Size Evolution Dynamics of Gold Nanoclusters at an Atom-Precision Level: Ligand Exchange, Growth Mechanism, Electrochemical, and Photophysical Properties

Abstract

Interpretation of size evolution is an essential part of nanocluster transformation processes for unraveling the mechanism at an atom-precision level. Here we report the transformation of a nonsuperatomic Au 23 to a superatomic Au 36 nanocluster via Au 28 cluster formation, activated by the bulky 4-tert-butylbenzenethiol ligand. Time-dependent matrix-assisted laser desorption ionization mass spectrometry data revealed that the conversion proceeds through ligand exchange followed by the size focusing method, ultimately leading to size growth. We also validated this transformation through time-dependent ultraviolet−visible data. Density functional theory calculations predicted that the kernel of the Au 28 cluster evolved through a linear combination of molecular orbitals of the fragment of 2e − units (Au 4 2+ and Au 3 + ) from the kernel of the Au 23 cluster. Periodic growth of gold cores through continuous growth of Au 4 tetrahedral unit leads to the formation of the Au 36 cluster from the Au 28 cluster. These results reinforce the plausibility of size evolution through the growth mechanism during the transformation process. Differential pulse voltammetry studies showed that the highest occupied molecular orbital−lowest unoccupied molecular orbital gap inversely varies with the kernel size of these clusters. Photophysical experiments support the molecular-like intersystem crossing rather than core−shell relaxation to these clusters. The trends of photoluminescence lifetime were found to be the reverse of those of the energy gap law. The increment of lifetimes for the larger cluster can be mainly due to the contribution of both hot carriers and band-edge carriers.

Synergistic Effect of Bridging Thiolate and Hub Atoms for the Aromaticity Driven Symmetry Breaking in Atomically Precise Gold Nanocluster

“…In our previous work, we have highlighted how ligand bulkiness entangled with aromaticity lead to the size evolution during ligand exchange in harsh conditions. 30 For the ligand exchange induced size/structural transformation (LEIST) process, molecular purity of [Au 23 (CHT) 16 ] − was confirmed by MALDI-MS and UV−vis spectroscopy (Figures S1 and S2). To a solution of 10 mg of [Au 23 (CHT) 16 ] − in 2 mL of DCM was added an excess of thiophenol (TP) (see SI).…”

“…The present studies constitute the third approach using the LEIST method on [Au 23 (CHT) 16 ] − . These approaches vary in terms of the nature of ligands (Scheme 3) 29,30 This proved that the aromaticity, electronic, and steric effect strongly influence the kernel's geometry and structure of the product.…”

Ligand exchange reactions on thiolate-protected gold nanoclusters

“…In these cases the conversion through ligand exchange followed by the size focusing ultimately lead to size growth. 127,129 …”

Gold Clusters: From the Dispute on a Gold Chair to the Golden Future of Nanostructures

“…Transformation of a non-superatom into a superatom nanocluster was obtained also in the case of the thiolate-protected cluster [Au 23 (SC 6 H 11 ) 16 ] − which was converted into Au 36 (TBBT) 24 (TBBT = 4- tert butylbenzenethiolate) via Au 28 (TBBT) 20 formation, by using the ligand exchange-induced size/structural transformation (LEIST) approach [ 73 ].…”