@article {157, title = {Light-Activated Intercluster Conversion of an Atomically Precise Silver Nanocluster}, journal = {ACS Nano}, volume = {15}, year = {2021}, pages = {15781-15793}, type = {Full Article}, abstract = {

Noble metal nanoclusters protected with carboranes, a 12-vertex, nearly icosahedral boron{\textendash}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{\textendash} (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{\textendash}vis absorption spectroscopy, mass spectrometry, transmission electron microscopy, X-ray photoelectron spectroscopy, infrared spectroscopy, and multinuclear magnetic resonance spectroscopy. Multiple UV{\textendash}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 {\textdegree}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{\textendash}Ag6 core{\textendash}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{\textendash} and [Ag35(CBDT)8(TPP)4]2{\textendash} were formed after 8 h of light irradiation, and the second set comprised of [Ag30(CBDT)8(TPP)4]2{\textendash}, [Ag26(CBDT)11(TPP)4]2{\textendash}, and [Ag26(CBDT)7(TPP)7]2{\textendash} 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.

}, keywords = {carboranes silver nanoclusters intercluster conversion near-infrared emission luminescence ultrafast electron dynamics}, doi = {https://doi.org/10.1021/acsnano.1c02602}, url = {https://pubs.acs.org/doi/abs/10.1021/acsnano.1c02602}, author = {Arijit Jana and Madhuri Jash and Ajay Kumar Poonia and Ganesan Paramasivam and Md Rabiul Islam and Papri Chakraborty and Sudhadevi Antharjanam and Jan Machacek and Sundargopal Ghosh and Kumaran Nair Valsala Devi Adarsh and Tomas Base and Thalappil Pradeep} } @article {149, title = {Acid-Base Control of Valency within Carboranedithiol Self-Assembled Monolayers: Molecules Do the Can-Can}, journal = {ACS Nano}, volume = {12}, year = {2018}, month = {02/2018}, pages = {2211{\textendash}2221}, type = {Full paper}, chapter = {2211}, abstract = {

We use simple acid-base chemistry to control the valency in self-assembled monolayers of two different carboranedithiol isomers on Au{111}. Monolayer formation proceeds via Au-S bonding, where manipulation of pH prior to or during deposition enables the assembly of dithiolate species, monothiol/monothiolate species, or combination. Scanning tunneling microscopy (STM) images identify two distinct binding modes in each unmodified monolayer, where simultaneous spectroscopic imaging confirms different dipole offsets for each binding mode. Density functional theory calculations and STM image simulations yield detailed understanding of molecular chemisorption modes and their relation with the STM images, including inverted contrast with respect to the geometric differences found for one isomer. Deposition conditions are modified with controlled equivalents of either acid or base, where the coordination of the molecules in the monolayers is controlled by protonating or deprotonating the second thiol/thiolate on each molecule. This control can be exercised during deposition to change the valency of the molecules in the monolayers, a process that we affectionately refer to as the {\textquotedblleft}can-can.{\textquotedblright} This control enables us to vary the density of molecule-substrate bonds by a factor of two without changing the molecular density of the monolayer.

}, keywords = {carborane, dipoles, molecules switch, nanoscience, scanning tunneling microscopy, self-assembled monolayer, self-assembly, two dimensional}, doi = {10.1021/acsnano.7b09011}, url = {https://pubs.acs.org/doi/10.1021/acsnano.7b09011}, author = {John C Thomas and Dominic P. Goronzy and Andrew C Serino and Harsharn S Auluck and Olivia R Irving and Elisa Jimenez-Izal and Jacqueline M Deirmenjian and Jan Machacek and Philippe Sautet and Anastassia N Alexandrova and Tomas Base and Paul S Weiss} }