Chiral tether-guided selective synthesis of D_n-symmetric chiral conjugated nanorings

Abstract

Chiral conjugated nanorings with D_n symmetry exhibit extraordinary circularly polarized luminescence (CPL) properties due to their unique cylindrical helical conjugated system. However, their synthesis faces challenges such as numerous atropisomers and tedious separation and chiral resolution processes, which severely hinder their development. In this work, we report a chiral tether-guided synthesis strategy. By introducing a strained planar chiral alkyl chain tether into the fused-ring building unit of the nanoring, the energy differences between the various atropisomers of the nanoring are significantly increased. This guides the formation of the thermodynamically most stable D_n-symmetric isomer during synthesis, thus greatly enhancing the selectivity. Four chiral nanorings, D₃-(P)-NR1, D₄-(P)-NR1, D₃-(M)-NR2, and D₄-(M)-NR2, as well as their enantiomers, were facilely obtained through this method. All molecules have shown remarkable and stable CPL capability, with a luminescence dissymmetry factor up to 0.076.

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Introduction

In recent years, organic luminescent materials have achieved widespread applications in fields such as electroluminescence, biological probes, information encryption, sensing and detection.^1–7 Chirality further endows them with circularly polarized luminescence (CPL) properties, significantly expanding their application potential and making them highly promising for 3D displays, optical storage, polarized imaging, chiral sensing, and spintronics.^8–15 Two key metrics for evaluating the performance of chiral luminescent materials are the photoluminescence quantum yield (φ) and the luminescence dissymmetry factor (g_lum). For organic luminescent molecules, the φ can reach 100% through molecular design and excited-state modulation. However, the intrinsic g_lum values of most organic chiral molecules typically fall within the range of 10⁻⁵ to 10⁻³,¹⁶ far below the theoretical extremes (±2). Developing organic chiral molecules with intrinsically large g_lum values holds significant scientific importance.

Theoretically, the g_lum of chiral luminescent molecules can be described by the following equation:

where μ_ij and m_ij represent the electric transition dipole moment and magnetic transition dipole moment, respectively, during the transition from excited state ‘i’ to ground state ‘j’, and θ is the angle between the two transition dipole moments.^17,18 Since the luminescence of most organic molecules follows Kasha's rule, the transition of interest is typically from the S₁ to S₀ state.¹⁹ The equation indicates that to maximize the g value while maintaining high luminescence intensity, both μ and m must be large and comparable in magnitude, while their dipole moments must be aligned parallel or antiparallel (i.e., θ = 0 or 180). However, for most organic chiral molecules, m is much smaller than μ, making it difficult to enhance g_lum.²⁰ Therefore, the key to improving g_lum lies in molecular design strategies that enhance m while ensuring μ and m remain parallel or antiparallel. In recent years, significant efforts have been devoted to exploring chiral organic luminescent molecules with high g_lum values.^21–47 Among all reported chiral organic emitters, conjugated nanorings with D_n symmetry exhibit exceptionally high intrinsic g_lum. For example, Isobe's D₄-symmetric (P)-(12,8)-[4]CC⁴⁵ and Du's D₄-symmetric (+)-[4]CAn_2,6 ref. 46 achieved |g_lum| of 0.152 and 0.103, respectively (Fig. 1a), representing the only two purely organic chiral emitters with |g_lum| on the order of 10⁻¹ at the molecular level. Notably, (P)-(12,8)-[4]CC also exhibited a high fluorescence quantum yield of 80%. The extraordinary |g_lum| in these molecules arises from their unique cylindrical helical conjugated systems. On one hand, this structure arranges the local electric transition dipole moments of the building units in a circular fashion, generating a large induced magnetic transition dipole moment along the helical axis.⁴⁸ On the other hand, their high D_n symmetry ensures that μ and m remain parallel or antiparallel, maximizing |cos θ| and thus achieving a large |g_lum|.^44,49 Long et al. further demonstrated through theoretical calculations that increasing the number of building units to synthesize higher-order D_n-symmetric nanorings could significantly enhance the magnetic transition dipole moment along the helical axis, enabling giant g values (Fig. 1b).⁵⁰ For instance, starting from Isobe's [4]CC framework, expanding to a D₈-symmetric [8]CC (8 units) increases g to 0.71, while a D₂₀-symmetric [20]CC (20 units) could further elevate g to 1.47, all while maintaining high transition oscillator strengths.

Fig. 1 (a) Previously reported D_n-symmetric chiral conjugated nanorings. (b) Theoretically predicted high-order D_n-nanorings with giant g-values. (c) Chiral tether-guided selective synthesis of D_n-nanorings in this work.

The above experimental and theoretical studies demonstrate that D_n-symmetric chiral conjugated nanorings represent a highly promising class of molecules, offering potential breakthroughs in organic luminescent materials with intrinsically giant g_lum values. However, their synthesis faces a critical challenge: the formation of atropisomers (conformational isomers arising from flipping of building units) during preparation. The number of atropisomers increases rapidly with higher symmetry order (n). Tanaka et al. reported a D₂-symmetric nanoring (S_p,S_p)-(M,M,M,M)-1a, which theoretically has 3 atropisomers (Fig. 1a). While an asymmetric catalytic cyclization enabled the selective synthesis of the D₂-symmetric isomer, its |g_lum| was only 0.005.⁵¹ Isobe et al. observed all 4 possible atropisomers in the preparation of D₃-symmetric nanoring (P)-(9,6)-[3]C^dbC. The optically pure (P)-(9,6)-[3]C^dbC was obtained via chiral HPLC purification.⁴⁸ For D₄-symmetric nanorings, the number of atropisomers rises to 6. Aforementioned (P)-(12,8)-[4]CC and (+)-[4]CAn_2,6 both required laborious chiral HPLC purification.^45,46 For higher-order systems like D₈-symmetric [8]CC and D₂₀-symmetric [20]CC proposed by Long et al., the atropisomer count escalates to 30 and 27012, respectively, making their synthesis and isolation extremely challenging.⁵⁰ Thus, developing a method to selectively access D_n-symmetric nanorings is crucial to advance their applications in chiral organic luminescent materials. In this work, we report a novel chiral tether-guided synthesis strategy for D_n-symmetric chiral conjugated nanorings (Fig. 1c). By incorporating a strained planar-chiral alkyl tether into the fused-ring building block of the nanoring, we significantly amplify the energy differences between various atropisomers. This thermodynamic control drives the formation of the most stable D_n-symmetric isomer with exceptional selectivity during synthesis. Using this innovative approach, we successfully synthesized four chiral nanorings: D₃-(P)-NR1, D₄-(P)-NR1, D₃-(M)-NR2, and D₄-(M)-NR2, along with their respective enantiomers. The helical chirality of these molecules is uniquely determined by the planar chirality of their tether moieties. These compounds exhibit remarkable CPL properties, with all derivatives demonstrating |g_lum| exceeding 10⁻².

Results and discussion

The synthetic routes for the nanorings are illustrated in Scheme 1. For D₃-(P)-NR1 and D₄-(P)-NR1 (Scheme 1a), starting from the previously reported planar chiral cyclophane (S_p)-1,⁵² the synthesis proceeded via acylation to afford the dibenzyloxy-terminated amide (S_p)-2. Subsequent intramolecular Yamamoto cyclization yielded the pentacyclic fused lactam (S_p)-3.^53–55 Deprotection of the benzyl groups followed by acylation furnished the triflate-terminated intermediate (S_p)-5, which was further converted into the boronic ester (S_p)-6 via Pd-catalyzed borylation. Equimolar reaction of (S_p)-6 with Pt(COD)Cl₂ generated the Pt-macrocyclic complex intermediates, and final reductive elimination promoted by PPh₃ afforded the chiral trimeric ring D₃-(P)-NR1 and the chiral tetrameric ring D₄-(P)-NR1 in yields of 40% and 3% (starting from (S_p)-6), respectively. The preferential formation of the trimer suggests that the highly curved backbone of the fused-ring unit (S_p)-6 favors smaller macrocycles in this Pt-mediated nanoring synthesis.⁴⁸ For D₃-(M)-NR2 and D₄-(M)-NR2 (Scheme 1b), (S_p)-1 first underwent Suzuki coupling with 3-chloro-2-fluorobenzeneboronic acid to afford (S_p)-7, which was cyclized via a potassium tert-butoxide-mediated intramolecular nucleophilic substitution to form the pentacyclic carbazole (S_p)-8.^52,56 Pd-catalyzed borylation then replaced the terminal chlorine with a boronic ester, yielding (S_p)-9. Subsequent Pt-mediated macrocyclization produced the chiral trimer D₃-(M)-NR2 and the chiral tetramer D₄-(M)-NR2 in 10% and 27% yields (starting from (S_p)-9), respectively. Unlike the fused-lactam-based system, the fused-carbazole-derived nanoring predominantly formed the tetrameric product. Using the enantiomeric planar chiral cyclophane (R_p)-1 as the starting material, we also synthesized the enantiomers of the above four nanorings—D₃-(M)-NR1, D₄-(M)-NR1, D₃-(P)-NR2 and D₄-(P)-NR2 (Scheme 1c). Detailed synthetic procedures are provided in the SI (Schemes S3 and S4). It is worth mentioning that all the nanorings were obtained through conventional column chromatography separation, without the need for chiral HPLC purification. All nanoring structures were characterized by NMR and mass spectroscopic methods. Both ¹H and ¹³C NMR spectra confirmed that each nanoring was obtained as a single isomer (see SI). Additionally, single-crystal X-ray diffraction (SCXRD) analysis unambiguously determined the structures of D₃-(P)-NR1, D₃-(M)-NR2, and the enantiomer D₃-(M)-NR1 (vide infra).

Scheme 1 Synthetic routes for (a) D₃-(P)-NR1 and D₄-(P)-NR1, (b) D₃-(M)-NR2 and D₄-(M)-NR2, and (c) the enantiomers. Reaction conditions: (i) Et₃N, 70 °C; (ii) Ni(COD)₂/2,2′-bipyridine, 70 °C; (iii) Pd/C, NH₄OOCH, 80 °C; (iv) Tf₂O/pyridine; (v) (Bpin)₂, Pd(OAc)₂/S-Phos, 80 °C; (vi) (COD)PtCl₂, CsF; (vii) PPh₃, 110 °C; (viii) Pd(PPh₃)₄, K₂CO₃, 70 °C; (ix) ^tBuOK, 80 °C; (x) PPh₃, 150 °C.

The single-crystal structures of D₃-(P)-NR1 and D₃-(M)-NR2 are shown in Fig. 2a, and that for D₃-(M)-NR1 is presented in Fig. S64. Crystallographic data reveal that all molecules adopt a single configuration without other atropisomers, and their ring skeletons exhibit D₃ symmetry. Although both D₃-(P)-NR1 and D₃-(M)-NR2 were synthesized from the same starting material, (S_p)-1, their macrocyclic structures differ significantly. In D₃-(P)-NR1, all the tethers are positioned on the outer periphery of the nanoring, and the three fused-ring lactam building blocks (S_p)-M1 adopt a clockwise P-helical arrangement. In contrast, in D₃-(M)-NR2, all the tethers are oriented inside the nanoring, and the three fused-ring carbazole units (S_p)-M2 form a counterclockwise M-helical arrangement. D₃-(M)-NR1, synthesized from (R_p)-1, shows the mirror-image structure of D₃-(P)-NR1, exhibiting M-helicity (Fig. S64). From the top view (Fig. 2b), the diameter of the lactam nanoring D₃-(P)-NR1 is larger (∼12.7 Å), whereas that of the carbazole nanoring D₃-(M)-NR2 is slightly smaller (∼12.1 Å). Regarding packing structures, D₃-(P)-NR1 molecules form a 2D layered arrangement, where adjacent nanorings within each layer are nearly perpendicular, resembling a herringbone pattern—similar to some known cycloparaphenylene (CPP) nanorings (e.g., [6]CPP, [7]CPP).^57,58 In contrast, D₃-(M)-NR2 crystals exhibit a triangular packing motif: three nanoring molecules assemble into a circular trimer, with disordered solvent molecules filling the triangular pores. This arrangement resembles the triangular stacking observed in Itami's previously reported carbon nanobelts (CNB) (e.g., [24]CNB).⁵⁵ To understand why D₃-(P)-NR1 has all tethers outward while D₃-(M)-NR2 has them inward, we examined the conformations of their building blocks, (S_p)-M1 and (S_p)-M2 (Fig. 2c). DFT-optimized structures show that the fused-ring backbone of (S_p)-M1 bends outward due to tether-induced strain, favoring an exterior tether placement, whereas (S_p)-M2 bends inward under the strain, directing its tethers inside the nanoring.

Fig. 2 (a) Single crystal structures for D₃-(P)-NR1 and D₃-(M)-NR2; (b) top view and packing structures for D₃-(P)-NR1 and D₃-(M)-NR2; (c) the fused-ring building blocks (S_p)-M1 and (S_p)-M2, and their DFT-optimized configurations. Note: the solvent systems used for single-crystal growth are hexane/dichloromethane and methanol/chloroform for D₃-(P)-NR1 and D₃-(M)-NR2, respectively; the solvent molecules in the crystals of D₃-(P)-NR1 and D₃-(M)-NR2 are dichloromethane and chloroform, respectively.

To elucidate the high selectivity in obtaining D_n-symmetric nanorings without observable formation of other atropisomeric products, we calculated the energies of all possible atropisomers. For comparison, we also calculated the energies of hypothetical tether-free nanorings (where one alkyl tether is replaced by two methyl groups). Fig. 3 shows the relative Gibbs free energies of all four possible atropisomers for the D₃-symmetric nanorings (D₃-(P)-NR1 and D₃-(M)-NR2) and their tether-free analogues. For D₃-(P)-NR1 and D₃-(M)-NR2, the lowest-energy isomers are Aooo and Biii (‘o’ (outside) and ‘i’ (inside) describe the tether's position with respect to the nanoring), respectively. These structures match the single-crystal configurations. Flipping one fused-ring unit to form Aooi and Biio raises the energy by 8.4 kcal mol⁻¹ and 24.6 kcal mol⁻¹, respectively. Obviously, the D₃-symmetric Aooo and Biii are much favored energetically over other isomers. On the other hand, the tether-free analogues exhibit low energy differences (a few kcal mol⁻¹) among atropisomers (‘a’ and ‘b’ denote the syn-facial and anti-facial arrangement of the fused-ring building units) (Fig. 3c and d), consistent with prior reports.⁵⁹ Similar energies imply the lack of a dominant product, as all are likely to form during the synthesis. The above results indicate that by introducing strained chiral tethers into the nanoring significantly increases the energy differences among atropisomers, thereby enabling one D_n-symmetric isomer to become the dominant product and greatly enhancing selectivity. We also conducted energy analyses on all atropisomers of the D₄-symmetric nanorings D₄-(P)-NR1, D₄-(M)-NR2, and their tether-free analogues, arriving at the same conclusion (Fig. S65 and S66). Notably, the tether does not significantly affect the rotational barriers between the atropisomers. Similar to the tether-free nanorings, D₃-(P)-NR1, D₃-(M)-NR2, D₄-(P)-NR1, and D₄-(M)-NR2 all exhibit high atropisomerization barriers (21.4–67.5 kcal mol⁻¹), indicating that they can maintain stable helical configurations with high chiral stability (Fig. S65 and S66).

Fig. 3 The relative Gibbs free energies for different atropisomers of (a) D₃-(P)-NR1 (A series), (b) D₃-(M)-NR2 (B series) and the tether-free analogues of (c) D₃-(P)-NR1 (A′ series) and (d) D₃-(M)-NR2 (B′ series).

The striking structural difference between the fused-lactam nanorings (D₃-(P)-NR1 and D₄-(P)-NR1) and fused-carbazole nanorings (D₃-(M)-NR2 and D₄-(M)-NR2), where the tethers are positioned exteriorly and interiorly respectively, results in significantly distinct chemical shifts of the tether protons in NMR spectra. Particularly, the most pronounced shift is observed for proton H₁, which is closest to the central benzene ring of the building block (Fig. 4a). For the fused-lactam building unit (S_p)-M1, its H₁ appears at −0.29 ppm due to its location above the central benzene ring, where it experiences shielding effects and resonates in a relatively upfield region. However, upon incorporation into nanorings D₃-(P)-NR1 and D₄-(P)-NR1, the chemical shift of H₁ moves to 0.68 ppm and 0.57 ppm respectively, indicating markedly reduced shielding in the exterior regions of the nanorings. Conversely, for the fused-carbazole building unit (S_p)-M2, H₁ initially appears at −1.86 ppm. After being integrated into nanorings D₃-(M)-NR2 and D₄-(M)-NR2, its chemical shift moves to −3.90 ppm and −3.11 ppm, respectively, demonstrating enhanced shielding within the interior cavity of the nanorings. These experimental observations align well with the trends predicted by DFT calculations. Previous theoretical studies have proposed that the exterior and interior of certain cyclic nanocarbons correspond to less-shielded and shielded regions, respectively.⁶⁰ In this study, H₁ worked as an NMR probe, providing direct experimental evidence. To further investigate the magnetic shielding environments, we computed the nucleus-independent chemical shift (NICS)^61–63 of the central benzene rings (Fig. 4b). The results reveal that for all nanorings, the NICS(−1) values (interior) are consistently more negative than the NICS(1) values (exterior), confirming stronger shielding inside the rings, in agreement with our NMR observations. Moreover, compared to the building blocks, all nanorings exhibit less negative NICS(1) values, while the NICS(−1) values tend to become more negative (except for D₄-(M)-NR2, which shows minimal change). This suggests that upon nanoring formation, the increased curvature of the building units leads to reduced shielding on the convex side (exterior) and enhanced shielding on the concave side (interior), consistent with prior literature reports.^64,65 The average values (NICS_avg) of NICS(1) and NICS(−1) show a clear trend toward less negative values from monomers to nanorings, indicating reduced aromaticity of the central benzene ring due to heightened curvature in the nanoring structures.

Fig. 4 (a) The change of the NMR chemical shifts (the values in parentheses are DFT-calculated chemical shifts) of proton H₁ from building blocks to nanorings; (b) the calculated NICS(1), NICS(−1) and the averages of NICS(1) and NICS(−1) for the building blocks and nanorings.

Next, we investigated the optical properties of the nanorings. Fig. 5a displays the UV-Vis absorption spectra of D₃-(P)-NR1, D₄-(P)-NR1, D₃-(M)-NR2 and D₄-(M)-NR2. Their respective enantiomers, D₃-(M)-NR1, D₄-(M)-NR1, D₃-(P)-NR2 and D₄-(P)-NR2, show identical spectra (Fig. S67). It can be observed that the spectra of the fused-lactam nanorings D₃-(P)-NR1 and D₄-(P)-NR1 primarily exhibit two absorption bands (one at 320–400 nm and another at 400–500 nm), whereas the fused-carbazole nanorings D₃-(M)-NR2 and D₄-(M)-NR2 show only one main absorption band at 320–420 nm. This difference is mainly attributed to the fact that some lower-energy electronic transitions (e.g., S₀ → S₂, S₀ → S₃) in the fused-lactam nanorings exhibit higher oscillator strengths (Table S1). The oscillator strengths of the S₀ → S₁ transitions are very low for all nanorings, likely due to the high molecular symmetry, which makes the S₀ → S₁ transition forbidden. Consequently, the absorption coefficients near the bandgap are relatively low for all nanorings. From the onset absorption, the optical bandgaps of D₃-(P)-NR1, D₄-(P)-NR1, D₃-(M)-NR2 and D₄-(M)-NR2 are calculated to be 2.40, 2.51, 2.54, and 2.62 eV, respectively. It is evident that, for both fused-lactam and fused-carbazole nanorings, the smaller-sized nanorings possess narrower bandgaps than their larger-sized counterparts, consistent with previously reported trends for CPP and CNB nanorings.^22,55,66 DFT calculations further confirm this observation, showing that smaller-sized nanorings have smaller HOMO–LUMO gaps (Fig. S69). Additionally, theoretical calculations indicate that the fused-carbazole nanorings have higher HOMO and LUMO energy levels compared to the fused-lactam nanorings, which aligns with the energy levels measured in electrochemical experiments (Fig. S70). The photoluminescence spectra of all nanorings and their enantiomers are shown in Fig. 5b and S71, respectively. All samples were measured in toluene solution. The excitation wavelengths were set at 360 nm for D₃-(P/M)-NR1, 370 nm for D₄-(P/M)-NR1, and 380 nm for both D₃-(M/P)-NR2 and D₄-(M/P)-NR2. The fluorescence peaks of D₃-(P)-NR1, D₄-(P)-NR1, D₃-(M)-NR2 and D₄-(M)-NR2 are located at 561, 520, 519, and 492 nm, respectively. The measured fluorescence quantum yields are 42%, 80%, 25%, and 43%, respectively. Notably, compared to the larger D₄ nanorings, the smaller D₃ nanorings exhibit red-shifted emission peaks and reduced quantum yields, similar to the size-dependent luminescence properties observed in CPP and methylene-bridged cycloparaphenylene (MCPP) nanorings.^67–69

Fig. 5 The UV-Vis absorption spectra (a) and photoluminescence spectra (b) for D₃-(P)-NR1, D₄-(P)-NR1, D₃-(M)-NR2 and D₄-(M)-NR2. The CD (left) and CPL (right) spectra for D₃-(P)-NR1 and D₃-(M)-NR1 (c and d), D₄-(P)-NR1 and D₄-(M)-NR1 (e and f), D₃-(P)-NR2 and D₃-(M)-NR2 (g and h), D₄-(P)-NR2 and D₄-(M)-NR2 (i and j) in toluene. Note: the dotted lines in the CD spectra are DFT-predicted ones.

Since the nanorings prepared via the chiral tether-guided approach possess uniquely defined configurations, chiral resolution is unnecessary, allowing direct testing of their chiroptical properties. The circular dichroism (CD) and circularly polarized luminescence (CPL) spectra of all nanorings and their enantiomers are shown in Fig. 5c–j. All measurements were conducted in dilute solutions (∼1 × 10⁻⁵ M) to ensure the signals originated from single molecules rather than aggregates. Each pair of enantiomers exhibited mirror-image CD and CPL spectra. For the CD spectra, all P-helical nanorings displayed a negative Cotton effect near the bandgap, while all M-helical nanorings showed a positive Cotton effect. The theoretically calculated CD spectra matched well with the experimental results. We further compared the CD spectra of the fused-lactam nanorings D₃-(P)-NR1 and D₄-(P)-NR1 before and after heating at 100 °C for 24 hours (Fig. S72a), revealing nearly overlapping spectra. Since the fused-carbazole nanorings D₃-(M)-NR2 and D₄-(M)-NR2 decompose upon heating, we assessed their chiral stability at room temperature. After one week of storage, no significant changes were observed in their CD spectra (Fig. S72b). These experiments confirm the earlier theoretical predictions that these molecules generally possess high atropisomerization barriers (Fig. S65), ensuring excellent chiral stability. All nanorings exhibited strong CPL signals. Consistent with the CD signals near the bandgap, all P-helical nanorings displayed a negative Cotton effect in CPL, while all M-helical nanorings showed a positive Cotton effect. Additionally, all nanorings demonstrated large luminescence dissymmetry factors (g_lum), exceeding 10⁻² in magnitude. Notably, D₃-(P)-NR2 exhibited a remarkably high g_lum of −0.076, making it one of the rare purely organic molecules with a large intrinsic g_lum. To understand why these nanorings generally exhibit large dissymmetry factors, we analyzed their S₁ → S₀ transitions by DFT. Fig. 6 illustrates their transition characteristics, revealing that all molecules possess a substantial magnetic transition dipole moment (m) along the helical axis. The |m| values for D₃-(P)-NR1, D₄-(P)-NR1, D₃-(M)-NR2 and D₄-(M)-NR2 are 8.32, 12.55, 9.14, and 14.18 Bohr magnetons (μ_B), respectively—among the largest reported for organic chiral molecules.⁷⁰ Moreover, the electric (μ) and magnetic (m) transition dipole moments are consistently aligned either parallel or antiparallel. In P-helical nanorings, the angles between μ and m are 179.5° and 180°, whereas in M-helical nanorings, they are 1.3° and 0°. These factors collectively contribute to the high g_lum. Furthermore, the carbazole-type nanorings exhibited larger m and smaller μ compared to the lactam-type nanorings, explaining their higher g_lum values. In both carbazole- and lactam-type nanorings, m increased with ring size, consistent with the reported “molecular solenoid inner area rule”.⁷⁰ From D₃ to D₄ nanorings, the increase in m was comparable to that in μ, resulting in minor changes (or even slight decreases) in g_lum. However, based on theoretical calculations by Long et al., synthesizing higher-order D_n-symmetric nanorings could further enhance m relative to μ, potentially leading to breakthroughs in g-values.⁵⁰

Fig. 6 The optimized geometry of S₁ state and the S₁ → S₀ transition characteristics for D₃-(P)-NR1, D₄-(P)-NR1, D₃-(M)-NR2 and D₄-(M)-NR2. Note: “a.u.” denotes the atomic unit; the vector arrow for μ is scaled up by a factor of 60.

Conclusion

In summary, we have developed a chiral tether-guided strategy to selectively prepare D_n-symmetric chiral conjugated nanorings. The high selectivity stems from the chiral tether induced strain, which amplifies the energy differences among the various atropisomers of the nanorings, thereby directing one D_n-symmetric isomer to become the thermodynamically favored product. All synthesized D₃ and D₄ nanorings exhibit exceptional circularly polarized luminescence properties, with a maximum luminescence dissymmetry factor reaching 0.076 and photoluminescence quantum yields up to 80%, demonstrating their great potential as high-performance CPL emitters. In the future, we will extend this strategy to synthesize higher-order D_n-symmetric nanorings, which may lead to breakthroughs in the development of organic molecules with intrinsically giant g_lum.

Author contributions

Z. X. conceptualized the work. T. A., Q. Y., Y. S., Z. D., X. Z. synthesized the compounds. T. A. and Y. W. performed the theoretical calculations. J. Y., Z. X., Y. G., Z. H., C. Z. and L. D. directed the experiments and discussed the results. Z. X., Z. H., M. L., C. Z. and L. D. directed the project. Z. X. wrote the manuscript.

Conflicts of interest

The authors declare no conflict of interest.

Data availability

CCDC 2440960, 2440962 and 2440966 contain the supplementary crystallographic data for this paper.^71a–c

All other data supporting the findings of this study are available within the article and its supplementary information (SI), as well as available from the corresponding authors upon reasonable request. Supporting information available: materials synthesis and characterization; theoretical calculation; Scheme S1–5, Fig. S1–72, Table S1. See DOI: https://doi.org/10.1039/d5sc06445g.

Acknowledgements

We thank the National Key Research and Development Program of China (2022YFB3803300, 2023YFE0116800), National Natural Science Foundation of China (22571057), and Beijing Natural Science Foundation (IS23037) for financial support. This work is supported by High Performance Computing Center of NCNST, China.

References

1. T. Zhang, Y. Xiao, H. Wang, S. Kong, R. Huang, V. Ka-Man Au, T. Yu and W. Huang, Highly Twisted Thermally Activated Delayed Fluorescence (Tadf) Molecules and Their Applications in Organic Light-Emitting Diodes (Oleds), Angew. Chem., Int. Ed., 2023, 62, e202301896.
2. A. Concellón, J. Castro-Esteban and T. M. Swager, Ultratrace Pfas Detection Using Amplifying Fluorescent Polymers, J. Am. Chem. Soc., 2023, 145, 11420–11430.
3. Y. Huang, W. Chen, J. Chung, J. Yin and J. Yoon, Recent Progress in Fluorescent Probes for Bacteria, Chem. Soc. Rev., 2021, 50, 7725–7744.
4. W. Xu, Q. He and J. Cheng, Organic Semiconductor Fluorescent Sensing Materials and Hazardous Chemicals Detection Applications, Sci. Sin Chem., 2020, 50, 92–107.
5. G. Yin, J. Zhou, W. Lu, L. Li, D. Liu, M. Qi, B. Z. Tang, P. Théato and T. Chen, Targeting Compact and Ordered Emitters by Supramolecular Dynamic Interactions for High-Performance Organic Ambient Phosphorescence, Adv. Mater., 2024, 36, 2311347.
6. H. Zhu, J. Fan, J. Du and X. Peng, Fluorescent Probes for Sensing and Imaging within Specific Cellular Organelles, Acc. Chem. Res., 2016, 49, 2115–2126.
7. Y. Zhang, J. Guan, L. Luo, X. Han, J. Wang, Y. Zheng and J. Xu, Chiral Twisted Molecular Carbons: Synthesis, Properties, and Applications, Interdiscip. Mater., 2024, 3, 453–479.
8. M. Zhang, Q. Guo, Z. Li, Y. Zhou, S. Zhao, Z. Tong, Y. Wang, G. Li, S. Jin and M. Zhu, et al., Processable Circularly Polarized Luminescence Material Enables Flexible Stereoscopic 3D Imaging, Sci. Adv., 2023, 9, eadi9944.
9. B. L. Feringa, R. A. van Delden, N. Koumura and E. M. Geertsema, Chiroptical Molecular Switches, Chem. Rev., 2000, 100, 1789–1816.
10. P. Stachelek, S. Serrano-Buitrago, B. L. Maroto, R. Pal and S. de la Moya, Circularly Polarized Luminescence Bioimaging Using Chiral Bodipys: A Model Scaffold for Advancing Unprecedented CPL Microscopy Using Small Full-Organic Probes, ACS Appl. Mater. Interfaces, 2024, 16, 67246–67254.
11. I. Song, J. Ahn, H. Ahn, S. H. Lee, J. Mei, N. A. Kotov and J. H. Oh, Helical Polymers for Dissymmetric Circularly Polarized Light Imaging, Nature, 2023, 617, 92–99.
12. X. Liang, W. Liang, P. Jin, H. Wang, W. Wu and C. Yang, Advances in Chirality Sensing with Macrocyclic Molecules, Chemosensors, 2021, 9, 279.
13. T. Kawasaki, M. Sato, S. Ishiguro, T. Saito, Y. Morishita, I. Sato, H. Nishino, Y. Inoue and K. Soai, Enantioselective Synthesis of near Enantiopure Compound by Asymmetric Autocatalysis Triggered by Asymmetric Photolysis with Circularly Polarized Light, J. Am. Chem. Soc., 2005, 127, 3274–3275.
14. Z. Shang, T. Liu, Q. Yang, S. Cui, K. Xu, Y. Zhang, J. Deng, T. Zhai and X. Wang, Chiral-Molecule-Based Spintronic Devices, Small, 2022, 18, 2203015.
15. W. Chen, B. Li, G. Gao and T. Sun, Chiral Supramolecular Nanomaterials: From Chirality Transfer and Amplification to Regulation and Applications, Interdiscip. Mater., 2023, 2, 689–713.
16. L. Liu, Y. Yang and Z. Wei, Chiral Organic Optoelectronic Materials and Circularly Polarized Light Luminescence and Detection, Acta Chim. Sinica, 2022, 80, 970–992.
17. F. S. Richardson and J. P. Riehl, Circularly Polarized Luminescence Spectroscopy, Chem. Rev., 1977, 77, 773–792.
18. E. M. Sánchez-Carnerero, A. R. Agarrabeitia, F. Moreno, B. L. Maroto, G. Muller, M. J. Ortiz and S. de la Moya, Circularly Polarized Luminescence from Simple Organic Molecules, Chem.–Eur. J., 2015, 21, 13488–13500.
19. M. Kasha, Characterization of Electronic Transitions in Complex Molecules, Discuss. Faraday Soc., 1950, 9, 14–19.
20. T. Zhao, J. Han, P. Duan and M. Liu, New Perspectives to Trigger and Modulate Circularly Polarized Luminescence of Complex and Aggregated Systems: Energy Transfer, Photon Upconversion, Charge Transfer, and Organic Radical, Acc. Chem. Res., 2020, 53, 1279–1292.
21. Z.-L. Gong, X. Zhu, Z. Zhou, S.-W. Zhang, D. Yang, B. Zhao, Y.-P. Zhang, J. Deng, Y. Cheng and Y.-X. Zheng, et al., Frontiers in Circularly Polarized Luminescence: Molecular Design, Self-Assembly, Nanomaterials, and Applications, Sci. China Chem., 2021, 64, 2060–2104.
22. S. Guo, L. Liu, X. Li, G. Liu, Y. Fan, J. He, Z. Lian, H. Yang, X. Chen and H. Jiang, Highly Luminescent Chiral Carbon Nanohoops Via Symmetry Breaking with a Triptycene Unit: Bright Circularly Polarized Luminescence and Size-Dependent Properties, Small, 2024, 20, 2308429.
23. Y. Liu, Z. Li, M.-W. Wang, J. Chan, G. Liu, Z. Wang and W. Jiang, Highly Luminescent Chiral Double π-Helical Nanoribbons, J. Am. Chem. Soc., 2024, 146, 5295–5304.
24. Z. Sun, W. Xu, S. Qiu, Z. Ma, C. Li, S. Zhang and H. Wang, Thia[n]helicenes with Long Persistent Phosphorescence, Chem. Sci., 2024, 15, 1077–1087.
25. L. Bian, M. Tang, J. Liu, Y. Liang, L. Wu and Z. Liu, Luminescent Chiral Triangular Prisms Capable of Forming Double Helices for Detecting Traces of Acids and Anion Recognition, J. Mater. Chem. C, 2022, 10, 15394–15399.
26. X. Kong, X. Zhang, B. Yuan, W. Zhang, D. Lu and P. Du, Synthesis and Photophysical Properties of a Chiral Carbon Nanoring Containing Rubicene, J. Org. Chem., 2024, 89, 8255–8261.
27. G. Li, L.-L. Mao, J.-N. Gao, X. Shi, Z.-Y. Huo, J. Yang, W. Zhou, H. Li, H.-B. Yang and C.-H. Tung, et al., A Helical Tubular Dyad of [9]Cycloparaphenylene: Synthesis, Chiroptical Properties and Post-Functionalization, Angew. Chem., Int. Ed., 2025, 64, e202419435.
28. Y.-F. Wu, S.-W. Ying, L.-Y. Su, J.-J. Du, L. Zhang, B.-W. Chen, H.-R. Tian, H. Xu, M.-L. Zhang and X. Yan, et al., Nitrogen-Embedded Quintuple [7]Helicene: A Helicene–Azacorannulene Hybrid with Strong near-Infrared Fluorescence, J. Am. Chem. Soc., 2022, 144, 10736–10742.
29. F. Zhao, J. Zhao, H. Liu, Y. Wang, J. Duan, C. Li, J. Di, N. Zhang, X. Zheng and P. Chen, Synthesis of π-Conjugated Chiral Organoborane Macrocycles with Blue to near-Infrared Emissions and the Diradical Character of Cations, J. Am. Chem. Soc., 2023, 145, 10092–10103.
30. X.-Y. Wang, J. Bai, Y.-J. Shen, Z.-A. Li and H.-Y. Gong, A Carbazole-Centered Expanded Helicene Stabilized with Hexabenzocoronene (HBC) Units, Angew. Chem., Int. Ed., 2025, 64(1), e202417745.
31. Y. Chen, C. Lin, Z. Luo, Z. Yin, H. Shi, Y. Zhu and J. Wang, Double π-Extended Undecabenzo[7]helicene, Angew. Chem., Int. Ed., 2021, 60, 7796–7801.
32. J.-K. Li, X.-Y. Chen, W.-L. Zhao, Y.-L. Guo, Y. Zhang, X.-C. Wang, A. C.-H. Sue, X.-Y. Cao, M. Li and C.-F. Chen, et al., Synthesis of Highly Luminescent Chiral Nanographene, Angew. Chem., Int. Ed., 2023, 62, e202215367.
33. Y. Zhu, G. Chen, Y. Deng, H. Yang, C. Wang, J. Gao, C. Zhang and J. Xiao, Synthesis and Characterization of Asymmetric Azatwistarenes with Chiroptical Property, Org. Lett., 2024, 26, 9486–9491.
34. J. Hu, Q. Xiang, X. Tian, L. Ye, Y. Wang, Y. Ni, X. Chen, Y. Liu, G. Chen and Z. Sun, S-Shaped Helical Singlet Diradicaloid and Its Transformation to Circumchrysene via a Two-Stage Cyclization, J. Am. Chem. Soc., 2024, 146, 10321–10330.
35. G.-F. Huo, W.-T. Xu, J. Hu, Y. Han, W. Fan, W. Wang, Z. Sun, H.-B. Yang and J. Wu, Perylene-Embedded Helical Nanographenes with Emission up to 1010 nm: Synthesis, Structures, and Chiroptical Properties, Angew. Chem., Int. Ed., 2025, 64, e202416707.
36. D. Yang, K. M. Cheung, Q. Gong, L. Zhang, L. Qiao, X. Chen, Z. Huang and Q. Miao, Synthesis, Structures and Properties of Trioxa[9]circulene and Diepoxycyclononatrinaphthalene, Angew. Chem., Int. Ed., 2024, 63, e202402756.
37. W. Niu, Y. Fu, Z.-L. Qiu, C. J. Schürmann, S. Obermann, F. Liu, A. A. Popov, H. Komber, J. Ma and X. Feng, π-Extended Helical Multilayer Nanographenes with Layer-Dependent Chiroptical Properties, J. Am. Chem. Soc., 2023, 145, 26824–26832.
38. G.-F. Huo, T. M. Fukunaga, X. Hou, Y. Han, W. Fan, S. Wu, H. Isobe and J. Wu, Facile Synthesis and Chiral Resolution of Expanded Helicenes with up to 35 cata-Fused Benzene Rings, Angew. Chem., Int. Ed., 2023, 62, e202218090.
39. M. Krzeszewski, H. Ito and K. Itami, Infinitene: A Helically Twisted Figure-Eight [12]Circulene Topoisomer, J. Am. Chem. Soc., 2022, 144, 862–871.
40. Y. Matsuo, M. Gon, K. Tanaka, S. Seki and T. Tanaka, Synthesis of Aza[n]helicenes up to n = 19: Hydrogen-Bond-Assisted Solubility and Benzannulation Strategy, J. Am. Chem. Soc., 2024, 146, 17428–17437.
41. X. Xiao, Q. Cheng, S. T. Bao, Z. Jin, S. Sun, H. Jiang, M. L. Steigerwald and C. Nuckolls, Single-Handed Helicene Nanoribbons Via Transfer of Chiral Information, J. Am. Chem. Soc., 2022, 144, 20214–20220.
42. R. Ammenhäuser, J. M. Lupton and U. Scherf, Chain-Length Dependence of the Optical Activity of Helical Triptycene-Based π-Conjugated Ladder Polymers, Adv. Opt. Mater., 2024, 12, 2301857.
43. S. Jena, A. Thayyil Muhammed Munthasir, S. Pradhan, M. Kitahara, S. Seika, Y. Imai and P. Thilagar, Single Molecular Persistent Room-Temperature Phosphorescence and Circularly Polarized Luminescence from Binaphthol-Decorated Optically Innocent Cyclotriphosphazenes, Chem.–Eur. J., 2023, 29, e202301924.
44. H. Kubo, D. Shimizu, T. Hirose and K. Matsuda, Circularly Polarized Luminescence Designed from Molecular Orbitals: A Figure-Eight-Shaped [5]Helicene Dimer with D2 Symmetry, Org. Lett., 2020, 22, 9276–9281.
45. S. Sato, A. Yoshii, S. Takahashi, S. Furumi, M. Takeuchi and H. Isobe, Chiral Intertwined Spirals and Magnetic Transition Dipole Moments Dictated by Cylinder Helicity, Proc. Natl. Acad. Sci. U. S. A, 2017, 114, 13097–13101.
46. J. Wang, G. Zhuang, M. Chen, D. Lu, Z. Li, Q. Huang, H. Jia, S. Cui, X. Shao and S. Yang, et al., Selective Synthesis of Conjugated Chiral Macrocycles: Sidewall Segments of (−)/(+)-(12,4) Carbon Nanotubes with Strong Circularly Polarized Luminescence, Angew. Chem., Int. Ed., 2020, 59, 1619–1626.
47. F. Xu, H. Su, J. J. B. van der Tol, S. A. H. Jansen, Y. Fu, G. Lavarda, G. Vantomme, S. Meskers and E. W. Meijer, Supramolecular Polymerization as a Tool to Reveal the Magnetic Transition Dipole Moment of Heptazines, J. Am. Chem. Soc., 2024, 146, 15843–15849.
48. K. Kogashi, T. Matsuno, S. Sato and H. Isobe, Narrowing Segments of Helical Carbon Nanotubes with Curved Aromatic Panels, Angew. Chem., Int. Ed., 2019, 58, 7385–7389.
49. Q. Zhou, X. Hou, J. Wang, Y. Ni, W. Fan, Z. Li, X. Wei, K. Li, W. Yuan and Z. Xu, et al., A Fused [5]Helicene Dimer with a Figure-Eight Topology: Synthesis, Chiral Resolution, and Electronic Properties, Angew. Chem., Int. Ed., 2023, 62, e202302266.
50. T. He, M. Lin, H. Wang, Y. Zhang, H. Chen, C.-L. Sun, Z. Sun, X.-Y. Wang, H.-L. Zhang and Y. Chen, et al., Chiral Cylindrical Molecule with Absorption Dissymmetry Factor Towards Theoretical Limit of 2, Adv. Theory Simul., 2024, 7, 2300573.
51. J. Nogami, Y. Nagashima, K. Miyamoto, A. Muranaka, M. Uchiyama and K. Tanaka, Asymmetric Synthesis, Structures, and Chiroptical Properties of Helical Cycloparaphenylenes, Chem. Sci., 2021, 12, 7858–7865.
52. K. Jin, Z. Xiao, H. Xie, X. Shen, J. Wang, X. Chen, Z. Wang, Z. Zhao, K. Yan and Y. Ding, et al., Tether-Entangled Conjugated Helices, Chem. Sci., 2024, 15, 17128–17149.
53. G. Povie, Y. Segawa, T. Nishihara, Y. Miyauchi and K. Itami, Synthesis of a Carbon Nanobelt, Science, 2017, 356, 172–175.
54. Y. Li, Y. Segawa, A. Yagi and K. Itami, A Nonalternant Aromatic Belt: Methylene-Bridged [6]Cycloparaphenylene Synthesized from Pillar[6]Arene, J. Am. Chem. Soc., 2020, 142, 12850–12856.
55. G. Povie, Y. Segawa, T. Nishihara, Y. Miyauchi and K. Itami, Synthesis and Size-Dependent Properties of [12], [16], and [24]Carbon Nanobelts, J. Am. Chem. Soc., 2018, 140, 10054–10059.
56. H. Wang, H. Zhao, S. Chen, L. Bai, Z. Su and Y. Wu, Effective Synthesis of Ladder-type Oligo(p-aniline)s and Poly(p-aniline)s via Intramolecular Snar Reaction, Org. Lett., 2021, 23, 2217–2221.
57. T. Fukushima, H. Sakamoto, K. Tanaka, Y. Hijikata, S. Irle and K. Itami, Polymorphism of [6]Cycloparaphenylene for Packing Structure-Dependent Host–Guest Interaction, Chem. Lett., 2017, 46, 855–857.
58. F. Sibbel, K. Matsui, Y. Segawa, A. Studer and K. Itami, Selective Synthesis of [7]- and [8]Cycloparaphenylenes, Chem. Commun., 2014, 50, 954–956.
59. S. Hitosugi, W. Nakanishi and H. Isobe, Atropisomerism in a Belt-Persistent Nanohoop Molecule: Rotational Restriction Forced by Macrocyclic Ring Strain, Chem.–Asian J., 2012, 7, 1550–1552.
60. Y. Han, S. Dong, J. Shao, W. Fan and C. Chi, Synthesis of a Sidewall Fragment of a (12,0) Carbon Nanotube, Angew. Chem., Int. Ed., 2021, 60, 2658–2662.
61. M. Toya, T. Omine, F. Ishiwari, A. Saeki, H. Ito and K. Itami, Expanded [2,1][n]Carbohelicenes with 15- and 17-Benzene Rings, J. Am. Chem. Soc., 2023, 145, 11553–11565.
62. P. V. R. Schleyer, C. Maerker, A. Dransfeld, H. Jiao and N. J. R. van Eikema Hommes, Nucleus-Independent Chemical Shifts: A Simple and Efficient Aromaticity Probe, J. Am. Chem. Soc., 1996, 118, 6317–6318.
63. Z. Chen, C. S. Wannere, C. Corminboeuf, R. Puchta and P. V. R. Schleyer, Nucleus-Independent Chemical Shifts (NICS) as an Aromaticity Criterion, Chem. Rev., 2005, 105, 3842–3888.
64. H. Xie, Z. Xiao, Y. Song, K. Jin, H. Liu, E. Zhou, J. Cao, J. Chen, J. Ding and C. Yi, et al., Tethered Helical Ladder-Type Aromatic Lactams, J. Am. Chem. Soc., 2024, 146, 11978–11990.
65. L. B. Casabianca, Effect of Curvature on Carbon Chemical Shielding in Extended Carbon Systems, J. Phys. Chem. A, 2016, 120, 7011–7019.
66. T. Iwamoto, Y. Watanabe, Y. Sakamoto, T. Suzuki and S. Yamago, Selective and Random Syntheses of [n]Cycloparaphenylenes (n = 8–13) and Size Dependence of Their Electronic Properties, J. Am. Chem. Soc., 2011, 133, 8354–8361.
67. H. Kono, Y. Li, R. Zanasi, G. Monaco, F. F. Summa, L. T. Scott, A. Yagi and K. Itami, Methylene-Bridged [6]-, [8]-, and [10]Cycloparaphenylenes: Size-Dependent Properties and Paratropic Belt Currents, J. Am. Chem. Soc., 2023, 145, 8939–8946.
68. E. R. Darzi, T. J. Sisto and R. Jasti, Selective Syntheses of [7]–[12]Cycloparaphenylenes Using Orthogonal Suzuki–Miyaura Cross-Coupling Reactions, J. Org. Chem., 2012, 77, 6624–6628.
69. S. Guo, L. Liu, L. Liu, Y. Fan, H. Yang, J. He, Y. Wang, Z. Bo, X. Xu and X. Chen, et al., Naphthalene Diimide-Embedded Donor–Acceptor Carbon Nanohoops: Photophysical, Photoconductive, and Charge Transport Properties, ACS Appl. Mater. Interfaces, 2025, 17, 5202–5212.
70. R. G. Uceda, C. M. Cruz, S. Míguez-Lago, L. Á. de Cienfuegos, G. Longhi, D. A. Pelta, P. Novoa, A. J. Mota, J. M. Cuerva and D. Miguel, Can Magnetic Dipole Transition Moment Be Engineered?, Angew. Chem., Int. Ed., 2024, 63, e202316696.
71. (a) CCDC 2440960: Experimental Crystal Structure Determination, 2025,  DOI:10.5517/ccdc.csd.cc2my0n8; (b) CCDC 2440962: Experimental Crystal Structure Determination, 2025,  DOI:10.5517/ccdc.csd.cc2my0qb; (c) CCDC 2440966: Experimental Crystal Structure Determination, 2025,  DOI:10.5517/ccdc.csd.cc2my0vg.

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Footnote

† These authors contributed equally to this work.

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