Abstract
Multielectron systems as possible components of molecular electronics devices are attracting compelling experimental and theoretical interest. Here we studied by electrochemical scanning tunneling techniques (EC-STMicroscopy and EC-STSpectroscopy) the electron transport properties of a redox molecule endowed with two redox levels, namely, the hydroquinone/quinone (H2Q/Q) couple. By forming self-assembled monolayers on Au(111) of oligo-phenylene-vinylene (OPV) derivatized H2Q/Q moieties, we were able to explore the features of the tunneling current/overpotential relation in the EC-STS setup. The behavior of the tunneling current sheds light onto the mechanism of electron transport involving the redox levels of the H2Q/Q redox pair coupled to tip and substrate electrodes.
Highlights
The exploitation of single molecules or single monomolecular layers as active elements of electronic circuits is the main goal of molecular electronics.[1,2] Single molecules can act as switches or rectifiers or can show features of negative differential conductance.[3,4] Most importantly, their properties could be designed, by synthetic chemistry, to meet the desired requirements.[5]
Many theoretical and experimental efforts have been devoted to studying the electron transport process in redox active molecules connecting two metal electrodes in the electrochemical scanning tunneling microscope setup.8À15 The scanning tunneling microscope offers the possibility of combining imaging with spectroscopic analysis of single molecules
We have studied the current/overpotential characteristics for the hydroquinone/quinone redox couple tethered to a Au(111) substrate in an electrochemical scanning tunneling microscopy (EC-STM) configuration.[17]
Summary
The exploitation of single molecules or single monomolecular layers as active elements of electronic circuits is the main goal of molecular electronics.[1,2] Single molecules can act as switches or rectifiers or can show features of negative differential conductance.[3,4] Most importantly, their properties could be designed, by synthetic chemistry, to meet the desired requirements.[5]. The new molecule should show a decreased separation between the two current enhancement regions with respect to the previous molecule This condition should allow us to test the coulomb blockade hypothesis and, at the same time, some predictions of theories developed for the interfacial electron transfer mechanism involving multiple redox levels.[22,23] In particular, a small separation between the peaks would permit us to study the features of the tunneling current/ overpotential relation for a bias voltage larger than peak separation. This investigation would shed further light on the electron transfer mechanism involved in the system at issue
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