Room-temperature photoluminescence in monocarboxylate-protected silver nanoclusters via steric hindrance-induced interfacial structure locking

Domain: physics
Published: 2025-12-21
Editorial outcome: minor_revision

Abstract
Tuning the optical properties of monolayer-protected nanoclusters through manipulation of their interfacial structures constitutes a compelling research direction. Herein, we report two atomically precise monocarboxylate-protected superatomic silver nanoclusters (RCO2-AgNCs), formulated as {Ag16(RCO2)12[(4-ClPh)3P]8}2+ [where R = 2,4,6-trimethylphenyl (2,4,6-Me3Ph) for Ma or 9-anthracenyl (9-An) for Mb], which features similar chemical composition, identical inner core while distinct interfacial coordination structures. When the RCO2-AgNCs undergoes a transition from an unlocked periphery ligand shell to a locked one, it evolves from exhibiting no luminescent properties at room temperature to possessing such properties. Photoluminescence and femtosecond transient absorption spectroscopies demonstrate that remarkable emission property of Ma is ascribed to the highly efficient energy transfer process occurring between phosphine ligand and metallic kernel, in conjunction with the suppression of molecular vibration imposed by the locked shell. This study not only elucidates the correlations between interfacial structure and photoluminescence properties of RCO2-AgNCs but also provides insights for designing nano-optical devices with atomic precision.

Introduction
Tuning the interfacial structure has been demonstrated as one of the most efficient strategies for modifying the properties of ligand-protected metal nanoparticles and nanoclusters1,2. Carboxylates, such as citrate3,4, ascorbate5, and formate6, have been extensively utilized as protecting ligands for the stabilization and functionalization of coinage metal nanoparticles and nanoclusters7–12. The versatile coordination mode and labile bonding characteristics between carboxylates and coinage metals endow these nanoparticles with diverse structures and tunable properties13. Over the past decade, extensive efforts have been devoted to synthesizing various carboxylate-protected coinage metal nanoparticles8,10,14. However, most of their atomic and interfacial structures remain unclear. The classic Hard-Soft-Acid-Base theory reveals that the bonding between the soft-acid coinage metals and the hard base O-donor ligands is relatively weak8. This significantly increases the difficulty of the formation and crystallization of carboxylate-protected coinage metal nanoparticles with atomic precision10. Indeed, finely controlling the interfacial structure and revealing how it influences the overall properties of the particles or clusters are particularly challenging tasks.

Although thiolate-protected silver clusters with identical shells yet different cores have been observed15, previous studies have demonstrated that altering the interfacial coordination motifs of conventional thiolate- or alkynyl-protected gold and silver nanoclusters results in significant structural changes to their metallic cores16. A notable example is Au42(TBBT)26 clusters (TBBT: 4-tert-butylbenzenethiolate) from Wu and co-workers, where variations in the interfacial structure can induce structural conversion of the metallic core between fcc and non-fcc architectures17. Additionally, Wu and co-workers reported two atomically precise thiolate-protected gold clusters, Au42(TBBT)26 and Au44(TBBT)28, which share an identical Au core but exhibit completely different ligand shell arrangements and compositions18. Jin and co-workers reported a series gold clusters Au52(SR)32 [SR=S-C6H4-CH3, S-C6H4-CH2CH3, S-C6H4-CH(CH3)2, S-C6H4-C(CH3)3] with a consistent metal core Au33, and revealed that reducing the para-bulkiness of the ligands can effectively inhibit non-radiative pathways, thereby enhancing photoluminescence quantum yield (PLQY)19. These interfacial structure variations lead to substantial differences in their photoluminescence properties. Despite extensive research conducted in this area, it remains unknown whether the interfacial structure of the cluster can be altered while retaining the identical core structure and a similar ligand composition.

Considering the aforementioned factors, our study focuses on carboxylate-protected silver nanoclusters (RCO2-AgNCs). The labile coordination between silver and oxygen presents an opportunity to achieve distinct interfacial structures only by varying the steric hindrance of the carboxylate ligands. Interestingly, comparing to thiolate-protected coinage metal nanoclusters (TMNCs), RCO2-AgNCs exhibit more distinct separation between the metallic core and the surface ligand layer. In the case of RCO2-AgNCs, there are no argentophilic interactions between the silver atoms in the staple motifs and the nearby core silver atoms (the average distance is over 3.4 Å)10. More importantly, the coordination mode of the staple motifs of the RCO2-AgNCs is more abundant than the TMNCs8,10. In contrast to the thiolate protected AgNCs, the coordination number of the silver atom in the surface staple motifs of RCO2-AgNCs can be 3 or 4 (Fig. 1), forming nearly planar tri-coordination (motif P) or tetrahedral coordination modes (motif T) with the auxiliary phosphine ligands10.

Herein, we report a comparative study of the synthesis, structure, and optical properties of two atomically precise RCO2-AgNCs, {Ag16(RCO2)12[(4-ClPh)3P]8}2+ (R=2,4,6-Me3Ph Ma or 9-An Mb), with identical kernel structure and similar chemical composition but different interfacial structure arrangement. Ma shows intense emission at 550 nm, whereas Mb presents no luminescence at room temperature. Density functional theory (DFT) calculations, photoluminescence (PL), and femtosecond to nanosecond transient absorption spectroscopy (fs/ns-TA) are utilized to clarify how the interfacial structure arrangement affects the photoluminescence characteristics of the clusters. The main results are reported and discussed here.

Results
Synthesis and general characterizations
The yellow block crystals of Ma were obtained by replacing the bulky 9-AnCO2H with 2,4,6-Me3PhCO2H (Fig. 2a, c) via a solvent-thermal method reported in our previous work10. The presence of coordinated carboxylate groups and trifluoromethanesulfonate (OTf) counter ions was confirmed by Fourier-transform infrared spectroscopy (FT-IR) spectra (Supplementary Fig. 1)20,21. X-ray photoelectron spectroscopy (XPS) (Supplementary Fig. 2) verified the coexistence of Ag0 and Ag+, with the Ag 3d5/2 peak being resolvable into two peaks having an approximately one-to-seven Ag0/Ag+ ratio22.

Electrospray ionization mass spectrometry (ESI-MS) in positive-ion mode (Fig. 2b, d) was employed to further determine the composition of Ma and Mb. As depicted in Fig. 2b, one prominent peak centered at m/z = 3304.58 is assigned to [Ma − 2OTf−]2+, where Ma = {Ag16(2,4,6-Me3PhCO2)12[(4-ClPh)3P]8}(OTf)2. As illustrated in Fig. 2d, the molecular ion peak A centered at m/z = 3652.83 is assigned to [Mb − 2OTf−]2+, where Mb = {Ag16(9-AnCO2)12[(4-ClPh)3P]8}(OTf)2 (Fig. 2d, inset). Additionally, two fragment ion peaks centered at m/z = 3305.21 (B) and 3140.41 (C) are observed, which corresponded to [Mb − 2(4-ClPh)3P+2H2O]2+ (Supplementary Fig. 3a) and [Mb − 3(4-ClPh)3P+4H2O]2+ (Supplementary Fig. 3b), respectively. The ESI-MS spectra confirmed that both compounds are neutral, and consequently, the charge state of the clusters structure is {Ag16(RCO2)12[(4-ClPh)3P]8}2+. Given that each carboxylate bears one negative charge, the metallic skeleton must be Ag1614+. Hence, both clusters possess the same molecular formula and free electron count of two8,23, in accordance with the XPS result.

Structural description
We then determined the cluster’s structure using single-crystal X-ray diffraction (Supplementary Table 1)24. The chemical formula of the crystal is {Ag16(2,4,6-Me3PhCO2)12[(4-ClPh)3P]8}(OTf)2·8DMF·4H2O (Ma·8DMF·4H2O), which contains a double charged positive {Ag16(2,4,6-Me3PhCO2)12[(4-ClPh)3P]8}2+ center, two counter ions (OTf−) and some solvents. Compared with the structure of our previously reported Mb, both clusters exhibit a typical Ag8@Ag8(RCO2)12[(4-ClPh)3P]8 core-shell structure arrangement (Fig. 3), which includes the same rhombohedral [Ag8]6+ cluster core (Supplementary Fig. 4a, d). Although the composition of their shell layer is nearly the same, which is consist of eight silver ions, twelve carboxylates and eight (4-ClPh)3P ligands, their interfacial coordination arrangements are completely different (Fig. 3a, b). The interfacial coordination structure of Ma consists of a so far unobserved locked octahedral assembly motif (see Fig. 1 motif OT), Ag8(2,4,6-Me3PhCO2)12[(4-ClPh)3P]8, which is composed of eight tetrahedrally coordinated silver atoms, eight phosphine ligands, and twelve μ4-η2,η2 trans-trans carboxylates (Fig. 3a). The cage-like periphery coordination shell structure, describing an octamer of the T type surface motif, is also revealed here for the first time. The interfacial coordination structure of Mb is composed of two types of staple motifs (Fig. 3b). The first motif consists of a hexameric assembly (see Fig. 1 motif H), {[(4-ClPh)3P)]Ag(9-AnCO2)}6, that surround the hexagonal base of the Ag8 kernel. This assembly is characterized by six trigonal-coordinated silver atoms, six phosphine ligands, and six μ3-η2,η2 trans-trans carboxylates. The second motif adopts a tetrahedral tie (see Fig. 1 motif T), formulated as {[(4-ClPh)3P]Ag(9-AnCO2)3}, and occupies the top and bottom of the Ag8 kernel (Fig. 3b). It features a tetrahedrally coordinated silver atom, one phosphine ligand, and three μ3-η1,η2 trans-trans carboxylate moieties.

As depicted in Fig. 3b, the geometric structure of the eight Ag+ centers within the 2T+H periphery shell of Mb constitutes a largely compressed octahedral hexasilver (Ag9 to Ag14) motif (H) in the middle, which is capped by two unconnected Ag+ centers (Ag15 and Ag16) (T) at the top and bottom along the C3 axes. The transformation from Mb to Ma involves three steps: (1) The octahedral hexasilver motif experiences elongation through the expansion of the interplanar spacing between the triangular faces (Ag9/Ag10/Ag11 at the top and Ag12/Ag13/Ag14 at the bottom, see Fig. 3a, b inset), with the spacing increasing from 1.4 Å (Fig. 3d) to 3.4 Å (Fig. 3c). (2) The triangular faces undergo shrinkage accompanied by a reduction in the Ag…Ag contact distances (red or cyan dashed lines), decreasing from Avg. 10.8 Å in Mb (Fig. 3d) to Avg. 9.1 Å in Ma (Fig. 3c). (3) The two unconnected motifs T perform a clockwise rotation along the C3 axes, while the angles of ∠O-Ag15-Ag10 decline from 23.6° in Mb (Supplementary Fig. 4e) to 18.1° in Ma (Supplementary Fig. 4b). This transformation results in the connection between the triangular faces (Fig. 3a, b inset) of the octahedral hexasilver (Ag9 to Ag14) and the two capping Ag+ centers (Ag15 and Ag16) via carboxylate bridging (Fig. 3a, c). Subsequently, all eight Ag+ centers in the periphery shell of Ma are linked together, forming a locked OT interfacial structure with enhanced compactness. This alteration of the interfacial structure is attributed to the steric hindrance of the functional groups of the carboxylate ligands. Specifically, replacing the bulky 9-AnCO2 (Mb) with 2,4,6-Me3PhCO2 (Ma) significantly decreases the steric hindrance among the periphery [(RCO2)xAg(4-ClPh)3P](x=2 or 3) staples, there by leading to a rotation and shrinkage of the cluster periphery shell, accompanied with decreased distances between the capping Ag+ centers (Ag15 and Ag16) and the ligand centers (Avg. 4.565 Å versus Avg. 4.367 Å) (Fig. 3e, f), and decreased distances between each ligand centers (Avg. 7.877 Å versus Avg. 7.462 Å) (Fig. 3e, f), respectively. On the other hand, the capping T motif is like an umbrella, which exhibits a larger open angle in Mb (∠84.9°) in comparison to that of Ma (∠80.6°) (Fig. 3e, f). This is due to larger steric hindrance of 9-AnCO2 in Mb expands the interfacial framework between the middle hexasilver motif and the two capping Ag+ centers, thus preventing the linkage between the H and T motifs (Supplementary Fig. 4c, f). In contrast, the reduced steric hindrance of the carboxylate ligands in Ma leads to a relatively closed umbrella, facilitating the connection between the middle octahedral hexasilver motif (Ag9 to Ag14) and the two capping Ag+ (Ag15 and Ag16) centers and thereby forming the locked OT interfacial structure with significantly enhanced compactness and rigidity.

Optical performance
To investigate how such interfacial structure variation influences the optical properties of clusters, the absorption and emission properties of the two clusters are systematically investigated. As shown in Supplementary Fig. 5, the UV–vis spectrum of Ma shows a double peak at ~440 nm and a stronger peak at ~290 nm. Whereas, the UV–vis spectrum of Mb exhibits two major absorptions includes a weaker peak at ~460 nm and a multiple peak at ~375 nm (Supplementary Fig. 5a). The correlations between the electronic structure and excitation property for the two clusters were further explored by DFT and TD-DFT calculations. The ideal symmetry for both of the two clusters is of S6, but their fully optimized structures were found to be slightly distorted to Ci. GGA-level calculations indicate that clusters Ma and Mb exhibit HOMO-LUMO gaps of 2.0 eV and 1.7 eV10, respectively (Fig. 4). These values are comparable to the optical gaps of 2.52 eV and 2.44 eV obtained from UV–vis diffuse reflectance spectra (Supplementary Fig. 6). In addition, the quantum theory of atoms in molecules analysis indicates that the charges of Ag atoms in Ma are ranging from 0.359 to 0.502, which is in agreement with their mixed valence nature (Supplementary Fig. 7). Interestingly, although the two clusters exhibit nearly identical chemical compositions with the same superatomic electron count of 2, their electronic structures are significantly different. (Fig. 4a). The HOMO, LUMO and LUMO+1 levels of Ma are of superatomic 1S, 1Px and 1Py orbitals, respectively. Those orbitals are mainly distributed over the inner Ag8 core with negligible contributions from the carboxylate ligands. On the contrary, the HOMO level of Mb is identified as a diffused 1S-type superatomic orbital, characterized by strong hybridization of the 5s(Ag) states with ligand states (9-anthracenecarboxylate). Owing to the structure distortion from the spherical symmetry, the next superatomic shells, LUMO+6 (1Px) and LUMO+7 (1Py), are splitted and situated higher in energy. The LUMO to LUMO+5 levels of Mb are of major π*(anthracenyl) characters (Right side of Fig. 4a).

The variations in the electronic structures between the two clusters consequently result in distinct excitation properties. According to our previous study10, the lowest excitation peak (~460 nm) of Mb corresponded to Ligand-to-Metal Charge Transfer (LMCT) from π(anthracenyl) type MOs to the 1P type LUMO+6 and LUMO+7. The other multiple peak at ~375 nm is associated with several transitions that are of major Ligand-to-Ligand Charge Transfer (LLCT) character (anthracenyl π→π* essentially)10. However, TD-DFT and Natural Transition Orbital (NTO) analysis of Ma indicating that its double peak at ~440 nm (α, β) is mainly corresponding to Cluster-Centered Transition (CCT), within its Ag8 6+ core, from the 1S type HOMO to the 1P type LUMO and LUMO+1 levels (Fig. 4b). Whereas the higher energy peak at ~290 nm (γ) is of major LLCT within the phosphine ligands exhibiting a σ(Ag-(4-ClPh)3P)→π*((4-ClPh)3P) character (Fig. 4b). These results reveal that interfacial structure rearrangement can substantially modify the electronic structure and excitation properties of monocarboxylate-protected AgNCs, strongly encouraging further exploration of the correlations between interfacial structures and optical properties of AgNCs. The stability of both clusters in DMF solution was evaluated by UV–vis spectroscopy (Supplementary Fig. 8). As shown in Supplementary Fig. 8a, b, when the temperature is increased to 90°C, the absorption peaks of Ma remain unchanged, while those of Mb gradually shift. Over 30 days of dark storage under ambient conditions (Supplementary Fig. 8c, d), the UV–vis absorption peaks of Ma remain nearly unchanged, while Mb’s core absorption peak (~460 nm) gradually diminishes. These results confirm that Ma exhibits greater stability than Mb in DMF solution. The solid-state stability of both clusters was further evaluated by Powder X-ray diffraction (PXRD) (Supplementary Fig. 9). Powder XRD patterns confirm that cluster Ma remains stable under room-temperature storage for over 2 weeks, while cluster Mb is stable for no more than 3 days under the same conditions. Unlike Mb, which has a loose 2T+H interface, Ma features a rigid OT interface that enhances metal core-ligand interactions, accounting for its substantially higher stability compared to Mb.

Interestingly, Ma displays intense bright yellow light emission in solid-state at room temperature (Fig. 5a), whereas Mb is non-emissive (Fig. 5c). To elucidate the origin of their luminescence, the emission spectra of both clusters were recorded at room temperature and 77 K. At 77 K, Ma displays a dual emission: one at λem = 465 nm (λex = 395 nm), and the other at λem = 541 nm, which is almost the same as the original signal at room temperature (Fig. 5a). In contrast, Mb exhibits a blue emission at λem = 471 nm (similar to the emission peak of Ma at 77 K, Fig. 5a) with a lifetime of 79.05 ns and a shoulder peak at 450 nm (Fig. 5c) due to the reduced thermal vibration. We further investigated the photophysical properties of (4-ClPh)3P, 2,4,6-Me3PhCO2H, and 9-AnCO2H (Supplementary Figs. 10–12). As shown in Supplementary Fig. 13, the excitation spectra of Ma, Mb, and three ligands demonstrate that the emission center of Ma at 450 nm only corresponds to the excitons of the (4-ClPh)3P ligand. On the contrary, the emission peaks of Mb at 471 nm and 450 nm arise from (4-ClPh)3P and 9-AnCO2H, respectively. Furthermore, the emission peak at ~541 nm for Ma can be identified as the cluster core intrinsic emission. The PL spectra and lifetime measurements of 2,4,6-Me3PhCO2H (Supplementary Figs. 11 and 13) suggest its negligible contribution to Ma emission. It is notable that the excitation spectrum of Ma (λem = 450 nm) overlaps with the emission signal of (4-ClPh)3P (Fig. 5a and Supplementary Fig. 10). This indicates the possibility of a Forster Energy Transfer process from (4-ClPh)3P to the Ag8 inner core of Ma25. Compared to Mb, Ma exhibits a more efficient utilization of the excitons of phosphine ligand, which significantly enhances its luminescence quantum yield (PLQY=53.11%, Supplementary Table 3). Therefore, the locked interfacial coordination arrangement of Ma can effectively restrict the vibrational deactivation of the entire cluster, thereby enhancing the luminescence performance of the cluster.

Temperature-dependent luminescence spectra of Ma and Mb were recorded within the temperature range from 303 to 83 K with an excitation at 395 nm, aiming to reveal the relationship between temperature and PL properties. Notably, Ma shows an abnormal variation process in its temperature-dependent luminescence intensity (Fig. 5b and Supplementary Fig. 4b)26. In the temperature range from 83 to 223 K, both of the dual emission peaks of Ma display a decreasing trend due to the enhanced thermal quenching effect. However, when the temperature rises above 223 K, the ligand-contributed emission peak (at λem = 465 nm) continues to decline, while the Ma intrinsic emission (at λem = 541 nm) clearly demonstrates thermal activation characteristics and rapidly intensifies27–29. This process is confirmed by measuring the emission lifetime at 550 nm at different temperatures, and the data are shown in Supplementary Fig. 16. Additionally, the lifetime of Ma measured at room temperature (at λem = 550 nm, τave = 74.60 μs, PLQY=53.11%, Supplementary Fig. 15b) exceeds that measured at 77 K (at λem = 541 nm, τave = 54.26 μs, PLQY=46.23%, Supplementary Fig. 14a), further verifying the existence of thermal activation processes30. Supplementary Fig. 14c displays the CIE coordinates of Ma under different temperature conditions. As shown in Fig. 5d and Supplementary 14e, the emission intensity of Mb decreases linearly as the temperature increases, without showing any obvious thermal activation. To further verify the impact of distinct interface structures of two clusters on luminescence, the Huang–Rhys factor (S) value and the phonon energy (ħwphonon) were calculated from their temperature-dependent emission spectra (83–303 K) (Supplementary Fig. 17). The results indicate that Ma and Mb exhibit similar values of S, implying comparable levels of electron-phonon coupling and lattice distortion. In contrast, Mb displays a larger ħw, suggesting that Mb’s loose 2T+H interface structure exhibits weaker constraints and a greater tendency for phonon generation compared to Ma’s locked OT interface structure, rendering it more susceptible to photon quenching31. Detailed photophysical data can be found in Supplementary Tables 3 and 4.

Excited-state dynamics
The distinct luminescence phenomena observed for the two clusters are further explored using femtosecond and nanosecond transient absorption spectroscopy (fs and ns-TA) to analyze the excited state dynamics of Ma and Mb. Under 480 nm excitation, the TA spectra of both Ma and Mb are dominated by a ground state bleach (GSB) at 470 nm and an excited state absorption (ESA) at 550 nm (Fig. 6a, b). The signals in the entire spectra of Ma and Mb decay monotonically over both the fs and ns timescales (Supplementary Fig. 18a, d). Notably, in addition to the decay (τ=2.1 ns, Supplementary Fig. 18c), which is similar to that of Mb (τ=3.85 ns, Supplementary Fig. 19a), the ns-TA data for Ma also reveal the existence of a longer decay process (τ=620 ns, Supplementary Fig. 18c), which might be related to the efficient utilization of (4-ClPh)3P ligands. The fast decay process could be related to the excited-state lifetime of the metal cores of the clusters.

According to the TD-DFT results, we chose 330 and 360 nm as pumping wavelengths to selectively excite the surface ligands in Ma and Mb. A kinetic process related to phosphine ligands was identified in Ma. As illustrated in Fig. 6c and Supplementary Fig. 20, the initial fs-TA spectrum (Fig. 6c) resembles that of the isolated excitation of the phosphine ligand, with the ESA centred at 650 nm under 330 nm excitation (Supplementary Fig. 20). Between 1 and 5 ps, the spectral shape gradually shifts towards that of the metal core excited state (Fig. 6c and Supplementary Fig. 22). During this period, the amplitude of the GSB at 475 nm and the ESA at 550 nm increases, while the ESA signal at 650 nm, which corresponds to the phosphine ligand, gradually disappears. This finding reveals an energy transfer from the phosphine ligand to the metal core, with a time constant of ~1.1 ps (Supplementary Fig. 19b), suggesting that the long-lifetime decay in Ma is due to energy transfer from the phosphine ligand to the cluster center. As depicted in Supplementary Fig. 21a, the fs-TA spectrum of 9-AnCO2H mainly consists of a broad singlet-state ESA spanning from 500 to 750 nm. In the ns-TA spectrum, the singlet ESA eventually decays, leaving only an ESA at 430 nm over longer time periods (Supplementary Fig. 21b). The same process is found in Mb (Fig. 6d and Supplementary Fig. 18e). It is worth noting that the decay process of the metal core under 360 nm excitation (τ=4.5 ns, Supplementary Fig. 18f) in Mb is nearly identical to that at 480 nm (τ=3.85 ns, Supplementary Fig. 19a). This suggests that the anthracene ligands have minimal influence on the excited state of the metal core during cluster excitation.

Based on the above discussion, Fig. 6e, f depicts the possible luminescence mechanisms of Ma and Mb, respectively. Under high pump energy excitation, the exciton of Ma is firstly excited to the phosphine ligands orbital, then transferring from the high excited state of phosphine ligands to the cluster inner core through a Ligand-to-Cluster-centered-Charge-Transfer (LCCT) process, leading to a longer excited state lifetime compared to that of Mb. The exciton subsequently moves down to the S1 state via CCT process, followed by a S1→S0 decay with a fluorescence emission of 550 nm. Therefore, the locked periphery ligand shell resulting in the efficient utilization of phosphine ligand excitons and metal energy levels, which constitutes a pivotal reason for the superior optical properties observed for Ma, which is distinct from other luminescent origin caused by factors like doping32, ligand exchange33, and mechanical grinding34.

Optical application
The remarkable temperature-dependent emission properties of Ma emphasize its potential applications as a cryogenic temperature sensor. This technology has been widely utilized in various research fields35,36, such as space exploration, polar studies, biological sample preservation, and the cryogenic transportation of food and medicine. We successfully fabricated a series of duck-shaped sensors by combining commercial light-cured resins with Ma, which are capable of visually indicating temperatures within the range from 77 to 298 K. As illustrated in Fig. 7a, when liquid nitrogen is added, the duck undergoes a rapid color change from yellow to green under UV irradiation. The duck-shaped sensors exhibit excellent cycling stability over 30 days of monitoring (Supplementary Fig. 23). Subsequently, as the liquid nitrogen gradually evaporates, the duck reverts to its originally yellow luminous color. Moreover, a heart-shaped sensor was successfully applied in a biological refrigerator at −80°C for practical purposes. Notably, the heart changes its luminous color from yellow to green (Fig. 7b), thereby demonstrating the potential of this technique for intuitive temperature sensing within product storage environments. Figure 7c presents the correlated color temperature spectra from 83 to 303 K, providing a clearer understanding of the relationship between temperature and luminous color [with the equation y=4229.15exp(-x/122.42)+4374.45 and R2=0.9989]. This offers perspectives and insights to the design and synthesis of temperature-dependent luminescent materials with atomic precision.

Methods
Synthesis of {Ag16(2,4,6-Me3PhCO2)12[(4-ClPh)3P]8}(OTf)2·8DMF·4H2O (Ma·8DMF·4H2O)
2,4,6-trimethylbenzoic acid (2,4,6-Me3PhCO2H, 0.049g, 0.3mmol) was added to AgOTf (OTf: trifluoromethanesulfonate) (0.077g, 0.3mmol) in N, N-dimethylformamide (DMF) (3mL) under ultra-sonication. 42μL of triethylamine (TEA, 0.3mmol) and tris(4-chlorophenyl)phosphine [0.036g, 0.1mmol, (4-ClPh)3P] were added to the resulting clear and transparent solution, which turned from colorless to yellow. The reaction mixture was sealed and kept at 70°C for 20 h. After cooled to room temperature, the solution was filtered. Slow evaporation of the yellow filtrate afforded Ma as yellow strip-shaped crystals. The resulting crystalline samples were collected for subsequent testing. Yield: 52~76% (0.074~0.108g, based on AgOTf). ESI-MS (CH2Cl2): A: [Ma − 2OTf−]2+, m/z=3304.58. IR (KBr, cm−1): 1679 (s, νC=O); 1276 (m, νC-F); 1013 (w, νS=O); 636 (m, νS-O).

Synthesis of {Ag16(9-AnCO2)12[(4-ClPh)3P]8}(OTf)2 (Mb)10
9-Anthracene carboxylic acid (9-AnCO2H, 0.067g, 0.3mmol) was added to a solution of AgOTf (0.077g, 0.3mmol) in acetonitrile (CH3CN, 6mL) under ultra-sonication. 42μL of TEA (0.3mmol) and 0.036g of (4-ClPh)3P (0.036g, 0.1mmol) were added to the resulting muddy solution, successively, which was still muddy. Then 1mL of DMF was added. A cloudy solution was obtained after ultrasound treatment. The reaction mixture was sealed and kept at 70°C for 20 h. After cooled to room temperature, the solution was filtered. Slow evaporation of the yellow filtrate afforded Mb as yellow block-shaped crystals. Yield: 34~55% (0.047~0.076g, based on AgOTf). ESI-MS (CH2Cl2): A: [Mb − 2OTf−]2+, m/z=3652.83; B: [Mb − 2OTf− − 2(4-ClPh)3P+2H2O]2+, m/z=3305.23; C: [Mb − 2OTf− − 3(4-ClPh)3P+CH3CN+CH3OH]2+, m/z=3140.95. IR (KBr, cm−1): 1630 (s, νC=O); 1225 (m, νC-F); 1015 (w, νS=O); 634 (m, νS-O).

Fabrication of Ma thin film
A 1:10 mixture of Ma and UV curable resin (CREALITY High Precision) was vigorously stirred under dark conditions for 2 h to ensure homogeneity. Subsequently, the mixture was cast into duck and heart-shaped molds and cured via 365 nm ultraviolet irradiation for 3 mins to fabricate the duck and heart-shaped sensors.

X-ray crystallography
Yellow strip-shaped crystals suitable for X-ray analysis were obtained by slowly evaporating DMF solution of Ma. Intensity data of Ma were collected on a Bruker SMART APEX CCD diffractometer (Mo Kα). Absorption corrections were applied by using the program CrysAlis (multi-scan). The structures were resolved by direct methods37,38. All non-hydrogen atoms were refined anisotropically by least-squares on F using the SHELXTL program39.

Other analysis and characterization
PXRD was tested by DX-2700 X-ray diffractometer, Fourier-transform infrared spectroscopy (FT-IR) was recorded from KBr pellets in the range of 4000–400 cm−1 with a IRAffinity-1S spectrometer. Ultraviolet-visible spectrophotometer (UV–vis) absorption spectra was measured on a Lambda 1050+. Luminescence, lifetime and quantum yields were measured on FLS-1000 apparatus. ESI-MS was performed on an Agilent Technologies ESI-TOF-MS. Qualitative analysis was carried out using GCMS-QP2010 Plus with EI ion source, EI-MS standard database, and an RTX-5 quartz capillary column. XPS studies were performed on PHI Quantum-2000 XPS. The samples were put under UHV to reach the 10−8 Pa range. At 10 kV and 10 mA, a non-monochromatized Al Kα source was employed. The C(1s) carbon peak (284.6 eV) was used as an internal reference to calibrate all binding energies. To attain the highest spectral resolution, high-resolution narrow-scan spectra were recorded at a take off angle of 55° and an electron pass energy of 50 eV.

Femtosecond and nanosecond transient absorption
The femtosecond transient absorption spectroscopy measurements were performed on a home-built pump-probe set-up. The laser pulse (800 nm, 35 fs pulse width, 1 kHz repetition rate) was generated by a regeneratively amplified Ti:sapphire laser (Coherent Astrella-Tunalbe-USP, USA). The output of the pulse is divided into two beams with a beam splitter. The 480 and 360 pump beams were produced by TOPAS, the power of pump pulse was set as 15 μw. The probe pulse was delayed by a computer-controlled optical delay line and then focused on a thin sapphire plate to generate the white light supercontinuum which split into two beams by using a broadband 50/50 beam splitter as the signal and reference beams (440–790 nm). The focused pump and probe pulses overlapped into a sample cuvette. The mutual polarization between the pump and probe pulses was set to the 54.7° by placing a half-wave plate in the pump beam. There is no photo-degrading after fs-TA experiments by checking the steady-state absorption spectra.

The ns-TA spectra were measured by a commercial spectrometer (Time-Tech Spectra). The generation of the pump beam is the same as that in fs-TA. The probe beam was generated from a supercontinuum laser (LEUKOS-DISCO, French) with the spectral region from 410 to 950 nm, the repetition rate is 2 kHz, pulse width is 700 ps–1 ns. There is also no photodegrading after ns-TA experiments by checking the steady-state absorption spectra.

Computational method
Geometry optimizations were performed within the DFT formalism using the ADF2023 program40,41. Scalar relativistic corrections via the ZORA Hamiltonian42 were included together with the Becke–Perdew (BP86) functional43,44. A triple-ξ Slater basis set plus a polarization (TZP) function was used45. The frozen core approximation was applied to the [1s2-4p6] shells for Ag, [1s2-2p6] for P and Cl, [1s2] for C and O, leaving the remaining electrons to be treated variationally. Grimme’s DFT-D3 empirical corrections46,47 were employed in order to take into account dispersion effects. For the sake of the computational limitations, the Gaussian16 package was used for calculating the UV–Vis optical transitions by time-dependent DFT (TD-DFT) at the Def2-SVP48/PBE049 level of theory. The plots of the natural transition orbitals were generated by using Multiwfn software50 with an isovalue of ±0.02 (e/bohr3)1/2.

Peer review rounds
[{"round": 1, "reviewer_comments": {"reviewer_1": "This paper by W.-Y. Jiang et al. presents a comparative study in the structure-properties relationship of two\nmonocarboxylate-protected silver nanoclusters (RCO2-AgNCs) with the formula {Ag (RCO ) [(4-ClPh) P] }2+ [where R =\n16 212 3 8\n2,4,6-trimethylphenyl (2,4,6-Me Ph) for Ma or 9-anthracenyl (9-An) for Mb]. These nanoclusters exhibit similar chemical\ncompositions and identical inner cores but feature distinct interfacial coordination structures. The study carefully elucidates\nthe relationships between the interfacial coordination structure and the optical properties of carboxylate-protected silver\nnanoclusters. Their findings are highly intriguing, and the results strongly validate their conclusions. Therefore, I strongly\nrecommend accepting this work pending minor revisions.\n1. The manuscript should be carefully checked for proper abbreviation usage, parenthetical formatting and other details. For\nexample, “characterized by strong hybridization of the 5s(Ag) states with ligand states (9-anthracene carboxylate)”; “the\nlowest … Ligand - to - Metal Charge Transfer (LMCT) from …” et al.\n2. Concerning the mass spectrometry discussion of Ma and Mb, additional mass spectrometry information for the shoulder\npeaks labeled A (Fig. 1b) and C (Fig. 1d) should be provided.\n3. Please align the wavelength ranges of Ma (Fig. 4a) and Mb (Fig. 4c) to better enable direct comparison of spectral shifts in\nthe PL emission maxima of Ma and Mb.\n4. PL images of (4-ClPh) P (Fig. S7) and 2,4,6-Me PhCOOH (Fig. S8) should be included in the supporting information.\n3 3\n5. In the manuscript, authors fabricated “duck”-shaped sensors by incorporating Ma into commercial light-cured resins, which\nvisually indicate temperatures from 77 K to 298 K. Do these sensors exhibit cyclable temperature-indicating behavior? If so,\nat least three cycles of data should be provided.\n6. The authors points out in PL properties section of the manuscript that: “However, when the temperature rises above 223 K,\nthe ligand-contributed emission peak (at λem = 465 nm) continues to decline, while the Ma intrinsic emission (at λem = 541\nnm) clearly demonstrates thermal activation characteristics and rapidly intensifies.” This statement requires supporting\ncitations.", "reviewer_2": "W.-Y. Jiang et al. reported a comparative study on two atomically precise silver nanoclusters (RCO2-AgNCs) stabilized by\ntwo monocarboxylates featuring distinct steric hindrance. The investigated clusters are well characterized by mass\nspectrometry, SCXRD, XPS, UV-vis, PL, TA spectra, and a detailed DFT investigation. The two nanoclusters show\nanalogous chemical compositions and identical inner cores, while differing in the interfacial coordination structures. The\nstudy reveals that the differences in their interfacial coordination structures play crucial roles in their PL properties. These\nfindings are of significant importance and unprecedented in existing literature, and the results strongly validate their\nconclusions. There is no doubt for me that this very well-written manuscript deserves publication in Nature Communications.\nI have only minor suggestions and comments, listed below.\n1. The stability of both clusters in their solid-state and in solutions should be evaluated.\n2. In figure 3a, authors illustrate ligand-metal hybridization at the HOMO energy level of Mb. However, the manuscript does\nnot thoroughly discuss how this hybridization accelerates nonradiative transitions. Please supply the Huang-Rhys factor\ndifference between Ma and Mb to quantify whether significant disparities in phonon coupling strength exist between the two\nclusters.\n3. Authors should carefully check the whole text; detailed issues like 'ligand-to-cluster-centered-charge-transfer (LCCT)\nprocess' in the computational analyses section should be 'Ligand-to-Cluster-centered-Charge-Transfer (LCCT) process'.\n4. The manuscript does not explicitly define whether the thermal activation process originates from the triplet energy level\nRISC or trap-state release in Figure 4a. It is proposed to incorporate variable-temperature lifetime analyses to determine\nwhether triplet energy level involvement occurs.\n5. The temperature sensor illustrated in Figure 6 only demonstrates luminescent color variation while omitting material\ncycling stability. The stability data of the sensor should be provided.", "reviewer_3": "This study by Wang et al. presents a systematic exploration of the influence of ligand-structure specifically on the\nphotoluminescence properties. The thought behind lock-unlock mechanism along with detailed PL investigations of clusters\nas well as individual ligands is impressive. The study is thorough and careful experiments have been carried out.\nI must mention, however that there are reports of nanoclusters showing similar trends of increased luminescence by\nrigidifying the structures upon moving from too bulky to less bulky ligands keeping the metals intact\n(https://doi.org/10.1021/jacs.3c09846). Change in luminescence properties moving from RT to 77 K was also seen earlier\n(https://doi.org/10.1038/s42004-023-00819-3 ).\nNovelty at the level needed for Nature Communications needs justification in view of such reports.\nSeveral minor issues are not clear and more comprehensive evidence is needed to support the conclusions drawn.\n1. “As depicted in Fig. 1b, one prominent peak centered at m/z = 3304.58 is assigned to [Ma - 2OTf−]2+, where Ma =\n{Ag16(2,4,6-Me3PhCO2)12[(4-ClPh)3P]8}(OTf)2.” Here, the ESI-MS shows a shoulder peak accompanied by several peaks in\nthe lower m/z range. These peaks should be assigned and their contribution to the luminescence properties should be\ntaken into account. Purity of the sample should be mentioned.\n2. A clarification of the nature of the material (crude powder or crystals) used for luminescence studies should be\nemphasised.\n3. The author presents the energy levels of the NCs through theoretical calculations. However, corresponding experimental\ndata should be provided. The band gaps can be experimentally verified using electrochemical methods such as differential\npulse voltammetry or UV-Vis Diffuse Reflectance Spectroscopy.\n4. Quantum yields at low temperatures should be added.\n5. “Interestingly, Ma displays intense bright yellow light emission in solid-state at room temperature (Fig. 4a), whereas Mb is\nno emissive (Fig. 4c).” The minor mistake in text should be corrected as “Mb is non-emissive”.\n6. “thereby leading to a rotation and shrinkage of the cluster periphery shell, accompanied with decreased distances\nbetween the capping Ag+ centers (Ag15 and Ag16) and the ligand centers (Avg. 4.565 Å versus Avg. 4.369 Å) (Fig. 2e, 2f),”\nHere, the average value calculated from Fig. 2e is 4.367 instead of 4.369.\n7. Previous reports showing origin of luminescence due to a few other factors like doping, ligand exchange, mechanical\ngrinding, etc. should be worth discussing. (https://www.nature.com/articles/s41467-025-56385-w,\nhttps://doi.org/10.1021/jacs.3c09846, https://doi.org/10.1021/acs.inorgchem.4c02617, https://doi.org/10.1021/jacs.0c02117 )"}, "author_response": "Response:\nWe really appreciate your comments and considerate suggestions. We carefully reviewed the\nmanuscript and standardized all bracket formats and abbreviation usage in the revised manuscript.\nWe have corrected “characterized by strong hybridization of the 5s (Ag) states with ligand states (9-\nanthracene carboxylate)” in the revised manuscript (Page 7, line 193), and all abbreviations follow\nan uppercase format, eg: “the classic Hard-Soft-Acid-Base (HSAB) …” in the revised manuscript\n(Page 2, line 44), “the lowest … Ligand - to - Metal Charge Transfer (LMCT) from …” in the revised manuscript\n(Page 7, line 199), “Ligand-to-Cluster-centered-Charge-Transfer (LCCT) process” in the revised manuscript\n(Page 11, line 310), et al.\n2. Concerning the mass spectrometry discussion of Ma and Mb, additional mass spectrometry\ninformation for the shoulder peaks labeled A (Fig. 1b) and C (Fig. 1d) should be provided.\nResponse:\nThank you for pointing this out. We retested the mass spectrometry of Ma and Mb. And ESI-\nMS data without shoulder peaks labeled A (Fig. 1b) and C (Fig. 1d) are now provided. The related\nresults and discussion have been included in the revised manuscript (Fig. 1 and Supplementary Fig.\nS3): “As illustrated in Fig. 1d, the molecular ion peak A centered at m/z = 3652.83 is assigned to\n[Mb - 2OTf−]2+, where Mb = {Ag (9-AnCO ) [(4-ClPh) P] }(OTf) (Fig. 1d, inset). Additionally,\n16 2 12 3 8 2\ntwo fragment ion peaks centered at m/z = 3305.21 (B) and 3140.41 (C) are observed, which\ncorresponded to [Mb - 2(4-ClPh) P + 2H O]2+ (Fig. S3a) and [Mb - 3(4-ClPh) P + 4H O]2+ (Fig.\n3 2 3 2\nS3b), respectively.”\nPage 25 in revised manuscript:\nFig. 1 | Synthetic process of Ma and Mb.\na, c Full structures of the cationic part of clusters Ma and Mb. View along the C axis. Color code:\n3\nsurface Ag+ with a coordination number of 4, green; surface Ag+ with a coordination number of 4,\nviolet; kernel Ag, pink with space-filling mode; O, red; C, gray; P, golden; Cl, cyan; H, white. Blue\ndashed lines represent the surface Ag−RCO −Ag bridging roles; b, d Positive-ion mode ESI-MS of\n16 3 2 12 3 8 2 16 2 12\nClPh) P] }(OTf) dissolved in CH Cl . Inset: Zoom-in of the experimental (black line) and\n3 8 2 2 2\nsimulated (red line) isotopic patterns for their molecular ion peaks of [Ma - 2OTf−]2+ at 3304.58\nand [Mb - 2OTf−]2+ at 3652.83.\nPage 2 in revised supporting information:\nFig. S3. Presentation of the Zoom-in ESI-MS of the Mb dissolved in CH Cl , the measured (black\n2 2\ntrace) and simulated (red trace) isotopic patterns of species B (a) and C (b) (see Fig. 1d of the main\ntext). Note: Mb = {Ag (9-AnCO ) [(4-ClPh) P] }(OTf) .\n16 2 12 3 8 2\nB = 3305.21: [Mb - 2OTf− - 2(4-ClPh) P + 2H O]2+,\n3 2\nC = 3140.41: [Mb - 2OTf− - 3(4-ClPh) P + 4H O]2+.\n3 2\n3. Please align the wavelength ranges of Ma (Fig. 4a) and Mb (Fig. 4c) to better enable direct\ncomparison of spectral shifts in the PL emission maxima of Ma and Mb.\nResponse:\nThank you for your comments. We have corrected the wavelength range of the excitation and\nemission spectra of Ma and Mb in the solid state (Fig.4a and 4c in the revised manuscript), and\ntheir wavelength ranges are now aligned. The related results have been included in the revised\nmanuscript (Fig. 4).\nFig. 4 | Luminescent properties of Ma and Mb.\na, c Excitation and emission spectra of Ma and Mb in the solid state. Inset: photographs of the\nluminescence; b, d Contour plots of temperature-dependent prompt emission spectra of Ma and Mb.\nInset: a linear fit to the temperature.\n4. PL images of (4-ClPh) P (Fig. S7) and 2,4,6-Me PhCOOH (Fig. S8) should be included in the\n3 3\nsupporting information.\nResponse:\nWe now provide the corresponding PL images of (4-ClPh) P (Fig. S7) and 2,4,6-Me PhCOOH\n3 3\n(Fig. S8) in the revised supporting information Fig. S10 and Fig. S11.\nPage 6 in revised supporting information:\nFig. S10. Luminescent properties of (4-ClPh) P in solid state. Excitation and emission spectra at 77\nex\nTemperature-dependent emission spectra of (4-ClPh) P with excitation at 380 nm; (e) Fluorescence\n3\ndecay curve at 459 nm (λ = 396 nm) at 298 K; (f) Corresponding CIE chromaticity diagram. Inset:\nex\nPhotographs of the luminescence of (4-ClPh) P in solid state.\n3 3\npurple emission at 77 K and 298 K.\nPage 6 in revised supporting information:\nFig. S11. (a) Photoluminescence analysis of 2,4,6-Me PhCO H in the solid state at 77 K; (b, c)\n3 2\nFluorescence decay curve at 328, 451 nm (λ = 299 nm) at 77 K; (d) Temperature-dependent\nex\nemission spectra of 2,4,6-Me PhCO H with excitation at 299 nm; (e) Photoluminescence analysis\n3 2\nat 298 K; (f) Fluorescence decay curve at 334 nm (λ = 305 nm) at 298 K. Inset: Photographs of\nex\nthe luminescence of 2,4,6-Me PhCO H in the solid state.\n3 2\nThe PL images of 2,4,6-Me PhCO H (Fig. S11a, S11d) shows that 2,4,6-Me PhCO H exhibits\n3 2 3 2\nblue emission at 77 K and blue purple emission at 298 K.\n5. In the manuscript, authors fabricated “duck”-shaped sensors by incorporating Ma into\ncommercial light-cured resins, which visually indicate temperatures from 77 K to 298 K. Do these\nsensors exhibit cyclable temperature-indicating behavior? If so, at least three cycles of data should\nbe provided.\nResponse:\nWe appreciate the reviewer’s detailed comments. We have supplemented the corresponding\nstability cycles data for Ma thin films under varying temperature and durations, and the result shows\nthat the “duck”-shaped sensors exhibit cyclable temperature-indicating behavior. The relevant\ndescription has been added in the revised manuscript (Page 12, line 328): “The “duck”-shaped\nsensors exhibit excellent cycling stability over 30 days of monitoring (Fig. S23).” The\ncorresponding stability cycles data for Ma thin films has been presented in the revised supporting\ninformation Fig. S23.\nPage 12 in revised supporting information:\nFig. S23. Photographs of Ma thin films under UV light at different temperatures and days. The Ma\nthin films were exposure to air and stored at 25 ℃.\n6. The authors points out in PL properties section of the manuscript that: “However, when the\ntemperature rises above 223 K, the ligand-contributed emission peak (at λ = 465 nm) continues to\nem\ndecline, while the Ma intrinsic emission (at λ = 541 nm) clearly demonstrates thermal activation\nem\ncharacteristics and rapidly intensifies.” This statement requires supporting citations.\nResponse:\nCitations for supporting these statements are now added in the revised manuscript, as follows:\n27. Luo, L. S., Liu, Z. Y., Du, X. S., Jin, R. C. Photoluminescence of the Au (SR) nanocluster\n38 26\ncomprises three radiative processes. Commun. Chem. 6, 22 (2023).\n28. Tian, W. D., Zhang, C. K., Paul, S., Si, W. D., Wang, Z., Sun, P. P., Anoop, A., Tung, C. H.,\nSun, D. Angew. Chem. Int. Ed. 64, e202421656 (2025).\n29. Yuan, Z. R., Wang, Z., Han, B. L., Zhang, C. K., Zhang, S. S., Zhu, Z. Y., Yu, J. H., Li, T.\nD., Li, Y. Z., Tung, C. H., Sun, D. Angew. Chem. Int. Ed. 61, e202211628 (2022).\nReviewer #2 (Remarks to the Author):\nW.-Y. Jiang et al. reported a comparative study on two atomically precise silver nanoclusters\n(RCO2-AgNCs) stabilized by two monocarboxylates featuring distinct steric hindrance. The\ninvestigated clusters are well characterized by mass spectrometry, SCXRD, XPS, UV-vis, PL, TA\nspectra, and a detailed DFT investigation. The two nanoclusters show analogous chemical\ncompositions and identical inner cores, while differing in the interfacial coordination structures. The\nstudy reveals that the differences in their interfacial coordination structures play crucial roles in their\nPL properties. These findings are of significant importance and unprecedented in existing literature,\nand the results strongly validate their conclusions. There is no doubt for me that this very well-\nwritten manuscript deserves publication in Nature Communications. I have only minor suggestions\nand comments, listed below.\n1. The stability of both clusters in their solid-state and in solutions should be evaluated.\nResponse:\nWe really appreciate your comments. The solution UV-vis spectra and the solid-state PXRD\npattern of two clusters with variable temperature and times are now provided (Fig. S7 and S8). A\nrelevant discussion has been added in the revised manuscript (Page 8, line 213): “The stability of\nboth clusters in DMF solution was evaluated by UV-vis spectroscopy (Fig. S8). As shown in Figure\nS8a and S8b, when the temperature is increased to 90 ℃, the absorption peaks of Ma remain\nunchanged, while those of Mb gradually shift. Over 30 days of dark storage under ambient\nconditions (Fig. S8c and S8d), the UV-vis absorption peaks of Ma remain nearly unchanged, while\nMb’s core absorption peak (⁓460 nm) gradually diminishes. These results confirm that Ma exhibits\ngreater stability than Mb in DMF solution. The solid-state stability of both clusters was further\nevaluated by PXRD (Fig. S9). Powder XRD patterns confirm that cluster Ma remains stable under\nroom-temperature storage for over two weeks, while cluster Mb is stable for no more than three\ndays under the same conditions. Unlike Mb, which has a loose \"2T + H\" interface, Ma features a\nrigid \"OT\" interface that enhances metal core-ligand interactions, accounting for its substantially\nhigher stability compared to Mb.”\nPage 5 in revised supporting information:\nFig. S8. The solution UV-vis spectra Ma and Mb at different temperatures (a, b) and times (c, d).\nPage 6 in revised supporting information:\nFig. S9. The PXRD patterns of the solid-state samples of Ma (a) and Mb (b) with variable times.\n2. In Figure 3a, authors illustrate ligand-metal hybridization at the HOMO energy level of Mb.\nHowever, the manuscript does not thoroughly discuss how this hybridization accelerates\nnonradiative transitions. Please supply the Huang-Rhys factor difference between Ma and Mb to\nquantify whether significant disparities in phonon coupling strength exist between the two clusters.\nResponse:\nWe thank the reviewer for pointing out this issue. We now supply the corresponding data of\nHuang-Rhys factor difference between Ma and Mb. The relevant description has been added (Page\n10, line 266), see below: “To further verify the impact of distinct interface structures of two clusters\non luminescence, the Huang-Rhys factor (S) value and the phonon energy (ħw ) were calculated\nphonon\nfrom their temperature-dependent emission spectra (83-303 K) (Fig. S17). The results indicate that\nMa and Mb exhibit similar values of S, implying comparable levels of electron-phonon coupling\nand lattice distortion. In contrast, Mb displays a larger ħw, suggesting that Mb’s loose “2T + H”\ninterface structure exhibits weaker constraints and a greater tendency for phonon generation\ncompared to Ma’s locked “OT” interface structure, rendering it more susceptible to photon\nquenching.”\nPage 9 in revised supporting information:\nFig. S17. Fitting results of the change of full-width at half-maximum (FWHM) at TADF with\ntemperature in Ma (a) and Mb (b).\n3. Authors should carefully check the whole text; detailed issues like 'ligand-to-cluster-centered-\ncharge-transfer (LCCT) process' in the computational analyses section should be 'Ligand-to-Cluster-\ncentered-Charge-Transfer (LCCT) process'.\nResponse:\nWe really appreciate your comments and considerate suggestions. We have corrected it in the\nrevised manuscript: “Under high pump energy excitation… ligand-to-cluster-centered-charge-\ntransfer (LCCT) process…” has rephrased to “Ligand-to-Cluster-centered-Charge-Transfer (LCCT)\nprocess” in the revised manuscript. Meanwhile, we have reviewed the manuscript carefully and\nstandardized all the abbreviations mentioned in the revised manuscript. For example, “the classic\nHard-Soft-Acid-Base (HSAB) …” in the revised manuscript (Page 2, line 44), “the lowest … Ligand\n- to - Metal Charge Transfer (LMCT) from …” in the revised manuscript (Page 7, line 199), et al.\n4. The manuscript does not explicitly define whether the thermal activation process originates from\nthe triplet energy level RISC or trap-state release in Figure 4a. It is proposed to incorporate variable-\ntemperature lifetime analyses to determine whether triplet energy level involvement occurs.\nResponse:\nWe thank the reviewer for pointing out this issue. We now add the corresponding variable-\ntemperature lifetime data. Fig. S16 demonstrates that the lifetime of emission peak of Ma at 480\nnm gradually decreases with increasing temperature, consistent with the decreasing trend of its\nfluorescence intensity. In contrast, the lifetime of intrinsic emission of Ma (λₑₘ=550 nm) continues\nto increase, consistent with its thermal activation behavior. Combined with the smaller Huang–Rhys\nfactor of Ma, it indicates that its structural deformation is relatively low and there is no obvious trap\nstate emission. Therefore, it is speculated that the thermal activation process of Ma originates from\nthe triplet energy level RISC.\nThe relevant description has been added in the revised manuscript (Page 9, line 256): “However,\nwhen the temperature rises above 223 K, the ligand-contributed emission peak (at λ = 465 nm)\nem\ncontinues to decline, while the Ma intrinsic emission (at λ = 541 nm) clearly demonstrates thermal\nem\nactivation characteristics and rapidly intensifies.27-29 This process is confirmed by measuring the\nemission lifetime at 550 nm at different temperatures, and the data are shown in Fig. S16.” The\ncorresponding temperature-dependent lifetime data of Ma has been presented in the revised\nsupporting information Fig. S16.\nPage 9 in revised supporting information:\nFig. S16. Temperature-dependent lifetime of Ma measured at 480 nm (a) and 550 nm (b) with\n395 nm excitation.\n5. The temperature sensor illustrated in Figure 6 only demonstrates luminescent color variation\nwhile omitting material cycling stability. The stability data of the sensor should be provided.\nResponse:\nWe now provide the corresponding stability cycles data of the Ma thin films at different\ntemperatures and days, and the result shows that the “duck”-shaped sensors exhibit cyclable\ntemperature-indicating behavior.\nThe relevant description has been added in the revised manuscript (Page 12, line 328): “The\n“duck”-shaped sensors exhibit excellent cycling stability over 30 days of monitoring (Fig. S23).”\nFig. S23. Photographs of Ma thin films under UV light at different temperature and days. The Ma\nthin films were exposure to air and stored at 25 ℃.\nReviewer #3 (Remarks to the Author):\nThis study by Wang et al. presents a systematic exploration of the influence of ligand-structure\nspecifically on the photoluminescence properties. The thought behind lock-unlock mechanism along\nwith detailed PL investigations of clusters as well as individual ligands is impressive. The study is\nthorough and careful experiments have been carried out.\nI must mention, however that there are reports of nanoclusters showing similar trends of increased\nluminescence by rigidifying the structures upon moving from too bulky to less bulky ligands\nkeeping the metals intact (https://doi.org/10.1021/jacs.3c09846). Change in luminescence\nproperties moving from RT to 77 K was also seen earlier (https://doi.org/10.1038/s42004-023-\n00819-3).\nNovelty at the level needed for Nature Communications needs justification in view of such reports.\nResponse:\nWe thank the reviewer for giving detailed comments and related references for improving the\nquality of our work. In the related references (https://doi.org/10.1021/jacs.3c09846), Prof.\nRongchao Jin and co-workers reported a series of gold nanoclusters Au₅₂(SR)₃₂ [SR = S-C H -CH ,\n6 4 3\nS-C H -CH CH , S-C H -CH(CH ) , S-C H -C(CH ) ] with a consistent Au44 metal core. They\n6 4 2 3 6 4 3 2 6 4 3 3\nrevealed that reducing the para-bulkiness of the ligands can effectively inhibit nonradiative\npathways, thereby enhancing PLQY. While their work primarily focuses on ligand steric hindrance,\nour study investigates changes in the clusters’ interface coordination structure (from a “loose” to a\n“locked” coordination interface), a topic not previously addressed in the literature. From the\nperspective of chemical bonding (Fig. 1), Prof. Jin’s research centers on altering covalent bonds\nwithin the inner surface layer of the nanoclusters, while our work focuses on modifying coordination\nbonds in the coordination layer.\nFig. 1. The main structure of coinage metal nanoclusters can be divided into four parts based on\nchemical bonding:\n(1) Nanocluster core, formed by aurophilic interactions or metallic bonds.\n(2) Coordination layer, formed by coordination bonds.\n(3) Inner surface layer, formed by covalent bonds.\n(4) Outer surface layer, mainly formed by hydrogen bonds. Adapted with permission from ref 1.\nCopyright © 2007, The American Association for the Advancement of Science.\n1. Jadzinsky, P. D., Calero, G., Ackerson, C. J., Bushnell, D. A., Kornberg, R. D. Structure\nof a thiol monolayer-protected gold nanoparticle at 1.1 Å resolution. Science 318, 430-\n433 (2007).\nHerein, we believe our work is highly significant in the following aspects: (1) It offers a facile\nand efficient strategy for regulating the interfacial coordination structure of atom-precise silver\nnanoclusters; (2) It reveals the relationships between the interfacial coordination structure and the\noptical properties of carboxylate-protected silver nanoclusters.\nThe relevant description of the reference has been added in the revised manuscript (Page 3,\nline 60): “Additionally, Wu and co-workers reported two atomically precise thiolate-protected gold\nclusters, Au (TBBT) and Au (TBBT) , which share an identical Au core but exhibit\n42 26 44 28 34\ncompletely different ligand shell arrangements and compositions.18 Jin and co-workers reported a\nseries gold clusters Au₅₂(SR)₃₂ [SR = S-C H -CH , S-C H -CH CH , S-C H -CH(CH ) , S-C H -\n6 4 3 6 4 2 3 6 4 3 2 6 4\nC(CH ) ] with a consistent metal core Au , and revealed that reducing the para-bulkiness of the\n3 3 44\nligands can effectively inhibit nonradiative pathways, thereby enhancing photoluminescence\nquantum yield (PLQY).19 These interfacial structure variations lead to substantial differences in\ntheir photoluminescence properties.”\n19. Wang, Y. T., Liu, Z. Y., Mazumder, A., Gianopoulos, C. G., Kirschbaum, K., Peteanu, L.\nA., Jin, R. C. Photoluminescence quantum yield from 3.8 to 18.3%. J. Am. Chem. Soc. 48,\n26328–26338 (2023).\nSeveral minor issues are not clear and more comprehensive evidence is needed to support the\nconclusions drawn.\n1. “As depicted in Fig. 1b, one prominent peak centered at m/z = 3304.58 is assigned to [Ma -\n2OTf−]2+, where Ma = {Ag (2,4,6-Me PhCO ) [(4-ClPh) P] }(OTf) .” Here, the ESI-MS shows\n16 3 2 12 3 8 2\na shoulder peak accompanied by several peaks in the lower m/z range. These peaks should be\nassigned and their contribution to the luminescence properties should be taken into account. Purity\nof the sample should be mentioned.\nResponse:\nWe appreciate you bringing this to our attention. We retested the mass spectrometry of Ma and\nMb. As shown in Fig. 1b, no shoulder peak is now observed, and Ma exhibits a single molecular\nion peak, assigned to [Ma - 2OTf−]2+. As shown in Fig. 1d, only molecular ion peak (A) and Mb-\nderived fragment ion peaks (B and C; Fig. S3) are observed. Given the ionization conditions of ESI-\nMS, the formation of Mb-based fragment ion peaks (B and C) is reasonable. These results confirm\nthat our cluster samples are relatively stable and of high purity.\nThe related results and discussion have been included in the revised manuscript (Fig. 1 and\nSupplementary Fig. S3): “As illustrated in Fig. 1d, the molecular ion peak A centered at m/z =\n3652.83 is assigned to [Mb - 2OTf−]2+, where Mb = {Ag (9-AnCO ) [(4-ClPh) P] }(OTf) (Fig.\n16 2 12 3 8 2\n1d, inset). Additionally, two fragment ion peaks centered at m/z = 3305.21 (B) and 3140.41 (C) are\nobserved, which corresponded to [Mb - 2(4-ClPh) P + 2H O]2+ (Fig. S3a) and [Mb - 3(4-ClPh) P\n3 2 3\n+ 4H O]2+ (Fig. S3b), respectively.”\nFig. 1 | Synthetic process of Ma and Mb.\na, c Full structures of the cationic part of clusters Ma and Mb. View along the C axis. Color code:\n3\nsurface Ag+ with a coordination number of 4, green; surface Ag+ with a coordination number of 4,\nviolet; kernel Ag, pink with space-filling mode; O, red; C, gray; P, golden; Cl, cyan; H, white. Blue\ndashed lines represent the surface Ag−RCO −Ag bridging roles; b, d Positive-ion mode ESI-MS of\n16 3 2 12 3 8 2 16 2 12\nClPh) P] }(OTf) dissolved in CH Cl . Inset: Zoom-in of the experimental (black line) and\n3 8 2 2 2\nsimulated (red line) isotopic patterns for their molecular ion peaks of [Ma - 2OTf−]2+ at 3304.58\nand [Mb - 2OTf−]2+ at 3652.83.\nPage 2 in revised supporting information:\nFig. S3. Presentation of the Zoom-in ESI-MS of the Mb dissolved in CH Cl , the measured (black\n2 2\ntrace) and simulated (red trace) isotopic patterns of species B (a) and C (b) (see Fig. 1d of the main\ntext). Note Mb = {Ag (9-AnCO ) [(4-ClPh) P] }(OTf) .\n16 2 12 3 8 2\nB = 3305.21: [Mb - 2OTf− - 2(4-ClPh) P + 2H O]2+,\n3 2\nC = 3140.41: [Mb - 2OTf− - 3(4-ClPh) P + 4H O]2+.\n3 2\n2. A clarification of the nature of the material (crude powder or crystals) used for luminescence\nstudies should be emphasized.\nResponse:\nWe thank the reviewer for pointing out this issue. To investigate the fluorescence properties of\nMa before and after grinding, we have provided powder XRD spectra (Fig. 2a) and the\ncorresponding normalized and non-normalized emission spectra (Fig. 2b, c) of Ma in crude powder\nor crystalline states. As shown in Figure 2a, the crystal structure of Ma is partially disrupted after\ngrinding; Nevertheless, while the emission peak position and shape of Ma remain unchanged, only\nminor variations in emission intensity are observed, confirming that grinding exerts a negligible\ninfluence on its PL properties. For the convenience of subsequent testing and characterization,\ncrystalline samples were selected as the luminescent research subjects in this work. And follow your\nadvice, we have emphasized the state of our samples in the preparation section, as follows: Slow\nevaporation of the yellow filtrate afforded Ma as yellow strip-shaped crystals. The resulting\ncrystalline samples were collected for subsequent testing. (Page 13, line 371 in the revised\nmanuscript).\nFig. 2. The powder XRD pattern (a) and emission spectra (b, c) of Ma at 298 K in crude powder\nand crystal states.\n3. The author presents the energy levels of the NCs through theoretical calculations. However,\ncorresponding experimental data should be provided. The band gaps can be experimentally verified\nusing electrochemical methods such as differential pulse voltammetry or UV-Vis Diffuse\nReflectance Spectroscopy.\nResponse:\nWe thank the reviewer’s comments and suggestions. We have now provided the UV-vis diffuse\nreflectance data of both clusters. Figure S6 shows that the optical HOMO-LUMO energy gaps of\nthe two clusters are estimated to be 2.52 eV and 2.44 eV, respectively. This is consistent with the\ntheoretical GGA energy level calculations, which show that the HOMO-LUMO energy gaps of Ma\nand Mb are 2.0 eV and 1.7 eV, respectively (Fig. 3).\nThe relevant description has been added to the revised manuscript (Page 7, line 181): “GGA-\nlevel calculations indicate that clusters Ma and Mb exhibit HOMO-LUMO gaps of 2.0 eV and 1.7\neV, respectively (Fig. 3). These values are comparable to the optical gaps of 2.52 eV and 2.44 eV\nobtained from UV-Vis diffuse reflectance spectra (Fig. S6).”\nPage 4 in revised supporting information:\nFig. S6. The diffuse reflectance spectra of Ma and Mb.\n4. Quantum yields at low temperatures should be added.\nResponse:\nWe have now added the quantum yields data of both clusters and their raw materials at low\ntemperatures. Table S3 reveals that cluster Ma exhibits a quantum yield of 46.23 % at 77 K, lower\nthan its room-temperature value of 53.11 %. This discrepancy in quantum yields between 77 K and\nMa. Meanwhile, cluster Mb have a weak blue emission at 77 K, with a quantum yield of 16.12 %.\nThe relevant description has been added to the revised manuscript (Page 9, line 260):\n“Additionally, the lifetime of Ma measured at room temperature (at λ = 550 nm, τ = 74.60 μs,\nem ave\nPLQY = 53.11 %, Fig. S15b) exceeds that measured at 77 K (at λ = 541 nm, τ = 54.26 μs, PLQY\nem ave\n= 46.23 %, Fig. S11a), further verifying the existence of thermal activation processes.”\nPage 13 in revised supporting information:\nTable S3. Photophysical date for the fluorescence of five solid materials.\nTemperature Material λ , nm λ , nm PLQY τ , μs\nex em ave\nMa 398 550 53.11 % 74.60\nMb - - < 1 % -\n9-AnCO H 395 488 11.01 % 2.92 × 10−2\n2\n2,4,6-Me PhCO H 305 334 4.83 % 2.40 × 10−3\n3 2\nMa 395 541 46.23 % 56.05\nMb 398 471 13.12 % 7.01 × 10−2\n3\n9-AnCO H 397 533 32.7 % 0.165\n2\n2,4,6-Me PhCO H 299 451 11.10% 9.75 × 104\n3 2\n5. “Interestingly, Ma displays intense bright yellow light emission in solid-state at room\ntemperature (Fig. 4a), whereas Mb is no emissive (Fig. 4c).” The minor mistake in text should be\ncorrected as “Mb is non-emissive”.\nResponse:\nWe really appreciate your comments and considerate suggestions. We have corrected it in the\nrevised manuscript: \"Interestingly, Ma displays intense bright yellow light emission in solid-state\nat room temperature (Fig. 4a), whereas Mb is no emissive (Fig. 4c)\" has rephrased to \"… whereas\nMb is non-emissive (Fig. 4c)\" in the revised manuscript.\n6. “thereby leading to a rotation and shrinkage of the cluster periphery shell, accompanied with\ndecreased distances between the capping Ag+ centers (Ag15 and Ag16) and the ligand centers (Avg.\n4.565 Å versus Avg. 4.369 Å) (Fig. 2e, 2f),” Here, the average value calculated from Fig. 2e is\n4.367 instead of 4.369.\nResponse:\nThank you for pointing this out. And we have corrected it in the revised manuscript: \"thereby\nleading to a rotation and shrinkage of the cluster periphery shell, accompanied with decreased\ndistances between the capping Ag+ centers (Ag15 and Ag16) and the ligand centers (Avg. 4.565 Å\nversus Avg. 4.369 Å) (Fig. 2e, 2f),\" has rephrased to \"… the ligand centers (Avg. 4.565 Å versus\nAvg. 4.367 Å) (Fig. 2e, 2f)\" in the revised manuscript.\n7. Previous reports showing origin of luminescence due to a few other factors like doping, ligand\nexchange, mechanical grinding, etc. should be worth discussing.\nResponse:\nWe really appreciate your comments and considerate suggestions. As you mentioned, factors\nlike doping, ligand exchange, and mechanical grinding can be seen as the origin of luminescence,\nfor example, we once reported a high PLQY gold cluster through the atomic precise doping of\ncopper into gold nanoclusters, simultaneously suppressing non-radiative decay and enhancing the\nintersystem crossing rate;32 Chakraborty et al. utilized ligand exchange approach to substitute BDT\n(benzene-1,3-dithiol) on Ag (BDT) with DHLA (dihydrolipoic acid), leading to a 44-fold\n29 12\nenhancement in PLQY for Ag (BDT) (DHLA) (x=1-6) clusters;33 Tang et al. employed\n29 12-x x\nmechanochemical techniques for the in-situ coupling of polymers with AIE prefluorophores,\nyielding modified polymers with vivid colors and high brightness.34 However, in our study of Ma\nand Mb, the distinct interfacial coordination structures of these clusters are considered the primary\nfactor of the origin of Ma’s luminescence. The evidence is as follows:\n(a) the DFT results (Fig. 3) indicate that Ma and Mb possess entirely different electronic\nstructures and excitation properties, and Ma’s HOMO, LUMO, and LUMO+1 energy levels\ncorrespond to superatomic orbitals. These orbitals are mainly distributed on the Ag core, and the\n8\ncontribution of carboxylate ligands can be ignored;\n(b) the PL spectra (Fig. 4) demonstrates that the excitation spectrum of Ma (λ = 450 nm)\nem\noverlaps with the emission signal of (4-ClPh) P, indicating a foster energy transfer process from (4-\n3 8\nefficiency for phosphine ligands. Further the charge transfer process from Ma’s phosphine ligand\nto cluster center was observed by TA spectra (Fig. 5). Since both clusters utilize the same phosphine\nligand, the above process illustrates that the origin of Ma’s luminescence is not due to carboxylate\nligand exchange.\n(c) no alterations to the fluorescence center were detected after mechanical grinding (Fig. 2).\nConsequently, the luminescent origin of this work is independent by factors such as doping, ligand\nexchange, or mechanical grinding. Based on the structural differentiation between Ma and Mb,\nherein we aim to explain Ma’s excellent PL performance from the perspective of their interface\ncoordination structures.\nThe relevant description has been added to the revised manuscript (Page 11, line 314):\n“Therefore, the “locked” periphery ligand shell resulting in the efficient utilization of phosphine\nligand excitons and metal energy levels, which constitutes a pivotal reason for the superior optical\nproperties observed for Ma, which is distinct from other luminescent origin caused by factors like\ndoping,32 ligand exchange,33 and mechanical grinding.34”\n32. Shi, W. Q., Zeng, L. L., He, R. L., Han, X. S., Guan, Z. J., Zhou, M., Wang, Q. M. Near-\nunity NIR phosphorescent quantum yield from a room-temperature solvated metal\nnanocluster. Science. 383, 326–330 (2024).\n33. Zeng, Y., Havenridge, S., Gharib, M., Baksi, A., Weerawardene, K. L. D., Ziefuß, A. R.,\nStrelow, C., Rehbock, C., Mews, A., Barcikowski, S., Kappes, M. M., Parak, W. J., Aikens,\nC. M., Chakraborty, I. Impact of ligands on structural and optical properties of Ag\n29\nnanoclusters. J. Am. Chem. Soc. 143, 9405–9414 (2021).\n34. Xie, H. L., Wang, J. C., Lou, Z. C., Hu, L. R., Segawa, S., Kang, X. W., Wu, W. J., Luo, Z.,\nKwok, R. T. K., Lam, J. W. Y., Zhang, J. Q., Tang, B. Z. Mechanochemical fabrication of\nfull-color luminescent materials from aggregation-induced emission prefluorophores for\ninformation storage and encryption. J. Am. Chem. Soc. 146, 18350–18359 (2024)."}, {"round": 2, "reviewer_comments": {"reviewer_1": "After careful evaluation of revised manuscript, I believe that the manuscript can be suitable for publication in journal “Nature\nCommunications” in presented form. All necessary additions and clarifications are made in the revised manuscript.", "reviewer_2": "The authors had addressed all my concerns, thus the current version is acceptable."}, "author_response": ""}]

Decision letter