Chiral-induced Spin Selectivity Effect Research Articles

Surface Magnetic Stabilization and the Photoemission Chiral-Induced Spin-Selectivity Effect.

The spinterface mechanism was suggested as a possible origin for the chirality-induced spin-selectivity (CISS) effect and was used to explain and reproduce, with remarkable accuracy, experimental data from transport experiments showing the CISS effect. Here, we apply the spinterface mechanism to explain the appearance of magnetization at the interface between nonmagnetic metals and chiral molecules, through the stabilization of otherwise fluctuating magnetic moments. We show that the stabilization of surface magnetic moments occurs for a wide range of realistic parameters and is robust against dephasing. Importantly, we show that the direction of the surface magnetic moments is determined by the chiral axis of the chiral molecules. Armed with the concept of stable surface magnetic moments, we then formulated a theory for the photoemission CISS effect. The theory, based on spin-dependent scattering, leads to direct predictions regarding the relation between the photoemission CISS effect, the chiral axis direction, the spinterface "size", and the tilt angle of the detector with respect to the surface. These predictions are within reach of current experimental capabilities and may shed new light on the origin of the CISS effect.

Dual Signature of Chirality Induced Spin Selectivity through Spontaneous Resolution of 2D Metal–Organic Frameworks

AbstractThe Chiral‐Induced Spin Selectivity (CISS) effect has emerged as a fascinating phenomenon within the realm of electron's spin manipulation, showcasing a unique interplay between electron's spin and molecular chirality. Subsequent to its discovery, researchers have been actively involved in exploring the new chiral molecules as effective spin filters. In the realm of observing the CISS effect, the conventional approach has mandated the utilization of two distinct enantiomers of chiral molecules. However, this present study represents a significant advancement by demonstrating the ability to control both spin states of electrons in a single system. In this work, we have demonstrated the preparation of chiral metal–organic frameworks (MOFs) via a “spontaneous resolution” process, obviating the requirement for chiral sources. This resulted in the production of chiral crystals exhibiting opposite handedness (1P and 1M) and these crystals were subsequently employed as a new class of spin filters based on CISS effect. Remarkably, this work signifies the first instance of achieving dual signature of spin selectivity from a single and exclusively achiral system through a spontaneous resolution process. This holds immense potential as it facilitates the production of two distinct spin‐filtering materials from a unified system. Furthermore, we investigated the contact potential differences (CPD) of these chiral crystals and, for the first time, associated it with the preferential spin transport properties. Our findings revealed a correlation between the CPD and the chirality of the crystals, as well as the magnetization orientations of the ferromagnetic substrate, which can be elucidated by the CISS effect. In overall, the significant findings achieved using these robust and easily synthesized MOF crystals without the requirement for chiral medium represent a crucial advancement in enhancing the effectiveness of spin filtering materials to produce spintronic devices.

What Can CISS Teach Us about Electron Transfer?

Electron transfer (eT) processes have garnered the attention of chemists and physicists for more than seven decades, and it is commonly believed that the essential features of the electron transfer mechanism are well understood─despite some open questions relating to the efficiency of long-range eT in some systems and temperature effects that are difficult to reconcile with the existing theories. The chiral induced spin selectivity (CISS) effect, which has been studied experimentally since 1999, demonstrates that eT through chiral systems depends on the electron's spin. Attempts to explain the CISS effect by adding spin-orbit coupling to the existing eT theories fails to reproduce the experimental results quantitatively, and it has become evident that the theory for explaining CISS must consider electron-vibration and/or electron-electron interactions. In this Perspective we identify some features of the CISS effect that imply that we should reconsider and refine the Marcus-Levich-Jortner mechanistic description for eT processes, especially for nonlinear systems and in the case of long-range eT.

Dual Signature of Chirality Induced Spin Selectivity through Spontaneous Resolution of 2D Metal-Organic Frameworks.

The Chiral-Induced Spin Selectivity (CISS) effect has emerged as a fascinating phenomenon within the realm of electron's spin manipulation, showcasing a unique interplay between electron's spin and molecular chirality. Subsequent to its discovery, researchers have been actively involved in exploring the new chiral molecules as effective spin filters. In the realm of observing the CISS effect, the conventional approach has mandated the utilization of two distinct enantiomers of chiral molecules. However, this present study represents a significant advancement by demonstrating the ability to control both spin states of electrons in a single system. In this work, we have demonstrated the preparation of chiral metal-organic frameworks (MOFs) via a "spontaneous resolution" process, obviating the requirement for chiral sources. Remarkably, this work signifies the first instance of achieving dual signature of spin selectivity from a single and exclusively achiral system through a spontaneous resolution process. This holds immense potential as it facilitates the production of two distinct spin-filtering materials from a unified system. In overall, the significant findings achieved using these robust and easily synthesized MOF crystals without the requirement for chiral medium represent a crucial advancement in enhancing the effectiveness of spin filtering materials to produce spintronic devices.

Electron Spin Polarization and Memory Effect in Supramolecular Gel Exclusively From Achiral Building Blocks.

Chirality has been identified as a crucial component in achieving high spin selectivity in organic polymers and π-conjugated molecules. In particular, chiral polymers and supramolecular structures have emerged as promising candidates for spin filtering due to the chirality-induced spin selectivity (CISS) effect. However, the CISS effect in supramolecular systems has not been extensively investigated, despite its potential for applications in spintronics. In this work, for the first time, the potential applications of the CISS effect in supramolecular gel materials and shed light on its untapped possibilities have been successfully explored. The ability of supramolecular gel exclusively made from achiral building blocks to selectively filter electron's spin through the symmetry breaking has been demonstrated. Furthermore, this study shows that their spin filtering efficacy can be improved by using chiral solvents. More importantly, the CISS effect has been employed to explore a novel phenomenon referred to as the "spin memory effect", where the desired spin information is preserved by retaining the helicity even in the absence of the chiral solvent. These findings underscore the immense potential for spintronics applications that rely solely on achiral components, thereby paving the way for new possibilities in device design and functionality.

Chiral Pd(II) Nanofiber Promoting Electron Transfer of g-C3N4 for Efficient Photocatalytic Hydrogen Production.

The rapid transfer and separation of photogenerated electrons is very important for the improvement of photocatalytic efficiency. Here, chiral induced spin selectivity effect (CISS effect) was developed to accelerate electron transfer for efficient photocatalytic hydrogen production. A chiral and achiral racemic supramolecular Pd(II) complex nanofiber was fabricated via supramolecular self-assembly of chiral L-Py or its racemes with Pd(II) and used to modify carbon nitride (g-C3N4). The obtained chiral photocatalyst L-Py-Pd/g-C3N4-4 and achiral photocatalyst Rac-Pd/g-C3N4-4, show enhanced photocatalytic activities with hydrogen evolution rates of 2476 and 1339 μmol g-1 h-1, respectively, while that of pure g-C3N4 is 30.5 μmol g-1 h-1. Chiral photocatalyst has 85% higher activity than achiral one and is 82.5-fold of pure g-C3N4, due to better suppression of the recombination of photogenerated electron-hole pairs in the interface of g-C3N4 contact with chiral molecule. Spectral tests and photoelectrochemical tests proved that the chiral supramolecular Pd(II) complex can act both as an electron spin filter and hydrogen reduction catalytic center to enhance photocatalytic efficiency. This work offers a new route to facilitate electron transfer by the CISS effect for photocatalytic hydrogen evolution.

Chiral spin selectivity and chiroptical activity in helical molecules.

Chiral structures, breaking spatial inversion symmetry, exhibit non-zero chiroptical activity (COA) due to the coupling between their electric and magnetic responses under external electromagnetic fields, an effect absent in achiral systems. Non-magnetic chiral structures also exhibit Chiral-Induced Spin Selectivity (CISS), primarily detected in two terminal measurements in the linear regime, where spin selection emerges without external magnetic influence. Despite the different origins of these physical phenomena, our model captures the relevant physics required to address CISS as an intrinsic molecular effect with the basic ingredients: (i) chirality/inversion asymmetry, (ii) meV atomic spin-orbit coupling, and (iii) decoherence as a source of reciprocity breaking. In this work, we derived how the electronic system couples with polarized electromagnetic radiation to yield a spin-dependent polarization rotation power, quantified through the Rosenfeld tensor, predicting characteristic spin signatures in the COA. The model also predicts that a net spin polarization manifests in the molecular terminations that have been surmised as an explanation for chiral species separation of racemic mixtures and interactions with surface magnetic domains. A recent sensitive spectroscopic measurement of electron transfer in donor-acceptor complexes is consistent with the standalone CISS effect.

Engineering spin-dependent catalysts: chiral covalent organic frameworks with tunable electroactivity for electrochemical oxygen evolution.

The chiral-induced spin selectivity (CISS) effect offers promising prospects for spintronics, yet designing chiral materials that enable efficient spin-polarized electron transport remains challenging. Here, we report the utility of covalent organic frameworks (COFs) in manipulating electron spin for spin-dependent catalysis via CISS. This enables us to design and synthesize three three-dimensional chiral COFs (CCOFs) with tunable electroactivity and spin-electron conductivity through imine condensations of enantiopure 1,1'-binaphthol-derived tetraaldehyde and tetraamines derived from 1,4-benzenediamine, pyrene, or tetrathiafulvalene skeletons. The CISS effect of CCOFs is verified by magnetic conductive atomic force microscopy. Compared with their achiral analogs, these CCOFs serve as efficient spin filters, reducing the overpotential of oxygen evolution and improving the Tafel slope. Particularly, the diarylamine-based CCOF showed a low overpotential of 430mV (vs reversible hydrogen electrode) at 10mAcm-2 with long-term stability comparable to the commercial RuO2. This enhanced spin-dependent OER activity stems from its excellent redox-activity, good electron conductivity and effective suppression effect on the formation of H2O2 byproducts.

Homochiral Covalent Organic Frameworks with Superhelical Nanostructures Enable Efficient Chirality-Induced Spin Selectivity.

Despite significant advancements in fabricating covalent organic frameworks (COFs) with diverse morphologies, creating COFs with superhelical nanostructures remains challenging. We report here the controlled synthesis of homochiral superhelical COF nanofibers by manipulating pendent alkyl chain lengths in organic linkers. This approach yields homochiral 3D COFs 13-OR with a 10-fold interpenetrated diamondoid structure (R = H, Me, Et, nPr, nBu) from enantiopure 1,1'-bi-2-naphthol (BINOL)-based tetraaldehydes and tetraamine. COF-13-OEt exhibits macroscopic chirality as right-handed and left-handed superhelical fibers, whereas others adopt spherical or non-helical morphologies. Time-tracking shows a self-assembly process from non-helical strands to single-stranded helical fibers and intertwined superhelices. Ethoxyl substituents, being of optimal size, balance solvophobic effects and intermolecular interactions, driving the formation of superhelical nanostructures, with handedness determined by BINOL chirality. The superhelical nature of these materials is evident in their chiral recognition and spin-filter properties, showing significantly improved enantiodiscrimination in carbohydrate binding (up to six times higher enantioselectivity) and a remarkable chiral-induced spin selectivity (CISS) effect with a 48-51% spin polarization ratio, a feature absent in non-helical analogs.

Chirality-Induced Spin Selectivity Enables New Breakthrough in Electrochemical and Photoelectrochemical Reactions.

To facilitate the transition from a carbon-energy-dependent society to a sustainable society, conventional engineering strategies, which encounter limitations associated with intrinsic material properties, should undergo the paradigm shift. From a theoretical viewpoint, the spin-dependent feature of oxygen evolution reaction (OER) reveals the potential of a spin-polarization strategy in enhancing the performance of electrochemical (EC) reactions. The chirality-induced spin selectivity (CISS) phenomenon attracts unprecedented attention owing to its potential utility in achieving novel breakthroughs. This paper starts with the experimental results aimed at enhancing the efficiency of the spin-dependent OER focusing on the EC system based on the CISS phenomenon. The applicability of spin-polarization to EC system is verified through various analytical methodologies to clarify the theoretical groundwork and mechanisms underlying the spin-dependent reaction pathway. The discussion is then extended to effective spin-control strategies in photoelectrochemical system based on the CISS effect. Exploring the influence of spin-state control on the kinetic and thermodynamic aspects, this perspective also discusses the effect of spin polarization induced by the CISS phenomenon on spin-dependent OER. Lastly, future directions for enhancing the performance of spin-dependent redox systems are discussed, including expansion to various chemical reactions and the development of materials with spin-control capabilities.

Regulation of chiral structure and spin polarization by circularly polarized light and electric field in copolymers

Combining chirality with ferromagnetism is challenging in organic materials and may bring potential application for the cross-integration of multiple disciplines. In this work, we achieved the intrinsic coexistence of chirality and spontaneous spin polarization in the diblock copolymers, where left-handed and right-handed circularly polarized lights present tunability on both the circular dichroism and spin polarization. Without electron dependence of transport in chiral copolymer, chirality is still coupled with spin. The phenomenon observed here is not the traditional chirality induced spin selectivity effect. Moreover, the electric field could also effectively tune the chirality dependence of circular dichroism to further affect the magnitude of spin polarization. Thus, a strong relationship between the chirality and spin polarization is formed in chiral copolymers. In addition, because of the different molecular packing for chiral enantiomers, electron–phonon coupling strengths are different to lead to a difference in spin polarization. Overall, the properties of chirality, spontaneous spin polarization, and photon-chirality-spin coupling are developed and studied, which effectively promotes the ability of potential applications of chiral copolymers.

A chemical perspective on the chiral induced spin selectivity effect.

This review discusses opportunities in chemistry that are enabled by the chiral induced spin selectivity (CISS) effect. First, the review begins with a brief overview of the seminal studies on CISS. Next, we discuss different chiral material systems whose properties can be tailored through chemical means, with a special emphasis on hybrid organic-inorganic layered materials that exhibit some of the largest spin filtering properties to date. Then, we discuss the promise of CISS for chemical reactions and enantioseparation before concluding.

Spatiotemporal-Dependent Confinement Effect of Bubble Swarms Enables a Fractal Hierarchical Assembly with Promoted Chirality.

The submarine-confined bubble swarm is considered an important constraining environment for the early evolution of living matter due to the abundant gas/water interfaces it provides. Similarly, the spatiotemporal characteristics of the confinement effect in this particular scenario may also impact the origin, transfer, and amplification of chirality in organisms. Here, we explore the confinement effect on the chiral hierarchical assembly of the amphiphiles in the confined bubble array stabilized by the micropillar templates. Compared with the other confinement conditions, the assembly in the bubble scenario yields a fractal morphology and exhibits a unique level of the chiral degree, ordering, and orientation consistency, which can be attributed to the characteristic interfacial effects of the rapidly formed gas/water interfaces. Thus, molecules with a balanced amphiphilicity can be more favorable for the promotion. Not limited to the pure enantiomers, chiral amplification of the enantiomer-mixed assembly is observed only in the bubble scenario. Beyond the interfacial mechanism, the fast formation kinetics of the confined liquid bridges in the bubble scenario endows the assembly with the tunable hierarchical morphology when regulating the amphiphilicity, aggregates, and confined spaces. Furthermore, the chiral-induced spin selectivity (CISS) effect of the fractal hierarchical assembly was systematically investigated, and a strategy based on photoisomerization was developed to efficiently modulate the CISS effect. This work provides insights into the robustness of confined bubble swarms in promoting a chiral hierarchical assembly and the potential applications of the resulting chiral hierarchical patterns in solid-state spintronic and optical devices.

Chirality-Induced Spin Selectivity: Analysis of Density Functional Theory Calculations.

Chirality-induced spin selectivity (CISS), which was demonstrated in several molecular and material systems, has drawn much interest recently. The phenomenon, described in electron transport by the difference in the transport rate of electrons of opposite spins through a chiral system, is however not fully understood. Herein, we employed density functional theory in conjunction with spin-orbit coupling to evaluate the percent spin-polarization in a device setup with finite electrodes at zero bias, using an electron transport program developed in-house. To study the interface effects and the level of theory considered, we investigated a helical oligopeptide chain, an intrinsically chiral gold cluster, and a helicene model system that was previously studied (Zöllner et al. J. Chem. Theory Comput. 2020, 16, 7357-7371). We find that the magnitude of the spin-polarization depends on the chiral system-electrode interface that is modeled by varying the interface boundary between the system's regions, on the method of calculating spin-orbit coupling, and on the exchange-correlation functional, e.g., the amount of exact exchange in the hybrid functionals. In addition, to assess the effects of bias, we employ the nonequilibrium Green's function formalism in the Quantum Atomistix Toolkit program, showing that the spin-flip terms could be important in calculating the CISS effect. Although understanding CISS in comparison to experiment is still not resolved, our study provides intrinsic responses from first-principles calculations.

Spin Filtering and Amplification in Self-Assembled Nanofibers Based on Chiral Asymmetric Building Blocks.

The cooperativity in artificial self-assembling systems can be enhanced to expand their applications and redesign their properties. Recently, chiral molecules have garnered renewed attention due to their potential as highly efficient spin filters through the chiral-induced spin selectivity (CISS) effect. However, the potential of asymmetric building blocks based on chiral perylene diimides (PDIs) self-assembled materials to generate a spin-polarized current is still not widely acknowledged. In this work, we have demonstrated that nanofibers derived from "asymmetric PDIs" molecules have been found to exhibit promising spin-filtering property and the amplification of spin polarization at room temperature. Also, the exploration of chiral amplification and correlating it with the amplification of spin polarization have been reported for the first time through this work. These findings underscore the significance of self-assembled materials in the realm of spintronics, as they offer fascinating platforms with evolving structure-property relationship. It also provides the feasible possibility of enhancing the CISS-based spintronic devices that can accomplish controllability and high spin-filtering efficiency simultaneously.

Current Induced Spin-Polarization in Chiral Molecules.

The inverse spin-galvanic effect or current-induced spin-polarization is mainly associated with interfaces between different layers in semiconducting heterostructures, surfaces of metals, and bulk semiconducting materials. Here, we theoretically predict that the inverse spin-galvanic effect should also be present in chiral molecules, as a result of the chiral induced spin selectivity effect. As proof-of-principle, we calculate the nonequilibrium properties of a model system that previously has been successfully used to explain a multitude of aspects related to the chiral induced spin selectivity effect. Here we show that current driven spin-polarization in a chiral molecule gives rise to a magnetic moment that is sensitive to external magnet field. The chiral molecule then behaves like a soft ferromagnet. This, in turn, suggests that magnetic permeability measurement in otherwise nonmagnetic systems may be used noninvasively to detect the presence of spin-polarized currents.

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.

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.