Metal nanoclusters and methods of using same

Abstract

Luminescent homometallic and heterometallic nanoclusters that include ditopic ligands with at least one N-heterocyclic carbene are presented. High photoluminescence quantum yields are reported, including one at 68%. These nanoclusters are thermally stable and are suitable for imaging, as photosensitizers, photosensors, and for photodynamic or X- ray photodynamic therapy..

Description

[0001] METAL NANOCLUSTERS

[0002] AND METHODS OF USING SAME

[0003] RELATED APPLICATION

[0004] This application claims the benefit of the filing date of United States Application No. 63 / 470,227, filed on June 1 , 2023, the contents of which are incorporated herein by reference in their entirety.

[0005] FIELD

[0006] The invention relates to metal nanoclusters that have luminescent or photoluminescent properties, and to methods of using such compounds.

[0007] BACKGROUND

[0008] Metal nanoclusters are an atomically precise class of nanomaterials that, unlike metal nanoparticles, feature precise compositions and structures, and are characterized by individual electronic transitions between discrete energy levels. Thiolates phosphines, and alkynyls, are commonly used organic ligands to stabilize metal nanoclusters. Clusters in which the only organic ligands are N-heterocyclic carbenes (NHCs) are limited to a handful of examples.

[0009] The size regime between nanoparticles and molecular complexes is an interesting space occupied by atomically precise nanoclusters. These unique materials have sizedependent properties similar to other nanomaterials, but they can be characterized by molecular techniques such as single-crystal X-ray diffraction, nuclear magnetic resonance spectroscopy, and mass spectrometry. Unlike nanoparticles, which are a conglomeration of materials with an average size distribution, nanoclusters are routinely obtained as single molecules, with specific molecular weights, and optical properties characterized by individual electronic transitions rather than electron oscillations (plasmonics). Metal nanoclusters are atomically precise molecular materials typically comprised of a few to several hundred metal atoms stabilized with organic ligands and halides, and most often existing on the <2 nm scale. These clusters bridge the gap between materials and molecules, providing valuable insight into the behaviour of nanomaterials with the knowledge of precise structure that comes from molecular characterization tools.

[0010] SUMMARY

[0011] In one aspect, the invention provides a heterometallic or homometallic metal nanocluster having general formula [MAui2(LAL)5X2]Yn, wherein M is a transition metal, LAL is a ditopic ligand comprising at least one / V-heterocyclic carbene, X is a monodentate ligand, Y is a counterion that may be the same or different than X, and n is a number such that the overall charge on the metal nanocluster is zero, wherein if M is Au, and LAL comprises bis benzimidazolyl, then LAL further comprises a 1 ,1'- (naphthalene-1 ,8-diylbis(methylene)) linker. In one embodiment, M is Au, Pt, Pd, Ag, Cu, Rh, Ir, or Ni. In one embodiment, / V-heterocyclic carbene comprises imidazolyl, benzimidazolyl, or naphthimidazolyl. In one embodiment, LAL comprises: bis benzimidazolyl, benzimidazolyl, bis naphthimidazolyl, or benzimidazolyl and phosphine. In one embodiment, the nanocluster is [PtAui2(LAL)5X2]Yn, where LAL comprises a ditopic ligand comprising b / sNHC, b / sbenzimidazolyl, or benzimidazolyl and phosphine. In one embodiment, the nanocluster is [PdAui2(LAL)5X2]Yn, where LAL comprises a ditopic ligand comprising b / sNHC. In one embodiment, heterometallic nanocluster, wherein the nanocluster is [lrAui2(LAL)5X2]Yn, where LAL comprises a ditopic ligand comprising b / sNHC. In one embodiment, the homometallic nanocluster has the formula: [Aui3(b / s benzimidazolyl)5X2]Yn with a 1 ,1'-(naphthalene-1 ,8-diylbis(methylene)) linker and benzyl wingtip groups (5-4a), or [Aui3(b / s naphtimidazole)5X2]Ynwith an ortho-xy\y\ linker and benzyl wingtip groups (5-4c), simplified version of 5-4a, or simplified version of 5-4c.

[0012] In one embodiment, the heterometallic nanocluster comprises [PtAui2(LAL4)5X2]Yn, where LAL4 is ditopic L-type benzimidazole-based ligand with ortho-xy\y\ linker and benzyl wingtips (5-4d), [PtAui2(LAL5)5X2]Yn, where LAL5 is ditopic L-type benzimidazole-phosphine ligand with aliphatic -(CH2)3- linker and benzyl wingtip on benzimidazole moiety (5-4e), [PdAui2(LAL4)5X2]Yn, where LAL4 is ditopic L-type benzimidazole-based ligand with ortho- xylyl linker and benzyl wingtips (5-4f), [PtAui2(LAL1)5X2]Yn, where LAL1 is ditopic L-type benzimidazole-based ligand with 1 ,1'-(naphthalene-1 ,8-diylbis(methylene)) linker and benzyl wingtips (5-4g), [PtAui2(LAL6)5X2]Yn, where LAL6 is ditopic L-type benzimidazole-based ligand with aliphatic -(CH2)3- linker and benzyl wingtips (5-4h), or [lrAui2(LAL4)5X2]Yn, where LAL4 is ditopic L-type benzimidazole-based ligand with ortho-xy\y\ linker and benzyl wingtips (5-4i) simplified 5-4d, simplified 5-4e, simplified 5-4f, simplified 5-4g, simplified 5-4h, or

[0013] Simplified 5-4i.

[0014] In one embodiment, the compound is photoluminescent or electroluminescent. In one aspect, the invention provides a photosensitizer. In one aspect, the invention provides a method of electrocatalysis comprising employing the nanocluster as an electrocatalyst. In one embodiment, the electrocatalyst is soluble in solvent. In one embodiment, the solvent is DCM, MeOH, acetonitrile, ethanol, chloroform. In one embodiment, the electrocatalyst catalyzes a carbon dioxide reduction. In one embodiment, the electrocatalyst is activated by heating before use.

[0015] In one aspect, the invention provides a method of photocatalysis comprising adding a nanocluster to a reaction mixture, and applying light to the reaction mixture. In one embodiment, light comprises radiation having wavelengths in the range of visible light, UV light.

[0016] In one aspect, the invention provides a photosensor. In one aspect, the invention provides a solar cell comprising the nanocluster. In one aspect, the invention provides an electroluminescent device. In one aspect, the invention provides a photoluminescent device that comprises a nanocluster. In one aspect, the invention provides a biosensor comprising the nanocluster. In one aspect, the invention provides a method of radiation therapy for a patient in need thereof comprising administering to the patient a nanocluster, and applying radiation. In one aspect, the invention provides a method of photodynamic therapy for a patient in need thereof comprising administering to the patient a nanocluster, and applying light. In one aspect, the invention provides a method of X-ray photodynamic therapy for a patient in need thereof comprising administering to the patient a nanocluster, and applying X-ray radiation.

[0017] In one aspect, the invention provides a method of cancer treatment for a patient in need thereof comprising administering to the patient a nanocluster, and applying radiation.

[0018] In one aspect, the invention provides a method of bioimaging comprising administering the nanocluster, applying radiation such that the nanocluster luminesces, and imaging the luminescence. In one aspect, the invention provides a method of producing photoluminescence, comprising the steps of providing a photoluminescent nanocluster, and applying radiation to the nanocluster whereby the nanocluster photoluminesces.

[0019] In one aspect, the invention provides a method of imaging cells in tissue in a subject comprising administering to the subject a nanocluster, and applying radiation to cells that are desired to be imaged, wherein the cells photoluminese. In one aspect, the invention provides a method of imaging cells in tissue comprising disposing the nanocluster into cells, and applying radiation, whereby the cells photoluminesce. In one embodiment, applying radiation comprises applying visible light, UV light, heat, Gamma radiation, or X-ray radiation. In one aspect, the invention provides a method of producing electroluminescence, comprising the steps of providing a nanocluster and applying a voltage across the nanocluster whereby the nanocluster electroluminesces. In one aspect, the invention provides a method of photocatalysis or electrocatalysis comprising a nanocluster. In one embodiment, the nanocluster is stable in vivo, in aqueous media, in bodily fluids, and in simulated bodily fluids.

[0020] In one aspect, the invention provides a method of obtaining a Magnetic Resonance Imaging (MRI) image of cells in tissue comprising disposing the nanocluster into cells, and applying radio waves using an MRI machine, and producing an image of cells whereby the cells with nanocluster present appear different than cells without nanocluster.

[0021] BRIEF DESCRIPTION OF THE DRAWINGS

[0022] For a better understanding of embodiments and to show more clearly how they may be carried into effect, reference will now be made by way of example to the accompanying drawings, which illustrate aspects and features according to preferred embodiments, and in which:

[0023] Fig. 1 shows synthetic routes from 5-1a / b and 5- 1c to 5-3a / b and 5-3c, respectively.

[0024] Fig. 2A shows synthetic route from 5-3a to 5-4a.

[0025] Fig. 2B shows a UV-vis spectrum of 5-4a.

[0026] Fig. 2C shows ESI-MS of 5-4a.

[0027] Fig. 2D shows an expanded region of major cluster peak in ESI-MS of 5-4a.

[0028] Fig. 2E shows synthetic route from 5-3c to 5-4c.

[0029] Fig. 2F shows a UV-vis spectrum of 5-4c.

[0030] Fig. 2G shows ESI-MS of 5-4c.

[0031] Fig. 2H shows an expanded region of a major cluster peak on ESI-MS of 5-4c.

[0032] Fig. 3A shows an ORTEP drawing for the crystal X-ray structure of 5-4a with thermal ellipsoids shown at 30% probability level.

[0033] Fig. 3B shows a simplified ORETP drawing for the crystal X-ray structure of 5-4a, where only the gold core and the atoms bonded to it are shown and labelled.

[0034] Fig. 4A shows a side view of the single-crystal X-ray structure of 5-4a; counterions and hydrogen atoms have been removed for clarity.

[0035] Fig. 4B shows a top-down view of a single-crystal X-ray structure of 5-4a; counterions and hydrogen atoms have been removed for clarity.

[0036] Fig. 5A shows spectra verifying thermal stability of 5-4a at 60 °C in acetonitrile monitored by UV-vis spectroscopy over 72 hours.

[0037] Fig. 5B shows spectra verifying thermal stability of clusters 5-4c at 60 °C in acetonitrile monitored by UV-vis spectroscopy over 72 hours. Fig. 6A shows structural formula for LAL4.

[0038] Fig. 6B shows structural formula for LAL5.

[0039] Fig. 6C shows structural formula for LAL6.

[0040] Fig. 7A shows a synthetic route to 5-4d.

[0041] Fig. 7B shows a UV-vis spectrum of 5-4d.

[0042] Fig. 7C shows ESI-MS of 5-4d.

[0043] Fig. 7D shows the expanded region of the major cluster peak in ESI-MS of 5-4d.

[0044] Fig. 8 shows synthetic route to gold complex 5-3e via intermediate 5-2e.

[0045] Fig. 9A shows a synthetic route to 5-4e.

[0046] Fig. 9B shows a UV-vis spectrum of 5-4e.

[0047] Fig. 9C shows ESI-MS of 5-4e.

[0048] Fig. 9D shows the expanded region of the major cluster peak in ESI-MS of 5-4e.

[0049] Fig. 9E shows emission spectrum of 5-4e.

[0050] Fig. 9F shows a plot of time-resolved photoluminescense decay of 5-4e.

[0051] Fig. 10A shows UV-vis absorbance spectrum of TiO2film sensitized by 5-4e.

[0052] Fig. 10B shows an emission spectrum of 5-4e on TiO2film; emission was excited at 405 nm.

[0053] Fig. 10C shows a plot of time-resolved photoluminescense decay of 5-4e on TiO2film, measured at 650 nm with a 405 nm excitation.

[0054] Fig. 11 A shows a linear sweep voltammogram JV curve for the photovoltaic cells sensitized by 5-4e. This cell shows a VOc of -0.4 V and a JSc of 1 .1 mA / cm2.

[0055] Fig. 11 B shows a chronoamperometry curve of the cells sensitized by 5-4e, demonstrating the efficiency of the cell performance over time.

[0056] Fig. 12A shows the synthetic route to 5-4f.

[0057] Fig. 12B shows a UV-vis spectrum of 5-4f.

[0058] Fig. 12C shows ESI-MS of 5-4f.

[0059] Fig. 12D shows the expanded region of the major cluster peak in ESI-MS of 5-4f.

[0060] Fig. 13A shows the synthetic route to 5-4g.

[0061] Fig. 13B shows a UV-vis spectrum of 5-4g.

[0062] Fig. 13C shows ESI-MS of 5-4g.

[0063] Fig. 13D shows the expanded region of the major cluster peak in ESI-MS of 5-4g.

[0064] Fig. 14A shows the synthetic route to 5-4h.

[0065] Fig. 14B shows a UV-vis spectrum of 5-4h.

[0066] Fig. 14C shows ESI-MS of 5-4h.

[0067] Fig. 14D shows the expanded region of the major cluster peak in ESI-MS of 5-4h. Fig. 15 shows a schematic of a naming technique for an example nanoclusters, including an NHC, wingtip, and linker.

[0068] Fig. 16A shows emission spectra of 5-4d under argon and air.

[0069] Fig. 16B shows emission spectra of 5-4d under argon and air (two cycles), plotted in 3D view.

[0070] Fig. 16C shows emission spectra of 5-C2 under argon and air.

[0071] Fig. 16D shows emission spectra of 5-C2 under argon and air (two cycles), plotted in 3D view.

[0072] Fig. 17A shows photodynamic therapy efficacy of 5-4a to treat KB cells.

[0073] Fig. 17B shows photodynamic therapy efficacy of 5-4e to treat KB cells.

[0074] Fig. 18 shows relative colony formation efficiency after treatment with 5-4e followed by exposure to different radiation doses from 2Gy to 4Gy

[0075] Fig. 19 shows the synthetic route to 5-4I.

[0076] DETAILED DESCRIPTION

[0077] Metal nanoclusters possess a metal core (typically 10 - 300 atoms) surrounded by a protective layer of organic molecules. Their unique properties, including biocompatibility and high luminescence, have made them a promising material for biomedical applications including bioimaging and biosensing. Additionally, nanoclusters that include gold are photosensitizers for use in cancer radiation therapy. Such nanoclusters accumulate in tumor cells either passively through the permeable tumor vasculature, due to their small size, or by functionalization of the organic surface layer with tumor targeting agents. They are then able to strongly absorb high energy radiation to generate secondary electrons which accelerate DNA breakdown in cancer cells. Historically, organic ligands on the surface of these nanomaterials included phosphine and thiols which are vulnerable to oxidation and ligand exchange in physiological conditions. / V-heterocyclic carbenes (NHC) have been shown to produce exceptionally stable gold nanoclusters (Albright, E. L., et al., JACS (2024) 146(9):5759-5780, DOI: 10.1021 / jacs.3c1 1031). They also do not suffer the same susceptibility to exchange and oxidation that thiols have in vivo.

[0078] Homometallic and heterometallic nanoclusters that are protected by ditopic ligands that have at least one NHC are reported herein. Importantly, these stable metal nanoclusters emit bright luminescence. One embodiment of this invention is metal nanoclusters that have a homometallic core that is AUI3. A high yielding synthesis of these superatom gold (0) clusters functionalized by NHCs is reported herein and its characterization includes structure

[0079] 7

[0080] RECTIFIED SHEET (RULE 91 ) determination by X-ray crystallography. Another embodiment of this invention is metal nanoclusters that have a heterometallic core that is M1AU12, where M is a transition metal other than gold.

[0081] A naming convention is used herein, and Fig. 15 shows a schematic of this convention including NHC, linker, and wingtip components. Linkers are moieties of a length that enables stable bridging of metal sites in the cluster. Wingtip groups are aryl or heteroaryl substituents located on a nitrogen of the at least one NHC. Non-limiting examples of wingtip groups include CH2Aryl, where Aryl is a substituted or unsubstituted monocyclic aromatic including phenyl, tolyl (o, m, p), xylyl, ort / 70-xylyl, or any heteroaromatic, wherein substituents include alcohol, ether, amine, nitro, ester, acetate, alkyl, and / or haloalkyl groups.

[0082] Non-limiting examples of linkers include ortho-xy\y\, naphthyl, 1 ,1'-(naphthalene-1 ,8- diylbis(methylene)), 1 ,1'-(naphthalene-2,7-diylbis(methylene)), C3H6, CH2-G-CH2, where G comprises CMe2, C(aliphatic)2, C(aryl)2, O, N, S, heteroatom, or similar compounds that are substituted or unsubstituted and may include heteroatoms that do not interfere with the binding of the linker to the cluster.

[0083] Non-limiting examples of an NHC include imidazolylidene, benzylimidazolylidene, naphthimidazolylidine, benzylimidazolylidene with one or two substituents on its backbone including but not limited to ethers, amines, halides, alkyl or aryl groups, alkenes, alkynes, halogenated alkyl or halogenated aryl.

[0084] Ditopic ligands protect the metal core of the nanocluster. Ditopic ligands are capable of coordination at two separate sites. There are several different ditopic ligands exemplified herein. The metal nanoclusters are protected by five identical ditopic ligands, each ligand has at least one NHC. NHCs are neutral ligands that include a divalent carbon with six valence electrons in its valence shell and at least one nitrogen within a ring.

[0085] In one embodiment, the ditopic ligand includes at least one ir-extended aromatic ring. In one embodiment, the at least one ir-extended aromatic ring is located on the NHC backbone. In another embodiment, the at least one ir-extended aromatic ring is located on the linker.

[0086] In one embodiment, the ditopic ligand includes a b / sNHC. Recent reports have demonstrated the use of b / sNHC ligands in particular give clusters with outstanding thermal stability and some of the highest reported photoluminescence quantum yields (PLQY) among Au nanoclusters. Thus, these ligands are suitable for organic photoredox catalysis, sensors, or solar cell applications. In another embodiment, the ditopic ligand includes one NHC linked through a linker to one phosphine group wherein linker moieties are described above.

[0087] Structural formaulae of representative ditopic ligands are shown in the Working Examples. Ligands 5-2a, 5-2b, and 5-2c are shown below as representative examples of the types of ligands that were prepared and characterized prior to their use in preparing homemetallic and heterometallic nanoclusters.

[0088] Structural Formulae of b / sNHC ligand salts

[0089] These clusters have unique photophysical properties, including high photoluminescence quantum yields. Specifically, b / sNHCs with linkers of various lengths and sizes were synthesized. See Table 1 for simplified structural formulae of the metal nanoclusters.

[0090] Referring to luminescence of homometallic nanoclusters, b / sNHC stabilized Au homometallic clusters 5-4a and 5-4c were determined to have photoluminescence quantum yields values of 40% and 13%, respectively (see Example 6). 5-4a is [AUI3(LAL1)5X2]3+, where LAL1 is ditopic L-type benzimidazole-based ligand with naphthalene-1 ,8- diylbis(methylene) linker and benzyl wingtips, and X is a monovalent ligand (e.g., halide); and 5-4c is [AUI3(LAL3)SX2]3+, where LAL3 is ditopic L-type naphthimidazole-based ligand with ortfto-xylyl linker and benzyl wingtips, and X is a monovalent ligand (e.g., halide).

[0091] Their electronic and photophysical properties were investigated and are reported upon herein. Structurally, 5-4a has an icosahedral core structure, and the ligands are oriented with helical chirality yielding a highly symmetrical cluster. Using NMR spectroscopy, it was possible to fully characterize the structure in solution and demonstrate the consistency in clusters’ structure in both solid and solution state (see Examples 3 and 5). Both clusters 5- 4a and 5-4c showed high thermal stability (see Example 7) with essentially no decomposition observed after multiple days at elevated temperature.

[0092] Referring to luminescence of heterometallic nanoclusters, several examples were prepared and evaluated, including clusters with platinum, palladium, and iridium.

[0093] 5-4d is [PtAui2(LAL4)sX2]2+, where LAL4 is ditopic L-type benzimidazole-based ligand with ortfto-xylyl linker and benzyl wingtips, and X is a monovalent ligand (e.g., halide).

[0094] 5-4e is [PtAui2(LAL5)5X2]2+, where LAL5 is ditopic L-type benzimidazole-phosphine ligand with aliphatic -(CH2)3- linker and benzyl wingtip on benzimidazole moiety, and X is a monovalent ligand (e.g., halide). This nanocluster under argon reached PLQY value of 68%. 5-4f is [PdAui2(LAL4)5X2]2+, where LAL4 is ditopic L-type benzimidazole-based ligand with ort / 70-xylyl linker and benzyl wingtips, and X is a monovalent ligand (e.g., halide).

[0095] 5-4g is [PtAui2(LAL1)5X2]2+, where LAL1 is ditopic L-type benzimidazole-based ligand with 1 ,1'-(naphthalene-1 ,8-diylbis(methylene)) linker and benzyl wingtips, and X is a monovalent ligand (e.g., halide).

[0096] 5-4h is [PtAui2(LAL6)5X2]2+, where LAL6 is ditopic L-type benzimidazole-based ligand with aliphatic -(CH2)3- linker and benzyl wingtips, and X is a monovalent ligand (e.g., halide).

[0097] 5-4i is [lrAui2(LAL4)5X2]2+, where LAL4 is ditopic L-type benzimidazole-based ligand with ortfto-xylyl linker and benzyl wingtips, and X is a monovalent ligand (e.g., halide).

[0098] These nanoclusters are stabilized by bidentate N-heterocyclic carbene ligands LAL4, LAL5 or LAL6, structures of which are shown in Fig. 6A-C). The heterometallic nanoclusters were synthesized and tested for optical absorption and photoluminescence properties (see Examples 8, 9, 14, 15, and 16. All the nanoclusters were characterized by bright emission. The photoluminescence lifetimes of the nanoclusters were found to be 2.34 and 4.56 ps for 5-4d and 5-4e, respectively. All the nanoclusters had high photoluminescence quantum yield in acetonitrile solutions under anaerobic conditions (for example, 48 and 68% for 5-4d and 5- 4e, respectively).

[0099] Although not wishing to be bound by theory, the inventors suggest that efficient photoluminescence from 5-4a, 5-4d, and 5-4e nanoclusters was due to suppression of nonradiative decay from photoexcited states by rigidification of these nanoclusters by bidentate ligands bearing aromatic substituents that favour intracluster ligand-ligand interactions. Efficient photoluminescence from heterometalic nanoclusters, such as 5-4d, and 5-4e, was due to retardation of the electronic relaxation due to changes in the highest occupied molecular orbital (HOMO) and the lowest unoccupied molecular orbital (LUMO) positions induced by the presence of Pt.

[0100] Photoluminescence of 5-4d nanocluster was found to be significantly quenched by dissolved O2upon exposure of argon-purged solutions to air (see Example 17). PL lifetime of 5-4d nanocluster under argon was calculated to be 2.34 ps, and under air it was 0.66 ps. PL lifetime of 5-4d nanocluster was shortened more than three times upon exposure to air. The absolute PLQY of 5-4d decreased to 23% under air.

[0101] The ease of synthesis, stability, and promising optical properties of these nanoclusters will make them excellent candidates for application in bioimaging (see Example 19) or as photosensitizers (e.g., for photodynamic therapy, see Example 20, or radiation therapy, see Example 21). Nanoclusters described herein photoluminesce and electroluminesce. Accordingly, they can be used as photoredox catalysts, that become active when radiation is applied. The radiation may take any form such as visible light, UV light, heat, or X-rays.

[0102] The nanoclusters can be used as photosensors, and for imaging. They could be used in a solar cell (see Example 11). They are also in an electroluminescent device or in a photoluminescent device.

[0103] One embodiment is a method of producing photoluminescence by providing a photoluminescent nanocluster, and applying radiation to the nanocluster whereby the nanocluster photoluminesces. In another embodiment, a method of imaging cells in tissue in a subject includes administering to the subject a nanocluster as described herein, and applying radiation to cells that are desired to be imaged, wherein the cells photoluminese. Similarly, in a method of imaging cells in tissue, the nanoclusters are taken up by cells or added to cells and radiation is applied, whereby the cells photoluminesce. Any type of radiation can be used, for example, visible light, UV light, heat, or X-rays. In a method of producing electroluminescence a nanocluster is provided, a voltage is applied across the nanocluster, and the nanocluster electroluminesces. One embodiment is a method of photocatalysis or electrocatalysis comprising a nanocluster as described herein. In one embodiment of these methods, the nanocluster is stable in vivo, in aqueous media, in bodily fluids, and in simulated bodily fluids. In one embodiment of these methods, the nanocluster is employed for imaging of specific cells in vitro and specific organs in vivo.

[0104] The following working examples further illustrate the present invention and are not intended to be limiting in any respect.

[0105] WORKING EXAMPLES All reactions were carried out under a nitrogen atmosphere unless otherwise noted.

[0106] Reagents were purchased from Aldrich chemical company (Oakville, ON, Canada) and used as received. All reactions and analyses were performed under ambient conditions unless otherwise specified. Benzyl chloride, potassium carbonate, and sodium borohydride were purchased from Sigma-Aldrich (Oakville, Canada), Wako (Richmaond, VA, USA), or TCI Chemicals (Portland, OR, USA). [2-[13C]benzimidazole, 1-benzyl[2-13C]benzimidazole, chloro(dimethylsulfide)gold(l) ,1H-naphtho[2,3-d]imidazole, 1 ,8- bis(chloromethyl)naphthalene, 2,7-bis(bromomethyl)naphthalene, and cluster 5-5 were synthesized according to literature procedures (see Yi, H., et al., Chem. Sci. 2021 , 72, 10436-10440; Collado, A., et al., Chem. Commun. 2013, 49, 5541-5543; Mathias, L. J., et al., J. Org. Chem. 1978, 43, 3518-3526; Rohde, J. J., et al., J. Med. Chem. 2007, 50, 149- 164.)

[0107] Example 1 . Synthesis and Structural Characterization of b / sNHC Ligands

[0108] General synthesis of 5-1 a-c

[0109] The following procedure for the preparation of 5-1 a-c was adapted from the literature (Fatima, T., et al., J. Organomet. Chem. 2017, 837, 50-54). Benzimidazole or naphthimidazole (2 mmol) was dissolved in 7 mL of DMSO. Potassium hydroxide (3 mmol) was added to the solution and was allowed to stir for half an hour. 1 ,8- bis(chloromethyl)naphthalene, 2,7-bis(bromomethyl)naphthalene or ort / 70-xylylene dibromide(1 mmol) was added to the reaction mixture which was further allowed to stir for 3 h at room temperature. The reaction mixture was then added to 200 mL of distilled water. The product 5-1 crystallized out and was then filtered and left to dry under vacuum. Compound was collected as beige or light-yellow powder.

[0110] Characterization of 5-1a: 1 ,8-bis((1 H-benzo[d]imidazol-1-yl)methyl)naphthalene

[0111] Benzimidazole (0.225 g, 2.0 mmol) afforded 1 ,8-bis((1 H- benzo[d]imidazol-1-yl)methyl)naphthalene 5-1a (0.250 g, 0.6 mmol) as a yellow solid in 68 % yield after purification.1H NMR (DMSO- d6, 600 MHz): 5 8.22 (s, 2H, NCHN), 7.92 (dd, J = 8.2, 1.3Hz, 2H,

[0112] ArH), 7.76 (dd, J = 7.0, 1.3Hz, 2H, ArH), 7.39 (dd, J = 7.1 , 1.4Hz, 2H, ArH), 7.35 (t, J = 7.7 Hz, 2H, ArH), 7.27-7.22 (m, 4H, ArH), 6.49 (d, J = 7.3 Hz, 2H, ArH), 6.39 (s, 4H, NCH2CH)13C{1H} NMR (CD2CI2, 151 MHz): 6 144.39 (NCHN), 143.47, 135.34, 133.96, 133.61 , 129.50, 129.45, 125.45, 124.79, 122.66, 121.87, 119.70, 110.67, 48.41. ESI-MS (m / z): major peak [C26H2IN4]+: calculated 389.176, found 389.177.

[0113] Characterization of 5-1 b: 2,7-bis((1 H-benzo[d]imidazol-1-yl)methyl)naphthalene Benzimidazole (0.200 g, 1.7 mmol) afforded 2,7-bis((1 H- benzo[d]imidazol-1-yl)methyl)naphthalene 5-1 b (0.266 g, 0.5 mmol) as a yellow solid in 60 % yield after purification.1H NMR

[0114] (DMSO-c / 6, 600 MHz): 0 8.64 (s, 2H, NCHN), 7.82 (d, J = 8.5 Hz, 2H, ArH), 7.78 (d, J = 1 .8

[0115] Hz, 2H, ArH), 7.67-7.65 (m, 2H, ArH), 7.55-7.54 (m, 2H, ArH), 7.42-7.40 (m, 2H, ArH), 7.23- 7.18 (m, 4H, ArH), 5.65 (s, 4H, NCH2CH)13C{1H} NMR (CD2CI2, 151 MHz): 5 143.92 (NCHN), 141.65, 134.66, 133.22, 132.54, 131.78, 128.29, 126.13, 125.69, 122.94, 122.30, 118.80, 111.05, 48.01 ESI-MS (m / z): [C26H2iN4]+: calculated 389.176, found 389.177.

[0116] Characterization of 5-1c: 1 ,2-bis((1H-naphtho[2,3-d]imidazol-1-yl)methyl)benzene

[0117] Naphthimidazole (0.400 g, 1.7 mmol) afforded 1 ,2-bis((1 H- naphtho[2,3-d]imidazol-1-yl)methyl)benzene 5-1c (0.526 g, 1.2 mmol) as a yellow solid in 96 % yield after purification.1H NMR (CDCh, 700 MHz): 5 8.64 (s, 2H, NCHN), 8.31 (s, 2H,), 8.06-8.04

[0118] (m, 2H, ArH), 7.86 (s, 4H,), 7.40-7.38 (m, 4H, ArH), 7.19 (dd, J = 5.7, 3.3 Hz, 2H), 6.81-6.80 (m, 2H, ArH), 5.86 (s, 4H, NCH2C).13C{1H} NMR (CD2CI2, 151 MHz): 5 149.03 (NCHN), 143.84, 129.94, 129.60, 128.33, 128.06, 127.39, 126.87, 124.34, 123.40, 116.59, 106.27, 45.24. ESI-MS (m / z): major peak [C3oH23N4]+: calculated 439.192, found 439.191.

[0119] General synthesis of b / sNHC salts 5-2a-c

[0120] The following procedure for the preparation of dibenzimidazolium salts 5-2a-c was adapted from the literature (Albright, E. L, et al. JACS 2024 146 (9), 5759-5780 DOI: 10.1021 / jacs.3c11031). A 25 mL glass pressure tube was charged with 5-1a, 5-1 b, or 5-1 c (1.0 mmol) and benzyl chloride (5.0 mmol). Acetonitrile (10 mL) was added, the tube was capped, and the mixture was then heated in a 90 °C oil bath for 48 hours, and then cooled to room temperature. After cooling, the solvent was removed in vacuo to afford a crude solid. The crude solid was washed with EtOAc (3 x 10 mL) and dried in vacuo to afford pure product as a white / light yellow solid.

[0121] Characterization of 5-2a: 1 ,1'-(dibenzyl)-3,3’-(naphthalene-1 ,8- diylbis(methylene))dibenzimidazolium dichloride salt , , , , , , , ,

[0122] 7.8 Hz, 4H, ArH), 7.55-7.52 (m, 6H, ArH), 7.40-7.38 (m, 6H, ArH), 7.07 (d, J = 7.3 Hz, 2H), 6.67 (s, 4H, NCH2C), 5.86 (s, 4H, NCH2C) .13C{1H} NMR (CD2CI2, 151 MHz): 5 143.18 (NCHN), 135.48, 134.00, 131.58, 131.22, 130.65, 129.80, 129.57, 128.98, 128.73, 128.29, 127.27, 127.04, 126.93, 125.83, 114.22, 114.19, 50.94, 50.10. ESI-MS (m / z): major peak [C40H34N4]2+: calculated 285.139, found 285.137.

[0123] Characterization of 5-2a13C: 1 ,1'-(dibenzyl)-3,3’-(naphthalene-1 ,8-diylbis(methylene))di[2-

[0124] 13C]benzimidazolium dichloride salt . , afford the crude solid. The crude solid was washed with EtOAc (3 x 10 mL) and dried in vacuo to afford the pure product 5-2a13C(0.157 g, 0.2 mmol) as a yellow solid in 51 % yield.

[0125] 1H NMR (CDCh, 700 MHz): 5 10.03 (d,1JC-H = 220.1 Hz, 2H, NCHN), 8.12 (d, J = 8.3 Hz, 2H, ArH), 8.04 (d, J = 8.4 Hz, 2H, ArH), 7.88 (d, J = 8.3 Hz, 2H, ArH), 7.69 (ddd, J = 8.4, 7.3, 1.1 Hz, 2H, ArH), 7.63 (ddd, J = 8.3, 7.3, 1.1 Hz, 2H, ArH), 7.53 (dd, J = 6.4, 1 .6 Hz, 6H, ArH), 7.40-7.39 (m, 6H, ArH), 7.09 (d, J = 7.3 Hz, 2H), 6.61 (s, 4H, NCH2C), 5.85 (s, 4H, NCH2C).13C{1H} NMR (CD2CI2, 151 MHz): 5 143.13 (NCHN). ESI-MS (m / z): major peak [13C2C38H34N4]2+: calculated 286.139, found 286.141.

[0126] Characterization of 5-2b: 1 ,1'-(dibenzyl)-3,3’-(naphthalene-2,7- diylbis(methylene))dibenzimidazolium dichloride salt 5-1 b (0.100 g, 0.3 mmol) afforded salt 5-2b (0.070 9’0 1mmol) as a yellow solid in 42 % yield after purification.1H NMR (CDCI3, 700 MHz): 5 10.14

[0127] (s, 2H, NCHN), 8.11 (d, J = 1.8 Hz, 2H, ArH), 7.99-7.98 (m, 6H, ArH), 7.67-7.65 (m, 6H, ArH), 7.54 (dd, J = 7.7, 2.2 Hz, 4H, ArH), 7.43 (dd, J = 8.1 , 6.5 Hz, 4H, ArH), 7.39 (d, J = 7.3 Hz, 2H), 5.98 (s, 4H, NCH2C), 5.82 (s, 4H, NCH2C).13C{1H} NMR (CD2CI2, 151 MHz): 5 142.91 (NCHN), 133.95, 132.49, 133.26, 131.17, 131.10, 129.01 , 128.79, 128.76, 128.29, 127.64, 127.27, 126.85, 126.83, 126.47, 124.44, 114.08, 114.03, 50.03, 43.05. ESI-MS (m / z): major peak [C4oH34N4]2+: calculated 285.139, found 285.138.

[0128] Characterization of 5-2c: 1 ,1 ’-(dibenzyl)-3,3’-(ort / 7o-xylylene)dinaphthoimidazolium dichloride salt

[0129] 5-1 c 0 350 0 8 mmol afforded salt 5-2c 0 381 m , , . , . , , , . . ,

[0130] 8H, ArH), 7.47 (d, J = 3.3 Hz, 2H, ArH), 7.42-7.39 (m, 8H, ArH), 6.23 (s, 2H, NCH2CH), 5.89 (s, 4H, NCH2CH).13C{1H} NMR (CD2CI2, 151 MHz): 5 147.61 (NCHN), 134.40, 132.56, 131.45, 131.33, 130.89, 130.52, 129.98, 129.55, 129.43, 129.18, 128.78, 128.74, 128.60,

[0131] 127.27, 112.00, 111.86, 50.57, 40.26. ESI-MS (m / z): major peak C44H35N4: calculated 619.286, found 619.286.

[0132] Example 2. General synthesis of NHC gold complexes

[0133] A glass pressure tube was charged with the appropriate NHC salt 5-2a-c (0.30 mmol), (Me2S)AuCI (0.60 mmol), K2CC>3 (1.8 mmol) and acetone (10 ml_). The mixture was heated in a 60 °C oil bath for 12 hours, and then cooled to room temperature. After cooling, the solvent was removed in vacuo to afford the crude residue. The crude residue was redissolved in DCM and filtered through celite to remove any inorganic salts. The filtrate was reduced down then precipitated in petroleum ether to afford the pure complex 5-3a-c as an off-white solid. Yields and characterization data for each compound are listed below.

[0134] Characterization of 5-3a: 1 ,1 ’-(dibenzyl)-3,3’-(naphthalene-1 ,8-diylbis(methylene)) dibenzo[d]imidazol-2-ylidene digold(l) dichloride

[0135] 5-2a (0.100 g, 0.2 mmol) afforded gold complex 5-3a purification.1H NMR (CDCh, 700 MHz): 5 7.90-7.87 (m, 4H, ArH), 7.82 (s, 1 H), 7.78 (dd, J =

[0136] 8.7, 2.0 Hz, 2H), 7.60 (dd, J = 8.5, 1.8 Hz, 2H), 7.43-7.37 (m, 16H), 5.95 (s, 4H, NCH2CH),

[0137] 5.81 (s, 4H, NCH2CH). Characterization of 5-3c: 1 ,1 ’-(dibenzyl)-3,3’-(ort / 7o-xylylene)dinaphtho[d]imidazole-2-ylidene digold(l) dichloride

[0138] 5-2c (0.050 g, 0.07 mmol) afforded gold complex 5-3c eld . , , , . . , , , . ,

[0139] 2H), 5.88 (s, 2H) 5.79 (s, 4H) 5.72 (s, 4H) 5.52 (s, 4H).

[0140] Example 3. General reduction of complexes 5-3a-c and isolation of clusters 5-4a-b

[0141] A round bottom flask (50 ml_), under air, was charged with a stir bar and 5-3 (0.01 mmol), and dichloromethane (7 mL) was added to dissolve the gold complex. The solution was cooled in an ice-bath for ~10 min then to the stirring solution of gold complex was added a thoroughly sonicated solution of NaBH4(0.02 mmol) in ethanol (99 %, 3.5 mL). The solution was stirred at 0 °C for 1 h and then at RT for 2 h. The solution changed quickly from colorless to burgundy to dark brown / red. Concentrated HCI (6.5 pL, 0.08 mmol) was added and stirred further for 30 minutes. The solution then changed from dark brown / red color to bright red. The suspension was filtered using a PTFE syringe filter with pores 0.2 pm, and solvents were removed using a rotary evaporator to give a dark brown / red solid. The crude residue was extracted with EtOH (4 x 2 mL), and the supernatant solutions were filtered through celite, removing a beige / white precipitate. The eluent from this filtration was dried in vacuo yielding the crude cluster mixture as a red-orange to dark-red residue. The crude cluster mixtures were purified by silica gel column chromatography (Fuji Silysia Chromatorex PSQ60AB silica; 9:1 to 3:1 DCM / MeOH eluent; ~3x10 cm column size). The final red band on column yields the purified clusters (cluster Rf (9:1 DCM / MeOH) = 0.3-0.4). Yields and characterization data for each compound are listed below. Reduction of 5-3a and Isolation of cluster 5-4a: [Aui3(b / sNHC)5CI2]3+ , , , , , , ,

[0142] ArH), 6.69-6.67 (m, 30H, ArH), 6.31 (dd, J = 16.9, 7.7 Hz, 30H), 5.83 (s, 5H), 4.55 (d, J = 8.5, 10H), 4.43 (d, J = 15.0, NCH2C, 10H), 3.00 (d, J = 16.6, NCH2C, 10H) ESI-MS (m / z): major peak [Aui3(C2ooHi6oN2o)CI2]3+: calculated 1823.95, found 1823.96. UV-vis (DCM): characteristic absorbances 328, 432, and 515 nm.

[0143] Note: The geminal coupling of the methylene CH2groups and dramatic shift of the peaks compared to the gold complex supports that this spectra is of the ligands on the cluster and not contamination of the starting gold complex 5-3a.

[0144] Reduction of 5-3a13Cand Isolation of 5-4a13C: [Aui3(b / sNHC)5CI2]3+

[0145] 5-3a13C(0.050 g, 0.05 mmol) afforded nanocluster 5-4a13C

[0146] 6.95 (t, J = 7.8 Hz, 20H), 6.74 (t, J = 7.1 Hz, 15H), 6.67 (t, J = 7.8 Hz, 15H), 6.33 (d, J = 8.5

[0147] Hz, 10H, ArH), 6.28 (d, J = 7.2 Hz, 10H, ArH), 5.45 (s, 5H), 5.35 (s, 5H), 4.55 (d, J = 8.5, 10H), 4.43 (d, J = 14.7, NCH2C, 10H), 3.00 (d, J = 16.6, NCH2C, 10H)13C{1H} NMR (CDCI3, 176 MHz): 5 206.99 (NCHN). ESI-MS (m / z): major peak [Aui3(13CiOCi9OHi6oN2o)CI2]3+: calculated 1827.28, found 1827.27. UV-vis (DCM): characteristic absorbances 327, 430, and 520 nm.

[0148] Reduction of 5-3b ed in >1

[0149] % yield. The UV-vis spectrum showed signals between 300-500 nm; However, no cluster peaks were identified in the ESI-MS. Reduction of 5-3c and Isolation of 5-4c: [Aui3(b / sNHC)5Cl2]3+

[0150] 8.3 Hz, 6H, Ar / - / ), 7.90 (d, J = 8.3 Hz, 5H), 7.89-7.84 (m, 8H), 7.76-7.71 (m, 20H), 7.52 (d, J =

[0151] 8.1 Hz, 20H), 7.40-7.36 (m, 40H), 7.14 (dd, J = 7.7, 3.5 Hz, 6H), 6.20 (s, 10H), 5.91 (s, 10H),

[0152] 5.47 (d, J = 2.9 Hz, 12H), 5.22 (s, 10H), 5.17-5.16 (m, 5H) ESI-MS (m / z): major peak

[0153] [Aui3(C22oHi7oN2o)CI2]3+: calculated 1908.29, found 1908.30. UV-vis (DCM): characteristic absorbances 342, 461 , and 528 nm.

[0154] Targeted NHC gold complexes were synthesized following the route outlined in the scheme shown in Fig. 1. b / sNHC salts 5-2a, 5-2b, 5-2c were prepared. First, benzimidazole or naphthimidazole was reacted with a desired linker compound (1 ,8- bis(chloromethyl)naphthalene, 2,7-bis(bromomethyl)naphthalene, or 1 ,2- bis(chloromethyl)benzene) in a presence of base (e.g., KOH), to give linked compounds 5- 1 a-c. Next, the benzyl wing-tip groups were introduced by an alkylation between 5-1 and benzyl chloride to give the target NHC salts, 5-2a, 5-2b, 5-2c. NHC salts 5-2 were characterized by NMR spectroscopy and high-resolution mass spectroscopy (HRMS). The corresponding Au complexes (£> / sNHC)Au2Cl2 5-3 were prepared by reaction with 5-2 and Au(SMe2)CI in the presence of K2CO3, according to a literature procedure.17 27This procedure gave the Au complexes as white solids in 27-66% yields, and the formation was determined by the disappearance of a proton peak approximately at 10 ppm in the1H NMR spectrum, and appearance of a signal at approximately 180 ppm in the13C {1H }NMR spectrum.

[0155] Direct reduction of (£> / sNHC)Au2Cl2 complexes 5-2 was accomplished with NaBH4in a 2:1 solution of DCM / EtOH followed by an HCI etching step (Figs. 2A and 2E). Addition of NaBH4to the mixture at 0 °C resulted in an immediate color change from colorless to red. As the reaction gradually warmed to room temperature over 1 hour, the solution became a dark red / brown color, indicative of nanocluster formation. The reaction was monitored by UV-vis spectroscopy, which also showed evidence of cluster formation, as new peaks appeared between 300-600 nm. After an additional 2 hours, no further changes were observed in the UV-vis spectra. One equivalent of cone. HCI was added to the solution, which turned the solution into a bright red color. After 30 minutes, the crude product was syringe filtered and isolated dry as a brown / red solid. Isolation and purification of the resulting clusters, 5-4a-c, involved an ethanol wash to remove unreacted starting material, followed by column chromatography. The purified yields of 5-4a and 5-4c were 44% and 9%, respectively. Isolation of cluster species was not successful for derivative 5-4b. The colored band isolated after the column resulted in a very low yield of > 1%, and still showed a mixture of products based on the UV-vis spectra. In initial studies, no cluster species was identified in the electrospray ionization mass spectrometry (ESI-MS) spectrum for 5-4b, despite UV-vis spectroscopy showing signs of cluster formation.

[0156] Example 4. UV-vis absorbance spectroscopy, fluorescence spectroscopy, and quantum yield measurements of clusters 5-4a and 5-4c

[0157] UV-vis absorbance spectra were recorded on a Shimadzu UV-1800 spectrometer or on an Agilent Cary60 spectrophotometer using 1 cm pathlength quartz cuvettes as dilute dichloromethane, acetonitrile, or toluene solutions of cluster samples. The fluorescence excitation and emission spectra, and fluorescence excitation-emission matrix (EEM) data for clusters 5-4a and 5-4c dissolved in dichloromethane were recorded on a Horiba Duetta Fluorescence and Absorbance Spectrometer with EzSpecTM software using a 1 cm pathlength quartz cuvettes. The absolute quantum yield of clusters 5-4a and 5-4c in dichloromethane was measured on a C11347-11 Quantaurus-QY Absolute PL quantum yield spectrometer (Hamamatsu Photonics K.K.) equipped with 3.3 inch integrating sphere to measure all luminous flux and cooled, back-thinned CCD sensor for detection at 1024 photosensitive channels. The samples were excited at 400 nm.

[0158] Referring to Figs. 2B and 2F, the UV-vis spectra of purified clusters 5-4a and 5-4c in dichloromethane displayed three distinct absorbance peaks at 328, 432, and 515 nm for 5- 4a and at 342, 461 , and 528 nm for 5-4c. The molecular formulas of the clusters, 5-4a and 5- 4c, were determined by ESI-MS (Figs. 2C and 2G). Based on the analysis of the ESI-MS spectra, the molecular formula for clusters 5-4a and 5-4c was confirmed as shown in Table 1 . The ESI-MS spectrum for 5-4a contained a major set of signals at 1823.96 m / z, which matched well when compared to the simulated isotope pattern with a value of 1823.96 m / z. The ESI-MS spectrum for 5-4c contained a major set of signals at 1908.29 m / z, which matched well to the simulated isotope pattern at 1908.29 m / z.

[0159] Example 5. X-ray crystallography of 5-4a

[0160] Crystals of appropriate quality for X-ray diffraction studies were grown from layering hexane onto a DCM / EtOH solution of 5-4a. The crystals were covered with a thin layer of hydrocarbon oil (Paratone-N). A suitable crystal was then selected, attached to a glass fibre or a microsampler, and quickly placed in a low-temperature stream of nitrogen. Data for 5-4a were collected at University of Tokyo using a Rigaku Varimax dual diffractometer using Cu Ka radiation with a Pilatus 200K hybrid pixel array detector. The data was corrected for Lorentz polarization, and absorption correction was performed analytically using CrysAlisPro software. The initial phases were determined by the direct method using SHELXS-2018, and the structures were refined using SHELXL-2018. The diffused electron density of the crystal was treated by SQUEEZE on the PLATON platform (see van der Sluis, P., et al., Acta Crystallogr. Sect. A 1990, 46, 194-201 , and Spek, A. L. J. Appl. Crystallogr. 2003, 36, 7- 13). All non-hydrogen atoms were refined anisotropically and hydrogen atoms were treated as riding models (cluster). Regarding the counter anions, only one TFA unit could be deconvoluted and was refined isotropically. However, the atomic positions of the two remaining TFA anions could not be located (presence of large solvent accessible voids in the structure) and have not been modelled in the final refinement. All aromatic rings were treated using rigid constraints to minimize the number of refinement parameters. CIF files were checked using checkClF. All images were created using Mercury program. See Figs. 3A-B and 4A-B for the X-ray crystal structure.

[0161] To provide more insight into the orientation of the ligands on the gold core, single crystals suitable for X-ray crystallography were necessary. Suitable crystals of cluster 5-4a were grown from layering hexane onto a DCM / EtOH solution of cluster 5-4a after an anion exchange with trifluoroacetate. However, the initial attempts to isolate crystals of 5-4c was unsuccessful and the work is on-going to obtain suitable crystals for XRD.

[0162] The highly symmetrical arrangement of the b / sNHCs ligands is driven by multiple CH — IT interactions as shown in Figs. 3A and 4A-B. The naphthalene linker is flexible enough to fold in such a way that the face is almost completely perpendicular to the adjacent benzimidazole units. This gives rise to the CH — IT interactions between the hydrogens of the naphthalene linker and the aromatic system of benzimidazole units in the adjacent b / sNHCs. The average distance between the hydrogen on the naphthalene linker and the adjacent IT system was measured to be 3.8(4) A.

[0163] Example 6. Emission Studies of Clusters 5-4a and 5-4c

[0164] Based on the precedents for NHC-stabilized clusters as potential photosensitizers, the optical properties of clusters 5-4a and 5-4c were characterized. Excitation-emission matrix (EEM) data showed that clusters 5-4a and 5-4c were emissive and resulted of a single emissive species, as emission characteristics are independent of excitation wavelength. The maximum emission for cluster 5-4a occurred at 724 nm when excited at 328 nm, whereas 5-4c was at 780 nm when excited at 342 nm. Compared to the known cluster 5-C2 (Yi, H.; Chem. Sci. 2021, 12, 10436-10440), cluster 5-4c has a similar emission, but 5-4a is blue-shifted by about 60 nm indicating the resulting properties are highly dependent on the ligands on the surface of clusters.

[0165] Preliminary absolute PLQY was determined to be an impressive 40% for cluster 5-4a which is almost double the value to the known cluster 5-C2 recorded at 19%. Cluster 5-4c absolute PLQY was slightly lower then both 5-4a and 5-C2 at 13%. It is known that an increase in rigidity can limit the non-radiative decay pathways, which may explain the increase in PLQY for cluster 5-4a since it has significantly more stabilizing interactions compared to 5-C2.

[0166] Example 7. Thermal Stability of Clusters 5-4a and 5-4c

[0167] The thermal stability of clusters 5-4a and 5-4c was assessed. The clusters were heated to 60 °C in acetonitrile and monitored by UV-vis spectroscopy to be consistent with the previous literature thermal studies of NHC stabilized clusters. As shown in Figs. 5A, the cluster 5-4a exhibited incredibly high thermal stability with virtually no changes to the UV profile even after 3 days. As shown in Fig. 5B, Cluster 5-4c also displayed excellent stability with only a small decrease in the absorbances over time. Compared to the previously reported NHC clusters, these clusters are more stable than the monodentate NHC stabilized clusters, which gradually decomposed with time and have similar stability behavior compared to other clusters stabilized by ditopic NHCs. In solid state, the clusters showed no indication of decomposition even after months of storage at room temperature.

[0168] Example 8. Synthesis and Optical Properties of 5-4d

[0169] Gold complex (b / sNHC)Au2Cl2 was synthesized by a published procedure (Yi, H. et al., Chem. Sci. 2021 , 72, 10436-10440). Heterometallic nanocluster 5-4d was synthesized by co-reduction by sodium borohydride of (£> / sNHC)Au2Cl2 and commercially available platinum complex Pt(coc / )Cl2 (where cod = cycloocta- 1 ,5-diene) (see Fig. 7A).

[0170] Product purification was achieved via HCI etching, extraction, and column chromatography. The identity and purity of cluster 5-4d were confirmed by the electrospray mass-spectroscopy (ESI-MS) analysis (see Fig. 7C). Calculated (m / z) for 5-4d: 2611.38; found: 2611.38.

[0171] Optical absorption and photoluminescence (PL) properties of 5-4d were examined in acetonitrile solutions at room temperature and compared with those of previously reported homometallic nanocluster 5-C2 bearing the same ligand LAL4 (Yi, H. et al., Chem. Sci. 2021 , 12, 10436-10440).

[0172] The UV-vis absorption spectrum of 5-4d shows distinct absorption bands at 299 and 455 nm along with the shoulder bands at ~330, ~412 and ~492 nm (see Fig. 7B). Interestingly enough, the absorption profiles of 5-4d and previously reported 5-C2 in the visible region look quite similar (in particular, both show three absorption bands of low intensity, with the middle one being the most resolved). In contrast, in the UV region, spectra of 5-4d and 5-C2 are more distinct. Optical absorption bands of metal nanoclusters in the visible region were previously related with the electronic transitions involving the stabilizing ligands. This illustrates that the absorption profile of 5-4d is significantly influenced by the b / sNHC ligands LAL4. The optical HOMO-LUMO gap for 5-4d was estimated from the onset of the UV-vis absorption spectra as 2.19 eV. The excitation spectrum of 5-4d matched well with its absorption spectrum. The emission band of 5-4d was found to be narrow (full width at half maximum 130 nm) at 678 nm. The position and profile of the emission band were found to be independent of the excitation wavelength. This was also supported by the PL excitation-emission matrix (EEM) data, which confirmed the absence of emissive impurities in the nanocluster sample. The PL quantum yield (QY) of 5-4d, determined by the absolute method under argon, reaches 48%.

[0173] Example 9. Synthesis and Optical Properties of 5-4e

[0174] Gold complex with heteroleptic bidentate ligand LAL5 was synthesised according to the reaction scheme shown in Fig. 8. Intermediate 5-2e and gold complex 5-3e were characterized by1H and31P{1H} NMR.

[0175] Heterometallic nanoclusters 5-4e were synthesised by co-reduction by sodium borohydride of gold complex 5-3e and Pt(coc / )Cl2 as shown in Fig. 9A. Product was purified via HCI etching, extraction, and column chromatography. The identity and purity of 5-4e were confirmed by ESI-MS analysis (Fig. 9C). Calculated (m / z) for [PtAui2(C29H27N2P)5Cl2]2+: 2400.93; found: 2400.93.

[0176] The UV-vis absorption spectrum of 5-4e showed a shoulder band at ~304 nm in the UV region along with a distinct band at 413 nm in the visible region. The optical HOMO- LUMO gap for 5-4e was estimated as 2.26 eV. Nanocluster 5-4e is characterized with very bright emission with emission maximum at 658 nm (Fig. 9E). The absolute PLOY of 5-4e under argon reached a value of 68%. Nanocluster 5-4e also has relatively long photoluminescence lifetime (see Fig. 9F) of 4.56 ps.

[0177] Example 10. Photovoltaic Applications of 5-4e Nanoclusters To establish that the metal nanoclusters can act as viable photocatalysts, they must be proven to efficiently and rapidly transfer an electron into a catalytic cycle. This implies that electron transfer must be a competitive process with other decay pathways, including radiative and non-radiative relaxation. To model this, one may use nanocluster-sensitized photovoltaic cells. In short, metal nanoclusters are physisorbed onto semiconductor film substrates, to provide contact with a potential acceptor species, to simulate a reaction to catalyze. A semiconductor is characterized by having manifolds of overlapping electronic states. Due to the infinitesimal energetic difference between some states (rendering them indistinguishable), they can be considered as a band. In the ground state, the valence band is populated by electrons, and electrons can be promoted to the conduction band if the energy necessary to overcome the band gap, Eg, is met. A semiconductor (distinguished from insulating and conducting materials by Eg), has a bandgap of approximately 1-3 eV. Therefore, for some semiconductors like TiO2the bandgaps are too large for visible light to induce promotion into the conduction band, and so the substrates cannot populate the conduction band through light stimulation without some form of aid, in this case, metal nanoclusters.

[0178] Efficiency of the photovoltaic cell can be defined as how effectively it converts solar power, Pin, into electric current, Pmax. This is expressed in Equation 1 . The current generated is dependent upon the open circuit voltage, Voc, and the short-circuit current density, Jsc

[0179] (Equation 1)

[0180] The fill factor uses the point of maximum power to find the efficiency (Equation 2). pp > Jmax' max (Equation 2) Jscvoc

[0181] Power is the product of current and voltage, and the fill factor relates to the Pmax value. Cell efficiency is affected by many factors, but photoluminescence lifetime is perhaps one of the most important, which is why 5-4e is a promising candidate for photovoltaic experiments.

[0182] Example 11 . Fabrication of Photovoltaic Cells

[0183] Solar cells were assembled according to a previously reported method (see J. Phys. Chem. C 2018, 122, 25, 13738-13744 https: / / doi.org / 10.1021 / acs.jpcc.8b00571). Fluorinedoped tin oxide (FTO) glass substrate, used for both the working and counter electrodes, was sonicated in a VersaClean solution for 30 min, rinsed with Milli-Q water and ethanol, and baked at 500 °C for 10 min to remove any organic residue. The counter electrode was prepared by dropping an H2PtCI6solution (2 mg in 1 mL of ethanol) on FTO glass and baking at 400 °C for 15 min. For the working electrode, the clean FTO glass was immersed in a 40 mM TiCU solution at 70 °C for 30 min and then rinsed with water and ethanol. A TiO2film (active layer, 0.1 cm2) was prepared on the glass by a doctor blade technique using TiO2paste (Solaronix, Ti-Nanoxide T / SP) and baked at 80 °C for 1 h and then 500 °C for 1 h. A scattering TiO2layer (Solaronix, Ti-Nanoxide R / SP) was prepared over the active layer by the same procedure. The photoanode with TiO2was again immersed in 40 mM TiCU for 30 min at 70 °C, followed by baking at 500 °C for 30 min. The TiO2films were then sensitized with 5-4e nanoclusters. The sensitizing solutions were prepared by dispersing the nanoclusters in dichloromethane. The working electrodes were submerged in the sensitizing solution for 12 h, rinsed with copious amount of dichloromethane, and dried under argon flow. The UV-vis spectra of the nanoclusters physisorbed on TiO2are shown in Fig. 10A. The two electrodes were assembled into a cell by heating with an iron and a Surlyn film (Solaronix, 60 pm thickness) as a spacer until sealed. A drop of the electrolyte solution was placed over a small hole drilled into the Pt counter electrode and driven into the cell by a vacuum backfilling technique. The hole was sealed using additional Surlyn and a piece of cover glass. Indium metal (99.999%, Sigma) was soldered to the contact points of both electrodes.

[0184] Example 12. Performance of 5-4e on TiO2Film

[0185] Preliminary experiments performed before solar cell fabrication confirmed that the 5- 4e cluster could potentially be used as sensitizers. In particular, a lack of interaction between the nanoclusters and TiO2would prohibit any photovoltaic effect from being possible. UV-vis absorption spectrum shows high loading of the nanocluster 5-4e onto the TiO2film (Fig. 10A). Sensitized TiO2film shows the characteristic emission of 5-4e nanocluster (Fig. 10B), suggesting no chemical changes of the cluster through the interaction with the TiO2substrate. The emission lifetime of the nanocluster 5-4e on TiO2film is shown in Fig. 10C. Fitting of the experimental data was performed using the following parameters: TI = 6.7 ns ± 0.16, Ai = 294 ± 3.92, T2= 79.4 ns ± 1.93, and A2= 91.3 ± 1.92.

[0186] Example 13. Photovoltaic Device Testing

[0187] The photovoltaic performance, IV curves, and photocurrent as a function of time were evaluated using a SolSimPVC system from Luzchem Inc. The system meets class AAA standards for AM 1 .5 G solar simulation and is equipped with a metrohm PGSTAT204 potentiostat / galvanostat.

[0188] Linear sweep voltammetry is used to measure the performance of the device and obtain measurements by which we can compare to other cells, including Voc, Jsc, Pmax, FF and efficiency, Fig. 11A.

[0189] The shape of the curve confirms the device is able to convert light energy into electrical energy and generate power. The duration of which was measured through chronoamperometry (Fig. 11B).

[0190] Example 14. Synthesis and Optical Properties of 5-4f

[0191] Heterometallic nanocluster 5-4f was synthesised by co-reduction by sodium borohydride of the corresponding gold complex and Pd(coc / )Cl2 as shown in Fig. 12A. Product was purified via HCI etching, extraction, and column chromatography. The identity and purity of 5-4f nanoclusters were confirmed by ESI-MS analysis (Fig.12C). The observed isotopic pattern (Fig. 12D) matches very well with the calculated one.

[0192] The UV-vis absorption spectrum of 5-4f shows band at 306, ~331 , ~360 and 495 nm (Fig. 12B). Note the similarity of the UV-vis absorption profiles in visible region for all the examined nanoclusters bearing LAL4 ligand (i.e., 5-4d, 5-4f, and previous reported 5-C2): three bands with the central one being well resolved and two others being shoulder-like in all the cased. For 5-4f, absorption bands are considerably red-shifted with respect to thos of 5- 4d. The optical HO MO- LU MO gaps (HL0) of 5-4f was estimated from the onset of the UV-vis absorption spectrum as 2.00 eV. Emission maximum of 5-4f at 805 nm. Emission maximum position for [MAui2(LAL4)5Cl2]n+blueshifts from M = Pd to Au and to Pt.

[0193] Example 15. Synthesis and Optical Properties of 5-4g

[0194] Heterometallic nanocluster 5-4g was synthesised by co-reduction by sodium borohydride of the corresponding gold complex and Pt(coc / )Cl2 as shown in Fig. 13A. Product was purified via HCI etching, extraction, and column chromatography. The identity and purity of 5-4g nanoclusters were confirmed by ESI-MS analysis (Fig. 13C). The observed isotopic pattern (Fig. 13D) matches very well with the calculated one.

[0195] The UV-vis absorption spectrum of 5-4g shows band at 325, 430 and ~470 nm (Fig. 13B).

[0196] Example 16. Synthesis and Optical Properties of 5-4h

[0197] Heterometallic nanocluster 5-4h was synthesised by co-reduction by sodium borohydride of the corresponding gold complex and Pt(coc / )Cl2 as shown in Fig. 14A. Product was purified via HCI etching, extraction, and column chromatography. The identity and purity of 5-4h nanoclusters were confirmed by ESI-MS analysis (Fig. 14C). The observed isotopic pattern (Fig. 14D) matches very well with the calculated one. The UV-vis absorption spectrum of 5-4h shows band at 313, ~415 and 453 nm (Fig.

[0198] 14B).

[0199] Example 17. Emission Studies of 5-4d: Solutions under Argon or Exposured to Air

[0200] To determine whether photo-excited gold nanoclusters as described herein are suitable as photocatalysts or photosensitizers (i.e., transfer energy or electrons to some substrate), studies were conducted in which changes in nanocluster emission, and emission lifetime in the presence of dissolved O2 were followed. If the bright emission of nanoclusters was quenched in the presence of dissolved O2, that shows that an alternative relaxation pathway occurrred, likely involving the energy or electron transfer.

[0201] Upon exposure of argon-purged solutions of 5-4d to air, emission intensity dropped more that three times. In contrast, previously known nanocluster 5-C2 (Yi, H., et al., Chem. Sci. 2021 , 72, 10436-10440) was found non-sensitive to the presence of O2(Fig. 16C). The quenching of emission of 5-4d in the presence of dissolved O2is fully reversible, as it was shown by emission measurements upon purging with argon and exposuring to air several times (Fig. 16B and 16D).

[0202] Example 18. Probing Generation of Reactive Oxigen Species by Photoexcited cluster 5-4a Considering high PLQY and sensitivity of nanocluster emission to the presense of dissolved oxygen, the nanoclusters are suitable as photosensitizers. Studies were performed to detect and quantify generation of rective oxygen species (ROS) by nanoclusters under irradiation.

[0203] Two different reactive oxygen species (ROS) probes were used to measure ROS production upon irradiation, 9,10-anthracenediyl-bis(methylene)dimalonic acid (ABDA) and 2,7-dichlorodihydrofluorescein (DCFH). ABDA is a chemical probe to measure singlet oxygen production from photo-excited clusters (Type II pathway) and DCFH measures nonsinglet oxygen ROS, for example, some oxygen-based radicals (Type I pathway). Upon irradiation of solutions containing 5-4a and ABDA, a decrease in the absorbance of ABDA was observed. This results from the selective and irreversible reaction of ABDA with singlet oxygen to generate an endoperoxide, resulted in a decrease in absorbance as it is consumed. Control experiments were performed to ensure that the decrease in absorbance was a result of singlet oxygen generation from photo-excited 5-4a. Using Rose Bengal as a reference, the quantum yield of singlet oxygen generation (SOG QY) for 5-4a was determined as ~7%. Next, DCFH was used to monitor the potential for Type I pathway ROS generation. DCFH is a non-emissive compound, but when oxidized by ROS, it forms 2,7- dichlorofluorescein (DCF), which has a fluorescence maximum at 525 nm. Upon irradiation of solution containing 5-4a and DCFH, no change in emission intensity was observed, indicating that no other types of ROS were generated from the excited state of 5-4a.

[0204] Example 19. Probing Cellular Uptake, Cytotoxicity and Imaging Using Nanoclusters 5-4a and 5-4c

[0205] To evaluate the potential of nanoclusters for biomedical application, cell internalization was tested for 5-4a and 5-4c, and compared to that of previously known nanoclusters 5-C2 (Yi, H., et al., Chem. Sci. 2021, 72, 10436-10440). First, cell uptake in human epithelial carcinoma cells (KB cells) after 24 hours of incubation was evalueted. It was found, that both 5-4a and 5-C2 demonstrated negligible cytotoxicity after 24 hours of incubation at concentrations up to 10pM. Additionally, both 5-4a and 5-C2 exhibited concentration-dependent uptake patterns, with comparable uptake confirmed by ICP-MS. Uptake into cells could also be measured by examination of cluster-treated cells using confocal microscopy. Consistent with differences in PLQY (57% versus 23% for 5-4a and 5- 2C), cluster 5-4a had a much brighter fluorescence signal in cells compared to 5-2C. Cluster 5-4c showed comparable fluorescence to 5 when incubated with cells at a 1 pM concentration for 24 hours.

[0206] The real-time uptake of 5-4a into cells was also monitored by confocal microscopy, revealing an expected time-dependent intracellular uptake, consistent with the absolute amount of Au taken up by cells as determined by the ICP-MS assay. Using different subcellular organelle trackers to stain lysosomes, mitochondria, and the nucleus, colocalization of 5-4a with lysotracker was observed, indicating that the majority of 5-4a localized in the lysosome of the cell after 24 hours of incubation.

[0207] Example 20. Exploring Potential of 5-4a and 5-4e for Photodynamic Therapy

[0208] The photodynamic therapy (PDT) efficacy of 5-4a and 5-4e was examined on human epithelial carcinoma cells (KB cells). As shown in Fig. 17A, after a 24-hour incubation with 5- 4a, negligible dark toxicity was observed up to a concentration of 7.5 pM. However, upon light treatment PDT using a 450 nm BioTable lightbox, 5-4a induced a significant reduction (>50%) in cell viability at 7.5 pM with a light dose of 20 J / cm2. This evidence indicats that 5- 4a can facilitate PDT for targeted cancer cell destruction. Furthermore, 5-4e demonstrated a more potent PDT response across all experimental concentrations and light doses Fig. 17B. Even at a lower concentrations of 3.75, 5-4e resulted in over 90% cell death under light irradiation at 20 J / cm2after a 24-hour incubation. Further optimization of the experimental conditions will be performed to uncover the full potential of 5-4a and 5-4e.

[0209] Example 21 . Exploring Potential of 5-4e for Radiation Therapy

[0210] To explore the potential of 5-4e for radiation therapy of cancer, the experiments were performed as described below.

[0211] KB cells were seeded at a density of 2*104cells per well in 24-well plates at 48 hours prior to the experiment. Subsequently, the medium in each well was replaced with medium containing 5-4e. The cells were incubated for 24 hours at 37 °C in a humidified atmosphere with 5% CO2. The cells were then washed with phosphate-buffered saline (PBS), incubated in fresh culture medium, and subjected to 2 and 4 Gy X-ray irradiation using a SmART-ATP research irradiator. After irradiation, the cells were allowed to incubate overnight before being re-plated in triplicate with low densities in fresh culture media to assess clonogenic ability. After 10-12 days, the colonies were fixed with cold methanol, stained with 0.01% w / v crystal violet solution, washed, and counted. Finally, the colony formation efficiency was calculated by comparing it to the no-treatment group.

[0212] As shown in Fig.18, cells in the control group and 5-4e groups had high survival rates, while the viability of cells exposed to 5-4e in combination with radiation decreased in a dose-dependent manner. A 2Gy irradiation alone induced a survival rate of 82% on KB cells while 5-4e enhanced the radiation effect, reducing the survival rate to 65% at 3.75 pm and 58% at 5 pM, respectively. Although the experimental condition need be optimized, this pilot study demonstrated that 5-4e enabled enhancing radiation efficiency at low radiation doses on KB cells.

[0213] Example 22. Synthesis and Optical Properties of 5-4i

[0214] Heterometallic nanocluster 5-4i was synthesised by co-reduction by sodium borohydride of the corresponding gold complex and [lr(coc / )CI]2 as shown in Fig. 19. ESI-MS analysis confirms the presence of desired product in reaction mixture; preliminary tests show bright emission. This confirms the possiblity to obtain the title nanocluster, while further optimization of reaction conditions required.

[0215] EQUIVALENTS

[0216] It will be understood by those skilled in the art that this description is made with reference to certain embodiments and that it is possible to make other embodiments employing the principles of the invention which fall within its spirit and scope.

[0217] Table 1 . Metal nanoclusters

Claims

WE CLAIM:1 . A heterometallic or homometallic metal nanocluster having general formula:[MAui2(LAL)5X2]Yn, wherein M is a transition metal,LAL is a ditopic ligand comprising at least one / V-heterocyclic carbene,X is a monodentate ligand,Y is a counterion that may be the same or different than X, and n is a number such that the overall charge on the metal nanocluster is zero, wherein if M is Au, and LAL comprises bis benzimidazolyl, then LAL further comprises a 1 ,1'- (naphthalene-1 ,8-diylbis(methylene)) linker.

2. The heterometallic or homometallic nanocluster of claim 1 , wherein M is Au, Pt, Pd, Ag, Cu, Rh, Ir, or Ni.

3. The heterometallic or homometallic nanocluster of claim 1 , wherein / V-heterocyclic carbene comprises imidazolyl, benzimidazolyl, or naphthimidazolyl.

4. The heterometallic or homometallic nanocluster of claim 1 , wherein LAL comprises: bis benzimidazolyl; benzimidazolyl; bis naphthimidazolyl; or benzimidazolyl and phosphine.

5. The heterometallic nanocluster of claim 1 , wherein the nanocluster is [PtAui2(LAL)5X2]Yn, where LAL comprises a ditopic ligand comprising: b / sNHC; b / sbenzimidazolyl; or benzimidazolyl and phosphine.

6. The heterometallic nanocluster of claim 1 , wherein the nanocluster is [PdAui2(LAL)5X2]Yn, where LAL comprises a ditopic ligand comprising b / sNHC.

7. The heterometallic nanocluster of claim 1 , wherein the nanocluster is [lrAui2(LAL)5X2]Yn, where LAL comprises a ditopic ligand comprising b / sNHC.

8. The homometallic nanocluster of claim 1 , wherein the cluster has the formula: [Aui3(b / s benzimidazolyl)5X2]Ynwith a 1 ,1'-(naphthalene-1 ,8-diylbis(methylene)) linker and benzyl wingtip groups (5-4a); or [Aui3(b / s naphtimidazole)5X2]YnWith an o / Y / io-xylyl linker andbenzyl wingtip groups (5-4c),simplified version of 5-4a, or simplified version of 5-4c.

9. The heterometallic nanocluster of claim 1 , wherein the cluster comprises:[PtAui2(LAL4)5X2]Yn, where LAL4 is ditopic L-type benzimidazole-based ligand with ortfto- xylyl linker and benzyl wingtips (5-4d);[PtAui2(LAL5)5X2]Yn, where LAL5 is ditopic L-type benzimidazole-phosphine ligand with aliphatic -(CH2)3- linker and benzyl wingtip on benzimidazole moiety (5-4e);[PdAui2(LAL4)5X2]Yn, where LAL4 is ditopic L-type benzimidazole-based ligand with ortfto- xylyl linker and benzyl wingtips (5-4f);[PtAui2(LAL1)5X2]Yn, where LAL1 is ditopic L-type benzimidazole-based ligand with 1 ,1'-(naphthalene-1 ,8-diylbis(methylene)) linker and benzyl wingtips (5-4g),[PtAui2(LAL6)5X2]Yn, where LAL6 is ditopic L-type benzimidazole-based ligand with aliphatic -(CH2)3- linker and benzyl wingtips (5-4h), or[lrAui2(LAL4)5X2]Yn, where LAL4 is ditopic L-type benzimidazole-based ligand with ortfto- xylyl linker and benzyl wingtips (5-4i)simplified 5-4d, simplified 5-4e,simplified 5-4f, simplified 5-4g,simplified 5-4h, orSimplified 5-4i.

10. The heterometallic or homometallic nanocluster of any one of claims 1 to 9, wherein the compound is photoluminescent or electroluminescent.

11. A photosensitizer comprising the nanocluster of any one of claims 1 to 10.

12. A method of electrocatalysis comprising employing the nanocluster of any one of claims 1 to 10 as an electrocatalyst.

13. The method of claim 12, wherein the electrocatalyst is soluble in solvent.

14. The method of claim 13, wherein the solvent is DCM, MeOH, acetonitrile, ethanol, chloroform.

15. The method of claim 13, wherein the electrocatalyst catalyzes a carbon dioxide reduction.

16. The method of claim 13 where the electrocatalyst is activated by heating before use.

17. A method of photocatalysis comprising adding a nanocluster of any one of claims 1 to 10 to a reaction mixture, and applying light to the reaction mixture.

18. The method of claim 17, wherein light comprises radiation having wavelengths in the range of visible light, UV light.

19. A photosensor comprising the nanocluster of any one of claims 1 to 10.

20. A solar cell comprising the nanocluster of any one of claims 1 to 10.21 . An electroluminescent device that comprises a nanocluster of any one of claims 1 to 10.

22. A photoluminescent device that comprises a nanocluster of any one of claims 1 to 10.

23. A biosensor comprising the nanocluster of any one of claims 1 to 10.

24. A method of radiation therapy for a patient in need thereof comprising administering to the patient a nanocluster of any one of claims 1 to 10; and applying radiation.

25. A method of photodynamic therapy for a patient in need thereof comprising administering to the patient a nanocluster of any one of claims 1 to 10, and applying light.

26. A method of X-ray photodynamic therapy for a patient in need thereof comprising administering to the patient a nanocluster of any one of claims 1 to 10, and applying X-ray radiation.

27. A method of cancer treatment for a patient in need thereof comprising administering to the patient a nanocluster of any one of claims 1 to 10, and applying radiation.

28. A method of bioimaging comprising administering the nanocluster of any one of claims 1 to 10, applying radiation such that the nanocluster luminesces, and imaging the luminescence.

29. A method of producing photoluminescence, comprising the steps of: providing a photoluminescent nanocluster of any one of claims 1 to 10, andapplying radiation to the nanocluster whereby the nanocluster photoluminesces.

30. A method of imaging cells in tissue in a subject comprising: administering to the subject a nanocluster of any one of claims 1 to 10, and applying radiation to cells that are desired to be imaged, wherein the cells photoluminese.31 . A method of imaging cells in tissue comprising: disposing the nanocluster of any one of claims 1 to 10 into cells, and applying radiation, whereby the cells photoluminesce.

32. The method of any one of claims 17, 24, 27 to 31 , wherein applying radiation comprises applying visible light, UV light, heat, Gamma radiation, or X-ray radiation.

33. A method of producing electroluminescence, comprising the steps of: providing a nanocluster of any one of claims 1 to 10 and applying a voltage across the nanocluster whereby the nanocluster electroluminesces.

34. A method of photocatalysis or electrocatalysis comprising a nanocluster of any one of claims 1 to 10.

35. The method of any one of claims 24 to 27, wherein the nanocluster is stable in vivo, in aqueous media, in bodily fluids, and in simulated bodily fluids.

36. A method of obtaining a Magnetic Resonance Imaging (MRI) image of cells in tissue comprising disposing the nanocluster of any one of claims 1 to 10 into cells, and applying radio waves using an MRI machine, and producing an image of cells whereby the cells with nanocluster present appear different than cells without nanocluster.

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