## 3 Results and Discussion
### Characterization of Monomers  
The electrochemical behavior of 2.2\({}^{\prime}\):5\({}^{\prime}\),2\({}^{\prime\prime}\)-terthiophene (**2**), 5-bromo-2,2\({}^{\prime}\):5\({}^{\prime}\),2\({}^{\prime\prime}\)-terthiophene (**3**), and 5-ethynyl-2,2\({}^{\prime}\):5\({}^{\prime}\),2\({}^{\prime\prime}\)-terthiophene (**5-ET**) was investigated by cyclic voltammetry both in CH\({}_{2}\)Cl\({}_{2}\) and in CH\({}_{3}\)CN as solvent, using 0.1 M TEAPF\({}_{6}\) as the supporting electrolyte. The cyclic voltammetry response of **2** in CH\({}_{2}\)Cl\({}_{2}\) (Figure 2a) shows a two-step anodic process, located at +1.13 V and at +1.18 V, with an associated process in the backward scan at +0.64 V. Both the second anodic process and the backward one evidence a sharp shape, suggesting adsorbing/desorbing phenomena on the electrode surface, according to investigations in different experimental conditions reported previously [25,44]. Using CH\({}_{3}\)CN as solvent in electrochemical investigations, a similar behavior is observed, with a double anodic system at lower potential values than in CH\({}_{2}\)Cl\({}_{2}\) (+1.05 and +1.09 V) and an associated backward peak (+0.82 V), the shape of the more anodic peak being reasonably attributed to the occurrence of absorptions (and corresponding desorptions) of oligomeric species on the electrode surface. The presence of an electron-withdrawing -Br substituent on the C-5 position (compound **3**) causes a shift of the process towards more anodic values, both in CH\({}_{2}\)Cl\({}_{2}\) and on CH\({}_{3}\)CN solvents. In particular, an anodic peak at +1.21 V (with an associated backward process at about +0.7 V), followed by a shoulder at 1.35 V is observed in CH\({}_{2}\)Cl\({}_{2}\) (Figure 2b). The voltammetric response in CH\({}_{3}\)CN again shows two anodic processes (+1.13 and +1.23 V, respectively), where the second one increases in current intensity at subsequent scans. The behavior of compound **5-ET**, where an ethynyl substituent is present in place of -Br, evidences a single anodic process at +1.15 V, with a backward associated signal at +0.73 V in CH\({}_{2}\)Cl\({}_{2}\) (Figure 2c). Changing the solvent to CH\({}_{3}\)CN, an anodic process at +1.12 V is observed. Electrochemical data of **2**, **3**, and **5-ET** are reported in Table 1, as well as 3\({}^{\prime}\)-ethynyl-2,2\({}^{\prime}\):5\({}^{\prime}\),2\({}^{\prime\prime}\)-terthiophene (**3\({}^{\prime}\)-ET**, [22]) as a comparison, where the ethynyl substituent is on the central ring of the terthiophene structure rather than on a peripheral ring. HOMO values were referred to the CH\({}_{3}\)CN solutions according to the analogous evaluation on the corresponding polymer species (Section 3.3). Table 1 evidences that an ethynyl substituent on the central ring makes the terthiophene structure more stable, whereas (Br- or ethynyl-) functionalization on the external ring does not meaningfully influence the voltammetric parameters and the corresponding HOMO values. Compounds **2**, **3**, and **5-ET** were also investigated by UV-Vis spectroscopy, both in CH\({}_{2}\)Cl\({}_{2}\) and CH\({}_{3}\)CN, and spectroscopic data were again compared to **3\({}^{\prime}\)-ET**. In all cases, \(\lambda_{\rm max}\) values are always in the range 340-390 nm, and are ascribed to \(\pi\)-\(\pi^{\rm e}\) transitions on the terthiophene [44; 45], as confirmed by theoretical calculations (Table 2).