Recent preparation and applications of chiral pillar[5]arene-based functional materials

Taotao Lu*^a, Hui Li*^b, Liang Zhao^b, Chenghua Lai^a, Daijiga Luo^a and Yanxing Qi*^b
aSchool of Chemical Engineering, Lanzhou City University, Lanzhou, 730070, P. R. China. E-mail: lzltt_2009@163.com
^bNational Engineering Research Center for Fine Petrochemical Intermediates, Lanzhou Institute of Chemical Physics, Chinese Academy of Sciences, Lanzhou 730000, P. R. China. E-mail: lihui@licp.cas.cn; qiyx@licp.cas.cn

First published on 14th August 2025

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1. Introduction

Chirality is a prevalent characteristic in both human life and nature, evident in proteins, sugars, nucleic acids, and drugs, among others.^1–3 The application of chirality spans numerous sectors, including pharmaceutical analysis, food safety, agricultural chemistry, and environmental protection.^4–8 Chiral molecules exhibit significant differences in activity and toxicity in various biological processes.^9–11 In terms of physico-chemical properties, the efficacy of chiral drugs often depends on their distinct enantiomers, despite these molecules exhibiting similar physicochemical characteristics. Therefore, the development of chiral materials has obtained considerable interests due to their potential applications in chiral recognition and separation,¹² optical devices,¹³ sensor and separation^14,15 and biomedicine.¹⁶

Pillar[n]arenes, a novel family of macrocyclic hosts, are characterized by their rigid, symmetrical, pillar-shaped structure and tunable properties resulting from their facile functionalization.^17–20 Among them, pillar[5]arenes, first synthesized and reported by Ogoshi and his team in 2008,²¹ have been the most widely studied regarding synthesis, host–guest complexation and supramolecular self-assembly to date.^22–26 Notably, pillar[5]arenes exhibit a dynamic racemic equilibrium in solution, owing to the swift interconversion of two stable conformers (pR and pS) via the rotation of hydroquinone units along the annulus.^27–30 However, the rotation of pillar[5]arenes can be inhibited by incorporating bulky substituents on both rings, resulting in the formation of planar chiral pR- and pS-forms of pillar[5]arene enantiomers.^31–33 Furthermore, pillar[5]arenes possess the ability to induce chiral signals and amplify chiral molecules through host–guest interactions.^34,35

In this review, we highlight the preparation of chiral pillar[5]arene-based functional materials and their applications in circularly polarized luminescent materials, chirality memory materials, chiral organic nanotube materials, and the separation and analysis of chiral molecules.

2. Preparation of chiral pillar[5]arene-based materials

2.1 Introducing stereogenic carbon atoms on the rims of pillar[5]arene

The upper and lower edges of pillar[5]arene are easily modifiable, which provides a significant an advantage for the incorporation of chiral auxiliaries into the structure of these compounds (Fig. 1a). Our collaborators have developed a series of derivatives of pillar[5]arenes. For example, in 2022, Li and colleagues³⁶ reported the first synthesis of chiral pillar[5]arene-functionalized silica microspheres as a chiral stationary phase, utilizing decabromohexyloxy pillar[5]arene, R/S-phenylethylamine, and aminopropyl silica. They demonstrated that the performance of enantioseparation of racemates was significantly enhanced by the introduction of pillar[5]arene and chiral centers. The prepared chiral stationary phase exhibited high enantioselectivity and good recognition ability towards alcohols, benzoin pesticides, and triazole fungicides. In 2024, they further developed three chiral pillar[5]arene^37,38 based stationary phases using bromoethoxy pillar[5]arene modified by three chiral molecules, respectively, functionalized onto mesoporous silica via the one-pot method (Fig. 1b). By introducing stereogenic carbon atoms into the pillar[5]arene framework, these pillar[5]arene-functionalized mesoporous silica materials demonstrated the capability to separate a variety of complex structural enantiomers with excellent reproducibility, thermal stability, and separation performance. Ogoshi et al.³⁹ prepared CuAAC (copper(I)-catalyzed alkyne–azide cycloaddition)-clickable azide-substituted pillar[5]arenes featuring S or R asymmetric carbon atoms on both rims. Additionally, azobenzene-substituted pillar[5]arene (denoted as R-azo, with a yield of 86%) was synthesized through a CuAAC click reaction between R-1 and an azobenzene derivative containing a terminal monoalkyne. The results indicated that a high diastereomeric excess of 90% de was achieved in both R-C16 and R-azo by incorporating long n-hexadecyl and bulky azobenzene substituents (Fig. 1c). The planar-chiral pillar[5]arenes with azobenzene substitutions exhibited amplified chirality, effectively propagating from the core structure of the pillar[5]arene to the azobenzene substituents, through molecular assembly on a surface. The alignment and collapse of these chiral assemblies can be controlled through the thermal and photoisomerization of the azobenzene groups, respectively.

2.2 The planar chirality of pillar[5]arene

Pillar[5]arenes exhibit two stable conformers, namely pS and pR, which can interconvert through the rotation of dialkoxy-benzene units around the methylene bridges in solution. However, these conformers are challenging to separate experimentally^40–43 (Fig. 2a). To obtain stable chiral pillar[5]arenes, bulky alkoxy substituents are typically introduced at the rims to inhibit the rotation of the units (Fig. 2a).^44,45 For example, in 2011, Ogoshi and co-workers were the first to successfully isolate both the (pS) and (pR) forms of pillar[5]arene enantiomers by modifying the structure with ten cyclohexylmethyl groups. The enantiomers were successfully separated using high-performance liquid chromatography (HPLC) (Fig. 2b).³² In 2019, Sun et al.⁴⁶ synthesized two chiral compounds by introducing the β-D-galactose group into the pillar[5]arene backbone, which were subsequently separated using silica gel chromatography. Furthermore, rigid π-conjugated systems are often employed as candidates to inhibit the free rotation of benzene rings. For instance, Ogoshi et al. developed a novel chiral molecule by introducing rigid π-conjugated units of 2,2′-bithiophene into the side arms of pillar[5]arene under palladium catalysis in 2013, successfully obtaining enantiopure isomers through chiral HPLC.³³ In 2012, Strutt et al.³¹ discovered that a bulky benzoic acid group in the pillar[5]arene backbone can also inhibit the free rotation of benzene rings, achieving enantiomers at the gram scale in the preparation of homochiral metal–organic framework materials in 2014.⁴⁷ Luan et al.⁴⁴ constructed inherently chiral pillar[5]arenes with high yields using an outstanding enantioselective palladium-catalyzed Suzuki–Miyaura cross-coupling strategy (Fig. 2d). They synthesized a total of 49 structurally diverse pillar[5]arenes, including 6-membered aryl, 5-membered heteroaryl, and alkenyl-substituted variants. Studies indicated that only bulky groups significantly impact the stabilization of planar chirality in pillar[5]arene, such as 9,10-diphenylanthracene,⁴⁸ and triarylamine-functionalized π-conjugated pillar[5]arene.⁴⁹ Xiao et al.⁵⁰ developed a chiral pillar[5]arene backbone via modification with a medium-sized substituent. Its chiral characteristics can be observed in n-hexane and CH₂Cl₂ at room temperature; however, increasing the temperature or using methylcyclohexane as a solvent can lead to a transition into a racemic mixture.

As previously mentioned, the chirality of pillar[5]arenes can be induced or amplified by external stimuli (Fig. 2a).^{39,44,51–53} In 2023, Yang et al.⁵⁴ synthesized a variety of bromoalkyl-substituted pillar[5]arenes of varying lengths to investigate the chiroptical responses induced by amino acid derivatives. Unexpectedly, only the 1-ethoxy-3-mercapto-1-oxopropan-2-aminium (L-G9) exhibited an inversion of planar chirality upon varying temperature (Fig. 3a). Before this, they noted that the addition of chiral alanine ethyl ester to bulky substituent-modified pillar[5]arenes resulted in time-dependent chirality induction. Moreover, the chiral inducer functions as both an activator and an inhibitor. While an increased number of chiral inducers led to more intense final chiroptical properties, chiral induction rates were lower in their study.⁵⁵ As natural molecules in the chiral pool, amino acids serve as fundamental units for a wide range of enzymes, hormones, proteins, and peptides. The pR or pS configurations of dynamically racemic water-soluble pillar[5]arene (WP5) can be induced by 19 different L-amino acid ethyl ester hydrochlorides. Due to distinct binding models involving the α-positioned side-chain moiety or ethyl ester moiety within the cavity of WP5, L-Arg-OEt and 18 other L-amino acid ethyl ester hydrochlorides can induce opposite-handed conformations of WP5. As shown in Fig. 3b, hydrogen-bonding (HB) interactions between the amino acid ethyl ester hydrochlorides and carboxyl groups on the upper and lower rims of WP5 were observed with H⋯O distances ranging from about 1.6 to 1.8 Å. In comparison, the conformation of pS-WP5⊃L-Ala-OEt is energetically more stable, featuring two ammonium salts as donors. However, in the case of L-Arg-OEt, the enhanced binding ability of the side-chain moiety allowed it enter the cavity of WP5. Conversely, in the conformation pS-WP5⊃L-Arg-OEt, only one N–H⋯π interaction exists between the guanidine H atom and WP5. In the conformation pR-WP5⊃L-Arg-OEt, two N–H⋯π interactions simultaneously form between two H atoms of the guanidine group and WP5. For guest molecules such as n-alkanes, however, adapting the chirality of hosts to the length of n-alkanes presents a significant challenge, as n-alkanes are neutral, achiral, and linear molecules.⁵² Ogoshi et al.³⁴ reported a pillar[5]arene-based macrocyclic host (S-Br) that contains five stereogenic carbons and five terminal bromine atoms at each rim. The inclusion of short n-alkanes, such as n-pentane (C5), favours the formation of the pS-form, while the presence of longer n-alkanes, like n-heptane (C7), promotes the pR-form. Single crystals of S-Br grown in C7 and C5 revealed that the pR-form is 28.8 kJ mol⁻¹ more stable than the pS-form in the crystal structure. Furthermore, temperature influences the adaptive chirality; n-hexane, which has an intermediate length, presented the pR-form of S-Br at elevated temperatures, whereas the pS-form was favored at lower temperatures.

3. Applications of chiral pillar[5]arene-based materials

3.1 Circularly polarized luminescent materials

Circularly polarized luminescence (CPL) is a significant characteristic of chiral materials arising from molecules or supramolecular aggregates that exhibit both chiral attributes and luminescent properties.^56–59 Recently, the synthesis of CPL-active molecules utilizing of pillar[5]arene has been demonstrated through their integration with suitable fluorophores.^56,60,61 Generally, the fabrication of pillar[5]arene-based CPL materials can be obtained by two strategies. The first strategy involves the covalent connection of chiral pillar[5]arene and fluorescent units to generate chiral luminescent small molecules, polymers, or their assemblies. The second strategy employs the concept of chirality transfer to non-covalently connect the chiral pillar[5]arene and fluorescent units. Various multifunctional pillar[5]arene-based CPL materials have been developed,^62–67 and their CPL properties are summarized in Table 1.

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Ogoshi et al. synthesized planar chiral pillar[5]arenes containing a π-conjugated unit due to the photoelectric properties exhibited by chiral molecules with π-conjugated structures, which display circular dichroism (CD) and CPL activity. The direct incorporation of π-conjugated units inhibited the rotation of pillar[5]arenes, resulting in optical resolution.³³ Chen and his colleagues⁶⁶ chemically integrated pillar[5]arenes with boron, employing π-conjugated triarylamine (Ar₃N) as an electron donor and triarylborane (Ar₃B) as acceptors to synthesize planar chiral organoborane (P5NN and P5BN), leveraging the easily accessible chirality transfer from pillar[5]arenes. This method achieves optical resolution of pR/pS isomers and yields thermal properties of CD and solid CPL emission. In the emission spectra, rac-P5BN exhibited a bathochromic shift as the temperature decreased from 345 to 130 K, while its color transitioned from blue to yellow in a 2-methyltetrahydro-furan solvent. The emission wavelength increased linearly, demonstrating a high correlation coefficient of 0.992 (Fig. 4a). The following year, they elucidated two highly luminescent organoboranes (NP5BN1 and NP5BN2) that exhibited dual chirality achieved through molecular functionalization of planar chiral pillar[5]arenes with naphthyl groups. Strong steric effects imposed by the triarylamine (Ar₃N) and triarylborane (Ar₃B) moieties, further enhanced by the proximity of the chiral building blocks, facilitated the isolation of multiple enantiomers via chiral high-performance liquid chromatography.⁶⁰ Additionally, Kato et al. connected five functionalized pyrene planes to a chiral macrocyclic pillar[5]arenes hydrocarbon through a five-fold SN2 reaction involving phenolic[5]arene hydrocarbons, forming multiple π-conjugated planes on the chiral macrocyclic ring and thus generating a set of chiral molecules. Despite the low luminescent quantum yield, the observed CPL response validates the design principles of the CPL-active pillar[5]arene molecules.⁶⁷

Besides, the configurations of planar chiral pillar[5]arenes have also been successfully stabilized through supramolecular assembly via metal–ligand coordination. For example, Zhu et al. reported the synthesis of four planar chiral platinum triangles exhibiting chiral optical activity, achieved by the self-assembly of 60° and 90° Pt(II) receptors with planar chiral pillar[5]arene ligands.⁶⁸ Characterization and optical studies proved that all metal rings possess CPL properties, indicating promising applications in optical materials. In 2025, Chen and their team⁶³ have engineered two rigid and flexible chiral organic ligands (L₁ and L₂) based on pillar[5]arenes, incorporating rigid terpyridine and N,O-chelated flexible moieties. The configurations of planar chiral pillar[5]arenes can be effectively stabilized by bulky substituents, leading to the optical resolution of enantiomers (>98% ee) via HPLC. Moreover, these enantiopure ligands exhibit versatile coordination capabilities with both metals ions and 4f lanthanides, displaying intense blue (Zn²⁺), green (Tb³⁺) and red (Eu³⁺) circularly polarized luminescence. The metal complexes show increased dissymmetry factors (g_lum up to 5.5 × 10⁻³) and CPL brightness (B_CPL up to 23.0 M⁻¹ cm⁻¹) compared to the corresponding ligands L₁ and L₂ (Fig. 4b).

Tang et al.⁶⁹ constructed chiral supramolecular polymers with remarkable CPL properties by combining the planar chirality of pillar[5]arene with aggregation-induced emission (AIE) luminogens, specifically the pyridine-conjugated TPE borate ester (pyridyl-TPE) unit. This combination not only imparts AIE properties to the corresponding monomers and polymers but also inhibits the rotation of the pillar[5]arene rings due to steric effects. As a result, planar chirality in the pillar[5]arene monomers (pR-TPE-P5 and pS-TPE-P5) was achieved through chiral HPLC. Furthermore, the supramolecular polymers were obtained by coordination reaction between the pyridyl-TPE-pillar[5]arene monomers and silver ions, leading to significantly enhanced CD signals and fluorescence intensity compared to their monomers. In the aggregate state, there was a 21-fold increase in the dissymmetry factor and over a 25-fold increase in the fluorescence quantum yield compared to the solution state (Fig. 4c). The formation of polymers restricts intramolecular motions because of the larger steric hindrance and the presence of multiple intra- and intermolecular interactions. Additionally, the polymer structure enhances the chirality fixation of pillar[5]arenes and exhibits pronounced CPL properties. Further aggregation of supramolecular polymers resulted in a significant improvement in CPL performance.

Ogoshi et al.⁷⁰ prepared a pair of water-soluble cationic pillar[5]arenes with stereogenic carbons (S-1 and R-1) and described their planar chirality. The chiral information was efficiently transferred from the planar chiral pillar[5]arene to the guest molecule APy through host–guest interactions. By adding a small amount of chiral pillar[5]arene (0.6 equiv.), CPL of APy was achieved, which could be finely tuned by varying the amount of chiral pillar[5]arenes. Notably, planar chiral pillar[5]arenes exhibited strong binding to the linear aliphatic chains of fluorescent guest molecules, resulting in effective chiral transmission with minimal impact on the physical properties of the fluorophores (Fig. 4d). In 2024, Ogoshi et al.⁶⁴ reported CPL spectra for pillar[5]arene with stable planar chirality using tetrahydrofuran (THF) and cyclohexane as solvents. They investigated neutral π-conjugated molecules such as 1,4-bis(phenylethynyl)benzene and 1,4-bis[(pentafluorophenyl)ethynyl]benzene, which exhibited good luminescence properties but weak complexing abilities. These molecules could form co-aggregates with pillar[5]arene in THF/H₂O mixtures due to the hydrophobic effect. The co-aggregates featuring the fluorinated π-rod displayed a new low-energy absorption peak, a broad emission band, and intense circular dichroism and CPL signals. Consequently, this system achieved the highest dissymmetry factor for CPL (2.9 × 10⁻² at 472 nm) among pillar[n]arene-based CPL materials, as the chiral information was efficiently transmitted from the enantiopure pillar[5]arene core to the co-aggregates with the π-conjugated rod. Therefore, future research should focus not only on developing feasible and powerful strategies for the constructing chiral luminescent materials but also on creating promising platforms for further exploration of practical applications, such as switchable CPL systems.

3.2 Chirality memory materials

Fa et al.⁷¹ have developed ternary non-direct chiral transfer systems based on pillar[5]arene, wherein a third factor is introduced as a regulator (e.g., rim-differentiated pillar[5]arene, chiral amine, and linear guest molecule) (Fig. 5a). In their study, the chiral amine compound induced planar chirality, while the linear guest molecule acted as a regulator to control the memorization of that chirality. The chiral memory of the pillar[5]arene was established through a two-component input, effectively forming a logic gate. The sequence in which the chiral amine and linear guest molecule were introduced significantly influenced the planar chiral memory capacity of the pillar[5]arene. The combined actions of the chiral inducer and regulator markedly enhanced the chiral memory ability of the acceptor. Furthermore, Ji and his team⁵⁵ have successfully developed a novel supramolecular chiral memory system by replacing chiral inducers with achiral competitive binders. They report an unprecedented example of self-inhibition during supramolecular chiral induction, memory, erasure, and reversal of pillar[5]arene derivatives. The incorporation of chiral alanine ethyl ester into the large-volume substituent-modified pillar[5]arenes resulted in time-dependent chiral induction, owing to a change in the balance of pS and pR conformations of ar[5]arenes. In tandem, multistep equilibria constituted by the complexation of a chiral guest with the pS and pR conformers, along with racemization between the enantiomeric conformers, led to chirality induction that resulted in enantio-biased complexation of the conformers. This process can preserve chirality, while enantiomeric inducers can eliminate and reverse chirality signals, demonstrating self-inhibition properties (Fig. 5b). These investigations into chiral smart materials based on pillar[5]arenes contribute to the advancement of smart materials and offer a novel approach to studying response recognition for planar chiral pillar[5]arenes.

3.3 Chiral organic nanotube materials

The unique structures of pillar[5]arenes render them optimal building blocks for the creation of chiral organic nanotube materials,^71–73 which are predominantly formed through non-covalent assembly and covalent interactions (Fig. 6a).^41,74–76 Several methodologies exist for constructing of non-covalent nanotubes, leveraging weak and reversible supramolecular interactions such as hydrogen bonds, hydrophobic forces, π–π stacking, and metal–ligand coordination. For example, Fa et al.⁴¹ detail the formation of pillar[5]arene-based chiral nanotubes through pre-regulation of the chirality of bulky blocks. Initially, the planar chirality of rim-differentiated pillar[5]arenes is modulated by chiral awakening, followed by further induction or inversion through sequential achiral external stimuli. The pre-regulated chiral information is well-stored in discrete nanotubes through interaction with a per-alkylamino-substituted pillar[5]arene. In addition, Wan et al. present a design strategy for constructing metal–organic pillars, achieved by precisely stacking pillar[5]arene building blocks⁷⁵ (Fig. 6b). In particular, pillar[5]arene-based ligands with pyridinyl moieties are assembled in a head-to-head fashion in the presence of silver salts through labile [N⋯Ag⁺⋯N] coordinative bonds. The resulting AgnL₂ complexes, which take the form of twisted pentagonal prisms approximately 2 nm in height, exhibit chiral self-sorting behavior and host–guest properties. Nevertheless, these tubular structures exhibit fragility due to their reliance on weak non-covalent bonds to maintain their architecture. In 2022, Shi et al.⁷⁶ engineered two pillar[5]arenes utilizing dynamic covalent bonds successfully preparing thermodynamically stable discrete covalent organic nanotubes that exhibit 5-fold symmetry. Three distinct chiral covalent organic nanotubes were isolated, including homo-covalent organic nanotubes, composed of two enantiomers (pR, pR and pS, pS), as well as hetero-covalent organic nanotube, formed from the meso form (pR, pS). These covalent organic nanotubes exhibit negative allosteric binding affinities for guest molecules, a phenomenon that is not observed in individual pillar[5]arenes (Fig. 6c).

3.4 Chiral molecular recognition and separation

Chiral recognition is significantly important to pharmaceutical and biological research, as the majority of active substances are chiral molecules.^77,78 As shown in Table 2, we summarize various chiral recognition-based pillar[5]arene materials. A direct way to introducing auxiliary chiral side groups in macrocyclic structures aims to establish a new chirality center.^32,79

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For a specific chiral inducer, the pair of enantiomeric conformers may exhibit differing binding affinities. The equilibrium between these conformers tends to shift in favor of the one with stronger complexation, thereby facilitating chirality induction. In 2020, Huang et al.⁸⁰ prepared a complexation-induced chirality amplification system utilizing carboxyl-functionalized water-soluble pillar[5]arene (WP5), for the detection of amino acids such as arginine (Arg) and lysine (Lys). When the racemic compound WP5 was added to an L-Arg solution, a temperature-responsive amplified CD signal was observed. Moreover, the same host demonstrated the capability to amplify the CD signals of Lys enantiomers. Therefore, WP5-TP exhibited a high affinity for Arg. This study not only broadens the applications of pillar[5]arene but also presents a novel approach for detecting chiral molecules that possess negligible intrinsic CD signals (Fig. 7a).

Furthermore, pillar[5]arenes are employed as electrode materials for the recognition of chiral molecules. For example, Yang et al.⁸¹ fabricated novel pillar[5]arene derivatives through metal–ligand coordination (Ru-tri(DPMUJ)), wherein a pillar[5]arene with a bipyridyl side ring is coordinated with Ru²⁺. The enantiomeric Ru-tri(DPMUJ), coated onto the electrode, showed significant electrochemiluminescence (ECL)-based chiral discrimination toward D/L-amino-acid alkyl ester hydrochloride (Fig. 7b). Additionally, Zhao et al.⁸² successfully assembled a cascade of water-soluble anionic pillar[5]arene (WP5) and cationic pillar[5]arene (CP5) on a carboxyl graphene (C-Gra) modified glass carbon electrode, investigating the electrochemical recognition of tryptophan isomers (L/D-Trp) using differential pulse voltammetry (DPV).

Chen et al.⁸⁴ developed peptide attachment pillar[n]arene (n = 5, 6) derivatives as a class of artificial transmembrane amino acid channels. The unique tubular structure, induced by intramolecular hydrogen bonds within the peptide chain, facilitates the efficient transport of amino acids across membranes in a single-molecule manner. Cheng et al.⁸⁵ fabricated chiral nanochannels by introducing a L-alanine-pillar[5]arene host into achiral ordered mesoporous silica (OMS), which exhibited excellent selectivity (enantiomeric excess value up to 90.2%) for the separation of racemic drugs, demonstrating promising reusability and stability. Meanwhile, Yu et al.⁸⁶ developed a simple and effective electrochemical chiral recognition method based on a chiral pillar[5]arene-functionalized nanochannel. The chiral N-acetyl-L-cysteine decorated pillar[5]arene (NALC-P5) was synthesized via the classical “thiol–ene” click reaction. This nanochannel can regulate the transport rate of R/S-PPL and achieve selective recognition of R/S-PPL based on differences in host–guest interactions between chiral NALC-P5 and R/S-PPL. Liu et al.⁸⁷ also prepared a nanochannel using the host–guest systems of pillar[5]arene (WAP5) and R-phenylethylamine (R-PEA), where the R-PEA induced chirality within the host–guest system, thereby enhancing the chiral selectivity of the nanochannel for S-ibuprofen as evidenced by circular dichroism spectra.

The membrane separation method, a recently developed chiral separation technique, has emerged as one of the most promising separation technologies due to its environmentally friendly nature, straightforward implementation, and ease of continuous operation. Wang et al.⁸⁸ successfully prepared a molecularly imprinted membrane (MIM) using the S-triazolone template molecule through photoinitiated polymerization. This MIM was developed based on biological semi-permeable membranes. The incorporation of macrocyclic molecules, specifically 1,4-bis(allyl)-pillar[5]arene, as functional monomers significantly enhanced the effectiveness of the target molecular chiral recognition sites, thereby improving the chiral selectivity of the MIM. The separation efficiency of S/R-triazolone in the MIM-II membrane achieved an enantiomeric excess (ee%) of 84.78% when pillar[5]arene was included as the second monomer (Fig. 7c).

Pillar[5]arenes have been extensively utilized in separation science, particularly for the preparation of solid-phase adsorbents and as stationary phases in liquid chromatography.^9,24,89–91 For example, Al-Azemi T. F. et al.⁹² proposed a method for the synthesis and separation of aromatic hydrocarbons using a planar chiral mono-hydroxyl functionalized pillar[5]arene, with debenzylation achieved through Pd/C catalysis. The chiral resolution was accomplished via column chromatography following the derivatization of (S)-(+)-α-methoxy-α-trifluoromethyl phenylacetyl chloride ((S)-(+)-mtPA-Cl). Recently, we and our cooperators reported a series of distinct chiral functional substances modified to pillar[5]arene-bonded silica, thereby creating novel chiral stationary phases for highly selective enantioseparation.^29,36–38 For instance, chiral phenylethylamine functionalized pillar[5]arene-based silica microspheres exhibited pronounced enantioselectivity and strong recognition capability for various racemates, including alcohols, benzoin pesticides, and triazole fungicides. Furthermore, two imidazole derivatives, (S)-1-(4-phenyl-1H-imidazol-2-yl)ethanamine and (S)-histidinol, were modified onto bromoethoxy pillar[5]arene-bonded silica, resulting in the development of new materials. These innovative chiral stationary phases displayed enhanced enantioselectivity for both chiral aromatic and aliphatic compounds (Fig. 7d).³⁶ Moreover, pillar[5]arene functionalized with L- and D-histidine (Table 3) was incorporated onto the surface of mesoporous silica. L/D-Histidine exhibits low steric hindrance and straightforward derivatization potential. Although the π–π interaction of the imidazole group is less potent than that of the benzene ring, the combination of the benzene ring with the imidazole-conjugated ring yielded superior enantioseparation effects. These materials showcased exceptional separation capabilities for thirty-one enantiomers, encompassing chiral drugs, pesticides, and additives.³⁸ Lv et al.⁹³ have designed and synthesized a novel pillar[5]arene-cup[4]pyrrole macrocyclic compound (PC) that exhibits anion recognition and host–guest properties. The enantiomers of PC can selectively bind to R/S-mandelic acid through hydrogen bonds and other host bonds interactions, facilitating the formation of supramolecular complexes. In addition, supramolecular optical chirality sensing is recognized as a rapid, cost-effective and high-throughput technique.

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4. Summary and outlook

In summary, this minireview presents a systematic introduction to the synthesis of chiral pillar[5]arene-functionalized materials and their applications in various fields, including circularly polarized luminescent materials, chirality memory materials, chiral organic nanotube materials, and the separation and analysis of chiral molecules. As described above, considerable progress has been achieved over ten years. Based on inherent chirality of pillar[5]arene, a variety of chiral pillar[5]arene-functionalized materials have been synthesized through chirality induction or the incorporation of chiral units.

However, there remains substantial potential for the development of chiral pillar[5]arene-functionalized materials. Enhancing the productivity of chiral pillar[5]arene is crucial, as the yield of the aforementioned chiral pillar[5]arene-functionalized materials is insufficient for large-scale applications. Moreover, it is imperative to design and synthesize larger cavity chiral pillar[n]arenes (n ≥ 6) and investigate their applications. In the realm of circularly polarized luminescent materials, the continuous development of novel chiral emitters with both high quantum efficiency (Φ) and large g_lum values remains a primary objective, as high Φ and 100% utilization of excitons are essential for achieving high device efficiency. Additionally, a combination of multiple components and the design of pillar[5]arenes should be employed to regulate chirality memory systems or to develop smart materials capable of immediately sensing, detecting or separating chiral substances. Moreover, regarding chiral molecular separation, researchers should focus on the practical application, in addition to develop new and highly efficient separation materials and study the mechanisms of separation.

Conflicts of interest

There are no conflicts to declare.

Data availability

No primary research results, software or code have been included and no new data were generated or analysed as part of this review.

Acknowledgements

This work is supported by the National Natural Science Foundation of China (22204169), the Natural Science Foundation of Gansu, China (23JRRA1177 and 23JRRA619), Scientific and Technological Program of Chengguan District, Lanzhou (2023JSCX0037), and Discipline Construction Project of Lanzhou City University.

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