What Happens to the Thiolates
Created by Reductively
Desorbing SAMs? An in Situ Study Using Fluorescence Microscopy and
Electrochemistry
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Abstract
In situ examination of the reductive desorption process
for Au
microelectrodes modified with a thiol self-assembled monolayer (SAM)
using fluorescence microscopy enabled the study of the fate of the
desorbed thiolate species. The Bodipy labeled alkyl-thiol SAM, when
adsorbed, is not fluorescent due to quenching by the Au surface. Once
reductively desorbed, the thiolate molecules fluoresce and their direction
and speed are monitored. At moderately negative reduction potentials,
the thiolate species hemispherically diffuse away from the microelectrode.
Also observed is the influence of a closely positioned counter electrode
on the direction of the desorbed thiolate movement. As the potential
becomes more negative, the molecules move in an upward direction,
with a speed that depends on the amount of dissolved H<sub>2</sub> produced by water reduction. Shown is that this motion is controlled,
in large part, by the change in the electrolyte density near the electrode
due to dissolved H<sub>2</sub>. These results should help in explaining
the extent of readsorption at oxidative potentials observed in cyclic
voltammetry (CV) reductive desorption measurements, as well as improving
the general understanding of the SAM removal process by reductive
desorption. The electrogenerated H<sub>2</sub> was also shown to be
able to reductively remove the thiol SAM from the Pt/Ir particles
that decorate the microelectrode glass sheath