TY - JOUR T1 - Acid-Base Control of Valency within Carboranedithiol Self-Assembled Monolayers: Molecules Do the Can-Can JF - ACS Nano Y1 - 2018 A1 - John C Thomas A1 - Dominic P. Goronzy A1 - Andrew C Serino A1 - Harsharn S Auluck A1 - Olivia R Irving A1 - Elisa Jimenez-Izal A1 - Jacqueline M Deirmenjian A1 - Jan Machacek A1 - Philippe Sautet A1 - Anastassia N Alexandrova A1 - Tomas Base A1 - Paul S Weiss KW - carborane KW - dipoles KW - molecules switch KW - nanoscience KW - scanning tunneling microscopy KW - self-assembled monolayer KW - self-assembly KW - two dimensional AB -

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.

UR - https://pubs.acs.org/doi/10.1021/acsnano.7b09011 ER -