Control of light, spin and charge with chiral metal halide semiconductors

Elucidating Interfacial Carrier Transfer Dynamics for Circularly Polarized Emission in Self-Assembled Perovskite Heterostructures

By integrating carrier transfer with spin-selectivity in mixed-dimensional perovskites heterostructures (HSs), exceptional chiroptical behaviors can be activated, offering avenues for advanced applications in spintronics and quantum information technologies. However, the critical role of interface effects in this photophysical process remains insufficiently explored. We demonstrate the fabrication of self-assembled chiral 2D/achiral nanocrystal (NC) HSs with different morphologies and chiroptical activities. Using femtosecond transient reflection spectroscopy, the underlying interface-dependent carrier transfer was unraveled. Spin-polarized holes generated in the chiral 2D component can transfer within an ultrafast time scale of ∼362 fs across the coherent heterointerface, inducing circularly polarized luminescence (CPL) in the intrinsically achiral NCs with a high Pc of ∼10.3%. Furthermore, interfacial halide exchange can be utilized to extend the CPL wavelength from green to near-infrared. Our findings reveal the correlation between interfacial properties, charge transfer, and CPL activity, providing insights for the development of high-quality HSs with optimized optical properties.

Tuning Interlayer Couplings and Stabilizing 2D Perovskite Lattices through Intercalation Chemistry

Two-dimensional (2D) organic-inorganic hybrid lead halide perovskites are promising semiconductors for optoelectronics, spintronics, and ferroelectrics due to their versatile structural and physical properties enabled by a variety of organic spacer cations. While previous research has focused on new spacer cations for templating 2D perovskite structures and influencing their properties, the intercalation of functional molecules within the organic layers has been less explored. Here, we demonstrate the intercalation of iodine within the organic sublattice as an effective tool to tune interlayer electronic interactions and stabilize 2D perovskite structures that would otherwise not form. We synthesized and determined the single-crystal structures of seven new iodine-intercalated 2D perovskites with varying spacer cations and inorganic compositions. The intercalated iodine bridges neighboring inorganic layers via halogen bonding with the apical iodides, leading to interlayer vibrational and electronic couplings. The iodine intercalation enhances the lattice rigidity, which decreases phonon-phonon scattering and exciton-phonon coupling. Adjusting the inorganic composition further tunes the electronic band structures, because iodine's frontier orbitals contribute differently to the band edge states, leading to varied band alignments and photoluminescence quenching behaviors. Moreover, a decreased anisotropic emission polarization is observed after iodine intercalation due to the decreased in-plane confinement of the excitons. Our results demonstrate iodine intercalation as a powerful tool for tuning the structural and optoelectronic properties of 2D perovskites.

Circularly Polarized Luminescence in Achiral Tin-Based Perovskites via Structural Isomer-Driven Coordination Interaction

A chiral bidentate ligand, (R)-(-)-1-amino-2-propanol (denoted as R1) or (R)-(-)-2-amino-1-propanol (denoted as R2), was used to modify achiral 2D tin-based perovskite HDASnBr4 (HDA: 1,6-hexamethylenediamine) to form R1-HDASnBr4 or R2-HDASnBr4 by an acid precipitation method. R1-HDASnBr4 exhibits a near-unity photoluminescence quantum yield (PLQY) and strong yellow circularly polarized luminescence (CPL) with a luminescence asymmetry g-factor (|glum|) of 8.3 × 10-3, while R2-HDASnBr4 shows a PLQY of 95% and |glum| of 3.2 × 10-3. Both exhibit strong CPL activities, attributed to the significant centro-asymmetric distortion induced by the interaction between the chiral ligand and the inorganic lattice of 2D perovskites. The |glum| of R1-HDASnBr4 is 2.6× that of R2-HDASnBr4, resulting from the direct coordination of the hydroxyl group attached to the chiral carbons in R1 with the [SnBr6]4- inorganic framework, which induces a higher degree of distortion than the amino group in R2. Furthermore, we explored the potential of R1-HDASnBr4 as a chiral inducer and a CPL source to facilitate asymmetric polymerization. This work offers a simple strategy to introduce chirality to achiral perovskites.

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.

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.

Two-dimensional organic-inorganic hybrid perovskite quantum-well nanowires enabled by directional noncovalent intermolecular interactions

Layered 2D semiconductors, when grown into 1D nanowires, can exhibit excellent optical and electronic properties, promising for nanoscale optoelectronics and photonics. However, rational strategies to grow such nanowires are lacking. Here, we present a large family of quantum-well nanowires made from 2D organic-inorganic hybrid metal halide perovskites with tunable well thickness, organic spacer cations, halide anions, and metal cations, achieved by harnessing directional nonvalent intermolecular interactions present among certain spacer cations. The unusual 1D anisotropic growth within the 2D plane is induced by preferential self-assembly of selected spacer cations along the direction of stronger intermolecular interactions and further promoted by crystal growth engineering. Owing to the intrinsic 2D quantum-well-like crystal structures and 1D photon confinement at the subwavelength scale, these nanowires exhibit robust exciton-photon coupling, with Rabi splitting energies of up to 700 meV, as well as wavelength-tunable and more efficient lasing compared to exfoliated crystals.

Humidity Disrupts Structural and Chiroptical Properties of Chiral 2D Perovskites

Chiral two-dimensional (2D) hybrid organic-inorganic metal halide perovskite semiconductors have emerged as an exceptional material platform with many design opportunities for spintronic applications. However, a comprehensive understanding of changes to the crystal structure and chiroptical properties upon exposure to atmospheric humidity has not been established. We demonstrate phase degradation to the 1D (MBA)PbI3 (MBA = methylbenzylammonium) and the hypothetical (MBA)3PbI5·H2O hydrate phases, accompanied by a reduction and disappearance of the chiroptical response. First-principle simulations show that water molecules preferentially locate at the interface between the organic cations and the inorganic framework, thereby disrupting the hydrogen bonding, impacting both the structural chirality and stability of the material. These findings provide critical insights into phase degradation mechanisms and their impact on chiroptical activity in chiral 2D perovskites.

Chiral-Polar Photovoltage-Driven Efficient Self-Powered Circularly Polarized Light Detection in Three-Dimensional Hybrid Perovskites

The chiral-polar photovoltaic effect (CPPE), widely present in chiral hybrid perovskites, has brought an unprecedented opportunity for self-powered circularly polarized light (CPL) detection. However, on account of spatial limitations of the crystal structure, currently reported CPPE primarily focuses on low-dimensional hybrid perovskites, which have a low CPL photoresponse restricted by lower carrier transport efficiency compared to three-dimensional perovskites. For the first time, we reported chiral-polar photovoltage-driven efficient self-powered CPL detection in three-dimensional chiral-polar perovskites, MHyPbBr3 (MHy = Methylhydrazinium). Coupled with significant spontaneous polarization (17.1 μC cm-2) and superior semiconductor properties, MHyPbBr3 exhibits a large mobility-lifetime product (1.9 × 10-2 cm2 V-1) and stable bulk photovoltage (3.9 V). Furthermore, the devices indicate significant chiral-polar photovoltage for self-powered CPL detection with a robust angle anisotropy factor of 0.39. More importantly, benefiting from excellent carrier transport performance, high responsivity and detectivity values of up to 39.2 mA W-1 and 5.8 × 1012 Jones, respectively, are presented at zero bias, which fall around the highest values of hybrid perovskites. This work will contribute to the research of novel chiral-polar three-dimensional hybrid perovskite semiconductors and promote their application in efficient self-powered CPL detection.

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.

Chiral europium halides with high-performance magnetic field tunable red circularly polarized luminescence at room temperature

Chiral organic-inorganic hybrid metal halides as promising circularly polarized luminescence (CPL) emitter candidates hold great potential for high-definition displays and future spin-optoelectronics. The recent challenge lies primarily in developing high-performance red CPL emitters. Here, coupling the f-f transition characteristics of trivalent europium ions (Eu3+) with chirality, we construct the chiral Eu-based halides, (R/S-3BrMBA)3EuCl6, which exhibit strong and predictable red emission with large photoluminescence quantum yield (59.8%), narrow bandwidth (≈2 nm), long lifetime (≈2 ms), together with large dissymmetry factor |glum| of 1.84 × 10-2. Compared with the previously reported chiral metal halides, these chiral Eu-based halides show the highest red CPL brightness. Furthermore, the degree of photoluminescence polarization in (R/S-3BrMBA)3EuCl6 can be manipulated by the external magnetic field. Particularly, benefiting from the field-generated Zeeman splitting and spin mixing at exciton states, an anomalously positive magneto-photoluminescence was observed at room temperature. This work provides an efficient strategy for constructing both high-performance and pure-red CPL emitters. It also opens the door for chiral rare-earth halides toward chiral optoelectronic and spintronic applications.

Efficient Spin-Light-Emitting Diodes With Tunable Red to Near-Infrared Emission at Room Temperature

Spin light-emitting diodes (spin-LEDs) are important for spin-based electronic circuits as they convert the carrier spin information to optical polarization. Recently, chiral-induced spin selectivity (CISS) has emerged as a new paradigm to enable spin-LED as it does not require any magnetic components and operates at room temperature. However, CISS-enabled spin-LED with tunable wavelengths ranging from red to near-infrared (NIR) has yet to be demonstrated. Here, chiral quasi-2D perovskites are developed to fabricate efficient spin-LEDs with tunable wavelengths from red to NIR region by tuning the halide composition. The optimized chiral perovskite films exhibit efficient circularly polarized luminescence from 675 to 788 nm, with a photoluminescence quantum yield (PLQY) exceeding 86% and a dissymmetry factor (glum) ranging from 8.5 × 10-3 to 2.6 × 10-2. More importantly, direct circularly polarized electroluminescence (CPEL) is achieved at room temperature in spin-LEDs. This work demonstrated efficient red and NIR spin-LEDs with the highest external quantum efficiency (EQE) reaching 12.4% and the electroluminescence (EL) dissymmetry factors (gEL) ranging from 3.7 × 10-3 to 1.48 × 10-2 at room temperature. The composition-dependent CPEL performance is further attributed to the prolonged spin lifetime as revealed by ultrafast transient absorption spectroscopy.

Chiral Inorganic Nanomaterial-Based Diagnosis and Treatments for Neurodegenerative Diseases

Chiral nanomaterials are widely investigated over recent decades due to their biocompatibility and unique chiral effects. These key properties have significantly promoted the rapid development of chiral nanomaterials in bioengineering and medicine. In this review, the basic principles of constructing chiral nanomaterials along with the latest progress in research are comprehensively summarized. Then, the application of chiral nanomaterials for the diagnosis of neurodegenerative diseases (NDDs) is systematically described. In addition, the significant potential and broad prospects of chiral nanomaterials in the treatment of NDDs are highlighted from several aspects, including the disaggregation of neurofibrils, the scavenging of reactive oxygen species, regulation of the microbial-gut-brain axis, the elimination of senescent cells, and the promotion of directed differentiation in neural stem cells. Finally, a perspective of the challenges and future development of chiral nanomaterials for the treatment of NDDs is provided.

Self-assembly of chiroptical ionic co-crystals from silver nanoclusters and organic macrocycles

Atomically precise nanoclusters can be assembled into ordered superlattices with unique electronic, magnetic, optical and catalytic properties. The co-crystallization of nanoclusters with functional organic molecules provides opportunities to access an even wider range of structures and properties, but can be challenging to control synthetically. Here we introduce a supramolecular approach to direct the assembly of atomically precise silver nanoclusters into a series of nanocluster‒organic ionic co-crystals with tunable structures and properties. By leveraging non-covalent interactions between anionic silver nanoclusters and cationic organic macrocycles of varying sizes, the orientation of nanocluster surface ligands can be manipulated to achieve in situ resolution of enantiopure nanocluster‒organic ionic co-crystals that feature large chiroptical effects. Beyond chirality, this co-crystal assembly approach provides a promising platform for designing functional solid-state nanomaterials through a combination of supramolecular chemistry and atomically precise nanochemistry.

Chiroptical Synaptic Perovskite Memristor as Reconfigurable Physical Unclonable Functions

Physical unclonable functions (PUFs), often referred to as digital fingerprints, are emerging as critical elements in enhancing hardware security and encryption. While significant progress has been made in developing optical and memory-based PUFs, integrating reconfigurability with sensitivity to circularly polarized light (CPL) remains largely unexplored. Here, we present a chiroptical synaptic memristor (CSM) as a reconfigurable PUF, leveraging a two-dimensional organic-inorganic halide chiral perovskite. The device combines CPL sensitivity with photoresponsive electrical behavior, enabling its application in optoneuromorphic systems, as demonstrated by its ability to perform image categorization tasks within neuromorphic computing. Furthermore, by leveraging a 10 × 10 crossbar array of the CSMs, we develop a PUF capable of generating reconfigurable cryptographic keys based on the combination of neuromorphic potentiation and polarized light conditions. This work demonstrates an integrated approach to optoneuromorphic functionality, data storage, and encryption, providing an alternative approach for reconfigurable memristor-based PUFs.

Is There an Optimal Spacer Cation for Two-Dimensional Lead Iodide Perovskites?

Two-dimensional lead iodide perovskites have attracted significant attention for their potential applications in optoelectronic and photonic devices due to their tunable excitonic properties. The choice of organic spacer cations significantly influences the light emission and exciton transport properties of these materials, which are vital for their device performance. In this Perspective, we discuss the impact of spacer cations on lattice dynamics and exciton-phonon coupling, focusing on three representative 2D lead iodide perovskites that exhibit distinct types of structural distortions. Minimizing structural distortions, such as dynamic out-of-plane octahedral tilting and lone pair distortion, appears to be essential for achieving narrow photoluminescence (PL) emission peaks, high PL quantum yields, and rapid exciton diffusion by suppressing exciton-phonon coupling, as demonstrated in 2D perovskites based on phenylethylammonium cation or its derivatives. We propose that designing spacer cations with enhanced intermolecular interactions and denser packing, combined with the close packing of inorganic ions to minimize the motions of both organic and inorganic lattices, would be the ideal scenario for yielding the most favorable optoelectronic properties in these materials.

Design of Two-Dimensional Hybrid Perovskites with Giant Spin Splitting and Persistent Spin Textures

Semiconductors with large energetic separation ΔE± of energy sub-bands with distinct spin expectation values (spin textures) represent a key target to enable control over spin transport and spin-optoelectronic properties. While the paradigmatic case of symmetry-dictated Rashba spin splitting and associated spin textures remains the most explored pathway toward designing future spin-transport-based quantum information technologies, controlling spin physics beyond the Rashba paradigm by accessing strategically targeted crystalline symmetries holds significant promise. In this paper, we show how breaking the traditional paradigm of octahedron-rotation based structure distortions in 2D organic-inorganic perovskites (2D-OIPs) can facilitate exceptionally large spin splittings (ΔE± > 400 meV) and spin textures with extremely short spin helix lengths (lPSH ∼ 5 nm). A simple bond angle difference captures the distortion-driven global asymmetry and correlates quantitatively with first-principles computed spin-splitting magnitudes. A multiband effective mass model that accounts for interlayer coupling provides a unified understanding of how specific symmetry elements dictate layer- and state-dependent spin polarizations within these multi-quantum-well structures. The general symmetry analysis methodology presented here, together with the potential for rationally creating 2D-OIPs with unique symmetry patterns, opens a pathway to design semiconductors with outstanding spin properties for next generation opto-spintronics.

Efficient circularly polarized luminescence from zero-dimensional terbium- and europium-based hybrid metal halides

Zero-dimensional (0D) chiral hybrid metal halides (HMHs) with narrow-band circularly polarized luminescence (CPL) show considerable promise in three-dimensional displays. In this work, 0D (S/R-3MOR)3TbCl6 and (S/R-3MOR)3EuCl6 (abbreviated as S/R-TbCl, S/R-EuCl) enantiomers with characteristic rare-earth ion emissions are synthesized. S/R-TbCl and S/R-EuCl exhibit narrow-band green and red emissions with high photoluminescence quantum yields of (85-91)% and (48-52)%, respectively. These materials present distinct CPL signals with dissymmetry factors up to ±0.006 and ±0.009 for S/R-TbCl and S/R-EuCl, respectively. These chiroptical properties confer the potential for their applications in circularly polarized light-emitting diodes for future displays.

A-Site Cation Chemistry in Halide Perovskites

Metal halide perovskites are an important class of semiconductors now being implemented as photovoltaic absorbers and explored for light emission, among other device applications. The semiconducting properties of halide perovskites are deeply intertwined with their composition and structure. Specifically the symmetry, tilting, and distortions of the metal halide octahedra impact the band structure and other optoelectronic properties. In this review, we examine the various compositions of monovalent A-site cations in three-dimensional (3D) halide perovskites AMX3 (M = divalent metal; X = halide). We focus on how the A-site cation templates the inorganic metal-halide perovskite framework, resulting in changes in the crystal structure symmetry, as well as M-X bonding parameters, summarized in a comprehensive table of AMX3 structures. The A-site cation motion, effects of alloying, and 2D Ruddlesden-Popper perovskite structures with unique A-site cations are further overviewed. Correlations are shown between these A-site cation dominated structural parameters and the resulting optoelectronic properties such as band gap. This review should serve as a reference for the A-site cation structural chemistry of metal halide perovskites and inspire continued research into less explored metal halide perovskite compositions and structures.

Remote chirality transfer in low-dimensional hybrid metal halide semiconductors

In hybrid metal halide perovskites, chiroptical properties typically arise from structural symmetry breaking by incorporating a chiral A-site organic cation within the structure, which may limit the compositional space. Here we demonstrate highly efficient remote chirality transfer where chirality is imposed on an otherwise achiral hybrid metal halide semiconductor by a proximal chiral molecule that is not interspersed as part of the structure yet leads to large circular dichroism dissymmetry factors (gCD) of up to 10-2. Density functional theory calculations reveal that the transfer of stereochemical information from the chiral proximal molecule to the inorganic framework is mediated by selective interaction with divalent metal cations. Anchoring of the chiral molecule induces a centro-asymmetric distortion, which is discernible up to four inorganic layers into the metal halide lattice. This concept is broadly applicable to low-dimensional hybrid metal halides with various dimensionalities (1D and 2D) allowing independent control of the composition and degree of chirality.

Macroscopic Twisting of Chiral Metal Halide Single Crystals Driven by Thermo-Induced Topochemical Dehydration

Dynamic twisting crystals, combining the features of dynamic crystals and twisting crystals, promise advanced applications in targeted drug delivery, biosensors, microrobots, and spiral optoelectronics. However, the determination of dynamic twisting crystals with specific directions remains a formidable challenge in practical applications. Herein, based on organic-inorganic hybrid metal halide (OIHMH) single crystals, we have realized the chirality-induced macroscopic twisting of single crystals driven by a thermo-induced topochemical dehydration reaction. These crystals exhibit molecular-chirality-induced twisting upon heating, along with reversals in their linear chiroptical circular dichroism and nonlinear chiroptical second harmonic generation circular dichroism. Such an induced twisting has been attributed to the alteration of the helical arrangement of chiral cation post-topochemical dehydration. The feasibility of tuning the macroscopic twisting of OIHMH single crystals and the switching in their linear and nonlinear chiroptical properties might open up new avenues for developing dynamic crystals for microactuating and optoelectronic applications.

Boosting circularly polarized luminescence by optimizing off-centering octahedral distortion in zero-dimensional hybrid indium-antimony halides

Chiral zero-dimensional hybrid metal halides (0D HMHs) are being extensively studied as they can directly generate circularly polarized luminescence (CPL) with high photoluminescence quantum yields (PLQYs), yet improving their luminescence dissymmetry factor (g lum) remains a challenge. This study proposes a general strategy to boost the g lum value of chiral 0D HMHs by optimizing the off-centering distortion of inorganic octahedra. Accordingly, (R/S-MBA)2(2MA)In0.95Sb0.05Cl6 (MBA = α-methylbenzylammonium, 2MA = dimethylamine) and (R/S-MBA)2(3MA)In0.95Sb0.05Cl6 (3MA = trimethylamine) with near-unity PLQYs are accordingly synthesized. With increasing the from 0.012 to 0.020, the |g lum| is accordingly increased from 7.8 × 10-3 to 2.0 × 10-2. Notably, the |g lum| can be further boosted to an impressive value of 3.8 × 10-2 while maintaining near-unity PLQYs by continuously increasing the . Experimental results reveal that the choice of achiral ligands and varied Sb3+ dopant concentrations can modulate the distribution and strength of hydrogen bonds around indium-antimony halogen octahedra, respectively, thus regulating the parameter of octahedra in 0D hybrid metal halides. Additionally, light-emitting diodes with a polarization of 1.6% are fabricated. This work sheds light on the relationship between the distortion of inorganic octahedra and the g lum value.

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 430 mV (vs reversible hydrogen electrode) at 10 mA cm-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.

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.

Fluorinated Organic Cations Derived Chiral 2D Perovskite Enabling Enhanced Spin-Dependent Oxygen Evolution Reaction

Chirality-induced spin selectivity observed in chiral 2D organic-inorganic hybrid perovskite holds promise to achieve spin-dependent electrochemistry. However, conventional chiral 2D perovskites suffer from low conductivity and hygroscopicity, limiting electrochemical performance and operational stability. Here, a cutting-edge material design is introduced to develop a stable and efficient chiral perovskite-based spin polarizer by employing fluorinated chiral cation. The fluorination approach effectively promotes the charge carrier transport along the out-of-plane direction by mitigating the dielectric confinement effect within the multi-quantum well-structured 2D perovskite. Integrating the fluorinated cation incorporated spin polarizer with BiVO4 photoanode considerably boosts the photocurrent density while reducing overpotential through a spin-dependent oxygen evolution reaction. Furthermore, the hydrophobic nature of fluorine in spin polarizer endows operational stability to the photoanode, extending the durability by 280% as compared to the device with non-fluorinated spin polarizer.

Chirality-Induced Memristor of Chiral Nanostructured Half-Metallic Fe3O4 Films

Spintronic memristors, which combine the nonvolatile characteristics of memristors with the scalability of a spin-transfer torque device, are expected to play a crucial role in advancing quantitative information processing. This field commonly relies on magnetic tunnel junctions, domain wall motion, and spin waves. Here, the discovery of chirality-induced memristor behavior in chiral nanostructured Fe3O4 films (CNFFs) is reported. These CNFFs are grown on fluorine tin oxide (FTO) substrates using enantiomeric glutamic acid (Glu) as symmetry-breaking agents and consist of arrays of oriented twisted nanofibers. At 100 K, the L-CNFF exhibits memristor behavior as a pinched hysteresis loop in the I-V curve, while the D-CNFF exhibits semiconductor behavior with constant electrical resistance. The intrinsic spin polarization of half-metallic Fe3O4 and the chirality-induced spin selectivity (CISS) are speculated to contribute to the memristor in one handedness of the chiral structure. These findings present a novel spinristor that combines the functions of a memristor and a spin-filter based on chiral structures, which may promote the development of spintronic devices.

Nonadiabatic Molecular Dynamics in Momentum Space Beyond Harmonic Approximation: Hot Electron Relaxation in Photoexcited Black Phosphorus

We simulated hot-electron relaxation in black phosphorus using the nonadiabatic molecular dynamics (NA-MD) approach with a non-Condon effect in momentum space beyond the harmonic approximation. By comparing simulations at the Γ point in a large supercell with those using a few k-points in a smaller supercell─while maintaining the same number of electronic states within the same energy range, we demonstrate that both setups yield remarkably consistent energy relaxation times, regardless of the initial state energy. This consistency arises from the complementary effects of supercell size in real space and the number of k-points in the reciprocal space. This finding confirms that simulations at a single k-point in large size supercells are an effective approximation for NA-MD with a non-Condon effect. This approach offers significant advantages for complex photophysics, such as intervalley scattering and indirect bandgap charge recombination, and is particularly suitable for large systems without the need for a harmonic approximation.

Room-temperature spin injection across a chiral perovskite/III-V interface

Spin accumulation in semiconductor structures at room temperature and without magnetic fields is key to enable a broader range of optoelectronic functionality1. Current efforts are limited owing to inherent inefficiencies associated with spin injection across semiconductor interfaces2. Here we demonstrate spin injection across chiral halide perovskite/III-V interfaces achieving spin accumulation in a standard semiconductor III-V (AlxGa1-x)0.5In0.5P multiple quantum well light-emitting diode. The spin accumulation in the multiple quantum well is detected through emission of circularly polarized light with a degree of polarization of up to 15 ± 4%. The chiral perovskite/III-V interface was characterized with X-ray photoelectron spectroscopy, cross-sectional scanning Kelvin probe force microscopy and cross-sectional transmission electron microscopy imaging, showing a clean semiconductor/semiconductor interface at which the Fermi level can equilibrate. These findings demonstrate that chiral perovskite semiconductors can transform well-developed semiconductor platforms into ones that can also control spin.

High Field Electrical Polarization and Magnetoelectric Coupling in Chiral Magnet [Cu(pym)(H2O)4]SiF6·H2O

The Heisenberg antiferromagnetic chain is a canonical model for understanding many-body gaps that emerge in quantum magnets, and as a result, there has been significant work on this class of materials for much of the past century. Chiral chains, on the other hand, have received markedly less attention. [Cu(pym)(H2O)4]SiF6·H2O (pym = pyrimidine) is an S = 1/2 chiral antiferromagnet with an unconventional spin gap and no long-range ordering at zero field, features that distinguish it from more conventional spin chains that host simple phase diagrams and no magnetoelectric coupling. Here, we report pulsed magnetic field electrical polarization measurements, strong magnetoelectric coupling, and extraordinary magnetic field - temperature phase diagrams for this system. In addition to three low field transitions, we find a series of phase transitions between 40 and 70 T that depend on the magnetic field direction. The observation of electric polarization in a material with a nonpolar crystal structure implies symmetry-breaking magnetic ordering that creates a polar axis - a mechanism that we discuss in terms of significant interactions between the chiral chains as well as Dzyaloshinskii-Moriya effects. Further, we find second-order magnetoelectric coupling, allowing us to deduce the magnetic point group of the highest polarization phase. These findings are in contrast to expectations for an unordered one-dimensional spin chain and reveal a significantly greater complexity of behavior in applied field.

Self-Powered Circularly Polarized Light Detection Enabled by Chiral Two-Dimensional Perovskites with Mixed Chiral-Achiral Organic Cations

Direct detection of circularly polarized light (CPL) holds great promise for the development of various optical technologies. Chiral 2D organic-inorganic halide perovskites make it possible to fabricate CPL-sensitive photodetectors. However, selectively detecting left-handed circularly polarized (LCP) and right-handed circularly polarized (RCP) light remains a significant challenge. Herein, we demonstrate a greatly enhanced distinguishability of photodiode-type CPL photodetectors based on chiral 2D perovskites with mixed chiral aryl (R)-(+),(S)-(-)-α-methylbenzylammonium (R,S-MBA) and achiral alkyl n-butylammonium (nBA) cations. The (R,S-MBA0.5nBA0.5)2PbI4 perovskites exhibit a 10-fold increase in circular dichroism signals compared to (R,S-MBA)2PbI4 perovskites. The CPL photodetectors based on the mixed-cation perovskites exhibit self-powered capabilities with a specific detectivity of 2.45 × 1012 Jones at a 0 V bias. Notably, these devices show high distinguishability (gres) factors of -0.58 and +0.54 based on (R,S-MBA0.5nBA0.5)2PbI4 perovskites, respectively, surpassing the performance of (R-MBA)2PbI4-based devices by over 3-fold and setting a record for CPL detectors based on chiral 2D n = 1 perovskites.

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

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

Structure-Guided Approaches for Enhanced Spin-Splitting in Chiral Perovskite

Hybrid organic-inorganic perovskites with diverse lattice structures and chemical composition provide an ideal material platform for novel functionalization, including chirality transfer. Chiral perovskites combine organic and inorganic sublattices, therefore encoding the structural asymmetry into the electronic structures and giving rise to the spin-splitting effect. From a structural chemistry perspective, the magnitude of the spin-splitting effect crucially depends on the noncovalent and electrostatic interaction within the chiral perovskite, which induces the local site and long-range bulk inversion symmetry breaking. In this regard, we systematically retrospect the structure-property relationships in chiral perovskite. Insight into the rational design of chiral perovskites based on molecular configuration, dimensionality, and chemical composition along with their effects on spin-splitting manifestation is presented. Lastly, challenges in purposeful material design and further integration into chiral perovskite-based spintronic devices are outlined. With an understanding of fundamental chemistry and physics, we believe that this Perspective will propel the application of multifunctional spintronic devices.

Bright Circularly Polarized Mechanoluminescence from 0D Hybrid Manganese Halides

Hybrid metal halides (HMHs) with efficient circularly polarized luminescence (CPL) have application prospects in many fields, due to their abundant host-guest structures and high photoluminescence quantum yield (PLQY). However, CPLs in HMHs are predominantly excited by light or electricity, limiting their use in multivariate environments. It is necessary to explore a novel excitation method to extend the application of chiral HMHs as smart stimuli-responsive optical materials. In this work, an enantiomeric pair of 0D hybrid manganese bromides, [H2(2R,4R)-(+)/(2S,4S)-(-)-2,4-bis(diphenylphosphino)pentane]MnBr4 [(R/S)-1] is presented, which exhibits efficient CPL emissions with near-unity PLQYs and high dissymmetry factors of ± 2.0 × 10-3. Notably, (R/S)-1 compounds exhibit unprecedented and bright circularly polarized mechanoluminescence (CPML) emissions under mechanical stimulation. Moreover, (R/S)-1 possess high mechanical force sensitivities with mechanoluminescence (ML) emissions detectable under 0.1 N force stimulation. Furthermore, this ML emission exhibits an extraordinary antithermal quenching effect in the temperature range of 300-380 K, which is revealed to originate from a thermal activation energy compensation mechanism from trap levels to Mn(II) 4T1 level. Based on their intriguing optical properties, these compounds as chiral force-responsive materials are demonstrated in multilevel confidential information encryption.

Perovskite versus Nonperovskite: Modulating the Nature and Optical Properties of One-Dimensional Chiral Lead-Bromide Networks

In the last 5 years, low-dimensional chiral metal-halide semiconductors have attracted great interest in the generation of chiroptical activity. Among this new family of materials, one-dimensional (1D) networks have appeared as the best candidates for strong circular dichroism (CD) and circularly polarized luminescence (CPL). Here, we present a new family of 1D chiral lead-bromide materials prepared from organic S/R/rac-1-hydroxypropyl-2-ammonium (S/R/rac-HP2A) cations. The presence or absence of polarity in the crystal structure as well as the perovskite or nonperovskite nature of the inorganic network depends on the initial stoichiometry of metal-halide salt and chiral amine during the crystallization. The perovskite-type networks exhibit strong CD and second harmonic generation (SHG) responses, while the nonperovskite compounds show the presence of polymorphism in the crystal phase and weak natural optical activity in the final material. These results underline the impact of synthetic conditions and thin film morphology on the structural and optical properties of metal-halide hybrid networks.

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

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

Multi-stimuli-responsive luminescence enabled by crown ether anchored chiral antimony halide phosphors

Stimuli-responsive optical materials have provided a powerful impetus for the development of intelligent optoelectronic devices. The family of organic-inorganic hybrid metal halides, distinguished by their structural diversity, presents a prospective platform for the advancement of stimuli-responsive optical materials. Here, we have employed a crown ether to anchor the A-site cation of a chiral antimony halide, enabling convenient control and modulation of its photophysical properties. The chirality-dependent asymmetric lattice distortion of inorganic skeletons assisted by a crown ether promotes the formation of self-trapped excitons (STEs), leading to a high photoluminescence quantum yield of over 85%, concomitant with the effective circularly polarized luminescence. The antimony halide enantiomers showcase highly sensitive stimuli-responsive luminescent behaviours towards excitation wavelength and temperature simultaneously, exhibiting a versatile reversible colour switching capability from blue to white and further to orange. In situ temperature-dependent luminescence spectra, time-resolved luminescence spectra and theoretical calculations reveal that the multi-stimuli-responsive luminescent behaviours stem from distinct STEs within zero-dimensional lattices. By virtue of the inherent flexibility and adaptability, these chiral antimony chlorides have promising prospects for future applications in cutting-edge fields such as multifunctional illumination technologies and intelligent sensing devices.

Topological Nodal-Point Superconductivity in Two-Dimensional Ferroelectric Hybrid Perovskites

Two-dimensional (2D) hybrid organic-inorganic perovskites (HOIPs) with enhanced stability, high tunability, and strong spin-orbit coupling have shown great potential in vast applications. Here, we extend the already rich functionality of 2D HOIPs to a new territory, realizing topological superconductivity and Majorana modes for fault-tolerant quantum computation. Especially, we predict that room-temperature ferroelectric BA2PbCl4 (BA for benzylammonium) exhibits topological nodal-point superconductivity (NSC) and gapless Majorana modes on selected edges and ferroelectric domain walls when proximity-coupled to an s-wave superconductor and an in-plane Zeeman field, attractive for experimental verification and application. Since NSC is protected by spatial symmetry of 2D HOIPs, we envision more exotic topological superconducting states to be found in this class of materials due to their diverse noncentrosymmetric space groups, which may open a new avenue in the fields of HOIPs and topological superconductivity.

Induced Circularly Polarized Luminescence and Exciton Fine Structure Splitting in Magnetic-Doped Chiral Perovskites

Magnetic impurity doping in semiconductors has emerged as an important strategy to endow exotic photophysical and magnetic properties. While most reported hosts are centrosymmetric semiconductors, doping magnetic ions into a noncentrosymmetric chiral semiconductor can offer additional control of photonic and spin polarization. In this work, we synthesized a Mn2+-doped chiral two-dimensional (2D) perovskite, Mn2+:(R-MPA)2PbBr4 (R-MPA+ = R-methyl phenethylammonium). We found that the optical activity of chiral 2D perovskites is enhanced with an increased concentration of Mn2+ ions. Additionally, efficient energy transfer from the chiral host to the Mn2+ dopants is observed. This energy transfer process gives rise to circularly polarized luminescence from the excited state of Mn2+ (4T1 → 6A1), exhibiting a photoluminescence quantum yield up to 24% and a dissymmetry factor of 11%. The exciton fine structures of undoped and Mn2+-doped (R-MPA)2PbBr4 are further studied through magnetic circular dichroism (MCD) spectroscopy. Our analysis shows that chiral organic cations lead to an exciton fine structure splitting energy as large as 5.0 meV, and the splitting is further increased upon Mn2+ doping. Our results reveal the strong impacts of molecular chirality and magnetic dopants on the exciton structures of halide perovskites.

MatGPT: A Vane of Materials Informatics from Past, Present, to Future

Combining materials science, artificial intelligence (AI), physical chemistry, and other disciplines, materials informatics is continuously accelerating the vigorous development of new materials. The emergence of "GPT (Generative Pre-trained Transformer) AI" shows that the scientific research field has entered the era of intelligent civilization with "data" as the basic factor and "algorithm + computing power" as the core productivity. The continuous innovation of AI will impact the cognitive laws and scientific methods, and reconstruct the knowledge and wisdom system. This leads to think more about materials informatics. Here, a comprehensive discussion of AI models and materials infrastructures is provided, and the advances in the discovery and design of new materials are reviewed. With the rise of new research paradigms triggered by "AI for Science", the vane of materials informatics: "MatGPT", is proposed and the technical path planning from the aspects of data, descriptors, generative models, pretraining models, directed design models, collaborative training, experimental robots, as well as the efforts and preparations needed to develop a new generation of materials informatics, is carried out. Finally, the challenges and constraints faced by materials informatics are discussed, in order to achieve a more digital, intelligent, and automated construction of materials informatics with the joint efforts of more interdisciplinary scientists.

Electron-donating functional groups strengthen ligand-induced chiral imprinting on CsPbBr3 quantum dots

Chiral perovskite nanoparticles and films are promising for integration in emerging spintronic and optoelectronic technologies, yet few design rules exist to guide the development of chiral material properties. The chemical space of potential building blocks for these nanostructures is vast, and the mechanisms through which organic ligands can impart chirality to the inorganic perovskite lattice are not well understood. In this work, we investigate how the properties of chiral ammonium ligands, the most common organic ligand type used with perovskites, affect the circular dichroism of strongly quantum confined CsPbBr3 nanocrystals. We show that aromatic ammonium ligands with stronger electron-donating groups lead to higher-intensity circular dichroism associated with the lowest-energy excitonic transition of the perovskite nanocrystal. We argue that this behavior is best explained by a modulation of the exciton wavefunction overlap between the nanocrystal and the organic ligand, as the functional groups on the ligand can shift electron density toward the organic species-perovskite lattice interface to increase the imprinting.

Chirality Versus Symmetry: Electron's Spin Selectivity in Nonpolar Chiral Lead-Bromide Perovskites

In the last decade, chirality-induced spin selectivity (CISS), the spin-selective electron transport through chiral molecules, has been described in a large range of materials, from insulators to superconductors. Because more experimental studies are desired for the theoretical understanding of the CISS effect, chiral metal-halide semiconductors may contribute to the field thanks to their chiroptical and spintronic properties. In this regard, this work uses new chiral organic cations S-HP1A and R-HP1A (HP1A = 2-hydroxy-propyl-1-ammonium) to prepare 2D chiral halide perovskites (HPs) which crystallize in the enantiomorphic space groups P43 21 2 and P41 21 2, respectively. The fourfold symmetry induces antiferroelectricity along the stacking axis which, combined to incomplete Rashba-like splitting in each individual 2D polar layer, results in rare spin textures in the band structure. As revealed by magnetic conductive-probe atomic force microscopy (AFM) measurements, these materials show CISS effect with partial spin polarization (SP; ±40-45%). This incomplete effect is efficient enough to drive a chiro-spintronic device as demonstrated by the fabrication of spin valve devices with magnetoresistance (MR) responses up to 250 K. Therefore, these stable lead-bromide HP materials not only represent interesting candidates for spintronic applications but also reveal the importance of polar symmetry-breaking topology for spin selectivity.

Free Halogen Substitution of Chiral Hybrid Metal Halides for Activating the Linear and Nonlinear Chiroptical Properties

Halogen substitution has been proven as an effective approach to the band gap engineering and optoelectronic modulation of organic-inorganic hybrid metal halide (OIHMH) materials. Various high-performance mixed halide OIHMH film materials have been primarily obtained through the substitution of coordinated halogens in their inorganic octahedra. Herein, we propose a new strategy of substitution of free halogen outside the inorganic octahedra for constructing mixed halide OIHMH single crystals with chiral structures, resulting in a boost of their linear and nonlinear chiroptical properties. The substitution from DMA4[InCl6]Cl (DMA = dimethylammonium) to DMA4[InCl6]Br crystals through a facile antisolvent vaporization method produces centimeter-scale single crystals with high thermal stability along with high quantum yield photoluminescence, conspicuous circularly polarized luminescence, and greatly enhanced second harmonic generation (SHG). In particular, the obtained DMA4[InCl6]Br single crystal features an intrinsic chiral structure, exhibiting a significant SHG circular dichroism (SHG-CD) response with a highest reported anisotropy factor (gSHG-CD) of 1.56 among chiral OIHMH materials. The enhancements in both linear and nonlinear chiroptical properties are directly attributed to the modulation of octahedral distortion. The mixed halide OIHMH single crystals obtained by free halogen substitution confine the introduced halogens within free halogen sites of the lattice, thereby ensuring the stability of compositions and properties. The successful employment of such a free halogen substitution approach may broaden the horizon of the regulation of structures and the optoelectronic properties of the OIHMH materials.

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

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

Synthesis and Optical Properties of One Year Air-Stable Chiral Sb(III) Halide Semiconductors

Chiral hybrid metal-halide semiconductors (MHS) pose as ideal candidates for spintronic applications owing to their strong spin-orbit coupling (SOC), and long spin relaxation times. Shedding light on the underlying structure-property relationships is of paramount importance for the targeted synthesis of materials with an optimum performance. Herein, we report the synthesis and optical properties of 1D chiral (R-/S-THBTD)SbBr5 (THBTD = 4,5,6,7-tetrahydro-benzothiazole-2,6-diamine) semiconductors using a multifunctional ligand as a countercation and a structure directing agent. (R-/S-THBTD)SbBr5 feature direct and indirect band gap characteristics, exhibiting photoluminescence (PL) light emission at RT that is accompanied by a lifetime of a few ns. Circular dichroism (CD), second harmonic generation (SHG), and piezoresponse force microscopy (PFM) studies validate the chiral nature of the synthesized materials. Density functional theory (DFT) calculations revealed a Rashba/Dresselhaus (R/D) spin splitting, supported by an energy splitting (ER) of 23 and 25 meV, and a Rashba parameter (αR) of 0.23 and 0.32 eV·Å for the R and S analogs, respectively. These values are comparable to those of the 3D and 2D perovskite materials. Notably, (S-THBTD)SbBr5 has been air-stable for a year, a record performance among chiral lead-free MHS. This work demonstrates that low-dimensional, lead-free, chiral semiconductors with exceptional air stability can be acquired, without compromising spin splitting and manipulation performance.

Nonlinear optical properties in chiral copper oxide nanosheets

Chiral transition metal oxides (TMOs) are in the forefront of research as potential active materials in various optoelectronic applications. However, the nonlinear optical (NLO) properties of the chiral TMOs have not been fully understood. Here, several kinds of copper oxide nanosheets capped with different chiral amino acids are synthesized. Notably, we investigate the NLO activities of these materials, including broadband second harmonic generation and transformation of nonlinear optical properties from saturable absorption to reverse saturable absorption. This work will broaden the use of chiral TMO materials in nonlinear photonic devices.

Chiral mesostructured NiFe2O4 films with chirality induced spin selectivity

Chiral mesostructured NiFe2O4 films (CMNFFs) were synthesized using L-/D-tyrosine as symmetry-breaking and structure-directing agents through a hydrothermal method. For the first time, chirality induced spin selectivity was directly observed in these ferrimagnetic materials using chirality-dependent magnetic-tip conducting atomic force microscopy (mc-AFM).

Fundamentals, Advances, and Artifacts in Circularly Polarized Luminescence (CPL) Spectroscopy

Objects are chiral when they cannot be superimposed with their mirror image. Materials can emit chiral light with an excess of right- or left-handed circular polarization. This circularly polarized luminescence (CPL) is key to promising future applications, such as highly efficient displays, holography, sensing, enantiospecific discrimination, synthesis of drugs, quantum computing, and cryptography. Here, a practical guide to CPL spectroscopy is provided. First, the fundamentals of the technique are laid out and a detailed account of recent experimental advances to achieve highly sensitive and accurate measurements is given, including all corrections required to obtain reliable results. Then the most common artifacts and pitfalls are discussed, especially for the study of thin films, for example, based on molecules, polymers, or halide perovskites, as opposed to dilute solutions of emitters. To facilitate the adoption by others, custom operating software is made publicly available, equipping the reader with the tools needed for successful and accurate CPL determination.

Broadband emission originating from the stereochemical expression of 6s2 lone pairs in two-dimensional lead bromide perovskites

The stereochemical expression of the 6s2 lone pair on the lead atom has a significant impact on the crystal structures and physical properties of lead halide perovskites. Two-dimensional (2D) lead bromide perovskites often exhibit a broadband emission, yet the structural origin of the broadband emission has been under debate. Here, we report the synthesis and characterization of a 2D lead bromide hybrid (4-chlorophenylammonium)2PbBr4 that consists of a combination of the octahedral unit PbBr6 and the rarely observed capped octahedral unit PbBr7 through corner-sharing and edge-sharing linkages. The seven-coordination geometry indicates a strong stereo-active lone pair on the Pb2+ cation. By comparing this structure with two representative 2D perovskites, (benzylammonium)2PbBr4 and (4-aminotetrahydropyran)2PbBr4, we establish how the lone pair expression affects the local coordination geometry of the Pb2+ cation and the resulting optical and electronic properties. As the Pb-Br bond length increases, the lone pair expression leads to off-centering displacement of Pb2+ within the octahedra and then the formation of seven-coordination capped octahedra. Density functional theory calculations indicate that the off-centering distorted octahedra and capped octahedra are due to the asymmetric distribution of the Pb electrons that have both s and p orbital characteristics. Spectroscopic studies show the photoluminescence spectra evolving from narrowband emission to broadband emission with increasing LPE, as well as softer and more anharmonic lattice vibrations that facilitate exciton self-trapping. Our results demonstrate that lone pairs could be a powerful design rule for developing light emitting materials.

Conditions for EPR detection of chirality-induced spin selectivity in spin-polarized radical pairs in isotropic solution

Chiral molecules can act as spin filters, preferentially transmitting electrons with spins polarized along their direction of travel, an effect known as chirality-induced spin selectivity (CISS). In a typical experiment, injected electrons tunnel coherently through a layer of chiral material and emerge spin-polarized. It is also possible that spin polarization arises in radical pairs formed photochemically when electrons hop incoherently between donor and acceptor sites. Here we aim to identify the magnetic properties that would optimise the visibility of CISS polarization in time-resolved electron paramagnetic resonance (EPR) spectra of transient radical pairs without the need to orient or align their precursors. By simulating spectra of actual and model systems, we find that CISS contributions to the polarization should be most obvious when at least one of the radicals has small g-anisotropy and an inhomogeneous linewidth larger than the dipolar coupling of the two radicals. Under these conditions there is extensive cancellation of absorptive and emissive enhancements making the spectrum sensitive to small changes in the individual EPR line intensities. Although these cancellation effects are more pronounced at lower spectrometer frequencies, the spectral changes are easier to appreciate with the enhanced resolution afforded by high-frequency EPR. Consideration of published spectra of light-induced radical pairs in photosynthetic bacterial reaction centres reveals no significant CISS component in the polarization generated by the conventional spin-correlated radical pair mechanism.

Chiral Inorganic Nanomaterials for Photo(electro)catalytic Conversion

Chiral inorganic nanomaterials due to their unique asymmetric nanostructures have gradually demonstrated intriguing chirality-dependent performance in photo(electro)catalytic conversion, such as water splitting. However, understanding the correlation between chiral inorganic characteristics and the photo(electro)catalytic process remains challenging. In this perspective, we first highlight the chirality source of inorganic nanomaterials and briefly introduce photo(electro)catalysis systems. Then, we delve into an in-depth discussion of chiral effects exerted by chiral nanostructures and their photo-electrochemistry properties, while emphasizing the emerging chiral inorganic nanomaterials for photo(electro)catalytic conversion. Finally, the challenges and opportunities of chiral inorganic nanomaterials for photo(electro)catalytic conversion are prospected. This perspective provides a comprehensive overview of chiral inorganic nanomaterials and their potential in photo(electro)catalytic conversion, which is beneficial for further research in this area.

Spatially Correlated Chirality in Chiral Two-Dimensional Perovskites Revealed by Second-Harmonic-Generation Circular Dichroism Microscopy

Understanding the chiral mechanism of chiral hybrid perovskites is a prerequisite for developing relevant chiroptoelectronic applications. Although conventional circular dichroism (CD) spectroscopy can be used to characterize chirality in chiral perovskites, it has a low signal-to-noise ratio and can provide only information about macroscopic chirality. Herein, with the aim of revealing the microscopic chiral mechanism in chiral perovskites, we utilize a spacer cation alloying strategy to construct chiral two-dimensional perovskites. For the first time, we demonstrate second-harmonic-generation CD microarea imaging in chiral perovskite thin films to unveil their spatially correlated chirality. In combination with theoretical calculations, it is revealed that the spatially correlated chirality is caused by localized out-of-plane supramolecular orientations. This work will not only advance the understanding of the mechanism of chiroptical activity in chiral perovskites but also provide inspiration for the rational design and synthesis of perovskites for chirality-related nonlinear optoelectronic devices.