Thiol-Modified Pyrrole Monomers:  1. Synthesis, Characterization, and Polymerization of 1-(2-Thioethyl)pyrrole and 3-(2-Thioethyl)pyrrole

Abstract

To try to solve the problem of delamination of polypyrrole from gold during electrochemical cycling, 1-(2-thioethyl)pyrrole and 3-(2-thioethyl)pyrrole were synthesized as adhesion promoters. These compounds were designed to bind to gold through the sulfur atom to form monolayers, and their alkyl chains were made short to permit electron transfer to and from the pyrrole moieties. It was hoped that during electropolymerization of unmodified pyrrole in solution, the pyrrole moieties of the monolayer would be incorporated into the growing film. In this first paper of the series, the synthesis and characterization of the monomers and their electrochemical polymerization to form thin films is presented. Nuclear magnetic resonance and infrared, Raman, UV-vis-NIR, and mass spectroscopy measurements form a basis for comparison with monolayers adsorbed on gold surfaces in the following papers.

Thioethylpyrrole Monolayers on Gold. A Spectroscopic Study in Ultrahigh Vacuum

“…The IRAS and XPS results obtained so far clearly show that intact 1-TEP layers are formed on gold regardless of preparation method provided that the layers are protected from air exposure. Deliberately air exposed 1-TEP samples exhibit CO and C−O species in the C 1s spectrum, Figure a (upper trace), which is consistent with chemical attack of oxygen at the α-carbons in the pyrrole ring. , …”

“…The IRAS spectrum was recorded in UHV with a sputter-cleaned gold sample as reference. All the strong characteristic pyrrole bands, , e.g., the pyrrole ring in-plane vibrations at 1067, 1088, 1284, and 1496 cm -1 in the transmission spectrum, are also seen in the IRAS spectrum with essentially the same relative intensities, indicating that a stable and isotropic layer of the molecule is formed. Furthermore, spectral simulations of peak intensities were used to estimate the thickness of the 1-TEP layer .…”

“…The synthesis of 1-TEP has been described earlier, but for 3-TEP a new synthetic scheme had to be developed. The processes are described in detail elsewhere . Ethanol (99.5%) was purchased from Kemetyl AB, Stockholm, and used as received.…”

Urea Biosensor Based on Conducting Polymer Transducers

“…The interaction between polymer film and underlying electronic conducting substrate is primarily hydrophobic in nature and is supported by some weak forces. Several attempts have been made to improve the adhesion of conducting polymer onto the conducting substrate for long term applications by using rough surface electrode, giving thiol modified polymer and by providing functional group over the substrate with the help of some chemical [78][79][80][81][82]. Through functional group chemistry, a stable deposition of the polymer has been achieved.…”

Novel Modified Pyrrole Monomers, 1: Synthesis and Characterization

“…Cossement and co-workers described the synthesis of 6-(pyrrol-1-yl hexyl)trimethoxysilane as well as 6-(pyrrol-1-yl hexyl)trichlorsilane and used them in surface modification of TiO 2 and ITO substrates and subsequent surface polymerization [8,9]. 2-(pyrrol-1-yl ethyl)thiol monolayers (TEP) were designed to enhance the adhesion of PPY films to the gold surface, serving as a molecular glue by attaching to gold through the thiol and covalently binding to pyrrole in solution during electrochemical growth of PPY [10,11]. The TEP monolayers are electrochemically inert after cycling or air exposure and, therefore, they did not function as intended.…”