单个、自生的RP-Au-PR结构增强金属纳米团簇的光致发光量子产率19倍

Single, Self-Born RP-Au-PR Motif Boosts 19-Fold Photoluminescence Quantum Yield of Metal Nanocluster

膦保护金纳米团簇的研究可追溯到1969年,“RP-Au-PR”(R为烷基)结构在膦保护的金纳米团簇上目前还未见报道,而相似的“RS-Au-SR”结构在硫醇保护金纳米团簇中经常被发现,其具有多种功能(例如增强团簇发光).本工作以双膦作为配体成功合成出原子层次单分布的金银纳米团簇[Au_(10)Ag_(4)(Dppp)_(5)Cl_(4)]Cl_(2)(Au_(10)Ag_(4) NC,Dppp为1,3-双(二苯基膦)丙烷),首次发现它具有“RP-Au-PR”结构.有趣的是,当二氯甲烷作为溶剂时,该结构可在Au_(10)Ag_(4) NC中自行消失,生成[Au_(9)Ag_(4)(Dppp)_(4)Cl_(4)]Cl(Au_(9)Ag_(4) NC);另一方面,当乙醇为溶剂时,该结构可在Au_(9)Ag_(4) NC中自行生成,从而转变成Au_(10)Ag_(4) NC.两个团簇的紫外-可见-近红外(UV/Vis/NIR)吸收峰除了有轻微的位移外,没有显著的区别,暗示着“RP-Au-PR”结构对团簇的电子结构没有根本影响,这一点也被密度泛函理论(DFT)计算所支撑.该结构促使Au_(10)Ag_(4) NC的光致发光量子产率比Au_(9)Ag_(4) NC的提高了19倍(达到10.32%),这归因于“RP-Au-PR”结构诱导的电荷转移和刚性的增强.本工作揭示了新的团簇结构和发光现象,对团簇构效关系的理解和性能改善有重要的启发.

The study of phosphine-protected gold nanocluster can be dated back to 1969,however,the RP-Au-PR motif has not been reported until now.Meanwhile,its analogue RS-Au-SR motif was often reported in thiolated gold nanoclusters,being of multiple functions(e.g.,enhancing the luminescence).Herein,we successfully synthesized a monodisperse gold-silver nanocluster:[Au_(10)Ag_(4)(Dppp)_(5)Cl_(4)]Cl_(2)(Au_(10)Ag_(4) NC,where the Dppp represents 1,3-diphenylphosphine propane,and NC represents nanocluster)by introducing the reducing agent(NaBH4)in an dichloromethane-ethanol solution of chlo-roauric acid,silver nitrate and 1,3-diphenylphosphine propane.Hydrochloric acid was added to promote the nanocluster size-focusing.Au_(10)Ag_(4) NC is unstable in dichloromethane and will be transformed into another nanocluster[Au_(9)Ag_(4)(Dppp)_(4)Cl_(4)]Cl(Au_(9)Ag_(4) NC).The structures and compositions of Au_(10)Ag_(4) and Au_(9)Ag_(4) NCs have been determined by single crystal X-ray crystallography and electrospray ionization mass spectrometry(ESI-MS).Au_(10)Ag_(4) NC possesses an ico-sahedral Au_(9)Ag_(4) core,which is protected by a special RP-Au-PR motif,diphosphine and halogen ligands;Au_(9)Ag_(4) NC has an icosahedral Au_(9)Ag_(4) metal core protected by bisphosphine and halogen ligands,thus the major structural difference between Au_(10)Ag_(4) and Au_(9)Ag_(4) NCs is the RP-Au-PR motif.The motif can be self-vanished in Au_(10)Ag_(4) NC when dichloromethane acts as the solvent,resulting in the formation of Au_(9)Ag_(4) NC as mentioned above;on the other hand,the motif can self-bear in Au_(9)Ag_(4) NC when the solvent is ethanol instead of dichloromethane,resulting in the formation of Au_(10)Ag_(4) NC.The two nanoclusters showed similar ultraviolet-visible-near infrared(UV/Vis/NIR)absorption spectra except for slight shift of the profile,indicating that the RP-Au-PR motif has no essential influence on the electronic structure of nanocluster,which was supported by density functional theory(DFT)calculations.However,the photoluminescence quantum yield of Au_(10)Ag_(4) NC(10.32%)is 19 times higher than that of Au_(9)Ag_(4) NC(0.52%),ascribing to the enhancement of charge transfer and structure rigidity induced by the motif.This work provides new views to the structure and photoluminescence of gold-silver nanoclus ter,has important implications for the structure-property understanding and the property improvement.