Introduction

Atomically precise information, encompassing diverse intermolecular interactions, is revealed in the hierarchical assembly of metal nanoclusters (NCs), which aids in comprehending the assembly behavior of complex organisms1 as well as traditional nanoparticles2 and supramolecular assemblies3,4,5,6,7,8,9. Promoting the ordered coherence among NCs within the crystal lattice is anticipated to further facilitate the regulation of their intrinsic properties10. Coinage (Au, Ag, Cu)-metallic NCs represent an effective class of building units, with several successful instances reported involving hierarchical complexity. Notably, these include double-helical assembly from heterodimeric Au2911, anisotropic Ag3012, chiral Ag7013, Cu1814, and triple-helical assembly from Au6Cu615. Intriguingly, recent advancements in NCs have demonstrated that solvent molecules and counterions can effectively modulate packing structures by altering inter-cluster interactions and surface dynamics16,17,18,19,20,21. However, these strategies have not yet been employed for regulating the complex multi-stranded hierarchical assembly of NCs.

Anisotropy or chirality are the common characteristics of complex multiple helical NC assemblies14,22. Wheel-like NCs possess significant potential as biomolecules23 in terms of hierarchy, complexity, and precision. The synthesis of these hollow structures is highly important for the development of metal cluster-based materials, due to their exceptional host-guest interactions, unique assembly behaviors, and broad application potential. While wheel-like structures have been reported in Mo24,25,26, Ln27,28,29,30,31, Al32,33,34, Pd35,36,37, Mn38,39, Ti40,41 NCs among others, only a few instances of macrocyclic gold NCs42,43,44,45,46 and Cu9647 have been reported for coinage metal NCs, and silver analogs still unavailable. Despite a proposed self-assembly mechanism based on building blocks42,43,44,45,46,47,48,49,50, synthesizing wheel-shaped metal NCs inherently involves complexity and unpredictability, lacking systematicity. Controlling the self-assembly process from building blocks to hollow structures and further achieving helical superstructures presents a nontrivial challenge.

Herein, we synthesized a Janus Ag nanocluster with a specific arc, [Ag9(QL-2-S)2(HQL-2-S)4(tBuS)4(NO3)3(CH3CN)·2AgNO3]·CH3CN·H2O (Ag11, QL-2-SH = quinoline-2-thiol = H6C9NSH, HQL-2-SH = protonated quinoline-2-thiol = H6C9NHSH). Based on the primary building blocks (PBBs, [Ag9(QL-2-S)2(HQL-2-S)5(iPrS)4(ROO)]2+, ROO‒ = NO3‒ or CF3COO‒), we achieved the directional construction of two types of assemblies: one-dimensional polymer ({[Ag9(QL-2-S)2(HQL-2-S)5(iPrS)4]·Ag·4NO3}n, {Ag10}n) and discrete silver nanowheel ({[Ag9(QL-2-S)2(HQL-2-S)5(iPrS)4]4·4Ag·6CF3COO}(NO3)10, Ag40) through epitaxial growth. By using chiral metal precursors (S-/R-TFLAg = silver S-/R-trifluorolactate) instead of the achiral CF3COOAg in Ag40, enantiomeric pair nanowheels {[Ag9(QL-2-S)2(HQL-2-S)5(iPrS)4]4·4Ag·7NO3·5S-/R-TFL·H2O}(NO3)4 (abbreviated as S-/R-Ag40, Fig. 1) were prepared. Furthermore, we confirmed host-guest interactions and inter-cluster assembly driving forces in the crystal lattices, including various types of hydrogen bonds and π···π stacking interactions. Adjusting the type of anions located on the surface and internal cavities resulted in silver nanowheels with different symmetries, which further self-assembled into complex triple- (Ag40) and double-helical (S-/R-Ag40) superstructures as well as one-dimensional chains {[Ag40(QL-2-S)8(HQL-2-S)19(iPrS)16]·Ag·7NO3·10C2F5COO}n ({Ag41}n) driven by conformational matching and diverse non-covalent interactions. Exploiting the cavities, the specific co-assembly of Ag40 with uridine monophosphate (UMP) was successfully achieved, and the water-mediated secondary assembly resulted in the formation of a chiral superstructure that induced the circular dichroism (CD) and circularly polarized luminescence (CPL) responses. The emergence of Ag40 extends the molecular wheel family to include Ag NC materials, while providing insights into regulating hierarchical crystalline superstructures of large-sized metal NCs promoted by small molecules.

Fig. 1: Hierarchical assembly based on Ag9 PBBs.
figure 1

a Ag9 building block, protected by two types of thiol ligands. b Monomer Ag11, blocked by two AgNO3 molecules at both ends, inhibited further aggregation. c One-dimensional aggregate {Ag10}n, where Ag9 PBBs are connected by Ag+ ions to form an infinite structure. d Tetramer Ag40 nanowheel, in which four PBBs are gathered together through the silver nodes to form a discrete structure. e One-dimensional aggregate {Ag41}n, in which Ag40 nanowheels are connected by additional Ag atoms to form an infinite structure. Color codes: Ag green, S yellow, C gray, N blue, F cyan, O red. All hydrogen atoms are omitted for clarity.

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Results

Synthesis and assembly of the building blocks

Due to the strong binding ability of Ag+ ions with VIA group elements (O/S/Se/Te), especially S, which allows various types of bonding and coordination geometries, silver-chalcogenolate clusters are particularly facile to form51,52,53. The introduction of anion templates further enhances the size of the NCs and expands the diversity of structures54,55,56,57,58. However, while the known large-sized Ag NCs generally have dense core-shell configurations, only a few instances of hollow cage structures have been reported, and their synthesis processes remain elusive59. To construct architectures distinct from those observed in traditional solid Ag NCs, we adopt a mixed-ligand strategy, wherein quinoline-2-thiol (QL-2-SH) and 2-propanethiol (iPrSH) serve as protective groups. The QL-2-SH ligand (Supplementary Figs. 1 and 2) possesses N and S donor atoms that tend to form more stable chelating coordination modes with the metal ions on the cluster surface, this is different from the traditional simple anchoring mechanism exhibited by mono-dentate thiols. In addition, the regular arrangement of QL-2-SH ligands on the NC surface facilitates aggregation of numerous aromatic plane groups, providing an ideal platform for establishing rich intra- and intermolecular interactions, such as π···π stacking and C‒H···π interactions. These diverse interactions play a crucial role in stabilizing metal NCs and achieving multiple hierarchical complexities as well as superstructures within crystal lattices. Additionally, incorporating iPrS‒ with reduced steric hindrance as inner stabilizers aids in circumventing the classical six-metal framework formed by the QL-2-SH ligands (Ag6(QL-2-S)6, Supplementary Figs. 3 and 4), thereby facilitating the formation of the anticipated hollow structure.

Based on the aforementioned strategies, Janus metal NCs (Ag11, Fig. 1b and Supplementary Figs. 5 and 6) with a specific arc were synthesized by introducing {tBuSAg}n into the synthesis of Ag6(QL-2-S)6, which holds potential for further assembly as PBBs to form non-highly symmetrical or infinite structures. The presence of two silver nitrates at both ends caps the middle Ag9(QL-2-S)2(HQL-2-S)4(tBuS)4(NO3)3(CH3CN) (Ag9 PBB) of Ag11, inhibiting its further aggregation (Supplementary Fig. 5a, b). Steric effects and inter-ligand interactions on the surface induce anisotropic arrangement of metal atoms and organic ligands, resulting in the formation of Janus Ag9 PBB. However, due to numerous intermolecular interactions and dense stacking forms, Ag11 is insoluble and challenging to assemble further. We attempted to optimize factors such as ligands, solvents, and synthesis conditions from their source and prepared a series of Ag9 PBB-based assemblies: (i) introduction of {iPrSAg}n produced a 1D infinite structure ({Ag10}n, Fig. 1c and Supplementary Figs. 7 and 8); (ii) using a ternary solvent system (CH3CN-DCM-THF), led to preparation of an all-nitrate-stabilized nanowheel (Ag40-NO3) was prepared; (iii) replacing AgNO3 with CF3COOAg and TOANO3 in Ag40-NO3 resulted in construction of a similar high-yielded Ag nanowheel (Ag40, Figs. 1d and 2); (iv) substituting achiral CF3COOAg with chiral metal precursors (S-/R-TFLAg) in Ag40 yielded chiral nanowheels S-/R-Ag40 (Fig. 3); and (v) employing larger metal precursor (C2F5COOAg) instead of achiral CF3COOAg in Ag40 allowed for preparation of a 1D nanowheel-assembled chain ({Ag41}n, Fig. 1e and Supplementary Figs. 9 and 10). Formation and structures of these products are highly sensitive to subtle changes in ligands selection and the choice of solvent system. Ligand engineering and solvent-mediated processes enabled the construction of correlated series, including Ag11, {Ag10}n, Ag40, Ag40-NO3, S-/R-Ag40, and {Ag41}n, which exhibit similar Ag9 PBBs (Fig. 1) with slight variations in the local ligand positioning. Investigating the formation mechanism of this distinctive wheel-like species will aid in the rational design of this fascinating structural family from its source. Compared with {Ag10}n and the nanowheels formed by iPrS‒, the bulkiness of the thiol ligands (tBuS‒) of Ag11 serves as a fundamental factor impeding its further assembly.

Fig. 2: Crystal structures of Ag40.
figure 2

a, b View of nanowheel Ag40 in the a axis (a) and b axis (b) directions. The metal framework of the nanowheel has a diameter of ~1.8 nm and an inner diameter of ~1.1 nm, with a thickness of ~1.2 nm. c Metal skeleton with a C2 symmetry of Ag40, constructed by four [Ag9(QL-2-S)2(HQL-2-S)5(iPrS)4(CF3COO)]2+ PBBs (Ag9, pale yellow shadow) and four [Ag(iPrS)2(HQL-2-S)2]‒ junctions (pale blue shadow). In Ag9 PBBs, two types of thiol ligands with different steric hindrances exhibit a Janus distribution. d Distribution of small sterically hindered iPrS‒ ligands on the metal skeleton of Ag40, highlighting the four iPrS‒ ligands inside the nanowheel (blue) and a ring composed of 12 metal atoms in almost the same plane (dark blue). For clarity, four metals far from the center of the Ag12 ring are omitted. e Distribution of quinoline-2-thiol ligands with larger steric hindrance on the metal skeleton of Ag40, highlighting the ligands on different PBBs in different colors. Color codes: Ag green and dark blue, S yellow, C gray, N blue, F cyan, O red. All hydrogen atoms are omitted for clarity.

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Fig. 3: Chiral acid ligand (S-/R-TFL‒)-induced separation of Ag40 enantiomers to form chiral nanowheels, S-Ag40, and R-Ag40, showing the complete solution of guest molecules.
figure 3

a Ag40 with an internal nanospace. b S-Ag40 and R-Ag40 nanowheels with C1 symmetry, possessing no crystallographic symmetry element and perfect mirror symmetry with respect to each other. S-Ag40 and R-Ag40 display the chiral structure and the non-coordinated guest anions (NO3‒ and S-/R-TFL‒) in the internal nanospace. c, d Non-coordinated guest anions confined in the internal or outer nanospace via hydrogen bonding and weak coordination. Dotted lines indicate non-covalent interactions mainly including weak Ag···O coordination (>2.6 Å) and hydrogen bonding, N(sp2)‒H···O (orange), C(sp2)‒H···O (pink), and C/N‒H···F (yellow) interactions. Color codes: Ag green, S yellow, C gray, N blue, F cyan, O red, H white.

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In {Ag10}n (Fig. 1c and Supplementary Figs. 7 and 8), the Ag9 PBBs are connected by [Ag(iPrS)2(HQL-2-S)2]‒ junctions, resulting in a one-dimensional polymer belonging to the zigzag chain. The formation of {Ag10}n represents a specific form of trans-co-assembly involving Ag9 PBBs as bitopic linkers and silver ions, which is significantly different from the cis-pattern observed in closed nanowheel structures (Fig. 1d and Supplementary Fig. 7d). Nanowheels (including Ag40, Ag40-NO3, and S-/R-Ag40; Fig. 1c and Supplementary Figs. 11‒22) can be considered as tetramers formed by the cis-co-assembly of Ag9 PBBs with Ag+ ions, resembling the aggregation pattern seen in cyclic polyoxometalate molecule P8W48 (Supplementary Fig. 13c; detailed structural discussions vide infra)60. By modifying the ligand bulkiness from NO3‒ (Ag40-NO3), CF3COO‒ (Ag40), and S-/R-TFL‒ (S-/R-Ag40) to C2F5COO‒, we further assembled these nanowheels into one-dimensional aggregates {Ag41}n (Supplementary Fig. 9). The driving forces behind the zigzag chain assembly of {Ag41}n likely arise from the unique size adaptability of C2F5COO‒, Ag‒S coordination interactions and π···π stacking achieved through the migration of surface-protecting ligands. Notably, {Ag41}n serves as an example demonstrating precise atomic structure control and confirms that controllable packing and assembly can be attained by adjusting composition and altering surface dynamics18. These nanowheels represent distinct stages (monomer, Ag11; tetramer, Ag40, Ag40-NO3 and S-/R-Ag40; and polymer {Ag41}n) and trends (trans-co-assembly: {Ag10}n; cis-co-assembly: Ag40, Ag40-NO3, and S-/R-Ag40) within hierarchical assembly based on Ag9, which allowed visualization of the formation process. From monomers to discrete assemblies to infinite superstructures, these atomically precise structures elucidate the building block assembly mechanism while offering some perspectives for constructing hierarchical superstructures.

Structure and composition determination of Ag40

Single-crystal X-ray diffraction (SCXRD) analysis shows that Ag40 crystallizes in the monoclinic C2/c space group (No. 15), revealing a unit cell composed of four nanowheel molecules (Supplementary Fig. 11). Due to the twofold rotation axis symmetry of the molecule, one-half of Ag40 is present in the asymmetric unit (Fig. 2 and Supplementary Fig. 12). The primary structure of Ag40 comprises 40 Ag+ ions, 8 bidentate QL-2-S‒, 20 protonated HQL-2-S (neutral), 16 iPrS‒ and 6 CF3COO‒ ligands (Fig. 2a‒b). Morphologically, Ag40 resembles an irregular wheel shape with a distinct cavity, possessing an outer diameter of ~1.8 nm and an inner diameter of ~1.1 nm, with a thickness of ~1.2 nm when the organic shell is removed (Fig. 2a‒b).

Structurally, the closed-loop tetramer Ag40 consists of four Ag9 PBBs ([Ag9(QL-2-S)2(HQL-2-S)5(iPrS)4(CF3COO)1-2]) and four [Ag(iPrS)2(HQL-2-S)2] linkers alternately assembled by sharing two pairs of μ2-HQL-2-S and μ3-iPrS‒ ligands (Fig. 2c). Four [Ag2(iPrS)4(CF3COO)]3‒ motifs and [Ag(iPrS)2(HQL-2-S)2]‒ junctions are connected in an alternate manner through iPrS‒ ligands to form a nearly coplanar Ag12 ring. Additionally, the [Ag7(QL-2-S)2(HQL-2-S)5]5+ units are distributed alternately on both sides of the nanowheel through PBB rotation and conformational matching of surface ligands (Fig. 2d, e and Supplementary Fig. 13). Some distances between metal ions are shorter than 3.44 Å (twice the van der Waals radius), which is attributed to the argentophilic interactions that contribute to the stability of the nanowheel (Fig. 2c)61,62. On the periphery of the hollow Ag‒S wheel-shaped skeleton of Ag40, surface ligands also exhibit regioselective distribution, originating from their conformational matching and the dislocation arrangement of the Ag9 PBBs (Fig. 2d, e and Supplementary Figs. 14‒17). Due to anisotropic arrangement, nonuniform distribution, and distortion (avoiding steric repulsion) of the various surface ligands directed by conformational matching and diverse intramolecular interactions, inversion (i) and mirror plane (σ) symmetry elements are absent in Ag40, making it chiral (Supplementary Fig. 18). The chirality generation of Ag40 is attributed to a typical outside-in mechanism63. There are two pairs of enantiomers per unit cell, resulting in a racemic mixture (Supplementary Fig. 11).

The distinctive internal nanospace of Ag40 is a notable characteristic that facilitates the investigation of host-guest interactions and phenomena in confinement scenarios (Fig. 3a). Owing to the highly disordered crystal lattices (Supplementary Fig. 12) and weak intensity of high-angle diffraction data, locating guest molecules within Ag40 using crystallography proves challenging. The free anions (CF3COO‒ and NO3‒) were revealed and confirmed by electrospray ionization mass spectrometry (ESI-MS, Supplementary Fig. 23) and charge balance. The formula of Ag40 was confirmed to be [Ag40(QL-2-S)8(HQL-2-S)20(iPrS)16(CF3COO)6](NO3)10. Ag40 dissolved in DCM shows a main grouped peak within the mass-to-charge ratio (m/z) range of 3600–3750 (+3 charge state) according to ESI-MS analysis (Supplementary Figs. 24 and 25). These +3 peaks are assigned to [Ag40(QL-2-S)8(HQL-2-S)20(iPrS)16(NO3)13-x(CF3COO)x]3+ (x = 0‒7), indicating that structural integrity of Ag40 remains intact in DCM and suggesting relatively strong ion pairing and host-guest interactions between the cationic nanowheel and the free anions (NO3‒).

To accurately confirm the positions of the guest molecules and reveal their host-guest interactions with Ag40, attempts were made to crystallize Ag40 in alternative space groups in order to modify the packing structure and eliminate the disorder phenomena. However, these efforts proved unsuccessful. Here, a simple method was developed by introducing chiral S-/R-trifluorolactate acids (S-/R-TFLH) into the synthesis system, which successfully resulted in the construction of chiral isomers (Fig. 3b). This alteration affected the molecular symmetry and subsequent superstructure formed by self-assembly (vide infra), leading to higher-quality crystals that allowed for complete resolution of guest molecules. The optically pure enantiomers S-Ag40 and R-Ag40 crystallize in the space group P21212, exhibiting low Flack parameters of 0.039(8) and 0.063(4), respectively. The asymmetric unit comprises one complete nanowheel (Supplementary Fig. 19), while the unit cell consists of four molecules (Supplementary Fig. 20). Compared to Ag40, the substitution of CF3COO‒ ligands (Supplementary Fig. 17) with chiral S-/R-TFL‒, NO3‒ and H2O results in a more twisted structure and a reduction in symmetry.

Due to the mirror symmetry between S-Ag40 and R-Ag40, we utilize S-Ag40 as a representative to accurately describe the precise positions of the guest molecules and their related interactions. The guest molecules (S-TFL‒ and NO3‒) are distributed within both the internal and external confined spaces of the nanowheel: (1) two S-TFL‒ and two NO3‒ anions are isolated in the internal nanospace due to the shielding effect provided by multiple peripheral quinoline-2-thiol ligands acting as the gates for S-Ag40. In addition, electrostatic interactions, weak coordination with the neighboring metal ions, and numerous hydrogen bonding (including N/C‒H···O and N/C‒H···F) occurs between these internal anions and adjacent organic ligands on the nanowheel (Fig. 3c and Supplementary Figs. 21 and 22); (2) four NO3‒ anions are confined within local cavities formed by HQL-2-S ligands outside the nanowheels (Fig. 3d and Supplementary Fig. 22) via diverse intermolecular interactions. The bulkiness of S-TFL‒ along with structural matching, leads to partial occupation of outer cavities by small amounts of NO3‒, further triggering transformation into complex hierarchical structures (vide infra). The composition and purity of Ag40, S-Ag40, and R-Ag40 were elucidated through powder X-ray diffraction, Fourier transform infrared spectroscopy, thermogravimetric analysis, energy-dispersive spectroscopy, elemental mapping, and 1H NMR (Supplementary Figs. 26‒36).

Multi-helical self-assembly of nanowheels into supercrystals

Hierarchical assemblies constructed from metal NCs with precise atomic structural information obtained by SCXRD provide valuable insights into the multiple non-covalent interactions between surface motifs and assembly dynamics. In particular, a double-helical assembly of heterodimeric Au29 NCs resembling DNA structures was found in the supercrystal, facilitating further research11. The size, morphology, and symmetry of the nanowheels (Ag40 and S-/R-Ag40, Supplementary Figs. 37‒47) and the variations in the surface patterns of four PBBs (Ag40: I, II, III, IV; S-/R-Ag40: I-1, II-1, III-1, IV-1; Supplementary Fig. 39) caused by guest anions and configuration matching contribute to evident anisotropic assembly affinities, enabling the formation of hierarchical architectures with appreciable complexity (Fig. 4). Specifically, when extending the unit cell along the a-axis direction, the Ag40 nanowheels form hierarchical triple-helical assemblies (Fig. 4a and Supplementary Fig. 42). Each pitch contains four nanowheels and possesses a length of ~7.5 nm and a width of ~4.6 nm. Interestingly, the S-/R-Ag40 nanowheels within the crystal lattice are arranged in ordered double-helical patterns along the c-axis (Fig. 4e), where each pitch (length: ~5.5 nm; diameter: ~5.3 nm) also contains four members.

Fig. 4: Helical assembly of Ag40 and S-Ag40 supported by the diverse non-covalent interactions in their supercrystals.
figure 4

a Self-assembly of Ag40 NCs into a triple-helical structure. Color codes: yellow, red, and turquoise, nanowheels in the different strands. b Helical linear chain of the triple-helical superstructure oriented and connected by two different surface motif pairs of Ag40 (A1/D1 and B1/C1). c Four types of motif matching between the neighboring nanowheels in the Ag40 supercrystal. d Intermolecular interactions of the two different surface motif pairs of Ag40, including π−π stacking (dark red), hydrogen bonding (C‒H···F, blue; and C/N‒H···O, pink), and C−H···π (black) interactions. e Self-assembly of S-Ag40 NCs into a double-helical structure. Color codes: pale blue and tan, nanowheels in the different strands. f Helical linear chain of the double-helical superstructure is orientally connected by two different surface motif pairs of S-Ag40 (A2/C2 and B2/D2). g Four types of motif matching between neighboring nanowheels in the S-Ag40 supercrystal. h Intermolecular interactions of two different surface motif pairs of S-Ag40, A2/C2: HQL-2-S···NO3‒···H2O···NO3‒···HQL-2-S hydrogen bonding path supported by C/N‒H···O (pink) and O‒H···O (dark blue); B2/D2: π−π stacking (dark red) interactions and hydrogen bonding (C/N‒H···O, pink). Color codes: Ag green, S yellow, C gray, N blue, F cyan, O red, H white.

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Based on the analysis of inter-cluster interactions (see Supplementary Figs. 38, 45‒47 for detailed discussion), the following contributions to the formation of helical superstructures are determined: (i) The torsion of adjacent nanowheel PBBs in the opposite direction (Supplementary Fig. 39) helps Ag40 to produce appropriate anisotropic interactions with neighboring enantiomers (Supplementary Fig. 41). (ii) Supported by a multitude of relatively strong non-covalent interactions, the PBBs from different nanowheels establish specific directional matchings to achieve pairing (A1, B1, C1, D1, Fig. 4b‒d). (iii) Electrostatic repulsion and attraction from various non-covalent interactions (such as π–π stacking, C‒H···π, and hydrogen bonds) fill both intra- and inter-strands, which serve as the fundamental elements in natural spiral structures.

The differences in spatial repulsion (stemming from symmetry, patchy surfaces, and guest anions; Ag40: CF3COO‒ + NO3‒; S-/R-Ag40: S-/R-TFL‒ + NO3‒; {Ag41}n: C2F5COO‒ + NO3‒) and intermolecular interactions guide the assembly of nanowheels into diverse superstructures (Ag40: triple-helical; S-/R-Ag40: double-helical; Fig. 4e‒f, see Supplementary Information for detailed discussion) and even coordination assembly materials (one-dimensional {Ag41}n, Fig. 1e). The synthesis process for these three crystalline materials involves silver salt (Ag40: CF3COOAg; S-/R-Ag40: S-/R-TFLAg; {Ag41}n: C2F5COOAg), demonstrating that subtle changes in small anions during the assembly of nanowheels in solution can trigger variations in the assembly behavior. The changes observed in the inter-nanowheels assembly behavior along with the analysis of internal driving forces fully based on atomically precise structures fully demonstrate that supercrystal engineering can be customized by adjusting the local surface pattern of the assembly primitive (Fig. 4).

Optical properties and AIEE behavior of Ag40

The stability of Ag40 in solution was confirmed by the 1H NMR spectra (Supplementary Fig. 36) and time-dependent UV‒vis absorption spectra (Supplementary Fig. 48). Ag40 showed extremely faint emission centered at 585 nm in DCM solution (Supplementary Fig. 49a) accompanied by a photoluminescence quantum yield (PLQY) of 0.2% (Supplementary Fig. 50) and a decay time of 4.4 μs (Supplementary Fig. 49b). The emission spectra of Ag40 in a mixture of DCM and n-hexane, as depicted in Supplementary Fig. 51, were examined to investigate the aggregation behavior systematically. When the fraction (f) of n-hexane exceeded 20%, there was a rapid increase in emission intensity, reaching its maximum at f = 90% with a PLQY of 2.4%. The red shift of the emission peak to 615 nm and level-off tail in the UV‒vis spectrum at f = 90% demonstrate the occurrence of Ag40 aggregation (Supplementary Fig. 52)64. This is further supported by dynamic light scattering (DLS) and transmission electron microscopy (TEM), which confirmed the larger size of the Ag40 particles at f = 90% (Supplementary Figs. 53 and 54). These results collectively indicate that Ag40 is an aggregation-induced emission enhancement (AIEE)-active molecule.

Ag40 crystals displayed an orange emission peaked at 603 nm (Supplementary Fig. 55a), accompanied by a PLQY of 5.4% and a decay time of 3.3 μs (Supplementary Fig. 55b), Similar to the aggregate states. Temperature-dependent PL spectra demonstrated that the PL intensity of Ag40 in the crystalline state gradually increased as the temperature decreased (Supplementary Fig. 56). At 83 K, the PLQY reached 42.9%, confirming the restriction of intermolecular motion (RIM) mechanism responsible for their AIEE properties64. Furthermore, the emission spectra of Ag40 crystals were independent of the excitation energy, indicating that the PL of Ag40 crystals originates from the same excited state (Supplementary Fig. 57)65. The optical properties observed in S-/R-Ag40 were comparable to those of Ag40 (Supplementary Figs. 50, 58 and 59). Despite extensive efforts, the CD and CPL signals of S-/R-Ag40 in both solution and solid-state could not be detected. This may be attributed to the superposition of multiple chirality arising from asymmetric molecular structures and multiple helical arrangements within the crystal lattice, as well as the dissociation of chiral acid from the primary metal skeleton in the solution (Supplementary Fig. 60)66,67,68.

H2O-mediated specific co-assembly of Ag40 with UMP nucleotides triggered CD and CPL responses

The nucleotides (Fig. 5a), as a prominent class of chiral biomolecules, can efficiently establish chiral assembly systems via non-covalent interactions with various small achiral molecules, including anions and/or nucleobases, thereby achieving specific recognition. This phenomenon has garnered significant attention in the field of supramolecular chemistry69,70. It is anticipated that Ag40 featuring cavities and multiple interaction sites possess the potential for chiral co-assembly with nucleotides through host-guest, coordination or other supramolecular interactions, thus expanding its application in biosensors. We evaluated the PL, CD, and CPL responses of Ag40 towards five commonly encountered nucleotides (Fig. 5). When the nucleotides dissolved in DMSO were added to the DCM solution of Ag40, only UMP-induced turbidity in the solution and exhibited a distinct yellow (abbreviated as Ag40 + UMP (M); Fig. 5b and Supplementary Fig. 61). The emission intensity increased by three-fold and was accompanied by a 10 nm blue-shift compared to that of Ag40 (Fig. 5c). This phenomenon suggests potential special interactions between Ag40 and UMP4,71,72. In comparison, the systems lacking Ag40, which only consisted of raw material and UMP were found to lack similar properties (Supplementary Fig. 62). These findings emphasize the potential of Ag40 for specific detection of UMP.

Fig. 5: Specific co-assembly of Ag40 and UMP nucleotides with their optical properties.
figure 5

a Molecular structure of various nucleotides. b CD and CPL activities triggered by the co-assembly process of Ag40 in DCM with UMP (dissolved in DMSO) and H2O, accompanied by an aggregation-induced luminescence enhancement process visible to the naked eye under visible (left) and UV (right) light irradiation. c Emission spectra of different stages (initial, Ag40; intermediate, Ag40 + UMP (M); final, Ag40 + UMP + H2O, abbreviated as Ag40 + UMP) in the recognition (λex = 430 nm). d Column chart of the emission intensity of the PL, CD, and CPL spectra for Ag40, Ag40 + H2O, and the co-assemblies with nucleotides. e Time-dependent CD spectra of the co-assemblies formed by Ag40 (1 × 10‒5 mol L‒1) in 3 mL of DCM with 20 μL of UMP (3 × 10‒2 mol L‒1) in DMSO and 20 μL of H2O. Interval: 4 min. f CD spectra of the co-assemblies formed by Ag40 (1 × 10‒5 mol L‒1) in 3 mL of DCM with 0‒50 μL of UMP (3 × 10‒2 mol L‒1) in DMSO and 20 μL of H2O. Interval: 5 μL. g CPL spectra of the co-assemblies formed by Ag40 (1 × 10‒5 mol L‒1) in 3 mL of DCM with 0‒50 μL of UMP (3 × 10‒2 mol L‒1) in DMSO and 20 μL of H2O. Interval: 5 μL.

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Unfortunately, the CD signals of the obtained Ag40 + UMP (M) aggregates within the absorption range of Ag40 are absent (Supplementary Fig. 63), potentially indicating inadequate chirality transfer from UMP to Ag40. Considering the crucial role played by water molecules in helical superstructure formation in S-/R-Ag40 (Fig. 4h), deliberate introduction of H2O is anticipated to facilitate ordered chiral assembly and subsequently trigger CD and CPL responses. When H2O was added to Ag40 + UMP (M), the PL exhibited changes in both color and intensity (Fig. 5b‒c). These changes were consistent with the aggregation state of Ag40 (Supplementary Fig. 51), and the co-assembly obtained here was denoted as Ag40 + UMP. The CD spectra of Ag40 + UMP displayed evident positive (at 365 nm) and negative (at 408 nm) signals, with a maximum anisotropy factor (gabs) of ~2.5 × 10‒3 (Fig. 5d and Supplementary Fig. 64). This pattern corresponded to a classic exciton-type cotton effect, indicating the emergence of interactions of the aromatic groups from Ag404. Note that UMP in DMSO exhibited only CD optical activity below 300 nm (Supplementary Fig. 65). The newly induced chiroptical signals revealed the transfer of chirality from UMP to Ag40, indicating that the introduction of H2O facilitated the chiral supramolecular assembly of Ag40 and UMP. Furthermore, due to the formation of relatively large-size chiral supramolecular assemblies, there was a significant increase in light scattering, and the absorption spectrum of Ag40 + UMP exhibited a hyperchromic shift (Supplementary Fig. 64). As depicted in Supplementary Fig. 66, the co-assembly of Ag40 + UMP displayed a strong CPL signal at 600 nm corresponding to emission peaks with a dissymmetry factor (|glum|) of 2.5 × 10‒3. Because CPL reflects differential emission intensity between right and left circularly polarized light on the excited state of chiral molecular systems73,74,75, the excited state of Ag40 + UMP assembly also has chiral characteristics.

The mechanism and kinetics of the chiral co-assembly formed by Ag40, UMP, and H2O were investigated through a series of parallel and tracking experiments (Fig. 5e–g and Supplementary Figs. 67‒76). Upon increasing the amount of H2O added, the CD signal exhibited distinct changes: no signal was observed at 0 μL; a signal appeared at 10 μL; the signal intensity amplified between 10‒20 μL; and finally disappeared within the range of 20‒30 μL (Supplementary Fig. 67). These results underscored the critical role played by the quantity of H2O in influencing the co-assembly system. The mixtures of Ag40 + AMP, Ag40 + GMP, Ag40 + CMP, and Ag40 + IMP exhibit turbidity and enhanced PL (Fig. 5d and Supplementary Fig. 68), while CD and CPL signals are absent (Supplementary Figs. 66 and 68). These results suggest that H2O can only promote the assembly of Ag40 + UMP (M), yet not for four other nucleotides. When H2O was replaced with other common solvents or when the solvent of UMP was changed from DMSO to H2O, the observation of chiral signals became impossible (Supplementary Figs. 69‒71), indicating that the choice and order of solvents play a crucial role in this process. These results provide evidence for the active involvement and mediation of water molecules in the co-assembly process.

The co-assembly evolution process of Ag40 + UMP was monitored by CD spectroscopy as a function of time after the addition of H2O (Fig. 5e and Supplementary Fig. 72). The CD signal and gabs at 365 nm and 408 nm exhibited a gradual increase before stabilizing within one hour. These findings suggest the active involvement of H2O molecules in the co-assembly of Ag40 and UMP, leading to the progressive formation of chiral superstructures. Furthermore, an increasing ratio of n(UMP):n(Ag40) resulted in a gradual increase in the intensity of the CD (Fig. 5f) and CPL (Fig. 5g) signals, as well as the gabs (Supplementary Fig. S73) and glum (Supplementary Fig. 74) values of the mixture. Additionally, UV−vis absorption exhibited hyperchromic shifts (Supplementary Figs. 72 and 73). These results indicated that an increase in UMP promotes further aggregation and chiral amplification of co-assembled Ag40, UMP, and H2O. Morphological changes before and after assembly were carefully analyzed to determine the mechanism behind chirality transfer in Ag40 + UMP co-assemblies. TEM images (Supplementary Fig. 75) revealed that individual Ag40 displayed good mono-dispersity with a uniform size distribution; UMP self-assembled into thin nanosheet structures; multiple Ag40 aggregates larger than 5 nm attached to these nanosheets formed by UMP in Ag40 + UMP (M); finally, both UMP nanosheets and mono-dispersed Ag40 nanowheel were observed on the mapping analysis for Ag40 + UMP assemblies (Supplementary Fig. 76). These results further demonstrate that the addition of H2O improves assembly order while promoting effective interactions leading to chiral transfer.

Density functional theory (DFT) calculations further revealed the co-assembly mechanism between UMP and Ag40. Figure 6a illustrates that the nucleobase of UMP can enter the Ag40 cavity, forming stable complexes through multiple strong non-covalent interactions. Specifically, the C=O group in the nucleobase of UMP forms N−H···O hydrogen bonds with the protonated quinoline ligand (HQL-2-S) inside the Ag40 cavity. Additionally, the N−H group in HQL-2-S of Ag40 engages in N−H···π interactions with the nucleobase of UMP. Furthermore, molecular dynamics simulations demonstrate the assembly process of Ag40 and UMP (Supplementary Movie 1). Based on these experimental and computational results, we reasonably determine a step-by-step H2O-mediated specific co-assembly process for Ag40 and UMP (Fig. 6b). The cavity structure of Ag40 possesses multiple internal interaction sites that specifically bind to UMP, leading to aggregation luminescence. The introduction of H2O facilitates an ordered chiral supramolecular assembly, thereby triggering the CD and CPL responses.

Fig. 6: Schematic representation of co-assembly process of Ag40, UMP nucleotides, and water.
figure 6

a DFT (PBE0/def2-SVP)-calculated structure of the Ag40 and UMP co-assembly, dotted lines indicate non-covalent interactions, including N-H···O (black line) and N-H···π (orange line). Color codes: Ag green, S yellow, C gray, N blue, F cyan, O red, H white. b Scheme showing the chiral co-assembly process of Ag40 and UMP mediated by H2O.

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Discussion

In summary, we developed a primary building block of rainbow-like Ag9 based on a mixed-ligands strategy. The monomer (Ag11) and two assemblies (discrete nanowheel Ag40 and 1D {Ag10}n) with distinct growth modes were prepared by ligand engineering and solvent mediation. Ag40 is a high-nuclearity wheel-like Ag NC with a hollow structure. By reducing the cluster symmetry through chirality (S-/R-Ag40), the disorder in Ag40 was eliminated, and the internal guest molecules and host-guest interactions were perfectly revealed. Subtle changes in acid ligands (CF3COO‒, S-/R-TFL‒, and C2F5COO‒) led to the differences in the spatial repulsion and intermolecular interactions, this resulted in the systematic regulation of the superstructures, including triple-helix (Ag40), double-helix (S-/R-Ag40) and 1D {Ag41}n structures, these results were based on the secondary building blocks Ag40 nanowheels and reflected the complexity and operability of the hierarchical structures. In addition to the above self-assembly, Ag40 could also specifically co-assemble with UMP and achieve chiral co-assemblies mediated by H2O, accompanied by CD and CPL responses. Ag40 will facilitate the precise design and controllable construction of large-sized metal cluster-based nanowheels and subsequent superstructure assembly with specific functions. Cavities76, including chiral ones77, within metal clusters are significant for host-guest systems and are poised to find various applications in sensing, catalysis, and molecular recognition.

Methods

Synthesis of quinoline-2-thiol (QL-2-SH)

QL-2-SH was synthesized according to the procedures described in the literature78. 2-Bromoquinoline (2-QL-Br, 2080 mg, 10 mmol), CuSO4·5H2O (125 mg, 0.5 mmol), KOH (2800 mg, 50 mmol), DMSO (20 mL), and water (2 mL) were added in 50 mL round-bottom flask. After flushing with argon, 1,2-ethanedithiol (1.8 mL, 20 mmol) was added. The mixture was heated to 90 °C and maintained for 20 h. After cooling to room temperature, the reaction mixture was distributed in aqueous HCl (5%) until the solution was slightly acidic. Then the reaction mixture was extracted with DCM (3 × 50 mL), and the combined organic layers were dried over anhydrous Na2SO4 and evaporated under reduced pressure. The crude product was further purified by silica gel column chromatography (ethyl acetate: n-hexane = 1:4) to provide the desired QL-2-SH as a yellow solid (yield: 65 %, based on QL-2-Br). 1H NMR (600 MHz, CDCl3): δ = 12.72 (s, 1H), 7.66 (dd, J = 19.0, 8.5 Hz, 2H), 7.62–7.57 (m, 2H), 7.48 (d, J = 9.0 Hz, 1H), 7.35 (m, 1H).

Synthesis of CF3COOAg

CF3COOAg was synthesized according to the procedures described in the literature68. Ag2O (12 g, 0.05 mol) was added to 100 mL of water and continuously stirred to obtain a black mixed solution. Then 8 mL CF3COOH was added to it until the precipitation dissolved completely, and the obtained colorless and transparent solution was stirred for 10 hours in darkness. Subsequently, the colorless solution was evaporated under reduced pressure to obtain the white product with a yield of 85% (based on Ag2O).

Synthesis of C2F5COOAg

C2F5COOAg was synthesized according to the procedures described in the literature68. The synthesis was the same as that of CF3COOAg with the exception of the use of C2F5COOH (11 mL) in place of CF3COOH (8 mL). (yield: 81 %, based on Ag2O).

Synthesis of S-/R-TFLAg

S-/R-TFLAg was synthesized according to the procedures described in the literature68. Ag2O (400 mg, 1.73 mmol) was added to 10 mL of water and continuously stirred to obtain a black mixed solution. Then S-/R-TFLH (500 mg, 3.47 mmol) was added to it until the precipitation dissolved completely, and the obtained colorless and transparent solution was stirred for 10 hours in darkness. Subsequently, the colorless solution was evaporated under reduced pressure to obtain the white product with a yield of 75% (based on Ag2O).

Synthesis of {iPrSAg}n

{iPrSAg}n was synthesized according to the procedures described in the literature68. AgNO3 (30 mmol, 5.1 g) was added to 75 mL acetonitrile, then mixed with 100 mL ethanol containing iPrSH (30 mmol, 2.8 mL) and 5 mL Et3N, and the obtained solution was stirred for 3 hours in darkness, the yellow powder of (iPrSAg)n was isolated by filtration and washed with ethanol then dried in the ambient environment (yield: 85 %, based on AgNO3).

Synthesis of Ag40

CF3COOAg (11.0 mg, 0.05 mmol), {iPrSAg}n (9.1 mg, 0.05 mmol), and TOANO3 (10.0 mg, 0.019 mmol) were added to the mixed solution of 2 mL DCM and 2 mL PhMe to form a pale yellow suspension under vigorous stirring. Then, 1 mL CH3CN was added to get a clear colorless solution. Subsequently, QL-2-SH (8.0 mg, 0.05 mmol) was added and the solution turned yellow immediately. After filtration, the filtrate was allowed to evaporate slowly in darkness at room temperature for a week to give yellow rod-like crystals. Yields: 12% (based on QL-2-SH). Elemental analysis based on C312H300Ag40F18N38O42S44 (found (calculated), %): C, 32.81 (33.10); H, 2.64 (2.67); N, 4.51 (4.70); S, 12.23 (12.46); Ag, 40.03 (39.87).

Synthesis of S-/R-Ag40

The synthesis method is similar to that of Ag40, except that CF3COOAg (11.0 mg, 0.05 mmol) is replaced by S-/R-TFLAg (12.5 mg, 0.05 mmol). The filtrate was allowed to evaporate slowly in darkness at room temperature for a week to give yellow octahedron-shaped crystals. Yields: 7.2% for S-Ag40; 8.4% for R-Ag40 (based on QL-2-SH). Elemental analysis of S-Ag40 based on C315H312Ag40F15N39O49S44 (found (calculated), %): C, 32.65 (33.08); H, 2.47 (2.75); N, 4.90 (4.78); S, 12.26 (12.33); Ag, 38.36 (38.57); and R-Ag40 based on C315H312Ag40F15N39O49S44 (found (calculated), %): C, 33.07 (33.08); H, 2.43 (2.75); N, 4.63 (4.78); S, 12.83 (12.33); Ag, 38.64 (38.57).

Synthesis of {Ag41}n

The synthesis method is similar to that of Ag40, except that CF3COOAg (11.0 mg, 0.05 mmol) is replaced by C2F5COOAg (13.5 mg, 0.05 mmol). The filtrate was allowed to evaporate slowly in darkness at room temperature for a week to give yellow plate-like crystals. Yields: 5.3% (based on QL-2-SH). Elemental analysis based on C321H293Ag41F50N34O41S43 (found (calculated), %): C, 32.21 (32.04); H, 2.25 (2.45); N, 3.46 (3.96); S, 11.68 (11.46); Ag, 40.47 (40.39).

Synthesis of Ag40-NO3

AgNO3 (8.5 mg, 0.05 mmol) and {iPrSAg}n (9.1 mg, 0.05 mmol) were added to a mixed solution of DCM, CH3CN, and tetrahydrofuran (THF) (5.0 mL, v:v:v = 2:2:1) to form colorless solution under vigorous stirring. QL-2-SH (8.0 mg, 0.05 mmol) was added, and the solution turned yellow immediately. After filtration, the filtrate was allowed to evaporate slowly in darkness at room temperature for a week to obtain crystalline products of Ag40-NO3.

Synthesis of Ag6

AgNO3 (8.5 mg, 0.05 mmol) was dissolved in a mixed solution of 2 mL CH3CN and 2 mL MeOH. Then, QL-2-SH (8.0 mg, 0.05 mmol) was added and the solution turned yellow presently. After filtration, the filtrate was allowed to evaporate slowly in darkness at room temperature for 3 days to give yellow block crystals of Ag6. Yields: 7.8% (based on QL-2-SH). Elemental analysis based on C54H36Ag6N6S6 (found (calculated), %): C, 40.40 (40.32); H, 2.15 (2.26); N, 5.06 (5.22); S, 12.11 (11.96); Ag, 40.08 (40.25).

Synthesis of Ag11

AgNO3 (8.5 mg, 0.05 mmol) and {tBuSAg}n (12.0 mg, 0.05 mmol) were dissolved together in a mixed solution of CH3CN and THF (5.0 mL, v:v = 3:2) to form a pale yellow suspension under vigorous stirring. Subsequently, QL-2-SH (8.0 mg, 0.05 mmol) was added and then the solution turned yellow presently. After filtration, the filtrate was allowed to evaporate slowly in darkness at room temperature for 5 days to give pale yellow block crystals of Ag11. Yields: 9.7% (based on QL-2-SH). Elemental analysis based on C74H84Ag11N13O16S10 (found (calculated), %): C, 30.21 (30.45); H, 2.79 (2.90); N, 6.40 (6.24); S, 10.81 (10.98); Ag, 40.50 (40.67).

Synthesis of {Ag10}n

The synthesis method is similar to that of Ag11, except that {tBuSAg}n (12.0 mg, 0.05 mmol) is replaced by {iPrSAg}n (9.1 mg, 0.05 mmol). The filtrate was allowed to evaporate slowly in darkness at room temperature for a week to give yellow needle crystals. Yields: 6.2% (based on QL-2-SH). Elemental analysis based on C75H75Ag10N11O12S11 (found (calculated), %): C, 32.50 (32.71); H, 2.94 (2.75); N, 5.76 (5.60); S, 12.61 (12.81); Ag, 39.36 (39.18).