Atomically precise nanoclusters (NCs) exhibit molecule-like fingerprints, yet their Raman response is usually buried under intense luminescence. Herein, we report the use of surface-enhanced Raman spectroscopy (SERS) to probe the molecular nature of the stable eight-electron silver NC, [Ag17(o1-carboranethiolate)12]3- (abbreviated as Ag17), by integrating it with plasmonic gold nanotriangles (Au NTs), forming an Ag17@Au NT nanohybrid. This is the first demonstration of an atomically precise NC functioning as a stable next-generation Raman probe under harsh laser conditions. Synergistic electromagnetic (EM) and chemical enhancement (CE) mechanisms yield an overall enhancement factor of up to ∼6 × 105, with ∼2 × 102 attributed to CE, consistent with time-dependent density functional theory (TDDFT) calculations. TDDFT reproduces the observed spectra and reveals low-lying hybrid charge-transfer excited states, underpinning the CE pathway. Plasmonic confinement and charge transfer cooperatively amplify the Raman scattering of the Ag-Ag bonds and carborane framework at the nanoscale junctions of the Ag17@Au NT nanohybrid.

The robust structure and tunable properties of 12-vertex carborane clusters make them highly attractive constituents of 2D and 3D self-assembled materials as well as for various potential applications. These molecules offer new possibilities related to their characteristic features such as low conformational freedom, high thermal and chemical stability, and relatively high inherent dipole moment. We synthesized and fully characterized bis-meta-carborane-thiol ( mm -SH), a rod-like molecule with two meta-carborane units connected by a single bond, acting as a molecular rotor. In its supramolecular crystal structure, this molecule exhibits an intriguing packing arrangement driven by the interplay between the SH group of a particular conformation, which affects intermolecular hydrogen interaction, and intramolecular dipole-dipole interactions. This interesting interplay manifests itself clearly in the single-crystal supramolecular arrangement, which we have analyzed experimentally as well as computationally. The respective self-assembled monolayer (SAM) of this dipole-responsive carborane constituent was prepared on flat silver and gold substrates and investigated using surface sensitive techniques such as X-ray photoelectron spectroscopy, scanning tunneling microscopy (STM), low-energy electron diffraction (LEED), and ellipsometry. The mm-SH molecules form a highly ordered structure on the Ag(111) surface, which was measured via LEED and STM with submolecular resolution. It is the first cluster constituent of SAMs that can, by rotation, change the orientation and magnitude of its inherent dipole moment ranging from 0.64 to 3.78 D. Furthermore, the formation of nanomembranes by low-energy electron irradiation of the SAMs (with an effective thickness of 5 ± 1 Å) is presented.

Atomically precise luminescent nanoclusters (NCs) with positional isomerism originating from the coordinating ligand shell represent an important group of functional nanomaterials. We report the synthesis of two neutral isomeric [Ag14(CBDT)6(TPP)4] NCs (where CBDT-H2 = ortho-carborane-9,12-dithiol, TPP = triphenylphosphine) having a stable 2e- superatomic configuration with face-centered cubic (fcc) Ag6@Ag8 core-shell geometry, where TPP ligand coordination makes the structural distinction. The positioning of four TPP ligands on the outer four Ag atoms results in distinct distortions of the Ag8 cubic shell and yields two Ag14 isomeric NCs: Ag14T (tetrahedral TPP binding) and Ag14S (square-planar TPP binding). Density functional theory (DFT) calculations confirm a narrowed HOMO-LUMO gap for Ag14S. The isomeric NCs exhibit markedly distinct photoluminescence (PL) properties, with room-temperature green and red phosphorescence for Ag14T and Ag14S, respectively. The former NC shows an especially complex PL behavior with multi-band emission at low temperatures. Furthermore, nanoindentation studies reveal slightly higher stiffness and hardness for Ag14S crystals than the other isomer. These findings establish phosphine binding as a versatile strategy to tune structure, luminescence, and mechanical characteristics in atomically precise NCs, enabling tailored platforms for optoelectronics and nanomechanics applications.

Carboranethiol self-assembled monolayers (SAMs) form stable, densely packed, ordered adlayers on Au{111} surfaces with identical lattice structures independent of molecular isomer. We utilize this property to study the dipole-induced changes...

In this study, we explore for the first time interactions of atomically precise noble metal nanoclusters (NCs) in the gas phase, revealing fundamental nanoscale reactivity beyond solvent effects. Using ion-selected mass spectrometry and theoretical calculations, we investigate and establish the formation of a Coulombic ion pair between two oppositely charged NC ions, [Ag17(o1-CBT)12]3- (o1-CBT = ortho-1-carboranethiol) and [Cu14(o9,12-CBDT)6]+ (o9,12-CBDT = ortho-9,12-carboranedithiol), that undergo metal exchange to form alloy NCs, focusing on how atom exchange processes can be understood in the isolated gas phase. The Coulombic contribution to the binding energy of the NC ion pair was estimated to be ∼66%, while the rest was from intercluster ligand interaction through van der Waals forces. Similar behavior across diverse oppositely charged NC ion pairs, including [Ag29(1,3-BDT)12]3- (1,3-BDT = 1,3-benzenedithiol), [PdAg28(1,3-BDT)12]4-, [PtAg28(1,3-BDT)12]4-, [Ag13Cu4(o1-CBT)12]3-, [Au25(2-PET)18]- (2-PET = 2-phenylethanethiol), [PdAg24(2,4-DMBT)18]2- (2,4-DMBT = 2,4-dimethylbenzenethiol), [PtAg24(2,4-DMBT)18]2-, [Cu14(o9,12-CBDT)6]+, [Ag21(m9-CBT)12]+ (m9-CBT = meta-9-carboranethiol), and [Ag22(2,5-DMBT)12Cl4(DPPB)4]+ (DPPB= diphenylphosphenobutane), confirms the universality of this process. Dithiol ligand exchange was observed between [Ag29(1,3-BDT)12]3- and [Cu14(o9,12-CBDT)6]+ in their Coulombic adducts for the first time. These results highlight the intrinsic, solvent-independent reactivity of NCs in the gas phase.

Electrocatalytic CO2 reduction using atomically precise nanomaterials has garnered significant research interest, owing to their controllable molecular structures. Here, we have synthesized an electrocatalyst composed of single crystals having a one-dimensional assembly of silver atoms bridged by sulfur atoms of meta-carborane-9-thiolates. The molecular structure of the framework was further characterized through high-resolution ESI-MS, which exhibited silver- and carborane-thiolate-containing ions originating from the fragmentation of the framework. This thermally stable solid acted as an efficient catalyst for the electrocatalytic conversion of CO2 to CO with a Faradaic efficiency of 85 +/- 3%. In situ Raman studies provided experimental verification of binding of CO2 to the framework. First-principles density functional theory calculations confirmed the feasible adsorption of CO2 with the Ag chains, highlighting its favorable interaction with the catalyst. Furthermore, free energy calculations revealed the rate-determining step of the conversion process to be the formation of *COOH. This study presents an efficient electrocatalyst featuring a one-dimensional silver-chalcogenide framework.

Atomically precise cluster crystals, with constituent units composed of tens to hundreds of atoms, are important for the construction of miniaturized solid-state devices. Understanding the mechanical characteristics of such crystals is crucial for these applications. In this study, we focused on the nanomechanical properties of crystals of two isomorphic copper nanoclusters (Cu4L4), protected by ortho-carborane-9-thiol, Cu4(oCBT)4, and meta-carborane-9-thiol, Cu4(mCBT)4. These two clusters possess identical square planar Cu4 cores embedded in butterfly-shaped Cu4S4 staples. Load-displacement measurements indicated that the crystals of Cu4(oCBT)4 (hardness of similar to 534.31 MPa) were harder than those of Cu4(mCBT)4 (hardness of similar to 335.49 MPa). Despite their lower density, crystals of Cu4(oCBT)4 demonstrated increased hardness, owing to the presence of locked slanted layers that efficiently interacted with each other through various short contact supramolecular interactions. During indentation studies, multiple "pop-in" events were observed for the crystals of both clusters, suggesting the dislocation of molecular layers within the crystal lattice. Dynamic mechanical analysis conducted at different loading frequencies indicated that crystals of Cu4(oCBT)4 have a higher storage modulus than Cu4(mCBT)4. Both the crystals are thermally robust, as evident from thermogravimetric analysis and attenuated total reflection-IR analysis. Using density functional theory, we calculated Young's modulus (E r) for both crystals at 1 and 2% strain and found that the high-density isomorph had a lower E r, consistent with experimental data showing E r of Cu4(oCBT)4 and Cu4(mCBT)4 to be 9.79 and 8.54 GPa, respectively. These findings highlight the significant role of subtle structural differences in governing the nanomechanical behavior of isomorphic cluster crystals, paving the way for their rational design in advanced solid-state device applications.

We report on the fabrication of a boron-based two-dimensional (2D) material via electron irradiation-induced cross-linking of carborane self-assembled monolayers (SAMs) on crystalline silver substrates. The SAMs of 1,2-dicarba-closo-dodecarborane-9,12-dithiol (O9,12) were prepared on flat crystalline silver substrates and irradiated with low-energy electrons, resulting in a 2D nanomembrane. The mechanical stability and compact character of the carborane nanomembrane were improved by using 12-(1',12'-dicarba-closo-dodecarboran-1'-yl)-1,12-dicarba-closo-dodecarborane-1-thiol (1-HS-bis-pCB), a longer, rod-like SAM precursor with two para-carborane units linked linearly together. The self-assembly, cross-linking process, and transfer of the resulting membranes onto holey substrates were characterized with different complementary surface-sensitive techniques including X-ray photoelectron spectroscopy (XPS), ultraviolet photoelectron spectroscopy (UPS), and low-energy electron diffraction (LEED) as well as scanning tunneling and electron microscopies (STM, SEM) to provide insight on the structural changes within the cross-linked SAMs. The presented methodology has potential for the development of boron-based 2D materials for applications in electronic and optical devices.

A series of B- and C-functionalized di- and trithiol chelating o-carborane ligands have been employed to explore the coordination chemistry with cyclopentadienyl titanium and vanadium complexes. Treatment of [Cp*TiCl3] with [LiBH4·THF], followed by thermolysis with a C-functionalized carborane-dithiol ligand [1,2-(SH)2-1,2-C2B10H10], yielded octacapped octahedral [(Cp*Ti)4{Ti(1,2-(S)2-1,2-C2B10H10)}2(μ3-S)6(μ3-O)2] (1) and hexacapped trigonal bipyramidal [(Cp*Ti)4{Ti(1,2-(S)2-1,2-C2B10H10)}(μ3-S)6] (2) clusters. One of the driving forces of these reactions is the cleavage of C-S bonds of carborane-dithiols that resulted in sulfide ligands and subsequently generated clusters 1 and 2. In contrast, a similar reaction with a B-functionalized carborane-dithiol [9,12-(SH)2-1,2-C2B10H10] led to B-B bond formation that yielded a κ2-hydridoborato complex, [(Cp*Ti){κ2-BH3(9,12-(S)2-1,2-C2B10H10)}] (3). To the best of our knowledge, complex 3 is the first example of a carborane-dithiol functionalized hydridoborato complex. Interestingly, when the reactions of [Cp*TiCl3] or [Cp2TiCl2] were carried out with a B-functionalized carborane-trithiol, [8,9,12-(SH)3-1,2-C2B10H9], they led to coordination complexes, [(Cp/Cp*Ti){8,9,12-(S)3-1,2-C2B10H9}] (Cp* (4a) and Cp (4b)). Similarly, when [(Cp*VCl2)3] was employed as a metal precursor, deboronation was observed at the icosahedral cage that resulted in a zwitterionic complex, [(Cp*V){1,5,6-(S)3-nido-7,8-C2B9H9}] (5). All the clusters have been characterized by NMR, IR, mass spectrometry, and X-ray diffraction analysis. Furthermore, the theoretical analyses provided valuable insights into the electronic structures of these unusual clusters.

We report the synthesis of [Ag17(o1-CBT)12]3- abbreviated as Ag17, a stable 8e⁻ anionic cluster with a unique Ag@Ag12@Ag4 core-shell structure, where o1-CBT is ortho-carborane-1-thiol. By substituting Ag atoms with Au and/or Cu at specific sites we created isostructural clusters [AuAg16(o1-CBT)12]3- (AuAg16), [Ag13Cu4(o1-CBT)12]3- (Ag13Cu4) and [AuAg12Cu4(o1-CBT)12]3- (AuAg12Cu4). These substitutions make systematic modulation of their structural and electronic properties. We show that Au preferentially occupies the core, while Cu localizes in the tetrahedral shell, influencing stability and structural diversity of the clusters. The band gap expands systematically (2.09 eV for Ag17 to 2.28 eV for AuAg12Cu4), altering optical absorption and emission. Ultrafast optical measurements reveal longer excited-state lifetimes for Cu-containing clusters, highlighting the effect of heteroatom incorporation. These results demonstrate a tunable platform for designing nanoclusters with tailored electronic properties, with implications for optoelectronics and catalysis. Tuning the structure and composition of atomically precise metal nanoclusters leads to property changes which, however, are still poorly understood. Here, the authors synthesize precisely substituted analogues of Ag17 clusters and study the changes in luminescence and electronic properties.

Investigating large metal nanoclusters decorated with three-dimensional molecular cages, with complete structural characterization, is challenging; however, their detailed understanding is important to study electronic confinement and associated properties. We have structurally resolved a nearly spherical 2.2 nm silver cluster with the molecular composition [Ag62S12(CBT)32]4+, altogether having 842 atoms, solely protected with meta-carborane-thiolates (CBTs). This is the largest nanocluster with carborane-based molecular cages reported so far. Abscission of the cluster reveals that it has a face-centered-cubic Ag14 inner core encapsulated with 12 sulfides, which is further surrounded by an outer scaffold of Ag48-S32 shell, protected with 32 meta-carboranes. The silver-sulfide skeleton of the nanocluster showed an assembly of multilayered polyhedra, having a mixture of Platonic and Archimedean solids. High-resolution mass spectrometric analyses and other spectroscopic studies further confirmed the molecular composition. This nanocluster exhibits characteristic molecular multiband optical absorption features along with a weak near-infrared (NIR) emission band. Ultrafast femtosecond transient absorption studies revealed stable photoexcited states linked to interlayer electron mobility between the neutral Ag14 core and the positively charged Ag48 shell, which are surrounded by negatively charged sulfide (S12 and S32) layers. Computational analysis shows that this cluster behaves as a two-electron superatom with a band gap of 1.77 eV, which is associated with the energy difference between the 1S symmetric and 1P nonsymmetric states. Successful structural characterization and associated optical properties of the nanocluster suggested that other larger metal nanoclusters encapsulated by three-dimensional molecular cages may be suitable for single-particle photonic and optoelectronic applications.

MicroED reveals insights into mechanochromic luminescence in copper nanoclusters, demonstrating structural transitions from crystalline to amorphous state upon grinding, with restoration of crystallinity following solvent exposure. Luminescence switching occurs due to reversible amorphization-recrystallization rather than chemical changes, providing critical design principles for such stimuli-responsive materials.

Electrochemical reduction of CO 2 (eCO 2 R) powered by renewable energy holds the potential to produce sustainable platform chemicals and decarbonize the hard‐to‐abate sectors. Herein, the structure‐activity correlation of atomically precise silver nanoclusters (NCs) in eCO 2 R to carbon monoxide (CO) is studied, elucidating the effect of the nuclearity of metal core and the electronic nature of the ligands. Electrocatalytic studies on Ag NCs, [Ag 21 (MCT) 12 (TPP) 2 ] + , [Ag 31 (TRZ) 10 ] 2− , [Ag 42 (CBDT) 15 (TPP) 4 ] 2− (shortly, Ag 21 , Ag 31 , and Ag 42 , respectively), reveal that the CO Faradaic efficiency (FE CO ) increases while the FE CO(max) (the maximum FE CO ) moves to higher positive potentials upon decreasing the nuclearity of these Ag NCs, almost in a quantitative correlation. Notably, every ≈ten Ag atoms variation in the cluster shifts the potentials for FE CO(max) and maximum partial current density, j CO ( max ) by ≈70 and ≈80 mV, respectively. The smallest nanocluster, Ag 21 , achieved a near‐unity FE CO(max) of 99.6% at −0.59 V vs RHE, and a competitive eCO 2 R‐to‐CO rate, producing a j CO ( max ) of 148 mA cm −2 at −0.7 V vs RHE. First principle calculations reveal that decreasing the atomicity in Ag NCs reduces the activation energy barriers for the 2e − reduction pathway due to the modulation of surface charge distribution and the electronic density of states of the active Ag sites.

Carboranedithiol isomers adsorbing with opposite orientations of their dipoles on surfaces are self-assembled together to form mixed monolayers where both lateral dipole-dipole and lateral thiol-thiolate (S-HS) interactions provide enhanced stability over single-component monolayers. We demonstrate the first instance of the ability to map individual isomers in a mixed monolayer using the model system carboranedithiols on Au{111}. The addition of methyl groups to one isomer provides both an enhanced dipole moment and extra apparent height for differentiation via scanning tunneling microscopy (STM). Associated computational investigations rationalize favorable interactions of mixed pairs and the associated stability changes that arise from these interactions. Both STM images and Monte Carlo simulations yield similarly structured mixed monolayers, where approximately 10% of the molecules have reversed dipole moment orientations but no direct chemical attachment to the surface, leading to homogeneous monolayers with no apparent phase separation. Deprotonating the thiols by depositing the molecules under basic conditions eliminates the lateral S-HS interactions while accentuating the dipole-dipole forces. The molecular system investigated is composed of isomeric molecules with opposite orientations of dipoles and identical surface packing, which enables the mapping of individual molecules within the mixed monolayers and enables analyses of the contributions of the relatively weak lateral interactions to the overall stability of the assemblies.

Copper nanoclusters exhibit unique structural features and their molecular assembly results in diverse photoluminescence properties. In this study, we present ligand-dependent multicolor luminescence observed in a Cu14 cluster, primarily protected by ortho-carborane-9,12-dithiol (o-CBDT), featuring an octahedral Cu6 inner kernel enveloped by eight isolated copper atoms. The outer layer of the metal kernel consists of six bidentate o-CBDT ligands, in which carborane backbones are connected through μ3-sulphide linkages. The initially prepared Cu14 cluster, solely protected by six o-CBDT ligands, did not crystallize in its native form. However, in the presence of N,N-dimethylformamide (DMF), the cluster crystallized along with six DMF molecules. Single-crystal X-ray diffraction (SCXRD) revealed that the DMF molecules were directly coordinated to six of the eight capping Cu atoms, while oxygen atoms were bound to the two remaining Cu apices in antipodal positions. Efficient tailoring of the cluster surface with DMF shifted its luminescence from yellow to bright red. Luminescence decay profiles showed fluorescence emission for these clusters, originating from the singlet states. Additionally, we synthesized microcrystalline fibers with a one-dimensional assembly of DMF-appended Cu14 clusters and bidentate DPPE linkers. These fibers exhibited bright greenish-yellow phosphorescence emission, originating from the triplet state, indicating the drastic surface tailoring effect of secondary ligands. Theoretical calculations provided insights into the electronic energy levels and associated electronic transitions for these clusters. This work demonstrated dynamic tuning of the emissive excited states of copper nanoclusters through the efficient engineering of ligands.

The chemistry and physics of macropolyhedral B18H22 clusters have attracted significant attention due to the interesting photophysical properties of anti-B18H22 (blue emission, laser properties) and related potential applications. We have focused our attention on the "forgotten" syn-B18H22 isomer, which has received very little attention since its discovery compared to its anti-B18H22 isomer, presumably because numerous studies have reported this isomer as nonluminescent. In our study, we show that in crystalline form, syn-B18H22 exhibits blue fluorescence and becomes phosphorescent when substituted at various positions on the cluster, associated with peculiar microstructural-dependent effects. This work is a combined theoretical and experimental investigation that includes the synthesis, separation, structural characterization, and first elucidation of the photophysical properties of three different monothiol-substituted cluster isomers, [1-HS-syn-B18H21] 1, [3-HS-syn-B18H21] 3, and [4-HS-syn-B18H21] 4, of which isomers 1 and 4 have been proved to exist in two different polymorphic forms. All of these newly substituted macropolyhedral cluster derivatives (1, 3, and 4) have been fully characterized by NMR spectroscopy, mass spectrometry, single-crystal X-ray diffraction, IR spectroscopy, and luminescence spectroscopy. This study also presents the first report on the mechanochromic shift in the luminescence of a borane cluster and generally enriches the area of rather rare boron-based luminescent materials. In addition, we present the first results proving that they are useful constituents of carbon-free self-assembled monolayers.

We present the fabrication and use of a film of a carborane-thiol-protected tetranuclear copper cluster with characteristic orange luminescence using ambient electrospray deposition (ESD). Charged microdroplets of the clusters produced by an electrospray tip deposit the clusters at an air-water interface to form a film. Different microscopic and spectroscopic techniques characterized the porous surface structure of the film. Visible and rapid quenching of the emission of the film upon exposure to 2-nitrotoluene (2-NT) vapours under ambient conditions was observed. Density functional theory (DFT) calculations established the favourable binding sites of 2-NT with the cluster. Desorption of 2-NT upon heating recovered the original luminescence, demonstrating the reusability of the sensor. Stable emission upon exposure to different organic solvents and its quenching upon exposure to 2,4-dinitrotoluene and picric acid showed selectivity of the film to nitroaromatic species.

Atomically precise nanomaterials with tunable solid-state luminescence attract global interest. In this work, we present a new class of thermally stable isostructural tetranuclear copper nanoclusters (NCs), shortly Cu4@oCBT, Cu4@mCBT and Cu4@ICBT, protected by nearly isomeric carborane thiols: ortho-carborane-9-thiol, meta-carborane-9-thiol and ortho-carborane 12-iodo 9-thiol, respectively. They have a square planar Cu4 core and a butterfly-shaped Cu4S4 staple, which is appended with four respective carboranes. For Cu4@ICBT, strain generated by the bulky iodine substituents on the carboranes makes the Cu4S4 staple flatter in comparison to other clusters. High-resolution electrospray ionization mass spectrometry (HR ESI-MS) and collision energy-dependent fragmentation, along with other spectroscopic and microscopic studies, confirm their molecular structure. Although none of these clusters show any visible luminescence in solution, bright μs-long phosphorescence is observed in their crystalline forms. The Cu4@oCBT and Cu4@mCBT NCs are green emitting with quantum yields (Φ) of 81 and 59%, respectively, whereas Cu4@ICBT is orange emitting with a Φ of 18%. Density functional theory (DFT) calculations reveal the nature of their respective electronic transitions. The green luminescence of Cu4@oCBT and Cu4@mCBT clusters gets shifted to yellow after mechanical grinding, but it is regenerated after exposure to solvent vapour, whereas the orange emission of Cu4@ICBT is not affected by mechanical grinding. Structurally flattened Cu4@ICBT didn't show mechanoresponsive luminescence in contrast to other clusters, having bent Cu4S4 structures. Cu4@oCBT and Cu4@mCBT are thermally stable up to 400 °C. Cu4@oCBT retained green emission even upon heating to 200 °C under ambient conditions, while Cu4@mCBT changed from green to yellow in the same window. This is the first report on structurally flexible carborane thiol appended Cu4 NCs having stimuli-responsive tunable solid-state phosphorescence.

We report the synthesis, structural characterization, and photophysical properties of a propeller-shaped Ag21 nanomolecule with six rotary arms, protected with m-carborane-9-thiol (MCT) and triphenylphosphine (TPP) ligands. Structural analysis reveals that the nanomolecule has an Ag13 central icosahedral core with six directly connected silver atoms and two more silver atoms connected through three Ag-S-Ag bridging motifs. While 12 MCT ligands protect the core through metal-thiolate bonds in a 3-6-3-layered fashion, two TPP ligands solely protect the two bridging silver atoms. Interestingly, the rotational orientation of a silver sulfide staple motif is opposite to the orientation of carborane ligands, resembling the existence of a bidirectional rotational orientation in the nanomolecule. Careful analysis reveals that the orientation of carborane ligands on the cluster's surface resembles an assembly of double rotors. The zero circular dichroism signal indicates its achiral nature in solution. There are multiple absorption peaks in its UV-vis absorption spectrum, characteristic of a quantized electronic structure. The spectrum appears as a fingerprint for the cluster. High-resolution electrospray ionization mass spectrometry proves the structure and composition of the nanocluster in solution, and systematic fragmentation of the molecular ion starts with the loss of surface-bound ligands with increasing collision energy. Its multiple optical absorption features are in good agreement with the theoretically calculated spectrum. The cluster shows a narrow near-IR emission at 814 nm. The Ag21 nanomolecule is thermally stable at ambient conditions up to 100 °C. However, white-light illumination (lamp power = 120-160 W) shows photosensitivity, and this induces structural distortion, as confirmed by changes in the Raman and electronic absorption spectra. Femtosecond and nanosecond transient absorption studies reveal an exceptionally stable excited state having a lifetime of 3.26 ± 0.02 μs for the carriers, spread over a broad wavelength region of 520-650 nm. The formation of core-centered long-lived carriers in the excited state is responsible for the observed light-activated structural distortion.

Noble metal nanoclusters protected with carboranes, a 12-vertex, nearly icosahedral boron-carbon framework system, have received immense attention due to their different physicochemical properties. We have synthesized ortho-carborane-1,2-dithiol (CBDT) and triphenylphosphine (TPP) coprotected [Ag42(CBDT)15(TPP)4]2- (shortly Ag42) using a ligand-exchange induced structural transformation reaction starting from [Ag18H16(TPP)10]2+ (shortly Ag18). The formation of Ag42 was confirmed using UV-vis absorption spectroscopy, mass spectrometry, transmission electron microscopy, X-ray photoelectron spectroscopy, infrared spectroscopy, and multinuclear magnetic resonance spectroscopy. Multiple UV-vis optical absorption features, which exhibit characteristic patterns, confirmed its molecular nature. Ag42 is the highest nuclearity silver nanocluster protected with carboranes reported so far. Although these clusters are thermally stable up to 200 °C in their solid state, light-irradiation of its solutions in dichloromethane results in its structural conversion to [Ag14(CBDT)6(TPP)6] (shortly Ag14). Single crystal X-ray diffraction of Ag14 exhibits Ag8-Ag6 core-shell structure of this nanocluster. Other spectroscopic and microscopic studies also confirm the formation of Ag14. Time-dependent mass spectrometry revealed that this light-activated intercluster conversion went through two sets of intermediate clusters. The first set of intermediates, [Ag37(CBDT)12(TPP)4]3- and [Ag35(CBDT)8(TPP)4]2- were formed after 8 h of light irradiation, and the second set comprised of [Ag30(CBDT)8(TPP)4]2-, [Ag26(CBDT)11(TPP)4]2-, and [Ag26(CBDT)7(TPP)7]2- were formed after 16 h of irradiation. After 24 h, the conversion to Ag14 was complete. Density functional theory calculations reveal that the kernel-centered excited state molecular orbitals of Ag42 are responsible for light-activated transformation. Interestingly, Ag42 showed near-infrared emission at 980 nm (1.26 eV) with a lifetime of >1.5 μs, indicating phosphorescence, while Ag14 shows red luminescence at 626 nm (1.98 eV) with a lifetime of 550 ps, indicating fluorescence. Femtosecond and nanosecond transient absorption showed the transitions between their electronic energy levels and associated carrier dynamics. Formation of the stable excited states of Ag42 is shown to be responsible for the core transformation.