TY - JOUR T1 - A Luminescent Cu4 Cluster Film Grown by Electrospray Deposition: A Nitroaromatic Vapour Sensor JF - Nanoscale Y1 - 2023 A1 - Arijit Jana A1 - B K Spoorthi A1 - Akhil S Nair A1 - Biswarup Pathak A1 - Tomas Base A1 - Thalappil Pradeep KW - carborane KW - Copper KW - luminescence KW - nanocluster KW - nitro organic KW - sensor AB -

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.

UR - https://pubs.rsc.org/en/content/articlelanding/2023/nr/d3nr00416c ER - TY - JOUR T1 - Macropolyhedral syn-B18H22, the “Forgotten” Isomer JF - Journal of the American Chemical Society Y1 - 2023 A1 - Deepak Kumar Patel A1 - B. S. Sooraj A1 - Kaplan Kirakci A1 - Jan Machacek A1 - Monika Kucerakova A1 - Jonathan Bould A1 - Michal Dusek A1 - Martha Frey A1 - Christof Neumann A1 - Sundargopal Ghosh A1 - Andrey Turchanin A1 - Thalappil Pradeep A1 - Tomas Base KW - boron KW - boron hydride KW - Cluster KW - luminescence KW - macropolyhedral KW - NMR KW - PXRD KW - SAM KW - self-assembly KW - single crystal KW - solid state KW - syn-B18H22 KW - XPS AB -

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.

VL - 145 UR - https://pubs.acs.org/doi/10.1021/jacs.3c05530 ER - TY - JOUR T1 - Carboranethiol-Protected Propeller-Shaped Photoresponsive Silver Nanomolecule JF - Inorganic Chemistry Y1 - 2022 A1 - Arijit Jana A1 - Parvathy M Unnikrishnan A1 - Ajay K Poonia A1 - Jayoti Roy A1 - Madhuri Jash A1 - Ganesan Paramasivam A1 - Jan Machacek A1 - Kumaran Nair Valsala Devi Adarsh A1 - Tomas Base A1 - Thalappil Pradeep KW - Ag21 KW - boron KW - carborane KW - clusters KW - double rotor KW - luminescence KW - silver KW - thiol AB -

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.

VL - 61 UR - https://pubs.acs.org/doi/10.1021/acs.inorgchem.2c00186 ER - TY - JOUR T1 - Light-Activated Intercluster Conversion of an Atomically Precise Silver Nanocluster JF - ACS Nano Y1 - 2021 A1 - Arijit Jana A1 - Madhuri Jash A1 - Ajay Kumar Poonia A1 - Ganesan Paramasivam A1 - Md Rabiul Islam A1 - Papri Chakraborty A1 - Sudhadevi Antharjanam A1 - Jan Machacek A1 - Sundargopal Ghosh A1 - Kumaran Nair Valsala Devi Adarsh A1 - Tomas Base A1 - Thalappil Pradeep KW - carboranes silver nanoclusters intercluster conversion near-infrared emission luminescence ultrafast electron dynamics AB -

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.

VL - 15 UR - https://pubs.acs.org/doi/abs/10.1021/acsnano.1c02602 IS - 10 ER -