4H-cyclopenta[3,2-b]dithiophene (CPDT): a useful model for the study of conducting polymers via electrochemical impedance spectroscopy

Research in the field of conducting organic polymers is currently attracting increasing attention, since these innovative smart materials are very promising for applications in different fields, from energetics to electronics and sensoristics. We have devoted special interest to the study of thiophene-based materials, paying attention, in particular, to the relationships between chemical structure and electronic properties. Relevant results in this field can be successfully achieved with a systematic characterization of the materials through a combination of voltammetric and electrochemical impedance spectroscopy (EIS) techniques. EIS, in particular, is fundamental for clarifying the conductive behavior, both electronic and ionic, of films of electroactive materials. In this frame, we are developing a systematic investigation of the role played by different experimental parameters on the charge transport mechanism in polythiophene-based systems, using the cyclopentadithiophene (CPDT) as the model monomer (see figure). There are two main reasons for this choice: CPDT molecule is planar and electronic conjugation is, by consequence, higher than that displayed by analogous compounds based on 2,2’-bithiophene. Furthermore, the C2v symmetry makes homotopic the two thiophene α-positions in CPDT, in the olygomers and in the polymers, thus assuring a full regioregularity to the materials resulting from the electroxidation process. The results of the EIS investigation on poly-CPDT will be presented, focusing attention in particular onto the effects i) of an increasing thickness of the film, ii) of the different applied potentials and iii) of the addition of redox mediators (ferrocene and decamethylferrocene) to the working medium.