Confined Star-like Polymer Unimolecular Micelles For Controlled Synthesis Of Gold Nanoclusters Assemblies

Gold nanoclusters(Au NCs,<2 nm)have recently attracted growing interest in the materials community,due to their discrete molecular-like orbitals,and intriguing electronic and geometric structures causing unique optical,physical and chemical properties,which are distinctly different from large colloidal nanoparticles.Due to the high surface energy,the obtained Au NCs are thermodynamically unstable and tend to aggregate and coalesce during their applications,especially in the catalytic process.These structural changes usually led to a sharp drop in catalytic activity and selectivity.Thus,the synthesis of stable gold nanoclusters is a challenge.In various developed strategies,encapsulating metal NCs by nanoshells or nanopores can prevent their migration and aggregation,thereby improving their stability in the application.In addition,through the aggregation of Au NCs in the encapsulation matrixes,the enhancement of the properties could be achieved.Recently,linear amphiphilic block copolymer micelles formed by weak interactions have been used as templates for the preparation of functional nanocrystals and NCs.However,when the conditions were changed,the structure and the morphology will be destroyed,thus the thermodynamic instability largely limits their applications.To address this issue,we recently developed a simple and general strategy to create high-quality gold nanoclusters assemblies by using stable star-like polymers unimolecular micelles as nanoreactors with the assistant of thiolate ligands or directly assembly.The star-like polymer were connected by stable covalent bond,and the size and composition of nanomaterials can be easily controlled by manipulating the molecular weight of the polymer template and selecting appropriate precursors,respectively.The properties and the application of the gold nanoclusters assemblies were investigated.The main work were listed as the followings:(1)A series of multi-arm star-like amphiphilic block copolymer β-CD-g-P4VP-b-PS and hydrophilic block copolymer β-CD-g-PAA-b-POEGA with different molecular weight were controlled synthesized by using atom transfer radical polymerization(ATRP).The successful preparation of star-like block polymer were confirmed by a series of characterization.(2)A robust and general strategy was proposed to in-situ synthesis of ultra-small gold NCs assemblies with well-controlled size and good stability by using the star-liked amphiphilic diblock copolymer β-CD-g-P4VP-b-PS as the scaffold.The size of the Au NCs assemblies can be controlled by regulating P4VP core size through adjusting the P4VP block segment of the scaffolds,which can be manipulated by the ATRP process.By changing the precursors,different kinds of metal nanoclusters including Ag,Cu,Pt,AuAg alloy nanoclusters were prepared successfully.The assemblies were used as catalysts for recyclable catalysis of the reduction of 4-NP,proving that the assemblies have high catalytic activity and stability.These findings suggest that our method is facile,feasible,and scalable,and can be used to create well-controlled and stable ultrasmall metal NCs assemblies for various applications.(3)A general and robust strategy is demonstrated to fabricate atomic precisely gold nanoclusters assemblies with tunable size by confining nanoclusters in star-like diblock copolymers β-CD-g-P4VP-b-PS as the scaffold.Such a structure would effectively stabilize gold nanoclusters due to the encapsulation of polymer templates.By further assembling the assemblies prepared before,the dimer,trimer,short worm-like,long worm-like,3-arm star-like,and sphere-like hierarchical structure assemblies were prepared.The assembly condition and mechanism were also investigated.(4)A robust and general strategy was proposed to in-situ synthesis of hydrophilic ultrasmall Au NCs assemblies with regular morphology,well-controlled size and good stability by using the star-like amphiphilic diblock copolymer β-CD-g-PAA-b-POEGA as the scaffo ld.The size of the Au NCs assemblies can be controlled by regulating PAA core size through adjusting the PAA block segment of the scaffolds,which can be manipulated by the ATRP process of PtBA.By changing the precursors,different kinds of metal nanoclusters including Ag,Cu,Pt,AuAg alloy nanoclusters were prepared successfully.The assemblies were used as catalysts for recyclable catalysis of the reduction of 4-NP,proving that the assemblies have high catalytic activity and stability.These findings suggest that our method is facile,feasible,and scalable,and can be used to create well-controlled and stable ultra-small metal NCs assemblies for various applications.(5)A robust and general strategy was proposed to in-situ synthesis of hydrophilic luminescent Au NCs assemblies with regular morphology,red fluorescence at 680 nm by using the star-like amphiphilic diblock copolymer β-CD-g-PAA-b-POEGA as the scaffold with the assistant of thiolate ligand.The emission mechanism was ascribed to the aggregation induced emission of the Au(I)-SR complex on the surface of the nanoclusters.The assemblies showing enhanced fluorescence when the existence of Ag+.The relationship between the concerntration of Ag+with the fluorescence intensity was investigated,and the enhancement mechanism was also proposed.It is a good fluorescent nanosensor for Ag+ with selective and sensibility detection.