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Sharp Transition from Nonmetallic Au246 to Metallic Au279 with Nascent Surface Plasmon Resonance Tatsuya Higaki, Meng Zhou, Kelly Lambright, Kristin Kirschbaum, Matthew Y. Sfeir, and Rongchao Jin J. Am. Chem. Soc., Just Accepted Manuscript • DOI: 10.1021/jacs.8b02487 • Publication Date (Web): 16 Apr 2018 Downloaded from http://pubs.acs.org on April 16, 2018
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Journal of the American Chemical Society
Sharp Transition from Nonmetallic Au246 to Metallic Au279 with Nascent Surface Plasmon Resonance Tatsuya Higaki,†,# Meng Zhou,†,# Kelly J. Lambright,‡ Kristin Kirschbaum,‡ Matthew Y. Sfeir,§ Rongchao Jin*,† †
Department of Chemistry, Carnegie Mellon University, Pittsburgh, Pennsylvania 15213, United States
‡
Department of Chemistry and Biochemistry, University of Toledo, Toledo, Ohio 43606, United States Center for Functional Nanomaterials, Brookhaven National Laboratory, Upton, New York 11973, United States
§
Supporting Information Placeholder ABSTRACT: The optical properties of metal nanoparticles have attracted wide interest. Recent progress in controlling nanoparticles with atomic precision (often called nanoclusters) provide new opportunities for investigating many fundamental questions, such as the transition from excitonic to plasmonic statewhich is a central question in metal nanoparticle research because it provides insights into the origin of surface plasmon resonance (SPR) as well as the formation of metallic bond. However, this question still remains elusive because of the extreme difficulty in preparing atomically precise nanoparticles larger than 2 nm. Here we report the synthesis and optical properties of an atomically precise Au279(SR)84 nanocluster. Femtosecond transient absorption spectroscopic analysis reveals that the Au279 nanocluster shows a laser power dependence in its excited state lifetime, indicating metallic state of the particle, in contrast with the nonmetallic electronic structure of the Au246(SR)80 nanocluster. Steady-state absorption spectra reveal that the nascent plasmon band of Au279 at 506 nm shows no peak shift even down to 60 K, consistent with plasmon behavior. The sharp transition from nonmetallic Au246 to metallic Au279 is surprising and will stimulate future theoretical work on the transition and many other relevant issues.
The optical properties of metal nanoparticles constitute one of the most exciting topics in nanoscience research.1-7 In recent years, significant progress in the synthesis has led to atomically precise nanoparticles in the ultrasmall size regime. Such unique nanoparticles (often called nanoclusters) offer exciting opportunities for both fundamental research8-22 and practical applications.2328 For example, thiolate-protected gold nanoclusters (Aun(SR)m) show strong photoluminescence and two-photon absorbance compared to their larger counterparts (i.e. plasmonic gold nanoparticles).23,27 The unique properties of gold nanoclusters are manifestations of quantum confinement effects due to ultra-small size (
