We report a one-step route for the synthesis of highly luminescent and water-soluble Au 18SG 14 (SG- glutathione in thiolate form) in nearly pure form using a slow reduction process. The cluster shows step-like behavior in its absorption profile. It emits red light in both aqueous and solid state under UV illumination. Quantum yield of the cluster is 0.053, nearly 25-fold higher than that of Au 25SG 18. The cluster exhibits distinct features corresponding to multiply charged ions in electrospray ionization mass spectrometry. This composition is also confirmed from MALDI MS along with other quantitative analyses. The cluster makes closed shell molecular ions in the gas phase. The possibility of making clusters of different core sizes is also demonstrated. The simplicity of this method and identification of the cluster with exact composition may facilitate the exploration of experimental and theoretical research on this material. © 2012 American Chemical Society.

Pradeep Thalappil

Department Of Chemistry

Atanu Ghosh

CLOSED SHELLS

Condensed phase

Core size

Electrospray ionization mass spectrometry

Gasphase

Glutathiones

MALDI-MS

Molecular ions

MULTIPLY CHARGED IONS

Red light

Reduction process

THEORETICAL RESEARCH

THIOLATES

UV ILLUMINATIONS

Gases

Luminescence

Mass spectrometry

quantum yield

Ion sources

IIT Madras is a public technical and research university located in Chennai, Tamil Nadu. Founded in 1959, it is recognised as an Institute of National Importance.

IIT Madras has been ranked as the top engineering institute in India for four years in a row by the National Institutional Ranking Framework of the MHRD

It currently offers undergraduate, postgraduate and research degrees across 16 disciplines in Engineering, Sciences, Humanities and Management. About 596 faculty belonging to science and engineering departments and centres of the Institute are engaged in teaching, research and industrial consultancy.

IIT Madras

Journal of Physical Chemistry Letters

Abstract: Materials emitting white luminescence are receiving increasing attention due to their potential applications in electroluminescent devices, information displays and fluorescent sensors. To produce white light, one must have either three primary colors, blue, green and red or two colors, blue and orange. In this paper, we have used thiol/phosphine protected red luminescent silver nanoclusters (Ag NCs), [Ag29(BDT)12(PPh3)4]3-(BDT=1,3-benzenedithiol), [AuxAg29-x(BDT)12(PPh3)4]3- and Ag 29(LA) 12 (LA = lipoic acid) as one of the fluorophores for white light emission. These clusters are mixed with blue luminescent silicon nanoparticles (Si NPs) and green luminescent fluorescein isothiocyanate (FITC). The mixtures show white luminescence with CIE coordinates of (0.31, 0.34), (0.33, 0.35) and (0.29, 0.31) which are in good agreement with pure white light (0.33, 0.33). The other clusters with yellow, blue, orange, etc., luminescence can also be used to make white light. This work provides a prospective pathway for white light emission based on atomically precise noble metal NCs. Graphical abstract: Synopsis Monolayer protected noble metal nanoclusters such as [Ag29(BDT)12(PPh3)4]3-(BDT=1,3-benzenedithiol), [AuxAg29-x(BDT)12(PPh3)4]3- and Ag 29(LA) 12 (LA = lipoic acid) are used as red luminophores which can produce white light emission when mixed with blue luminescent silicon nanoparticles (Si NPs) and green luminescent fluorescein isothiocyanate (FITC). The mixtures produce white luminescence with CIE (Commission Internationale d’Eclair) coordinates of (0.31, 0.34), (0.33, 0.35) and (0.29, 0.31), respectively. All-cluster-based white light emission is indeed possible.[Figure not available: see fulltext.]. © 2018, Indian Academy of Sciences.

Fulltext

Journal of Chemical Sciences

Atomically precise cluster-based white light emitters §

We report the formation of naked cluster ions of silver of specific nuclearities, uncontaminated by other cluster ions, derived from monolayer-protected clusters. The hydride and phosphine co-protected cluster, [Ag18(TPP)10H16]2+ (TPP, triphenylphosphine), upon activation produces the naked cluster ion, Ag17 +, exclusively. The number of metal atoms present in the naked cluster is almost the same as that in the parent material. Two more naked cluster ions, Ag21 + and Ag19 +, were also formed starting from two other protected clusters, [Ag25(DPPE)8H22]3+ and [Ag22(DPPE)8H19]3+, respectively (DPPE, 1,2-bis(diphenylphosphino)ethane). By systematic fragmentation, naked clusters of varying nuclei are produced from Ag17 + to Ag1 + selectively, with systematic absence of Ag10 +, Ag6 +, and Ag4 +. A seemingly odd number of cluster ions are preferred due to the stability of the closed electronic shells. Sequential desorption of dihydrogen occurs from the cluster ion, Ag17H14 +, during the formation of Agn +. A comparison of the pathways in the formation of similar naked cluster ions starting from two differently ligated clusters has been presented. This approach developed bridges the usually distinct fields of gas-phase metal cluster chemistry and solution-phase metal cluster chemistry. We hope that our findings will enrich nanoscience and nanotechnology beyond the field of clusters. © 2017 American Chemical Society.

ACS Nano

Sequential Dihydrogen Desorption from Hydride-Protected Atomically Precise Silver Clusters and the Formation of Naked Clusters in the Gas Phase

We report the synthesis of a new silver cluster, [Ag59(2,5-DCBT)32]3- (I) (2,5-DCBT: 2,5-dichlorobenzenethiol), which acts as a precursor for the synthesis of three well-known silver clusters, [Ag44(2,4-DCBT/4-FTP)30]4- (II) (4-FTP: 4-fluorothiophenol and 2,4-DCBT: 2,4-dichlorobenzenethiol), [Ag25(2,4-DMBT)18]- (III) (2,4-DMBT: 2,4-dimethylbenzenethiol) and [Ag29(1,3-BDT)12(PPh3)4]3- (IV) (1,3-BDT: 1,3-benzenedithiol and PPh3: triphenylphosphine). This newly synthesized silver cluster, I, is characterized using UV-vis absorption studies, high resolution electrospray ionization mass spectrometry (ESI MS) and other analytical tools. The optical absorption spectrum shows distinct features which are completely different from the previously reported silver clusters. We perform the rapid transformations of I to other well-known clusters II, III and IV by reaction with different thiols. The time-dependent UV-vis and ESI MS measurements reveal that I dissociates into distinct thiolate entities in the presence of thiols and the thiolates recombine to produce different clusters. The conversion mechanism is found to be quite different from the previous reports where it occurs through the initial formation of ligand exchanged products. Here, we also show the synthesis of a different cluster core, [Ag44(2,4-DCBT)30]4- (IIa) using 2,4-DCBT, a structural isomer of 2,5-DCBT under the same synthetic conditions used for I. This observation demonstrates the effect of isomeric thiols on controlling the size of silver clusters. The conversion of one cluster to several other clusters under ambient conditions and the effect of ligand structure in silver cluster synthesis give new insights into the cluster chemistry. © 2017 The Royal Society of Chemistry.

Nanoscale

[Ag59(2,5-DCBT)32]3-: A new cluster and a precursor for three well-known clusters

A new strategy to synthesize a diverse array of organic-soluble, atomically precise silver clusters has been developed. The technique is based on the miscibility principle of solvents and uses no phase-transfer agents; various clusters of masses 8.0, 13.4, 22.8, 29.2, and 34.4 kDa were synthesized by changing the reactant composition. We have also synthesized the well-known Au<inf>25</inf>(SR)<inf>18</inf> cluster by the same method. Among the silver clusters formed, we have studied the new 13.4 kDa species, which has unique steplike features in its UV/Vis spectrum, in detail by mass spectrometry and other analytical techniques. The compound has been assigned as Ag<inf>68</inf>(SR)<inf>34</inf>, which is reported for the first time. By time-dependent studies, we have shown that the synthetic route follows the bottom-up approach. The material forms microcrystals. We hope that the proposed synthetic strategy will extend the area of atomically precise clusters. © 2014 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

European Journal of Inorganic Chemistry

Synthesis of atomically precise silver clusters by using the miscibility principle

Clusters composed of a 32 silver atom core, protected with thiolates of glutathione (GSH) and N-(2-mercaptopropionyl)glycine (MPGH), were synthesized by a solid-state route in milligram scale. They do not exhibit surface plasmon resonance unlike their larger sized nanoparticle analogues but show molecule-like features in absorption and luminescence spectra, falling in the visible window. The compositions Ag32SG19 (SG: thiolate of glutathione) and Ag32MPG19 (MPG: thiolate of MPGH) were identified from electrospray ionization mass spectrometry (ESI MS). Matrix-assisted laser desorption/ionization mass spectrometry (MALDI MS) was not successful for -SG protected clusters as reported before, but for Ag 32MPG19 a peak at 6.1 kDa was seen at a threshold laser intensity. This peak shifted to low mass region with increasing laser intensity due to systematic losses of Ag2S. Further confirmation of the composition Ag32SG19 was made using various studies such as XPS and EDAX. One-dimensional (1D) and two-dimensional (2D) NMR spectroscopic investigations of Ag32SG19 provided interesting spectral features which indicated the dominant -[SR-Ag-SR]- structural motif. This structural motif as the predominant entity is found for the first time in silver clusters. © The Royal Society of Chemistry 2013.

Thiolate-protected Ag32 clusters: Mass spectral studies of composition and insights into the Ag-thiolate structure from NMR

Quantum clusters (QCs) of silver such as Ag7(H2MSA)7, Ag8(H2MSA)8 (H2MSA, mercaptosuccinic acid) were synthesized by the interfacial etching of Ag nanoparticle precursors and were loaded on metal oxide supports to prepare active catalysts. The supported clusters were characterized using high resolution transmission electron microscopy, scanning electron microscopy, X-ray photoelectron spectroscopy, and laser desorption ionization mass spectrometry. We used the conversion of nitro group to amino group as a model reaction to study the catalytic reduction activity of the QCs. Various aromatic nitro compounds, namely, 3-nitrophenol (3-np), 4-nitrophenol (4-np), 3-nitroaniline (3-na), and 4-nitroaniline (4-na) were used as substrates. Products were confirmed using UV-visible spectroscopy and electrospray ionization mass spectrometry. The supported QCs remained active and were reused several times after separation. The rate constant suggested that the reaction followed pseudo-first-order kinetics. The turn-over frequency was 1.87 s-1 per cluster for the reduction of 4-np at 35°C. Among the substrates investigated, the kinetics followed the order, SiO2 &gt; TiO2 &gt; Fe2O3 &gt; Al2O3. © 2011 Leelavathi et al.

Nanoscale Research Letters

Supported quantum clusters of silver as enhanced catalysts for reduction

We have prepared Au15 quantum clusters anchored to α, β, and γcyclodextrin (CD) cavities. The synthesis process involves the core etching of larger clusters and the simultaneous trapping of the clusters formed inside the CD cavities. The clusters were characterized by various tools, such as optical absorption and luminescence spectroscopies, electrospray ionization-mass spectrometry (ESI-MS), X-ray photoelectron spectroscopy (XPS), circular dichroism spectroscopy, and two-dimensional nuclear magnetic resonance (2D NMR) spectroscopy. Trapping of the cluster in the CD cavity was proven by circular dichroism and also by rotational Overhauser effect spectroscopy (ROESY), in terms of the distinct cross peak between proton "e" of the glutathione (-SG) ligand and the ∼3 "e" proton of CD. Dynamic light scattering (DLS) studies showed a hydrodynamic diameter of ∼3-4 nm, indicating one CD molecule per cluster with an extension of one water of hydration. The clusters are intensely luminescent, with major lifetime components of 28, 71, and 24 ps for Au 15@ αCD, Au15atβCD, and Au 15atγCD, respectively. The clusters also are strongly luminescent in the solid state. Both in the solution and in the solid state, the luminescence is sensitive to solvents/vapors. The clusters adhere to glass plates, and the solvent dependency of luminescence was used to create patterns that are erased upon gradual evaporation of the solvent. This self-erasing property was further demonstrated with clusters supported on a thin layer chromatography (TLC) plate. Selective detection of metal ions using the luminescence of the clusters is reported. Evaporation of the cluster solutions leads to luminescent gel-like materials. © 2011 American Chemical Society.

Chemistry of Materials

Quantum clusters in cavities: Trapped Au15 in cyclodextrins

The synthesis of a luminescent quantum cluster (QC) of gold with a quantum yield of ∼4% is reported. It was synthesized in gram quantities by the core etching of mercaptosuccinic acid protected gold nanoparticles by bovine serum albumin (BSA), abbreviated as AuQC@BSA. The cluster was characterized and a core of Au38 was assigned tentatively from mass spectrometric analysis. Luminescence of the QC is exploited as a "turn-off" sensor for Cu 2+ ions and a "turn-on" sensor for glutathione detection. Metal-enhanced luminescence (MEL) of this QC in the presence of silver nanoparticles is demonstrated and a ninefold maximum enhancement is seen. This is the first report of the observation of MEL from QCs. Folic acid conjugated AuQC@BSA was found to be internalized to a significant extent by oral carcinoma KB cells through folic acid mediated endocytosis. The inherent luminescence of the internalized AuQC@BSA was used in cell imaging. © 2010 Wiley-VCH Verlag GmbH &amp; Co. KGaA, Weinheim.

Chemistry - A European Journal

Luminescent quantum clusters of gold in bulk by albumin-induced core etching of nanoparticles: Metal ion sensing, metal-enhanced luminescence, and biolabeling

A silver cluster having the composition Ag9(H 2MSA)7 (H2MSA = mercaptosuccinic acid) was synthesized in macroscopic quantities using a solid-state route. The clusters were purified by PAGE and characterized by UV-vis, FTIR, luminescence, and NMR spectroscopy, TEM, XPS, XRD, TG, SEM/EDAX, elemental analysis, and ESI MS. The solid-state route provides nearly pure Ag9 clusters, and nanoparticle contamination was insignificant for routine studies. Formation of various clusters was observed by modifying the conditions. The effect of ligands on the synthesis was checked. The cluster decomposed slowly in water, and the decomposition followed first-order kinetics. However, it could be stabilized in solvent mixtures and in the solid state. Such materials may be important in cluster research because of their characteristic absorption profiles, which are similar to those of Au25 and Au38. The cluster showed luminescence with a quantum yield of 8 × 10-3 at 5 °C. © 2010 American Chemical Society.

Journal of the American Chemical Society

Ag9 quantum cluster through a solid-state route

chemical equation presentation Interfacial etching of silver nanoparticles and separation of the products by Polyacrylamide gel electrophoresis afforded Ag8 and Ag7 clusters with red and bluegreen fluorescence emission, respectively (see picture). The strongly temperaturedependent emission of the clusters suggests potential applications, whilst their facile phase transfer to organic media facilitates further studies. © 2010 Wiley-VCH Verlag GmbH &amp; Co. KCaA, weinheim.

Journal	Journal of Physical Chemistry Letters
ISSN	19487185
Open Access	No