ABSTRACT
The novel azothiophene derivatives [AT-di(CnSAc) (n=6 and 12)], an azo linkage (N=N) that bridges one phenyl ring with an N-bridging dialkylthioacetate tail and one thiophene ring, are synthesized and characterized. The azothiophene derivatives substituted with electron-withdrawing groups are blue in color, exhibit a bathochromic shift of a longer wavelength, and are electrochemically active. The formation and characterization of AT-di(CnSAc) SAMs with a bidentate tail group of the N-bridging dialkylthioacetate have been studied by surface sensitive techniques such as grazing angle Fourier transform infrared (FT-IR), a quartz crystal microbalance (QCM), spectroscopic ellipsometry, X-ray photoelectron spectroscopy (XPS), and cyclic voltammetry (CV). It has been shown that the adsorption reaction of the thioacetate group is almost spontaneous and the N-bridging dialkylthioacetate SAMs with longer methylene length have a packing density higher than that with a shorter methylene length. However, the sulfur tethers of the N-bridging dialkylthioacetate show incomplete binding of sulfur atoms in AT-di(CnSAc) SAMs.
Subject(s)
Coloring Agents/chemistry , Gold/chemistry , Thiophenes/chemistry , Adsorption , Binding Sites , Buffers , Electrochemistry , Kinetics , Models, Molecular , Molecular Conformation , Oxidation-Reduction , Spectroscopy, Fourier Transform Infrared , Spectrum Analysis , Sulfhydryl Compounds/chemistry , Sulfur/chemistry , WettabilityABSTRACT
Recently, it has become increasingly important to control molecular layers, especially with regard to the formation of bilayers, in order to avoid electrical shorts in molecular electronics. In this paper, we report on the characterization of an in situ thiol-terminated bilayer that is formed by hydrogen bonding between the amine group of an aminoalkanethiol monolayer on a gold surface and the free amine group of aminoalkanethiolates in a bulk solution. We also report on the use of a rose bengal (RB) monolayer on a thiol-terminated bilayer for the purpose of application in a molecular memory device. Using surface-sensitive techniques such as grazing angle Fourier transform infrared (FT-IR) spectroscopy, quartz crystal microbalance (QCM) measurement, ellipsometry, X-ray photoelectron spectroscopy (XPS), and cyclic voltammetry (CV), we characterized a thiol-terminated bilayer (TUA-AUT) and an RB functionalized monolayer on a bilayered surface (RB-TUA-AUT). For a control experiment, we prepared a single RB monolayer attached by an ethanethiol group to a gold surface. In order to assess the feasibility of the present approach with respect to application in molecular electronics, we tested the switching property of the self-assembled monolayers (SAMs) using conducting-probe atomic force microscopy (CP-AFM). The RB monolayer on the bilayered surface exhibited hysteresis, while a single RB monolayer gave an electrical short.
