Electrochemical impendance spectroscopy: a useful tool to study conducting polymers and the electroreductive cleavage of carbon-halogen bond

The electrochemical impedance spectroscopy (EIS) is a powerful and polyhedral technique that can find application in many fields of scientific research; actually it can be exploited for the study of practically any kind of electron transfer process. Considering the EIS potentialities we employed the technique in two quite different fields: the characterization of conducting organic polymers and the mechanistic study of the electroreductive cleavage of carbon-halogen (C-X) bonds in non-catalytic and catalytic conditions. We will present the main results of the thesis project. The work focused on the conducting polymers was structured as follows: i) a preliminary study focused on poly(4H-cyclopenta[3,2-b]dithiophene), poly-CPDT, chosen as a conducting polymer model which made us able to understand the behavior of these materials in different experimental conditions (see figure); ii) the study of a very promising class of inherently chiral conducting polymers with a particular attention to electrodeposited oligomeric films of 2,2’-bis(2,2’-bithiophen-5- yl)-3,3’-bi-1-benzothiophene, applying EIS (in combination with cyclic voltammetry, CV) in order to prove the enantiorecognition capability of its enantiopure films. A further investigation was aimed to test EIS as an auxiliary and/or complementary technique to CV in mechanistic electron transfer studies, applying it, for the first time, to the investigation of the electroreductive cleavage of C-X bond in a series of aromatic and heteroaromatic organic bromides, on non-catalytic GC, moderately catalytic Au, and highly catalytic Ag electrode. EIS very nicely and neatly accounted for the “orientation effect” of bromo-thiophenes on gold electrode surfaces by the anchoring sulphur atom, affording to monitor the variation of the charge transfer resistance for the C-Br bond cleavage on two ad-hoc chosen constitutional isomers (see figure).