Synthesis,Structure And Photoluminescence Properties Of Gold-Silver Nanoclusters Based On Cyclic Trinuclear Complexes

Metal nanoclusters are a new class of nanomaterials known for their precise atomic structure and fascinating properties.Among them,nanoclusters based on noble metals have become research hotspots for scientists in recent years due to their low toxicity,good biocompatibility,structural diversity,and easy chemical modification.The silver nanoclusters usually suffer from the disadvantages of poor stability and low emission quantum yield.In recent years,many strategies have been designed to overcome these shortcomings of silver nanoclusters.Among them,the doping of precious metals can build mixed metal clusters with bright phosphorescence.The cyclic trinuclear complexes(CTCs)of noble metals exhibit highly adjustable?-acidity or?-basicity by changing the central metal,bridging ligands,and substituents on the ligand.They can not only form dimer or polymer by metal-metal interactions,but also form new complexes with electron-deficient substances.In the first part of this dissertation,a series of Ag/Au clusters were synthesized by reacting?-acidic cyclic trinuclear Ag(I)pyrazolate and its Au(I)analog with 3-substituted phenylacetylene.Single crystal X-ray studies reveal that the 13-atom bimetallic clusters are isostructural with anions and have a rotaxane-like structure.Interestingly,the Ag/Au clusters exhibit adjustable high-energy phosphorescence from blue to cyan by adjusting the substituents on the phenylacetylene ligand.Although there is only a small amount of Au doping,compared with their isostructural silver nanoclusters Ag₁₃,the phosphorescence quantum yield of these isostructural metal-doped Ag/Au clusters has increased by more than 23 times.Together with our previously reported Ag/Cu clusters that can provide low-energy phosphorescence by adjusting the amount of Cu doping,the luminescence problem of bimetallic Ag/M clusters with phosphorescence emission covering the entire visible light region is completed.In second part,two pyrazole ligands,ethyl 5-(Hydroxymethyl)pyrazole-3-carboxylate and ethyl3-methyl-1H-pyrazole-5-carboxylate were used to build two cyclic trinuclear Au(I)complexes(Au CTC-1 and Au CTC-2),which were further reacted with Ag⁺to synthesize two sandwich-like Ag/Au clusters(Au₆Ag-1 and Au₆Ag-2).The quantum yields of the two sandwich Ag/Au clusters are both higher than trinuclear precursors.In their solution states,the quantum yields of Au CTC-1 and Au₆Ag-1 with hydroxyl substituents are higher than Au CTC-2 and Au₆Ag-2 without hydroxyl substituents.In particular,the quantum yield of Au₆Ag-1 in dichloromethane solution can reach up to95%,and it does not change with the concentration of the solution.Hydrogen bonds are likely formed between the Ag/Au clusters due to the introduction of hydroxyl groups,which inhibit molecular vibration and rotation;therefore,greatly increase the rate of radiation transition.This work provides a new approach for the design and synthesis of luminescent materials.