pH-Induced Surface Modification of Atomically Precise Silver Nanoclusters: An Approach for Tunable Optical and Electronic Properties

Abstract

Noble metal nanoclusters (NCs) play a pivotal role in bridging the gap between molecules and quantum dots. Fundamental understanding of the evolution of the structural, optical, and electronic properties of these materials in various environments is of paramount importance for many applications. Using state-of-the-art spectroscopy, we provide the first decisive experimental evidence that the structural, electronic, and optical properties of Ag(MNBA) NCs can now be tailored by controlling the chemical environment. Infrared and photoelectron spectroscopies clearly indicate that there is a dimerization between two adjacent ligands capping the NCs that takes place upon lowering the pH from 13 to 7.

Atomically Precise Clusters of Noble Metals: Emerging Link between Atoms and Nanoparticles

“…Compared to gold, silver in zerovalent state is much more reactive and easily oxidizable, making it difficult to explore its clusters in greater detail . The Dickson group has studied extensively fluorescent silver clusters made under dendritic and DNA templates. − The Pradeep group has tried to examine the chemistry of silver clusters using mass spectrometry and other characterization tools. ,,, Other groups such as those of Bigioni, Kitaev, Bakr, etc., are also working on silver clusters. ,,,, Crystal structures of a few mixed ligand protected silver clusters have been solved, , but well-defined mass spectra were missing for a few years. Crystal structures of the highly stable Ag 44 (SR) 30 cluster (initially known as intensely and that of broadly absorbing nanoparticles (IBAN)) with diverse ligands and Ag 25 (SR) 18 cluster have been determined, which has enhanced our understanding of Ag cluster systems .…”

“…11,14,16,37 Other groups such as those of Bigioni, Kitaev, Bakr, etc., are also working on silver clusters. 13,28,30,448,449 Crystal structures of a few mixed ligand protected silver clusters have been solved, 39,40 but well-defined mass spectra were missing for a few years. Crystal structures of the highly stable Ag 44 (SR) 30 cluster (initially known as intensely and that of broadly absorbing nanoparticles (IBAN)) 450 with diverse ligands and Ag 25 (SR) 18 46 cluster have been determined, which has enhanced our understanding of Ag cluster systems.…”

Ag(I)-Thiolate-Protected Silver Nanoclusters for Solar Cells: Electrochemical and Spectroscopic Look into the Photoelectrode/Electrolyte Interface

“…Regardless of the types of substrate, all Ag NCs showed a broad excited-state absorption extending over the whole visible light spectrum. Unlike larger clusters (e.g., Ag 32 (SG) 19 , Ag 44 (MNBA) 30 ) where strong bleaching along with a distinct excited-state absorption feature are observed, ,,,− the TAS spectra of the Ag NCs were rather featureless with no bleaching, which resembled the TAS spectrum of small Ag NCs (e.g., Ag 15 (SG) 11 ) . This result implied that the Ag(0)/Ag­(I)-thiolate NCs were primarily composed of small NCs that were no larger than Ag 15 (SG) 11 .…”

“…In our new strategy, Ag NCs were initially formed by heating Ag­(I)-thiolate complexes in a basic solution; then, a subsequent pH change made the solution acidic and promoted the aggregation of unreacted Ag­(I)-thiolate complexes onto the preformed Ag(0) NC core. This was possible because lowering the pH resulted in the protonation of carboxylic groups of GSH that initiated the formation of Ag­(I)-thiolate shells via hydrogen bonding. , Thermal reduction was carried out at pH 11 at different temperatures (60, 70, and 90 °C) to control the core size. The as-obtained Ag NCs were very weakly emissive because there was no aggregation of Ag­(I)-thiolate complexes on the Ag(0) NC core because of the negative charge that developed in the basic solution.…”

Solvent-Dependent Photophysical Properties of a Semiconducting One-Dimensional Silver Cluster-Assembled Material

“…Encouraged by the concept of atom-precision, the research in nanotechnology is now blossoming in a new direction to counteract the inherent disadvantages of metal nanoparticles. Structure–property correlation with great control over the atomic homogeneity in size, shape, and composition makes this new area of metal nanoclusters (NCs) very alluring. , Besides, owing to their subnanometer size range, the quantum confinement effect makes these NCs more appealing for exhibiting molecular-like behavior, exotic optical properites with discrete energy levels, highest occupied molecular orbital (HOMO)–lowest unoccupied molecular orbital (LUMO) transition, catalysis, sensing, etc. − Because of their unique metallophilic interactions, these NCs are also attractive for their luminescence properties. − Although researches to synthesize new metal NCs along with periodic elements have been diversified since the beginning, the exploration of noble-metal NCs is still going on. − In recent years, silver NCs stabilized by organic ligands (such as −SR, PR 3 , and alkynes) have gained tremendous potential because of their fascinating structures to control the supramolecular assembly of solids and distinct photophysical properties. − However, the inherent ultrainstability of silver NCs disrupts their extensive study in nanoscience because they are susceptible to oxidation …”