%0 Journal Article %J Nanoscale %D 2023 %T A Luminescent Cu4 Cluster Film Grown by Electrospray Deposition: A Nitroaromatic Vapour Sensor %A Arijit Jana %A B K Spoorthi %A Akhil S Nair %A Biswarup Pathak %A Tomas Base %A Thalappil Pradeep %K carborane %K Copper %K luminescence %K nanocluster %K nitro organic %K sensor %X

We present the fabrication and use of a film of carborane-thiol protected tetranuclear copper cluster with characteristic orange luminescence using ambient electrospray deposition (ESD). Charged microdroplets of the clusters produced by an electrospray tip deposit clusters at an air-water interface to form a film. Different microscopic and spectroscopic techniques characterized the porous surface structure of the film. Visible and rapid quenching of the emission of the film upon exposure to 2-nitrotoluene (2-NT) vapours at ambient condition was observed. Density functional theory (DFT) calculations established the favourable binding sites of 2-NT with the cluster. Desorption of 2-NT upon heating recovered the original luminescence, demonstrating the reusability of the sensor. Stable emission upon exposure to different organic solvents and quenching of it upon the exposure to 2, 4-dinitrotoluene and picric acid showed selectivity of the film to nitroaromatic species.

%B Nanoscale %G eng %U https://pubs.rsc.org/en/content/articlelanding/2023/nr/d3nr00416c %9 Communication %R https://doi.org/10.1039/D3NR00416C %0 Journal Article %J Journal of the American Chemical Society %D 2023 %T Macropolyhedral syn-B18H22, the “Forgotten” Isomer %A Deepak Kumar Patel %A B. S. Sooraj %A Kaplan Kirakci %A Jan Machacek %A Monika Kucerakova %A Jonathan Bould %A Michal Dusek %A Martha Frey %A Christof Neumann %A Sundargopal Ghosh %A Andrey Turchanin %A Thalappil Pradeep %A Tomas Base %K boron %K boron hydride %K Cluster %K luminescence %K macropolyhedral %K NMR %K PXRD %K SAM %K self-assembly %K single crystal %K solid state %K syn-B18H22 %K XPS %X

The chemistry and physics of macropolyhedral B18H22 clusters have attracted significant attention due to the interesting photophysical properties of anti-B18H22 (blue emission, laser properties) and related potential applications. We have focused our attention on the “forgotten” syn-B18H22 isomer, which has received very little attention since its discovery compared to its anti-B18H22 isomer, presumably because numerous studies have reported this isomer as nonluminescent. In our study, we show that in crystalline form, syn-B18H22 exhibits blue fluorescence and becomes phosphorescent when substituted at various positions on the cluster, associated with peculiar microstructural-dependent effects. This work is a combined theoretical and experimental investigation that includes the synthesis, separation, structural characterization, and first elucidation of the photophysical properties of three different monothiol-substituted cluster isomers, [1-HS-syn-B18H21] 1, [3-HS-syn-B18H21] 3, and [4-HS-syn-B18H21] 4, of which isomers 1 and 4 have been proved to exist in two different polymorphic forms. All of these newly substituted macropolyhedral cluster derivatives (1, 3, and 4) have been fully characterized by NMR spectroscopy, mass spectrometry, single-crystal X-ray diffraction, IR spectroscopy, and luminescence spectroscopy. This study also presents the first report on the mechanochromic shift in the luminescence of a borane cluster and generally enriches the area of rather rare boron-based luminescent materials. In addition, we present the first results proving that they are useful constituents of carbon-free self-assembled monolayers.

%B Journal of the American Chemical Society %V 145 %P 17975−17986 %8 August 2, 2023 %G eng %U https://pubs.acs.org/doi/10.1021/jacs.3c05530 %& 17975 %R https://doi.org/10.1021/jacs.3c05530 %0 Journal Article %J Inorganic Chemistry %D 2022 %T Carboranethiol-Protected Propeller-Shaped Photoresponsive Silver Nanomolecule %A Arijit Jana %A Parvathy M Unnikrishnan %A Ajay K Poonia %A Jayoti Roy %A Madhuri Jash %A Ganesan Paramasivam %A Jan Machacek %A Kumaran Nair Valsala Devi Adarsh %A Tomas Base %A Thalappil Pradeep %K Ag21 %K boron %K carborane %K clusters %K double rotor %K luminescence %K silver %K thiol %X

We report the synthesis, structural characterization, and photophysical properties of a propeller-shaped Ag21 nano-molecule with six rotary arms, protected with m-carborane-9-thiol (MCT) and triphenylphosphine (TPP) ligands. Structural analysis reveals that the nanomolecule has an Ag13 central icosahedral core with six directly connected silver atoms and two more silver atoms connected through three Ag−S−Ag bridging motifs. While 12 MCT ligands protect the core through metal−thiolate bonds in a 3−6−3-layered fashion, two TPP ligands solely protect the two bridging silver atoms. Interestingly, the rotational orientation of a silver sulfide staple motif is opposite to the orientation of carborane ligands, resembling the existence of a bidirectional rotational orientation in the nanomolecule. Careful analysis reveals that the orientation of carborane ligands on the cluster’s surface resembles an assembly of double rotors. The zero circular dichroism signal indicates its achiral nature in solution. There are multiple absorption peaks in its UV−vis absorption spectrum, characteristic of a quantized electronic structure. The spectrum appears as a fingerprint for the cluster. High-resolution electrospray ionization
mass spectrometry proves the structure and composition of the nanocluster in solution, and systematic fragmentation of the molecular ion starts with the loss of surface-bound ligands with increasing collision energy. Its multiple optical absorption features are in good agreement with the theoretically calculated spectrum. The cluster shows a narrow near-IR emission at 814 nm with a Stokes shift of 355 nm. The Ag21 nanomolecule is thermally stable at ambient conditions up to 100 °C. However, white-light illumination (lamp power = 120−160 W) shows photosensitivity, and this induces structural distortion, as confirmed by changes in the Raman and electronic absorption spectra. Femtosecond and nanosecond transient absorption studies reveal an exceptionally stable excited state having a lifetime of 3.26 ± 0.02 μs for the carriers, spread over a broad wavelength region of 500−650 nm. The formation of core-centered long-lived carriers in the excited state is responsible for the observed light-activated structural distortion.

%B Inorganic Chemistry %V 61 %P 8593−8603 %8 May 27, 2022 %G eng %U https://pubs.acs.org/doi/10.1021/acs.inorgchem.2c00186 %9 Article %& 8593 %R https://doi.org/10.1021/acs.inorgchem.2c00186 %0 Journal Article %J ACS Nano %D 2021 %T Light-Activated Intercluster Conversion of an Atomically Precise Silver Nanocluster %A Arijit Jana %A Madhuri Jash %A Ajay Kumar Poonia %A Ganesan Paramasivam %A Md Rabiul Islam %A Papri Chakraborty %A Sudhadevi Antharjanam %A Jan Machacek %A Sundargopal Ghosh %A Kumaran Nair Valsala Devi Adarsh %A Tomas Base %A Thalappil Pradeep %K carboranes silver nanoclusters intercluster conversion near-infrared emission luminescence ultrafast electron dynamics %X

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.

%B ACS Nano %V 15 %P 15781-15793 %G eng %U https://pubs.acs.org/doi/abs/10.1021/acsnano.1c02602 %N 10 %9 Full Article %R https://doi.org/10.1021/acsnano.1c02602