Direct Detection of Circularly Polarized Light Using Chiral Copper Chloride-Carbon Nanotube Heterostructures

Unraveling the Role of Structural Topology on Chirality Transfer and Chiroptical Properties in Chiral Germanium Iodides

Chiral hybrid organic-inorganic metal halides are highly promising chiroptoelectronic materials with potential applications in several fields, such as circularly polarized photodetectors, second-order nonlinear optics, and spin-selective devices. However, the ability of manipulating the chiroptical response and the chirality transfer from the organic ligands require one to shed light on structure-property correlations. Herein, we devised and prepared two novel Ge-based chiral hybrid organic-inorganic metal halides showing a different structural topology, namely, a 1D and a 2D arrangement, but composed of the same chemical building blocks: (R/S-ClMBA)3GeI5 and (R/S-ClMBA)2GeI4. Through a combined experimental and computational investigation on these samples, we discuss the impact of structural dimensionality on chiroptical properties, chirality transfer, and spin-splitting effects; also, we highlight the impact of structural distortions. The approach presented here paves the way for a solid understanding of the factors affecting the properties of chiral metal halides, thus allowing a future wise materials engineering.

Giant chiral amplification of chiral 2D perovskites via dynamic crystal reconstruction

Chiral hybrid perovskites show promise for advanced spin-resolved optoelectronics due to their excellent polarization-sensitive properties. However, chiral perovskites developed to date rely solely on the interaction between chiral organic ligand cations exhibiting point chirality and an inorganic framework, leading to a poorly ordered short-range chiral system. Here, we report a powerful method to overcome this limitation using dynamic long-range organization of chiral perovskites guided by the incorporation of chiral dopants, which induces strong interactions between chiral dopants and chiral cations. The additional interplay of chiral cations with chiral dopants reorganizes the morphological and crystallographic properties of chiral perovskites, notably enhancing the asymmetric behavior of chiral 2D perovskites by more than 10-fold, along with the highest dissymmetry factor of photocurrent (gPh) of ~1.16 reported to date. Our findings present a pioneering approach to efficiently amplify the chiroptical response in chiral perovskites, opening avenues for exploring their potential in cutting-edge optoelectronic applications.

Strain-Amplified Exciton Chirality in Organic-Inorganic Hybrid Materials

Chiral organic-inorganic hybrids combining chirality of organic molecules and semiconducting properties of inorganic frameworks generate chiral excitons without external spin injection, creating the potential for chiroptoelectronics. However, the relationship between molecular chirality and exciton chirality is still unclear. Here we show the strain-amplified exciton chirality in one-dimensional chiral metal halides. Utilizing chirality-induced spin-orbital coupling theory, we quantitatively demonstrate the impact of the strain-engineered molecular assembly of chiral cations on exciton chirality, offering a feasible way to amplify exciton chirality by molecular manipulation.

Influence of Material Properties on Surface Chemistry Induced Circular Dichroism in Halide Perovskite: Computational Insights

The chirality transfer phenomenon is attractive for enhancing the optical functionality of nanomaterials by inducing sensitivity to the circular polarization states of photons. An underexplored aspect is how material properties of the achiral semiconductor impact the induced chiroptical signatures. Here we apply atomistic time-dependent density functional theory simulations to investigate the material properties that influence the chiroptical signatures of a lead halide perovskite nanocrystal with a chiral molecule bound to the surface. First, we find that both lattice disorder created by surface strain and halide substitution can increase the chiroptical response of the perovskite quantum dots by an order of magnitude. Both phenomena are attributed to a broadening of the density of the electronically excited states. Second, the intensity of the anisotropy spectra decreases with increasing dot size with a power law decay. Overall, these insights can be used to help guide experimental realization of highly resolvable polarized optical features in semiconducting nanomaterials.

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

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

Introducing Chiro-optical Activities in Photonic Synapses for Neuromorphic Computing and In-Memory Logic Operations

In artificial synaptic devices aimed at mimicking neuromorphic computing systems, electrical or optical pulses, or both, are generally used as stimuli. In this work, we introduce chiral materials for tailoring the characteristics of photonic synaptic devices to achieve handedness-dependent neuromorphic computing and in-memory logic gates. In devices based on a pair of chiral perovskites, the use of circularly polarized light (CPL) as the optical stimuli mimicked a series of electrical and opto-synaptic functionalities in order to emulate the multifunctional complex behavior of the human brain. Upon illumination in this two-terminal device, anisotropy in current has been observed due to the out-of-plane carrier transport, originating from spin-selective carrier transport. More importantly, the logic gate achieved in devices based on optoelectronic memristors turned out to be chirality-dependent; while an R-device functioned as an AND gate, the device based on the same perovskite of the opposite chirality (S-device) acted as a NOR gate toward in-memory logic operations. These findings in chiral perovskite-based artificial synapses can identify further strategies for future neuromorphic computing, vision simulation, and artificial intelligence.

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.

Chiral Materials for Optics and Electronics: Ready to Rise?

Chiral materials have gained burgeoning interest in optics and electronics, beyond their classical application field of drug synthesis. In this review, we summarize the diverse chiral materials developed to date and how they have been effectively applied to optics and electronics to get an understanding and vision for the further development of chiral materials for advanced optics and electronics.

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.

Ligand-Induced Chirality in ClMBA2 SnI4 2D Perovskite

Chiral perovskites possess a huge applicative potential in several areas of optoelectronics and spintronics. The development of novel lead-free perovskites with tunable properties is a key topic of current research. Herein, we report a novel lead-free chiral perovskite, namely (R/S-)ClMBA2 SnI4 (ClMBA=1-(4-chlorophenyl)ethanamine) and the corresponding racemic system. ClMBA2 SnI4 samples exhibit a low band gap (2.12 eV) together with broad emission extending in the red region of the spectrum (∼1.7 eV). Chirality transfer from the organic ligand induces chiroptical activity in the 465-530 nm range. Density functional theory calculations show a Rashba type band splitting for the chiral samples and no band splitting for the racemic isomer. Self-trapped exciton formation is at the origin of the large Stokes shift in the emission. Careful correlation with analogous lead and lead-free 2D chiral perovskites confirms the role of the symmetry-breaking distortions in the inorganic layers associated with the ligands as the source of the observed chiroptical properties providing also preliminary structure-property correlation in 2D chiral perovskites.

Chiral Induced Spin Selectivity

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

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.

Circular polarization-resolved ultraviolet photonic artificial synapse based on chiral perovskite

Circularly polarized light (CPL) adds a unique dimension to optical information processing and communication. Integrating CPL sensitivity with light learning and memory in a photonic artificial synapse (PAS) device holds significant value for advanced neuromorphic vision systems. However, the development of such systems has been impeded by the scarcity of suitable CPL active optoelectronic materials. In this work, we employ a helical chiral perovskite hybrid combined with single-wall carbon nanotubes to achieve circularly polarized ultraviolet neuromorphic vision sensing and imaging. The heterostructure demonstrates long-term charge storage as evidenced by multiple-pulsed transient absorption measurements and highly sensitive circular polarization-dependent photodetection, thereby enabling efficient CPL-resolved synaptic and neuromorphic behaviors. Significantly, our PAS sensor arrays adeptly visualize, discriminate, and memorize distinct circularly polarized images with up to 93% recognition accuracy in spiking neural network simulations. These findings underscore the pivotal role of chiral perovskites in advancing PAS technology and circular polarization-enhanced ultraviolet neuromorphic vision systems.

Enhanced Circular Dichroism and Polarized Emission in an Achiral, Low Band Gap Bismuth Iodide Perovskite Derivative

Lead halide perovskites and related main-group halogenido metalates offer unique semiconductor properties and diverse applications in photovoltaics, solid-state lighting, and photocatalysis. Recent advances in incorporating chiral organic cations have led to the emergence of chiral metal-halide semiconductors with intriguing properties, such as chiroptical activity and chirality-induced spin selectivity, enabling the generation and detection of circularly polarized light and spin-polarized electrons for applications in spintronics and quantum information. However, understanding the structural origin of chiroptical activity remains challenging due to macroscopic factors and experimental limitations. In this work, we present an achiral perovskite derivative [Cu2(pyz)3(MeCN)2][Bi3I11] (CuBiI; pyz = pyrazine; MeCN = acetonitrile), which exhibits remarkable circular dichroism (CD) attributed to the material's noncentrosymmetric nature. CuBiI features a unique structure as a poly-threaded iodido bismuthate, with [Bi3I11]2- chains threaded through a cationic two-dimensional coordination polymer. The material possesses a low, direct optical band gap of 1.70 eV. Notably, single crystals display both linear and circular optical activity with a large anisotropy factor of up to 0.16. Surprisingly, despite the absence of chiral building blocks, CuBiI exhibits a significant degree of circularly polarized photoluminescence, reaching 4.9%. This value is comparable to the results achieved by incorporating chiral organic molecules into perovskites, typically ranging from 3-10% at zero magnetic field. Our findings provide insights into the macroscopic origin of CD and offer design guidelines for the development of materials with high chiroptical activity.

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.

Optical Memory, Switching, and Neuromorphic Functionality in Metal Halide Perovskite Materials and Devices

Metal halide perovskite based materials have emerged over the past few decades as remarkable solution-processable optoelectronic materials with many intriguing properties and potential applications. These emerging materials have recently been considered for their promise in low-energy memory and information processing applications. In particular, their large optical cross-sections, high photoconductance contrast, large carrier-diffusion lengths, and mixed electronic/ionic transport mechanisms are attractive for enabling memory elements and neuromorphic devices that are written and/or read in the optical domain. Here, recent progress toward memory and neuromorphic functionality in metal halide perovskite materials and devices where photons are used as a critical degree of freedom for switching, memory, and neuromorphic functionality is reviewed.

Ligand-Assisted Self-Assembly of 3D Perovskite Nanocrystals into Chiral Inorganic Quasi-2D Perovskites (n = 3) with Ligand-Ratio-Dependent Chirality Inversion

Chiral inorganic quasi-2D perovskites are prepared by self-assembling 3D perovskites in solution for the first time. The quasi-2D perovskite synthesized is a pure-phase perovskite with = 3 and is periodically arranged, which is a big breakthrough in quasi-2D inorganic perovskites.  With the individual chiral CsPbBr3 nanocrystals (NCs) assemble into quasi-2D perovskite, the g-factor significantly improved (≈5 × 10-3 ). In addition, the chiroptical activity of quasi-2D perovskites is explored to be improved with the lateral size increasing. In the first stage of assembly, chiral optical activity is increased due to the lateral size-dependent optical activity, while the changes in the later stages are attributable to the chiral morphology. Interestingly, chirality inversion is found to be correlated to the number of ligands. It is believed that different conformers of chiral ligands caused by steric hindrance of the original ligand oleylamine result in opposite circular dichroism (CD) polarities. The chirality inversion phenomenon is universal, regardless of the choice of ligands. This work opens up a new path for the synthesis of quasi-2D perovskites and provides more opportunities for the modulation of chiral optical activity.

An Organic Chiroptical Detector Favoring Circularly Polarized Light Detection from Near-Infrared to Ultraviolet and Magnetic-Field-Amplifying Dissymmetry in Detectivity

Circularly polarized light detection has attracted growing attention because of its unique application in security surveillance and quantum optics. Here, through designing a chiral polymer as a donor, a high-performance circularly polarized light detector is fabricated, successfully enabling detection from ultraviolet (300 nm) to near-infrared (1100 nm). The chiroptical detector presents an excellent ability to distinguish right-handed and left-handed circularly polarized light, where dissymmetries in detectivity, responsivity, and electric current are obtained and then optimized. The dissymmetry in electric current can be increased from 0.18 to 0.23 once an external magnetic field is applied. This is a very rare report on the dissymmetry tunability by an external field in chiroptical detectors. Moreover, the chirality-generated orbital angular momentum is one of the key factors determining the performance of the circularly polarized light detection. Overall, the organic chiroptical detector presents excellent stability in detection, which provides great potential for future flexible and compact integrated platforms.

Unraveling chirality transfer mechanism by structural isomer-derived hydrogen bonding interaction in 2D chiral perovskite

In principle, the induced chirality of hybrid perovskites results from symmetry-breaking within inorganic frameworks. However, the detailed mechanism behind the chirality transfer remains unknown due to the lack of systematic studies. Here, using the structural isomer with different functional group location, we deduce the effect of hydrogen-bonding interaction between two building blocks on the degree of chirality transfer in inorganic frameworks. The effect of asymmetric hydrogen-bonding interaction on chirality transfer was clearly demonstrated by thorough experimental analysis. Systematic studies of crystallography parameters confirm that the different asymmetric hydrogen-bonding interactions derived from different functional group location play a key role in chirality transfer phenomena and the resulting spin-related properties of chiral perovskites. The methodology to control the asymmetry of hydrogen-bonding interaction through the small structural difference of structure isomer cation can provide rational design paradigm for unprecedented spin-related properties of chiral perovskite.

Helical polymers for dissymmetric circularly polarized light imaging

Control of the spin angular momentum (SAM) carried in a photon provides a technologically attractive element for next-generation quantum networks and spintronics1-5. However, the weak optical activity and inhomogeneity of thin films from chiral molecular crystals result in high noise and uncertainty in SAM detection. Brittleness of thin molecular crystals represents a further problem for device integration and practical realization of chiroptical quantum devices6-10. Despite considerable successes with highly dissymmetric optical materials based on chiral nanostructures11-13, the problem of integration of nanochiral materials with optical device platforms remains acute14-16. Here we report a simple yet powerful method to fabricate chiroptical flexible layers via supramolecular helical ordering of conjugated polymer chains. Their multiscale chirality and optical activity can be varied across the broad spectral range by chiral templating with volatile enantiomers. After template removal, chromophores remain stacked in one-dimensional helical nanofibrils producing a homogeneous chiroptical layer with drastically enhanced polarization-dependent absorbance, leading to well-resolved detection and visualization of SAM. This study provides a direct path to scalable realization of on-chip detection of the spin degree of freedom of photons necessary for encoded quantum information processing and high-resolution polarization imaging.

Zero-Dimensional Hybrid Cuprous Halide of [BAPMA]Cu2Br5 as a Highly Efficient Light Emitter and an X-Ray Scintillator

Lead halide perovskites have been explored as a new kind of promising X-ray with wide applications in radiation-associated fields, but low light yield and serious toxicity extremely restrict further applications. To address these issues, we herein demonstrated one new zero-dimensional (0D) organic-inorganic hybrid cuprous halide of [BAPMA]Cu₂Br₅ (BAPMA = N,N-Bis(3-aminopropyl) methylamine) containing discrete [Cu₄Br₁₀]^6- tetramers as excellent lead-free scintillators. Upon UV light excitation, [BAPMA]Cu₂Br₅ displays highly efficient broadband yellowish-green light emission with one dominant peak at 526 nm, a large Stokes shift of 244 nm, and a high photoluminescent quantum yield of 53.40%. Significantly, this broadband light emission can also be excited by higher-energy X-ray as radioluminescence with a high scintillation light yield of 43,744 photons/MeV. The detection limit of 0.074 μGy_air/s is also far less than the required value for regular medical diagnostics of 5.5 μGy_air/s. The solution-assembled hybrid structure facilely enables the [BAPMA]Cu₂Br₅-based scintillation screen to display high-performance X-ray imaging with a spatial resolution of 15.79 lp/mm showcasing potential application in X-ray radiography. In brief, combined merits of low toxicity and cost, negligible self-absorption, a low detection limit, considerable light yield, and spatial resolution highlight the excellent scintillation performance of 0D hybrid cuprous halide.

Toward Efficient Two-Photon Circularly Polarized Light Detection through Cooperative Strategies in Chiral Quasi-2D Perovskites

Organic-inorganic hybrid perovskites carry unique semiconducting properties and advanced flexible crystal structures. These characteristics of organic-inorganic hybrid perovskites create a promising candidacy for circularly polarized light (CPL) detection. However, CPL detections based on chiral perovskites are limited to UV and visible wavelengths. The natural quantum well structures of layered hybrid perovskites generate strong light-matter interactions. This makes it possible to achieve near-infrared (NIR) CPL detection via two-photon absorption in the sub-wavelength region. In this study, cooperative strategies of dimension increase and mixed spacer cations are used to obtain a pair of chiral multilayered perovskites (R-β-MPA)EA₂ Pb₂ Br₇ and (S-β-MPA)EA₂ Pb₂ Br₇ (MPA = methylphenethylammonium and EA = ethylammonium). The distinctive bi-cations interlayer and multilayered inorganic skeletons provide enhanced photoconduction. Moreover, superior photoconduction leads to the prominent NIR CPL response with a responsivity up to 8.1 × 10^-5 A W^-1 . It is anticipated that this work can serve as a benchmark for the fabrication and optimization of efficient NIR CPL detection by simple chemical design.

Strain-Driven Solid-Solid Crystal Conversion in Chiral Hybrid Pseudo-Perovskites with Paramagnetic-to-Ferromagnetic Transition

Hybrid organic-inorganic perovskites (HOIPs) are promising stimuli-responsive materials (SPMs) owing to their molecular softness and tailorable structural dimensionality. The design of mechanically responsive HOIPs requires an in-depth understanding of how lattice strain induces intermolecular rearrangement that impacts physical properties. While chirality transfer from an organic cation to an inorganic lattice is known to influence chiral-optical properties, its effect on strain-induced phase conversion has not been explored. As opposed to achiral or racemic organic cations, chiral organic cations can potentially afford a new dimension in strain-responsive structural change. Herein, we demonstrate that mechanical strain induces a solid phase crystal conversion in chiral halide pseudo-perovskite single crystals (R/S)-(FE)₂CuCl₄ (FE = (4-Fluorophenyl)ethylamine) from a 0D isolated CuCl₄ tetrahedral to 1D corner-sharing CuFCl₅ octahedral framework via the incorporation of Cu···F interaction and N-H···F hydrogen bonding. This strain-induced crystal-to-crystal conversion involves the connection of neighboring 0D CuCl₄ tetrahedra via Cu²⁺-Cl^--Cu²⁺ linkages as well as the incorporation of a F-terminated organic cation as one of the X atoms in BX₆ octahedra, leading to a reduced band gap and paramagnetic-to-ferromagnetic conversion. Control experiments using nonchiral or racemic perovskite analogs show the absence of such solid phase conversion. To demonstrate pressure-sensitive properties, the 0D phase is dispersed in water-soluble poly(vinyl alcohol) (PVA) polymer, which can be applied to a large-scale pressure-induced array display on fibrous Spandex substrates via a screen-printing method.

Metal Halide Perovskite Heterostructures: Blocking Anion Diffusion with Single-Layer Graphene

The development of metal halide perovskite/perovskite heterostructures is hindered by rapid interfacial halide diffusion leading to mixed alloys rather than sharp interfaces. To circumvent this outcome, we developed an ion-blocking layer consisting of single-layer graphene (SLG) deposited between the metal halide perovskite layers and demonstrated that it effectively blocks anion diffusion in a CsPbBr₃/SLG/CsPbI₃ heterostructure. Spatially resolved elemental analysis and spectroscopic measurements demonstrate the halides do not diffuse across the interface, whereas control samples without the SLG show rapid homogenization of the halides and loss of the sharp interface. Ultraviolet photoelectron spectroscopy, DFT calculations, and transient absorbance spectroscopy indicate the SLG has little electronic impact on the individual semiconductors. In the CsPbBr₃/SLG/CsPbI₃, we find a type I band alignment that supports transfer of photogenerated carriers across the heterointerface. Light-emitting diodes (LEDs) show electroluminescence from both the CsPbBr₃ and CsPbI₃ layers with no evidence of ion diffusion during operation. Our approach provides opportunities to design novel all-perovskite heterostructures to facilitate the control of charge and light in optoelectronic applications.

Charge-Transfer Complex Doped Photothermal Hydrogels for Discriminating Circularly Polarized Near-Infrared Light

Hydrogels behave as potential candidates to investigate circularly polarized light (CP)-matter interaction, which however suffer from small sensitivity towards circular polarization. Here we report a general protocol to build hydrogels from π-conjugated amino acids with coassembled charge-transfer (CT) complexes, covering a wide scope of donors and acceptors, which were incorporated into stable hydrogel matrices. CT complexes formed block coassemblies with gelators, induced the emergence of macroscopic chiral helices, where efficient chirality transfer occurs to realize tunable Cotton effects from visible light to NIR-I region depending on the structures of CT pairs. The hybrid hydrogels showed tunable photothermal performances with excellent heating-cooling cycling durability. Circularly polarized NIR light selectively triggered gel-solution phase transition at different timescales. Left- and right-CP illumination generates up to 2.5 folds difference in gel collapse time that allows for direct discrimination by naked eyes.

Spin-Selective Charge Transport in Lead-Free Chiral Perovskites: The Key towards High-Anisotropy in Circularly-Polarized Light Detection

A pair of zero-dimensional lead-free chiral perovskites is introduced towards the detection of circularly polarized light (CPL). Although spin-polarized carriers are generated in the perovskites under the CPL, the absorption anisotropy remained low leading to mostly similar density of photogenerated carriers under the two CPLs. Interestingly, due to the intrinsic chirality in the perovskites, they exhibited chirality-induced spin-selectivity (CISS) allowing the transport of only one type of spin-half states. A high anisotropy in photocurrent along the out-of-plane direction has therefore appeared resulting in a spin-dependent photovoltaic effect in vertical heterojunction devices and making them suitable for CPL detection. While a self-powered CPL detector showed a limited (but one of the highest to date) anisotropy factor of 0.3 due to possible spin-flips during the transport process, the factor rose to 0.6 under bias prompting extension of the effective spin-diffusion length.

Revealing the Intrinsic Chiroptical Activity in Chiral Metal-Halide Semiconductors

The combination of chirality and semiconducting properties has enabled chiral metal-halide semiconductors (MHS) to be promising candidates for spin- and polarization-resolved optoelectronic devices. Although several chiral MHS with rich chemical and structural diversity have been reported lately, the macroscopic origin of chiroptical activity remains elusive. Here, combining spectroscopic measurements and Mueller matrix analysis, we discover that the previously reported "apparent" anisotropy factor measured from circular dichroism (CD) in chiral MHS thin films is not an intrinsic chiroptical property, but rather, arising from an interference between the film's linear birefringence (LB) and linear dichroism (LD). We verify the presence of LB and LD effects in both one-dimensional and zero-dimensional chiral MHS thin films. We establish spectroscopic methods to decouple the genuine CD from other spurious contributions, which allows a quantitative comparison of the intrinsic chiroptical activity across different chiral MHS. The relationship between the structure and the genuine chiroptical activity is then uncovered, which is well described by the chirality-induced spin-orbit coupling in the chiral structures. Our study unveils the macroscopic origin of chiroptical activity of chiral MHS and provides design principles for obtaining high anisotropic factors for future chiral optoelectronic applications.

Spin Selectivity in Chiral Hybrid Cobalt Halide Films with Ultrasmooth Surface

Introducing chirality into low-dimensional hybrid organic-inorganic halides (HOIHs) creates brand-new opportunities for HOIHs in spintronics and spin-related optoelectronics owing to chirality-induced spin selectivity (CISS). However, preparing smooth films of low-dimensional HOIHs with small roughness is still a great challenge due to the hybrid and complex crystal structure, which severely inhibits their applications in spintronic devices. Exploring new lead-free chiral HOIHs with both efficient spin selectivity and excellent film quality is urgently desired. Here, cobalt-based chiral metal halide crystals (R/S-NEA)₂ CoCl₄ constructed by 0D [CoCl₄ ] tetrahedrons and 1-(1-naphtyl)ethylamine (NEA) are synthesized. The orderly configuration of NEA molecules stabilized by noncovalent CH···π interaction endows (NEA)₂ CoCl₄ with good film-forming ability. (NEA)₂ CoCl₄ films exhibit strong chiroptical activity (g_CD  ≈ 0.05) and significant spin-polarized transport (CISS efficiency up to 90%). Furthermore, ultrasmooth films (roughness ∼ 0.3 nm) with enhanced crystallinity can be achieved by incorporating tiny amount tris(8-oxoquinoline)aluminum that has analogous conjugated structure to NEA. The realization of highly efficient spin selectivity and sub-nanometer roughness in lead-free chiral halides can boost the practical process of low-dimensional HOIHs in spintronics and other fields.

Direct Detection of Near-Infrared Circularly Polarized Light via Precisely Designed Chiral Perovskite Heterostructures

Chiral metal halide perovskites (CMHPs) have recently shown great potential for direct circularly polarized light (CPL) detection. However, owing to the limited cutoff wavelength edge of these CMHPs, most of the detectors presented thus far are characterized only in the ultraviolet and visible range; CMHPs that target at the near-infrared (NIR) region are still greatly desired. Here, we design a novel CMHP heterostructure, synthesized via solution-processed epitaxial growth of crystalline 3D MAPbI₃ on a 2D chiral (R-BPEA)₂PbI₄ (R-BPEA = (R)-1-(4-bromophenyl)ethylammonium) crystal, and provide the first demonstration of self-powered direct NIR-CPL detection. Compared with individual chiral (R-BPEA)₂PbI₄, the heterostructure not only retains the spin selectivity but also allows much broader absorbance, especially beyond 780 nm, where the (R-BPEA)₂PbI₄ cannot absorb. Furthermore, the built-in electric potential in the heterojunction forces spontaneous separation/transport of photogenerated carriers, enabling the fabrication of devices operating without external energy supply. By making use of the abovementioned advantages, the self-powered CPL detectors of the (R-BPEA)₂PbI₄/MAPbI₃ heterostructures hence show competitive circular polarization sensitivity at 785 nm with a high anisotropy factor of up to 0.25. In addition, a large on/off switching ratio of ∼10⁵ and an impressive detectivity of ∼10¹⁰ Jones are also achieved. As a pioneer study, our results may broaden the material scope for future chiroptical devices based on CMHPs.

Best practices in the measurement of circularly polarised photodetectors

Circularly polarised light will revolutionise emerging technologies, including encrypted light-based communications, quantum computing, bioimaging and multi-channel data processing. In order to make use of these remarkable opportunities, high performance photodetectors that can accurately differentiate between left- and right-handed circularly polarised light are desperately needed. Whilst this potential has resulted in considerable research interest in chiral materials and circularly polarised photodetecting devices, their translation into real-world technologies is limited by non-standardised reporting and testing protocols. This mini-review provides an accessible introduction into the working principles of circularly polarised photodetectors and a comprehensive overview of the performance metrics of state-of-the-art devices. We propose a rigorous device characterisation procedure that will allow for standardised evaluation of novel devices, which we hope will accelerate research and investment in this area.

Enantiomorphic Single Crystals of Linear Lead(II) Bromide Perovskitoids with White Circularly Polarized Emission

Chiroptical hybrid organic-inorganic perovskites are emerging as a new class of promising materials with mirror optical signal responses for optoelectronic applications. However, chiroptical white-emission materials have been scarcely unearthed. Herein, four pairs of hybrid lead(II) bromide perovskitoids were obtained, namely, (R)- and (S)-(H₂ MPz)PbBr₄ (R/S-MPz=(R)-(-)/(S)-(+)-2-methylpiperazine) (1 and 2), (R)- and (S)-(H₂ MPz)₃ Pb₂ Br₁₀ ⋅2 DMAc (3 and 4), (R)- and (S)-(H₂ MPz)PbBr₄ ⋅0.5 MeCN (5 and 6) and (R)- and (S)-(H₂ MPz)₂ Pb₂ Br₈ ⋅DCM (7 and 8). Notably, they all exhibit ultrabroadband emission and chiroptical signals. Perovskitoids 3-6 even achieve white circularly polarized emission with a high dissymmetric factor (g_lum ) (±3×10^-3 for 3 and 4; ±8×10^-3 for 5 and 6). This new type of hybrid perovskitoids will attract attention and find applications in chiroptical fields because of the extensively and easily tunable photophysical properties.

Incident Angle Dependence of the Waveform of the Polarization-Sensitive Photoresponse in CuSe/Se Thin Film

The results of studying the waveforms of longitudinal and transverse photocurrent pulses generated in thin, semitransparent CuSe/Se films as a function of the angle of incidence (α) of a femtosecond laser beam at linear and circular polarizations are presented. It has been established that the durations of unipolar longitudinal photocurrent pulses at linear and circular polarizations of laser pumping do not depend on the angle α. It is shown that the evolution of the temporal profile of the helicity-sensitive transverse photocurrent with a change in α strongly depends on polarization. At linear polarization, the shape of the unipolar pulses remains virtually constant; however, at circular polarization, the generation of unipolar and bipolar pulses is possible, with the waveforms strongly depending on the angle α. The influence of the incidence angle on the waveforms of transverse photocurrent pulses is explained by the transformation of linear and circular polarization into an elliptical upon the refraction of light at the air/semitransparent film interface and by the interplay of photocurrents arising due to linear and circular surface photogalvanic effects in the film. The presented findings can be utilized to develop polarization and incidence angle-sensitive photovoltaic devices.

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

The relationship between the structural asymmetry and optoelectronic properties of functional materials is an active area of research. The movement of charges through an oriented chiral medium depends on the spin configuration of the charges, and such systems can be used to control spin populations without magnetic components - termed the chiral-induced spin selectivity (CISS) effect. CISS has mainly been studied in chiral organic molecules and their assemblies. Semiconductors are non-magnetic extended systems that allow for the control of charge transport, as well as the absorption and emission of light. Therefore, introducing chirality into semiconductors would enable control over charge, spin and light without magnetic components. Chiral metal halide semiconductors (MHSs) are hybrid organic-inorganic materials that combine the properties of small chiral organic molecules with those of extended inorganic semiconductors. Reports of CISS in chiral MHSs have resulted in breakthroughs in our understanding of CISS and in the realization of spin-dependent optoelectronic properties. This Review examines the fundamentals and applications of CISS in chiral MHSs. The structural diversity and key structure-property relationships, such as chiral transfer from the organic to the inorganic components, are summarized. With a focus on the underlying chemistry and physics, the control of spin, light and charge in these semiconductors is explored.

Organic donor-acceptor heterojunctions for high performance circularly polarized light detection

Development of highly efficient and stable lateral organic circularly polarized light photodetector is a fundamental prerequisite for realization of circularly polarized light integrated applications. However, chiral semiconductors with helical structure are usually found with intrinsically low field-effect mobilities, which becomes a bottleneck for high-performance and multi-wavelength circularly polarized light detection. To address this problem, here we demonstrate a novel strategy to fabricate multi-wavelength circularly polarized light photodetector based on the donor-acceptor heterojunction, where efficient exciton separation enables chiral acceptor layer to provide differentiated concentration of holes to the channel of organic field-effect transistors. Benefitting from the low defect density at the semiconductor/dielectric interface, the photodetectors exhibit excellent stability, enabling current roll-off of about 3–4% over 500 cycles. The photocurrent dissymmetry value and responsivity for circularly polarized light photodetector in air are 0.24 and 0.28 A W⁻¹, respectively. We further demonstrate circularly polarized light communication based on a real-time circularly polarized light detector by decoding the light signal. As the proof-of-concept, the results hold the promise of large-scale circularly polarized light integrated photonic applications.

Here, the authors report a strategy to fabricate multi-wavelength circularly polarized light photodetectors consisting of bilayer donor-acceptor heterojunctions with chiral active layers.

Anion-coordination-driven single-double helix switching and chiroptical molecular switching based on oligoureas

Synthetic foldamers with helical conformation are widely seen, but controllable interconversion amongst different geometries (helical structure and sense) is challenging. Here, a family of oligourea (tetra-, penta-, and hexa-) ligands bearing stereocenters at both ends are designed and shown to switch between single and double helices with concomitant inversion of helical senses upon anion coordination. The tetraurea ligand forms a right-handed single helix upon chloride anion (Cl-) binding and is converted into a left-handed double helix when phosphate anion (PO4 3-) is coordinated. The helical senses of the single and double helices are opposite, and the conversion is further found to be dependent on the stoichiometry of the ligand and phosphate anion. In contrast, only a single helix is formed for the hexaurea ligand with the phosphate anion. This distinction is attributed to the fact that the characteristic phosphate anion coordination geometry is satisfied by six urea moieties with twelve H-bonds. Our study revealed unusual single-double helix interconversion accompanied by unexpected chiroptical switching of helical senses.

Synergistic Effect of Chiral Nanofibers Amplifying the Orbit Angular Momentum To Enhance Optomagnetic Coupling

Manipulating magnetic bits by photon in spintronics, opto-magnetic coupling, is lagging far behind what we could expect. To investigate the issue, one should face the problem to find photon dependence of spin dynamics and spin manipulation. In this work, through introducing chiral orbit in organic crystals, circularly polarized photon can manipulate spin via the channel of photon-orbit-spin interactions. Under the stimulus of the magnetic field, strong spin polarization will feed back to the change in polarized state of light. Moreover, twisting several chiral nanofibers into a thick one, a more pronounced opto-magnetic coupling is clearly observed due to the chirality generated larger chiral orbit. Meanwhile, spin dynamics (or spin response times) inside the aggregated thick chiral fiber can be further tuned by circularly polarized light. Hopefully, this study can deepen the understanding of organic chiral spin-photonics and enhance the application of organic functional crystals in the future.

High Responsivity Circular Polarized Light Detectors based on Quasi Two-Dimensional Chiral Perovskite Films

Circularly polarized light (CPL) has considerable technological potential, from quantum computing to bioimaging. To maximize the opportunity, high performance photodetectors that can directly distinguish left-handed and right-handed circularly polarized light are needed. Hybrid organic-inorganic perovskites containing chiral organic ligands are an emerging candidate for the active material in CPL photodetecting devices, but current studies suggest there to be a trade-off between the ability to differentially absorb CPL and photocurrent responsivity in chiral perovskites devices. Here, we report a CPL detector based on quasi two-dimensional (quasi-2D) chiral perovskite films. We find it is possible to generate materials where the circular dichroism (CD) is comparable in both 2D and quasi-2D films, while the responsivity of the photodetector improves for the latter. Given this, we are able to showcase a CPL photodetector that exhibits both a high dissymmetry factor of 0.15 and a high responsivity of 15.7 A W^-1. We believe our data further advocates the potential of chiral perovskites in CPL-dependent photonic technologies.

Phthalocyanine-Triggered Helical Dipeptide Nanotubes with Intense Circularly Polarized Luminescence

Nanotubes with circularly polarized luminescence (CPL) are attracting much attention due to many potential applications, such as chiroptical materials, displays, and sensing. However, it remains a challenge to change the assemblies of ordinarily molecular building blocks into CPL supramolecular nanotubes. Herein, the regulation of quite common dipeptide (Fmoc-FF) assemblies into unprecedented helical nanotubes exhibiting intense CPL is reported by simply doping a few phthalocyanine (octakis(carboxyl)phthalocyaninato zinc complex (Pc)) molecules. Interestingly, altering the Fmoc-FF/Pc molar ratios over a wide range cannot change the nanotubes structures according to transmission electron microscopy (TEM) and atomic force microscope (AFM) measurements. Although molecular dynamics simulations suggest that the noncovalent interactions between Fmoc-FF and Pc are quite weak, few Pc molecules can still change the secondary structures of a large number of Fmoc-FF assemblies, which hierarchically form helical supramolecular nanotubes with long-range ordered molecular packing, leading to intense CPL signals with large luminescence dissymmetry factor (g_lum  = 0.04). Consequently, the chiral reorganization of Fmoc-FF assemblies is dependent on the coassembly between Pc molecule and Fmoc-FF supramolecular architectures. These results open the possibility for the fine-tuning of helix and supramolecular nanotubes with CPL properties by using a small number of cofactors.

Spin selectivity in chiral metal-halide semiconductors

Controlling the spin states of freedom represents a significant challenge for the next-generation optoelectronic and spintronic devices. Chiral metal-halide semiconductors (MHS) have recently emerged as an important class of materials for spin-dependent photonic and electronic applications. In this Minireview, we first discussed the chemical and structural diversity of chiral MHS, highlighting the chirality formation mechanism. We then provided our current understanding on the spin-sensitive photophysical and transport process with a focus on how chirality enables the spin selectivity in chiral MHS. We summarized recent progress on the experimental demonstration of spin control in various photonic and spintronic devices. Finally, we discussed ongoing challenges and opportunities associated with chiral MHS.

Highly Efficient Spin-Filtering Transport in Chiral Hybrid Copper Halides

Chiral Pb(Sn)-I hybrid organic-inorganic perovskites exhibit outstanding chiral-induced spin selectivity (CISS) performance, but the nontoxic lead-free hybrid materials with high stability are still greatly desired for spin filtering in spintronic applications. We synthesize chiral hybrid copper halides (R/S-MBA)₂ CuX₄ (MBA=methylbenzylammonium; X=Cl, Br) with characteristic 0D CuX₄ tetrahedral structural motifs, combining the low toxicity of Cu²⁺ and air stability of halide ions (Cl^- and Br^- ). Despite similar structural and electronic features, (R/S-MBA)₂ CuBr₄ shows much smaller chiroptical activity than the chloride counterpart. Magnetically conductive atomic force microscopy measurements display a typical spin-polarized charge-transport property with high efficiency up to 90 % for both copper halides. Our work expands the CISS effect into eco-friendly and stable metal-organic halides, which is promising for applications in spintronics based on transition-metal hybrid systems.

Chirality-Dependent Second-Order Nonlinear Optical Effect in 1D Organic-Inorganic Hybrid Perovskite Bulk Single Crystal

The introduction of chirality into organic-inorganic hybrid perovskites (OIHPs) is expected to achieve excellent photoelectric and nonlinear materials related to circular dichroism. Owing to the existence of asymmetric center and intrinsic chirality in the chiral OIHPs, the different efficiencies of second harmonic generation (SHG) signal occurs when the circularly polarized light (CPL) with different phases passes through the chiral crystal, which is defined as second harmonic generation circular dichroism (SHG-CD). Here, the SHG-CD effect is developed in bulk single crystals of chiral one-dimensional (1D) [(R/S)-3-aminopiperidine]PbI₄ . It is the first time that CPL is distinguished using chirality-dependent SHG-CD effect in OIHPs bulk single crystals. Such SHG-CD technology extends the detection range to near infrared region (NIR). In this way, the anisotropy factor (g_SHG-CD ) through SHG-CD signal is as high as 0.21.

Great Amplification of Circular Polarization Sensitivity via Heterostructure Engineering of a Chiral Two-Dimensional Hybrid Perovskite Crystal with a Three-Dimensional MAPbI3 Crystal

Chiral hybrid perovskites have brought an unprecedented opportunity for circularly polarized light (CPL) detection. However, the circular polarization sensitivity of such a detector remains extremely low because of the high exciton recombination rate in those single-phase hybrid perovskites. Here, a heterostructure construction strategy is proposed to reduce the electron-hole recombination rate in a chiral hybrid perovskite and achieve CPL detectors with greatly amplified circular polarization sensitivity. A heterostructure crystal, namely, [(R)-MPA]2MAPb2I7/MAPbI3 ((R)-MPA = (R)-methylphenethylamine, MA = methylammonium), has been successfully created by integrating a chiral two-dimensional (2D) perovskite with its three-dimensional counterpart via solution-processed heteroepitaxy. Strikingly, the sharp interface of the as-grown heterostructure crystal facilitates the formation of a built-in electric field, enabling the combined concepts of charge transfer and chirality transfer, which effectively reduces the recombination probability for photogenerated carriers while retaining chiroptical activity of chiral 2D perovskite. Thereby, the resultant CPL detector exhibits significantly amplified circular polarization sensitivity at zero bias with an impressive anisotropy factor up to 0.67, which is about six times higher than that of the single-phase [(R)-MPA]2MAPb2I7 (0.1). As a proof-of-concept, the strategy we presented here enables a novel path to modulate circular polarization sensitivity and will be helpful to design chiral hybrid perovskites for advanced chiroptical devices.