## 3 Results and Discussion
### Electrochemical Polymerization and Polymer Characterization  
Electrochemical polymerization of **2**, **3**, and **5-ET** was performed on a Pt disk as a working electrode by cyclic voltammetry (Figure 4), as well as, when successful, by chronoamperometry on a 2 \(\times\) 10\({}^{-3}\) M solution of each monomer in CH\({}_{2}\)Cl\({}_{2}\)/TEAPF\({}_{6}\). The potentiodynamic polymerization of terthiophene **2** by cycling the potential between 0 and 1.3 V evidences an increase in the current intensity when increasing the scan number. After 10 scans, a homogeneous deep-red polymer film was observed on the electrode surface. A film of poly-**2** obtained by potentiostatic polymerization proved to be scarcely stable on the electrode surface, maybe due to the absorption/desorption processes mentioned in the previous section, as well as to a possible partial solubility of low-molecular-weight oligomer species. The polymerization behavior of the Br-derivative **3** was similar to the unsubstituted terthiophene **2**, and a red polymer film of poly-**3** was obtained only by cyclic voltammetry, whereas the potentiodynamic polymerization was unsuccessful. Lastly, the polymer form of 5-ethyl-terthiophene (poly-**5-ET**) was initially obtained by cyclic voltammetry, scanning the potential from 0 and +1.25 V for 10 cycles. The potentiostatic approach was also successful in the polymerization of **5-ET**, being performed  
Figure 4: Cyclic voltammetry polymerization of **2** (a), **3** (b) and 5\(-\)ET (c) on a Pt disk electrode in CH\({}_{2}\)Cl\({}_{2}\)/TEAPF\({}_{6}\) 0.1 M solvent system. Potential scan rate: 100 mV s\({}^{-1}\). Figure 3: Energy surfaces as function of dihedral angles in 2,2,2,5,2,  
at +1.12 V for 300 s, then neutralizing the film at 0 V for 60 s. In both cases, a stable brown-red film of poly-**5-ET** formed on the electrode surface. To compare the electrochemical behavior of the polymer species here reported and poly-**3'-ET**[22], the voltammetric characterization of poly-**2**, poly-**3** and poly-**5-ET** was performed in CH\({}_{3}\)CN/TEAPF\({}_{6}\) 0.1 M solution (Figure 5 and Table 4). The voltammetric response of poly-**2** shows a doping/de-doping process at +1.26/0.57 V. The sharp shape of the anodic peak, quite unusual for a conducting polymer, is commonly ascribed to a narrow distribution of molecular weights along the polymer chains, leading to a harder oxidation process and to less conductive polymers [25]. On the following scans, the doping peak shifts to +1.1 V and becomes broader, suggesting a rearrangement of the polymer chains with different internal interactions. The voltammetric behavior of poly-**3** is similar to poly-**2**, showing a sharp doping at 1.24 V, with a double-step de-doping at +1.03 V and +0.80 V. In the case of the polymer form of Br-terthiophene, besides the narrow molecular weight distribution (attributed to the high conjugation of terthiophene monomer), the C-5 position is not available to the growth of the polymer chain due to the presence of -Br, hence reasonably only dimer species are formed. Both poly-**2** and poly-**3** show a cathodic process at -1.44 and -1.48 V, respectively, associated to the n-doping process on the polymer chain. The voltammetric response of poly-**5-ET** evidences a significative lowering in the potential value of the doping/de-doping process, that appears at +1.05/+0.87 V. Furthermore, a pre-peak at +0.5 V is visible, maybe due to charge trapping phenomena [22]. The cathodic scan shows a sharp peak at -1.39 V and a second, broad at -1.68 V, suggesting the presence of charge trapping processes also in the negative section of the potential window. UV-Vis characterization of neutral polymers (Table 4 and Figure 6) was performed on films grown on ITO as a working electrode. The spectra of poly-**2** and poly-**3** show three broad absorption bands between 600 and 450 nm ascribed to short-chain oligomers, and a transition around 360 nm due to the unreacted monomer.