Thiol-Modified Pyrrole Monomers:  3. Electrochemistry of 1-(2-Thioethyl)pyrrole and 3-(2-Thioethyl)pyrrole Monolayers in Propylene Carbonate

Abstract

The electrochemical oxidation of 1-(2-thioethyl)pyrrole (1-TEP) and 3-(2-thioethyl)pyrrole (3-TEP) monolayers on gold was studied. Their cyclic voltammograms were different, with, for example, 1-TEP having three oxidation peaks and 3-TEP just one. Moreover, the cyclic voltammetry of both TEP monolayers was unusual and did not follow the expected behavior for simple electron transfer from an adsorbed monolayer. The chronoamperometry for 1-TEP was also surprising, showing nucleation-like peaks; this was not seen for 3-TEP. Air exposure left the 1-TEP, but not the 3-TEP, surface electrochemically inert. Spectroscopic data on the oxidation products of surface-bound pyrroles are presented for the first time. IRAS, XPS, and UV-vis-NIR showed that, after electrochemical cycling, all the pyrrole rings were absent. This demonstration that the molecules decompose calls into question the generality of the grafting mechanism of adhesion promotion for this type of compound.

Electrochemical Formation of a Polyaniline-Analogue Monolayer on a Gold Electrode

“…0.6 V for all cases, and the first cycle of the potential scan gave especially remarkable currents as given by broken curves. Successive second and third cycles caused a decrease in anodic currents and an appearance of anodic and cathodic waves at potentials ranging between 0.4 and 0.6 V. If the same experiment was made by using a naked Au electrode, any significant increase in oxidation currents was not observed at the potential range given in Figure , but a small undulation of the base currents appeared as for the case of Au in an electrolyte solution of propylene carbonate 17b were ascribed to redox reaction of the surface-confined species or effects of the electrode substrate.…”

“…A self-assembled monolayer (SAM) of alkanethiol provides a convenient way to attach special functions to the electrode substrates such as Au, Ag, and Cu. − Especially much attention has been paid to attachment of redox activities to the electrodes − and fabrication of electrode surfaces allowing control of electrochemical reactions such as deposition of conducting polymers. − As recognized from these studies, SAMs can be electrochemically utilized, but the potential window where the SAM-coated electrodes are useful is limited by oxidative or reductive desorption of thiols. ,− Crooks et al recently reported that photopolymerized SAM made of thiols having diacetylene groups was very durable against desorption, suggesting that the polymerization of the SAM provides reinforcement of durability of the SAM. Polymerization of SAMs was also attempted by McCarley et al, Collard et al, and Smela et al with the use of alkylthiols having pyrrole units. Nonaka et al reported that a SAM of o -aminobenzenethiol could be polymerized by electrochemical oxidation if the SAM was formed on a poly-Au substrate under ultrasonic irradiation.…”

Significant Enhancement of PEDOT Thin Film Adhesion to Inorganic Solid Substrates with EDOT-Acid

“…18 Smela reported the use of thiol-modified pyrrole derivatives to increase the adhesion of polypyrrole coatings on gold. 19,20 Jerome et al enhanced the adhesion of polypyrrole via copolymerizing polypyrrole with other polymers that can be grafted onto metal surfaces. 21 However, only a few studies have investigated the adhesion and mechanical stabillity of PEDOT coatings.…”

Electrochemical deposition of conductive and adhesive polypyrrole-dopamine films

“…However, the adhesion of PPY coatings on electrode surfaces is poor due to the lack of strong molecular interactions between PPY and the electrode, which greatly hinders the practical applications of PPY-based electrode modification 10 . Many researchers have attempted to improve the adhesion and electrical properties of PPY films with various approaches, such as pre-treating electrodes 11 12 13 , selecting proper polymerizing solvents 14 15 , introducing interfacial adhesive layers 16 , and modifying the pyrrole derivatives 17 18 19 20 . However, the majority of attempts caused several critical issues, such as insufficient improvement in the mechanical adhesion of the PPY film 21 , preparation difficulties 22 , or severe impairment of the electrical performance of the electrodes 23 .…”