Unprecedented TPE-Embedded Butterfly Bis-Crown Ether with Controllable Conformation and Supramolecular Chiroptical Property

doi:10.21203/rs.3.rs-4143303/v1

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Unprecedented TPE-Embedded Butterfly Bis-Crown Ether with Controllable Conformation and Supramolecular Chiroptical Property

https://doi.org/10.21203/rs.3.rs-4143303/v1

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Understanding how subtle structural differences between macrocyclic conformational isomers impact their properties and separation has garnered increasing attention in the field of supramolecular synthetic chemistry. In this work, a series of tetraphenylene (TPE)-embedded butterfly bis-crown ether macrocycles (BCE[n], n = 4-7), comprising two crown ether side rings and a TPE core, were synthesized through intramolecular McMurry coupling. Unexpectedly, the presence of flexible oligoethylene chains with varying lengths were found to influence molecular conformation via intramolecular interactions, resulting in the formation of two stabilized conformers with specific semi-rigid symmetric/asymmetric structures (sym-BCE[n] and asym-BCE[n], n = 5, 6). Moreover, it is noteworthy that neither symmetric nor asymmetric conformers are present in the more rigid BCE[4] or the more flexible BCE[7]. Interestingly, these conformers display distinct fluorescence properties and host-guest binding abilities, and only sym-BCE[5] can serve as a host for chiral polymer binding, resulting in the formation of chiral supramolecular assemblies through host-guest interaction induced chirality. Moreover, both circular dichroism (CD) and circularly polarized luminescence (CPL) signals of the obtained assemblies could be switched off by the addition of sodium ion (Na⁺), suggesting potential applications in the field of dynamic chiral materials.

Physical sciences/Chemistry/Supramolecular chemistry/Self-assembly

Physical sciences/Chemistry/Supramolecular chemistry

bis-crown ether

aggregation-induced emission enhancement

controllable conformation

host-guest interaction

supramolecular chirality

Tetraphenylethylene (TPE) represents one of the most prevalent aggregation-induced emission (AIE)-active moieties, making it an ideal fluorescent building block for integration into macrocycles.^[1–6] It is noteworthy that a TPE derivative theoretically possesses a diverse range of conformations, which are determined by the varying angles of the C_(Ar)—C═C bond within the TPE core. And the alteration in conformational change can lead to variable photophysical properties.^[7–12] By restricting the angles of the C_(Ar)—C═C bond in the AIE compounds, these molecules with diverse conformations hold great potential for precise modulation of material functionalities.^[13–16] Moreover, the TPE group exhibits either clockwise or anticlockwise rotational patterns in its propeller-like P or M configurations, respectively, by restricting the intramolecular flipping of phenyl rings. For example, the P or M configurations of TPE can also be constrained through the introduction of a rigid cyclic structure, offering the possibility for construction of chiral materials.^[17–20] So far, achieving distinct conformations for TPE compounds remains a challenging task.

Herein, we report the synthesis of a series of TPE-based bis-crown ethers (BCE[n], n = 4–7) through intramolecular McMurry coupling interaction. In order to achieve AIE-active macrocycles with distinct conformations in both solution and solid state, chains with appropriate length were introduced to connect the phenyl-substituents, thereby restricting the angles of the C_(Ar)—C═C bond with benzene rings. The TPE unit was cyclized through flexible ethylene glycol chains, and it was found that varying chains lengths led to distinct degrees of distortion in the TPE core due to intramolecular tension. Surprisingly, both BCE[5] and BCE[6] exhibit two conformations, namely sym-BCE[n] and asym-BCE[n] (n = 5, 6), respectively. Moreover, it is noteworthy that neither symmetric nor asymmetric conformer is present in the more rigid BCE[4] or the more flexible BCE[7]. Furthermore, variations in cavity size and shape result in diverse fluorescence and binding properties among different conformers. It is worth noting that only sym-BCE[5] can act as a host for chiral polymer guest binding, thereby enabling the generation of chiral materials with controllable handedness through supramolecular chiral amplification induced by host-guest interaction (Fig. 1).

2.1 Synthesis and structural characterization

Through a facile three-step process, TPE units were embedded into crown ether to synthesize TPE-cored butterfly-shaped macrocycles (Fig. 2). Our methodology distinguishes itself from previous reports on crown ether-functionalized TPE-based macrocycles obtained by the direct intermolecular cyclization,^[21–23] as it is challenging to achieve high yields of smaller-sized crown ether ring-functionalized TPE-macrocycles due to the strain resulting from intramolecular cyclization.

BCE[n] (n = 4–7) with identical skeletal structures but varying lengths of crown ether chains were synthesized, and the synthesis route as well as the detailed procedures are elaborated in the supporting information (Scheme S1-S3). Taking BCE[5] as a representative example, we first obtained the cyclic diketone through reacting two dihydroxybenzophenone molecules with two equivalents of tetraethylene glycol ditosylate in a highly concentrated reaction solution (Figure S1-S12). With the diketone in hand, the target macrocycle BCE[5] could be efficiently obtained via an intramolecular McMurry reaction in the final coupling step. As expected, three additional BCE[n] (n = 4, 6, 7) were also successfully prepared using this convenient methodology with moderate yields (Scheme S2, S3). The BCE[n] were fully characterized by ¹H NMR, ¹³C NMR, HR-ESI-MS, and single crystal analyses to validate their structural integrity (Figure S13‐S30, Supporting Information).

The reaction of diketone compound with zinc powder (5 equiv.) and TiCl₄ (2.5 equiv.) resulted in the formation of BCE[5] product, which was obtained with a moderate yield (38%). This product exhibited blue color in solid state under UV-irradiation. To further optimize the yield, we explored the feasibility of increasing the quantity of zinc powder by varying its ratio from 5 to 40 equivalents. The ¹H NMR spectra revealed slight variations in the products obtained under different equivalents of zinc powder conditions (Figure S36). In Fig. 3a and S13, it is evident that reducing the quantity of zinc powder used in the reaction resulted in the observation of two distinct peaks at 6.68 and 6.91 ppm for the C-H protons of the aromatic protons in the product, as observed in CDCl₃. However, when increasing the amount of zinc powder to 20 equiv. and 30 equiv., a broadening peak resembling a mixture was observed, indicating gradual formation of side-products (Figure S36). By employing 40 equiv. of zinc powder, another pure product was successfully obtained as evidenced by the ¹H NMR spectra (Figure S16). Interestingly, this product exhibits a distinct green color in its solid state under UV-irradiation. Additionally, its ¹H NMR spectrum shows slight differences compared to the previously mentioned product. For example, its resonance peaks at 6.82 and 6.88 ppm become closer to each other, and its (-OCH₂) signal corresponding to the ether chains displays a slightly downfield chemical shift (Fig. 3a). Notably, there is also noticeable disparity between the chemical shifts of these two products around 130–140 ppm on the ¹³C NMR spectra (Figure S14, S17). Furthermore, mass spectrometry analysis confirmed that both products possessed identical molecular weight consistent with our target molecule, suggesting the formation of two conformers (Figure S15, S18). By varying the amount of zinc powder from 5 to 40 equiv., column chromatography demonstrated controllable production of the two products with different yields (Fig. 3b). The yield of the blue conformer gradually decreased as the amount of zinc powder increased, while the yield of the green conformer gradually increased.

The single crystals of both products were obtained through slow vapor diffusion of n-hexane into chloroform solution containing the macrocycles (Figure S40, S41). The crystal structures confirm that the macrocycles consist of a TPE core and two crown ether rings positioned on either side (Fig. 4a, 4b). Similar to other TPE derivatives, the four phenyl rings are not coplanar with the central C = C double bond, resulting in a characteristic propeller-like structure. The solid state structure of the product obtained with 10 equiv. of zinc powder exhibits an asymmetric structure (asym-BCE[5]) with C_(Ar)—C═C bond angles measuring 121.05°, 123.46°, 123.59° and 122.79° between four phenyl rings and C = C bond, respectively. However, the crystal of the other product obtained with 40 equiv. of zinc powder adopts a highly symmetric butterfly-shaped conformation (sym-BCE[5]), with the C_(Ar)—C═C bond angles between the phenyl rings and the C = C bond measuring 121.75°, 121.75°, 122.15° and 122.15°, respectively. Those two conformations arise from different degrees of distortion induced by flexible crown ether ring units on the phenyl rings. Both left-handed helical (M) conformation and right-handed (P) conformations can be equally observed within one unit cell, indicating that these two crystals are racemic.

The combination of NMR and single crystal data reveals that BCE[5] adopts two stable conformations in both solid state and solution. The crystal structures of these conformers suggest the presence of potential weak intramolecular interactions, which are likely crucial for maintaining the conformational state within this confined environment. The existence of multiple intramolecular interaction, such as C-H⸱⸱⸱O and C-H⸱⸱⸱π interaction, within the BCE[5] skeleton may influence both cavity shape and TPE angle. For example, due to the spatial proximity (Fig. 4a, 4b), asym-BCE[5] is expected to exhibit a higher number of C-H⸱⸱⸱O interactions compared to sym-BCE[5]. Moreover, there are notable disparities in their respective stacking configurations. As shown in Fig. 4c, the crystal packing structure of symmetrical sym-BCE[5] reveals intermolecular interactions within the three adjacent molecules through C–H···O bond. In contrast, asymmetrical asym-BCE[5] displays intermolecular interactions around the neighboring four molecules, leading to a more tightly packed arrangement (Fig. 4d). This close packing restricts the rotation of TPE in the crystalline phase. Consequently, sym-BCE[5] exhibits a more obvious cyan color compared to its asymmetric counterpart.

To further investigate the disparities in molecular conformations and structures between sym-BCE[5] and asym-BCE[5], density functional theory (DFT) calculations were performed based on their respective crystal structures with Gaussian 09 software package (Revision D. 01) using M06-2X functional with 6-311G(d, p) basis.^[24] Computationally optimized geometries confirm that both conformations resemble their original crystal structures, indicating their thermodynamic stability. The twisted conformation of asym-BCE[5] exhibits a lower energy state compared to the sym-BCE[5] conformer (E_asym=2382.0772 vs E_sym=2382.0890 according to the DFT calculation), suggesting its enhanced stability. Consequently, the structure of asym-BCE[5] is more thermodynamically stable than that of sym-BCE[5] (Figure S45).

Based on the aforementioned experimental data and analyses, it is evident that the yields of these two conformers are influenced by the McMurry reaction condition.^[25–28] The varying amount of zinc powder may induce a templated effect, leading to a preference for one conformer in the product. Additionally, the polar surface of low-valent titanium would serve as an additional template, simultaneously promoting the formation of one stable conformer structure.^[29–32] However, insufficient Zn²⁺ concentration within the reaction mixture leads to formation of a more stable asymmetrical asym-BCE[5] conformation as typically observed in McMurry reactions.^[33] To confirm that the amount of Zn²⁺ is significant to the selectivity of sym-BCE[5]/asym-BCE[5], we added additional ZnCl₂ to the reaction system mentioned above, which initially had insufficient Zn²⁺. As a result, the yield of sym-BCE[5] increased by 62.5%. Although 10 equiv. of zinc powder may seem excessive, due to the limited solubility of zinc powder in THF, the actual concentration of Zn²⁺ remains insufficient. Considering that diketone 2 with an electron rich cavity and exhibits exceptional capability in accommodating Zn²⁺ metal ions, ¹H NMR titration experiments were conducted to confirm that Zn²⁺ can bind with diketone 2 (Figure S47). Furthermore, Job’s plot experiment indicated that diketone 2 could form complexes with Zn²⁺ in a 1:1 stoichiometry (Figure S48). Therefore, we hypothesize that a sufficient amount of Zn²⁺ ions can be pre-organized within the cavity of ether rings in diketone during reagent preparation, leading to the adoption of a specific conformation by diketone (Figure S49).

To further validate the role of potential weak interactions in maintaining distinct conformations, CD₃OD was introduced into the CDCl₃ solution of sym-BCE[5] to investigate its ability to attenuate their intramolecular interactions (Fig. 5). An increase in H_a' and H_b' protons and a gradual disappearance of H_a and H_b protons were observed, providing evidences for the successful transformation from sym-BCE[5] to asym-BCE[5]. In contrast, when CD₃OD was added to the CDCl₃ solution of asym-BCE[5], no significant change in chemical shift occurs (only solvent-induced chemical shift changes were observed). In addition, variable-temperature ¹H NMR experiments were conducted to investigate the stability and dynamic transformation process of BCE[5]. To avoid the potential disruption of weak intramolecular interaction, CDCl₃ was chosen as the solvent. No merging or splitting phenomena were observed in the NMR spectra for any protons, indicating that increasing the solution temperature would not disrupt the intramolecular interaction and thus the conformation of sym-BCE[5] or asym-BCE[5] could be maintained (Figure S50 and S51).

Subsequently, two conformers of TPE-based bis-crown ethers BCE[6] with longer pentaethylene glycol linkers, namely sym-BCE[6] and asym-BCE[6], were successfully synthesized (Figure S19-S24, S37). However, it should be noted that the yield of sym-BCE[6] is significantly lower. The crystal structure of asym-BCE[6] was also obtained, as shown in Figure S42, similar to asym-BCE[5], the C_(Ar)—C═C bond angles were measured to be 122.69°, 121.19°, 121.05° and 122.46°, respectively. However, our attempts to obtain the crystal structure of sym-BCE[6] were unsuccessful, so we employed DFT calculation to model its structure (Figure S46). The results showed that the C_(Ar)—C═C bond angles of sym-BCE[6] were 121.58°, 121.58°, 121.34° and 121.34°. Interestingly, the presence of multiple intramolecular interactions results in the formation of a small pocket within the side chain, leading to a distinct conformation of sym-BCE[6] compared to asym-BCE[6] (Fig. 6a, 6b). The size of the asym-BCE[6] cavity is restricted by this pocket, potentially hindering its binding with ions. The different conformations arise from varying degrees of C_(Ar)—C═C bond induced by flexible crown ether ring units on phenyl rings. Furthermore, we successfully obtained a cocrystal of asym-BCE[6] and K⁺ ion through slow vapor diffusion of n-hexane into acetone solution. As shown in Fig. 6c, asym-BCE[6] can bind with K⁺ ion in a 1:1 ratio (Figure S44), while another cavity is occupied by one H₂O molecule. This indicates that the binding process between K⁺ ion and one cavity may result in reduced electron density within the adjacent cavity, thereby hindering its ability to bind another K⁺ ion.

In order to further investigate the effect of glycol-linked chain length on the conformation of bis-crown ethers, we synthesized BCE[4] with shorter triethylene glycol side chains and BCE[7] with longer hexaethylene glycol side chains (Figure S25- S30). Interestingly, only one conformer was formed in each case (Figure S35, S38). This can be attributed to the fact that the short rigid side chain fixes the conformation in a twisted structure, while the long flexible side chain fails to restrict the C_(Ar)—C═C bond of TPE core, resulting in an inability to fix the conformation into specific structures. To confirm their conformations, single crystals of BCE[4] and BCE[7] were obtained through slow vapor diffusion of n-hexane into chloroform solution containing the macrocycles (Figure S39, S43). The crystal data strongly indicate that BCE[4] and BCE[7] exhibit a single conformation (the C_(Ar)—C═C bond angles of TPE core in BCE[4] and BCE[7] is 122.74°, 122.16°, 121.01°, 122.98° and 121.84°, 122.31°, 121.62°, 121.85°, respectively). By integrating all experiment data, it can be deduced that the occurrence of different conformers also relies on the level of flexibility within the crown ether skeleton. This distinctive phenomenon can only be observed in the semi-rigid macrocycles BCE[5] and BCE[6].

2.2 Photophysical properties

Furthermore, the photophysical properties of the macrocycle isomers were investigated. Taking BCE[5] as an example, the sym-BCE[5] and asym-BCE[5] conformers both exhibited a comparable absorption profile, characterized by two distinct bands in the range of 230–430 nm (Figure S52). Given that BCE[5] possesses typical aggregation-induced emission (AIE) characteristics, we examined the AIE effect of sym-BCE[5] and asym-BCE[5] using fluorescence emission spectroscopy in chloroform-acetone mixtures with varying acetone fractions, respectively. The fluorescence intensity of sym-BCE[5] in pure chloroform initially shows a detectable response, which gradually increases upon the addition of acetone as a poor solvent, accompanied by bluish-green emission. The maximum fluorescence intensity is achieved at 455 nm when the acetone fraction reaches 90%, indicating that sym-BCE[5] exhibits typical AIE characteristics (see Fig. 7a and 7c). Further increasing the volume fraction of acetone to 95% leads to a slight decrease in fluorescent intensity due to precipitate formation. For asym-BCE[5], it shows no significant fluorescence emission when the acetone content ranges from 0 to 90%. However, when the acetone fraction reaches 95%, it exhibits intense emission as well (Fig. 7b). In comparison to sym-BCE[5], the fluorescence emission enhancement and intensity were relatively low under identical conditions. It is noteworthy that the maximum emission wavelength of asym-BCE[5] at 430 nm is blue-shifted compared to that of sym-BCE[5]. This spectral shift can be attributed to their distinct packing arrangements.^{[34, 35]}

2.3 Host-guest chemistry

The inherent helical chirality of TPE is widely recognized when the rotation of the phenyl rings is constrained.^[36] Inspired by the chirality amplification phenomenon observed in supramolecular systems, we aim to utilize host-guest interaction between chiral guest molecule and achiral host to induce and amplify the chirality of our macrocycles.^[37–41] Additionally revealing the chirality of amino acid-containing copolymers poses significant challenges due to the absence of chromophoric groups and racemic mixture of amino acid enantiomers.^[42] To address these issues, we propose an approach to design a predominant single-handed conformation between chiral amino acid co-polymer guest and BCE[n], with the anticipation that the intrinsic chirality of BCE[n] can be induced in the presence of an additional chiral guest.

Subsequently, we constructed a supramolecular assembly through host-guest interactions between achiral BCE[n] and a chiral amino acid polymer L_G (D_G). The structures and detailed synthesis procedures of chiral polymers L_G (D_G) are provided in the Supporting Information (Scheme S4, Figure S31-S34). Prior to investigating the chiral amplification between the host and the guest, we initially examined their host-guest interaction by employing benzyl N-benzoyl-L-alaninate (G_m) as a model guest monomer. The complexation between BCE[n] and G_m were investigated using ¹H NMR titration experiments. However, except for sym-BCE[5], none of the proton signals exhibited any significant shift when mixed with G_m for the other four bis-crown ethers, indicating no complexation occurred (Figure S56-S59). As depicted in Fig. 8 and Figure S53, the sym-BCE[5] host experienced significant chemical shifts of the protons with increasing equivalents of G_m. The peak of H_a, H_b, H_c and H_e,f in sym-BCE[5] exhibited splitting and upfield shifts. A slight upfield shift was also observed in the chemical shift of proton H₁ in G_m. When the amount of G_m reached 1.0 equiv. or more, no significant change were observed in NMR spectra, indicating a saturated condition. These observations suggest that the monomer guest G_m can form a stable 1:1 complex with sym-BCE[5], and the complexation between G_m and sym-BCE[5] exhibited a slow-exchange process. Furthermore, Job’s Plot analysis further verified the binding ratio is 1:1, which may be attributed to steric hindrance limiting the binding ability of sym-BCE[5] towards a second guest (Figure S54). The association constant (K_a) for the sym-BCE[5]⊃G_m complex was determined to be 9.3×10² M^− 1 by UV/Vis titration (Figure S55).

2.4 Chiral amplification and regulation

Due to the induced chiral amplification from the chiral polymer guest L_G (D_G) to the AIE-active host sym-BCE[5], we inferred that this supramolecular assembly could exhibit circular dichroism (CD) properties (Fig. 9a). Therefore, CD spectra were carefully examined at varying molar ratios of sym-BCE[5]/L_G ranging from 1:0 to 1:1.1. Upon addition of L_G to the achiral sym-BCE[5] solution, a strong negative cotton effect at 350 nm could be observed in the CD spectrum. This can be attributed to chiral amplification of the macrocycle sym-BCE[5] induced by host-guest complexation. The highest CD intensity is achieved when L_G is present in an equimolar ratio with sym-BCE[5]. Further increasing L_G up to 1.1 equiv. did not result in significant changes in the intensity of CD signals. Therefore, our focus primarily lies on investigating the optimal stoichiometric ratio of 1:1 for achieving chiral amplification in the sym-BCE[5]⊃L_G system. Under identical conditions, D_G exhibited a positive cotton effect at 350 nm, representing mirror image CD signals compared to those obtained for the sym-BCE[5]⊃L_G system.

The circularly polarized luminescence (CPL) properties of the host-guest assemblies between sym-BCE[5] and chiral guest were also explored. As shown in Fig. 9b, both sym-BCE[5]⊃L_G and sym-BCE[5]⊃D_G complexes exhibited a pair of mirror-image CPL signals in the range of 400–500 nm due to the chiral amplification facilitated by strong host-guest interactions and well-order assembled nanostructures. The maximum g_lum values of CPL for sym-BCE[5]⊃L_G and sym-BCE[5]⊃D_G were determined to be ‒1.80 × 10^− 2 and 1.84 × 10^− 2 at 455 nm, respectively. In contrast, no CPL signals could be observed at any wavelength for the guest L_G and D_G alone, highlighting the crucial role played by the host in providing optical performance.

Subsequently, transmission electron microscopic (TEM) and scanning electron microscopy (SEM) measurements were utilized to explore the morphologies of polymeric guests and their assemblies. TEM images revealed that L_G or D_G self-assembled into nanowire structure with average widths of approximately 100 nm and 200 nm in chloroform, respectively (Figure S67). When sym-BCE[5] was mixed with L_G, SEM and TEM images clearly showed that the resulting supramolecular complex sym-BCE[5]⊃L_G exhibited a left-handed linear nanostructure with helixes, while D_G with the opposite molecular chirality formed a right-handed nano-helical structure (Fig. 9c and S67).

Based on the aforementioned investigation of host-guest interactions, sym-BCE[5] exhibited superior binding properties towards guests, making it an ideal candidate for further comprehensive exploration. Considering the potential site for metal ion binding with crown ether rings, the introduction of competitive metal ions can effectively regulate the chiral assemblies. It is widely recognized that sodium cations exhibit a stronger affinity towards crown ethers compared to secondary amines.^[43–48] Therefore, sodium tetrakis[3,5-bis(trifluoromethyl)-phenyl]borate (NaBArF) was selected as a competitive guest to modulate the CD and CPL switching behavior of the host-guest complex, presenting an innovative approach for fabricating dynamic CPL-active materials.^[49]

The binding behavior of the Na⁺ cation to sym-BCE[5] was investigated using ¹H NMR spectroscopy in CDCl₃ solution. Upon addition of Na⁺, significant chemical shift changes were observed, with the maximum chemical shift reached when one equivalent of Na⁺ was added (Figure S60). This observation suggests the formation of a 1:1 complex between sym-BCE[5] and Na⁺. Furthermore, the binding behavior exhibited fast exchange kinetics on the NMR spectroscopic timescale. Job’s Plot confirmed a 1:1 stoichiometry similar to BCE[6] in its binding with K⁺ ion (Figure S61), and the association constant (K_a) was calculated as 2.70×10³ M^− 1 by analyzing sequential changes in UV-vis absorbance of sym-BCE[5] in the presence of varying concentrations of Na⁺ (Figure S62). This indicates that Na⁺ competes effectively in regulating the self-assembly of sym-BCE[5]-based assemblies. In contrast, minimal changes in chemical shifts were observed in the CDCl₃ solution of asym-BCE[5] under identical conditions, suggesting a lack of strong binding affinity between asym-BCE[5] and Na⁺ cation (Figure S63). This could be attributed to the unfavorable effect of its more twisted and smaller-sized cavities on guest binding of asym-BCE[5].

Titration experiments were further conducted to investigate the CD spectra changes upon adding Na⁺ cations (0 to 1.0 eq.), aiming to induce the CD/CPL switching process. As a result, CD spectra exhibited a quenching effect on the CD signal with increasing amounts of Na⁺ (Figure S66). Consequently, as shown in Fig. 9d, the addition of Na⁺ resulted in a decrease in CD intensity for both sym-BCE[5]⊃L_G and sym-BCE[5]⊃D_G, indicating disassembly of assemblies. Based on these observations, it can be inferred that competitive binding of Na⁺ to the host leads to a simultaneous switch-off in both CD and CPL signals (Fig. 10).

In conclusion, a series of bis-crown ether named BCE[n] (n = 4–7) with AIE-active TPE cores were synthesized by intramolecular coupling of cyclic precursor diketone compounds. The incorporation of flexible side chains into the rigid TPE core resulted in specific strain on the molecules, leading to the existence of two conformers in semi-rigid BCE[5] and BCE[6], depending on the chain length. These conformers exhibit varying C_(Ar)—C═C bond angles within the TPE core and variations in the shapes of crown ether cavities. Additionally, they can be effectively purified using conventional column chromatography. Due to subtle differences in conformation and ring size, we systematically investigated their unique host-guest selective binding behaviors as well as their photophysical properties. By utilizing host-guest interaction and supramolecular chiral amplification, sym-BCE[5]-based chiral assemblies were constructed to demonstrate both CD and CPL signals in the presence of chiral polymeric guests. Furthermore, these assemblies also exhibit Na⁺-responsive switch-off for CD and CPL signals. This highlights the importance of conformational diversification in elucidating the exceptional properties of supramolecular macrocycles while providing valuable insights into their structure-property relationships.

Author Contributions

X. Tian and M. Zuo contributed equally to this work. X. Tian and M. Zuo drafted the manuscript and conceived the project. X.-Y. Hu supervised the project and revised the manuscript. X. Tian, Y. Shen, N. Mao, Y. Sheng, and K. Velmurugan performed the experiments. K. Wang and J. Jiao helped with X-ray crystallography characterization. J. Niemeyer provided analysis and helpful suggestions for this work. All authors collectively analyzed the data, discussed the results, and provided comments on the manuscript.

Notes

The authors declare no competing financial interests.

Acknowledgment

This work was supported by the National Natural Science Foundation of China (Nos. 22271154 and M-0411), the Natural Science Foundation of Jiangsu Province (No. BK20211179), and the China Postdoctoral Science Foundation project (2022M721601). The authors thank Prof. Myongsoo Lee, Prof. Leyong Wang, and Prof. Yong Liang for their valuable suggestions.

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Unprecedented TPE-Embedded Butterfly Bis-Crown Ether with Controllable Conformation and Supramolecular Chiroptical Property

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1. Introduction

2. Results and discussion

2.1 Synthesis and structural characterization

2.2 Photophysical properties

2.3 Host-guest chemistry

2.4 Chiral amplification and regulation

Conclusion

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