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Article

Luminescence of Tiopronin Monolayer-Protected Silver Clusters Changes To That of Gold Clusters upon Galvanic Core Metal Exchange^†

Tao Huang and Royce W. Murray*

Kenan Laboratories of Chemistry, University of North Carolina, Chapel Hill, North Carolina 27599-3290

J. Phys. Chem. B, 2003, 107 (30), pp 7434–7440

DOI: 10.1021/jp0276956

Publication Date (Web): May 20, 2003

†

Part of the special issue “Arnim Henglein Festschrift”.

Corresponding author: e-mail rwm@email.unc.edu.

Abstract

Water-soluble tiopronin monolayer-protected silver clusters (Ag MPCs), with 1.6 nm average diameter cores, exhibit visible luminescence at 500 nm with a quantum yield estimated near 10^-4 when excited at 400 nm. The Ag MPCs become organic-soluble upon conversion to poly(ethylene glycol) quaternary ammonium salts of the carboxylates of the N-2-mercaptopropionylglycine ligand monolayer. The Ag MPC luminescence becomes more intense in nonpolar organic solvents. The luminescence may arise from interband recombination transitions between the d band and the sp conduction band. Atoms in the Ag MPC core can be replaced by Au atoms via a galvanic metal exchange reaction between the silver clusters and Au(I)[SCH₂(C₆H₄)C(CH₃)₃]. The reaction was detected by observing the time-dependent change of the surface plasmon absorbance and emission spectra of the Ag MPC to spectra characteristic of Au MPCs. The reaction was also assessed by transmission electron microscopy (TEM) and elemental analysis.

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