%0 Journal Article %J Chemistry of Materials %D 2020 %T Influence of Terminal Carboxyl Group on Structure and Reactivity of Functionalized m-Carboranethiolate Self-Assembled Monolayers %A Dominic P Goronzy %A Jan Stanek %A Erin Avery %A Han Guo %A Zdenek Bastl %A Michal Dusek %A Nathan M Gallup %A Saliha Gun %A Monika Kucerakova %A Brian J Levandowski %A Jan Machacek %A Vaclav Sicha %A John C Thomas %A Adem Yavuz %A K N Houk %A M Fatih Danisman %A Ersen Mete %A Anastassia N Alexandrova %A Tomas Base %A Paul S Weiss %K acidity %K carborane %K carboxyl %K monolayer %K SAM %K self-assembly %X

The structure and function of self-assembled monolayers (SAMs) at the nanoscale are determined by the steric and electronic effects of their building blocks. Carboranethiol molecules form pristine monolayers that provide tunable two-dimensional systems to probe lateral and interfacial interactions. Additional ω-functionality, such as carboxyl groups, can be introduced to change the properties of the exposed surfaces. Here, two geometrically similar isomeric m-carborane analogs of m-mercaptobenzoic acid, 1 COOH-7-SH-1,7-C2B10H10 and racem-1-COOH-9-SH-1,7-C2B10H10, are characterized and their SAMs on Au{111} are examined. The latter isomer belongs to the rare group of chiral cage molecules and becomes, to our knowledge, the first example assembled on Au{111}. Although different in symmetry, molecules of both isomers assemble into similar hexagonal surface patterns. The nearest neighbor spacing of 8.4 ± 0.4 Å is larger than that of non-carboxylated isomers, consistent with the increased steric demands of the carboxyl groups. Computational modeling reproduced this spacing and suggests a tilt relative to the surface normal. However, tilt domains are not observed experimentally, suggesting the presence of strong lateral interactions. Analyses of the influence of the functional groups through the pseudo-aromatic m carborane skeleton showed that the thiol group attached to either carbon or boron atoms increases the carboxyl group acidity in solution. In contrast, the acidity of the exposed carboxyl group in the SAMs decreases upon surface attachment; computational analyses suggest that the driving force of this shift is the dielectric of the environment in the monolayer as a result of confined intermolecular interactions, proximity to the Au surface, and partial desolvation.

%B Chemistry of Materials %V 32 %P 6800−6809 %8 07/2020 %G eng %U https://pubs.acs.org/doi/10.1021/acs.chemmater.0c02722 %9 Article %& 6800 %R https://doi.org/10.1021/acs.chemmater.0c02722 %0 Journal Article %J J. Phys. Chem. C %D 2019 %T Formation of Highly Ordered Terminal Alkyne Self-Assembled Monolayers on the Au{111} Surface through Substitution of 1-Decaboranethiolate %A Shenkai Wang %A Dominic P Goronzy %A Thomas D Young %A Natcha Wattanatorn %A Logan Stewart %A Tomas Base %A Paul S Weiss %K alkyne %K decaborane %K gold %K self-assembly %K surface %K thiol %X

The reaction aimed at completing and closing the open cages of 1-decaboranethiol self-assembled monolayers (SAMs) on Au{111} with 4-phenyl-1-butyne results in highly ordered monolayers of 4-phenyl-1-butyne. The initially disordered 1-decaboranethiolate changed into ordered (√3×√3)R 30° lattices on Au{111} typical of alkyne SAMs, indicating the complete substitution of 1-decaboranethiolate moieties, as determined by nanoscale imaging with scanning tunneling microscopy and X-ray photoelectron spectroscopy. Vibrational spectroscopy results indicate that the process happens gradually and that alkynyl groups are not totally oxidized in the ordered 4-phenyl-1-butyne monolayer.

%B J. Phys. Chem. C %V 123 %P 1348–1353 %G eng %U https://pubs.acs.org/doi/10.1021/acs.jpcc.8b11033 %N 2 %R 10.1021/acs.jpcc.8b11033 %0 Journal Article %J ACS Nano %D 2018 %T Acid-Base Control of Valency within Carboranedithiol Self-Assembled Monolayers: Molecules Do the Can-Can %A John C Thomas %A Dominic P. Goronzy %A Andrew C Serino %A Harsharn S Auluck %A Olivia R Irving %A Elisa Jimenez-Izal %A Jacqueline M Deirmenjian %A Jan Machacek %A Philippe Sautet %A Anastassia N Alexandrova %A Tomas Base %A Paul S Weiss %K carborane %K dipoles %K molecules switch %K nanoscience %K scanning tunneling microscopy %K self-assembled monolayer %K self-assembly %K two dimensional %X

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 “can-can.” 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.

%B ACS Nano %G eng %U https://pubs.acs.org/doi/10.1021/acsnano.7b09011 %9 Full paper %R 10.1021/acsnano.7b09011 %0 Journal Article %J JACS %D 2016 %T Surface Dipole Control of Liquid Crystal Alignment %A Jeffrey J Schwartz %A Alexandra M. Mendoza %A Natcha Wattanatorn %A Yuxi Zhao %A Vinh T Nguyen %A Alexander M Spokoyny %A Chad A Mirkin %A Tomas Base %A Paul S Weiss %K carborane %K Dipole %K liquid crystal %K surface %X

Detailed understanding and control of the intermolecular forces that govern molecular assembly are necessary to engineer structure and function at the nanoscale. Liquid crystal (LC) assembly is exceptionally sensitive to surface properties, capable of transducing nanoscale intermolecular interactions into a macroscopic optical readout. Self-assembled monolayers (SAMs) modify surface interactions and are known to influence LC alignment. Here, we exploit the different dipole magnitudes and orientations of carboranethiol and dithiol positional isomers to deconvolve the influence of SAM-LC dipolar coupling from variations in molecular geometry, tilt, and order. Director orientations and anchoring energies are measured for LC cells employing various carboranethiol and dithiol isomer alignment layers. The normal component of the molecular dipole in the SAM, toward or away from the underlying substrate, was found to determine the in-plane LC director orientation relative to the anisotropy axis of the surface. By using LC alignment as a probe of interaction strength, we elucidate the role of dipolar coupling of molecular monolayers to their environment in determining molecular orientations. We apply this understanding to advance the engineering of molecular interactions at the nanoscale.

%B JACS %V 138 %P 5957-5967 %8 April 19, 2016 %G eng %U http://pubs.acs.org/doi/abs/10.1021/jacs.6b02026 %N 18 %& 5957 %R 10.1021/jacs.6b02026 %0 Journal Article %J Chemistry of Materials %D 2015 %T Self-Assembled p-Carborane Analog of p-Mercaptobenzoic Acid on Au{111} %A John C Thomas %A Ishtvan Boldog %A Harsharn S Auluck %A Pablo J Bereciartua %A Michal Dusek %A Jan Machacek %A Zdenek Bastl %A Paul S Weiss %A Tomas Base %K boron compounds %K carborane %K crystallography %K scanning tunneling microscopy %K self-assembly %X

Thep-carborane cluster analog of p-mercaptobenzoic acid, 1

%B Chemistry of Materials %8 06/2015 %G eng %U http://pubs.acs.org/doi/pdf/10.1021/acs.chemmater.5b02263 %9 Article %R 10.1021/acs.chemmater.5b02263