Luminescence Onset and Mechanism of the Formation of Gold(I)–Thiolate Complexes as the Precursors to Nanoparticles

Abstract

Gold(I) (Au(I))−thiolate complexes are widely believed as the precursors to Au nanoparticle formations. While the literature suggests that the Au(III)-to-thiol ligand stoichiometric ratio of 1:3 is required to reduce a Au(III) and yield a Au(I)−thiolate, other stoichiometric ratios are also known to produce Au nanoparticles upon reduction. Using the characteristic red luminescence of Au(I)-alkanethiolates, we examined the process of their formations and their implications on the Au nanoparticle synthesis in detail. The onset of the luminescence, correlated with the Au(I)−thiolate formation, as well as the kinetics of the luminophore formation were evaluated in terms of the Au(III)-to-alkanethiol ratios. The onset of the luminescence was affected significantly by the solvent polarity during reaction but not post reaction. We found that the kinetics of the luminophore formation can vary widely, requiring from minutes to 24 h for completion depending on the thiol ligands and molar ratios, as well as solvents. This information could help in designing Au nanoparticle syntheses with the logical choice of Au(III)-to-thiol ratio, solvent, and the timing of reduction.

Precision nanoengineering for functional self-assemblies across length scales

“…Unlike plasmonic nanoparticles, in AuNCs, the presence of Au(0) core and Au( i )–S staple units on the surface contribute to the short bonding distances that affects their photoluminescent properties. 127 Extensive studies have been performed to understand the size-dependent luminescence properties, the effect of ligands, and aggregation-induced emissions. 128 However, the NCs suffer from low efficiency and quantum yield, and the luminescence is restricted to a certain type of NCs with specific ligands and composition.…”

Three‐ligand Co‐assembled 2D Au(I)‐Thiolate Nanosheets

“…Au(I)-thiolate (AT) is a type of one-dimensional (1D) coordination polymer by linear binding between Au(I) and thiolate ligand, [1][2][3] which can self-assemble to various structures with aurophilic interactions [4] and show broad applications as drugs, [5,6] optical materials [7][8][9] and precursors of gold nanoparticles/clusters. [10][11][12][13] Among various AT structures, two-dimensional (2D) AT assemblies, which consist of a robust inorganic AuÀ S slab in the centre and organic substituents of the thiolate ligands on both surfaces via side-by-side stacking of linear AT chains with aurophilic interactions, combine the advantages of covalent 2D materials [14] and non-covalent organic 2D materials, [15,16] exhibiting both high structural stability and vast surface functions. [17,18] Therefore, they are powerful building blocks of biocompatible hydrogels [19,20] and bio-mimic hierarchical structures, [8] in which either covalent or organic noncovalent 2D materials are hard to function.…”

Common Motif at the Red Luminophore in Bovine Serum Albumin–, Ovalbumin–, Trypsin–, and Insulin–Gold Complexes

“…The slow lifetime is generally seen in complexes involving ligand-to-metal/metal-to-ligand charge transfer (LMCT/MLCT). To this end, it is worthwhile noting the properties of Au ← S LMCT, which is the mechanism typically assigned to the red luminescence of Au­(I)–thiolates. − Thus, we measured the lifetimes using glutathione reacted with Au­(III), which is known to form Au­(I)–thiolate complexes. ,, The red luminescence of GSH–Au compound, or Au­(I)–glutathiolate (Figure B, Figure S16), exhibited a slow lifetime component of τ ∼ 200 ns, which is significantly shorter than those of protein–Au­(III) complexes. We attribute the observed differences in the lifetimes to LMCT/MLCT with Cys and with another residue in the luminophores of protein–Au­(III) complexes.…”

“…28−31 Thus, we measured the lifetimes using glutathione reacted with Au(III), which is known to form Au(I)−thiolate complexes. 30,32,33 The red luminescence of GSH−Au compound, or Au(I)− glutathiolate (Figure 5B, Figure S16), exhibited a slow lifetime component of τ ∼ 200 ns, which is significantly shorter than those of protein−Au(III) complexes. We attribute the observed differences in the lifetimes to LMCT/MLCT with Cys and with another residue in the luminophores of protein− Au(III) complexes.…”

“…Known stable metal coordination in proteins indeed involves multiple residues. It is possible that the oxidation state of Au may change (to Au­(I)) by the coordination to Cys − in proteins.…”