Atomically precise large-sized Au_n(SR)_m nanoclusters and scaling relationships among size, bandgap and excited-state...

The synthesis of atomically precise, large-sized Au_n(SR)_m nanoclusters (SR = thiolate) with n of 100 or more atoms has long been a challenge. In this work, we report the synthesis of Au₁₀₀(Napt)₄₂ and Au₁₀₂(IPBT)₄₄ nanoclusters (where Napt stands for 1-naphthalenethiolate and IPBT for 4-isopropylbenzenethiolate). Their optical absorption, single-electron charging, and femtosecond electron dynamics are investigated. Both Au₁₀₀(Napt)₄₂ and Au₁₀₂(IPBT)₄₄ exhibit multiple discrete absorption bands in their optical spectra owing to a quantized electronic structure in ultrasmall metal nanoclusters. Electrochemical analysis determines the precise HOMO-LUMO gaps of Au₁₀₀(Napt)₄₂ and Au₁₀₂(IPBT)₄₄ by single-electron charging. The electronic excited-state lifetimes of Au₁₀₀(Napt)₄₂ and Au₁₀₂(IPBT)₄₄ are determined by femtosecond transient absorption spectroscopy. The scaling relationship between the E_g and size (n) and the relationship of the excited state lifetime versus the E_g of large-sized Au_n(SR)_m are discussed. The findings provide a fundamental understanding of large-sized metal nanoclusters, which will benefit their future applications in optics, electronics, and other fields.