Optical Properties And Modulated Morphology Of Copper Nanoclusters Based On N-Containing Ligand Structures

Metal nanoclusters（NCs） is composed of inorganic metal ions and organic ligands to form nanometers with various structures,morphologies and sizes.Because of its precisely atomic structural information,discontinuous electronic energy levels give NCs excellent photoelectric performance,and the large specific surface area make it catalytic potential.So far,it has become a research hotspot in the fields of materials,chemistry and biology.Among them,luminescent NCs have become a promising research direction.However,luminescent NCs still have some shortcomings,such as low luminescence intensity,poor photostability and single luminescence wavelength,which greatly limit their application prospects.So,it is necessary for researchers to deeply understand the structural characteristics and controllability of NCs.In this dissertation,we research the effects of different N-containing ligands on Cu NCs by using Cu element of low price and large reserves.And N-containing ligands also effectively provide multiple interactions,such as electron transfer,hydrogen bonding interactions,coordination interactions and so on.According to the structural characteristics of N-containing ligands,high-luminescent Cu NCs with controllable morphology and adjustable wavelength were designed comprehensively.The specific research contents include the following three parts:（1）Flexible and alkyl ligand,Cysteine（Cys）,as reducing agent and protecting agent used to synthesize red and blue dual emissive Cu NCs.Under acidic conditions（p H=3）,as-synthesized red emitted and aggregated R-Cu NCs@Cys have low luminescence intensity and poor photostability;under alkaline conditions（p H=10）,monodispersed blue emitted B-Cu NCs@Cys with high luminescence intensity and strong photostability from R-Cu NCs@Cys.The density functional theory（DFT）calculations and experimental results show that the aggregated red Cu NCs is mainly attracted by electrostatic interactions,while the monodispersed blue Cu NCs dominate by Cu-N bond and electrostatic repulsive interactions.It is due to the conformation transformation of ligands in different microenvironments that the newly formed Cu-N bond at the anchoring points strongly promotes the electron transfer and restricts the energy decay.Apparently,it is the Cu-N bond that give Cu NCs great luminescence properties（high luminescence intensity and strong photostability）.Some other amine-containing small molecule ligands,such as glutathione（GSH）,cysteamine（CS）,polyethyleneimine（PEI）and so on,could also produce blue emitted Cu NCs.It further indicates that N-containing ligands have great development spaces to improve the luminescence properties.（2）Rigid and phenyl ligand,m-aminothiophenol（m-AT）,as reducing agent and protecting agent to prepare self-assembled Cu NCs with orange luminescence by one-step strategy.Theπ-πinteractions of benzene ring structure promotes the formation of NCs-based superstructures,and the presence of-NH₂ endows it with the possibility of regulation.Through the adjustment of p H,a variety of morphological controlled transformations could be achieved,namely,monodisperse,nanospheres,nanomeshes and nanosheets.It establishes the relationship between the state of the macro-solution and the micro-structures.In order to further verify that the self-assembly process is mainly composed of hydrogen bonding interactions of-NH₂,we intervene in an aprotic solvent（Dimethyl sulfoxide,DMSO）to research the evolution of hydrogen bonding interactions,and through the external intervention of organic carboxylate to reconstruct the hydrogen bonding interactions to achieve unique anion-induced emission.According to the internal mechanism of anion-induced emission and hydrophobic benzene ring structure,we could achieve the phase transfer process（from hydrophily to lipophilicity）.Finally,use the isomers of AT to research its structure-dependent properties,we find that it was difficult to synthesize luminescent Cu NCs with o-AT and p-AT as ligands.This may be due to the structures of m-AT has different electronic structures,which indicate that unique electronic structures play a key role in the synthesis of Cu NCs N-containing ligands.（3）Using N-rich heterocyclic molecule,3-amino-5-mercapto-1,2,4-triazole（AMT）as protectant and tetramethylmethyl phosphorus chloride（THPC）as reductant.The yellow emitted Cu NCs@AMT is synthesized,but its luminescence intensity is weak because the heterocyclic ligand has a large steric hindrance and fast non-radiative transition.FTIR,XPS N1s and ¹H NMR reveal that the-NH₂ is exposed as an effective active site.Based on the Schiff base reaction to form imine bond（-C=N-）,glutaraldehyde（GA）with the proper long chain and double active sites modified to form Cu NCs@AMT/GA play a significant role,the luminescence intensity increased of which by more than 25 times.After multiply dialysis and purification,we still find obvious-CHO in Cu NCs@AMT/GA is analyzed by ¹H NMR,it assumes that there are still weak hydrogen bonding interactions formed by the incomplete-CHO.The introduction of ethylene glycol（EG）could form acetal with the-CHO,and the luminescence intensity of Cu NCs@AMT/GA/EG is further improved,and the wavelength is changed from 590 nm to 550 nm.Similarly,due to the internal coating mechanism,the addition of flexible sulfhydryl small molecules（Cysteine）can also achieve the luminescence intensity of Cu NCs@AMT significantly improved.Ultra-small Cu NCs@AMT with low surface coverage give it excellent photocatalytic performance,but the encapsulated Cu NCs@AMT/GA had less much attracted,indicating that the catalytic center located in the Cu cores,which further enriches the research and development of CuNCs in the field of catalysis.