English

• 1. Introduction

  Supramolecular luminescent materials (SLMs) have aroused great interests in recent years due to their simple synthesis, unique luminescent properties, and dynamically reversible and versatile function features [1]. Utilizing supramolecular strategies into different photophysical processes, such as fluorescence [2], thermally activated delayed fluorescence (TADF) [3], room-temperature phosphorescence (RTP) [4], energy transfer and electron transfer processes [5], have wide applications in bioimaging [6,7], optical sensors [8,9], molecular switches [10,11], anti-counterfeiting materials [12,13] and organic light-emitting diodes (OLEDs) [14]. Due to the existence of dynamic and reversible noncovalent interactions, such as hydrogen bonding, C—H···π, π-π stacking, hydrophobic effects, electrostatic effects, charge transfer (CT) interactions and so on [15], SLMs exhibit outstanding luminescence properties and intelligent regulation through diverse assembly approaches. Additionally, the supramolecular strategies also offer advantages in synthesis routes over traditional covalent synthesis methods, which lead to the reduced synthesis costs and simpler preparation processes. Therefore, SLMs have become one of the most frontier and hot topics in supramolecular chemistry and materials chemistry.

  Among various SLMs, those ones constructed through the host-guest interaction of macrocycles have attracted considerable attention in recent years owing to the ability of macrocyclic intrinsic cavities to effectively dynamic encapsulate guest molecules, leading to the formation of supramolecular luminescent materials. Moreover, the flexible and tunable conformation and multiple noncovalent complexation sites of the macrocyclic hosts also afford a new opportunity to create such dynamic smart luminescent materials.

  Macrocyclic arenes are a type of macrocyclic compound with rich-electron aromatic rings bridged by sp³ carbon atoms [16,17]. In recent years, an increasing number of novel macrocyclic arenes have been reported [18-21]. They have shown wide applications in diverse research fields including molecular machines [22,23], molecular recognition and assemblies [24-26], and biomedical science [27]. With the rapid development of macrocyclic and supramolecular chemistry, macrocyclic arenes with novel structures have emerged as one of the most significant and extensively studied classes of synthetic macrocyclic hosts [19]. In comparison to other macrocyclic hosts, macrocyclic arenes have flexible and definite conformation, unique optical features, and multiple binding sites. Integration of these macrocyclic arenes into supramolecular luminescent materials can promise diverse photophysical phenomena and regulatory mechanisms, thereby offering opportunities for deeper exploration in this field [28-31].

  In recent years, more and more novel supramolecular luminescent materials based on macrocyclic arenes have been constructed and found their wide applications in molecular recognition and sensing, information encryption, bioimaging and so on. Therefore, it is urgent to systematically and comprehensively summarize the recent advances in the preparation strategies, properties, and applications of the supramolecular luminescent materials based on macrocyclic arenes. In this review, we will present the research progress of SLMs based on macrocyclic arenes in the last several years. Consequently, we will introduce these SLMs from the perspective of the supramolecular assembly strategies, including host-guest complexes, supramolecular polymers, nanoparticles and other assemblies. Moreover, we will also offer some insights into future directions for this research area. We believe this review focusing on SLMs based on the macrocyclic arenes will promote the development of macrocycle and supramolecular chemistry and also provide some guidance toward the design and construction of smart supramolecular luminescent materials.

  2. Host-guest complexes

  Macrocyclic arenes possess well-defined cavities and multiple binding sites, which allow them to form host-guest complexes with a wide variety of guests through noncovalent interactions. In these complexes, the cavities of the macrocyclic arenes often restrict the free rotation of the guest molecules or alter their aggregation states, thereby influencing the photophysical properties of the complexes.

  In 2019, Yang's group obtained a host-guest complex G1 ⊂ 1 [32]. The host-guest complexation between 1 and G1 restricted the intramolecular rotation of G1, reducing non-radiative relaxation. As a result, G1 ⊂ 1 (Fig. 1) exhibited strong blue emission with a significantly higher quantum yield and a longer fluorescence lifetime compared to free G1. Additionally, the fluorescence of G1 ⊂ 1 could be quenched by the ligand interaction of 1 with Fe³⁺, which was highly selective and sensitive. They also synthesized G2 ⊂ 2 (Fig. 1) [33]. The fluorescence of G2 ⊂ 2 could be quenched by Hg²⁺, and the formation of G2 ⊂ 2@Hg could also be used for the sensitive recognition of L-cysteine. This luminescent material was expected to wide applications in fluorescence sensing, cell imaging and visualized monitoring.

  Figure 1

  

  Figure 1.  Chemical structures of 1, 2, G1 and G2.

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  In host-guest complexes, macrocyclic arenes can also alter the stacking modes of the guest molecules, thereby preventing the aggregation-induced quenching (ACQ) effect or changing the emission state of the guests. In 2022, Yang's group [34] synthesized a methoxy pillar[5]arene (P5) dimer 3 bridged by a 2,3,6,7-tetramethoxy-9,10-di-p-tolylanthracene linker (Fig. 2b). The P5 units prevented intermolecular π-π stacking, resulting in 3 exhibiting stronger fluorescence emission than the monomer in both solution and solid state. They also designed fluorescent guest molecules G3, G4, and G5 to interact with 3 (Fig. 2a), forming three host-guest complexes: G3 ⊂ 3, G4 ⊂ 3, and G5 ⊂ 3. These host-guest complexes exhibited highly controllable luminescence. Interestingly, adjusting the host/guest ratio or changing the solvent could produce multiple colors of fluorescence, including white light emission (Fig. 2c, G4 ⊂ 3 with a host/guest molar ratio of 1:4.5).

  Figure 2

  

  Figure 2.  Chemical structures of (a) G3, G4, G5 and (b) 3. (c) Schematic illustration of the supramolecular assembly based on 3 and G4, and the white-light emission adjusted by the host-guest interactions. Reproduced with permission [34]. Copyright 2019, Wiley Publisher.

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  In 2021, Ma's group [35] constructed a host-guest complex G6 ⊂ 4 using pyrene derivatives G6 as the guest and p-sulfonatocalix[4]arenes 4 as the host. The emission color of the G6 ⊂ 4 changed from indigo blue to cyan due to the excimer formation, and it gradually returned to the indigo blue of the monomer within 72 h (Fig. 3). Additionally, it was also possible to construct a dynamic artificial light-harvesting system by incorporating the cationic energy acceptor ethidium bromide (EB). This system was capable of exhibiting red-blue emission color variations. This time-dependent luminescence provided a direct visual approach into the dynamic processes involved in the self-assembly process.

  Figure 3

  

  Figure 3.  Chemical structures of 4 and G6, and schematic illustration of the self-assembly process and Förster resonance energy transfer (FRET) process of G6 ⊂ 4. Reproduced with permission [35]. Copyright 2023, the Royal Society of Chemistry.

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  Similarly, Chen's group [36] reported the water-soluble chiral derivatives of 2,6-helic[6]arene, 5a and 5b, which could bind 4-[(4′-N,N-diphenylamine)-styryl]-N-methylpyridinium iodide G7 to form 1:1 host-guest complex G7 ⊂ 5a and G7 ⊂ 5b (Fig. 4). The fluorescence enhancement of host-guest complexes compared to monomeric G7 could be attributed to the restriction of the ACQ effects. Subsequently, chiral assemblies were obtained based on the host-guest interactions, exhibiting clear mirror-image CD and circularly polarized luminescence (CPL) spectra in an aqueous solution. This demonstrated a consecutive chirality transfer from the chiral macrocyclic cavities of 5a and 5b to G7. Moreover, these assemblies also exhibited responsive CPL activities to the changes in temperature and pH.

  Figure 4

  

  Figure 4.  Chemical structures of 5a, 5b and G7, and schematic illustration of pH-responsive complex G7 ⊂ 5a. Copied with permission [36]. Copyright 2019, Frontiers Media S.A.

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  In 2022, Chen and coworkers also utilized the enantiomeric 2,6-helix[6]arylene 6 in combination with the nanocluster Ag₂₀ (G8) through host-guest interactions to create a chiral host-guest complex G8 ⊂ 6 (Fig. 5) [37]. This complex exhibited CD property due to the successive chirality transfer from the chiral macrocycles to the achiral silver clusters. Additionally, the singlet excited state of G8 was encapsulated by the cavity of 6, resulting in G8 ⊂ 6 exhibiting enhanced luminescence properties at room temperature as well as multicolor luminescence with decreasing temperature.

  Figure 5

  

  Figure 5.  Chemical structures of P/M-6 and G8. Copied with permission [37]. Copyright 2022, MDPI.

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  The flexible conformation of macrocyclic arenes results in the racemization of some intrinsic chiral macrocycles due to the rapid transitions between enantiomers. In 2021, Chen's group synthesized saucer[4]arene 7 with strong fluorescent property [38] with quantum yields of 19.6% (Fig. 6a). It was noteworthy that the chiral quaternary ammonium guest G9 could induce the chirality in the dynamic racemic intrinsically chiral 7. The resulting host-guest complexes exhibited mirror-image CD signals and CPL property (Fig. 6b), thereby providing a new strategy for the construction of CPL materials through host-guest interactions.

  Figure 6

  

  Figure 6.  (a) Chemical structures of S_ic/R_ic-7 and R/S-G9. (b) Schematic illustration of competitive conformation chirality of 7 induced by R/S-G9. Reproduced with permission [38]. Copyright 2021, Wiley Publisher.

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  In 2021, Yang and coworkers [39] proposed a strategy to control the photophysical properties of a complex by controlling the motion of the guest within the cavity of macrocyclic arenes. They designed a CPL switch based on the host-guest complex G10 ⊂ 8 (Fig. 7a). By adding and removing acetate anions, they controlled the reversible axial movement of 8 in G10 ⊂ 8 along the alkyl chain of guest G10 to achieve the switch function. This process enhanced the chiral information transfer and regulated the aggregation state of G10 ⊂ 8, resulting in reversible switching between the two CPL emission states with g_lum of 2.14 × 10⁻³ and 1.36 × 10⁻² (Fig. 7b).

  Figure 7

  

  Figure 7.  (a) Synthetic route of G10 ⊂ 8. (b) Schematic illustration of CPL switching system based on G10 ⊂ 8 upon the addition or removal of external stimuli. Reproduced with permission [39]. Copyright 2021, Wiley Publisher.

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  In 2022, Wei's group [40] used a similar strategy by employing UV-light irradiation to induce the guest phenazine derivatives G11 to pass through the cavity of the P5, forming the host-guest complex G11 ⊂ P5 (Fig. 8a). The fluorescence of G11 ⊂ P5 was completely quenched, but the fluorescence emission of G11 could be restored upon exposure to natural light due to the free shuttling of G11 within the cavity of P5 (Fig. 8b).

  Figure 8

  

  Figure 8.  (a) Chemical structures of P5 and G11. (b) Schematic illustration of internal-driven interaction induced by the UV-light (254 nm). Reproduced with permission [40]. Copyright 2022, Elsevier Publishers.

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  Due to their electron-rich properties, macrocyclic arenes can act as effective electron donors and form intermolecular charge transfer states when they combined with electron-deficient guests. In 2020, Ogoshi's group [41] reported the vapoluminescence behavior triggered by host-guest complexation in the crystal state. Compound 9 and the guest molecule did not exhibit fluorescence in the visible region when they existed alone. However, in the crystal state, 9 was able to form complexes with guests G12, G13, and G14 through host-guest interactions (Fig. 9). These complexes exhibited blue fluorescence, which may be induced by electron transfer facilitated by the host-guest interactions.

  Figure 9

  

  Figure 9.  Vapoluminescence behaviors triggered by crystal-state complexation between 9 and guests (G12, G13, and G14). Reproduced with permission [41]. Copyright 2020, American Chemical Society.

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  In practice, host-guest charge-transfer complexes with strong fluorescence emission are rare because charge transfer usually leads to fluorescence quenching upon the formation of the host-guest complex. However, the charge-transfer properties are highly beneficial for thermally activated delayed fluorescence (TADF). In 2022, Chen's group [3] prepared a host-guest cocrystal by utilizing the interaction between calix[3]acridan 10 and G15 (Fig. 10a). The cocrystal showed green-blue TADF emission due to the strong intermolecular charge transfer (ICT) between 10 and G15 (Fig. 10b). This was because of the spatial separation of HOMO-LUMO energy level and a small ΔE_ST (0.014 eV). Additionally, the photoluminescence quantum yield was as high as 70%.

  Figure 10

  

  Figure 10.  (a) Preparation of G15 ⊂ 10 by cocrystal growth. (b) Optical microscopy images of 10 and G15 ⊂ 10. (c) Crystal structures of G15 ⊂ 10. Reproduced with permission [3]. Copyright 2022, Wiley Publisher.

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  A general supramolecular strategy for constructing the TADF materials [42] was further proposed. Consequently, they obtained a series of host-guest cocrystals by combining 10 as an electron donor and various guests (G16-G22) as electron acceptors (Figs. 11a and b). The cocrystals exhibited efficient TADF properties due to the mediation of multiple non-covalent interactions in the process of intramolecular charge-transfer (ICT). It was noteworthy that the luminescence color of these cocrystals could be continuously tuned from blue to red by finely tuning the electron-withdrawing abilities of the guest molecules (Fig. 11c), achieving a photoluminescence quantum yield of up to 87%. This study provided a general method for the preparation of TADF materials and established a reliable supramolecular strategy for the design of advanced luminescent materials.

  Figure 11

  

  Figure 11.  (a) The TADF emission realized by formation of ICT state between the macrocyclic donor and guest. (b) Chemical structures and electrostatic potential maps of 10 and guests G16-G22. (c) Optical microscopy images of G16 ⊂ 10-G22 ⊂ 10 under sunlight (up) and UV light (down). Reproduced with permission [42]. Copyright 2024, Springer Nature.

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  Very recently, Liu and his colleagues [43] proposed a novel strategy for preparing two solid-state supramolecular systems with organic room-temperature phosphorescence by using 1,2-/1,3-dicyanobenzene (G15/G17) and calix[3]phenothiazine 11 (Fig. 12c). Despite the regular arrangement of 11 in crystals, the vibrational dissipation of the phenyl ring resulted in 11 emitting only 508 nm of fluorescence at room temperature. In contrast, G15 and G17 were found to immobilize 11 and inhibit molecular vibrations, thereby reducing the nonradiative relaxation (Fig. 12a). This resulted in the room-temperature phosphorescence (RTP) emission of 11 at 566 nm and 524 nm, respectively (Fig. 12b). Subsequently, they prepared G15 ⊂ 11 and G17 ⊂ 11 as a Quick Response code (QR code) through solvent evaporation, resulting in a colorful QR code that could be recognized by smartphones under 365 nm UV irradiation. After exposure to dichloromethane vapor, the color of the QR code faded due to the weakening of the interactions between G15/G17 and 11, making the code no longer recognizable by cell phones. However, upon solvent evaporation, the colorful QR code reappeared without damage (Fig. 12d). This material exhibits excellent fatigue resistance and allows for multiple conversions.

  Figure 12

  

  Figure 12.  Schematic illustration of (a) the RTP emission and (b) the RTP emission of selectively activated 11. (c) Chemical structures of G15, G17, and 11. (d) Phosphorescence QR code and information storage/encryption of solvent response. Reproduced with permission [43]. Copyright 2023, Wiley Publisher.

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  More recently, Chen's group [44] utilized macrocycle-to-macrocycle conversion to synthesize a novel macrocyclic arene, namely naphth[4]arene 12 (Fig. 13a). This macrocycle could selectively form 1,3- and 1,2-alternate conformations in the solid state. Interestingly, it could assemble with 1,2,4,5-tetracyanobenzene (TCNB) via π-π stacking to form two distinct supramolecular crystals: 1,3–12@TCNB and 1,2–12@TCNB (Fig. 13b). Despite having the same compositions, the conformational change in the macrocyclic arene resulted in different fluorescence property. Co-assembly 1,3–12@TCNB exhibited green fluorescence with a quantum yield of 43%, while 1,2–12@TCNB exhibited yellow fluorescence with a quantum yield of 45%. Especially, it was further found that depending on the different conformations of 12, the two co-assemblies also showed color-tunable two-photon excited up conversion emission due to the intermolecular charge transfer (Fig. 13c).

  Figure 13

  

  Figure 13.  (a) Macrocycle-to-macrocycle conversion synthetic strategy of 12. (b) Schematic illustration of the construction of color-tunable supramolecular luminescent co-assemblies 1,3–12@TCNB and 1,2–12@TCNB. (c) The two co-assemblies excited by NIR light emit distinct upconversion fluorescence. Reproduced with permission [44]. Copyright 2023, Wiley Publisher.

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  The modulation of the photophysical properties of fluorescent guests or fluorescent macrocycles by multiple non-covalent interactions within host-guest complexes can facilitate the fabrication of various functional materials. Furthermore, the synthesis of these host-guest complexes is relatively straightforward due to the electron-rich cavities of the macrocyclic arenes and the exo-wall interactions that facilitate the efficient binding of a range of guests. However, these host-guest complexes are poorly processable and typically exist in solution or crystalline, restricting their practical applications.

  3. Supramolecular polymers

  Supramolecular polymers [45] are polymeric arrays formed by connecting monomeric units through reversible and highly directional non-covalent interactions, such as hydrogen bonding, π-π stacking, and coordination interactions. Benefiting from their facile functionalization and rich host-guest chemistry, macrocyclic arenes are widely utilized in the preparation of supramolecular luminescent polymers. These polymers combine the unique properties of polymers and macrocyclic arenes, and exhibit fascinating reversibility and responsiveness, making them an attractive strategy for the preparation of SLMs.

  In 2019, Xia's group [46] introduced a salicylaldehyde azine group into P5, resulting in formation of 13. Subsequently, they obtained a linear AIE supramolecular polymer through host-guest interaction between 13 and G23 (Fig. 14). The fluorescence emission intensity of the polymer increased as the increase of the concentrations of 13 and G23 in chloroform. Additionally, upon drying, the fluorescence was enhanced upon drying due to the closer aggregation of the salicylaldehyde azine groups. Moreover, the salicylaldehyde azine group could coordinate with Cu²⁺, leading to the cross-linking of the polymer chains and a quenching of the fluorescence. However, the fluorescence could be restored by the addition of cyanide (Fig. 14).

  Figure 14

  

  Figure 14.  Chemical structures of 13 and G23, and schematic illustrations of the linear AIE supramolecular polymer and the reversible cross-linking process of the linear polymer by Cu²⁺ and CN⁻. Reproduced with permission [46]. Copyright 2019, American Chemical Society.

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  Similarly, Wang's group [47] prepared the linear fluorescent supramolecular polymers with AIE effect based on the host-guest interaction between P5 derivative 14 and TPE derivative G24. These polymers showed significantly enhanced fluorescence emission compared to that of free G24. Simultaneously, introducing competitive molecules such as 1,4-butanedinitrile and P5 into the system triggered the disruption of the polymer, leading to fluorescence quenching (Fig. 15). Furthermore, this supramolecular polymer could detect Pb²⁺ due to the presence of a triazole group in 14, which coordinated with Pb²⁺ and led to a reduction in the fluorescence intensity of the polymer.

  Figure 15

  

  Figure 15.  Chemical structures of 14 and G24, and schematic illustration of the formation of linear supramolecular polymer and its dissociation by the addition of 1,4-butanedinitrile and P5. Reproduced with permission [47]. Copyright 2024, Elsevier Publishers.

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  In 2020, Huang's group [48] introduced another method to enhance the fluorescence emission in supramolecular polymers. They used supramolecular polymerization to regulate the aggregation and emission behaviour of dyes in the solid-state. By utilizing the host-guest interaction between guests G25 or G26 and the pillar[5]arene derivative 15, they prepared linear fluorescent supramolecular polymers. The polymerization process reorganized the parallel arrangement of G25 or G26 into a well-organized head-to-tail structure (Fig. 16). This reorganization suppressed the ACQ effect and significantly improved the photoluminescence efficiency of the polymer. Additionally, the system exhibited two-photon emission property.

  Figure 16

  

  Figure 16.  Chemical structures and distributions of the electrostatic potential mapped onto the electron density surfaces of G25, G26 and 15, and the self-assembled modes of G26 and G26 ⊂ 15 in the solid state. Reproduced with permission [48]. Copyright 2020, American Chemical Society.

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  Moreover, supramolecular polymers can be prepared from self-complementary monomers, which are constructed by covalently attaching the guest fragment to the macrocyclic arenes. In 2021, Qu and co-workers [49] connected the oxazolo[4,5-b]phenazine-2-thiol group to P5 through covalent bonds and obtained monomer 16 (Fig. 17). A linear supramolecular polymer with fluorescent property was then formed through host-guest interactions between the cavity of P5 and the oxazolo[4,5-b]phenazine-2-thiol group in CHCl₃. Due to the excellent processability of this fluorescent supramolecular polymer, fluorescent thin films were further prepared. These films exhibited vapochromic behaviour and were effectively used for the direct detection of aliphatic aldehyde micropollutants.

  Figure 17

  

  Figure 17.  Chemical structure of 16 and schematic illustration of the formation of the fluorescent supramolecular polymer and its application in the detection of n-butyraldehyde (C₄) and caprylicaldehyde (C₈) vapors. Reproduced with permission [49]. Copyright 2022, Wiley Publisher.

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  Recently, Qu's group [50] modified the TPE and nitrile groups at both rims of P5 to obtain monomer 17. Subsequently, supramolecular polymers were prepared based on the host-guest interactions between the nitrile group and P5 (Fig. 18). These supramolecular polymers exhibited significant AIE effect due to the restricted intramolecular rotation of the TPE groups. Moreover, the polymer was able to further self-assemble in THF/H₂O mixed solvent to form spherical aggregates.

  Figure 18

  

  Figure 18.  Chemical structure of 17 and schematic illustration of the construction of the luminescent spherical aggregates based on the self-assembly of 17. Reproduced with permission [50]. Copyright 2023, the Royal Society of Chemistry.

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  In 2023, Li's group [51] constructed a supramolecular polymer that did not require conventional chromophores. They obtained linear supramolecular polymers by the self-assembly of 18 in solution. The rigid structure of the P5 contributed to the increased rigidity of the supramolecular polymer (Fig. 19), which impeded the movement of the polymer chains, reduced the non-radiative relaxation and endowed the polymer with photoluminescent properties.

  Figure 19

  

  Figure 19.  Chemical structure of 18 and schematic illustration of linear supramolecular polymers. Reproduced with permission [51]. Copyright 2023, Wiley Publisher.

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  Another approach for preparing supramolecular polymers based on host-guest interactions of macrocyclic arenes is to introduce macrocyclic arenes into the covalent polymers and then form supramolecular crosslinked networks by host-guest interactions. In 2020, Tang's group [52] synthesized a covalent polymer 19 with P5 and TPE units incorporated into the molecular backbone. Due to the host-guest interactions, various conjugated ditopic guests (G27, G28, and G29) could be sequestered between the polymeric host chains without experiencing ACQ (Fig. 20a). Additionally, the polymer chains could be entangled with each other or form supramolecular crosslinks network through binding with the guest molecules to achieve aggregation-induced emission (Fig. 20b). In addition, using 19 as the donor and G27, G28 and G29 as the acceptors, the supramolecular polymer network exhibited remarkably efficient energy transfer. It exhibited a high antenna effect of 35.9 in solution and 90.4 in solid film. Furthermore, by modifying the molecular structures of the acceptors and donors or adjusting their ratio, the emission characteristics of the supramolecular polymer network could be tuned (Fig. 20d). This resulted in a color gamut covering approximately 96% of the sRGB area, including an accurate white emission at (0.33, 0.33) in CIE coordinates (Fig. 20c).

  Figure 20

  

  Figure 20.  (a) Chemical structures of 19, G27, G28 and G29. (b) Schematic illustration of supramolecular polymer network. (c) CIE 1931 chromaticity diagram. Gray quadrilateral: the color gamut of the supramolecular polymer network. Black triangle: the sRGB gamut. (d) Fluorescence photographs of the supramolecular polymer network in the co-solvent of CHCl₃/cyclohexane (3:7 by volume), including a white emission of (0.33, 0.33) in CIE coordinates. λ_ex = 368 nm. Reproduced with permission [52]. Copyright 2020, Wiley Publisher.

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  Subsequently, Liao's group [53] obtained covalent polymer 20 with P5 side chains and employed a similar strategy to introduce pyridinium salts containing polyethylene glycol (G30) and TPE (G31) into 20 via host-guest interaction (Fig. 21). The polymers were then able to self-assemble in solution to form micelles and exhibited an AIE effect with increased fluorescence intensity. Moreover, the addition of the competitive guest 1,4-butanedinitrile resulted in a decrease in fluorescence intensity, which was attributed to the disruption of the micelle structure.

  Figure 21

  

  Figure 21.  Chemical structures of 20, G30 and G31, and schematic illustration of the supramolecular material constructed by host-guest interactions. Reproduced with permission [53]. Copyright 2022, the Royal Society of Chemistry.

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  More recently, Chen's group [54] constructed a color-tunable TADF polymer via ICT interaction between the calix[3]acridan-modified polymer with various acceptors (Fig. 22a). The TADF properties of the polymers were due to through-space charge transfer between the macrocyclic donor and the electron-deficient guests (G17, G18, G20, G21). In particular, by modifying the electron-withdrawing capacity of the guests, they were able to achieve multi-color emission and achieve a PLQY of up to 40%. Furthermore, the polymers displayed favourable processability, stability and tunability. Based on these properties, they created anti-counterfeiting labels on various substrates and constructed multi-color two-dimensional barcodes that could be scanned and read by smart devices (Fig. 22).

  Figure 22

  

  Figure 22.  (a) Chemical structures of the color-tunable TADF polymers. (b) Schematic illustration of thin films prepared by spin-coating method and coatings prepared by spray-coating method. (c) The process of multiple reuses of anti-counterfeit labels (pattern 1: ♥CAS; pattern 2: dragon; pattern 3: phoenix) produced by TADF polymers. (d) Schematic illustration of binary information conversion of multi-color two-dimensional barcode. (e) A conceptual application of multi-color two-dimensional barcode.

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  Macrocyclic arenes can also form supramolecular polymers with metal ions through coordination due to the ease of functionalization. Yang's group [55] synthesized a color-tunable supramolecular polymer using 21 as the ligand and Eu³⁺ and Tb³⁺ as metal ions. Due to its inherent blue fluorescence and electron-rich structure, 21 played a dominant role in the blue emission of the polymer and served as an excellent energy donor for lanthanide metal ions. The concentrations of Eu³⁺ and Tb³⁺ could determine the red and green intensity of the system, respectively. Consequently, by adjusting the molar ratio of Eu³⁺ and Tb³⁺, the fluorescence color of the polymer can be tuned from red to green. Moreover, the polymer exhibited white light emission at a molar ratio of 1:3 (Fig. 23) and could selectively detect nitroaromatic pollutants through the electron transfer mechanism.

  Figure 23

  

  Figure 23.  Chemical structure of 21 and schematic illustrations of the color-tunable polymer constructed by tuning the molar ratio of Eu³⁺ and Tb³⁺ in the system and the fluorescence on/off sensing of nitroaromatic pollutants. Reproduced with permission [55]. Copyright 2022, the Royal Society of Chemistry.

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  In a recent study, Tang and colleagues [56] integrated the planar chirality of P5 with the AIE effect of TPE through coordination interactions. They synthesized macrocycle 22, where the TPE units provided the AIE effect, and the spatial effects restricted the rotation of the benzene units in the P5. They then obtained a pair of optically pure enantiomers, pR-22 and pS-22. Supramolecular polymers were created by coordinating pR-22/pS-22 with silver ions (Fig. 24a). This coordination led to a 1.5-fold enhancement in the CD signal and an increase in the quantum yield from approximately 0.9 to 2.0. The enhancement of chiral and fluorescent properties allowed the pR-polymers and pS-polymers to exhibit significant CPL property in dilute solution, with g_lum values of 1.30 × 10^–4 and −0.65 × 10^–4, respectively. Notably, the polymers formed aggregates in aqueous media (Fig. 24b), resulting in a more than a 25-fold increase in quantum yield compared to their solution state. Additionally, the g_lum value of the pR-aggregates increased to 2.69 × 10^–3, representing a 21-fold enhancement compared to that of the pR-polymers.

  Figure 24

  

  Figure 24.  (a) Chemical structures and synthetic routes of pR/pS-22 and the corresponding coordination supramolecular polymers. (b) Schematic illustration of the construction of P5-based materials with polymerization and aggregation enhanced CPL. Reproduced with permission [56]. Copyright 2023, Wiley Publisher.

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  In 2020, Shi's group [57] synthesized a P5 derivative 23 containing two pyrene groups. This compound formed a linear supramolecular polymer by π-π stacking due to the large conjugated structure of pyrene. The fluorescence of the polymer changed from blue to green as the concentration of 23 or solvent polarity increased. Later, the researchers introduced the red emissive Eu-terpyridine complex G32 into the system. Through the host-guest interaction between the P5 and G32, a supramolecular network was formed. By adjusting the concentration and solvent polarity, this network exhibited white light emission and tunable fluorescence (Fig. 25).

  Figure 25

  

  Figure 25.  Chemical structures of 23 and G32, and schematic illustration of solvent-controlled aggregation of 23 and the modulation process of white emission. The inset picture shows the white fluorescence of the supramolecular system under UV light. Reproduced with permission [57]. Copyright 2020, the Royal Society of Chemistry.

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  In 2023, Liu and co-workers [58] reported a full-color supramolecular switch. The system was assembled through various non-covalent interactions involving 2,6-pyridine dicarboxylic acid-modified P5 (24), lanthanide ions (Tb³⁺ and Eu³⁺), and a dicationic diarylethene derivative (G33). By adjusting the molar ratio of Tb³⁺ and Eu³⁺ within the system, they achieved full-color luminescence, including white light emission in dichloromethane (CIE: 0.31, 0.33) and aqueous (CIE: 0.31, 0.32) solutions. Furthermore, the interconversion between G33a and G33b was controlled by alternating UV/visible light irradiation, demonstrating the capability to control the fluorescence switch of the polymer (Fig. 26). This supramolecular polymer was successfully applied to anti-counterfeiting by using intelligent multi-colored writing inks.

  Figure 26

  

  Figure 26.  Chemical structures of 24, G33a and G33b, and schematic illustration of the construction of a full-color lanthanide supramolecular light switch based on noncovalent assembly. Reproduced with permission [58]. Copyright 2023, the Royal Society of Chemistry.

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  Recently, Wang's group [59] combined 25 and G34 via host-guest interactions to obtain [3]pseudorotaxane (Fig. 27a). This was followed by the formation of a supramolecular fluorescent polymer crosslinked network through hydrogen bonding between Schiff-base groups and van der Waals forces between cholesterol groups (Fig. 27b). Moreover, the reversible metal coordination between the Schiff-base groups induced by cyanide ions and Cu²⁺ enabled the system to exhibit fluorescence switching (Fig. 27b). Utilizing the surface binding capability of the supramolecular polymer and the fluorescence emission properties of Schiff-base groups, they prepared rewritable fluorescent paper by dip-coating polymer on cellulose paper. This paper allowed for cyclic writing with Cu²⁺ ions as ink and CN⁻ ions as erasers (Fig. 27c).

  Figure 27

  

  Figure 27.  (a) Chemical structures of 25 and G34. Schematic illustration of (b) two supramolecular polymer networks (SPNs) and the reversible quenching and recovery property of the fluorescence by Cu²⁺ and CN⁻ ions, and (c) the recyclable writing and erasing processes of SPN-based rewritable paper. Reproduced with permission [59]. Copyright 2023, the Royal Society of Chemistry.

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  Stimulus responsiveness is one of the most important features of supramolecular luminescent polymers due to the dynamic and reversible non-covalent interactions. In recent years, Yang and his colleagues [60-63] have reported a variety of stimuli-responsive fluorescent supramolecular polymers.

  In 2019, they designed a [2]biphenyl-extended pillar[6]arene 26 [60], which was used as a building block in the synthesis of a supramolecular polymer through the host-guest interaction between 26 and the TPE derivative G35. In the presence of Hg²⁺, the polymer formed a supramolecular network and self-assembled into spherical nanoparticles due to the coordination between Hg²⁺ and thymine on the edge of 26. This process restricted the intramolecular rotation of G35, leading to supramolecular assembly-induced emission enhancement, and exhibited strong AIE fluorescence (Fig. 28). The polymer had the potential for the fluorescence detection of Hg²⁺ and the efficient removal of Hg²⁺, with a rapid adsorption rate and high adsorption capacity. Remarkably, the polymer could be effectively regenerated and recycled without any loss by simple treatment with Na₂S.

  Figure 28

  

  Figure 28.  Chemical structures of 26 and G35 and schematic illustration of the sensing and removal of Hg²⁺ from water based on the “switch-on” fluorescence of the supramolecular polymers and the regeneration−recycling process. Reproduced with permission [60]. Copyright 2019, American Chemical Society.

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  Recently, they [63] synthesized a supramolecular polymer network with AIE emission using 27 and a homoditopic guest G36 (Fig. 29). In addition, they prepared a Fe³⁺ ion responsive film based on the polymer. Upon the addition of Fe³⁺ to the system, 27 and Fe³⁺ formed a non-emissive 1:1 complex due to coordination (Fig. 29), enabling the selective detection of Fe³⁺ with lowest detection limit (LOD) of 3.0 × 10^–6 mol/L.

  Figure 29

  

  Figure 29.  Chemical structures of 27 and G36, and schematic illustrations of the assembly process of supramolecular polymer and the sensing to Fe³⁺. Reproduced with permission [63]. Copyright 2023, Elsevier Publishers.

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  Supramolecular polymers based on macrocyclic arenes can also form supramolecular gels [25,64]. In 2022, Chen's group [65] introduced CPL property into the supramolecular polymers. They synthesized a pair of enantiomeric bishelic[6]arenes 28 (Fig. 30a). Through host-guest interactions, 28 could form linear supramolecular polymers with two achiral luminescent guests, G37 and G38, which exhibited enhanced fluorescence and induced CD property. As the concentration of the polymer increased, the linear supramolecular polymer could transform into a gel through the synergistic effect of hydrogen bonding and host-guest interactions, accompanied by a significant enhancement of the induced CD property. Furthermore, the supramolecular gels exhibited CPL property as a result of the efficient chiral transfer from 28 to G37 and G38 (Fig. 30b). Remarkably, by adjusting the ratio of the two guests, chiral supramolecular gels with white light emission with a g_lum value of about 1.3 × 10^–3 were obtained.

  Figure 30

  

  Figure 30.  (a) Chemical structures of 28, G37, and G38. (b) Schematic illustration of the supramolecular polymerization based on host-guest interaction and hydrogen bonding (inset: photo of the supramolecular gels under natural light and 365 nm UV light). Reproduced with permission [65]. Copyright 2022, American Chemical Society.

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  In the preceding years, Wei and coworkers have prepared a variety of stimuli-responsive supramolecular polymer gels and utilized them for the detection and separation of a diverse range of metal ions and pollutants [66-72]. In 2019, they successfully constructed a gel [69] with AIE property by introducing multiple interaction sites and assembling a bisnaphthalimide-functionalized P5 29 and a 4,4′-bipyridinium salt G39 (Fig. 31). The gel demonstrated the capacity to sense a broad spectrum of pollutants, including organic dyes, organic pollutants, volatile organic compounds, and so on. Additionally, it exhibited the ability to separate these pollutants, with a separation rate of heavy metal ions, metal oxides, various organic dyes, and organic pollutants reaching 99.8%.

  Figure 31

  

  Figure 31.  (a) Chemical structures of 29 and G39, and possible assembly mechanism of the gel and photo showing the broad-spectrum detection and adsorption separation properties for broad-spectrum pollutants for (b) cations and anions, (c) volatile organic compounds (VOCs), and (d) various organic dyes, organic pollutants, and oxyanions. Reproduced with permission [69]. Copyright 2019, American Chemical Society.

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  Recently, they synthesized phenazine-bridged P5 30 and naphthalene diimide G40 [72], which could self-assemble into spherical structures in dilute solution through host-guest interactions, exhibiting yellow fluorescence. Furthermore, the spherical structure transformed into a supramolecular polymer gel with the increase of concentration (Fig. 32). Subsequently, a novel biogenic amine-responsive platform was obtained based on this gel by adjusting the concentration of the host and guest. This platform is sensitive to most amine compounds and can detect alkaline amine gas or liquid amine in solid, solution, and gel states.

  Figure 32

  

  Figure 32.  Chemical structures of 30 and G40, and schematic illustration of the assembly process between 30 and G40 and its response mechanism. Reproduced with permission [72]. Copyright 2023, Elsevier Publishers.

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  Supramolecular polymers based on macrocyclic arenes have excellent processability, recyclability, and self-healing properties. Furthermore, the host-guest interactions between the macrocyclic arenes and guests facilitate the entry of these supramolecular polymeric materials into the field of environmentally responsive materials. However, the synthesis process of these polymers is relatively complex, and the starting materials are not commercially available. Consequently, it is challenging for macrocyclic arenes-based supramolecular polymers to realize their full potential in practical applications, at least for the time being.

  4. Supramolecular nanoparticles

  In recent years, supramolecular nanoparticles (SNs) have been widely used in drug delivery [73], bioimaging and cancer therapy [74]. Macrocyclic arenes have become essential in the preparation of these SNs [30,75] due to their inherent cavities and facile functionalization.

  In 2020, Ding's group [75] reported a method to prepare supramolecular AIE nanodots using the host-guest interaction between calix[5]arene 31 (Fig. 33) and aggregation-induced emission luminogens (AIEgens). The co-assembly between the two components constrained the intramolecular motions of AIEgens, reducing ISC and thermal inactivation pathways. The AIE dots, loaded with G41 (Fig. 33), exhibited an exceptionally high quantum yield of 0.72. Additionally, the researchers found that the AIE nanodots had minimal side effects in vivo, indicating their potential as ultrasensitive fluorescent imaging agents for guiding cancer surgeries through in vivo studies of peritoneal carcinomatosis mouse models.

  Figure 33

  

  Figure 33.  Chemical structures of 31 and G41.

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  Shen's group [76] developed a host-guest complex using carboxylate-modified P5 32 as the host and G42, which had a tetraphenylethene core, as the guest. The fluorescence intensity of this complex was significantly higher compared to free G42. They used a nanoprecipitation method to create SNs with enhanced fluorescence emission (Fig. 34a). Intriguingly, these SNs could encapsulate doxorubicin (DOX), and the fluorescence of the system was quenched due to FRET and ACQ effects. When DOX was released intracellularly, the fluorescence of the SNs was restored, allowing for in situ visualization of drug release (Fig. 34b). Furthermore, the nanoparticles retained the anticancer efficacy of DOX, indicating their potential for application in cancer therapy.

  Figure 34

  

  Figure 34.  (a) Chemical structures of 32 and G42. (b) The fabrication of SNPs@DOX using SNPs as drug nanocarriers and schematic illustration of imaging-guided drug delivery. Reproduced with permission [76]. Copyright 2021, the Royal Society of Chemistry.

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  In the same year, Hu's group [77] introduced tetrastyrene into the backbone of the pillar[5]arenes to obtain a water-soluble pillar[5]arenes 33 (Fig. 35), which combined both the AIE effect and the host-guest property. It could bind with DNS-G (obtained by using SN-38) to form AIE-SNs based on host-guest interactions and fluorescence resonance energy transfer. The nanoparticles were employed to construct a glutathione (GSH)-responsive supramolecular drug delivery system with yellow fluorescence emission. The system was capable of releasing SN-38 efficiently at high GSH concentrations in the microenvironment of tumor cells, which was anticipated to be utilized for cancer therapy.

  Figure 35

  

  Figure 35.  Chemical structures of 33 and DNS-G, and schematic illustrations of the formation of SNs and their stimuli-responsive drug release. Reproduced with permission [77]. Copyright 2021, American Chemical Society.

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  Realizing reversible control of morphological transformation between various nano-assemblies is very important in the field of smart materials. In 2020, Yao and co-workers [78] constructed SNs based on the host-guest interactions of 34 and a bicyanostilbene derivative G43. These SNPs exhibited a two-step sequential fluorescence enhancement (Fig. 36). Initially, G43 formed nanofibers in an aqueous solution with weak fluorescence, which transformed into nanosheets with enhanced fluorescence upon the addition of 34. Subsequently, the interaction with sodium dodecylbenzene sulfonate (SDBS) further enhanced the fluorescence, forming nanoparticles that could specifically target mitochondria in live cells with the help of the target molecule HDPP, making them useful for cellular imaging applications.

  Figure 36

  

  Figure 36.  Chemical structures of 34, G43, SDBS and target molecule (HDPP), and schematic illustration of supramolecular self-assemblies from G43, 34/G43, and 34/G43/SDBS. Reproduced with permission [78]. Copyright 2020, the Royal Society of Chemistry.

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  In 2021, Wei and his colleagues [79] reported a method to control the reversible transformation between nanoparticles and nano-film. They designed and synthesized a tri-[2]rotaxane based on 35 and G44. Tri-[2]rotaxane could self-assemble into nanoparticles, which could be reversibly transformed into nano-film by the addition of trimethylamine and suberic acid alternately (Fig. 37). Moreover, the fluorescence of the tri-[2]rotaxane showed an “off-on-off’” switching behavior.

  Figure 37

  

  Figure 37.  Chemical structures of 35 and G44, and schematic illustration of constructing nano-film by the guest induction to regulate fluorescent nanoparticles that formatted from the tri-[2]rotaxane. Reproduced with permission [79]. Copyright 2021, the Royal Society of Chemistry.

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  Transformation of the morphology of the nano-assemblies can also be used for detection. Zhang's group [80] recently used water-soluble pillar[5]arene 34 and guest G45 to construct fluorescent nanoparticles, which exhibited strong fluorescence emission in L-glutamic acid (L-Glu) and L-aspartic acid (L-Asp) were present in solution, the SNPs were converted into weakly fluorescent nanosheets (Fig. 38), resulting in highly selective detection of L-Glu and L-Asp with LODs of 4.03 × 10^–7 mol/L and 2.09 × 10^–7 mol/L, respectively.

  Figure 38

  

  Figure 38.  Chemical structure of G45 and schematic illustrations of the construction of fluorescent nanoparticles and its application in detection of L-Asp and L-Glu in water. Reproduced with permission [80]. Copyright 2022, Wiley Publisher.

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  A strategy for in situ detection of Pb²⁺was recently reported by Lin's group [81]. They first synthesized the P5 derivative 36 (Fig. 39a), which in aqueous solution was able to self-assemble with the guest G46 in aqueous solution to form nanoparticles without fluorescence emission. The S^2- derivative was then able to cross-link these nanoparticles to form fluorescent nanorods, which could be induced by Pb²⁺ to be converted into PbS quantum dots (QDs) in the presence of Pb²⁺, with a significant increase in the quantum yield of the system accompanied by a significant fluorescence color change (Fig. 39b). These processes could be utilized for highly sensitive and selective fluorescence detection of S^2- and Pb²⁺ with LOD of 3.17 × 10^–7 mol/L and 4.52 × 10^–7 mol/L, respectively. Moreover, it was also a feasible way to detect Pb²⁺ in cells in situ by the formation of PbS QDs.

  Figure 39

  

  Figure 39.  (a) Synthetic routes of 36 and G46. (b) Schematic illustration of the proposed assembly mode of the supramolecular system and ions inducing them to transition from the nanomaterials to QDs. Reproduced with permission [81]. Copyright 2022, American Chemical Society.

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  Recently, supramolecular light-harvesting systems (LHSs) based on FRET have attracted significant interest due to their great potential in photocatalysis, bioimaging and tunable photoluminescent devices [82-85]. Macrocyclic arenes possessed the ability to bind donor molecules via host-guest interactions and to self-assemble into SNs, which were able to load acceptor molecules. Therefore, macrocyclic arenes were widely used in the construction of supramolecular LHSs [86-88].

  Yang's group developed various color-tunable SNs based on pillar[n]arenes [89,90]. In 2019, they attached P5 to the side chains of the polymers to obtain 37 [89]. Subsequently, they obtained supramolecular polymer networks via host-guest interactions between 37 and two TPE derivatives, G47 and G2 (Fig. 40). Furthermore, by finely adjusting the parameters, an exceptionally high fluorescence quantum yield of 98.22% was achieved for the polymers in THF. Additionally, G3 was introduced into the polymer, leading to the formation of a series of color-tunable SNs for light-trapping systems by varying the guest ratio.

  Figure 40

  

  Figure 40.  Chemical structures of 37, G2, G3 and G47, and schematic illustrations of the construction and property study of supramolecular polymer networks. Reproduced with permission [89]. Copyright 2019, Wiley Publisher.

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  In 2020, Wang and co-workers [91,92] reported supramolecular LHSs with sequential energy transfer processes. Initially, they constructed nanoparticles through the self-assembly of host-guest complexes composed of 34 and G48 [91]. These nanoparticles exhibited significantly enhanced fluorescence compared to free G48. Subsequently, they encapsulated the hydrophobic fluorescent dye Eosin Y (ESY) through non-covalent interactions, enabling energy transfer from G44 to ESY. ESY further transferred energy to a second acceptor, Nile Red (NiR), achieving an efficient two-step energy transfer process (Fig. 41). Additionally, by adjusting the donor/acceptor ratio to 100:5:2 (G48/ESY/NiR), the system achieved white light emission with CIE coordinates of (0.33, 0.33).

  Figure 41

  

  Figure 41.  Chemical structure of G48 and schematic illustration of the self-assembly of pillar[5]arene-based LHS with two-step sequential energy transfer. Reproduced with permission [91]. Copyright 2019, Wiley Publisher.

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  Recently, Wang et al. constructed one kind of fluorescent supramolecular vesicles using a clamp-like host 38 containing two P5 units and G2 through host-guest interactions and hydrophobic interactions [93]. The vesicles exhibited enhanced fluorescence intensity, photostability, and thermal stability. Subsequently, a LHS was developed by employing cyano-vinyl derivatives as energy donors, enabling fluorescence color modulation via FRET (Fig. 42). Notably, fluorescent ink based on the supramolecular vesicles was successfully prepared, demonstrating the system's potential applications in information encryption.

  Figure 42

  

  Figure 42.  Chemical structures of 38 and G2, and schematic illustrations of color-tunable supramolecular fluorescent vesicles with photostability and thermostability and their application in information delivery/encryption. Reproduced with permission [93]. Copyright 2022, Wiley Publisher.

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  More recently, Sun's group [94] constructed a supramolecular LHS with red light emission in water. They first used 34 and G49 to form yellow fluorescent nanoparticles by self-assembly in aqueous solution, which served as the energy donor. Subsequently, they encapsulated NIR as the energy acceptor through non-covalent interactions, achieving red light-emitting nanoparticles (Fig. 43) with just 1% co-assembled NiR (as low as 2 × 10^–7 mol/L). These red-emitting nanomaterials were suitable for typical powder dusting approach to develop latent fingerprint patterns on various substrate surfaces, producing high-resolution fluorescent images and showing potential for high-contrast imaging applications.

  Figure 43

  

  Figure 43.  Chemical structure of G49, and schematic illustrations of the construction of the supramolecular LHS based on 34 and G49, as well as its application in latent fingerprint imaging. Reproduced with permission [94]. Copyright 2023, the Royal Society of Chemistry.

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  In recent years, Liu's group had made significant contributions to the field of supramolecular ALHs [95,96]. In 2021, Liu's group developed a light-responsive supramolecular nanocomponent capable of switchable white light emission [95]. They first prepared supramolecular assemblies G50/39[1 + 1] and G50/39[2 + 2] through host-guest interactions between compound 39 and the photochromic anthracene derivative G50. These assemblies could further self-assemble into nanoparticles with cyan fluorescence (Fig. 44a). Next, they incorporated the energy acceptor NiR into the nanoparticles to form a supramolecular LHS. This system exhibited a tunable photoluminescence color depending on the donor/acceptor ratio, with white light emission appearing at a CIE coordinate of (0.33, 0.34). Additionally, G50 could switch between G50a and G50b under different light conditions, thereby reversibly blocking and restoring the resonance energy transfer (RET) between 39 and NiR (Fig. 44b). Consequently, the system could turn white light emission on or off based on the wavelength of the light (Fig. 44a). Importantly, this light-responsive supramolecular material could be used in erasable multicolor fluorescent inks for creating colored QR codes and special patterns, offering reversible hiding and revealing capabilities with significant potential for information encryption applications (Fig. 44c).

  Figure 44

  

  Figure 44.  (a) Chemical structures of G50/39[1 + 1] and G50/39[2 + 2] and schematic illustration of the controllable light-harvesting nanosystem based on photo-modulation. (b) Schematic illustration of G50 reversible control of energy transfer from 39 to NiR. (c) The photo-switched chromatic fluorescent QR code and photo-manipulative data storage, anticounterfeiting, and data confidence. Reproduced with permission [95]. Copyright 2021, Elsevier Publishers.

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  Recently, they also constructed SNs using calix[4]arene 40, tetra-(4-pyridylphenyl)ethylene G51, and photoacid sulfonato-merocyanine (MEH) [97]. Within the nanoparticle, MEH could reversibly release and capture protons, while G51 displayed pH-sensitive luminescence property. Upon irradiation at 420 nm, G51 was converted to its positively charged form through proton transfer from the ring-closed isomer spiropyran (SP). This positively charged G51 then assembled with the negatively charged calix[4]arene 40 via electrostatic interactions, forming a supramolecular assembly. The fluorescence emission of the system changed from blue to yellow and then returned to blue when the light source was removed. Furthermore, Rhodamine B (RhB) was introduced as an energy acceptor, facilitating an effective energy transfer process and resulting in the system exhibiting orange fluorescence (Fig. 45a).

  Figure 45

  

  Figure 45.  (a) Chemical structures of 40 and G51, and schematic illustration of constructing photo-activated multicomponent supramolecular assembly. (b) Schematic illustration of the 3D code encryption. (c) Photographs of photo-responsive 3D code transformation and corresponding information. Reproduced with permission [97]. Copyright 2023, Wiley Publisher.

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  Based on the light-controlled multicolor luminescence of these components, they were applied to a 3D code system. Different color blocks were used to form a color array, which could be scanned by software to read the information. As shown in Fig. 45b, the color block array was yellow in sunlight, and there was no significant difference in the luminescence color in each container under 365 nm UV light. Therefore, no information could be obtained at this time. After a 15-min exposure to 420 nm light, the fluorescent color changed, revealing Code F under UV light. This code was then scanned by software to reveal the hidden information "NKU". When the blue light exposure was removed, the fluorescent gradually returned to its original state, and the information was concealed again. Furthermore, dynamic coding was possible by adjusting the position of the color blocks. For instance, changing the position altered Code F to Code G could change the stored information from "NKU" to "C" (Fig. 45c). Code G could also respond to 420 nm irradiation, allowing for encryption of information. The dynamic transformations of the code could be repeated by irradiation and physical repositioning of the color block.

  Fluorescent nanoparticles based on macrocyclic arenes have been employed in biomedical applications, including bioimaging, intracellular sensing, cancer diagnosis, and drug delivery, due to their low biotoxicity and distinctive ability to recognize biomolecules. Nevertheless, the preparation process is relatively complex and their biocompatibility is yet to be deeply explored.

  5. Other assemblies

  The facile modification of macrocyclic arenes allows for the formation of more complex assemblies, such as nanocrystalline materials [98], metallocycles [99,100] and hybrid materials [31,101], through the synergistic effect of multiple noncovalent interactions.

  In 2019, Yang's group [98] prepared the luminescent molecular crystals of macrocycle 41, and found that the crystals exhibited enhanced blue fluorescence due to the unique stacking mode of 41 in the crystal structure. Moreover, the coordination luminescent nanocrystals with significantly long luminescence lifetimes were also obtained by the coordination of 41 and Cu(I), resulting in tunable emission property (Fig. 46).

  Figure 46

  

  Figure 46.  Chemical structure of 41, and the formation of luminescent molecular crystals via crystal growth, and coordination-driven luminescent Cu(I)−41 nanocrystals and microscope images of 41 crystals and Cu(I)−41 nanocrystals under sunlight and UV light (365 nm). Reproduced with permission [98]. Copyright 2021, American Chemical Society.

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  In 2020, Stang and co-workers [99,100] prepared a hexagonal Pt metallacycle 42 through the self-assembly driven by coordination interactions. The P5 in this metallacycle was able to bind G52 through host-guest interactions, facilitating coaggregation between G52 and P5 (Fig. 47a). This coaggregation significantly enhanced the fluorescence intensity of the system. Additionally, they constructed four triangular metallocycles (Fig. 47b) using planar chiral 43, and found that all these metallocycles exhibited CPL property, indicating their potential applications in optical materials.

  Figure 47

  

  Figure 47.  (a) Synthetic route of 42, chemical structures of 42 and G52, and host-guest interaction between 42 and G52. Reproduced with permission [99]. Copyright 2020, American Chemical Society. (b) Chemical structure of pS/pR-43 and schematic illustration of metallacycles based on 43. Reproduced with permission [100]. Copyright 2020, the Royal Society of Chemistry.

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  By using 41, oligo(phenylenevinylene) (44) and Cd(II) metal cores, Yang's group [102] synthesized a hybrid material (Fig. 48). The hybrid material showed enhanced fluorescence emission due to the minimized π-π stacking and efficient charge transfer property benefitting from the presence of 41. Additionally, the material displayed tunable multicolor emission in response to various external stimuli, such as solvents, ions and acid (Fig. 48). For instance, the hydrolyzation of Fe³⁺ ions resulted in pyridinic protonation of 44, intercepting the charge transfer process and changing the fluorescence emission of the hybrid material from yellowish-green to cyanic.

  Figure 48

  

  Figure 48.  Chemical structures of 41 and 44, and schematic illustrations of the synthesis of hybrid material, the proposed fluorescence tuning mechanisms, and the tunable luminescent responses of hybrid material toward different external stimuli. Reproduced with permission [102]. Copyright 2021, Oxford University Press.

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  In 2022, Ogoshi's group [103] reported a CPL on/off control system based on helical fibre assemblies. They synthesized water-soluble pillar[5]arene S-45 and R-45. S-45/R-45 as chiral sources, which could transfer chiral information to the assembly of a water-soluble compound G53, through host-guest interaction, thereby providing CPL property. Due to the large size and strong host-guest binding ability of S-45/R-45, the chiral transfer efficiency and resulting CPL property were highly sensitive to the feed ratio of the S-45/R-45. When the limited amounts (0.6 equiv.) of S-45/R-45 were mixed with G53, they could assemble into helical fibres with CPL property. However, a large amount (2 equiv.) of S-45/R-45 disrupted the helical fibres, resulting in the loss of chirality and CPL property (Fig. 49). This strategy demonstrates that the chirality of supramolecular CPL materials could be finely regulated by using macrocyclic arenes as the chiral sources.

  Figure 49

  

  Figure 49.  Chemical structures of S/R-45 and G53, and schematic illustration of new supramolecular CPL on/off controllable materials using water-soluble planar chiral pillar[5]arenes S-45 and R-45. Reproduced with permission [103]. Copyright 2022, the Royal Society of Chemistry.

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  6. Conclusion

  Supramolecular luminescent materials are notable for their exceptional responsiveness to stimuli and dynamic tunability, which stem from the reversible nature of non-covalent interactions. These materials offered significant advantages over traditional luminescent materials in terms of regulating construction and photophysical properties. In recent years, a growing number of macrocyclic arenes-based SLMs have been prepared, providing a diverse range of regulatory mechanisms and photophysical properties for SLMs. The diverse applications of these macrocyclic arenes-based SLMs in various fields have also been extensively investigated. This review provided a comprehensive summary of novel SLMs based on macrocyclic arenes that have emerged in the last several years. Based on the structures of the assemblies, we highlighted the employment of supramolecular assembly strategies to fabricate luminescent materials, involving host-guest complexes, supramolecular polymers, nanoparticles, and other assemblies. Moreover, the applications of these SLMs in the fields of fluorescence sensing, information encryption, and bio-imaging were also mentioned.

  Although more and more SLMs based on the macrocyclic arenes have been constructed, there are still some key points which need to be considered for improving their properties and achieving their practical applications. Firstly, the majority construction of SLMs based on macrocyclic arenes were derived from classic macrocyclic arenes, while novel macrocyclic arenes were rarely reported. However, a growing number of novel macrocyclic arenes composed of various aromatic building blocks with diverse special properties have been reported in the last several years. The construction of supramolecular luminescent materials based on novel macrocyclic arenes can bring better performance and inject fresh blood into this field. Secondly, TADF and RTP had attracted growing attention because of their unique generation processes and long-lived luminescence, which can be widely applied to the fields of optoelectronic devices, luminescence imaging, sensing, information encryption, and so on [104-108]. However, most of the SLMs based on macrocyclic arenes showed fluorescence emission. Only a few SLMs have been employed in constructing supramolecular TADF or RTP materials. Development of novel supramolecular strategy to construct TADF or RTP materials offers a new way and perspective for their practical applications in materials science. Thirdly, some macrocyclic arenes based crystalline materials exhibited excellent luminescent properties; however, they were difficult to prepare on a large scale, and they had long preparation cycle and poor operability, which significantly constrained their potential applications. Thus, it is necessary to develop other assembly forms, such as polymer materials that maintain their original luminescent property while also possessing excellent thermal stability and excellent processability. Finally, chiral macrocyclic arenes also represented a research hotspot due to their potential in the construction of CPL materials. However, the g_lum values of these materials were relatively low. Therefore, in order to solve these current problems and realized their potential applications, it is necessary to develop more novel macrocyclic arenes with various functions, especially those with luminescence or chirality, which are still few and far between. Furthermore, the complexation properties between the hosts and guests will be studied in detail to develop new strategies for constructing supramolecular luminescent materials. Last but not least, new assembly behaviour should be studied to improve their performance and achieve their applications.

  Altogether, the study endeavour for supramolecular luminescent materials is still at the preliminary stage. There also exist many challenges and limitations for the practical applications of SLMs. For example, the synthesis steps are often lengthy and costly, and difficult to prepare on a large scale, resulting in increased application costs. Supramolecular forces including hydrogen bonding, C—H···π, π-π stacking, hydrophobic effects, electrostatic effects, charge transfer interactions and so on are relatively weak compared to covalent bonds, and during the process of making devices, they are often disrupted, making it difficult to reach technical specifications. The functionality achieved through supramolecular assembly is unstable, and there may still be the issues of repeatability. However, everything has two sides, and supramolecular systems can provide good responsiveness to external stimuli, thus having great applications in the field of smart luminescent materials. We hope that this review will not only be very helpful for the development of macrocyclic arene chemistry, but also provide some valuable guidance toward the design of smart supramolecular luminescent materials.

  Declaration of competing interest

  The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper.

  CRediT authorship contribution statement

  Yu-Jie Long: Writing – original draft, Formal analysis, Data curation, Conceptualization. Xiao-Ni Han: Writing – review & editing, Formal analysis, Data curation. Ying Han: Writing – review & editing, Writing – original draft, Funding acquisition, Formal analysis, Conceptualization. Chuan-Feng Chen: Writing – review & editing, Supervision, Funding acquisition, Conceptualization.

  Acknowledgments

  We thank the National Natural Science Foundation of China (Nos. 22171272, 22031010), the Strategic Priority Research Program of the Chinese Academy of Sciences (No. XDB0520302) and the Youth Innovation Promotion Association CAS (No. 2021035) for financial support.

  
  
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• 

  Figure 1  Chemical structures of 1, 2, G1 and G2.

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  Figure 2  Chemical structures of (a) G3, G4, G5 and (b) 3. (c) Schematic illustration of the supramolecular assembly based on 3 and G4, and the white-light emission adjusted by the host-guest interactions. Reproduced with permission [34]. Copyright 2019, Wiley Publisher.

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  Figure 3  Chemical structures of 4 and G6, and schematic illustration of the self-assembly process and Förster resonance energy transfer (FRET) process of G6 ⊂ 4. Reproduced with permission [35]. Copyright 2023, the Royal Society of Chemistry.

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  Figure 4  Chemical structures of 5a, 5b and G7, and schematic illustration of pH-responsive complex G7 ⊂ 5a. Copied with permission [36]. Copyright 2019, Frontiers Media S.A.

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  Figure 5  Chemical structures of P/M-6 and G8. Copied with permission [37]. Copyright 2022, MDPI.

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  Figure 6  (a) Chemical structures of S_ic/R_ic-7 and R/S-G9. (b) Schematic illustration of competitive conformation chirality of 7 induced by R/S-G9. Reproduced with permission [38]. Copyright 2021, Wiley Publisher.

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  Figure 7  (a) Synthetic route of G10 ⊂ 8. (b) Schematic illustration of CPL switching system based on G10 ⊂ 8 upon the addition or removal of external stimuli. Reproduced with permission [39]. Copyright 2021, Wiley Publisher.

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  Figure 8  (a) Chemical structures of P5 and G11. (b) Schematic illustration of internal-driven interaction induced by the UV-light (254 nm). Reproduced with permission [40]. Copyright 2022, Elsevier Publishers.

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  Figure 9  Vapoluminescence behaviors triggered by crystal-state complexation between 9 and guests (G12, G13, and G14). Reproduced with permission [41]. Copyright 2020, American Chemical Society.

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  Figure 10  (a) Preparation of G15 ⊂ 10 by cocrystal growth. (b) Optical microscopy images of 10 and G15 ⊂ 10. (c) Crystal structures of G15 ⊂ 10. Reproduced with permission [3]. Copyright 2022, Wiley Publisher.

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  Figure 11  (a) The TADF emission realized by formation of ICT state between the macrocyclic donor and guest. (b) Chemical structures and electrostatic potential maps of 10 and guests G16-G22. (c) Optical microscopy images of G16 ⊂ 10-G22 ⊂ 10 under sunlight (up) and UV light (down). Reproduced with permission [42]. Copyright 2024, Springer Nature.

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  Figure 12  Schematic illustration of (a) the RTP emission and (b) the RTP emission of selectively activated 11. (c) Chemical structures of G15, G17, and 11. (d) Phosphorescence QR code and information storage/encryption of solvent response. Reproduced with permission [43]. Copyright 2023, Wiley Publisher.

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  Figure 13  (a) Macrocycle-to-macrocycle conversion synthetic strategy of 12. (b) Schematic illustration of the construction of color-tunable supramolecular luminescent co-assemblies 1,3–12@TCNB and 1,2–12@TCNB. (c) The two co-assemblies excited by NIR light emit distinct upconversion fluorescence. Reproduced with permission [44]. Copyright 2023, Wiley Publisher.

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  Figure 14  Chemical structures of 13 and G23, and schematic illustrations of the linear AIE supramolecular polymer and the reversible cross-linking process of the linear polymer by Cu²⁺ and CN⁻. Reproduced with permission [46]. Copyright 2019, American Chemical Society.

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  Figure 15  Chemical structures of 14 and G24, and schematic illustration of the formation of linear supramolecular polymer and its dissociation by the addition of 1,4-butanedinitrile and P5. Reproduced with permission [47]. Copyright 2024, Elsevier Publishers.

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  Figure 16  Chemical structures and distributions of the electrostatic potential mapped onto the electron density surfaces of G25, G26 and 15, and the self-assembled modes of G26 and G26 ⊂ 15 in the solid state. Reproduced with permission [48]. Copyright 2020, American Chemical Society.

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  Figure 17  Chemical structure of 16 and schematic illustration of the formation of the fluorescent supramolecular polymer and its application in the detection of n-butyraldehyde (C₄) and caprylicaldehyde (C₈) vapors. Reproduced with permission [49]. Copyright 2022, Wiley Publisher.

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  Figure 18  Chemical structure of 17 and schematic illustration of the construction of the luminescent spherical aggregates based on the self-assembly of 17. Reproduced with permission [50]. Copyright 2023, the Royal Society of Chemistry.

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  Figure 19  Chemical structure of 18 and schematic illustration of linear supramolecular polymers. Reproduced with permission [51]. Copyright 2023, Wiley Publisher.

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  Figure 20  (a) Chemical structures of 19, G27, G28 and G29. (b) Schematic illustration of supramolecular polymer network. (c) CIE 1931 chromaticity diagram. Gray quadrilateral: the color gamut of the supramolecular polymer network. Black triangle: the sRGB gamut. (d) Fluorescence photographs of the supramolecular polymer network in the co-solvent of CHCl₃/cyclohexane (3:7 by volume), including a white emission of (0.33, 0.33) in CIE coordinates. λ_ex = 368 nm. Reproduced with permission [52]. Copyright 2020, Wiley Publisher.

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  Figure 21  Chemical structures of 20, G30 and G31, and schematic illustration of the supramolecular material constructed by host-guest interactions. Reproduced with permission [53]. Copyright 2022, the Royal Society of Chemistry.

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  Figure 22  (a) Chemical structures of the color-tunable TADF polymers. (b) Schematic illustration of thin films prepared by spin-coating method and coatings prepared by spray-coating method. (c) The process of multiple reuses of anti-counterfeit labels (pattern 1: ♥CAS; pattern 2: dragon; pattern 3: phoenix) produced by TADF polymers. (d) Schematic illustration of binary information conversion of multi-color two-dimensional barcode. (e) A conceptual application of multi-color two-dimensional barcode.

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  Figure 23  Chemical structure of 21 and schematic illustrations of the color-tunable polymer constructed by tuning the molar ratio of Eu³⁺ and Tb³⁺ in the system and the fluorescence on/off sensing of nitroaromatic pollutants. Reproduced with permission [55]. Copyright 2022, the Royal Society of Chemistry.

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  Figure 24  (a) Chemical structures and synthetic routes of pR/pS-22 and the corresponding coordination supramolecular polymers. (b) Schematic illustration of the construction of P5-based materials with polymerization and aggregation enhanced CPL. Reproduced with permission [56]. Copyright 2023, Wiley Publisher.

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  Figure 25  Chemical structures of 23 and G32, and schematic illustration of solvent-controlled aggregation of 23 and the modulation process of white emission. The inset picture shows the white fluorescence of the supramolecular system under UV light. Reproduced with permission [57]. Copyright 2020, the Royal Society of Chemistry.

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  Figure 26  Chemical structures of 24, G33a and G33b, and schematic illustration of the construction of a full-color lanthanide supramolecular light switch based on noncovalent assembly. Reproduced with permission [58]. Copyright 2023, the Royal Society of Chemistry.

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  Figure 27  (a) Chemical structures of 25 and G34. Schematic illustration of (b) two supramolecular polymer networks (SPNs) and the reversible quenching and recovery property of the fluorescence by Cu²⁺ and CN⁻ ions, and (c) the recyclable writing and erasing processes of SPN-based rewritable paper. Reproduced with permission [59]. Copyright 2023, the Royal Society of Chemistry.

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  Figure 28  Chemical structures of 26 and G35 and schematic illustration of the sensing and removal of Hg²⁺ from water based on the “switch-on” fluorescence of the supramolecular polymers and the regeneration−recycling process. Reproduced with permission [60]. Copyright 2019, American Chemical Society.

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  Figure 29  Chemical structures of 27 and G36, and schematic illustrations of the assembly process of supramolecular polymer and the sensing to Fe³⁺. Reproduced with permission [63]. Copyright 2023, Elsevier Publishers.

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  Figure 30  (a) Chemical structures of 28, G37, and G38. (b) Schematic illustration of the supramolecular polymerization based on host-guest interaction and hydrogen bonding (inset: photo of the supramolecular gels under natural light and 365 nm UV light). Reproduced with permission [65]. Copyright 2022, American Chemical Society.

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  Figure 31  (a) Chemical structures of 29 and G39, and possible assembly mechanism of the gel and photo showing the broad-spectrum detection and adsorption separation properties for broad-spectrum pollutants for (b) cations and anions, (c) volatile organic compounds (VOCs), and (d) various organic dyes, organic pollutants, and oxyanions. Reproduced with permission [69]. Copyright 2019, American Chemical Society.

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  Figure 32  Chemical structures of 30 and G40, and schematic illustration of the assembly process between 30 and G40 and its response mechanism. Reproduced with permission [72]. Copyright 2023, Elsevier Publishers.

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  Figure 33  Chemical structures of 31 and G41.

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  Figure 34  (a) Chemical structures of 32 and G42. (b) The fabrication of SNPs@DOX using SNPs as drug nanocarriers and schematic illustration of imaging-guided drug delivery. Reproduced with permission [76]. Copyright 2021, the Royal Society of Chemistry.

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  Figure 35  Chemical structures of 33 and DNS-G, and schematic illustrations of the formation of SNs and their stimuli-responsive drug release. Reproduced with permission [77]. Copyright 2021, American Chemical Society.

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  Figure 36  Chemical structures of 34, G43, SDBS and target molecule (HDPP), and schematic illustration of supramolecular self-assemblies from G43, 34/G43, and 34/G43/SDBS. Reproduced with permission [78]. Copyright 2020, the Royal Society of Chemistry.

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  Figure 37  Chemical structures of 35 and G44, and schematic illustration of constructing nano-film by the guest induction to regulate fluorescent nanoparticles that formatted from the tri-[2]rotaxane. Reproduced with permission [79]. Copyright 2021, the Royal Society of Chemistry.

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  Figure 38  Chemical structure of G45 and schematic illustrations of the construction of fluorescent nanoparticles and its application in detection of L-Asp and L-Glu in water. Reproduced with permission [80]. Copyright 2022, Wiley Publisher.

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  Figure 39  (a) Synthetic routes of 36 and G46. (b) Schematic illustration of the proposed assembly mode of the supramolecular system and ions inducing them to transition from the nanomaterials to QDs. Reproduced with permission [81]. Copyright 2022, American Chemical Society.

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  Figure 40  Chemical structures of 37, G2, G3 and G47, and schematic illustrations of the construction and property study of supramolecular polymer networks. Reproduced with permission [89]. Copyright 2019, Wiley Publisher.

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  Figure 41  Chemical structure of G48 and schematic illustration of the self-assembly of pillar[5]arene-based LHS with two-step sequential energy transfer. Reproduced with permission [91]. Copyright 2019, Wiley Publisher.

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  Figure 42  Chemical structures of 38 and G2, and schematic illustrations of color-tunable supramolecular fluorescent vesicles with photostability and thermostability and their application in information delivery/encryption. Reproduced with permission [93]. Copyright 2022, Wiley Publisher.

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  Figure 43  Chemical structure of G49, and schematic illustrations of the construction of the supramolecular LHS based on 34 and G49, as well as its application in latent fingerprint imaging. Reproduced with permission [94]. Copyright 2023, the Royal Society of Chemistry.

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  Figure 44  (a) Chemical structures of G50/39[1 + 1] and G50/39[2 + 2] and schematic illustration of the controllable light-harvesting nanosystem based on photo-modulation. (b) Schematic illustration of G50 reversible control of energy transfer from 39 to NiR. (c) The photo-switched chromatic fluorescent QR code and photo-manipulative data storage, anticounterfeiting, and data confidence. Reproduced with permission [95]. Copyright 2021, Elsevier Publishers.

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  Figure 45  (a) Chemical structures of 40 and G51, and schematic illustration of constructing photo-activated multicomponent supramolecular assembly. (b) Schematic illustration of the 3D code encryption. (c) Photographs of photo-responsive 3D code transformation and corresponding information. Reproduced with permission [97]. Copyright 2023, Wiley Publisher.

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  Figure 46  Chemical structure of 41, and the formation of luminescent molecular crystals via crystal growth, and coordination-driven luminescent Cu(I)−41 nanocrystals and microscope images of 41 crystals and Cu(I)−41 nanocrystals under sunlight and UV light (365 nm). Reproduced with permission [98]. Copyright 2021, American Chemical Society.

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  Figure 47  (a) Synthetic route of 42, chemical structures of 42 and G52, and host-guest interaction between 42 and G52. Reproduced with permission [99]. Copyright 2020, American Chemical Society. (b) Chemical structure of pS/pR-43 and schematic illustration of metallacycles based on 43. Reproduced with permission [100]. Copyright 2020, the Royal Society of Chemistry.

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  Figure 48  Chemical structures of 41 and 44, and schematic illustrations of the synthesis of hybrid material, the proposed fluorescence tuning mechanisms, and the tunable luminescent responses of hybrid material toward different external stimuli. Reproduced with permission [102]. Copyright 2021, Oxford University Press.

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  Figure 49  Chemical structures of S/R-45 and G53, and schematic illustration of new supramolecular CPL on/off controllable materials using water-soluble planar chiral pillar[5]arenes S-45 and R-45. Reproduced with permission [103]. Copyright 2022, the Royal Society of Chemistry.

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