Single Molecular Switches:
Electrochemical Gating
of a Single Anthraquinone-Based Norbornylogous Bridge Molecule
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Abstract
Herein we report the electrochemical gating of a single
anthraquinone-based
molecule bridged between two gold electrodes using the STM break-junction
technique. Once a molecule is trapped between the STM gold tip and
the gold substrate, the potential is swept in order to alternate between
the oxidized anthraquinone (AQ) and the reduced hydroanthraquinone
(H<sub>2</sub>AQ) forms. It is shown that the conductance increases
about an order of magnitude with a net conversion from the oxidized
AQ form to the reduced H<sub>2</sub>AQ form. The results obtained
from sweeping the potential (dynamic approach) on a single molecule
are compared to those obtained from measuring the conductance at several
fixed potentials (static approach). By comparing the static and dynamic
approach, qualitative information about the kinetics of the redox
conversion was achieved. The threshold potential of the conductance
enhancement was found to shift to more negative potentials when the
potential is swept at a single molecule. This shift is attributed
to a slow redox conversion between the AQ and the H<sub>2</sub>AQ
forms. The hypothesis, of slow redox kinetics being responsible for
the observed differences in the single-molecule conductance studies,
was supported by electron transfer kinetics studies of bulk self-assembled
monolayers using both cyclic voltammetry at different sweeping rates
and electrochemical impedance spectroscopy