Madhuri Jash

Bio: Madhuri Jash is an academic researcher from Indian Institute of Technology Madras. The author has contributed to research in topics: Luminescence & Cluster (physics). The author has an hindex of 5, co-authored 12 publications receiving 80 citations. Previous affiliations of Madhuri Jash include University of Hyderabad.

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

Abstract: 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...

Atomically Precise Noble Metal Clusters Harvest Visible Light to Produce Energy

Abstract: Atomically precise gold and silver clusters are a new class of sensitizers which can be used as substitutes for dyes in the classical dye-sensitized solar cells (DSCs). Here noble metal clusters protected by proteins and thiols (Au30@BSA, Au25SBB18, and Ag44MBA30) have been used for photovoltaic studies. These metal clusters were used as sensitizers for the photoanodes fabricated using TiO2 nanotubes (NTs) and the commercial P25 TiO2 nanoparticles. The TiO2, clusters and the solar cells were characterized by spectroscopy, microscopy, current-voltage (I-V) and incident photon-to-current conversion efficiency (IPCE) measurements. A systematic I-V study revealed a conversion efficiency of 0.35 % for the Au30@BSA sensitized solar cell made from TiO2 NTs which showed an IPCE maximum of 3 % at ∼ 400 nm.

Light-Activated Intercluster Conversion of an Atomically Precise Silver Nanocluster.

Abstract: Noble metal nanoclusters protected with carboranes, a 12-vertex, nearly icosahedral boron-carbon framework system, have received immense attention due to their different physicochemical properties. We have synthesized ortho-carborane-1,2-dithiol (CBDT) and triphenylphosphine (TPP) coprotected [Ag42(CBDT)15(TPP)4]2- (shortly Ag42) using a ligand-exchange induced structural transformation reaction starting from [Ag18H16(TPP)10]2+ (shortly Ag18). The formation of Ag42 was confirmed using UV-vis absorption spectroscopy, mass spectrometry, transmission electron microscopy, X-ray photoelectron spectroscopy, infrared spectroscopy, and multinuclear magnetic resonance spectroscopy. Multiple UV-vis optical absorption features, which exhibit characteristic patterns, confirmed its molecular nature. Ag42 is the highest nuclearity silver nanocluster protected with carboranes reported so far. Although these clusters are thermally stable up to 200 °C in their solid state, light-irradiation of its solutions in dichloromethane results in its structural conversion to [Ag14(CBDT)6(TPP)6] (shortly Ag14). Single crystal X-ray diffraction of Ag14 exhibits Ag8-Ag6 core-shell structure of this nanocluster. Other spectroscopic and microscopic studies also confirm the formation of Ag14. Time-dependent mass spectrometry revealed that this light-activated intercluster conversion went through two sets of intermediate clusters. The first set of intermediates, [Ag37(CBDT)12(TPP)4]3- and [Ag35(CBDT)8(TPP)4]2- were formed after 8 h of light irradiation, and the second set comprised of [Ag30(CBDT)8(TPP)4]2-, [Ag26(CBDT)11(TPP)4]2-, and [Ag26(CBDT)7(TPP)7]2- were formed after 16 h of irradiation. After 24 h, the conversion to Ag14 was complete. Density functional theory calculations reveal that the kernel-centered excited state molecular orbitals of Ag42 are responsible for light-activated transformation. Interestingly, Ag42 showed near-infrared emission at 980 nm (1.26 eV) with a lifetime of >1.5 μs, indicating phosphorescence, while Ag14 shows red luminescence at 626 nm (1.98 eV) with a lifetime of 550 ps, indicating fluorescence. Femtosecond and nanosecond transient absorption showed the transitions between their electronic energy levels and associated carrier dynamics. Formation of the stable excited states of Ag42 is shown to be responsible for the core transformation.

Diborane(6) and Its Analogues Stabilized by Mono-, Bi-, and Trinuclear Group 7 Templates: Combined Experimental and Theoretical Studies.

Abstract: Irradiation of [Re2(CO)10] in the presence of BH3·thf resulted in the formation of several rhenium diborane(6) species, for example, [{(OC)4Re}{Re(CO)3}2(μ3-η2:η2:η2-B2H6)(μ-H)], 1; [{(OC)4Re}2{Re(...

Preparation of gas phase naked silver cluster cations outside a mass spectrometer from ligand protected clusters in solution.

Abstract: Gas phase clusters of noble metals prepared by laser desorption from the bulk have been investigated extensively in a vacuum using mass spectrometry. However, such clusters have not been known to exist under ambient conditions to date. In our previous work, we have shown that in-source fragmentation of ligands can be achieved starting from hydride and phosphine co-protected silver clusters leading to naked silver clusters inside a mass spectrometer. In a recent series of experiments, we have found that systematic desorption of ligands of the monolayer protected atomically precise silver cluster can also occur in the atmospheric gas phase. Here, we present the results, wherein the [Ag18H16(TPP)10]2+ (TPP = triphenylphosphine) cluster results in the formation of the naked cluster, Ag17+ along with Ag18H+ without mass selection, outside the mass spectrometer, in air. These cationic naked metal clusters are prepared by passing electrosprayed ligand protected clusters through a heated tube, in the gas phase. Reactions with oxygen suggest Ag17+ to be more reactive than Ag18H+, in agreement with their electronic structures. The more common thiolate protected clusters produce fragments of metal thiolates under identical processing conditions and no naked clusters were observed.

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

Abstract: Atomically precise pieces of matter of nanometer dimensions composed of noble metals are new categories of materials with many unusual properties. Over 100 molecules of this kind with formulas such as Au25(SR)18, Au38(SR)24, and Au102(SR)44 as well as Ag25(SR)18, Ag29(S2R)12, and Ag44(SR)30 (often with a few counterions to compensate charges) are known now. They can be made reproducibly with robust synthetic protocols, resulting in colored solutions, yielding powders or diffractable crystals. They are distinctly different from nanoparticles in their spectroscopic properties such as optical absorption and emission, showing well-defined features, just like molecules. They show isotopically resolved molecular ion peaks in mass spectra and provide diverse information when examined through multiple instrumental methods. Most important of these properties is luminescence, often in the visible–near-infrared window, useful in biological applications. Luminescence in the visible region, especially by clusters prot...

Atomically Precise Noble Metal Nanoclusters as Efficient Catalysts: A Bridge between Structure and Properties.

Abstract: Improving the knowledge of the relationship between structure and properties is fundamental in catalysis. Recently, researchers have developed a variety of well-controlled methods to synthesize atomically precise metal nanoclusters (NCs). NCs have shown high catalytic activity and unique selectivity in many catalytic reactions, which are related to their ultrasmall size, abundant unsaturated active sites, and unique electronic structure different from that of traditional nanoparticles (NPs). More importantly, because of their definite structure and monodispersity, they are used as model catalysts to reveal the correlation between catalyst performance and structure at the atomic scale. Therefore, this review aims to summarize the recent progress on NCs in catalysis and provide potential theoretical guidance for the rational design of high-performance catalysts. First a brief summary of the synthetic strategies and characterization methods of NCs is provided. Then the primary focus of this review—the model ...

Tailoring the photoluminescence of atomically precise nanoclusters.

Abstract: Due to their atomically precise structures and intriguing chemical/physical properties, metal nanoclusters are an emerging class of modular nanomaterials. Photo-luminescence (PL) is one of their most fascinating properties, due to the plethora of promising PL-based applications, such as chemical sensing, bio-imaging, cell labeling, phototherapy, drug delivery, and so on. However, the PL of most current nanoclusters is still unsatisfactory-the PL quantum yield (QY) is relatively low (generally lower than 20%), the emission lifetimes are generally in the nanosecond range, and the emitted color is always red (emission wavelengths of above 630 nm). To address these shortcomings, several strategies have been adopted, and are reviewed herein: capped-ligand engineering, metallic kernel alloying, aggregation-induced emission, self-assembly of nanocluster building blocks into cluster-based networks, and adjustments on external environment factors. We further review promising applications of these fluorescent nanoclusters, with particular focus on their potential to impact the fields of chemical sensing, bio-imaging, and bio-labeling. Finally, scope for improvements and future perspectives of these novel nanomaterials are highlighted as well. Our intended audience is the broader scientific community interested in the fluorescence of metal nanoclusters, and our review hopefully opens up new horizons for these scientists to manipulate PL properties of nanoclusters. This review is based on publications available up to December 2018.

Surface strategies for catalytic CO2 reduction: from two-dimensional materials to nanoclusters to single atoms

Abstract: Redox catalysis, including photocatalysis and (photo)electrocatalysis, may alleviate global warming and energy crises by removing excess CO2 from the atmosphere and converting it to value-added resources. Nano-to-atomic two-dimensional (2D) materials, clusters and single atoms are superior catalysts because of their engineerable ultrathin/small dimensions and large surface areas and have attracted worldwide research interest. Given the current gap between research and applications in CO2 reduction, our review systematically and constructively discusses nano-to-atomic surface strategies for catalysts reported to date. This work is expected to drive and benefit future research to rationally design surface strategies with multi-parameter synergistic impacts on the selectivity, activity and stability of next-generation CO2 reduction catalysts, thus opening new avenues for sustainable solutions to climate change, energy and environmental issues, and the potential industrial economy.

Endohedrally Doped Cage Clusters

Abstract: The discovery of carbon fullerene cages and their solids opened a new avenue to build materials from stable cage clusters as “artificial atoms” or “superatoms” instead of atoms. However, cage clust...