Hierarchical assembly of Ag40 nanowheel ranging from building blocks to diverse superstructure regulation

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 form^51,52,53. The introduction of anion templates further enhances the size of the NCs and expands the diversity of structures^{54,55,56,57,58}. 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 (Ag_10n, 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 (Ag_41n, 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, Ag_10n, Ag₄₀, Ag₄₀-NO₃, S-/R-Ag₄₀, and Ag_41n, 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 Ag_10n and the nanowheels formed by ⁱPrS^‒, the bulkiness of the thiol ligands (^tBuS^‒) of Ag₁₁ serves as a fundamental factor impeding its further assembly.

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.

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.

In Ag_10n (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 Ag_10n 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 Ag_41n (Supplementary Fig. 9). The driving forces behind the zigzag chain assembly of Ag_41n 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, Ag_41n 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 Ag_41n) and trends (trans-co-assembly: Ag_10n; 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.

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.

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^‒; Ag_41n: 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 Ag_41n, Fig. 1e). The synthesis process for these three crystalline materials involves silver salt (Ag₄₀: CF₃COOAg; S-/R-Ag₄₀: S-/R-TFLAg; Ag_41n: 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 chemistry^69,70. 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 UMP^4,71,72. 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.

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 (λ_ex = 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.

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 (g_abs) 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 (|g_lum|) 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 systems^73,74,75, 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 g_abs 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 g_abs (Supplementary Fig. S73) and g_lum (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.

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.