Induction of Chiral Hybrid Metal Halides from Achiral Building Blocks

Inverted Chiroptical Properties of Hybrid Metal Halides Through Reversible Chiral Induction Driven by External and Internal Chirality Transfer

Chiral organic-inorganic hybrid metal halides (OIHMHs) are commonly constructed by introducing pairs of enantiomorphic chiral precursors through a single chirality transfer pathway, which may limit the regulation of chiral structural diversity and chiroptoelectronic properties. Herein, we propose a new strategy for achieving reversible chiral induction of OIHMHs with inverted chiroptical properties through external and internal chirality transfer pathways, by utilizing a single chiral reagent R-/S-α-methylbenzylamine (R-/S-MBA). Specifically, R-MBA can externally induce chiral enrichment of M-DMA4(Bi0.486In0.511Sb0.003)Cl7 (M-DMA4(Bi-In-Sb)Cl7, DMA = dimethylammonium cation) without integrating into structure. Conversely, R-MBA can insert into structure, internally inducing the formation of DMA(R-MBA)2(Bi0.634In0.362Sb0.004)Cl6 (DMA(R-MBA)2(Bi-In-Sb)Cl6), which reverses the structural arrangements and inverts both linear and nonlinear chiroptical properties. Both externally and internally induced chiral OIHMHs exhibit significant chiroptical responses with high photoluminescence quantum yield (PLQY) and second harmonic generation (SHG). Moreover, the externally induced centimeter-sized rhombic single crystal enables morphology- and angle-dependent inverted circularly polarized luminescence with a dissymmetry factor of ∼0.02, through single crystal anisotropy. The internal induction enhances SHG intensity by nine-fold and increases PLQY to 98.9%. This multi-path chirality transfer, based on a single chiral reagent, can significantly broaden the structural scope of functional chiral OIHMH materials and facilitate the regulation of chiroptoelectronic properties.

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.

Extendable Synthesis of Organic Cations for In Situ Construction of Hybrid Metal Halides with Near-Unity Photoluminescence and Strong Second Harmonic Generation

The A-site organic components of organic-inorganic hybrid metal halides (OIHMHs) significantly impact their crystal structure and optoelectronic properties. However, chemical modification of A-site cations has been mostly limited to commercial organic precursors, which restricts the structural variability of OIHMHs for optimal functionalities. Herein we have proposed an extendable synthesis approach to the direct procurability of various organic cations with desireable structures for the in situ construction of a library of OIHMH materials. The template condensation reaction between dimethyl sulfoxide and acetone derivatives yields A-site organic cations with exquisite control of modularization and regioselectivity within the OIHMH crystallization system. The as-fabricated OIHMHs demonstrated highly efficient linear optical photoluminescence or nonlinear optical second harmonic generation, promising potential applications in photonic devices. This in situ synthetic strategy offers a structural extension of OIHMHs and establishes a fundamental methodological platform for screening functional OIHMH materials.

Stepwise kinetics of the early-stage nucleation in chiral perovskites via ab initio molecular dynamics and free-energy calculations

This study provides a comprehensive molecular-level understanding of the early-stage nucleation process in chiral hybrid organic-inorganic perovskites (HOIPs). A combination of ab initio molecular dynamics (AIMD) based on density functional theory (DFT) and parallel bias metadynamics simulations was designed to explore a broad spectrum of the nucleation scenarios, disclosing how structural deviations affect the formation of chiral aggregates at the atomic scale. The workflow uses parallel replicas initialized from configurations characterised by different root-mean-square deviations (RMSD) relative to the crystallographic coordinates of the chiral ligands. The free-energy landscape and the kinetic pathways involved in chiral aggregate formation indicate a stepwise mechanism that governs the transition from disordered to chiral states. The computed free-energy barriers and corresponding transition timescales uncover several critical stages in this process, including rapid initial relaxations as well as slower, free-energy-intensive steps, with overall timescales on the order of microseconds as the system approaches its most chiral configuration.

Thermoelastic twisting-assisted crystal jumping based on a self-healing molecular crystal

Adaptive crystals have attracted significant attention from solid-state chemists and crystal engineers for their promising applications in memories, capacitors, sensors, and actuators. Among them, thermosalient crystals are particularly favored thanks to their efficient energy conversions and rapid responses. However, the mechanisms for the mechanical responses of thermosalient crystals remain largely unclear. Herein we demonstrate that thermosalient effects of molecular crystals could be driven by thermoelastic twisting behaviors. The crystal, based on a model compound with rigid dibenzothiophene sulfone planes and flexible ethoxy chains, can spontaneously self-heal from mechanical fractures. Upon heating, the crystal undergoes remarkable thermosalient behaviors driven by a distinctive left- or right-handed twisting. This thermoelastic twisting converts thermal energy into elastic potential energy, which is further released as kinetic energy upon untwisting to drive the crystal jump. Our demonstration on thermoelastic twisting-induced crystal jumping offers a different perspective on the origins of thermosalient crystals and could provide inspiration for future engineering and application of dynamic molecular crystals.

Supramolecular Assembly Enhanced Linear and Nonlinear Chiroptical Properties of Chiral Manganese Halides

Chiral hybrid organic-inorganic metal halides (HOMHs) hold great promise in broad applications ranging from ferroelectrics, spintronics to nonlinear optics, owing to their broken inversion symmetry and tunable chiroptoelectronic properties. Typically, chiral HOMHs are constructed by chiral organic cations and metal anion polyhedra, with the latter regarded as optoelectronic active units. However, the primary design approaches are largely constrained to regulation of general components within structural formula. Herein, supramolecular approaches have been taken for the functionalization of chiral enantiomers by anchoring chiral cations with crown ether hosting molecules. Chiral HOMHs of R-/S-(18-crown-6@ClMBA)2MnBr4 have been thus obtained with boosted linear and nonlinear chiroptical properties. The self-assembled cations lead to enhanced structural rigidity, which promote near-unity green light emission and strong circularly polarized luminescence with a high asymmetry factor, along with high efficiency second-order nonlinear optical responses. In particular, these chiral HOMH single crystals demonstrate a sensitive discrimination for circularly polarized laser in the near-infrared region with the nonlinear optical asymmetry factor (gSHG-CD) as high as 1.8. This work highlights the contribution of supramolecular assembly in improving chiroptical performances, offering valuable insights for the design of new chiral HOMH materials with promising application potentials as linear and nonlinear CPL emitters and detectors.

Enhanced Coplanarity and Giant Birefringence in Hydroxypyridinium Nitrate via Hydrogen Bonding between Planar Donors and Planar Acceptors

Birefringent crystals, which possess optical anisotropy, are important optical components. However, designing and synthesizing birefringent crystals faces the challenge of achieving anisotropic structures, especially coplanar geometries. Herein, we achieve a significant birefringence in an ionic compound (C5H6ON)+(NO3)-, (4-hydroxypyridinium nitrate, 4HPN) by hydrogen bonding between planar donors and planar acceptors. We demonstrate that the interactions between the planar hydrogen bond donor ((C5H6ON)+) and planar hydrogen bond acceptor ((NO3)-) ensure the coplanarity during the crystal packing, generating the desired giant optical anisotropy. On two manually cut crystal chips, we observe aΔ n o b v . ${\Delta {n}^{obv.}}$ =0.494 (Δ n m a x c a l . ${\Delta {n}_{max}^{cal.}}$ =0.593), which is the largest among nitrates, or hydroxypyridinium derivatives. ThisΔ n o b v . ${\Delta {n}^{obv.}}$ value already surpasses those of the benchmark crystals, e.g., YVO4 and CaCO3, commonly used in the UV to visible and near IR spectral range. 4HPN also exhibits a strong second harmonic generation response (9.55×KDP). This strategy offers a promising avenue for the design and development of birefringent crystals with potential applications in optical communication, sensing and signal processing devices.

Mechanical Twisting-Induced Enhancement of Second-Order Optical Nonlinearity in a Flexible Molecular Crystal

Flexible molecular crystals are essential for advancing smart materials, providing unique functionality and adaptability for applications in next-generation electronics, pharmaceuticals, and energy storage. However, the optical applications of flexible molecular crystals have been largely restricted to linear optics, with nonlinear optical (NLO) properties rarely explored. Herein, we report on the application of mechanical twisting of flexible molecular crystals for second-order nonlinear optics. The crystal formed through the self-assembly of the model compound 9-anthraldehyde (AA) features an intrinsic chiral and noncentrosymmetric structure, demonstrating high efficiency second harmonic generation (SHG) and NLO circular dichroism, which could be greatly enhanced by macroscopic mechanical twisting. The anisotropic molecular stacking imparts the AA crystal with mechanical flexibility of combined elastic bending and plastic twisting. The isochiral mechanical twisting could greatly enhance the SHG intensities by an order of magnitude depending on their M- or P-configuration. Meanwhile, the SHG circular dichroism factor gSHG-CD of the isochiral twisted crystal is greatly increased, achieving the highest reported NLO anisotropy factor among organic NLO materials. These boosted NLO performances of SHG intensity and nonlinear chiroptical response are expected to greatly expand the photonic applications of flexible molecular crystals.

Chiral Bimetallic Cuprous-Lead Hybrid Iodide Single Crystals toward Occurrence of Second Harmonic Generation

Hybrid bimetallic halides with two different optical activities have exhibited excellent optical properties, which demonstrates great potential in the optoelectronic fields. To develop hybrid cuprous-lead bimetallic halides with unique non-centrosymmetric structures, we introduced the chiral cations R/S-2-C5H14N22+ (C5H14N22+ = methylpiperazinium) into inorganic frameworks containing two different heterometallic cuprous and lead cations, respectively, and successfully obtained the novel chiral hybrid bimetallic halides of (R/S-2-C5H14N2)3Cu2Pb2I12 single crystals by the hydrothermal method. Bimetallic anionic [Cu2Pb2I12]6- framework structures were constructed from two different [PbI6]4- and two different [CuI4]3- twisted polyhedra, and band gap calculations were demonstrated. Most importantly, chiral crystal structures of (R/S-2-C5H14N2)3Cu2Pb2I12 were confirmed by circular dichroism (CD), and their anisotropy factor (gCD) values were -5.98 × 10-5 and +5.79 × 10-5, respectively. Besides, significant second harmonic generation of (R/S-2-C5H14N2)3Cu2Pb2I12 single crystals was also exhibited through the coupling of chiral organic cations and inorganic anionic [Cu2Pb2I12]6- frameworks. This work not only provides guidance for understanding the structure-property relationship of novel chiral hybrid bimetallic halides, but also extends the further optoelectronic applications of these hybrid halide systems.

Reversible Local Protonation-Deprotonation: Tuning Stimuli-Responsive Circularly Polarized Luminescence in Chiral Hybrid Zinc Halides for Anti-Counterfeiting and Encryption

Precise control over the organic composition is crucial for tailoring the distinctive structures and properties of hybrid metal halides. However, this approach is seldom utilized to develop materials that exhibit stimuli-responsive circularly polarized luminescence (CPL). Herein, we present the synthesis and characterization of enantiomeric hybrid zinc bromides: biprotonated ((R/S)-C12H16N2)ZnBr4 ((R/S-LH2)ZnBr4) and monoprotonated ((R/S)-C12H15N2)2ZnBr4 ((R/S-LH1)2ZnBr4), derived from the chiral organic amine (R/S)-2,3,4,9-Tetrahydro-1H-carbazol-3-amine ((R/S)-C12H14N2). These compounds showcase luminescent properties; the zero-dimensional biprotonated form emits green light at 505 nm, while the monoprotonated form, with a pseudo-layered structure, displays red luminescence at 599 and 649 nm. Remarkably, the reversible local protonation-deprotonation behavior of the organic cations allows for exposure to polar solvents and heating to induce reversible structural and luminescent transformations between the two forms. Theoretical calculations reveal that the lower energy barrier associated with the deprotonation process within the pyrrole ring is responsible for the local protonation-deprotonation behavior observed. These enantiomorphic hybrid zinc bromides also exhibit switchable circular dichroism (CD) and CPL properties. Furthermore, their chloride counterparts were successfully obtained by adjusting the halogen ions. Importantly, the unique stimuli-responsive CPL characteristics position these hybrid zinc halides as promising candidates for applications in information storage, anti-counterfeiting, and information encryption.

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.

Manipulating Chiroptical Activities in 0D Chiral Hybrid Manganese Bromides by Solvent Molecular Engineering

0D hybrid metal halides (0D HMHs) with fully isolated inorganic units provide an ideal platform for studying the correlations between chiroptical activities and crystal structures at atomic levels. Here, through the incorporation of different solvent molecules, a series of 0D chiral manganese bromides (RR/SS-C20H28N2)3MnBr8·2X (X = C2H5OH, CH3OH, or H2O) are synthesized to elucidate their chiroptical properties. They show negligible circular dichroism signals of Mn absorptions due to C2v-symmetric [MnBr4]2- tetrahedra. However, they display distinct circularly polarized luminescence (CPL) signals with continuously increased luminescence asymmetry factors (glum) from 10-4 (X = C2H5OH) to 10-3 (X = H2O). The increased glum value is structurally revealed to originate from the enhancement of [MnBr4]2- tetrahedral bond-angle distortions, due to the presence of different solvent molecules. Furthermore, (RR/SS-C20H28N2)MnBr4·H2O enantiomers with larger bond-angle distortions of [MnBr4]2- tetrahedra are synthesized based on hydrobromic acid-induced structural transformation of (RR/SS-C20H28N2)3MnBr8·2H2O enantiomers. Therefore, such (RR/SS-C20H28N2)MnBr4·H2O enantiomers exhibit enhanced CPL signals with |glum| up to 1.23 × 10-2. This work provides unique insight into enhancing chiroptical activities in 0D HMH systems.

l-Homoproline-Directed Synthesis of Organic-Inorganic Metal Iodides for Second Harmonic Generation

Three organic-inorganic metal iodides, namely, (NH4)(l-hp)ZnI3 (1), [Cd(l-hp)4]Cd3I8 (2), and (l-Hhp)(l-hp)PbI3 (3), have been synthesized using l-homoproline (l-hp) as the structure-directing agent. These compounds feature different noncentrosymmetric structures and optical properties. In particular, compound 3 shows a large second-harmonic-generation response of 3.4 times that of KH2PO4. Density functional theory calculations were performed to gain insight into its structure-property relationship.

Chiral 3D Perovskite Formation Induced by Chiral Templates

Chiral 3D perovskites pose challenges compared to lower-dimensional variants due to limited chiral organic cation options. Here, we present a universal and controlled method for synthesizing chiral 3D lead halide perovskites using organic amines or alcohols as chiral templates. Introducing these templates to PbCl2 in N,N-dimethylformamide (DMF) under acidic conditions induces the crystallization of R/S [DMA]PbCl3 (DMA = dimethylamine). The resulting structure aligns with the templates used, stemming from the helical Pb2Cl95- chain as verified by single-crystal X-ray diffraction. Furthermore, the chiral perovskite exhibits absorption and circular dichroism (CD) signals in the high-energy band, enabling the circularly polarized light (CPL) detection in the UV spectrum. A CPL detector constructed by this chiral perovskite demonstrates excellent performance, boasting an anisotropy factor for photocurrent (gIph) of 0.296. Our work not only introduces a novel and controllable method for crafting chiral perovskites but also opens new avenues for circularly polarized light detection.

Chiral Induction in a Self-Assembled Pd4 Coordination Cage with Chiral Guests

The dynamic interplay of coordination bonds within metal-organic cages offers a unique avenue for structural evolution in response to external stimuli, presenting a promising strategy for the construction of chiral assemblies. This adaptability is crucial for the selective synthesis of homochiral assemblies and advancement of asymmetric catalysis. In this study, we report the self-assembly of an achiral square-planar Pd(II) acceptor with a C2-symmetric tetrapyridyl donor resulted in the formation of a racemic mixture of the chiral octahedral cage Pd4L2. The existence of this racemic mixture was confirmed using circular dichroism spectroscopy as well as single crystal X-ray diffraction analysis. We encoded chiral information into the asymmetric cavity of the cage by encapsulating chiral aromatic guests through efficient π-π stacking and hydrophobic interactions in aqueous media. The inclusion of a chiral guest induces a preference for one enantiomeric conformation of the cage over the other, effectively shifting the equilibrium towards a single, enantiopure host-guest complex. While the concept of chiral guest recognition by a chiral host is well-established, this work constitutes a remarkable example of guest-mediated chirality transfer leading to the formation of a single enantiopure coordination complex from achiral building blocks.

Tailoring topology and bio-interactions of triazine frameworks

The construction of covalent organic frameworks with special geometery and optical properties is of high interest, due to their unique physicochemical and biological properties. In this work, we report on a new method for the construction of triazine frameworks with defined topologies using coordination chemistry. Ball milling and wet chemical reactions between cyanuric chloride and melamine were directed in spatial arrangements and opposite optical activity. Cobalt was used as a directing agent to drive reactions into special morphologies, optical properties and biological activity. The enantiorecognition ability of triazine frameworks that was manifested in their activities against bacteria, demonstrated a new way for the construction of materials with specific interactions at biointerfaces.

Achieving Strong Circularly Polarized Luminescence through Cascade Cationic Insertion in Lead-free Hybrid Metal Halides

Generating circularly polarized luminescence (CPL) with simultaneous high photoluminescence quantum yield (PLQY) and dissymmetry factor (glum) is difficult due to usually unmatched electric transition dipole moment (μ) and magnetic transition dipole moment (m) of materials. Herein we tackle this issue by playing a "cascade cationic insertion" trick to achieve strong CPL (with PLQY of ~100 %) in lead-free metal halides with high glum values reaching -2.3×10-2 without using any chiral inducers. Achiral solvents of hydrochloric acid (HCl) and N, N-dimethylformamide (DMF) infiltrate the crystal lattice via asymmetric hydrogen bonding, distorting the perovskite structure to induce the "intrinsic" chirality. Surprisingly, additional insertion of Cs+ cation to substitute partial (CH3)2NH2 + transforms the chiral space group to achiral but the crystal maintains chiroptical activity. Further doping of Sb3+ stimulates strong photoluminescence as a result of self-trapped excitons (STEs) formation without disturbing the crystal framework. The chiral perovskites of indium-antimony chlorides embedded on LEDs chips demonstrate promising potential as CPL emitters. Our work presents rare cases of chiroptical activity of highly luminescent perovskites from only achiral building blocks via spontaneous resolution as a result of symmetry breaking.

Chiral Induction in 2D Borophene Nanoplatelets through Stereoselective Boron-Sulfur Conjugation

Chirality is a structural metric that connects biological and abiological forms of matter. Although much progress has been made in understanding the chemistry and physics of chiral inorganic nanoparticles over the past decade, almost nothing is known about chiral two-dimensional (2D) borophene nanoplatelets and their influence on complex biological networks. Borophene's polymorphic nature, derived from the bonding configurations among boron atoms, distinguishes it from other 2D materials and allows for further customization of its material properties. In this study, we describe a synthetic methodology for producing chiral 2D borophene nanoplatelets applicable to a variety of structural polymorphs. Using this methodology, we demonstrate feasibility of top-down synthesis of chiral χ3 and β12 phases of borophene nanoplatelets via interaction with chiral amino acids. The chiral nanoplatelets were physicochemically characterized extensively by various techniques. Results indicated that the thiol presenting amino acids, i.e., cysteine, coordinates with borophene in a site-selective manner, depending on its handedness through boron-sulfur conjugation. The observation has been validated by circular dichroism, X-ray photoelectron spectroscopy, and 11B NMR studies. To understand how chiral nanoplatelets interact with biological systems, mammalian cell lines were exposed to them. Results showed that the achiral as well as the left- and right-handed biomimetic χ3 and β12 borophene nanoplatelets have distinct interaction with the cellular membrane, and their internalization pathway differs with their chirality. By engineering optical, physical, and chemical properties, these chiral 2D nanomaterials could be applied successfully to tuning complex biological events and find applications in photonics, sensing, catalysis, and biomedicine.

Boosted Second Harmonic Generation of a Chiral Hybrid Lead Halide Resonant to Charge Transfer Exciton from Metal Halide Octahedra to Ligand

Chiral hybrid organic-inorganic metal halides (HOMHs) offer an ideal platform for the advancement of second-order nonlinear optical (NLO) materials owing to their inherent noncentrosymmetric structures. The enhancement of optical nonlinearity of chiral HOMHs could be achieved by matching the free exciton and/or self-trapped exciton energy levels with desired NLO frequencies. However, the current scarcity of resonance modes and low resonance ratio hamper the further improvements of NLO performance. Herein, we propose a new resonant channel of charge transfer (CT) excited states from metal halide polyhedra to organic ligand to boost the second-order optical nonlinearity of chiral HOMHs. The model lead halide (C7H10N)PbBr3 (C7H10N=1-ethylpyridinium) exhibits a drastically enhanced second harmonic generation in resonance to the deep CT exciton energy, with intensity of up to 111.0 times that of KDP and 10.9 times that of urea. The effective NLO coefficient has been determined to be as high as ~40.2 pm V-1, balanced with a large polarization ratio and high laser damage threshold. This work highlights the contribution of organic ligands in the construction of a resonant channel for enhancing second-order NLO coefficients of metal halides, and thus provides guidelines for designing new chiral HOMHs materials for advanced nonlinear photonic applications.

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.

Colloidal Chiral Carbon Dots: An Emerging System for Chiroptical Applications

Chiral CDots (c-CDots) not only inherit those merits from CDots but also exhibit chiral effects in optical, electric, and bio-properties. Therefore, c-CDots have received significant interest from a wide range of research communities including chemistry, physics, biology, and device engineers. They have already made decent progress in terms of synthesis, together with the exploration of their optical properties and applications. In this review, the chiroptical properties and chirality origin in extinction circular dichroism (ECD) and circularly polarized luminescence (CPL) of c-CDots is briefly discussed. Then, the synthetic strategies of c-CDots is summarized, including one-pot synthesis, post-functionalization of CDots with chiral ligands, and assembly of CDots into chiral architectures with soft chiral templates. Afterward, the chiral effects on the applications of c-CDots are elaborated. Research domains such as drug delivery, bio- or chemical sensing, regulation of enzyme-like catalysis, and others are covered. Finally, the perspective on the challenges associated with the synthetic strategies, understanding the origin of chirality, and potential applications is provided. This review not only discusses the latest developments of c-CDots but also helps toward a better understanding of the structure-property relationship along with their respective applications.

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.

In Situ Chiral Template Approach to Synthesize Homochiral Lead Iodides for Second-Harmonic Generation

Homochiral halide perovskites have gained increasing attention because of their fascinating optoelectronic properties and prospective applications in laser technologies. However, the limited choice of chiral organic templates severely restricts their structural diversity and second-harmonic generation (SHG) effects. Here, we present an in situ chiral template approach for the synthesis of one-dimensional (1D) homochiral lead iodides. A chiral imine (L-ipp) template was generated in situ by reacting L-proline (L-pro) and acetone under ambient conditions. Notably, L-ipp can cooperate with L-pro to direct the formation of a homochiral lead iodide with dual chiral templates, which is unprecedented in crystalline metal halides. The homochiral lead iodide containing both L-ipp and L-pro shows a strong SHG response of 8.0 times that of KH2 PO4 (8.0×KDP). The SHG efficiency is one of the largest values reported to date for any homochiral lead halides under 1064 nm laser irradiation. A comparative study shows that homochiral 1D lead iodides containing either L-ipp or L-pro exhibit relatively weak SHG responses (≤1.0×KDP). This work demonstrates the advantage of using two different chiral templates over a single chiral template in enhancing the SHG responses of halide materials.

Chiral and Polar Duality Design of Heteroanionic Compounds: Sr18 Ge9 O5 S31 Based on [Sr3 OGeS3 ]2+ and [Sr3 SGeS3 ]2+ Groups

Chirality and polarity are the two most important and representative symmetry-dependent properties. For polar structures, all the twofold axes perpendicular to the principal axis of symmetry should be removed. For chiral structures, all the mirror-related symmetries and inversion axes should be removed. Especially for duality (polarity and chirality), all of the above symmetries should be broken and that also represents the highest-level challenge. Herein, a new symmetry-breaking strategy that employs heteroanionic groups to construct hourglass-like [Sr3 OGeS3 ]2+ and [Sr3 SGeS3 ]2+ groups to design and synthesize a new oxychalcogenide Sr18 Ge9 O5 S31 with chiral-polar duality is proposed. The presence of two enantiomers of Sr18 Ge9 O5 S31 is confirmed by the single-crystal X-ray diffraction. Its optical activity and ferroelectricity are also studied by solid-state circular dichroism spectroscopy and piezoresponse force microscopy, respectively. Further property measurements show that Sr18 Ge9 O5 S31 possesses excellent nonlinear optical properties, including the strong second harmonic generation efficiency (≈2.5 × AGS), large bandgap (3.61 eV), and wide mid-infrared transparent region (≈15.3 µm). These indicate that the unique microstructure groups of heteroanionic materials are conducive to realizing symmetry-breaking and are able to provide some inspiration for exploring the chiral-polar duality materials.

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.

Oxidation-Induced Dissolution Recrystallization Structural Transformation Strategy Enhanced Nonlinear Optical Effect of Hybrid Chiral Tin Bromide Single Crystals

In order to reveal the integrated effect of inorganic lattice structure disturbances and chiral ligands on the structure of tin halide hybrid materials, we show the synthesis, crystal growth, dissolution recrystallization structural transformation (DRST), optical properties, energy band structure, and nonlinear optical properties of a class of chiral tin bromide R/S-2-mpip[SnBr3]Br (2-mpip is 2-methylpiperazinium) and R/S-2-mpipSnBr6 for the first time. The formation of R/S-2-mpipSnBr6 in solution was interestingly caused by irreversible DRST of R/S-2-mpip[SnBr3]Br. The second-harmonic generation response of the new phase R-2-mpipSnBr6 is significantly enhanced compared to that of the initial phase R-2-mpip[SnBr3]Br. These structural transformations of chiral tin bromides reflect, to some extent, the DRST commonality of the tin halide family induced by oxidation and serve as a starting point for investigating the structural chirality and asymmetry of chiral metal hybrid halides.

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.

Second-Harmonic Generation in Homochiral Antimony Halides Directed by l-Histidine

Three homochiral organic-inorganic hybrid antimony halides, namely, (L-Hhis)2Sb2Cl8 (1), L-H2his·SbBr5·H2O (2), and (L-H2his)2·Sb3I13·4H2O (3), were prepared to investigate the structure-directing roles of l-histidine (l-his). These compounds feature dimeric, chainlike, and trimeric structures with different optical bandgaps. They display second-harmonic-generation (SHG) responses of 0.1, 2.6, and 0.05 times that of KH2PO4, respectively. Theoretical calculations for compound 2 were carried out to get insights into its structure-property relationship.

Multiple Stimuli-Responsive Luminescent Chiral Hybrid Antimony Chlorides for Anti-Counterfeiting and Encryption Applications

Stimuli-responsive circularly polarized luminescence (CPL) materials are ideal for information anti-countering applications, but the best-performing materials have not yet been identified. This work presents enantiomorphic hybrid antimony halides R-(C5 H12 NO)2 SbCl5 (1) and S-(C5 H12 NO)2 SbCl5 (2) showing mirror-imaged CPL activity with a dissymmetry factor of 1.2×10-3 . Interestingly, the DMF-induced structural transformation is realized to obtain non-emissive R-(C5 H12 NO)2 SbCl5  ⋅ DMF (3) and S-(C5 H12 NO)2 SbCl5  ⋅ DMF (4) upon exposure to DMF vapor. The transformation process is reversed upon heating. DFT calculations showed that the DMF-induced-quenched-luminescence is attributed to the intersection of the ground and excited state curves on the configuration coordinates. Unexpectedly, the nanocrystals of the chiral antimony halides 1 and 2 were prepared and indicate the excellent solution process performance. The reversible PL and CPL switching gives the system applications in information technology, anti-counterfeiting, encryption-decryption, and logic gates.

Linear optical afterglow and nonlinear optical harmonic generation from chiral tin(IV) halides: the role of lattice distortions

The striking chemical variability of hybrid organic-inorganic metal halides (HOMHs) endows them with fascinating optoelectronic properties. The inorganic skeletons of HOMHs are often flexible and their lattice deformations could serve as an effective factor for enabling the functionalities of HOMHs. Here, the linear and nonlinear optical properties of zero-dimensional (0D) tin(IV) halides have been tuned by structural distortion facilitated by the chiral amines. Enantiopure α-methylbenzyl ammoniums (XMBA, X = Cl, F) effectively transfer their chirality to the inorganic scaffolds when forming the tin(IV) halides, which enables polar arrangements in their crystals and leads to outstanding second-order nonlinear optical performances. In contrast, the racemic mixture of R- and S-FMBA results in the formation of HOMHs with room temperature phosphorescence. The lower lattice deformation in (rac-FMBA)₂SnCl₆ restrains the non-radiative decay from electron-phonon coupling and facilitates the photoluminescence. Meanwhile, the marked π-π interaction stabilizes the T₁ state for phosphorescent emission. These distinct linear and nonlinear optical properties denote the important role that the lattice distortion plays in tuning the optical properties of low-dimensional HOMHs, and offer a promising perspective of 0D tin(IV) halides for applications in optoelectronic materials and devices.

Cobalt-Induced Phase Transformation of Ni3Ga4 Generates Chiral Intermetallic Co3Ni3Ga8

The scientific community has found immense difficulty to focus on the generation of chiral intermetallics compared to the chiral molecular structure, probably due to the technical difficulty in producing them as no general controlled protocol is available. Herein, using a conventional metal flux technique, we have discovered a new ternary intermetallic Co₃Ni₃Ga₈, substituting Co at the Ni sublattice in a highly symmetric Ni₃Ga₄ (Ia3̅d). Co₃Ni₃Ga₈ crystallizes in the I4₁32 space group, a Sohncke type, and can host the chiral structure. To the best of our knowledge, this is the first report of a ternary intermetallic crystallizing in this space group. The chiral structure of Co₃Ni₃Ga₈ is comprehensively mapped by various techniques such as single-crystal X-ray diffraction (XRD), synchrotron powder XRD, X-ray absorption spectroscopy (XAS), scanning transmission electron microscopy (STEM) and theoretically studied using density functional theory. The discovery of this chiral compound can inspire the researchers to design hidden ternary chiral intermetallics to study the exotic electrical and magnetic properties.

Biomimetic Self-Assembled Chiral Inorganic Nanomaterials: A New Strategy for Solving Medical Problems

The rapid expansion of the study of chiral inorganic structures has led to the extension of the functional boundaries of inorganic materials. Nature-inspired self-assembled chiral inorganic structures exhibit diverse morphologies due to their high assembly efficiency and controlled assembly process, and they exhibit superior inherent properties such as mechanical properties, chiral optical activity, and chiral fluorescence. Although chiral self-assembled inorganic structures are becoming more mature in chiral catalysis and chiral optical regulation, biomedical research is still in its infancy. In this paper, various forms of chiral self-assembled inorganic structures are summarized, which provides a structural starting point for various applications of chiral self-assembly inorganic structures in biomedical fields. Based on the few existing research statuses and mechanism discussions on the chiral self-assembled materials-mediated regulation of cell behavior, molecular probes, and tumor therapy, this paper provides guidance for future chiral self-assembled structures to solve the same or similar medical problems. In the field of chiral photonics, chiral self-assembled structures exhibit a chirality-induced selection effect, while selectivity is exhibited by chiral isomers in the medical field. It is worth considering whether there is some correspondence or juxtaposition between these phenomena. Future chiral self-assembled structures in medicine will focus on the precise treatment of tumors, induction of soft and hard tissue regeneration, explanation of the biochemical mechanisms and processes of its medical effects, and improvement of related theories.