Carboranedithiols: building blocks for self-assembled monolayers on copper surfaces

Macropolyhedral syn-B18H22, the "Forgotten" Isomer

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.

Acid-Base Control of Valency within Carboranedithiol Self-Assembled Monolayers: Molecules Do the Can-Can

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 2 without changing the molecular density of the monolayer.

From boron clusters to gold clusters: new label-free colorimetric sensors

Based on boron clusters, AuNPs were successfully prepared and exhibited high performance in phase transfer and heavy-metal ion sensing.

Carboranes in the chemist's toolbox

Once seldom encountered outside of a few laboratories, carboranes are now everywhere, playing a role in the development of a broad range of technologies encompassing organic synthesis, radionuclide handling, drug design, heat-resistant polymers, cancer therapy, nanomaterials, catalysis, metal-organic frameworks, molecular machines, batteries, electronic devices, and more. This perspective highlights selected examples in which the special attributes of carboranes and metallacarboranes are being exploited for targeted purposes in the laboratory and in the wider world.

Versatile matrix for constructing enzyme-based biosensors

A versatile matrix was fabricated and utilized as a universal interface for the construction of enzyme-based biosensors. This matrix was formed on the gold electrode via combining self-assembled monolayer of 2,3-dimercaptosuccinic acid with gold nanoparticles. Gold nanoparticles were electrochemically deposited. Electrochemistry of three redox enzymes (catalase, glucose oxidase, and horseradish peroxidase) was investigated on such a matrix. The electrocatalytic monitoring of hydrogen peroxide and glucose was conducted on this matrix after being coated with those enzymes. On them the monitoring of hydrogen peroxide and glucose shows rapid response times, wide linear working ranges, low detection limits, and high enzymatic affinities. This matrix is thus a versatile and suitable platform to develop highly sensitive enzyme-based biosensors.

Interface control in organic electronics using mixed monolayers of carboranethiol isomers

We employ mixed self-assembled monolayers of carboranethiols to alter the work function of gold and silver systematically. We use isomers of symmetric carboranethiol cage molecules to vary molecular dipole moments and directions, which enable work function tunability over a wide range with minimal alterations in surface energy. Mixed monolayers of carboranethiol isomers provide an ideal platform for the study and fabrication of solution-processed organic field-effect transistors; improved device performance is demonstrated by interface engineering.