**4.2 Extension to the use of other spacers**

As previously said, this second method of electropolymerization allows to avoid the synthesis of the monomeric substituted porphyrin (ZnOEP(bpy)+ for example). Thus, this new way of electropolymerization more conveniently allows the use of the commercial free base porphyrin (H2OEP) or metalloporphyrins (MOEP) with different central metals (M = CoII, MgII, NiII, RuII(CO)…) (Giraudeau et al., 2010). For all of them, an electropolymerization process has been observed, even when porphyrins with oxidable central metal (CoOEP and NiOEP) have been used. Consequently, further applications could be envisaged. For example, polymer with CoOEP could be promising for dioxygen reduction, cobalt porphyrins being known to catalyze this reaction (Chen et al., 2010; Collman et al., 1980).

Moreover, it is also possible to modulate easily the nature of the bridging spacers between the porphyrin macrocycles. Indeed, instead of using free bpy, this process of electropolymerization can be extended to other spacers by varying the nature of the nucleophile, since each compound having two pendant pyridyl groups can be used as spacer. The spacers can be selected for their specific chemical and structural properties: rigid or not; long or short; electron conducting or not; electroreducible or not; with conjugated π bonds (aromatic/alkene/alkyne chains) or successive σ bonds (alkyl chains)… For instance, electropolymerization has been successfully carried out with different nucleophilic compounds (named Py-R-Py) as 1,2-bis(4-pyridyl)ethane (bpe), trans-1,2-bis(4 pyridyl)ethylene (tbpe), but also with reducible spacers as 4,4'-azopyridine (azpy) and 3,6 bis(4-pyridyl)-*s*-tetrazine (tzpy) (Fig. 9) (Giraudeau et al., 2010; Schaming et al., 2011b).

Fig. 9. Several Lewis bases (Py-R-Py) used as spacers: 1,2-bis(4-pyridyl)ethane (bpe), trans-1,2-bis(4-pyridyl)ethylene (tbpe), 4,4'-azopyridine (azpy) and 3,6-bis(4-pyridyl)-*s*-tetrazine (tzpy).
