped silver nanoparticle (AgNPs) aggregate by simple incubation of the metallic substrates. The effective chemisorption was checked by means of ultrahigh vacuum x-ray photoelectron spectroscopy (XPS) and by electro-desorption experiments, i.e., cyclic voltammetry (CV) scans showing a first electro-desorption peak at about -1.0V. The Au|1 and Au|2 chiral electrodes were successfully used in CV experiments exploiting chiral redox probes. Finally, the hybrid interfaces Ni|enantiopure 1 or 2|AgNPs served as working electrodes in SDE experiments. In particular, the hybrid chiral interfaces Ni|(R)-2|AgNPs and Ni|(S)-2|AgNPs exhibited a significant spin-filtering ability, as a manifestation of the CISS effect, with average spin polarization values of 15%.

Electron Spin-Dependent Electrocatalysis for the Oxygen Reduction Reaction in a Chiro-Self-Assembled Iron Phthalocyanine Device.

The chiral-induced spin selectivity effect (CISS) is a breakthrough phenomenon that has revolutionized the field of electrocatalysis. We report the first study on the electron spin-dependent electrocatalysis for the oxygen reduction reaction, ORR, using iron phthalocyanine, FePc, a well-known molecular catalyst for this reaction. The FePc complex belongs to the non-precious catalysts group, whose active site, FeN4, emulates catalytic centers of biocatalysts such as Cytochrome c. This study presents an experimental platform involving FePc self-assembled to a gold electrode surface using chiral peptides (L and D enantiomers), i.e., chiro-self-assembled FePc systems (CSAFePc). The chiral peptides behave as spin filters axial ligands of the FePc. One of the main findings is that the peptides' handedness and length in CSAFePc can optimize the kinetics and thermodynamic factors governing ORR. Moreover, the D-enantiomer promotes the highest electrocatalytic activity of FePc for ORR, shifting the onset potential up to 1.01 V vs. RHE in an alkaline medium, a potential close to the reversible potential of the O2 /H2 O couple. Therefore, this work has exciting implications for developing highly efficient and bioinspired catalysts, considering that, in biological organisms, biocatalysts that promote O2 reduction to water comprise L-enantiomers.