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

• Published in: Langmuir Vol. 14; no. 11; pp. 2984 - 2995
• Main Authors: Smela, Elisabeth, Kariis, Hans, Yang, Zhongping, Mecklenburg, Michael, Liedberg, Bo
• Format: Journal Article
• Language: English
• Published: Washington, DC American Chemical Society 26.05.1998
• Subjects: Chemistry; Exact sciences and technology; General and physical chemistry; Solid-liquid interface; Surface physical chemistry; Reaction intermediate; Infrared spectrometry; Monolayer; Five membered ring; Liquid solid interface; Surface reaction; Nitrogen heterocycle; Oxidation; Chronoamperometry; Experimental study; Electrochemical reaction; Organic radical cation
• ISSN: 0743-7463; 1520-5827
• DOI: 10.1021/la970862m

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.