摘要/Abstract

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[Au₁₀Ag₄(Dppp)₅Cl₄]Cl₂ (Au₁₀Ag₄ 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Au₁₀Ag₄ NC中自行消失, 生成[Au₉Ag₄(Dppp)₄Cl₄]Cl (Au₉Ag₄ NC); 另一方面, 当乙醇为溶剂时, 该结构可在Au₉Ag₄ NC中自行生成, 从而转变成Au₁₀Ag₄ 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Au₁₀Ag₄ NC的光致发光量子产率比Au₉Ag₄ 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.
关键词: 金属纳米团簇, “RP-Au-PR”结构, 光致发光
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: [Au₁₀Ag₄(Dppp)₅Cl₄]Cl₂ (Au₁₀Ag₄ 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 chloroauric acid, silver nitrate and 1,3-diphenylphosphine propane. Hydrochloric acid was added to promote the nanocluster size-focusing. Au₁₀Ag₄ NC is unstable in dichloromethane and will be transformed into another nanocluster [Au₉Ag₄(Dppp)₄Cl₄]Cl (Au₉Ag₄ NC). The structures and compositions of Au₁₀Ag₄ and Au₉Ag₄ NCs have been determined by single crystal X-ray crystallography and electrospray ionization mass spectrometry (ESI-MS). Au₁₀Ag₄ NC possesses an ico sahedral Au₉Ag₄ core, which is protected by a special RP-Au-PR motif, diphosphine and halogen ligands; Au₉Ag₄ NC has an icosahedral Au₉Ag₄ metal core protected by bisphosphine and halogen ligands, thus the major structural difference between Au₁₀Ag₄ and Au₉Ag₄ NCs is the RP-Au-PR motif. The motif can be self-vanished in Au₁₀Ag₄ NC when dichloromethane acts as the solvent, resulting in the formation of Au₉Ag₄ NC as mentioned above; on the other hand, the motif can self-bear in Au₉Ag₄ NC when the solvent is ethanol instead of dichloromethane, resulting in the formation of Au₁₀Ag₄ 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 Au₁₀Ag₄ NC (10.32%) is 19 times higher than that of Au₉Ag₄ 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 nanocluster, has important implications for the structure-property understanding and the property improvement.
Key words: metal nanocluster, RP-Au-PR motif, photoluminescence


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