Electrochemical Write and Read Functionality through
Oxidative Dimerization of Spiropyran Self-Assembled Monolayers on
Gold
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Abstract
In contrast to their photochromism,
the electrochemistry of spiropyrans
in self-assembled monolayers has attracted only modest attention in
recent years. In this contribution the electrochemical oxidation of
self-assembled monolayers (SAMs) of 6-nitro-BIPS spiropyran (SP) prepared
on polycrystalline gold surfaces is described. The SAMs were characterized
with cyclic voltammetry, X-ray photoelectron spectroscopy (XPS), surface-enhanced
Raman scattering (SERS), and UV/vis absorption spectroelectrochemistry.
The electrochemical oxidation of spiropyrans in solution results in
aryl C–C coupling of the indole units and thereby the formation
of a symmetric spiropyran dimer. Comparison of spectroscopic data
obtained for electrochemically oxidized spiropyran dimers in solution
with data from monolayers confirms that a similar oxidative coupling
occurs in the SAMs on gold also. The dimer formed can be oxidized
electrochemically to monocationic and dicationic states and shows
remarkably good stability in UHV and ambient conditions in all three
redox states. In addition, the dimerized spiropyran self-assembled
monolayer show photochromism, which was characterized by XPS and SERS
spectroscopy