Chiral Induced Spin Selectivity

Robust large-area molecular junctions of self-assembled monolayers of a model helical paddlewheel complex

We report the preparation of a helical complex and its study in molecular junctions. We show that the SAMs of this racemic compound present electrically robust behaviour which will pave the way for future studies on the CISS effect with analogous enantiopure compounds.

Spin-polarized electron transfer in chiral tartaric acid-engineered Ni(OH)2 unlocks NiOOH activation for urea electrooxidation

Chiral tartaric acid (TA)-modified Ni(OH)2 shows chiral-induced spin selectivity (CISS) effect, creating spin channels that significantly enhance electron transfer to promote the formation of NiOOH species. D-TA-Ni(OH)2 achieves a current density of 100 mA cm-2 at 1.38 V with a Tafel slope of 21.88 mV dec-1, highlighting its potential for the urea oxidation reaction.

Nanoarchitectonics for Pentagon Defects in Carbon: Properties and Catalytic Role in Oxygen Reduction Reaction

The oxygen reduction reaction (ORR) is a crucial process in electrochemical energy technologies, featuring fuel cells and metal-air batteries in the coming carbon-neutral society. Carbon materials have garnered significant attention as economical, sustainable alternatives to precious metal catalysts. In particular, there have been increasing reports recently that pentagons introduced into graphitic carbons promote catalytic activity for ORR. In addition, interesting studies are reported on carbon materials' synthesis, characterization, and spin polarization properties with pentagonal defects. This review comprehensively summarizes the formation mechanism, characterization, spin, oxygen (O2) adsorption, and ORR catalytic activity of carbon catalysts with pentagonal defects. By connecting the dots between theoretical insights and experimental results, this review elucidates the fundamental principles governing pentagon-related activity and offers perspectives on future directions for designing efficient ORR catalysts based on carbon materials.

Spin-orbit interactions, time-reversal symmetry, and spin selection

Spin selective transport is usually associated with spin-orbit interactions. However, these interactions are invariant under time-reversal symmetry, and the Onsager relations and Bardarson's theorem imply that such interactions cannot yield spin selectivity for transport through a junction between two electronic reservoirs. Here, we review several ways to overcome this restriction, using a Zeeman magnetic field, the Aharonov-Bohm phase, time-dependent electric fields that generate time-dependent spin-orbit interactions, time-dependent transients, more than two terminals, leakage, and more than one level per ion on the junction. Our considerations focus on the transport of noninteracting electrons at low temperatures. A possible connection with the phenomenon of chiral-induced spin selectivity is pointed out in one of the systems considered.

Spin effects in metal halide perovskite semiconductors

Metal halide perovskite semiconductors (MHSs) are emerging as potential candidates for opto-spintronic applications due to their strong spin-orbit coupling, favorable light emission characteristics and highly tunable structural symmetry. Compared to the significant advancements in the optoelectronic applications of MHSs, the exploration and control of spin-related phenomena remain in their early stages. In this minireview, we provide an overview of the various spin effects observed both in achiral and chiral MHSs, emphasizing their potential for controlling interconversion between spin, charge and light. We specifically highlight the spin selective properties of chiral MHSs through the chirality-induced spin selectivity (CISS) phenomena, which enable innovative functionalities in devices such as spin-valves, spin-polarized light-emitting diodes, and polarized photodetectors. Furthermore, we discuss the prospects of MHSs as spintronic semiconductors and their future development in terms of material design, device architecture and stability.

Spin Filtering with Surface-Active Helicene- and Twistacene-Based Perylene Diimides

Creating new chiral molecular and macromolecular systems that can polarize the spin of electrons has the dual promise of both applications in spintronics and a fundamental understanding of their origins. Here, we put forward two optically active helical ladder dimers from perylene diimide-based twistacenes and helicenes. We detail a scalable method to separate the helices for each of these systems and methods to functionalize them with thiol groups that allow for self-assembled monolayer formation on metal surfaces. We probed these monolayers with conductive atomic force microscopy, revealing that they are highly conductive. If the substrate is magnetized, then the current we measure with conductive atomic force microscopy is controlled by the handedness of the helices used to form the monolayers. Furthermore, helices of the same handedness for either the twistacene or helicene (right-handed helices vs left-handed helices) produce high (or low) currents in devices with the same magnetization. Importantly, we find a correlation between the magnetic field dependence of the conductivity and the helicity of the molecules, suggesting a link between these two properties, independent of the sign of their electronic circular dichroism.

Axial and helical chirality in multinuclear group 13 complexes: pathways to functional optical materials

Main-group element complexes have emerged as promising functional dyes owing to their unique photophysical properties and potential applications in sensors, luminescent devices, and photocatalysis. Among these, multinuclear main-group complexes that incorporate multiple elements within a single ligand have garnered significant attention, particularly for their ability to exhibit chirality with optical functions. Axial and helical chirality, resulting from unique coordination geometries, represent a critical frontier in the design of functional materials. These complexes enable diverse functionalities, including circular dichroism and circularly polarized luminescence. This Frontier article highlights recent advances in the synthesis of multinuclear main-group element complexes with chirality, focusing on their structural uniqueness and photochemical characteristics. Particular emphasis is placed on group 13 element complexes, including boron(III), aluminum(III), gallium(III), and indium(III), which exhibited unique chiral properties and photophysical behaviors. Key topics include the design strategies for chiral multinuclear frameworks, their photophysical properties, and their integration into advanced functional materials.

Role of Electron Spin, Chirality, and Charge Dynamics in Promoting the Persistence of Nascent Nucleic Acid-Peptide Complexes

Primitive nucleic acids and peptides likely collaborated in early biochemistry. What forces drove their interactions and how did these forces shape the properties of primitive complexes? We investigated how two model primordial polypeptides associate with DNA. When peptides were coupled to a ferromagnetic substrate, DNA binding depended on the substrate's magnetic moment orientation. Reversing the magnetic field nearly abolished binding despite complementary charges. Inverting the peptide chirality or just the cysteine residue reversed this effect. These results are attributed to the chiral-induced spin selectivity (CISS) effect, where molecular chirality and electron spin alter a protein's electric polarizability. The presence of CISS in simple protein-DNA complexes suggests that it played a significant role in ancient biomolecular interactions. A major consequence of CISS is enhancement of the kinetic stability of protein-nucleic acid complexes. These findings reveal how chirality and spin influence bioassociation, offering insights into primitive biochemical evolution and shaping contemporary protein functions.

Pathway Complexity of Kinetically Trapped Dipeptide-Based Metastable State: Supramolecular Structural Transformation and Helicity Tuning

Understanding the complexity of nanostructures involved during the supramolecular polymerization process can be achieved by kinetic control rather than thermodynamic stability. Study on supramolecular pathway complexity and associated nanostructures will provide precise control over the materials' properties. This work illustrates the pathway complexity and structural transformation of a naphthalimide-(NMI)-conjugated dipeptide from monomer to thermodynamically stable aggregated state in a binary mixed solvent system (DMSO and water). The self-assembly propensity can be modulated by changing the ratio of water, which offers an effective approach to provide kinetic stability to the on-pathway gel state before reaching its thermodynamically stable crystalline precipitate state. An in-depth spectroscopic and microscopic investigation suggested that the self-assembly process initiated the formation of tiny particles, which further nucleated to form a helical nanofibrilar assembly. At higher water percentages, the supramolecular gel state showed a transient behavior and proceeded toward its thermodynamic stability. However, at lower water percentage, the self-assembly process is kinetically trapped in its gel state. Here, the helicity of nanofibers can be modulated by altering the percentage of water in the mixed solvent. The self-assembled system is completely thermoreversible and can retain its chiral memory even after complete dissolution in the respective solvent composition.

A basis-free phase space electronic Hamiltonian that recovers beyond Born-Oppenheimer electronic momentum and current density

We present a phase-space electronic Hamiltonian ĤPS (parameterized by both nuclear position X and momentum P) that boosts each electron into the moving frame of the nuclei that are closest in real space. The final form for the phase space Hamiltonian does not assume the existence of an atomic orbital basis, and relative to standard Born-Oppenheimer theory, the newly proposed one-electron operators can be expressed directly as functions of electronic and nuclear positions and momentum. We show that (i) quantum-classical dynamics along such a Hamiltonian maintains momentum conservation and that (ii) diagonalizing such a Hamiltonian can recover the electronic momentum and electronic current density reasonably well. In conjunction with other reports in the literature that such a phase-space approach can also recover vibrational circular dichroism spectra, we submit that the present phase-space approach offers a testable and powerful approach to post-BO electronic structure theory. Moreover, the approach is inexpensive and can be immediately applied to simulations of chiral induced spin selectivity experiments (where the transfer of angular momentum between nuclei and electrons is considered critical).

Chiral All-Inorganic Perovskite Subnanowires

The phenomenon of chiral symmetry breaking during the crystallization of achiral molecules or ions, which leads to the formation of controllable enantiomerically pure crystals, has garnered significant interest but remains a challenge to fully overcome. This presents a particularly formidable obstacle in the creation of three-dimensional (3D) structured chiral all-inorganic perovskites, further complicated by their achiral crystalline space groups. In this report, we successfully synthesized right- or left-handed (P/M) chiral 3D P/M-CsPbX3 (X = Cl, Cl-Br, Br, Br-I) perovskite subnanowires (SNWs), in which Pb(II) can be partially substituted by hetero ions, such as Cu(II), Sn(II), and Mn(II). The selective control of the SNW handedness was achieved through the strategic incorporation of trace chiral amine enantiomers. The chiroptical activity arises from the helical structure of the SNWs. The mechanisms underlying the formation of this chiral structure were systematically investigated and interpreted by using a thermodynamic model. We utilized the chiral P/M-CsPbBr3 SNWs to fabricate circularly polarized light (CPL) photodetectors, which exhibited an impressive photocurrent dissymmetry factor (gIph) of 0.75. In the field of spin light-emitting diodes (spin-LEDs), circularly polarized electroluminescence (CPEL) was accomplished by employing the SNWs as a dual-functional material that provides both chiral-induced spin selectivity (CISS) and CPL emission capabilities.

Homochiral Carboxylate-Anchored Truxene Tripods: Design, Synthesis, and Monolayer Formation on Ag(111)

The design of well-defined assemblies of chiral molecules is a prerequisite for numerous applications, such as chirality-induced spin selectivity (CISS). In this context, tripodal molecular films bear the advantage of better control of molecular orientation and alignment than analogous monopodal systems. To this end, we report on the synthesis and assembly property of C3 chiral syn-5,10,15-truxene triacetic acid. (S,S,S) and (R,R,R) enantiomers were isolated and adsorbed on underpotential deposited Ag(111)/Au/mica both individually and as a racemate. The enantiomers form a densely packed and well-ordered structure (including the azimuthal alignment), even though with small sizes of individual domains. The molecules adsorb predominantly in tripodal configuration, with all three docking groups bound to the substrate as carboxylates in a bidentate fashion. The truxene backbone is then oriented parallel to the substrate surface but the fluorene blades are twisted to some extent. The racemate monolayer turned out to be less densely packed and less well-ordered compared to the films of individual enantiomers, which underlines the fact that uniform chirality is primarily important for molecular ordering of the truxenes. We hope that the designed system will be useful in the context of CISS and stimulate further activities regarding chiral tripods.

Decoupling Activity and Specificity in Coronazymes

Specificity and activity are often at odds for natural enzymes. In this work, specificity and activity in coronazymes made of an Au nanoparticle (AuNP) and coated with DNA aptamer for glucose substrates are decoupled. By single-molecule fluorescent MT-HILO (magnetic tweezers coupled with highly inclined and laminated optical sheet) microscopy, it is found that this coronazyme has ≈30 times higher activity on the d-glucose compared to bare AuNP nanozymes. Significantly, the new coronazyme demonstrates long-range modulations by circularly polarized light (CPL) according to the matching chirality between the CPL and DNA corona, which follows the rule of chiral induced spin selectivity (CISS). Although the aptamer in the coronazyme is evolved against d-glucose, surprisingly, this coronazyme catalyzes l-glucose better than d-glucose, likely due to the faster rates for the aptamer to interact with the l- over d-glucose. These results demonstrate, for the first time, an artificial enzyme with its catalytic activity controlled by short-range intermolecular forces, whereas its chiral specificity is modulated by long-range CPLs. This decoupled arrangement is pivotal to forge premier catalysts with activity and specificity superior to natural enzymes by separately optimizing these two properties.

Chiral light-matter interactions in solution-processable semiconductors

Chirality is a fundamental property widely observed in nature, arising in objects without a proper rotation axis, therefore existing as forms with distinct handedness. This characteristic can profoundly impact the properties of materials and can enable new functionality, especially for spin-optoelectronics. Chirality enables asymmetric light and spin interactions in materials, with widespread potential applications ranging from energy-efficient displays, holography, imaging, and spin-selective and enantio-selective chemistry to quantum information technologies. This Review focuses on the emerging material class of solution-processable chiral semiconductors, a broad material class comprising organic, inorganic and hybrid materials. These exciting materials offer the opportunity to design desirable light-matter interactions based on symmetry rules, potentially enabling the simultaneous control of light, charge and spin. We briefly discuss the various types of solution-processible chiral semiconductors, including small molecules, polymers, supramolecular self-assemblies and halide perovskites. We then examine the interplay between chirality and spin in these materials, the various mechanisms of chiral light-matter interactions, and techniques utilized to characterize them. We conclude with current and future applications of chiral semiconductors that take advantage of their chiral light-matter interactions.

Anode Alchemy on Multiscale: Engineering from Intrinsic Activity to Impedance Optimization for Efficient Water Electrolysis

The past decade has seen significant progress in proton exchange membrane water electrolyzers (PEMWE), but the growing demand for cost-effective electrolytic hydrogen pushes for higher efficiency at lower costs. As a complex system, the performance of PEMWE is governed by a combination of multiscale factors. This review summarizes the latest progress from quantum to macroscopic scales. At the quantum level, electron spin configurations can be optimized to enhance catalytic activity. At the nano and meso scales, advancements in atomic structure optimization, crystal phase engineering, and heterostructure design improve catalytic performance and mass transport. At the macro scale, innovative techniques in gas bubble management and internal resistance reduction drive further efficiency gains under ampere-level operating conditions. These modifications at the quantum level cascade through meso- and macro-scales, affecting charge transfer, reaction kinetics, and gas evolution management. Unlike conventional approaches that focus solely on one scale-either at the catalyst level (e.g., atomic, or crystal modifications) or at the device level (e.g., porous transport layers design)-combining multiscale optimizations unlocks greater performance improvements. Finally, a perspective on future opportunities for multiscale engineering in PEMWE anode design toward commercial viability is offered.

Operando evidence on the chirality-enhanced oxygen evolution reaction in intrinsically chiral electrocatalysts

Electrolytic hydrogen is identified as a crucial component in the desired decarbonisation of the chemical industry, utilizing renewable energy to split water into hydrogen and oxygen. Water electrolysis still requires important scientific advances to improve its performance and lower its costs. One of the bottlenecks in this direction is related to the sluggish anodic oxygen evolution reaction (OER). Producing anodes with competitive performance remains challenging due to the high energy losses and the harsh working conditions typically required by this complex oxidation process. Recent advancements point to spin polarization as an opportunity to enhance the kinetics of this spin-restricted reaction, yielding the paramagnetic O2 molecule. One powerful strategy deals with the generation of chiral catalytic surfaces, typically by surface functionalisation with chiral organic molecules, to promote the chiral-induced spin selectivity (CISS) effect during electron transfer. However, the relationship between optical activity and enhanced electrocatalysis has been established only from indirect experimental evidence. In this work, we have exploited operando electrochemical and spectroscopic tools to confirm the direct relationship between the faster OER kinetics and the optical activity of enantiopure Fe-Ni metal oxides when compared with that of achiral catalysts in alkaline conditions. Our results show the participation of chiral species as reactive intermediates during the electrocatalytic reaction, supporting the appearance of a mechanistic CISS enhancement. Furthermore, these intrinsically chiral transition-metal oxides maintain their enhanced activity in full cell electrolyser architectures at industrially relevant current densities.

A Phase-Space View of Vibrational Energies without the Born-Oppenheimer Framework

We show that following the standard mantra of quantum chemistry and diagonalizing the Born-Oppenheimer (BO) Hamiltonian ĤBO(R) is not the optimal means to construct potential energy surfaces. A better approach is to diagonalize a phase-space electronic Hamiltonian, ĤPS(R, P), which is parameterized by both nuclear position R and nuclear momentum P. Such a nonperturbative phase-space electronic Hamiltonian can be constructed using a partial Wigner transform and the method has exactly the same cost as BO for a semiclassical calculation (and only a slight increase in cost for a quantum nuclear calculation). For a three-particle system, with two heavy particles and one light particle, numerical results show that a phase-space electronic Hamiltonian produces not only meaningful electronic momenta (which are completely ignored by BO theory) but also far better vibrational energies. As such, for high level results and/or systems with degeneracies and spin degrees of freedom, we anticipate that future electronic structure and quantum chemistry packages will need to take as input not just the positions of the nuclei but also their momenta.

1.5D Chiral Perovskites Mediated by Hydrogen-Bonding Network with Remarkable Spin-Polarized Property

In this study, we developed new chiral hybrid perovskites, (R/S-MBA)(GA)PbI4, by incorporating achiral guanidinium (GA+) and chiral R/S-methylbenzylammonium (R/S-MBA+) into the perovskite framework. The resulting materials possess a distinctive structural configuration, positioned between 1D and 2D perovskites, which we describe as 1.5D. This structure is featured by a hydrogen-bonding-network-induced arrangement of zigzag inorganic chains, further forming an organized layered architecture. The structural dimensionality affects both electronic and spin-related properties. Density functional theory (DFT) calculations reveal Rashba splitting induced by the inversion asymmetry of the crystal structure, while circularly polarized transient absorption spectroscopy confirms spin lifetime on the nanosecond timescale. Magnetic conductive-probe atomic force microscopy (mCP-AFM) measurements demonstrate exceptional chiral-induced spin selectivity (CISS) with maximum spin polarization degrees of (92±1)% and (-94±2)% for (R-MBA)(GA)PbI4 and (S-MBA)(GA)PbI4, respectively. These findings underscore the potential of (R/S-MBA)(GA)PbI4 as promising candidates for next-generation spintronic devices, also highlight the critical role of chemical environment in sculpturing the structural dimension and spin-polarized property of chiral perovskites.

Circularly polarized electroluminescence from chiral supramolecular semiconductor thin films

Current organic light-emitting diode (OLED) technology uses light-emitting molecules in a molecular host. We report green circularly polarized luminescence (CPL) in a chirally ordered supramolecular assembly, with 24% dissymmetry in a triazatruxene (TAT) system. We found that TAT assembled into helices with a pitch of six molecules, associating angular momentum to the valence and conduction bands and obtaining the observed CPL. Cosublimation of TAT as the "guest" in a structurally mismatched "host" enabled fabrication of thin films in which chiral crystallization was achieved in situ by thermally triggered nanophase segregation of dopant and host while preserving film integrity. The OLEDs showed external quantum efficiencies of up to 16% and electroluminescence dissymmetries ≥10%. Vacuum deposition of chiral superstructures opens new opportunities to explore chiral-driven optical and transport phenomena.

Mechanistic insights into hole spin dynamics in colloidal Ag+-doped CdSe nanosheets: Interplay between two counteracting surface effects

We present a mechanistic study of hole spin dynamics in colloidal cadmium selenide (CdSe) nanosheets, aiming to gain insights into the elusive interplay between two counteracting surface effects, i.e., hole-trapping interaction [between the valence-band heavy-hole (HH) state and its nearby localized surface trap (LST) state] vs spin-exchange interaction [between the HH spin state and the surface dangling-bond spin (DBS) state]. Differently from our previous work adopting a strategy of ligand engineering [see Wu et al., Adv. Opt. Mater. 12, 2400583 (2024)], we here implement an alternative strategy of element doping to regulate the LST and DBS states in the Ag+-doped CdSe nanosystem. It is observed that the hole spin-flip lifetime is shortened when the Ag+-doping level is elevated, demonstrating that the hole-DBS exchange interaction can effectively compete against the coexisting hole-LST trapping interaction, mainly due to the doping-induced increase in the density of the DBS state. Markedly, this observation is contrary to that in the ligand-engineering case, where the hole-trapping interaction plays a predominant role due to the strong ligand/CdSe orbital hybridization. This work elucidates the interplay between the two surface effects and enriches the understanding about the subtle DBS-related effect, providing valuable mechanistic information for rational design and optimization of spintronic applications based on colloidal nanostructures.

Universal Chiral Nanopaint for Metal Oxide Biomaterials

Chirality is widespread in nature and governs the properties of various materials including inorganic nanomaterials. However, previously reported chiral inorganic materials have been limited to a handful of compositions owing to the physicochemical restrictions that impart chirality. Herein, chiral nanopaint applicable to diverse inorganic materials is presented. Various metal oxide nanoparticles (NPs) show chiroptical properties after coating with our chiral nanopaint, while maintaining their properties, such as magnetic properties. The combination of magnetism and chirality brings biomedical functionalities to chiral NPs, such as anticancer hyperthermia treatment. In vitro, d-nanopainted iron oxide NPs showed more than 50% higher cellular uptake compared to l-nanopainted iron oxide NPs, and this was due to the enantiospecific interaction between the cellular receptors on the cell surface and the chiral NPs. In vivo, d-nanopainted iron oxide NPs showed 4-fold superior anticancer efficiency by magnetic hyperthermia compared to l-nanopainted iron oxide NPs owing to improved adsorption to tumors. These chiral nanoparticles may provide potential synthesis strategies for chiral inorganic biomaterials, which exhibit elaborate combinations of intrinsic physical properties and extrinsic enantioselective properties for a variety of applications.

Chiral Pd2L4 Capsules from Readily Accessible Tröger's Base Ligands Inducing Circular Dichroism on Fullerenes C60 and C70

The induction of chirality on pristine fullerenes through non-covalent embedding in an asymmetric nano-confinement has only been rarely reported. Bringing molecules with such a unique electronic structure and broad application range into a chiral environment is particularly appealing for the development of chiroptical materials, enantioselective photoredox catalysts and systems showing chirality-induced spin selectivity (CISS). In this study, we report the formation of a chiral, configurationally stable Pd2L4 capsule assembled from a C2-symmetric, 'ribbon-shaped' ligand with a Tröger's base naphthalimide (TbNaps) backbone, easily synthesized in three steps from commercially available compounds. Embedding chirality directly into the ligand backbone ensures a relatively lightweight receptor design whose aromatic panels create a strongly shielded inner cavity of about 700 Å3 volume. Fullerenes C60 and C70, as well as a pair of corannulenes, can be bound in acetonitrile (where unsubstituted fullerenes are insoluble) and X-ray structures of host-guest complexes were obtained. Tight interactions between the chiral host and the fullerene guests leads to the induction of a circular dichroism (CD) on the characteristic absorption bands of the forbidden π-π* transitions of the fullerenes, backed up by sTDA TD-DFT calculations and detailed investigation of the electronic excited states.

Optimizing photocatalysis via electron spin control

Solar-driven photocatalytic technology holds significant potential for addressing energy crisis and mitigating global warming, yet is limited by light absorption, charge separation, and surface reaction kinetics. The past several years has witnessed remarkable progress in optimizing photocatalysis via electron spin control. This approach enhances light absorption through energy band tuning, promotes charge separation by spin polarization, and improves surface reaction kinetics via strengthening surface interaction and increasing product selectivity. Nevertheless, the lack of a comprehensive and critical review on this topic is noteworthy. Herein, we provide a summary of the fundamentals of electron spin control and the techniques employed to scrutinize the electron spin state of active sites in photocatalysts. Subsequently, we highlight advanced strategies for manipulating electron spin, including doping design, defect engineering, magnetic field regulation, metal coordination modulation, chiral-induced spin selectivity, and combined strategies. Additionally, we review electron spin control-optimized photocatalytic processes, including photocatalytic water splitting, CO2 reduction, pollutant degradation, and N2 fixation, providing specific examples and detailed discussion on underlying mechanisms. Finally, we outline perspectives on further enhancing photocatalytic activity through electron spin manipulation. This review seeks to offer valuable insights to guide future research on electron spin control for improving photocatalytic applications.

Proximity Effect of Optically Active h-BCN Nanoflakes Deposited on Different Substrates to Tailor Electronic, Spintronic, and Optoelectronic Properties

Hexagonal BCN (h-BCN), an isoelectronic counterpart to graphene, exhibits chirality and offers the distinct advantage of optical activity in the vacuum ultraviolet (VUV) region, characterized by significantly higher wavelengths compared to graphene nanoflakes. h-BCN possesses a wide bandgap and demonstrates desirable semiconducting properties. In this study, we employ Density Functional Theory (DFT) calculations to investigate the proximity effects of adsorbed h-BCN flakes on two-dimensional (2D) substrates. The chosen substrates encompass monolayers of 3D transition metals and WSe2, as well as a bilayer consisting of WSe2/Ni. Notably, the hydrogen-terminated h-BCN nanoflakes retain their planar configuration following adsorption. We observe a strong interaction between h-BCN and fcc-based monolayers such as Ni(111), resulting in the closure of the optical bandgap, while the adsorption energy on WSe2 is significantly weaker, preserving an approximate 1.1 eV bandgap. Furthermore, we demonstrate the magnetism induced by the proximity of adsorbed chiral h-BCN molecules, and the chiral-induced spin selectivity within the proposed systems.

Chiral perovskites with a unique 1D chain structure: impact of chiral ligand geometry on local inversion asymmetry and chiral-induced spin selectivity

Chiral hybrid organic-inorganic perovskites (HOIPs) have demonstrated significant potential in spintronics, primarily due to inversion symmetry breaking as well as strong spin-orbit coupling (SOC) arising from their heavy-element composition. Numerous studies have confirmed that chiral perovskites exhibit superior chiral-induced spin selectivity (CISS). However, the key factors underlying such pronounced spin polarization selectivity, especially within organic-inorganic hybrid systems, are not well understood. This oversight marks a critical area for deeper exploration in spintronics research. We introduce R/S-1-amino-2-propanol (R/S-HP1A) as a chiral spacer to synthesize chiral perovskites, (R/S-HP1A)PbI3, characterized by a distinct 1D chain structure with two layers of inorganic octahedrons in each chain. In (R/S-HP1A)PbI3, the chiral carbon locates away from the perovskite's inorganic skeleton, resulting in a slight degree of inversion asymmetry within the inorganic sublattice while maintaining a global chiral space group (P212121). As a result, (R/S-HP1A)PbI3 exhibits small Rashba-Dresselhaus spin-splitting, a purely in-plane spin texture, a short spin lifetime (4 ± 1.5 ps) and a relatively low polarization degree of the CISS effect (58% and 66% for R- and S-forms, respectively), in comparison to other reported low-dimensional chiral perovskites. These findings emphasize that the local inversion asymmetry of the inorganic octahedrons, beyond global chirality, significantly influences the CISS effect in chiral perovskites, which is important for targeted improvements in spintronic applications.

Precision Intercalation of Organic Molecules in 2D Layered Materials: From Interface Chemistry to Low-Dimensional Physics

The past few decades have witnessed significant development in intercalation chemistry research aimed at precisely controlling material properties. Intercalation, as a powerful surface and interface synthesis strategy, facilitates the insertion of external guests into van der Waals (vdW) gaps in two-dimensional (2D) layered materials, inducing various modulation effects (the weakening of interlayer interactions, changes in electronic structures, interfacial charge transfer, and symmetry manipulation) to tailor material properties while preserving intralayer covalent bonds. Importantly, benefiting from the very diverse structures and properties of organic molecules, their intercalation enables the integration of various molecules with a wide array of 2D materials, resulting in the creation of numerous organic-inorganic hybrid superlattices with exotic properties, which brings extensive potential applications in fields such as spintronics, superconductor electronics, optoelectronics, and thermoelectrics. Herein, based on recent advancements in organic intercalation systems, we briefly discuss a summary and classification of various organic guest species. We also discuss three modulation effects induced by organic intercalation and further introduce intriguing modulations in physicochemical properties, including superconductivity, magnetism, thermoelectricity and thermal conductivity, chiral-induced spin selectivity (CISS) effects, and interlayer-confined chemical reaction. Finally, we offer insights into future research opportunities and emerging challenges in organic intercalation systems.

Many-Body Effects at Heterogeneous Interfaces from First-Principles: Progress, Challenges, and Opportunities

Heterogeneous interfaces are pivotal in numerous nanoscale devices and applications. First-principles approaches based on quantum mechanics and atomistic structures provide critical insights into structure-property relationships, enabling the informed design of materials and devices. Accurate first-principles methods must reliably capture many-body effects, i.e., electron-electron interactions, which significantly influence system properties compared to the predictions from models using free or noninteracting electrons. In this Perspective, we survey a few computational tools in this context and attempt to be forward looking by discussing the current challenges and emerging research opportunities. We examine diverse manifestations of many-body effects across several domains: geometries and reaction barriers (total-energy properties), orbital energy levels and band alignments (one-particle properties), and optical excited states (two-particle properties).

Symmetry Breaking: Case Studies with Organic Cage-Racemates

ConspectusSymmetry is a pervasive phenomenon spanning diverse fields, from art and architecture to mathematics and science. In the scientific realms, symmetry reveals fundamental laws, while symmetry breaking─the collapse of certain symmetry─is the underlying cause of phenomena. Research on symmetry and symmetry breaking consistently provides valuable insights across disciplines, from parity violation in physics to the origin of homochirality in biology. Chemistry is particularly rich in symmetry breaking studies, encompassing areas such as asymmetric synthesis, chiral resolution, chiral structure assembly, and so on. Across different disciplines, a well-defined methodology is fundamental and necessary to analyze the symmetry or symmetry breaking nature behind the phenomenon, enabling researchers to uncover the underlying principles and mechanisms. Basically, three key points underpin symmetry-related research: the scale-dependency of symmetry/symmetry breaking, the driving force behind symmetry breaking phenomena, and the properties arising from symmetry breaking.This Account will focus on the three aforementioned key points elucidated with organic cages as proof-of-concept models, as organic cages exhibit shape-persistent 3D molecular frameworks, well-defined molecular motion, and a high propensity for crystallization.First, we examine racemization processes of organic cages with dynamic molecular motions to illustrate that symmetry and symmetry breaking are time-scale-dependent. Specifically, the racemization, driven by molecular motion, is influenced by hydrogen bonding and the rigidity of the cage framework, which may or may not be observable within the experimental temporal scale. This determines whether the enantiomeric excess system, namely, the symmetry broken system, can be detected experimentally. We also investigate the hierarchical structures self-assembled by racemic organic cages, demonstrating that symmetry and asymmetry manifest differently across spatial scales, from molecular to supramolecular and macroscopic levels. Second, we discuss the driving force behind spontaneous chiral resolution─a classic symmetry-breaking event during crystallization─from a thermodynamic perspective. We suggest that racemic compounds, compared to conglomerates, are more entropy-favored, explaining their greater prevalence in nature. Spontaneous chiral resolution can take place only when a favorable enthalpy compensates for unfavorable entropy. In conglomerates composed of organic cages, strong intermolecular interactions along the screw axes provide the necessary compensation. Finally, we explore the unique properties that emerge from symmetry-broken molecular packing within crystals of cage racemates, such as second-harmonic generation and piezoelectricity. It turns out that the symmetry operation in molecular packing plays a critical role in determining material properties. By comprehensively analyzing symmetry and symmetry-breaking in organic cage racemates, this Account provides insights into symmetry-related phenomena across scientific disciplines. It also paves the way for designing novel materials with tailored properties for applications in optics, electronics, and beyond.

Hyperfluorescence circularly polarized OLEDs consisting of chiral TADF sensitizers and achiral multi-resonance emitters

Developing circularly polarized organic light-emitting diodes (CP-OLEDs) that simultaneously achieve narrow-spectrum emission and high electroluminescence (EL) efficiency remains a formidable challenge. This work prepares two pairs of efficient circularly polarized thermally activated delayed fluorescence (CP-TADF) materials, featuring high photoluminescence quantum yields, short delayed fluorescence lifetimes, good luminescence dissymmetry factors and large horizontal dipole ratios. They can function as emitters for efficient sky-blue CP-OLEDs, providing high maximum external quantum efficiencies (ηext,maxs) (33.8%) and good EL dissymmetry factors (gELs) (-2.64 × 10-3). More importantly, they can work as sensitizers for achiral multi-resonance (MR) TADF emitters, furnishing high-performance blue and green hyperfluorescence (HF) CP-OLEDs with intense narrow-spectrum CP-EL and good ηext,maxs (31.4%). Moreover, tandem HF CP-OLEDs are fabricated for the first time by employing CP-TADF sensitizers and achiral MR-TADF emitters, which radiate narrow-spectrum CP-EL with an extraordinary ηext,maxs (51.3%) and good gELs (4.87 × 10-3). The circularly polarized energy transfer as well as chirality-induced spin selectivity effect of CP-TADF sensitizers are considered to contribute greatly to the generation of efficient CP-EL from achiral MR-TADF emitters. This work not only explores efficient CP-TADF materials but also provides a facile approach to construct HF CP-OLEDs with achiral MR-TADF emitters.

Emerging devices based on chiral nanomaterials

As advanced materials, chiral nanomaterials have recently gained vast attention due to their special geometry-based physical and chemical properties. The fast development of the related science and technology means that various devices involving polarization-based information encryption, photoelectronic and spintronic devices, 3D displays, biomedical sensors and measurement, photonic engineering, electronic engineering, solar devices, etc., been explored extensively. These fields are at their beginning, and much effort needs to be made, including improving the optical, electronic, and magnetic properties of advanced chiral nanomaterials, precisely designing materials, and developing more efficient construction methods. This review tries to offer a whole picture of these state-of-the-art conditions in these fields and offers perspectives on future development.

Chirality Assisted Triplet Electron Pairing

Redox processes that involve pairs of electrons are common in nature. Some of these reactions involve oxygen molecules. The understanding of the efficiency of the oxygen reduction reaction (ORR), for example, is a challenge since the reaction is spin forbidden and requires the transfer of two pairs of electrons. Past experimental and theoretical studies demonstrated that by controlling the spin of the transferred electrons, it is possible to overcome the barrier resulting from the spin mismatch between the reactants and the products. In other works, it was suggested that the reaction is enhanced if the two electrons in each pair have phase relation, namely, they possess the property of a triplet state. Since in nature electrons are transferred through chiral systems, we probed if chirality affects the formation of paired electrons with the same spin, namely, a triplet like state. The model calculations demonstrate that chirality enhances the probability of the formation of electron pairing in the triplet states, even at room temperature. This enhancement originates from breaking the spin degeneracy, enabled by chirality and interaction of the spins with vibrations.

Chirality-Dependent Anisotropic Nonlinear Optical Effect in Low-Dimensional Hybrid Metal Halides

Low-dimensional hybrid metal halides (LDHMHs) have emerged as a highly promising class of functional materials for a wide range of optoelectronic applications. Their exceptional structural tunability, facilitated by the hybridization of metal halides with organic compounds, enables the formation of three-, two-, one-, or zero-dimensional structures. This flexibility in structural design also allows the incorporation of chirality into the crystalline lattice, giving rise to novel LDHMH materials that are capable of selectively interacting with the spin angular momentum of electrons and photons. Among the unique optoelectronic properties of LDHMHs, the focus of this concept article is their chiroptical nonlinear optical (NLO) effect. LDHMHs demonstrate a highly effective discrimination and generation of circularly polarized (CP) light in the NLO regime, particularly in the second harmonic generation (SHG) process, referred to as SHG-circular dichroism (SHG-CD) and CP-SHG. These anisotropic responses are several orders of magnitude larger than linear chiroptical responses, such as CD and CP luminescence; consequently, LDHMHs are expected to be promising candidates for future optical-information devices and encryption systems. This article introduces recently reported chiral LDHMH materials that exhibit excellent CP-dependent anisotropic SHG responses.

Probing spin effects in phycocyanin using Janus-like ferromagnetic microparticles

In an era of interdisciplinary scientific research, new methodologies are necessary to simultaneously advance several fields of study. One such case involves the measurement of electron spin effects on biological systems. While magnetic effects are well known in biology, recent years have shown a surge in published evidence isolating the dependence on spin, rather than magnetic field, in biological contexts. Herein we present a simple method for the distinction between the two effects in solution-based samples. The induction of a single uniform spin upon molecules can be achieved by interacting them with a magnetized surface, thereby exposing them to controlled electron spin orientations. With many live biological systems, adsorption to a single surface severely limits the experimental output. A low signal to noise ratio from monolayers interacting with a relatively small surface area, and conformational restrictions due to immobilization, are common challenges when performing biological measurements on macroscopic magnetized surfaces. Here we demonstrate the use of Janus-like ferromagnetic microparticles, originally developed for a spin-based enantiomer separation procedure, as a platform for the spin-controlled measurement of biological molecules in solution. We find new evidence for electron spin involvement in biological systems, with influence observed on the kinetics, and to a lesser degree on the spectrum, of phycocyanin fluorescence. Our results provide both new scientific findings and proof of concept for the use of these unique magnetic particles as a flexible, soluble, high surface area, spin-controlled tool for scientific research.

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. 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.

Chiral induction at the nanoscale and spin selectivity in electron transmission in chiral methylated BEDT-TTF derivatives

Great efforts have been made in the last few decades to realize electronic devices based on organic molecules. A possible approach in this field is to exploit the chirality of organic molecules for the development of spintronic devices, an applicative way to implement the chiral-induced spin selectivity (CISS) effect. In this work we exploit enantiopure tetrathiafulvalene (TTF) derivatives as chiral inducers at the nanoscale. The aim is to make use of TTF's well-known and unique semiconducting properties, to be expressed in the fields of enantio-selectivity and the chiral-induced spin selectivity (CISS) effect. The experimental results shown in this paper further demonstrate how chirality and spin are deeply interrelated, as foreseen within the CISS effect theory, paving the way for the application of TTF derivatives in the field of spintronics. In this work, we demonstrate that tetramethyl-bis(ethylenedithio)-tetrathiafulvalene (TM-BEDT-TTF) (1) behaves as an efficient spin filter, as evidenced by magneto-atomic force microscopy (mc-AFM) measurements. Additionally, it is shown to be effective in transferring chirality to CdS/CdSe core-shell nanoparticles, as inferred from the analysis of circularly resolved photoluminescence spectra. This makes 1 a promising candidate for a variety of applications, ranging from plasmonics to quantum computing.

Chirality à la carte

Light drives a fast switching between achiral and chiral states in a crystal.

Enantiomorphic single component conducting nickel(II) and platinum(II) bis(diethyl-dddt) crystalline complexes

Monoanionic and neutral nickel(II) and platinum(II) bis(dithiolene) complexes based on the 5,6-diethyl-5,6-dihydro-1,4-dithiin-2,3-dithiolate (de-dddt) chiral ligand have been prepared in racemic and enantiopure forms. Neutral closed-shell species have been generated from monoanionic precursors upon electrocrystallization. The racemic anionic (TBA)[Ni(S,S-de-dddt)(R,R-de-dddt)] complex crystallized in the centrosymmetric space group P21/c, while the neutral complexes crystallized in the enantiomorphic tetragonal space group P41212 or P43212. Very subtle conformational differences concerning the orientation of the ethyl substituents are observed between the racemic and the enantiopure compounds, thus impacting the intermolecular interactions at the nanoscale level. Indeed, in the former, the ethyl substituents are all-axial in both independent complexes, while in the latter, one of the independent complexes shows a mixed (eq, eq, ax, ax) conformation and the other independent complex of the asymmetric unit shows the all-axial conformation. Such a tenuous difference at the molecular/nanoscale level strongly impacts the conductivity of the materials. Temperature dependent high pressure single crystal conductivity measurements show activated conductivity for all the materials, with room temperature conductivity values of up to 1.3 × 10-3 S cm-1 for [Ni(S,S-de-dddt)2] at 12.3 GPa and 3.0 × 10-4 S cm-1 for [Pt(R,R-de-dddt)2] at 12.9 GPa. Nevertheless, the racemic compounds are more conductive, i.e. 3.8 × 10-2 S cm-1 for [Ni(rac-de-dddt)2] at 10.0 GPa and 1.5 × 10-3 S cm-1 for [Pt(rac-de-dddt)2] at 10.5 GPa, in agreement with the shorter and more numerous S⋯S intermolecular contacts observed in the crystal structures of the racemic complexes. Moreover, a detailed analysis of DFT calculations suggests that smaller band gaps and higher conductivities should occur for the racemic solids and for the Pt versus Ni complexes.

Chirality induced spin selectivity in electron transport investigated by scanning probe microscopy

Chirality induced spin selectivity (CISS) effect implies the relationship between chirality and magnetism, attracting extensive attention in the fields of physics, chemistry and biology. Since it was first discovered with photoemission method in 1999, the CISS effect has been investigated and measured by a variety of methods. Among different means of measurements, scanning probe microscopy (SPM) as a powerful tool to explore the CISS effect, can directly measure and present the spin filtering property of chiral molecules in electron transport. In this paper, we summarize the recent experiments on the CISS effect studied with scanning tunneling microscopy and atomic force microscopy, analyzing the experimental setups and results, and delving into the underlying mechanisms. The present review offers a concise introduction to several chiral molecules which are investigated by SPM for the CISS effect, and a detailed exploration of various experimental techniques tailored to the unique adsorption structures of these molecules. The impact of molecular structure on spin selectivity and the profound implications of CISS are also demonstrated together with a concise overview of CISS theory. A conclusive synopsis and forward-looking perspectives on the investigation of the CISS effect in electron transport utilizing SPM techniques are presented.

Chiral Metal Coating to Enhance Water Electrolysis

Producing hydrogen through water splitting often faces challenges of overpotential, stability, and expensive catalysts, which limit its efficiency and hinder the advancement of hydrogen production technologies. Nickel foam and nickel meshes have emerged as promising materials for electrolyzer electrodes due to their high surface area and the ability to produce electrolyzers with a very small gap between the anode and cathode. This study presents a simple method for coating Ni-based electrodes with a chiral Ni-Au film, using electroplating, thus enhancing its efficiency dramatically. We introduce chirality to the electroplating layer by incorporating an enantiopure chiral reagent into the electroplating solution. The chiral layer enhances the oxygen evolution reaction due to the chiral-induced spin selectivity effect. By optimizing the chiral electroplating process, we demonstrate the reduction of the overpotential and an increase in the reaction efficiency by 95% at 1 M KOH at room temperature.

Influence of nonequilibrium vibrational dynamics on spin selectivity in chiral molecular junctions

We explore the role of molecular vibrations in the chirality-induced spin selectivity (CISS) effect in the context of charge transport through a molecular nanojunction. We employ a mixed quantum-classical approach that combines Ehrenfest dynamics for molecular vibrations with the hierarchical equations of motion method for the electronic degrees of freedom. This approach treats the molecular vibrations in a nonequilibrium manner, which is crucial for the dynamics of molecular nanojunctions. To explore the effect of vibrational dynamics on spin selectivity, we also introduce a new figure of merit, the displacement polarization, which quantifies the difference in vibrational displacements for opposing lead magnetizations. We analyze the dynamics of single trajectories, investigating how the spin selectivity depends on voltage and electronic-vibrational coupling. Furthermore, we investigate the dynamics and temperature dependence of ensemble-averaged observables. We demonstrate that spin selectivity is correlated in time with the vibrational polarization, indicating that the dynamics of molecular vibrations is the driving force of CISS in this model within the Ehrenfest approach.

Responsive Chirality: Tailoring Supramolecular Assemblies with External Stimuli as Future Platforms for Electronic/Spintronic Materials

Supramolecular chirality is the major branch of supramolecular chemistry, which not only plays important roles in biological processes but also in synthetically designed aggregated systems. To understand the complex processing of biological systems, the only way is to design supramolecular chiral ensembles that mimic natural biomolecules such as Deoxyribonucleic acid (DNA), Ribonucleic acid (RNA), amino acids, etc. In addition, chiral systems and self-assemblies as molecular motifs with breaking spatial inversion symmetry have been regarded as key substances in electronics and spintronics as well as in fundamental chemistry and physics. Here, in this review, our major concern is understanding modulation in spatial arrangements and packing modes under the impact of any external stimuli, which results in tailoring the handedness of resulted supramolecular chiral superstructures. We, in this review, highlighted the role of external stimuli such as solvent, chemical additives, photo exposure, etc. in altering the supramolecular chirality for their future utility as "active switches" in optoelectronic and spintronic devices and applications.

Why Mixed Halides in 2D Chiral Perovskites Weaken Chirality-Induced Spin Selectivity

2D Ruddlesden-Popper (RP) perovskites, upon inclusion of a chiral amine, exhibit chirality-induced spin selectivity (CISS). Although alloying at the halogen site in MBA-based RPs (MBA: methylbenzylammonium) is one of the suitable routes to tune the CISS effect, the mixed-halide RP perovskites exhibited complete suppression of chirality when probed through circular dichroism (CD). Here, we present the CISS effect in a series of mixed-halide RP perovskites. We show that photoinduced halide segregation is the origin for the apparent chirality suppression. The spin-dependent charge transport was evidenced through magnetic-conducting atomic force microscopy (mc-AFM) studies and magnetoresistance (MR) measurements. The mc-AFM results show that in (R/S-MBA)2PbI4(1-x)Br4x, the CISS effect decreases with bromide inclusion, nonmonotonically; the microstrain developed in the lattice and the spin-polarized charge transport are found to be correlated. Such a behavior has been explained through an inhomogeneity in the strength of the hydrogen bond between the organic moieties and halogens in the inorganic framework of the compounds. Our results further inferred that the hydrogen-bond-induced coupling transfers the chirality from the amine to the inorganic sublattice. The work explains the weakened CISS effect in mixed-halide chiral RP perovskites and provides a strategy to tune the spin-polarized charge transport as well.

A semiclassical non-adiabatic phase-space approach to molecular translations and rotations: Surface hopping with electronic inertial effects

We demonstrate that working with a correct phase-space electronic Hamiltonian captures electronic inertial effects. In particular, we show that phase space surface hopping dynamics do not suffer (at least to very high order) from non-physical non-adiabatic transitions between electronic eigenstates during the course of pure nuclear translational and rotational motion. This work opens up many new avenues for quantitatively investigating complex phenomena, including angular momentum transfer between chiral phonons and electrons as well as chiral-induced spin selectivity effects.

Enantiomerically Pure Helical Bilayer Nanographenes: A Straightforward Chemical Approach

The semiconductor properties of nanosized graphene fragments, known as molecular nanographenes, position them as exceptional candidates for next-generation optoelectronics. In addition to their remarkable optical and electronic features, chiral nanographenes exhibit high dissymmetry factors in circular dichroism and circularly polarized luminescence measurements. However, the synthesis of enantiomerically pure nanographenes remains a significant challenge. Typically, these materials are synthesized in their racemic form, followed by separation of the enantiomers using high-performance liquid chromatography (HPLC). While effective, this method often requires expensive instrumentation, extensive optimization of separation conditions, and typically yields analytical quantities of the desired samples. An alternative approach is the enantioselective synthesis of chiral molecular nanographenes; however, to date, only two examples have been documented in the literature. In this work, we present a straightforward chemical method for the chiral resolution of helical bilayer nanographenes. This approach enables the effective and scalable preparation of enantiomerically pure nanographenes while avoiding the need for HPLC. The incorporation of a BINOL core into the polyarene precursor facilitates the separation of diastereomers through esterification with enantiomerically pure camphorsulfonyl chloride. Following the separation of the diastereomers by standard chromatographic column, the hydrolysis of the camphorsulfonyl group yields enantiomerically pure nanographene precursors. The subsequent graphitization, achieved through the Scholl reaction, occurs in an enantiospecific manner and with the concomitant formation of a furan ring and a heterohelicene moiety. The absolute configurations of the final enantiomers, P-oxa[9]HBNG and M-oxa[9]HBNG, have been determined using X-ray diffraction. Additionally, electrochemical, photophysical, and chiroptical properties have been thoroughly evaluated.

Factors influencing the chiral imprinting in perovskite nanoparticles

Chiral perovskites have emerged as a new class of nanomaterials for manipulation and control of spin polarized current and circularly polarized light for applications in spintronics, chiro-optoelectronics, and chiral photonics. While significant effort has been made in discovering and optimizing strategies to synthesize different forms of chiral perovskites, the mechanism through which chirality is imbued onto the perovskites by chiral surface ligands remains unclear. In this minireview, we provide a detailed discussion of one of the proposed mechanisms, electronic imprinting from a chiral ligand.

Efficient Transfer of Chirality in Complex Hybrid Materials and Impact on Chirality-induced Spin Selectivity

Transfer of chirality, or transmission of asymmetric information from one system to another, plays an essential role in fundamental biological and chemical processes and, therefore, is essential for life. This phenomenon also holds immense potential in spintronics in the context of chirality-induced spin selectivity (CISS). In the CISS, the spatial arrangement of chiral molecules influences the spin state of electrons during the charge-transfer processes. Transfer of chirality from chiral molecules to an achiral material in a hybrid environment enables induction of spin polarization in the achiral material, thus vastly expanding the library of CISS-active electronic materials. Such "induced" CISS signals could have different responses compared to pure chiral molecules because the electronic properties of the achiral material come into play in the former case. In addition, multiple chiral sources can be used, which can have a nontrivial contribution to the induced CISS effect and can act either synergistically or antagonistically. This opens the way to achieving tunability of the CISS signals via chemical means. Earlier, such a chirality-transfer phenomenon and the resulting induced CISS effect were demonstrated in a hybrid system containing carbon nanotubes (CNTs) functionalized with a chiral agent (Fmoc-diphenylalanine l/d). In this context, we extend this result by investigating the role of an additional chiral moiety (l-lysozyme enzyme crystals) in this system. Here, the chiral crystal surrounds the chiral-functionalized CNTs, and we show that synergistic interactions result in more efficient chirality transfer, resulting in nontrivial changes in the CISS effect. This manifests in the form of (a) a stronger CISS signal compared to only one single chiral agent, (b) nonmonotonic temperature dependence and sign reversal of the CISS signal, and (c) persistence of the CISS signal at higher temperatures. Hybrid chiral materials with multiple chiral sources could, therefore, offer intricate control of the CISS signal via modification of its constituents, which is not possible in homogeneous chiral systems with single chiral sources.

Improved Catalyst Performance for the Oxygen Evolution Reaction under a Chiral Bias

The oxygen evolution reaction (OER) remains an important bottleneck for widespread implementation of a hydrogen economy. While improvements in the OER can be realized by spin polarizing the reaction intermediates, these methods often rely on applying external magnetic fields to ferromagnetic catalysts or by adsorbing chiral molecules onto the catalyst. Here, we show that the addition of chiral additives to the conductive binder supporting the catalysts enhances the selectivity for O2 formation and results in exceedingly high mass activities. The results are explained within the context of a statistical model in which the additives are hypothesized to act as a localized chiral bias that enhances radical intermediate coupling. More broadly, these studies illustrate a flexible design motif for improving OER catalysis that persists under different pH conditions, is independent of the choice of catalyst, and can be extrapolated to other chemical reactions.

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.

Odd-Even Law Mediated Supramolecular Chirality of Luminescent Dipeptides for Chiroptical Energy Transfer

Inherent luminescent short peptides essentially provide opportunities to rationally manipulate supramolecular chirality and chiral luminescence. Herein, a facile protocol to construct a series of naphthalimide-appended dipeptides is reported that show ultrasound wave-activated supramolecular chirality regulated by odd-even law. Naphthalimide luminophores are conjugated to the dipeptide skeleton with variable alkyl spacers. The presence of tyrosine interferes the kinetic aggregation into achiral nanoparticles without chirality transfer to supramolecular scale. However, ultrasound treatment initiates the nanoparticle-to-helix transition accompanied with the appeared chiral optics, including Cotton effect and circularly polarized luminescence (CPL). The supramolecular chiral parameters, including handedness of helices and chiroptical behaviors, follow the odd-even law of alkyl spacers in dipeptides bearing non-substituted naphthalimides. The amine-substitution boosted the quantum yields of dipeptide whereas no odd-even effect. The two types of dipeptides constituted ideal energy transfer pairs that enable the efficient energy transfer as well as the transportation of odd-even law to dipeptides containing substituted naphthalimides. This work sheds light on the construction of luminescent dipeptides with applications in precise control over chirality transportation and chiral luminescence.

Intense Circular Dichroism and Spin Selectivity in AgBiS2 Nanocrystals by Chiral Ligand Exchange

Chiral semiconducting nanomaterials offer many potential applications in photodetection, light emission, quantum information, and so on. However, it is difficult to achieve a strong circular dichroism (CD) signal in semiconducting nanocrystals (NCs) due to the complexity of chiral ligand surface engineering and multiple, uncertain mechanisms of chiroptical behavior. Here, a chiral ligand exchange strategy with cysteine on the ternary metal chalcogenide AgBiS2 NCs is developed, and a strong, long-lasting CD signal in the near-UV region is achieved. By carefully optimizing the ligand concentration, the CD peaks are observed at 260 and 320 nm, respectively, giving insight into the different ligand binding mechanisms influencing the CD signal of AgBiS2 NCs. Using density-functional theory, a large degree of crystal distortion by the bidentate mode of ligand chelation, and efficient ligand-NC electron transfer, synergistically resulting in the strongest CD signal (g-factor over 10-2) observed in chiral ligand-exchanged semiconductor NCs to date, is demonstrated. To demonstrate the effective chiral properties of these AgBiS2 NCs, a spin-filter device with over 86% efficiency is fabricated. This work represents a considerable leap in the field of chiral semiconductor NCs and points toward their future applications.