Structural Evolution And Property Study Of Thiol-protected Gold-based Nanoclusters

Ligand-protected metal nanoclusters with sizes ranging from about ten to a few hundred atoms constitute a novel class of nanomaterials.Their ultra-small size(<2 nm)make them as a bridge between small-sized metal-ligand complexes and big-sized plasmonic metal nanoparticles.Metal nanoclusters manifest discrete electronic energy states due to quantum size effects,exhibiting excellent physical and chemical properties,such as optics and electrochemistry.Monodisperse atomically precise nanoclusters can form single crystal,which allow their structural determination to be achieved.Based on the determined structrue,the transformation process of nanoclusters can be studied,and the structure-dependent properties can be investigated,which lay a foundation for the further practical application of nanoclusters.In this dissertation,a series of transition-sized noble metal nanoclusters were prepared by ligand-exchange method.The precise structure was determined by X-ray single crystal diffraction.The transformations on geometric and electronic structure between nanoclusters were studied based on the structure and the DFT theoretical calculation.The nanoclusters were assembled into three-dimensional framework structure with the inorganic as the linker.The assembled materials show a "ture on/off"property for protic solvents.The electrochemiluminescence of the bi-metal nanocluster was investigated.The self-annihilation ECL mechanism was studied by electrochemical experiments.The main contents and innovations of this paper are as follows:1.The transformation research on small-sized metal complexes to metal nanoclusters and between metal nanoclusters based on the determind structure of transition-sized gold nanoclusters.(1)The[Au18(SC6H11)14]nanocluster was successfully synthesized by using the[Au18(SG)14](SG=1-glutathione)nanocluster as the starting material to react with cyclohexylthiol.The[Au18(SR)14]cluster has an Aug bi-octahedral kernel(or inner core),which is consist of two octahedral Au6 cores sharing one triangular face.One transitional gold atom is identified in the Aug core,which also belongs to the Au4(SR)5 staple motif.These findings offer new insight in terms of understanding the evolution from[AuI(SR)]complexes into Au nanoclusters.(2)A new nanocluster formulated as Au21(S-Adm)15 was prepared converting from Au18(SR)14 nanocluster with its structure solved by X-ray crystallography.It is discovered that the hcp Au9-core in Au18(SR)14 is transformed to a fcc Auio-core in Au2i(SAdm)15.Combining with density functional theory(DFT)calculations,we provide critical information about the growth mechanism(geometrical and electronic structure)and the origin of fcc-structure formation for the thiolate-protected gold nanoclusters.The collapse of the outer Au atoms and the distortion of the structure are responsible for the structural transformation.This research will benefit fundamental understanding of the geometrical structure and electronic structure of gold nanomaterial at the atomic level.(3)Two new nanoclusters in the transition regime,including the thus far smallest thiolated alloy nanocluster CdiAu14(StBu)12 and the homogold nanocluster Aui6(S-Adm)12,are obtained and their atomic structures are fully determined by single crystal X-ray diffraction.We further predict the geometry structure of Au15(SR)12-and Au15(SR)13 via DFT calculations based on the precise atomic structures of CdiAu14(StBu)12 and Au16(S-Adm)12.Overall,this work bridges the gaps between gold complexes and nanoclusters.2.The assembly of superatomic complexes(nanoclusters)into a three-dimensional framework by the SbF6-as a linker.A supreatom complex(SC)AuiAg22(SR)123+protected by rigid adamantane thiol ligand was prepared.The assembly of Au1Ag22(SR)123+into 3D framework structures(superatom complex inorganic framework,SCIF)was achived by adding SbF6-as a linker.The film of SCIF material exhibit photoluminescence(PL)"turn on/ofF"behavior for protic solvent.The PL "turns off"under vacuum with the solvent removed,but"turns on"with strong red fluorescence in the present of protonic molecules(e.g.,methanol,ethanol,and water).Overall,this work presents a novel approach to assemble superatom clusters into 3D framework material,which exhibit PL "turn on/off" property for protic solvents.3.The electrochemical luminescene of rod-shape bi-metal Au12Ag13 nanocluster.Voltammetric analysis reveals both oxidative and reductive ECLs under scanning electrode potentials.Transient ECL signals(tens milliseconds)and decay profiles are captured by potential step experiments.An extremely strong and transient self-annihilation ECL is detected by activating LUMO and HOMO states(-1.2 to 1.0 V)sequentially via electrode reactions.The ECL generation pathways and mechanism are proposed based on the key anodic and cathodic activities arising from the energetics of Au12Ag13 nanocluster.With ECL standard tris(bipyridine)ruthenium(II)complex as reference,the self-annihilation ECL of Aui2Agi3 nanoclusters is about 10 times higher than Ru(bpy)32+.The coreactant ECL of Aui2Ag13 is about 400 times stronger than Ru(bpy)32+with the same 1 mM tripropylamine coreactant.These fundamental researches are expected to gain a deeper understanding of self-annihilation ECL emission of nanoclusters and exploit practical applications electroanalytical sensing and immunoassays.