## 1 Introduction  
Conducting polymers (CPs) are a well-known, wide class of compounds where the structural flexibility and the mechanical properties of \"classical\" polymers are coupled to the electronic and optical properties typical of inorganic semi-conductors. Since the Nobel Prize that was awarded to [PERSON], [PERSON], and [PERSON] in 2000, CPs have received a large attention from the scientific community due to their possible application in different technological fields such as sensors [1, 2, 3, 4, 5, 6], photosensitive and electrochromic devices [7, 8, 9, 10, 11, 12, 13], rechargeable batteries [14, 15, 16], corrosion protection [17, 18, 19], and biomedicine [20, 21]. In this context, polythiophenes (PTs) are especially appealing because of their structural versatility, as well as their environmental and thermal stability in the doped and undoped states, moderate band gap values, ease in p- and n-doping, and high conductivity [22]. CPs, including PTs, are often successfully achieved by electrochemical polymerization, with some interesting advantages to this methodology compared to the classical synthetic approach. The electrochemical synthesis of a conducting polymer allows for obtaining a polymer film on an electrode surface, tuning the thickness by the deposition charge, and monitoring the growth process by electrochemical or spectroelectrochemical techniques. Furthermore, the CP-modified electrode surface can be directly used in some specific applications, as in the case of sensors. Additionally, the electro-generated polymer can be firstly characterized on the same electrode surface where it is grown [23]. The features of the film can be controlled through an appropriate selection of the experimental conditions, namely electrode material, monomer concentration, solvent and supporting electrolyte, temperature, pH (in case of aqueous solutions), and the electrochemical technique of deposition. From a general point of view, the electrical and optical properties of PTs are due to the extended charge delocalization along the polymer backbone as a consequence of the overlapping of the \(\pi\) orbital of the thiophene rings, which tend to be coplanar. On the other hand, the rigidity of the structure causes insolubility of unsubstituted PTs, making their chemical characterization difficult. The insertion of flexible chains as substituents on the polymer skeleton increases the solubility of PTs but produces a twisting in the structure, and consequent changes in the properties of the polymer [24]. Furthermore, the presence of substituents in the \(\beta\) position of the heterocyclic ring facilitates \(\alpha\)-\(\alpha\) couplings rather than the \(\alpha\)-\(\beta\), leading mostly to stereoregular chains. In order to promote \(\alpha\)-\(\alpha\) couplings, as well as to reduce the value of the potential in electrochemical polymerization of thiophenes, chemically synthetized oligomers can be used as starting materials [25; 26]. A combination of all these aspects influences the mean effective conjugation length of the polymer chain and, consequently, its band gap energy and conductivity values. However, the effect of using monomers/oligomers as starting materials on the properties of the electrogenerated conducting polymers is not totally defined. In 1986, [PERSON] et al. [25] proved that polythiophenes obtained by mono-, bi- and ter-thiophene showed an increasing doping potential moving from poly (thiophene) to poly (terthiophene), suggesting a decrease of the mean conjugation length when increasing the number of heterocyclic rings in the relative oligomer. On the other hand, [PERSON] and [PERSON] [26] reported that polythiophenes obtained from bi- and ter-thiophene showed comparable conductivity, whereas the polymer obtained by thiophene monomer showed lower conductivity values, maybe because of overoxidation processes that generate degradation phenomena.