Chirality Engineering and Properties in Two‐Dimensional Layered Materials

ABSTRACT

Chirality engineering offers a plethora of fascinating properties and ushers in compelling applications in spintronics, chiroptics, superconductivity, catalysis, etc. Atomically thin two‐dimensional (2D) layered materials have extraordinarily inherent optical, electronic, and quantum properties, accompanied by highly tunable van der Waals heterostructures, making them ideal platforms to engineer chirality. Although the deliberate incorporation of chiral molecules into local coordination environments has imparted remarkably tailored chiroptical and spintronic responses in synthetic systems, such as organic frameworks and hybrid organic‐inorganic perovskites, translating such chiral control into the well‐explored 2D layered materials (e.g., graphene and transition metal dichalcogenides) faces substantial hurdles, including precise nanostructure fabrication, molecular assembly, subtle chiral coupling, and reliable electronic and optical characterization. This review systematically outlines up‐to‐date feasible strategies for chiral engineering in 2D layered materials to leverage their functional landscape and unlock the emergent chiral properties. It begins with intrinsic and extrinsic engineering approaches, highlighting the underlying design principles and the resulting novel physical and chemical behaviors. We further discuss potential extensions of these chirality‐engineering approaches and explore future promising opportunities that harness rationally tailored chiral functionalities in 2D systems for next‐generation optoelectronics, spintronics, and quantum information science.

This review comprehensively focuses on the chirality engineering and properties in two‐dimensional layered materials (e.g., graphene and transition metal dichalcogenides), highlighting advanced strategies for both intrinsic structural modification and extrinsic chiral coupling induction. It further explores the novel chiroptical, spintronic properties and emerging applications in optoelectronics, enantioselective sensing arising from these engineered chiral properties.

1. Introduction

Chirality, the property where an object cannot be superimposed on its mirror image, is ubiquitous in nature. It is essential in biomolecules and enantiomeric chemistry. Furthermore, it confers materials with a unique helical potential field that induces spin‐orbit coupling (SOC), leading to phenomena such as circular dichroism (CD) and the chiral‐induced spin selectivity (CISS) effect. These distinctive properties make chiral materials highly promising for applications in polarization optics and spintronic devices [1, 2, 3, 4]. Moreover, chiral nanomaterials, characterized by their ultrahigh specific surface area and unique quantum confinement effects, have achieved significant research progress through the incorporation of chirality. For instance, chiral functionalization of nanoparticles has demonstrated enhanced optical and biochemical properties [5, 6, 7, 8, 9]. In the quest to expand the boundaries of chirality, two‐dimensional (2D) layered materials have emerged as a promising frontier.

Since the discovery of graphene in 2004 [10], 2D materials have evolved and expanded rapidly, with a plethora of unique and intriguing optoelectronic properties. Materials including hexagonal boron nitride (h‐BN), transition metal dichalcogenides (TMDs), MXenes, and others have been exfoliated [11, 12] or directly synthesized for studies in optics [13, 14, 15], electronics [16, 17], magnetics [18, 19], and other fields. Modification [20, 21] and assembly [22, 23] are also key research interests, and their potential applications across various domains have been extensively explored [24, 25, 26, 27]. Chirality has now been successfully introduced into the 2D materials family. Organic materials like covalent organic frameworks (COFs) and metal‐organic frameworks (MOFs) can create tunable chiral pore structures within 2D planes through precise ligand design and assembly [28, 29]. Although these materials have shown remarkable progress in enantiomer separation [30, 31] and catalysis [32, 33], with electrical properties evolving from insulating to broadly tunable semiconducting [34], they face essential limitations such as high cost, complex synthesis, and insufficient stability due to their organic components. Moreover, the mechanism by which molecular chirality translates into global structural chirality remains unclear [35]. Directly incorporating chirality into more widely studied inorganic 2D materials (e.g., graphene, TMDs, and MXenes) could overcome some limitations of organic materials while leveraging the inherent superior electrical, optical, and mechanical properties of inorganic systems. However, naturally chiral inorganic 2D materials are relatively rare compared to their organic counterparts. Broadly introducing chirality into 2D materials would significantly expand the research scope of chiral 2D systems and open new application avenues in optoelectronics, spintronics, novel catalysts, and chiral sensing.

While a few reviews and perspectives exist on introducing chirality into 2D materials [36, 37, 38, 39, 40], most focus on chiral organic molecule‐inorganic hybrid perovskites beyond the scope of COFs/MOFs [35, 41, 42, 43, 44, 45, 46, 47, 48]. Reviews addressing general 2D materials like graphene and TMDs lack a systematic summary of chirality‐introduction strategies and resultant emergent properties. This review aims to comprehensively explore diverse strategies for imparting chirality to 2D materials, the novel properties they enable, and future research directions and applications, thereby providing new insights for designing chiral functional materials (Figure 1). Due to length and logical constraints, we focus primarily on chiral materials that are directly derived from exfoliable 2D materials—i.e., structures topologically equivalent to them that exhibit 2D confinement effects and stacking properties. This excludes 2D thin films and topologically distinct systems like carbon nanotubes. However, since atomic‐level precision remains challenging, bottom‐up synthesis approaches for certain structures are also discussed. The review is organized as follows: Section 2: strategies for introducing chirality into 2D materials, including intrinsic (constructing chiral structures) and extrinsic (incorporating chiral guest sources) approaches. Section 3: novel properties imparted by chirality and their underlying mechanisms, covering optics, electronics, catalysis, and enantioselective chemistry. Section 4: systematic conclusions and perspectives on future research and applications.

FIGURE 1.

Schematic for chiral engineering in 2D materials. Strategies are divided into the intrinsic (left) and extrinsic (right) in the middle ring. Typical properties are listed in the outer ring. Note that the scales in all schematics do not necessarily match the ones in reality.

2. Strategies for Introducing Chirality Into 2D Materials

In this section, we consider utilizing 2D materials themselves to construct chiral structures or introducing external chiral sources into 2D materials. To build intrinsic chiral structures, multiple techniques are employed, such as mechanically stacking or reshaping 2D materials, or growing chiral structures directly using bottom‐up methods. For extrinsic chirality, guest elements are introduced into 2D materials via methods such as physisorption, chemisorption, and intercalation, or by coupling the materials with chiral surfaces, including chiral layers represented by perovskites and engineered metamaterials.

2.1. Engineering Structural Chirality

Regardless of whether materials possess intrinsic chirality, structural chirality can be introduced by designing screw configurations [38]. Structural chirality has garnered significant attention in metal nanoparticles [63], macromolecules [64], and supramolecular materials [47]. 2D materials provide a novel platform for creating structural chirality. By inducing structural asymmetry, chirality can be realized in 2D materials. The typical examples of chiral structures are listed in Table 1. This enables the design of diverse chiral architectures ranging from 1D (e.g., nanoscrolls) to 2D (e.g., twisted bilayers) and 3D (e.g., helices), even though the building blocks remain 2D. Twist‐stacked 2D materials retain their intrinsic 2D morphology, while shape manipulation can transform them into 1D or 3D structures. For the latter, chirality manifests macroscopically as helical structures, while microscopically it reveals itself through specific deformations of chemical bonds and lattice rearrangements. Macroscopic morphologies, such as spirals and twisted ribbons, can create chiral structures regardless of the lattice type. However, symmetry constraints prevent certain twist angles from producing microscopic chirality—for instance, in twisted stacking or scrolls—as chirality depends on lattice anisotropy.

TABLE 1.

Typical approaches to introduce structural chirality to 2D materials.

Type	Material	Method	Maximum chirality strength	Refs.	Pros	Cons
Twisted stacking	Graphene	PMMA‐assisted Transfer	6.5 deg µm−1 (CD ellipticity)	[49]	Angle control, flexible design	Hard to scale up
	Graphene	Folding	—	[50]		Hard to control precisely
	MoS2	CVD	—	[51]	High yield	Poor selectivity
Scroll	Graphene, TMDs	Liquid‐assisted rolling	0.37 (Raman optical activities at G‐peak)	[52]	Combines 1D properties	Random morphology, introducing defects
Spiral	MoS2	CVD	—	[53]	High stability	Poor selectivity
	WSe2	CVT	12.7% (Raman optical activities at E2g 1)	[54]		Substrate dependence, limited selectivity.
	Graphene	Wrinkle‐tearing and CVD	—	[55]		Hard to remove residual
	MoS2	Chiral‐ligand‐assisted hydrothermal synthesis	0.01 (g‐factor of CD)	[56, 57]	Tunable handedness and magnitude	Poor crystal quality
Helix	Graphene	Photoresist‐assisted self‐assembly	1.4 (g‐factor of CD in THz band)	[58]	Simple operation, tunable morphology	mm scale, cannot resolve from polymer
In‐plane Pattern	Blue phosphorene	Substrate engineering CVD	—	[59]	2D chirality	Risk of structural relaxation
Distorted Flakes	MoS2	Chiral‐ligand‐assisted exfoliation	0.26 deg (M ligand)−1 (CD, unknown concentration)	[60]	Tunable handedness and magnitude	Reduced crystal quality
Nanobowties	Cu2‐xS	Surfactant‐Mediated Synthesis	0.0045 (g‐factor of CD)	[61]
Spatial Redistribution	Porous Graphene	Stirring	0.015 deg g−1 L (CD, unknown thickness)	[62]	Tunable handedness and magnitude	Poor crystal quality

2.1.1. Twisted Stacking

2D materials with atomically flat surfaces can readily form multilayered structures through stacking [22, 23]. Twist‐stacked 2D materials, particularly van der Waals homo‐ and hetero‐structures, have emerged as hotspots in condensed matter physics and materials science due to their unique moiré superlattices and induced novel physical phenomena. By precisely controlling interlayer twist angles and stacking sequences, one can finely engineer the electronic and optical properties of these materials [65, 66, 67, 68]. 2D planar structures in 3D space are inherently achiral due to mirror symmetry. In real 2D materials, however, only particle behaviors (e.g., of electrons and phonons) are confined to the plane, while the atomic lattices retain 3D character. Moreover, 2D materials are often placed on a substrate, which breaks the out‐of‐plane symmetry and forbids mirror flipping. Therefore, the realization of chirality in planar 2D material systems becomes possible [38, 69], with twist stacking representing the simplest method for introducing and modulating chirality. Left‐ and right‐handed configurations exhibit identical interlayer coupling at equivalent angles [70], while maintaining intrinsic chiral distinctions.

Advancements in transfer techniques now enable rapid and convenient artificial fabrication of twisted structures [71, 72]. Early research focused on twisted bilayer graphene (TBG) assembled via PMMA‐assisted wet transfer, with crystal orientations verified by TEM diffraction patterns. Typical schematics are shown in Figure 2a,b. This study not only revealed tunable giant CD responses originating from large in‐plane magnetic moments (Figure 2c) but also explored the modulation of CD in multilayer twisted graphene [49]. Furthermore, theoretical calculations demonstrated that chiral rotation of Dirac fermions' helicities in top/bottom layers induces CD activity in TBG [73], which was later confirmed in h‐BN systems [74]. Since CD originates from interlayer electronic coupling, polymer‐free transfer techniques have been developed to minimize interfacial contamination and thereby enhance coupling, though precise control remains challenging [75].

FIGURE 2.

Chirality in twisted stacking graphene. a) Schematic for creating chirality in TBG films. A vertical line represents a mirror plane. b) Schematic for electronic band structures (top) and atomic arrangements (bottom) of left‐ and right‐handed TBG films. c) CD spectra, measured from a pair of chiral TBG with θ  =  16.5° and single‐layer graphene. The CD spectra of left‐ and right‐handed twisted bilayer graphene each show two strong peaks, denoted Peak A and B. Adapted with permission [49]. Copyright 2016, Springer Nature Ltd. d) Schematic for voltage probe detection of chirality of TBG in the presence of a magnetic field. The reading of voltage V₃ is opposite for the opposite chirality. The green or violet color means a layer twisted by a positive or negative angle, respectively. Adapted under terms of the CC‐BY license [76]. Copyright 2024, The Authors, published by American Chemical Society.

Besides CD, there are other properties related to the chirality of TBG. Interestingly, twist‐induced chirality propagates to adjacent few‐layer regions, in which the interlayer shearing phonons show polarization degrees reaching 0.5 in circularly polarized Raman spectra. Due to the resonance enhancement effect in Raman spectroscopy, this polarization degree can be modulated by matching different excitation energies with transition pathways determined by twist angles [77]. Additionally, unpolarized incident light on TBG generates transmitted/reflected light carrying spin and orbital angular momentum (SAM/OAM), modulated by twist angle through near‐field interactions and interference of angular momentum conversion [78]. Further evidence emerges from linear transport experiments: even without magnetic fields to break time‐reversal symmetry, asymmetric interlayer electrical responses occur as opposite transverse currents in adjacent layers, whose direction reverses upon chirality reversal (Figure 2d) [76].

TBG also serves as an ideal platform for chiral plasmonic modes, where twisted stacking creates novel plasmon resonances and generates a giant effective magnetic field acting on plasmonic edge states [79, 80]. Moreover, chiral TBG exhibits enantiomer‐dependent adsorption strengths and efficiencies of resonance energy transfer with organic molecules, offering potential applications for TBG in chiral separation and detection [81]. In TBG, moiré‐derived flat bands modulate the electrochemical electron transfer process, resulting in a strong dependence of heterogeneous charge transfer kinetics on the TBG structure [82]. Whether this phenomenon can be utilized for enantioselective chemistry in chiral TBG remains an open question.

Other 2D materials, such as TMDs, can likewise be exploited in twist engineering. Shen et al. developed a relatively clean transfer method for fabricating chiral twisted structures in even‐layered MoS₂/MoSe₂, establishing quantitative structure‐activity relationships linking CD signatures to twist angle and layer number, respectively [83]. Anisotropic materials (e.g., black phosphorus and ReS₂) can form chiral stacks with exceptional ellipticity values surpassing other twisted systems [84]. For intrinsically chiral 1T′‐ReS₂, different stacking sequences create chiral/racemic structures even in the absence of twisting, which can be identified through circularly polarized Raman spectroscopy [85, 86].

Stacking involves sequential van der Waals bonding of multiple flakes, while simply using a single flake by methods like folding can achieve analogous effects. Although techniques like high‐energy pulse lasers (Figure 3a) [87], focused ion beam (FIB) [88], atomic force microscope (AFM) probe manipulation [89, 90], or direct mechanical tearing [91] allow stacking from a single crystal and eliminate the need for recognizing lattice orientation, they either require extreme conditions or introduce significant defects. Considering the drawbacks, folding offers a new path to create homostructures. This approach facilitates precise twist angle determination, reduces uncertainties from sample variations, and creates edge stresses for modulation of crystal structure. Early folding methods employ deionized water intercalation, which suffers from poor controllability [92, 93]. Thermal expansion mismatch between monolayers and polymers can generate graphene folds through wrinkling [94], while cold contraction of spin‐coated paraffin results in MoS₂ folding similarly [95, 96]. Although lacking precise control of folding direction, these methods offer straightforward approaches with moderate yield.

FIGURE 3.

Using one single flake to controllably achieve twisted stacking structures. a) Schematic for the cutting‐rotation‐stacking technique used to fabricate TBG and further double TBG. Cutting is achieved by a femtosecond laser. Reproduced with permission [87]. Copyright 2016, Wiley‐VCH GmbH. b) Schematic for the folding process of a monolayer graphene film, including: substrate modification, folding driven by delamination from only the hydrophilic surface region. Adapted with permission [50]. Copyright 2017, American Chemical Society. c) Left: Schematic for the concept of the microdome‐shaped‐polymer‐based micromanipulation of a 2D‐material flake. Right: Schematic and optical micrographs of the folding of a h‐BN flake. Adapted with permission [97]. Copyright 2020, American Chemical Society.

Inspired by the methods above, Wang et al. controlled folding regions and directions using hydrophobic/hydrophilic patterned substrates. As shown in Figure 3b, the hydrophobic surface inhibits the intercalation of deionized water, preventing the attached graphene‐PMMA from detaching. In contrast, the one on the hydrophilic surface detaches and folds onto the undetached one under surface tension. After folding is completed, the PMMA layer can be removed via a series of subsequent operations to obtain bare folded graphene [50]. Micro‐mechanical techniques pioneered by AFM represent the most direct controllable folding method, yielding successfully folded structures [98, 99, 100], while the expense of AFM limits free and wide use. Fortunately, the interaction probes can be replaced by polymers. Polydimethylsiloxane (PDMS)‐based micro‐dome polymers coated with polyvinylchloride (PVC) adhesion layers mimic AFM tips, enabling temperature‐regulated sliding, rotating, folding, flipping, and exfoliating of 2D materials (Figure 3c) [97].

Other smart techniques are being invented to produce wrinkles on 2D materials. Pre‐stretched substrates form wrinkles upon sudden relaxation, with thinner materials collapsing into bi/tri‐layer folds due to instability [101, 102]. Beyond reshaping, growth on corrugated templates followed by etching can also induce folding collapse [103]. Similar to the stacking of anisotropic 2D materials mentioned above, potential applications of folding include creating separated inverted configurations in ReS₂ for probing distinct chiral Raman responses [104]. The application of folded structures for engineering structural chirality remains largely unexplored, particularly because isolating the influence of the fold crease is challenging.

Compared to mechanical stacking above, chemical vapor deposition (CVD) enables large‐scale growth of twisted structures without organic/solvent contamination from transfer processes. However, its extreme growth conditions and lack of in‐situ control pose challenges for precise control [105]. Despite the limitations, several CVD‐grown chiral twisted structures have been reported. TBG tends to adopt specific energetically favorable stacking orientations when grown on Cu(111) single‐crystal surfaces [106, 107]. A similar effect is achieved in the growth of TMDs, where gas flow is perturbed through nested tubes, thereby inducing orientation variations during nucleation (Figure 4a,b). The yields of twisted bilayers can be controlled by the growth conditions, such as gas flow rate and salt ratio (Figure 4c) [51]. While this method limits the freedom and controllability of the twist angle, the diversity of preferential angles is enough to support certain research applications (Figure 4d). Furthermore, the heating rate is another parameter to control the twisted angle. Unlike conventional isothermal growth, achieving epitaxial growth during the heating process helps overcome the kinetic barrier for stable stacking and introduces orientational perturbations. This provides a novel strategy to grow twisted bilayers by tuning the synthesis conditions [108]. Nevertheless, the approaches mentioned above still face the challenge of poor selectivity. They are unable to control the twist angle with single‐degree precision. Moreover, the systems involve numerous uncertain variables, making it potentially difficult to reproduce the exact conditions across different experimental setups.

FIGURE 4.

CVD‐grown twisted 2D materials. a) Schematic for CVD setup for the growth of twisted bilayer MoS_2. b) Schematic for the growth mechanism of the twisted nucleation process under turbulent flow. c) Schematic for the salt‐assisted growth process for the reconfiguring nucleation and growth. d) Twisted angle distribution and Gaussian fitting curve of the as‐grown twisted bilayer MoS₂. Adapted under terms of the CC‐BY license [51]. Copyright 2024, The Authors, published by Springer Nature Ltd. e) Schematic for the hetero‐site nucleation for growing TBG on a Cu substrate. The side view illustrates that the second‐layer graphene grows beneath the first layer. Adapted under terms of the CC‐BY license [109]. Copyright 2021, The Authors, published by Springer Nature Ltd. f) Schematic for the Cu‐foil‐assisted CVD growth of TBG. Adapted with permission [110]. Copyright 2022, Springer Nature Ltd.

Furthermore, deliberately perturbing local flow fields through substrate design to control nucleation behaviors offers an additional strategy for angle manipulation [51, 109]. Figure 4e shows the TBG formation progress and angle distribution grown on the stepped Cu substrate. The nucleation site and twisted angle are influenced by the edges of the steps. Compared to the preferred distribution in Figure 4d, a relatively even angular distribution was achieved. The method of disturbing the flow field provides a simple and feasible approach for growing twisted bilayers, but it results in a wide angular distribution and cannot achieve precise control. The inherent lattice structure of copper directs the growth orientation of graphene, enabling controlled CVD growth angles. Consequently, precise control over the twisted angle in TBG is achieved by predefining the rotational alignment between two single‐crystal Cu(111) foils, followed by surface etching to isolate Cu‐foils‐sandwiched TBG (Figure 4f) [110].

2.1.2. Stitch and Scroll

Connecting 2D materials end‐to‐end yields seamless 1D tubular structures. For example, carbon nanotubes not only retain graphene‐like properties but also exhibit unique characteristics owing to the confinement effect expanded to a new dimension. Chirality in nanotubes arises from axial misalignment of graphene unit cells, where zigzag (or armchair) edges neither connect end‐to‐end nor extend axially, instead forming helical spirals. This chiral configuration has been realized in carbon nanotubes [111], BN nanotubes [112], and TMD nanotubes [113]. Chirality endows nanotubes with novel properties: tunable electronic structures [114], flat bands upon collapse [115, 116], superconductivity [117], CD [111], and nonlinear optics (NLO) [112, 118]. Direct fabrication of chiral nanotubes from stacked 2D materials represents a highly innovative approach.​ A focused high‐energy electron beam in a scanning transmission electron microscope can break intralayer chemical bonds, followed by interlayer stitching at elevated temperatures. For instance, when TBG is cut along the symmetry axis of the Moiré pattern, the two resulting nanoribbons are seamlessly connected, which further collapses into chiral carbon nanotubes oriented parallel to the layers [119]. Similarly, BN nanotubes oriented perpendicular to the layers can be created directly by drilling holes [120]. This cut‐and‐join technique enables the fabrication of nanotubes with arbitrary chirality and topology; however, the edge‐stitching process inevitably introduces massive defects. Moreover, other material systems—especially heterostructures with significant lattice mismatch—remain relatively rare [121].

Nanoscrolls—structurally analogous to nanotubes but with genus 0 topology (unlike the genus 1 of closed nanotubes)—are formed by rolling deformable 2D materials through techniques including liquid intercalation and surface tension [122, 123, 124, 125, 126], micro‐mechanical friction [127], tension gradients induced by vacancy [128, 129], thermal differential expansion [130], pre‐strained metal electrodes [131, 132], and even wet‐chemical nanotube templating assembly [133] or molecular self‐assembly [134]. Among these methods, large‐area flat flakes grown by bottom‐up methods like CVD are typically used as starting materials.

Nanoscrolls exhibit nanotube‐like chirality (Figure 5a), enabling strong NLO and CD responses [135, 136, 137, 138], as well as spin polarization [52]. The majority of the aforementioned methods lack the capability for controlled synthesis of chiral nanoscrolls. Therefore, several approaches have been developed as detailed below. For liquid‐assisted spontaneous scrolling, as illustrated in Figure 5b, the rolling direction of the flakes is determined by the edge that is first intercalated and detached from the substrate. Since CVD‐grown MoS₂ possesses zigzag edges, the scrolls formed from triangular flakes all exhibit a consistent chirality, while the rolling of large‐area polycrystalline films is random. FIB patterning provides effective chirality control as the rolling direction (axial) is identical to the edge orientation [125]. Alternatively, angle‐insensitive but easily operative macroscopic templates (e.g., wax [52]) provide another option. The change in surface tension induced by spin‐coated wax can regulate the rolling behavior of graphene in a hot solvent (Figure 5c). Spontaneous scrolling without additional treatment yields scrolls with a chiral angle of 0° (Figure 5d). In contrast, direct rolling produces a wide range of chiral angles due to the varied orientation of each flake (Figure 5e), while cut‐and‐roll provides precise control of chiral angles (Figure 5f), like the FIB‐patterned one mentioned before. In this process, in addition to the rolling method and solvent polarity, the wettability of the substrate in the solvent and its adhesion to the materials are also expected to play a critical role. The polarity, anisotropy, and flatness of the substrate surface may regulate the rolling behaviors, which have not been thoroughly explored.

FIGURE 5.

2D material formed chiral nanoscrolls. a) Schematic for rolling direction determining chirality in graphene, where rolling along zigzag‐ or armchair‐edge obtains achiral rolls. b) Schematic for self‐scrolling (spontaneously roll) of TMD monolayer flakes by one drop of ethanol. c) Fabrication of chiral graphene rolls by the wax‐aided method, including direct roll and cut‐and‐roll procedure. d–f) Distribution of the chiral angle of graphene rolls fabricated by spontaneous roll, direct roll, and cut‐and‐roll, respectively. s.d., standard deviation. (a) and (c–f), adapted with permission [52]. Copyright 2025, Springer Nature Ltd. (b), adapted under terms of the CC‐BY license [125]. Copyright 2018, The Authors, published by Springer Nature Ltd.

Chirality engineering by rolling in vertically asymmetric Janus materials and multilayer homo/heterostructures remains largely unexplored. Due to the asymmetric lattice structure, the out‐of‐plane curling behavior of such materials also exhibits asymmetry, which may result in spontaneous scrolling along specific directions and make chirality control distinct from ordinary 2D materials [139, 140]. Recent work demonstrates spontaneous scrolling in electrochemically intercalated polar layered materials driven by out‐of‐plane polarization, with curvature modulated by the option of intercalants. However, scrolling occurs only along specific crystallographic directions ([100] and [$\overline{1}20$]), lacking arbitrary angular control like most existing methods above [141]. In MXene superlattices with hydrogen‐bonded rather than van der Waals‐bonded interlayer connections, the introduction of active solid‐solution atoms enhances vacancy formation capabilities. After customizing the bending stiffness of the layers, rapid exfoliation into curling structures occurs [142]. The decisive role of crystal structure in scrolling behavior is manifested in these two special materials, leading to the concept of precisely controlling scroll chirality through targeted doping. These works simultaneously inspire exploration of scroll formation in superlattices, where cooperation with guest substances creates composite structures with tunable interlayer spacing and enhanced functionality [125, 143]. Strategically designed dopants may simultaneously modify properties and control chirality.

2.1.3. Spiral

Screw dislocations, a type of linear crystal defect, exhibit properties in 2D materials analogous to those in bulk crystals. With inherent left/right‐handedness, introducing screw dislocations into nanomaterials creates chirality [144, 145]. Catalytically enhanced epitaxial growth occurs more readily at dislocation sites, enabling the formation of multilayer spiral structures in 2D materials. These spirals manifest in diverse configurations: conventional uniform‐orientation spirals, hybrid structures, and twisted spirals with varying interlayer orientations [146].

Conventional spiral structures have been realized in graphene and TMDs via CVD and chemical vapor transfer (CVT) [53, 147, 148, 149]. The initial dislocation orientation dictates the helicity of subsequent growth (Figure 6a,b) [150], though achieving enantioselective control remains challenging. In TMDs, the thermodynamic selectivity of different handedness can be modulated by growth temperature [54], while engagement of L‐/D‐tartaric acid as templates in hydrothermal synthesis of chiral 1T‐MoS₂ yields helicity with P‐/M‐handedness, respectively, with subsequent annealing enabling 1T‐to‐2H phase transition (Figure 6c,d) [56, 57]. Dislocation‐driven spirals modify band structures [151, 152, 153] and NLO responses [150, 154], though chiral properties remain underexplored beyond circularly polarized Raman variations [54].

FIGURE 6.

Chiral 2D materials with single spirals. a) Schematic for the nucleation and growth of the MoS₂ spiral in the lattice. b) AFM micrograph of MoS₂ spirals with right‐ (top) and left‐handedness (bottom). Reproduced with permission [53]. Copyright 2014, American Chemical Society. c) Scheme for the synthesis of chiral 1T and 2H MoS₂ nanosheets. Reproduced with permission [56]. Copyright 2025, Wiley‐VCH GmbH. d) High magnification scanning electron microscope (SEM) micrographs and CD spectra of chiral 1T‐MoS₂. Adapted under terms of the CC‐BY license [57]. Copyright 2024, The Authors, published by Wiley‐VCH GmbH. e) Schematics for Eshelby twist in GeS nanowires. Adapted with permission [159]. Copyright 2025, Springer Nature Ltd. f) SEM micrograph of two twisted GeS crystals with opposite chirality. g) Distribution of left‐ and right‐handed structures, whose population is approximately equal. Adapted with permission [158]. Copyright 2019, Springer Nature Ltd. h) Schematic for supertwisted spirals with different twisted angles. i–k) Screw dislocation sits at the flat surface, top of protrusion, and edge of a protrusion, yielding aligned, fastened, and unfastened spirals, respectively. Reproduced with permission [160]. Copyright 2020, AAAS.

While theoretically no stress is imposed on planes perpendicular to the Burgers vector, John D. Eshelby discovered that a screw dislocation induces a macroscopic twist in the finite crystal cylinder. This twist transforms the defect's chirality into a helical structure observable at the macroscopic scale. The orientation of each atomic layer in the crystal changes linearly along the axis, and this variation is governed by the diameter of the helix and the Burgers vector of the dislocation [155, 156, 157]. For example, chirality in screw dislocations facilitates the CVT growth of chiral GeS nanowires with Eshelby twists (Figure 6e–g). After the nanowire undergoes twisting, further radial growth accommodates fixed twist rates through a series of discrete jumps. This produces nanostructures with varying twist angles, where the twisting topology is controlled by the radial size [158].

Similar to nanowires exhibiting Eshelby twists, 2D material spirals anchored to a substrate can also develop a layer‐by‐layer twist. This controllable orientation shift enables fabrication of supertwisted spirals, exhibiting modulated photoluminescence (PL)/NLO [161, 162, 163, 164], giant magnetoresistance (MR) [165], and theoretically predicted magic angular momenta and 3D Landau levels [166]. In conventional planar spiral growth, the lower energy configuration of uniformly oriented layer stacking prevents the spontaneous formation of supertwisted spiral structures. Achieving such configurations thus requires substrate engineering. A non‐Euclidean surface offers an alternative route to control supertwisted chirality (Figure 6e–h). For example, during the growth of WS₂ and WSe₂, protrusions such as SiO₂ or WO₃ particles can be intentionally introduced as growth seeds to guide this distortion. Randomly located screw dislocations at the center of protrusions (bulge surface) or at the edges (depression surface) can yield fastened or unfastened supertwisted scrolls, corresponding to positive and negative chiral angles [146, 160, 167]. Building on the strategy for growing twisted bilayer structures—different orientations between adjacent layers induced from external perturbations beyond intrinsic substrate design—an analogous effect may occur in spiral structures, where a random misorientation introduced during nucleation or the earliest growth stages could result in the formation of a supertwisted spiral.

Beyond single spirals, paired counter‐rotating dislocations at grain boundaries generate double spirals, as realized in AA′‐stacked h‐BN [168]. Similarly, Wang et al. developed a graphene origami‐kirigami technique converting 1D wrinkle into 2D twisted chirality, creating enantiomeric dual‐spirals in a single origami process (Figure 7a). The direction of collapse after wrinkle tearing determines the orientation of the subsequent double helix growth (Figure 7b,c). They further proposed in‐situ SPM manipulation of nucleation and twist in CVD [55]. Complex structures emerge when new spirals share dislocation sites: co‐handed spirals with the same or different phases form overlapped triangle configurations, while opposite‐handed pairs evolve into hexagonal architectures (Figure 7d–g) [169]. Compared to the aforementioned origami‐kirigami technique, this method exhibits greater randomness as a critical drawback, yet offers the advantage of yielding individual, isolated structures with the simplest procedure. Key challenges remain for future research. These include achieving independent control over dislocation helicity and twisted chirality, as well as manipulating layer scale and thickness. For precisely controllable methods, enhancing reliability and ease of operation are essential. For general stochastic methods, the major focus should be on improving selectivity and cross‐laboratory reproducibility in subsequent work.

FIGURE 7.

Chiral 2D materials with dual‐ and multi‐spirals. a) In‐situ environmental SEM micrographs of graphene spirals with opposite screw dislocation handedness. b,c) Kinetic Monte Carlo simulations of the formation of spirals. Adapted with permission [55]. Copyright 2020, Springer Nature Ltd. d–g) AFM micrographs (left) and schematic stacking structure (right) of single, double (with the same and different phases and orientation), and five spiral patterns. Adapted with permission [169]. Copyright 2018, American Chemical Society.

2.1.4. Other Chiral Structures

Along with the aforementioned chiral architectures, similar novel structures continue to be explored. These can be systematically organized into three categories, including 2D in‐plane chiral patterns, 3D chiral torsion, and 3D chiral distributions.

Similar to twisted stacking, 2D materials can exhibit intrinsic microscopic chirality manifested through specific atomic arrangements within a 2D plane. As noted previously, ReS₂ adopts two distinct chiral configurations. Epitaxial growth of highly oriented single‐crystalline domains with high chiral selectivity is achievable via substrate engineering. In epitaxy, the use of terraced/stepped substrates with designed kinks creates a chiral surface, which resolves energy degeneracy among enantiomers [170]. Meantime, introducing specific atomic arrangements in achiral layers can also induce chirality. Constructing grain boundary networks by strain represents a method to break the original crystal symmetry, primarily achieved by modulating growth conditions (e.g., introducing mild chalcogen deficiency) and selecting or engineering substrates with specific lattice mismatches during epitaxy. In MoSe₂ twin grain boundary networks, six boundaries extending radially from a node form a vortex‐like hexagonal asterisk pattern, with opposing orientations not necessarily coinciding (Figure 8a) [171].

FIGURE 8.

2D materials with in‐plane chiral patterns. a) Chiral (left) and achiral (right) grain boundary pattern in MoSe₂. Parallel lines are twin grain boundaries. Thick and thin orange arrows represent the direction of one grain boundary and chirality, respectively. Adapted with permission [171]. Copyright 2017, American Chemical Society. b) STM micrograph of monolayer CoTe₂ after defect healing. Chirality is represented as a red or blue spiral schematic. D.B., domain boundary. c) STM micrograph of a hexagonal pattern (orange) with triangles (shaded red and blue). Adapted with permission [172]. Copyright 2025, American Chemical Society. d) Schematics for the initial structure (left) relaxing to the distorted spiral (right). The brown and blue dots represent Cu atoms on the surface and sub‐surface layers, respectively. (n‐)FCC and (n‐)HCP represent near‐face‐centered cubic and near‐hexagonal close‐packed, respectively. e) High‐resolution STM micrograph of blue phosphorene with left‐handedness (top) and right‐handedness (bottom). Reproduced under terms of the CC‐BY license [59]. Copyright 2024, The Authors, published by Springer Nature Ltd.

Similar chiral engineering via a strain‐mediated mechanism is realized in epitaxial CoTe₂ monolayers using molecular beam epitaxy (MBE)‐grown chiral AuTe/Au(111) templates. Interfacial tensile strain triggers the formation of a chiral pinwheel lattice of Te vacancies that breaks symmetry as Co deposits on the buffer surface. Subsequent Te deposition then heals the defects, yielding a uniform chiral spiral‐patterned monolayer (Figure 8b,c) [172]. For pure substrate design, lattice mismatch between the 2D material and the substrate surface enables relaxation into stable but asymmetric configurations that may exhibit chirality. In blue phosphorene on Cu(111), strong interfacial interaction generates lattice mismatch stress through rotational or semi‐coherent stacking, leading to chiral configurations characterized by highly periodic dislocation networks upon stress release (Figure 8d,e) [59, 173]. Since this type of in‐plane chirality is constructed based on stress‐laden boundaries or Moiré patterns, it may relax—under extreme conditions such as high temperature—into a lattice without chiral features. The stability of such non‐permanent chiral structures may require further investigation through theoretical simulations, such as molecular dynamics or Monte Carlo simulations.

Under external torsional forces, a material sample can form a distorted chiral structure in 3D space, with the overall size spanning from hundreds of nanometers to millimeters. Unlike a spiral, where the twist axis is typically perpendicular to the layers, this axis can form a twisted ribbon, not necessarily orthogonal to the material layers. These ribbon‐like structures and derived segments possess helical configurations, both featuring continuous bonded planes. Within such systems, molecular templates and engineered forces serve as the primary strategies for creating macroscopic structures with torsion, offering a robust pathway to induce chirality. For small molecular ligands, coordination interactions can induce a chiral distortion. Cysteine/penicillamine‐assisted exfoliation of MoS₂ yields a CD response far exceeding those from chiral dopants alone (Figure 9a). Theoretical calculation attributes this to hybridized excitonic quantum states—a mechanism validated across multiple nanomaterial systems [60]. Nevertheless, this work does not primarily focus on the potential chiral transfer facilitated by chiral ligands via orbital hybridization. This aspect will be discussed in the subsequent section on covalent functionalization. Bottom‐up liquid‐phase synthesis can also use chiral substrates to enable chiral control over product morphology. The anionic surfactant sodium dodecyl sulfate (SDS) facilitates the anisotropic growth and amplification of Cu²⁺‐Cysteine coordination complexes into twisted Cu_2–xS nanobowties (Figure 9b) [61].

FIGURE 9.

Chiral distortion and spatial distribution of 2D materials. a) Schematic for the formation of CD active MoS₂ in the presence of D‐penicillamine. Adapted with permission [60]. Copyright 2018, American Chemical Society. b) Schematic for the formation of chiral Cu_2‐xS nanobowties. Adapted with permission [61]. Copyright 2026, American Chemical Society. c) Schematic for supramolecular chirally functionalized graphene. The green and orange molecules and shells represent D‐/L‐Fmoc‐FF and corresponding supramolecular structures, respectively. Reproduced under terms of the CC‐BY license [174]. Copyright 2023, The Authors, published by American Chemical Society. d,e) Schematic for the formation mechanism of graphene‐SU‐8 photoresist helix. f,g) Schematic for the formation of a graphene helix. Adapted under terms of the CC‐BY license [58]. Copyright 2024, The Authors, published by Wiley‐VCH GmbH. h) Scheme for the synthesis of porous graphene membrane with vortex structures. Adapted with permission [62]. Copyright 2020, American Chemical Society. i) Schematic for one pitch of oxidized graphene chiral liquid crystal. j) CD spectra of GO aqueous dispersions and solid film as the volume fraction of GO (φ) changes. k) Normalized CD activity as a function of NaCl concentration (φ = 1.0%). Adapted with permission [175]. Copyright 2011, Springer Nature Ltd.

In contrast to chirality transfer by small‐molecule ligands, supramolecule‐assembled helix fibers exhibit greater stability even at larger scales. L‐/D‐(9‐fluorenylmethyloxycarbonyl)‐diphenylalanine (Fmoc‐FF) and graphene self‐assemble into chiral twisted supramolecular ribbons via hydrophobic interactions. They exhibit CD responses and display CISS in giant MR measurements (Figure 9c) [174]. On a more macroscopic scale, macro‐templates such as photo‐crosslinked polymers can form millimeter‐scale helical structures under light and thermal control. This strategy enables controlled and precise bending and alignment of graphene. (Figure 9d,e) [176]. Leveraging this technology, graphene cylindrical helices vertically aligned on a substrate with a high aspect ratio of ∼2700 have been fabricated (Figure 9f,g) [58].

For composite or assembled materials, chirality can also be created by organizing the spatial arrangement in a spiral pattern in 3D space. Macro‐mechanical vortex‐directed momentum imparts chirality to nanosheets [177], a phenomenon that has been reported in porous graphene and GO (Figure 9h) [62, 178]. Intense mechanical stirring, such as injecting 2D flake dispersions into vortexed Pluronic P123 solutions, can also induce chiral helices, producing pure left‐handed nanofibers [179]. Meanwhile, in water, chiral structures can spontaneously form through self‐assembly. Multiple GO layers stack with intercalated water molecules to form superlattice blocks, which link to each other and form chiral liquid crystals in a twisted configuration to minimize free energy from negative charge repulsion (Figure 9i). Consequently, both salt and graphene concentration adjustments tune chirality by altering the helical morphology (Figure 9j,k) [175]. Also, graphene can be spatially arranged by attaching it to carbon nanotubes, using sidewall defects as nucleation sites to form a branch‐leaf‐like structure [180]. Precisely controlling etching sites, such as with a focused electron beam, may guide helical graphene growth, enabling chiral arrays. When multiple graphene nanodisks are arranged along a helical assembly, the strong near‐field coupling between adjacent nanodisks makes the system a chiral metamaterial. The resulting mid‐infrared CD response can be tuned by the distance and diameter of the nanodisks [181].

2.2. Inherited Chirality From the Guest

The exceptionally high specific surface area of 2D materials enables efficient acquisition of chirality from guest species. Functioning as robust substrates that are both relatively chemically active and stable, 2D materials facilitate the assembly and integration of chiral substances. Simultaneously, through covalent or non‐covalent interactions, guest materials can extend their chirality to the host 2D systems. This chirality transfer may occur via orbital hybridization and electron transfer pathways, thereby amplifying chiral information and converting it into detectable signals. Incorporation of chiral molecules has been successfully implemented in 2D COFs, MOFs, and organic/inorganic hybrid perovskites [35, 41, 46, 47], yielding novel properties. Beyond molecular doping, an alternative effective strategy involves van der Waals (vdW) coupling between 2D materials and intrinsically chiral surfaces—such as perovskite, COFs, and metamaterials—to induce chirality. Typical approaches to introduce extrinsic chirality to 2D materials are listed in Table 2.

TABLE 2.

Typical approaches to introduce extrinsic chirality to 2D materials.

Type	Material	Guest	Possible Mechanism	Maximum Chirality Strength	Ref.	Pros	Cons
Covalent functionalization	Graphene oxide	Cysteine	—	0.01 deg g−1 L (Unknown thickness)	[182]	Simple to fabricate	Limited types of ligands
	MoS2	Penicillamine	Crystalline Distortion	3.23 deg µm−1 (CD ellipticity)	[183]
	Germanane	Cysteine	Spin‐orbit coupling	—	[184]
	Borophene	Cysteine	—	0.003 (g‐factor of CD)	[185]
Intercalation	TiS2, TaS2	MBA	Self‐assembled chiral molecular layers	—	[186]	High spin‐polarization rate	Limited types of intercalants, reduced crystal quality
Coupling	WSe2	(MBA)2PbI4	Spin‐polarized charge transfer	10% (ρXA of CPPL at 78 K) 13% (ρIX of CPPL at 78 K)	[187, 188]	On‐chip fabrication	Requires low temperature and strong interface coupling
		kgm and sql chiral COFs		8.1% (DOCP of CPL at 78 K)	[189]
		chGNR [15]		45.9% (transient CP reflectance kinetics at RT)	[190]
	MoS2	Gold crescent plasmonic antennae	Hot carrier injection	26.73% (ρXA of CPPL at RT)	[191]	Strong enhancement, tunable working range	High manufacturing cost
	MoSe2	WS2 metasurface	Purcell effect	30% (ρXA of CPPL at RT)	[192]
	MoS2	Gold nanorods sandwich		47% (ρXA of CPPL at RT)	[193]

2.2.1. Covalent Functionalization

The absence of dangling bonds on 2D material surfaces limits their reactivity for covalent bonding. Nevertheless, suitable chemical treatments enable molecular functionalization without structural degradation, allowing tailored modifications through specific functional groups. This expands the application horizons of 2D materials across diverse fields [194, 195]. Strategically designed chiral molecules grafted onto 2D substrates can transfer molecular chirality to the host material via covalent bonding. However, current covalently chiral functionalization efforts primarily utilize the high surface area and superior electrical conductivity of 2D platforms to amplify the performance of chiral molecules, rather than focusing on inducing novel intrinsic properties in the 2D materials themselves or discussing the mechanism of chirality transfer.

Graphene oxide (GO), a common graphene derivative featuring oxygen‐containing functional groups, offers enhanced reactivity and colloidal stability compared to pristine graphene. These properties make GO a versatile platform for functionalizing 2D materials. Diverse chiral organic molecules—notably amino acids and sugars—have been covalently bonded on GO for targeted applications [36, 40]. Amino acids possess at least one carboxyl group and one amino group in the same molecular structure. The high reactivity enables amino acids to undergo substitution reactions (with hydroxyl and carboxyl groups) or addition reactions (with epoxy groups) on readily GO. The chirality associated with the carbon atom connected to the residue is preserved. Figure 10a presents several functionalized GO starting with cysteine‐derived modifications. By loading chiral amino acids in this way, the resulting composites have proven effective in many fields, such as enantiomer recognition [196, 197] and separation [198, 199], asymmetric catalysis [200], and simulating biological membranes to study the effect of surface chirality on protein conformation [182]. Besides direct bonding with oxygen‐containing groups, amino acids can also be introduced via coupling molecules such as silane reagents [201].

FIGURE 10.

Chemical decoration of chiral molecules on graphene/GO flakes. a) Chemical structures of GO modified with R‐/S‐cysteine (R‐/S‐Cys‐GO), esterified R‐/S‐cysteine (R‐/S‐ECys‐GO), sulfur‐methylated R‐/S‐cysteine (R‐/S‐MCys‐GO), and diethylene glycol modified R‐/S‐cysteine (R‐/S‐DCys‐GO). Reproduced with permission [182]. Copyright 2014, American Chemical Society. b) Scheme for the preparation of alkynyl‐GO and polymer1/GO. Reproduced with permission [202]. Copyright 2014, American Chemical Society.

Carbohydrates represent another class of naturally chiral substances. Their chirality is retained after polymerization. Cyclodextrin, a commonly employed chiral compound, is a cyclic oligomer formed from a monosaccharide. It can form inclusion complexes with guest molecules and is widely used in drug delivery [203]. The chirality of the monosaccharide building blocks endows cyclodextrins with multiple chiral centers, making them extensively studied for enantiomer recognition and separation [204, 205]. Grafting cyclodextrins onto GO has been utilized for enantiomer recognition and separation, such as in active layers on glassy carbon electrodes for electrochemical analysis [206, 207] and in temperature‐responsive separation media on magnetic GO [208]. Similarly, polysaccharides like amylose [209] and cellulose [210] can also be loaded onto GO.

Other molecules have also been grafted onto GO, including R‐mandelic acid calix[4]arene for inducing a visible macroscopic chirality‐responsive wettability variation [211], NH₂‐binol for asymmetric catalytic addition reactions [212], thionine‐linked ds‐DNA for detecting chiral tryptophan isomers in the presence of Cu²⁺ [213], and 2,3‐diaminopropionic acid cross‐linked graphene sponges for coagulation [214]. The grafting strategy can also be used to synthesize chiral polymers on GO (Figure 10b) for enantioselective crystallization [202].

In TMDs, the unoccupied orbitals of transition metals can accept electrons from chiral ligands via substitution of chalcogen atoms or vacancies. Chiral thiol‐containing compounds can be utilized to functionalize TMDs [215, 216]. In the fabrication of chiral quantum dots and nanoparticles from TMDs, chiral thiols similarly transfer molecular chirality to the TMDs, generating applications in enantioselective catalysis [217], in vivo reactive oxygen species monitoring [218, 219], and tissue regeneration [220]. Beyond the macroscopic chiral distortion observed in MoS₂ flakes exfoliated with L‐/D‐penicillamine and cysteine [60], a giant molar ellipticity has also been detected in substrate‐grown MoS₂ after treatment in aqueous or vapor reactions (Figure 11a). The strong anisotropy can be applied to phototransistors for fabricating a gate‐tunable circularly polarized light detector (Figure 11b,c). Through DFT calculations, the chirality transfer is attributed to symmetry‐breaking crystalline distortion induced by the adsorption of chiral thiols, indicating the emergence of microscopic rather than macroscopic structural chirality [183]. This mechanism resembles the chiral octahedral twisting driven by chiral organic molecules in perovskites, which is considered the key origin of chirality [221]. However, compared to the complete and highly aligned non‐covalent arrangement in perovskites, the chemisorption in the former case is less uniform, which may result in an overall weaker chiral structural distortion. Moreover, in a liquid‐phase environment, such subtle chiral distortions are highly susceptible to relaxation due to disturbances. Nevertheless, pronounced chiroptical signals are still observed. This suggests that the role of chiral ligands may extend beyond simply inducing lattice distortion and likely involves orbital overlap.

FIGURE 11.

Other 2D materials beyond graphene for chiral molecule decoration. a) Chemical structure of L‐/D‐PEN and schematic for functionalized monolayer MoS₂. b) Schematic for the structure of a phototransistor for circularly polarized light detection. c) Photoresponse of MoS₂/L‐PEN. Adapted under terms of the CC‐BY license [183]. Copyright 2025, The Authors, published by American Chemical Society. d) Scheme for the synthesis of borophene sheets of different phases and ligands. Adapted with permission [185]. Copyright 2024, American Chemical Society. e) Crystal structure of MXenoids with and without organic substitutions. Blue atoms, metal; white atoms, Groups IVA to VIA elements; green atoms, halogen. Brown molecules, organic substitutions. f) Normalized absorption and CD spectra of multilayered TiN{Cl,H}_x(hda/MBA)_y MXenoids. Adapted with permission [222]. Copyright 2025, American Chemical Society.

Examples of covalent bonding between chiral molecules and other 2D materials also exist. Analogous to the orbital delocalization and hybridization observed in chiral quantum dots [223], chirality and the subsequent CISS effect have also been achieved in cysteine‐modified germanane, a phenomenon attributed to SOC between the germanane and the ligands, implying that chirality originates from orbital overlap [184]. Ultrasonically exfoliated χ3 and β₁₂ borophenes react exclusively with thiol‐containing amino acids compared to other amino acids under stirring at room temperature, owing to the formation of boron‐sulfur bonds (Figure 11d). The chirality of the amino acids imparts a CD response to the nanosheets and leads to differential cellular internalization [185].

MXenoids represent another class of 2D materials amenable to covalent modification, wherein the halogen atoms can be substituted by organic ligands (Figure 11e). Modification of TiN{Cl,H}_x(hda)_y with R‐/S‐methylbenzylamine (MBA) yields identical absorption and emission behaviors but exhibits distinctly opposite CD spectra, with a spectral coverage spanning from 230 nm to approximately 770 nm (Figure 11f) [222]. The more organized ligands in MXenoids make the material more suitable than random chemisorption examples for drawing analogies to from chiral perovskite. In the systems involving the above different materials, various chiral molecules have been introduced. However, the influence of different types of chiral molecules on individual materials has not yet been systematically investigated. For example, in the case of cysteine, the residue structure and carbon chain length may further affect the chiral strength [224]. Furthermore, the formation mechanism of chirality needs to be reconsidered, as structural distortion may play a crucial role if giant chiral responses are desired. The possibility of creating structural chirality on a larger scale warrants investigation. For example, in chiral hybrid organic‐inorganic perovskites, a slight enantiomeric excess can induce helical superstructural domains. However, such superstructural domains, or more macroscopic chirality, have not yet been observed in the aforementioned materials [225].

2.2.2. Adsorption and Intercalation

Non‐covalent interactions—such as electrostatic forces, hydrogen bonds, van der Waals forces, and π–π stacking—can also facilitate the binding of chiral molecules to 2D materials, typically through adsorption or intercalation [226]. Although these weaker interactions may not directly transfer chirality to the 2D material, the resulting chiral organic molecule‐2D material hybrid structures can exhibit both the inherent properties of the 2D material and chiral characteristics.

Similar to the covalent bonding discussed earlier, amino acids [227, 228] and cyclodextrin [229, 230] can also be immobilized onto GO via non‐covalent interactions, demonstrating promising performance in catalyzing aldol reactions and recognizing enantiomers, respectively. The interaction between 2D materials and adsorbates is bidirectional. For instance, 2D materials can alter the CD response of the adsorbates. In various 2D materials exfoliated with R/S‐1,1′‐bi(2‐naphthol) (BINOL), the changes of CD signals originate from multiple mechanisms, including plasmonic resonance, excitonic resonance, charge transfer, and adsorption enhancement [231]. On the other hand, adsorbates can modulate the electrical conductivity of 2D materials [232]. For example, by immobilizing acetylcholinesterase (AChE) on GO, the asymmetric interaction between AChE and chiral pesticide isomers is transferred to the GO substrate, enabling the fabrication of a flexible microelectrochemical sensor array [233]. Beyond these examples, several reports describe property changes in 2D materials induced by adsorbed chiral molecules [234, 235]. The helical structure of DNA can induce a giant asymmetric helical field. When DNA is wrapped around carbon nanotubes, it creates a spin filter effect [236, 237], with analogous phenomena observed in other assembly systems [238, 239]. While examples of DNA binding to 2D materials exist [240, 241], the extent of chirality induction achievable through such assemblies remains unexplored.

Compared to experimentally simpler adsorption methods, intercalation can dope each layer within the multilayer structure, rather than being confined to the outer surface. The characteristic weak van der Waals interactions between layered materials enable the free diffusion or electrochemically driven diffusion of guest molecules into the interlayer spaces. While decoupling within the interlayer and altering lattice parameters, guest molecules impart their own properties to the host 2D materials [242, 243]. Chiral organic molecules, such as R‐/S‐MBA, diffuse into TMDs, like TaS₂ and TiS₂, driven by concentration gradients during soaking, arranging into ordered structures along the interlayer direction via van der Waals interactions. This forms chiral molecular intercalation superlattices (CMIS), expanding the interlayer distance while preserving the properties of the individual monolayer TMDs (Figure 12a). The intercalated superlattice not only accommodates multiple layers of oriented chiral molecules within the interlayer space but also achieves a cumulative effect with increasing layer number, enabling strong spin‐polarized current transport. By integrating the spin‐filtering CMIS layer with the spin‐polarizing Cr₃Te₄ ferromagnet, a spin tunnel junction was fabricated, achieving a tunnelling MR ratio of more than 300% and a spin polarization ratio of more than 60% [186]. Notably, due to the absence of covalent bonding, the new and obvious CD response commonly observed in covalently functionalized systems discussed earlier was not detected here. A similarly high spin polarization was also observed in an intercalated MoS₂ system synthesized using the same hydrothermal intercalation [244]. Based on this, the strong spin filtering of CMIS enables the fabrication of spin electroluminescent diodes that operate at room temperature without magnetic components, achieving a polarization degree of 16.7% [245].

FIGURE 12.

Chiral molecule intercalated 2D materials. a) Schematic for intercalation of R‐ and S‐MBA chiral molecules into 2D materials. Adapted with permission [243]. Copyright 2024, Springer Nature Ltd. b) Schematic of TiS₂_PEA (MBA) superlattice stabilized by PEG, where intercalants are confined from escaping. Redrawn from Ref. [246]. c) Schematic for the electrochemical intercalation of CTA–SnSe₂ hybrid materials. Redrawn from Ref. [248].

Beyond transport, chiral molecules promote the oxygen evolution reaction (OER) in water electrolysis by reducing the H₂O₂ generation rate and increasing the O₂ (³Σ_g) generation rate [244]. In their subsequent work, using polyethylene glycol (PEG)‐stabilized R‐/S‐1‐phenethylamine (PEA, identical to MBA) intercalated into TiS₂ (Figure 12b), a spin polarization ratio nearing 100% was observed, along with significantly enhanced OER catalytic performance due to a giant increase in current density compared to the earlier MoS₂ system [246]. Chiral molecules also render 2D materials differentially responsive to other foreign chiral molecules, such as the SERS chiral recognition of L‐/D‐glucose using R‐/S‐MBA intercalated TaS₂ [247].

The non‐centrosymmetry created by chiral molecule intercalation into conventional superconductors may further enable chiral superconductivity. In R‐MBA‐intercalated TaS₂, an in‐plane upper critical magnetic field well beyond the Pauli paramagnetic limit was observed, along with a robust π‐phase shift in Little–Parks measurements and a field‐free superconducting diode effect [249]. The same H‐TaS₂ intercalated with chiral cations (L‐/D‐prolinium derivative tetra‐alkylammonium) is observed with T_c up to 4.9 K, surpassing that of monolayer H‐TaS₂ and other achiral‐cation‐intercalated H‐TaS₂. This elevated T_c originates from the stronger doping effect of the carboxyl‐containing chiral molecules. Similarly, an achiral superconducting transition at approximately 5 K is observed in electrochemically intercalated R‐/S‐3‐chloro‐2‐hydroxypropyltrimethyl‐ammonium (CTA)‐SnSe₂ (Figure 12c) [248]. Detailed mechanism and properties discussions are presented in Section 3.3.

Numerous reports have described CMIS and their properties, yet the specific orientations adopted by different chiral molecules within the layers remain elusive. It is also noteworthy that even achiral molecule intercalation can induce superconducting effects by breaking spatial inversion symmetry rather than time‐reversal symmetry. For instance, the Ising superconductivity characteristic of monolayers in bulk NbSe₂ is presented through intercalative decoupling [250], though this is distinct from chiral superconductivity. Further designing chiral intercalation molecules and investigating the mechanism of superconductivity in 2D chiral superlattices would provide a foundation for discovering more superconductors and their associated novel phenomena. Additionally, while the chiral inversion barrier is generally high for typical chiral molecules, certain molecules with stereo‐flexibility (e.g., (NH₃(CH₂)₂SS(CH₂)₂NH₃)²⁺ in perovskites) can undergo helical conformational inversion rather than orientational inversion under electric field polarization, leading to unique ferroelectricity [251], which has not been observed in 2D materials. However, it remains unclear whether alterations in the chirality of such enantiomeric molecules can induce distinct doping effects in 2D materials, as observed with geometric isomers [252].

2.2.3. Coupling With Chiral Spin‐Active Layers

Compared to the methods mentioned above that introduce various molecules, directly growing/transferring 2D materials onto the flat surface of chiral substances—whether 2D or bulk—is a simpler, more convenient, and non‐destructive approach. Such surfaces transfer their inherent chirality to the 2D materials through spin‐polarized electron filtering at the coupled interface, enabling properties like valley polarization without the need for magnetic fields or magnetic materials. Under optical excitation, spin‐polarized carriers are generated and selectively injected into specific valleys of the TMDs through the high‐quality van der Waals interface. This results in the TMDs to emit circularly polarized light, ultimately enabling the control of valley polarization. Meanwhile, if only the TMDs are excited, the role of the chiral material shifts from a spin source to a spin sink, extracting carriers exclusively from specific valleys, which can similarly result in valley imbalance.

Perovskites, with their strong absorption, tunable bandgap, robust SOC, and long carrier diffusion length, represent highly promising optoelectronic materials. Chiral molecules act as filters and break local inversion symmetry, introducing spin polarization into inorganic‐organic hybrid perovskites [39, 254]. It paves the way for chiral optoelectronics and spintronics [42, 255], such as selective transport of spin‐polarized electrons and circularly polarized luminescence (CPL).

Layered perovskites can be exfoliated into 2D structures and, similar to conventional 2D materials, form twistable stacking configurations with themselves or other 2D materials (Figure 13a,b) [256, 257]. This positions chiral 2D perovskites as strong candidates for constructing stacked heterostructures with unique chiral functionalities. Chiral 2D perovskites such as (R‐/S‐MBA)₂PbI₄ exhibit strong coupling effect and thus selectively inject spin‐polarized carriers into the K/K′ valleys of monolayer TMDs via type‐II band alignment, achieving valley polarization in TMDs excitons (Figure 13c,d) and interlayer excitons (Figure 13e,f) within TMD/perovskite heterostructures at 78 K. Notably, the (S‐MBA)₂PbI₄/WSe₂ heterostructure maintains ∼10% valley polarization even at 200 K [187, 188]. Similar chirality transfer phenomena have been realized in other exfoliable flat systems, such as 1D R‐/S‐1‐(1‐naphthyl)ethylammonium lead iodide (R‐/S‐NEA)PbI₃‐MoS₂[258] and lead‐free 0D (MBA)₄Bi₂I₁₀‐WSe₂ [259]. In these examples, the chiral perovskites function as spin extraction layers, leading to weaker emission and opposite control of valley polarization compared to the former cases. As a result, the facile tunability of perovskite structures and compositions offers diverse pathways for manipulating properties of 2D materials.

FIGURE 13.

Coupling 2D materials with chiral layers. a) Schematic for the crystal structure and b) optical micrographs of the chiral 2D perovskite/TMD heterostructure. Scale bar: 10 µm. c) Schematic for type II band alignment of (R‐MBA)₂PbI₄/MoS₂ heterostructures. d) Polarization‐resolved PL spectra of monolayer MoS₂ and it coupling with (R‐MBA)₂PbI₄, (S‐MBA)₂PbI₄, and (rac‐MBA)₂PbI₄ under a linearly polarized 532 nm laser excitation. Reproduced with permission [187]. Copyright 2020, American Chemical Society. e) Schematic for the formation of interlayer excitons in type‐II band alignment of (iso‐BA)₂PbI₄/WSe₂ heterostructure. f) Polarization‐resolved PL spectra of (S‐MBA)₂PbI₄/WSe₂ under σ⁺ (top) and σ^– (bottom) polarized excitation from a 633 nm laser. Reproduced with permission [188]. Copyright 2020, American Chemical Society. g) Schematic for the kgm and sql chiral COFs inject spin‐polarized electron into WSe₂. Percentages, degree of circular polarization under 78 K measurements. h) Schematic for charge transfer in type‐II and type‐I band alignment of TPE‐SQL/WSe₂ and TPE‐KGM/WSe₂ heterostructures, respectively. Adapted with permission [189]. Copyright 2026, American Chemical Society. i) Chirality in graphene nanoribbon helices. j) Schematic setup for reflectance microscopy on WSe₂/chGNR heterostructures, where a type‐II band alignment forms. k) Kinetic reflectance of WSe₂ exciton for σ⁺ versus σ^– pump on the WSe₂/R‐ or S‐chGNR [15] heterostructure. Reproduced with permission [190]. Copyright 2026, American Chemical Society. Adapted with permission [253]. Copyright 2025, Wiley‐VCH GmbH.

In addition to perovskites, other organic materials with lattice or structural chirality can also be used for spin injection and extraction. Exfoliable chiral COFs with two distinct networks, TPE‐KGM with only weak local geometric chirality and TPE‐SQL with amplified long‐range structural chirality, were synthesized based on Zn(salen). TPE‐KGM and TPE‐SQL form type‐I and type‐II band alignments with WSe₂, respectively. The resulting spin‐polarized charge transfer, similar to that observed in perovskites, leads to circular polarization degrees of 8.1% and 3.9% at 78 K, respectively (Figure 13g,h). Increasing the thickness of COFs enhances π‐π interactions, thereby improving spin polarization [189]. Chiral graphene nanoribbons (chGNRs) represent another class of organic materials capable of generating and modulating chirality (Figure 13i). The helical twist of their main chain is regulated through side‐chain functionalization, endowing the resulting chGNRs with strong chiral responses (|Δε| values up to 6780_M ⁻¹ cm⁻¹). Heterostructures with a type‐II band alignment were fabricated by spin‐coating a chGNR[∼15] solution onto WSe₂. Under selective excitation of WSe₂ excitons, σ⁺ pumping resulted in faster charge injection kinetics and higher steady‐state signal intensity compared to σ⁻ pumping, an effect that reversed upon chirality inversion and remained stable at room temperature (Figure 13j,k). Enhancing film uniformity and molecular alignment consistency could potentially further increase the polarization rate [190].

The modulation of valley polarization in TMDs by chiral layers is influenced by multiple factors, making it a multivariate complex system. For instance, temperature affects both the spin filtering efficiency at the interface and the intervalley scattering probability in TMDs [189], while doping resulting from the band alignment between the spin layer and TMDs influences the proportion of trions and other exciton states [260]. All these factors collectively determine the final degree of valley polarization. Leveraging tools like machine learning [261] to explore and understand how different chiral layers influence the degree of valley polarization in 2D materials—and to achieve strong valley polarization, especially at room temperature—may become one of the future directions in this field.

The aforementioned examples are all based on charge transfer between chiral layers and TMDs. Meanwhile, energy transfer—another mechanism that can facilitate chirality transfer—has not yet been reported in 2D material systems. For donors that exhibit strong PL and CPL, both relatively short‐range Förster resonance energy transfer (FRET) and longer‐range radiative energy transfer, offer promising pathways for coupling chiral emission into 2D materials [262, 263]. Further investigating whether such systems can achieve strong circularly polarized PL/electroluminescence (CPPL/CPEL) would significantly broaden their potential in application [264].

2.2.4. Coupling With Metamaterials

Metamaterials are artificial materials composed of subwavelength units. Due to their strong electromagnetic interaction with the light field, their most significant feature is the ability to control wavelength‐ and polarization‐selective complex diffraction, enabling arbitrary phase transformation and light field regulation. Metasurfaces, a 2D form of metamaterials, are thin nanostructured film arrays of these units [265, 266]. This size compatibility enhances their interaction with light compared to general chiral molecules. Meanwhile, the flexibility in structural design contributes to their functional diversity, making them among the most powerful candidates for introducing chirality. While some structural units possess intrinsic geometric chirality (e.g., helices), chiral metasurfaces do not necessarily require chirality at the structural level. Notably, even achiral structures can achieve regulatory effects similar to chiral metasurfaces, as microscopic faceting, rounding, and illumination direction can induce optical anisotropy [267, 268, 269].

Different structural designs lead to distinct underlying mechanisms. Besides carrier injection similar to aforementioned coupling with chiral layers, the most direct approach is that chiral metasurfaces generate strong chiral near‐field distributions, where the asymmetric localization of left‐ and right‐handed circularly polarized light results in unequal excitation of the two valleys in TMDs. For already formed excitons, the strong localized plasmonic modes of the metasurface can participate in the formation of polaritons [69, 270], thereby altering the rates of favorable exciton recombination and unfavorable spin flipping, ultimately enhancing valley polarization through the manipulation of exciton dynamics. Chiral metasurfaces can regulate not only the excitation process but also the emission process by the Purcell effect. This directionally enhances and radiates luminescence from one valley while suppressing the other, thereby significantly enhancing the observed far‐field valley polarization.

Metasurfaces can inject polarized electrons into valley materials like monolayer TMDs (Figure 14a,b), which are then detectable through the valley Hall effect [191]. The metamaterial design, rather than the absorptive material, dictates the detector's operating wavelength, making the fabrication of highly sensitive and broadband devices possible [271]. Besides the valley Hall effect, light emission involving electron transitions represents another aspect of spin‐polarized electron manipulation.

FIGURE 14.

Coupling of 2D materials with metamaterials. a) The calculated local enhancement of the optical chirality and b) schematic of hot carrier injection to valleys in MoS₂. Incident source laser, 1,550 nm. Black arrow, polarization direction. Scale bar: 40 nm. Reproduced with permission [191]. Copyright 2020, Springer Nature Ltd. c) Schematic for valley polarized emission from monolayer MoSe₂ on WS₂ metasurface. d) Polarization vector field distributions in the momentum space for different WS₂ metasurfaces. Reproduced with permission [192]. Copyright 2024, Wiley‐VCH GmbH.

The integration of metasurfaces with 2D materials offers remarkable versatility. This is first manifested in the design of nanostructures. For instance, the enhancement capabilities of chiral and achiral units can be compared to identify the role of chirality in the system. Single‐ and dimer‐Au‐prism arrays enhance both surface‐enhanced Raman spectroscopy (SERS) and PL intensity in WS₂ while imparting room‐temperature valley polarization. The enhancement ratio of the chiral dimer configuration significantly surpasses that of the achiral single one [272]. Moreover, the scope of the regulation targets has been extended. This is not only reflected in the selection of TMDs types, but also in the observation that valley polarization of interlayer excitons in heterostructures can be regulated by metasurfaces, exhibiting a strong correlation with CD [273]. Furthermore, apart from conventional exciton emission, spin‐valley‐exciton‐locked second‐harmonic generation (SHG) is observed at the excitonic resonances of the K and K′ valleys in monolayer WS₂ coupled with gold metasurfaces, and this SHG response is significantly enhanced by the localized plasmonic field [274].

Furthermore, the choice of metasurfaces has been greatly expanded. Beyond noble metal plasmonic metasurfaces, integrating monolayer TMDs with multilayer TMDs metasurfaces not only achieves valley‐polarized emission but also realizes ultrathin integrated platforms for controllable polarization and directional control in all‐TMDs systems (Figure 14c,d). Another reason for employing TMDs is the significant change in their refractive index near excitonic resonances. This enables metasurfaces made from TMDs to achieve superior electric field confinement and lower absorption loss compared to other materials (such as silicon) [192]. Other 2D materials like graphene can not only serve as substrates for conventional metasurfaces [275, 276], but also be patterned into metasurfaces themselves, acting as chiral sources to introduce chirality into 2D materials [277, 278, 279, 280]. Numerous additional examples have shown high valley‐polarized PL [281, 282, 283, 284]. Besides regulating valley‐polarized luminescence, chiral metasurfaces can also induce CD responses in TMDs [285]. Moreover, the twisted stacking strategy, as mentioned earlier, has attracted significant attention and research in metasurface fabrication due to its highly flexible tunability [69, 286, 287, 288, 289]. However, the application of twisted‐stacked bilayer metasurfaces based on 2D materials, especially for modulating 2D materials, remains unexplored.

The regulation of valley excitons in TMDs extends well beyond metasurfaces.​ Optical cavities that exhibit asymmetric reflectance for left‐ and right‐handed circularly polarized light also serve as excellent platforms for chirality injection [290, 291]. This regulation can be achieved through various structural designs. Discrete nanostructures, for instance, enable control in a localized area. MoS₂ interacting with silver nanoparticles achieved 48.7% valley polarization at room temperature [292], while self‐assembly of fused‐silica microsphere enhanced WSe₂ valley polarization at low temperatures by promoting the recombination decay rate and reducing intervalley scattering rate [293].

Beyond individual nanoparticles, designed periodic photonic structures​ provide another effective strategy. Circular Bragg gratings coupled with TMDs generated valley polarization, where the geometric symmetry enables directional outcoupling of emitted photons [294]. Based on the effective modulation of metasurfaces, 43% valley polarization of MoS₂ was observed in gold chiral metasurface‐gold layer cavities [295], with similar phenomena reported in other systems [296]. Furthermore, cavities with wide‐range continuous tunability​ are particularly intriguing, as they allow for in‐situ adjustments of the operational band and enhance the modulation strength. For example, stereoscopic antennas—tuned via AFM with MoS₂ sandwiched between two gold nanorods—demonstrate that the valley‐polarization can be modulated by altering the antenna configuration [193]. Analogous to twisted stacking in 2D materials, the formation of tunable modes is achieved by rotational stacking of periodic gold nanohole array cavities, thereby regulating the radiation dynamics of WSe₂ valley excitons [297].

This highly tunable structure also raises another intriguing question: can the chirality of the nanostructures be dynamically regulated in‐situ through simple operational conditions, and simultaneously exert opposite effects on 2D materials? Specifically, resonant absorption of circularly polarized light irradiation alters the local electric field and temperature distribution, thereby influencing the formation and stabilization of the two chiral nanoparticle enantiomers. Under the same coupling strength, switching the chirality of the nanoparticles offers an additional dimension of control over the luminescence of the 2D material [298, 299].

Beyond structural design modifications to enhance metasurface capabilities, the engineering of external excitation light fields (e.g., vortex beams carrying orbital angular momentum) can unlock novel optical modes [300], enabling expanded tunability. Also, for 2D materials themselves, the design of nanocavities enables probing of a wider range of exciton states, such as dark excitons [301]. Another noteworthy consideration in structural design is the influence of stress induced by the uneven surfaces of micro‐nanostructures on the material itself, especially given that valley polarization is modulated by strain [302, 303]. In addition, different environments (e.g., silica, metals, suspended) may introduce varying degrees of weak doping and degradation effects, which could also affect the experimental results [304, 305].

3. Properties and Applications of 2D Chiral Materials

Chirality introduces numerous novel properties into 2D materials, which in turn provides a criterion for confirming its presence within the system. In terms of optics and electronics, beyond structural asymmetry, the fundamental nature of chirality is a helical potential field that influences electron motion. This can lead to SOC, giving rise to a series of phenomena based on this mechanism. For chemistry, chirality manifests more prominently through the CISS effect and chirality‐dependent interaction forces, exhibiting properties such as catalytic activity and differential effects on enantiomers. At its core, chirality originates from the asymmetric interaction between the chiral host and the chiral guest. Owing to their intrinsic spin angular momentum, the concept of chirality can be extended to electrons and photons.

3.1. Chiroptics

Circularly polarized light originates from the ±90° phase difference between mutually perpendicular electric and magnetic field vectors. The symmetry breaking induced by chirality disrupts the orthogonality and phase difference between the induced electric dipole moment and magnetic dipole moment. Consequent unequal interference effect further influences the absorption and emission processes, giving rise to phenomena such as CD and CPL [4].

Another remarkable property of circularly polarized light is its locking to valleys, which are defined as local extrema in the conduction and valence bands. 2D materials, particularly monolayer TMDs, exhibit broken spatial inversion symmetry, leading to strong Ising‐type SOC and two energy‐degenerate valleys with opposite pseudospins. This causes valley‐dependent spin splitting and links spin to valley index—known as spin‐valley locking. It also determines optical selection rules: right‐ and left‐handed circularly polarized light correspond to accessing the K and K′ valleys, respectively. In the absence of intervalley scattering induced by phonons or electron‐hole exchange interactions [306, 307], carriers can be asymmetrically distributed between the two valleys, creating valley polarization under selective excitation or doping. This provides a valley degree of freedom, similar to spin, forming the basis of valleytronics [308, 309, 310, 311]. Many‐body interactions can further lead to more complex excitonic states [312].

3.1.1. Circularly Polarized Emission

CPL arises from the differential emission of left‐ and right‐handed circularly polarized light by chiral substances under unpolarized excitation. Beyond its development as a spectroscopy technique for probing material chirality and band structures, CPL has attracted extensive research interest in optical information storage and encryption due to its inherent polarization information [313]. Chiral perovskites represent a typical class of materials with strong CPL. Their 2D forms can also generate it, and the quantum yield and asymmetry factor can be controlled through composition and structural design [314, 315, 316]. This property is likely extendable to other 2D materials. For example, theoretical calculations indicate that chirally stacked TMDs can generate circularly polarized PL under non‐resonant pumping conditions [317], which has been observed in interlayer moiré excitons within twisted MoSe₂/WSe₂ heterostructures. This emission is independent of incident light polarization but significantly diminishes under an out‐of‐plane magnetic field [318].

Crucially, when excitation light carries angular momentum (i.e., circularly polarized light), the differential population distribution of carriers with distinct spins enables circularly polarized PL under circularly polarized excitation. When excited by right‐handed (σ⁺ ) circularly polarized light, the relative difference in intensity between emitted right‐handed and left‐handed (σ⁻ ) circularly polarized light is defined as the valley polarization degree, expressed by the following formula:

$${\rho }_{{\sigma }^{+}}=\frac{I_{{\sigma }^{+}}-I_{{\sigma }^{-}}}{I_{{\sigma }^{+}}+I_{{\sigma }^{-}}}\times 100\%$$ (1)

where $I_{{\sigma }^{+}}$ and $I_{{\sigma }^{-}}$ denote the PL intensity of the right‐ and left‐handed circular component, respectively. For excitation with left‐handed circularly polarized light, the subtraction order in this formula is reversed. This phenomenon can also occur in non‐chiral materials due to SOC‐induced valence band splitting into levels with different angular quantum numbers. Thus, chirality contributes in two ways: enabling spin‐selective charge transfer and enhancing SOC. Also, the external electromagnetic field may regulate the scattering and recombination rate of carriers (Figure 15).

FIGURE 15.

Schematics for valley‐dependent optical selection rules and valley polarization in TMDs. Valence and conduction bands are split because of SOC. The excitation and recombination processes are polarized due to spin‐valley locking. Carrier injection and intervalley scattering will cause the redistribution of the spin population.

Spin‐selective charge transfer enables carriers with a specific spin to be selectively injected into or extracted from a spin‐allowed valley, creating an uneven charge distribution between valleys. Chiral substances, especially chiral perovskites and COFs, can efficiently inject spin‐polarized carriers into TMDs (Figure 13c–h) [187]. In experimental measurements at a given temperature, when a specific valley is excited using circularly polarized light of a particular handedness, spin‐selective charge transfer disrupts the equilibrium in carrier populations between the valleys. This alters the original emission ratio from the two valleys, effectively modifying the material's intrinsic degree of valley polarization. Alternatively, linearly polarized light—which contains equal amounts of left‐ and right‐handed circularly polarized components—can simultaneously excite both valleys identically. If spin‐charge transfer occurs, the emission intensities from the two valleys become unequal. This imbalance is manifested as a mismatch between the left‐ and right‐handed circularly polarized components of the emitted light, which corresponds to normal CPL tests. Electromagnetic interactions between superchiral near fields induced by metasurfaces and spin‐distinct excitons modulate exciton radiation across different valleys (Figure 14a) [295].

In addition to spin injection, the redistribution of charge polarization within chiral molecules can mimic the effects of an external magnetic field [319, 320], breaking valley degeneracy to manipulate valley excitons [321, 322]. The spin splitting between valleys is amplified by charge redistribution in chiral molecules and their participation in strong orbital hybridization [234]. Chiral molecules can disrupt local symmetry in perovskite lattices, inducing chirality within inorganic frameworks [323]. Similarly, covalent functionalization can partially disrupt graphene's sp²‐conjugated planar structure, creating localized lattice distortions; however, it remains unexplored in TMDs.

3.1.2. Circular Dichroism

CD refers to the differential absorption of left‐ and right‐handed circularly polarized light by a material (Figure 16a). The strength of CD activity is termed g‐factor, defined as follows:

$$g=\frac{\mathrm{\Delta }A}{A}=\frac{A_{{\sigma }^{-}}-A_{{\sigma }^{+}}}{(A_{{\sigma }^{-}}+A_{{\sigma }^{+}})/2}\times 100\%$$ (2)

where A represents the absorbance of different circularly polarized light. In practical measurements, the transmittance of left‐handed and right‐handed light differs, resulting in receiving elliptically polarized light rather than linearly polarized light. Simultaneously, the absorption difference is very small, and a first‐order expansion yields the ellipticity θ in mdeg of the combined light as:

$$\theta =1000\left(\frac{\ln 10}{4}\right)\left(\frac{180}{\pi }\right)(A_{{\sigma }^{-}}-A_{{\sigma }^{+}})=32980\mathrm{\Delta }A$$ (3)

FIGURE 16.

CD in chiral 2D materials. a) CD spectra in chiral TBG. b) CD plot of chiral TBG. Top inset: Schematics for CD measurement. Bottom inset: Dirac cone alignment from the top layer (blue) and bottom layer (yellow) of TBG. Adapted with permission [49]. Copyright 2016, Springer Nature Ltd. b) UV–vis absorption spectra of exfoliated MoS₂ without functionalization and with cysteine and penicillamine. c) CD spectra of D‐/L‐penicillamine functionalized MoS₂. The peaks originate from the hybrid structure rather than the ligands themselves. Adapted with permission [60]. Copyright 2018, American Chemical Society.

Ellipticity can only represent the chirality of the entire system, rather than the chiral strength per unit or per structural unit of substance. For quantitative analysis, molar ellipticity is conventionally employed, defined as:

$$\left[\theta \right]=\frac{\theta }{cl}=32980g\epsilon$$ (4)

where c is the molar concentration, l is the path length, and ε is the average molar absorption coefficient. Note that the numerical values may be adjusted according to the choice of units.

The distinct absorption of chiral materials toward oppositely polarized light establishes CD as a powerful spectroscopic probe. While CPL focuses on excited‐state properties, CD targets the excitation process itself. This enables CD to probe materials with low luminescence quantum yields, broadening its applicability. However, its ability to detect transitions that do not terminate in a thermally accessible ground state or involve non‐direct processes is limited. Therefore, detailed studies of transitions require comparative CD/CPL investigations [324]. For typical organic molecules, symmetric positive/negative peaks in CD spectra indicate preferential absorption of circularly polarized light by electronic transitions in chiral chromophores. Beyond chiral carbon atoms bonded to four distinct functional groups, larger chiral structures—even those lacking chiral carbons—can generate CD signals [177]. CD spectroscopy thus infers potential material structures, such as probing the secondary structures of proteins [325]. CD activity in achiral nanostructures can be induced via extrinsic chirality [326], encompassing pre‐existing chiral environments, charge transfer mechanisms, and emergent chiral configurations [327]. Consequently, engineered chiral structures can generate CD in specific spectral regions [328, 329]. Enhanced or shifted optical activity at original wavelengths, alongside new activity at other wavelengths, characterizes chirality introduction.

In chiral 2D structures, CD arises intrinsically from electronic transitions without guest chiral species. As the scales of macroscopic chiral structures approach optical wavelengths, their CD g‐factors exceed those of typical small chiral molecules [330]. Take TBG for an example: its absorption peaks originate from interlayer electronic transitions at van Hove singularities generated by overlapping mismatched Dirac cones in momentum space [331, 332]. When the Dirac cones (K and K′) of one layer asymmetrically couple to those of the adjacent layer (i.e., twisted angles ≠ 30°), two absorption peaks emerge with distinct dependencies of energy and polarization. For a given peak, the twisted direction dictates the CD sign h (Figure 16a) [49]. Detailed theoretical derivations of this model can be found in Ref. [333, 334, 335]. This framework also explains twisted structures in materials like TMDs. CD responses originate from the C‐exciton at the deep energy gap, with intensity varying sinusoidally with stacking angle (C₃ symmetry with a rotation period of 120°) and linearly with layer count [83]. Similar phenomena occur in chirality‐induced structures like nanoscrolls [135, 136], nanospirals [56, 57], and stirred porous GO membranes [62, 178], where CD peaks correlate with the material's intrinsic electronic transitions.

For 2D materials incorporating guest chirality, beyond introducing long‐range [60, 336] or local asymmetry [329, 337], chiral transfer occurs via electronic hybridization at the interface—manifested as spatial overlap between the wavefunctions of ligands and excitons of host materials. The new Cotton peaks in the CD spectrum can correspond to the transition peaks in the UV–vis absorption spectrum (Figure 16b,c) [60, 183]. This differential absorption leads to different photocarrier concentrations, which can be utilized for circularly polarized light detection. Furthermore, when transitions in the ligand's chromophore interact with material transitions, exciton coupling splits excited states, generating bi‐signate peaks above and below the original transition energy [338, 339].

Compared to materials with chiral structures and chiral covalent modifications that exhibit solid new CD responses, CMIS exhibits contradictory CD results. Weak non‐bonding interactions (e.g., MBA‐intercalated TaS₂ superlattices) exhibit CD signals indistinguishable from the intrinsic optical activity of the chiral molecules alone (Figure 17a,b) [186]. Similarly, due to the weak but present electronic effect, the PEA (MBA)‐intercalated TiS₂ exhibits slight differences in CD signals compared to the molecule itself (Figure 17c,d) [246]. In contrast, the MBA‐intercalated MoS₂ displays new CD peaks (Figure 17e,f), possibly originating from significant excitonic modulation by the organic molecules [244]. The origin of this discrepancy—whether it stems from differences in the interaction strength between intercalants and 2D materials or arises from experimental condition biases and errors [340]—remains unresolved.

FIGURE 17.

CD changing in chiral molecule intercalated 2D materials. a) CD spectra of R‐ and S‐MBA in isopropanol (IPA) and b) intercalating into H‐TaS₂. The positions of the CD peaks remain unchanged. Reproduced with permission [186]. Copyright 2022, Springer Nature Ltd. c) CD spectra of R‐ and S‐PEA (MBA)·HCl in ethanol and d) intercalating into 1T‐TiS₂. The positions of the CD peaks exhibited slight shifts. Reproduced with permission [246]. Copyright 2023, Wiley‐VCH GmbH. e) CD spectra of R‐ and S‐MBA in ethanol and f) intercalating into MoS₂. A series of new peaks after 300 nm is observed. Adapted under terms of the CC‐BY license [244]. Copyright 2022, The Authors, published by Wiley‐VCH GmbH.

3.1.3. Nonlinear Optics

NLO refers to the phenomenon where, when light irradiates a material, the polarization density P(t) does not change linearly with the intensity of the electric field E(t), which can be expressed as follows:

$$P\left(t\right)={\chi }^{\left(1\right)}E\left(t\right)+{\chi }^{\left(2\right)}E{\left(t\right)}^2+{\chi }^{\left(3\right)}E{\left(t\right)}^3+\cdots$$ (5)

where χ⁽ⁿ⁾ denotes nth order susceptibility. Since NLO processes diminish exponentially with increasing order n, SHG, with an exponent of 2, has attracted the most attention [341]. In SHG, ground‐state electrons can be excited to virtual states rather than real energy levels [342]. The SHG polarization density $P_i^{(2)}(t)$ can be expressed as follows:

$$P_i^{\left(2\right)}\left(t\right)=\epsilon {\mathrm{\Sigma }}_{jk}{\chi }_{ijk}^{\left(2\right)}{E}_i{E}_j{e}^{-2i\omega t}$$ (6)

where ${\chi }_{ijk}^{(2)}$ (or χ² ) is a rank‐3 tensor related to the symmetry. The generation and enhancement of SHG can be considered through two variables in the equations [343]. First, in crystals with inversion symmetry, χ² is always zero. Therefore, breaking this symmetry can induce an SHG response. For instance, strong SHG is observed in monolayer MoS₂, but not in AB‐stacked bilayers (2H‐MoS₂) [344]. Second, the local optical environment can be modified to enhance the optical field and its interaction with the material [345]. The structural diversity and tunability of 2D materials have sparked extensive discussion in the field of NLO [341, 342].

Chiral molecules can induce asymmetric structural distortions in perovskites, generating SHG [346, 347]. However, whether chiral molecules or other chiral sources can similarly break band degeneracy to produce chiral nonlinear optics remains unexplored. Similarly, in TMD materials, valley‐spin selectivity enables multiphoton processes to correlate with circularly polarized light [348]. Just as with valley‐polarized luminescence, SHG can be enhanced by designing metasurfaces to achieve spin‐valley‐locked nonlinear selection rules [274].

In chiral structures, alterations to crystalline symmetry and electronic structure induced by twisting deformation can also modulate the second‐harmonic generation response. Symmetry breaking in nanoscrolls during sheet bending activates SHG, with signal strength dependent on bending orientation and curvature and potentially linked to scroll chirality [141]. Going a step further, this system also exhibits SHG‐CD governed by the chiral angle, which manifests as a difference in SHG intensity between left‐ and right‐circularly polarized excitation (Figure 18a,b). The CD‐active response of SHG here is attributed to dipolar Mie resonance [138]. In TMD supertwisted spirals, interlayer crystalline symmetry breaking enhances SHG [163], which can be tuned by not only excitonic resonance but also resonances involving large inter‐band Berry connections contributing to specific high‐energy optical transitions [349]. While the SHG signatures of helical structures are impressive, their correlation with chirality (i.e., the direction of screw dislocation and interlayer twist) has not yet been established. Chiral NLO responses have been observed in chiral perovskites [350, 351, 352, 353]. In contrast, although monolayer TMDs exhibit strong intrinsic SHG responses, no similar phenomena have been reported after chirality functionalization.

FIGURE 18.

SHG‐CD in chiral nanoscroll. a) Schematic for SHG‐CD measurement of MoS₂ nanoscroll. There is a difference in SHG intensity when the incident light possesses the opposite direction of circular polarization. b) SHG‐CD as a function of chiral angle. Inset: Chiral angle is defined as the angle between the scroll axis and an armchair edge. Reproduced with permission [138]. Copyright 2025, American Chemical Society.

3.2. Spintronics

When spin‐bearing charges (such as electrons) move through an ordered chiral structure, spin polarization occurs due to SOC, manifesting as observable spin currents. Specifically, considering a simple helical motion model, the chiral electrostatic field provides electrons with a centripetal force perpendicular to their direction of motion, causing them to follow a helical trajectory. This effect is analogous to that of the Lorentz force, generating an equivalent chiral magnetic field. This field interacts with the electron's magnetic moment, linking its momentum and spin—thereby inducing SOC. When electrons move along a specific direction within a chiral molecule, one spin orientation becomes stabilized while the other is destabilized. Consequently, one spin state exhibits a higher tunnelling probability and lower spin relaxation rate [354]. According to the Boltzmann distribution, the orbital splitting must be sufficiently large—meaning the strength of SOC must be substantial—to ensure that the backscattering probability without spin relaxation remains low enough to produce strong spin polarization. Note that CISS effect and other phenomena related to spintronics remain largely debated, the model above provides the most simplified understanding. For a comprehensive theory framework, readers can refer to Ref. [3, 354, 355]. for more information.

3.2.1. Spin‐selective Transport

Voltage‐driven spin‐selective transport of carriers in a two‐terminal device is the most direct manifestation of the CISS effect. One terminal is used to inject carriers with a specific spin, while the other receives the signal. For channels of different chirality, carriers of the same spin exhibit distinguishable nonlinear current‐voltage responses. Conductance is higher when the spin direction is parallel to the preferred direction, enabling chiral materials to act as spin valves. Here, the definition for polarization degree parallels that employed in valley‐polarized luminescence. Besides custom‐made ferromagnet‐channel‐metal structures, magnetic conductive atomic force microscopy (mc‐AFM) can be used to probe the transport characteristics in selected micro‐regions, where the ferromagnetic probe tip becomes polarized under the influence of a magnet.

Extrinsic chiral sources (primarily chiral organic molecules) inherently possess spin‐polarized transport characteristics, which are preserved upon integration with 2D materials. In 2D material‐chiral molecule hybrid structures, the 2D material primarily serves as a substrate and connector; if its influence on the chiral molecule's structure and polarization is neglected, it does not significantly contribute to spin‐polarized transport. A typical example is the superlattice formed by intercalating chiral molecules into TMDs. These chiral molecules can arrange orderly between layers with nitrogen atoms oriented towards the 2D material layers, promoting specific orientations that enhance the CISS effect (Figure 19a). Due to the series effect of multilayer tunnel junctions, exceptionally high spin selectivity is achieved (Figure 19b,c). Because organic chiral molecules play the decisive role in CISS, superlattices intercalated with racemic mixtures exhibit no significant spin selectivity (Figure 19d) [244].

FIGURE 19.

Spin‐polarized transport in chiral 2D materials. a) Schematic for c‐AFM of R‐/S‐/rac‐MBA_MoS₂. b–d) I–V curves of R‐/S‐/rac‐MBA_MoS₂. Reproduced under terms of the CC‐BY license [244]. Copyright 2023, The Authors, published by Wiley‐VCH GmbH. e) Determination of CISS in chiral graphene structures by applying spatial inversion (P), time inversion (T), magnetic field (B), and electric field (E). f,g) I–V curves of right‐ and left‐handed rolls. Adapted under terms of the CC‐BY license [359]. Copyright 2025, The Authors, published by Tsinghua University Press. h) Spin polarization structure of achiral and chiral rolls in the momentum space. s_y denotes the spin polarization along the tangential rolling direction. Spin flip symmetry is broken in the chiral roll. i) Spin selectivity for Dirac fermions near Fermi energy. Reproduced with permission [52]. Copyright 2025, Springer Nature Ltd.

Unlike organic molecules, chiral structures may exhibit chiral optical responses but not necessarily spin‐selective transport. This reveals a critical issue: judging chirality solely based on spatial inversion asymmetry is insufficient to predict the chirality‐induced spin selectivity (CISS) effect. Here, the concept of true and false chirality proposed by Laurence D. Barron must be introduced [356, 357, 358]. Specifically, the two enantiomeric states cannot be interconverted by any combination of time reversal (T), spatial inversion (P), and spatial rotation operations (R_π). Only when a system possesses spatial chirality (false chirality) and remains invariant under time reversal operation, does it exhibit true chirality. In other words, chirality should not rely on time‐reversal symmetry breaking. This concept is particularly suitable for explaining the origin of the CISS effect. During the CISS process, the filtering effect of a chiral potential couples two physical quantities: the momentum associated with translational motion and the spin angular momentum from intrinsic rotation. The former changes sign under both P and T, while the latter only changes sign under T. In the case of having only spin angular momentum, P and T can be made equivalent by introducing an additional rotation. However, in the presence of momentum, it becomes impossible for both momentum and spin angular momentum to maintain synchronized sign changes under inversion. That is, the symmetry of the system fundamentally differs depending on whether momentum is involved. When electrons pass through a chiral structure, both P and T operations must be considered simultaneously; otherwise, there is no symmetry basis for coupling electron momentum and spin angular momentum. Therefore, the CISS effect should arise from the material's intrinsic SOC, rather than from external time reversal symmetry‐breaking fields such as magnetic fields.

Applying this theoretical framework to relevant systems, electron motion is governed by electric and magnetic field vectors: the former changes sign only under P, and the latter only under T. According to this model, chiral carbon nanotubes, twisted‐stacked graphene, and the axial direction of chiral carbon nanoscrolls are false chiral systems. Only the radial electron motion in chiral carbon nanoscrolls exhibits true chirality (Figure 19e). Here, we identify that the source of asymmetry lies in the trajectory of electrons moving along the surface. In other words, while structural chirality provides the foundation for “true chirality,” the actual spin‐selective transport is realized through the dynamic process of charge moving along an asymmetric path within the structure [359]. In fact, although this theory has not been widely discussed, most chiral molecules already experience the effect of true chirality in their wavefunctions, thereby exhibiting the CISS effect. The concept of true and false chirality contributes significantly to a deeper understanding of the CISS effect, yet a more robust and universal theory is still needed to connect them.

Chiral nanoscrolls exhibit spin‐selective transport only radially in the semiconducting state (Figure 19f,g), while it is not significantly observed axially as mentioned before [52]. For graphene scrolls, electron spin polarization characteristics, which are dependent on chiral angle, are shown in Figure 19h,i. Electrons on curved surfaces, influenced by SOC and rolling curvature effects, achieve polarization rates up to 90% at room temperature. This also provides a basis for the absence of spin‐selective transport in the metallic state: the density of states at the conduction band bottom is higher in semiconductors and susceptible to spin splitting induced by Van Hove singularities, which are absent in the metallic phase [52]. Note that the symmetry results arising from chirality‐related electrical transport in Figure 2d have not yet been correlated with this model, as they do not fall within the domain of spin‐polarized transport, and electrons propagate laterally within the layers rather than penetrating vertically.

3.2.2. Magnetoresistance

When electrons move through a magnetic field, their trajectories are curved by the Lorentz force, leading to an increased resistance. This ordinary magnetoresistance (OMR) effect, however, takes on a completely different nature when the spin‐dependent scattering of electrons in a magnetic field is considered. In the giant magnetoresistance (GMR) effect, ferromagnetic layers act as filters, allowing only electrons with spins aligned in a specific polarization direction to pass through more easily. This mechanism closely resembles the CISS effect [360]. Magnetic fields are used to induce ferromagnets to inject spin‐polarized carriers, rather than to influence chiral channels. Applying magnetic fields with equal magnitude but opposite directions yield unequal resistance measurements. The magnetoresistance effect and the spin‐selective transport mentioned in the previous subsection differ in that they respectively reflect the voltage‐bias and the magnetic‐field dependence of resistance or conductance.

Devices with spin‐selective transport can simultaneously exhibit MR effects. For example, in the CMIS mentioned earlier, abrupt changes in current occur when the magnetic field strength exceeds the coercive field of the ferromagnetic material [186]. The MR curve of such a spin valve displays step‐like features determined by the ferromagnetic layers, with the direction dependent on the spin‐filtering layer (Figure 20a,b). In contrast, supramolecular‐functionalized graphene nanoribbons exhibit distorted MR curves; after separating the symmetric even‐function component, the odd‐function component shows characteristics similar to those of chiral‐molecule‐intercalated superlattices (Figure 20c,d). This MR effect can be attributed to the structural chirality and deformation and magnetic effects of local impurities jointly enhancing the SOC [174].

FIGURE 20.

Magnetoresistance in chiral 2D materials. a, b) Magnetic‐field‐dependent tunnelling current measured in the R‐/S‐MBA/H‐TaS₂ CMIS. Adapted with permission [186]. Copyright 2022, Springer Nature Ltd. c,d) Odd (main) and even (insets) components of the asymmetry magnetoresistance response in single‐layer and multi‐layer graphene with D‐/L‐Fmoc‐FF. Reproduced under terms of the CC‐BY license [174]. Copyright 2023, American Chemical Society.

For the graphene nanoscrolls mentioned earlier, although spin‐selective transport was not observed along the axial direction, MR effects were consistently detected. The shape of the MR curve is influenced by chirality [52], resembling previous observations of MR in TMD nanoscrolls [143]. Similarly, while spin‐selective transport has not been observed in twisted graphene, twisted graphene spirals also exhibit significant MR [165]. Nevertheless, this MR effect fundamentally differs from that in chiral molecules. Due to the absence of spin selectivity, the spin population of electrons in the channel depends solely on the direction of the applied magnetic field rather than on both the field direction and the material itself [360]. Consequently, disregarding hysteresis, MR becomes independent of magnetic direction, displaying a symmetric curve [361].

Phonons, or molecular vibrations, open new transport channels for spin transmission through electron‐phonon coupling [362, 363]. Chiral organic molecules in contact with non‐ferromagnetic metals can generate thermally driven spin polarization, exhibiting MR that increases with temperature [364]. This behavior has not yet been observed in typical 2D material/chiral molecule structures. The electrical transport characteristics of other chiral structures, such as helices, have also been studied [148], but spin‐related transport in these systems awaits further exploration.

3.2.3. Spin Hall Effect

In the absence of an external magnetic field and when the material itself lacks intrinsic magnetism, if the material possesses SOC, it can induce distinct motion for electrons with opposite spins. Under an applied bias, this results in deflection in opposite directions, generating a transverse net spin flow. This phenomenon does not violate the time‐reversal symmetry present within the system and is known as the spin Hall effect [365]. If the number of spin‐up and spin‐down electrons is unequal, as in ferromagnetic materials, a Hall voltage can be detected, referred to as the anomalous Hall effect. In TMDs, the two valleys exhibit opposite effective magnetic fields associated with Berry curvature, leading to the aforementioned valley polarization phenomenon. Analogous to the spin Hall effect, valley carriers driven by an electric voltage experience a Lorentz force due to this effective magnetic field during transport, giving rise to the valley Hall effect. Here, carriers from the two valleys with opposite spins deflect in opposite directions, producing a spin current perpendicular to the bias direction. If a population imbalance of valley carriers is created via methods such as circularly polarized light excitation or spin‐selective charge injection, the valley Hall effect can be experimentally observed by measuring the Hall voltage [366, 367].

In supertwisted spirals featuring helical moiré patterns that match the wavelength of light, the response of higher‐order quantum geometric quantities to photon momentum leads to the opto‐twistronic Hall effect. Here, the magnetic field is replaced by polarized light, resulting in a polarization‐dependent Hall voltage. When the twisted angle of the structure or the direction of incident circularly polarized light is reversed, the Hall voltage response inverts (Figure 21a,b). This response also exhibits layer‐ and wavelength‐dependence [368]. Plasmonic near‐field electron injection from a metasurface into a 2D material under optical excitation can directly generate valley‐polarized carriers, producing the valley Hall effect (Figure 21c,d) [191, 271]. Similarly, the proximity effect of chiral molecules can modulate the electronic states of a surface ferromagnetic layer, inducing a chirality‐dependent anomalous Hall effect. This is attributed to chiral phonons carrying angular momentum coupling to the ferromagnetic order at the interface, thereby breaking time‐reversal symmetry. Alternatively, it may arise from spin‐polarized dipoles selecting a preferred magnetization direction through molecular vibrations and spin‐selective charge transfer (Figure 21e) [319, 369].

FIGURE 21.

Hall effect in chiral 2D materials. a,b) Schematic and spectra of Hall conductivity σ_HC (C denotes the part dependent on circular polarization) in +8° and −8°WS₂ supertwisted spiral. Reproduced with permission [368]. Copyright 2024, Springer Nature Ltd. c) Schematic for valley Hall effect device composed of MoS₂ and chiral plasmonic antennae array. d) Valley Hall voltage as a function of V_ds. Linearly polarized lasers (1,550 nm and 532 nm) illuminate the region around the source (S) and drain (D) electrodes. Adapted with permission [191]. Copyright 2020, Springer Nature Ltd. e) Schematic for spin‐polarized electron transfer to molecules with opposite chirality (top). Imbalances in spin populations cause magnetization (bottom). Adapted under terms of the CC‐BY license [319]. Copyright 2017, The Authors, published by Springer Nature Ltd.

3.3. Superconductivity

Chiral superconductivity refers to a state where the phase of the complex superconducting order parameter exhibits chirality as it varies along the Fermi surface, meaning that it changes in opposite directions, requiring the breaking of time‐reversal symmetry [370]. Introducing chiral molecules into conventional superconductors may break time‐reversal symmetry, creating chiral superconductivity. Currently, this process has only been achieved via intercalation, which serves as an effective method for modulating superconductivity [371]. In liquid intercalated 2H‐TaS₂/R‐/S‐MBA chiral organic/inorganic superlattices, researchers observed an intrinsic superconducting diode effect without an external magnetic field, which is absent in the pristine material, demonstrating successful breaking of time‐reversal symmetry. Simultaneously, this structure exhibits an in‐plane upper critical magnetic field significantly exceeding the Pauli paramagnetic limit [249]. However, this unconventional Ising superconductivity cannot be induced by molecular chirality alone, as evidenced by dissipationless transport showing no signs of inversion‐symmetry breaking [372]. The origin of this superconductivity may not necessarily be the intercalated chiral molecules, but rather could arise from Josephson coupling between adjacent layers [373]. This effect requires further investigation as the mechanism is not systematically explored. As for electrochemically intercalated R‐/S‐CTA‐SnSe₂, although the inserted molecules are chiral, the mechanism differs fundamentally from that of chiral superconductivity. The racemate inserts more readily due to stereo‐complementarity, and the stronger decoupling effect leads to enhanced superconductivity [248].

3.4. Catalysis

The edges and defects of 2D materials can serve as active sites to participate in reactions. When combined with active catalysts such as single atoms, they can synchronously enhance the catalytic activity of both the 2D material and the catalyst through intense charge transfer, providing an exceptionally large catalytic active area [374]. The adsorption of chiral ligands onto achiral materials may replace or block active sites [375]. However, the inherent attraction and steric hindrance of the ligands can form selective interactions with reactants, enabling chirality‐dependent enantioselective catalytic processes [376]. More importantly, the CISS effect allows chiral catalysts to induce parallel electron spins in reactant intermediates at active sites via charge transfer, promoting the reaction and suppressing side reactions [377].

For instance, in water‐decomposition reactions, electrons under general conditions align with antiparallel spins, causing •OH radical intermediates to adsorb onto singlet‐potential active sites. This leads to the formation of hydrogen peroxide or singlet oxygen (¹Δ_g), which competes with the main reaction and produces toxic byproducts, thereby reducing catalyst activity. In contrast, when the catalyst is chiral, the •OH radicals exhibit parallel electron spins. Triplet‐potential states catalyze the conversion of •OH radicals into O₂ (³∑_g), a state that cannot form hydrogen peroxide. Thus, the CISS effect suppresses hydrogen peroxide formation, thereby enhancing the efficiency of the main reaction [378]. CMIS is capable of achieving the aforementioned effects, and its immobilization on glassy carbon electrodes enables efficient and selective OER reactions (Figure 22a,b). Compared to the racemate, CMIS exhibits stronger linear sweep voltammetry peaks and a lower Tafel slope, indicating faster OER kinetics (Figure 22c,d). Furthermore, spectrophotometric tests using o‐tolidine as an indicator for H₂O₂ production revealed that CMIS did not exhibit absorption peaks for oxidation products, confirming its effective suppression of H₂O₂ generation (Figure 22e).

FIGURE 22.

Chiral 2D materials for catalysis. a) Schematic for the three‐electrode cell setup. GCE: glassy carbon electrode. Adapted under terms of the CC‐BY license [244]. Copyright 2022, The Authors, published by Wiley‐VCH GmbH. b) Mechanism of the CISS effect in chiral and racemic catalysts. c,d) Linear sweep voltammetry curves and Tafel plots of the TiS₂_R‐/S‐/rac‐PEA (MBA)_PEG superlattice crystals. e) UV–vis absorption spectra after bulk electrolysis measurement with o‐tolidine as a redox indicator using chiral and racemic TiS₂ electrodes. Reproduced with permission [246]. Copyright 2023, Wiley‐VCH GmbH.

Additionally, the involvement of chiral molecular orbitals in hybridization and changes in the band structure induced by chiral lattice distortion alter electron configurations. This modifies the electron density distribution while generating carrier spin polarization, similar to the selective filtering effect of the CISS phenomenon [379]. In photocatalysis, band splitting caused by SOC enables spin polarization of photogenerated carriers. The non‐radiative recombination pathways of these carriers, influenced by phonons, are suppressed, resulting in longer lifetimes and slower recombination rates [380]. This increases the likelihood of diffusion to the surface and transfer to reactants, leading to higher catalytic activity. Spin‐polarized band splitting induced by the Zeeman effect further enhances catalytic activity, as demonstrated in perovskite systems [381, 382].

3.5. Enantiomer Recognition and Separation

Owing to the stability and ultrathin thickness of 2D materials, they can be fabricated into separation membranes with minimal transport resistance and maximum flux. Foreign substances permeate through tortuous interlayer channels or precisely designed pores on the layers [383, 384]. Chiral separation requires specific sites to form three‐point interactions with target substances—including electrostatic forces, hydrogen bonding, π–π stacking, and vdW forces—resulting in differential binding strengths for different chiral species, thereby enabling stereoselectivity [385].

The pore size and geometry of organic porous frameworks, like COFs and MOFs, can be precisely tuned through structural design, achieving exceptional enantiomer separation efficiency [386, 387]. Atomic‐level manipulation of micro‐region chemical structures in 2D materials remains challenging, making structurally chiral binding rare. Introducing exogenous chiral substances via physical/chemical methods offers a viable approach [388]. Chiral molecules bonded to graphene surfaces can serve as chiral selectors to differentially adsorb enantiomers, functioning as adsorbents or chromatographic stationary phases [389, 390]. The mechanism of porous filtration materials resembles that of membrane‐based systems. For instance, introducing 1‐Aminoethanol as a chiral “bouncer” into porous graphene creates energy barriers where the maximum energy hurdle and total Gibbs free energy change determine pore preference for enantiomers matching the bouncer's chirality (Figure 23a,b) [391].

FIGURE 23.

Chiral 2D materials for the recognition and separation of enantiomers. a,b) Schematic reaction pathways for the propagation of 1‐aminoethanol through a graphene pore with opposite (a) or same (b) chirality. Numbers are Gibbs free energies in kcal mol⁻¹. Adapted with permission [391]. Copyright 2014, Wiley‐VCH GmbH. c) Schematic for interactions between AChE and methamidophos. The blue arrow represents a hydrogen bond pointing to the electron donors. The green and violet balls represent van der Waals forces and electrostatic forces between the amino acid and methamidophos, respectively. The larger number (docking scores) indicates a stronger interaction. d) Schematic and performance for AChE‐ERGO resistance sensor. Adapted with permission [233]. Copyright 2019, American Chemical Society. e) Schematic for spin polarization in molecules with opposite chirality. f) Schematic for a spin‐polarized molecule interacting differently with a magnetized substrate. g) Calculated interaction energies between Ni atoms aligned in a 2×2×2 cube with a hydrogen atom with parallel (red) or antiparallel (blue) spin. Reproduced with permission [392]. Copyright 2018, AAAS.

Chiral recognition in 2D materials relies on binding mechanisms similar to separation. Strategies include enhancing optical detection (e.g., CD spectroscopy) by enrichment to lower detection limits, and developing novel electrical detection methods that convert chiral molecular signals into electrical responses via different charge doping effects [232, 233]. A typical example is presented in Figure 23c,d. Simulation calculations revealed that AChE exhibits stronger interactions with (‐)‐methamidophos due to differences in non‐bonding interactions caused by spatial configurations, which is further reflected by the variation in resistance sensitivity of the device.

While conventional recognition depends on asymmetric interactions, the CISS effect offers an alternative model [1]. Analogous to the anomalous Hall effect but with reversed host‐guest roles, CISS causes spin‐polarized charge displacement when chiral molecules develop induced dipoles under electric fields. The resulting spin distribution depends on molecular handedness (Figure 23e) [393]. Substrates with spin‐polarized electrons (e.g., ferromagnetic surfaces or homochiral molecules) can induce preferential adsorption: Pauli exclusion favors antiparallel spin alignment between specific molecular poles and the substrate, creating chirality‐dependent binding energy differences (Figure 23f,g). Separation effectiveness depends on the chiral molecule's polarizability and spin polarizability, while substrate performance depends on surface charge density and chemical environment [392, 394]. Such models remain unexplored but promising in 2D materials.

4. Challenges and Prospects

Chiral materials with exotic properties have been prepared using 2D materials, which enable promising applications in multiple fields, including spintronics, chiroptics, superconductivity, and catalysis. Various facile methods incorporating chemical reactions in dispersion media to load chiral molecules onto 2D materials have been developed, especially for the comparatively mature techniques in graphene systems. These primarily rely on several oxygen‐containing functional group chemistries (e.g., esterification and condensation reactions). Beyond membrane structures for enantiomer recognition and separation, catalysts can be designed for drug synthesis and fine chemical chiral molecular modifications, exhibiting concurrent high enantioselectivity, broad substrate scope, and recyclability. Alternatively, leveraging biocompatibility and chiral selectivity enables the construction of drug carriers and imaging probes.

However, effectively integrating the advantages of each component within chiral hybrid materials while simultaneously overcoming their inherent limitations remains a key challenge. Addressing this may require high‐throughput theoretical computations and experimental validation to explore novel functional hybrid materials. Regarding synthesis, grafting methodologies for porous graphene warrant further exploration, utilizing the immense specific surface area of 2D materials to enhance isomer selection efficacy in separation and recognition. Furthermore, given the conductivity of graphene and reduced GO, advancing micro/nano‐devices or e‐ink coated devices based on chiral molecular grafting will create additional application pathways for isomer recognition.

A more profound approach to chirality in 2D materials moves beyond their use as passive substrates for chiral molecules. An equally compelling avenue lies in engineering chirality directly within or from the 2D lattice itself—whether by constructing intrinsically chiral architectures using 2D materials as building blocks, or by creating hybrid interfaces where 2D crystals couple strongly with external chiral sources. These strategies can unlock distinct and enhanced chiroptical, electronic, and spin‐dependent properties. However, the vast structural and compositional diversity within this emerging field means that the resulting phenomena—spanning optical activity, CPL, and CISS—often resist description by simple, universal theoretical models, presenting a significant challenge for systematic design and prediction. Key challenges remain in the following aspects:

4.1. Precise Synthesis and Methodology

Many chiral structures suffer from imprecise synthetic control, lacking a comprehensive methodological framework. Top‐down mechanical manipulations like stacking and folding offer precise construction of chiral structures, but are inefficient and difficult to scale. For more complex chiral structures and composites, synergistic self‐assembly strategies combining covalent bonding and non‐covalent interactions between 2D materials and templates provide new opportunities across diverse systems. Molecular assembly in liquid phases can also induce flake twisting into specific chiral morphologies, however, this promising approach is bottlenecked by the lack of a universal molecular selection strategy. The significant disparities in mechanical strength, chemical activity, and edge/surface states among different 2D materials result in vastly different outcomes for the same molecular template across material systems.

A highly promising, yet systematically underexplored strategy involves establishing “molecular template libraries” for specific 2D material systems. Analogous to selecting building blocks to form various polygons [395], molecules with diverse structures, sizes, chirality, and functionalities could be chosen to induce varying degrees of chiral distortion in the 2D material. Researchers could systematically screen and design molecular templates with specific attributes for a target material, studying the rules governing induced chiral distortion to build predictive “template‐structure” relationship libraries. This would significantly enhance the controllability and design freedom of liquid‐phase assembly. The primary bottleneck lies in the lack of a high‐throughput experimental screening platform and the absence of a quantitative structure‐property relationship between molecular properties (such as geometry, chirality, and binding affinity) and the final chiral morphology of 2D materials. Accelerating the construction of a “component–template–structure” relationship map requires the concurrent integration of data‐driven automated experimentation, and machine learning towards molecular dynamics simulations.

Within “bottom‐up” strategies like CVD, template‐directed growth is crucial for improving chirality control and reproducibility. Examples include using bilayer Cu foil confinement to precisely control the stacking angle of TBG, or leveraging pre‐designed wrinkles or step edges to guide screw dislocation formation for oriented helical growth. Future efforts urgently require developing more operationally simple, mild‐condition (e.g., low‐temperature), broadly applicable, and highly controllable green bottom‐up strategies to lower synthesis barriers and increase yield. We contend that template‐directed synthesis, whether through top‐down or bottom‐up methods, represents the most promising cornerstone methodology for advancing chirality toward practical applications.

The research scope may be expanded beyond graphene and TMDs. The systematic introduction of chirality into materials with distinct properties—such as MXenes (rich surface chemistry), black phosphorus (strong anisotropy), 1T'‐ReS₂ (intrinsic chiral distortion)—as well as multi‐layer homo/heterostructures, and its impact on modulating electronic band structures, optical responses, spin/valley polarization, and catalytic activity, remains largely unexplored.

4.2. Characterization of Chiral Properties

Current research on chiral structures often prioritizes synthesis over property investigation, hindering the development of a comprehensive understanding of their functional behavior. Most studies on chiral interfaces with 2D materials concentrate on phenomena like valley‐polarized luminescence and the valley Hall effect in TMDs. Since these effects primarily arise from spin‐selective electron injection from the chiral layer, they tap into only a subset of potential chirality‐specific properties. This obscures critical structure‐chirality‐property relationships. While chiral molecule‐modified or intercalated 2D materials have seen more extensive property investigations, the mechanisms by which different molecular guests transfer chirality—with varying efficiency and strength—to the 2D host remain poorly understood. There is a pronounced lack of quantitative, universal principles describing the efficiency, spatial range, and underlying pathways (e.g., electronic hybridization and induced lattice distortion) of chirality transfer across diverse hybrid systems. Apart from the investigation of mechanisms behind observed properties, other chirality‐induced properties (such as ferroelectricity, piezoelectricity, and biocompatibility) still await further discovery and exploration.

Nearly all existing work examines the static chiral configurations; however, the dynamic and real‐time control of chiral states in 2D materials represents a highly promising yet almost entirely unexplored frontier. Exploring external fields, such as light, electric, magnetic, strain, and chemical treatment, to reversibly and rapidly modulate both chirality and its emergent properties, offers a compelling potential for next‐generation tunable chiral devices.

4.3. Limited Quantitative Assessment of Chirality Strength

Current quantification of chiral strength relies primarily on qualitative or semi‐quantitative confirmation, lacking rigorous quantitative analysis and cross‐comparison. CD spectroscopy, the predominant technique for chirality assessment, faces significant challenges when applied to solid‐state samples on substrates. First, growth and fabrication constraints often require opaque or optically complex substrates (e.g., silicon wafers), precluding direct CD measurement. Transferring samples to suitable transparent substrates is costly, technically challenging, and risks degrading or contaminating delicate chiral architectures that are incompatible with existing transfer methods. Second, the microscopic dimensions of many chiral structures lead to weak signals under conventional large‐spot illumination. While confocal micro‐CD setups can improve spatial resolution, they introduce operational complexity and hinder standardization. Even when CD spectra are successfully acquired for a chiral structure, normalizing the measured ellipticity poses a fundamental difficulty. For example, chirality in molecularly modified materials may be normalized by molecular density, whereas chiral helices might use length (thickness), yielding divergent results under different standards.

Compared to ellipticity, the g‐factor, as a relative deviation value, is more suitable for cross‐system comparisons. However, its universal application has not yet been achieved in current research. The absence of a unified, dimensionless metric for chiral strength hinders meaningful comparison across different systems, from macroscopic chiral metamaterials to molecule‐functionalized 2D crystals, underscoring the urgent need for a cross‐platform quantifiable standard. Meanwhile, ultrafast time‐resolved and spatially‐resolved chiral spectroscopic imaging techniques are under active development and making steady progress, which holds great promise for both comprehensively and accurately characterizing CD properties [396, 397].

4.4. Bidirectional Structure‐Property Relationship

For synthesized chiral structures, computational modeling offers indispensable advantages in elucidating structure‐property relationships by providing inaccessible atomic‐scale insights—electronic density of states, optical transition matrix, phonon spectra, and free energy shifts. While successfully applied to systems like TBG, nanoscroll, and chiral ligand exfoliated MoS₂, the interfacial interactions between chiral molecules and 2D materials require deeper investigation. Nevertheless, a critical gap exists in the universal complex computational framework, which is capable of efficiently handling the diverse complexities across chiral 2D systems. Constructing quantitative models that directly link structure to specific properties remains challenging. More fundamentally, establishing inverse design—deriving optimal structural parameters (e.g., twist angle, helical pitch, molecular configuration/arrangement) from targeted functionalities (e.g., specific‐wavelength/intensity circularly polarized emission, enantioselective catalysis, spin‐polarized currents)—represents a disruptive yet formidable frontier. Achieving these demands integrating high‐throughput computation, machine learning, and materials genomics into intelligent design platforms. Realization of such “programmable chirality,” coupled with advanced synthesis, would enable precise tuning of chiral responses. This pathway promises devices with tailorable chiral properties, paving the way for next‐generation chiral optoelectronics, spintronics, quantum technologies, and asymmetric catalysis.

Currently, the development of this pathway faces bottlenecks: The lack of universal and well‐defined theoretical models necessitates extensive theoretical derivation and substantial computational resources when dealing with multi‐objective parameters and multi‐scale modeling. Moreover, the absence of high‐quality datasets leaves the reliability of derived feasible pathways uncertain. These challenges are further limited by insufficient synthesis methods and a lack of standardized testing protocols. At present, the most urgent need is to establish a unified theoretical model for different chiral systems from the perspective of quantum mechanics, in order to describe chirality and explain the influencing factors of certain chiral properties. Even with high‐quality datasets, traditional computational methods are unable to handle systems that are too computationally intensive. This may necessitate the integration of various deep learning approaches for distributed computing, and once the methods are validated, high‐throughput computational scaling can be implemented [398].

4.5. Practical Barriers

Translating chiral 2D materials into functional devices faces considerable barriers. Present synthesis methods remain largely confined to laboratory scales, lacking scalable, semiconductor‐compatible fabrication routes capable of producing uniform, wafer‐scale chiral architectures and ordered device arrays. Critically, key functional responses—such as valley polarization—often only manifest under cryogenic conditions, necessitating advances toward efficient room‐temperature operation for practical deployment. Furthermore, the long‐term operational stability of most chiral structures under realistic stresses—such as electrical bias, thermal cycling, or ambient exposure—remains largely unverified. Potential degradation pathways include molecular desorption or decomposition, as well as structural relaxation or distortion, which could undermine the durability and fatigue resistance required for sustained device operation. Another important point that cannot be overlooked is that current research on some properties relies heavily on laboratory settings without effective solutions. For example, PL requires intense light sources, while superconductivity demands extremely low temperatures and high pressures, lacking a foundation for practical applications. This indicates a long way to go before the device implementation of introducing chirality into 2D materials.

5. Conclusion

In summary, 2D materials have emerged as exceptional candidates with extraordinary properties in optoelectronics, spintronics, and quantum communication and computation. Through intrinsic structural design or extrinsic chiral induction, these materials have acquired chirality, thereby establishing a novel platform for expanding chiral science at the nanoscale. Specifically, twisted stacking, scrolling, growing spirals, and creating torsion can produce chiral lattices or macroscopic chiral geometric structures. Also, chirality can be transferred to 2D materials by introducing chiral molecules or their assemblies, chiral crystals, or chiral metasurfaces. Currently, chirality is abundantly manifested in optics, spintronics, superconductivity, catalysis, and enantiomer chemistry, demonstrating highly competitive properties for further research and applications. It is of importance to develop a broader range of low‐cost, controllable, and efficient chiral induction methods in the future and uncover more compelling properties with rapidly advancing characterization techniques, such as four‐dimensional (4D) STEM, confocal solid‐state CD spectroscopy, and mc‐AFM. Furthermore, established structure‐property relationships for chirality will pave the avenue for advanced spintronic devices and miniaturized chiral sensors. Ultimately, overcoming the critical hurdles we discussed could trigger transformations in integrating chirality‐engineered 2D materials into practical applications, providing competitive alternatives for miniaturized low‐power encoding/decoding and storage, green catalytic water electrolysis for hydrogen production, enantiomer separation and detection, and beyond.

Funding

The National Natural Science Foundation of China (52272158), the Natural Science Foundation of Shanghai (23ZR1431200), the Fundamental Research Funds for the Central Universities (YG2024ZD28, YG20260NB29, and YG2023QNA26), and the Shenzhen Medical Research Fund (A2403056).

Conflicts of Interest

The authors declare no conflict of interest.

Data Availability Statement

Data sharing not applicable to this article as no datasets were generated or analysed during the current study.