π-Interactions as a tool for an easy deposition of meso-tetraferrocenylporphyrin on surfaces

A bottom-up approach was employed to prepare novel Self-Assembled Monolayers (SAMs) in which a naphthyl moiety acted as a ‘‘p-binder’’ for unfunctionalised meso-tetraferrocenylporphyrin (H2TFcP). Four naphthalene derivatives with an appropriate functional group were synthesized and SAMs were prepared both on gold and ITO surfaces. Mixed H2TFcP–naphthalene films were thoroughly characterized using UV-Vis, XPS and electrochemical techniques. In particular, angle-dependent XPS experiments revealed an almost perpendicular orientation of the porphyrin on surfaces, suggesting that an intercalation occurred among naphthalene units. A large amount of porphyrin was deposited on both the surfaces (in the order of 10 10 mol cm 2), comparable to that afforded by more conventional covalent linkages. However, significant differences in homogeneity between SAMs on gold and ITO resulted in a diverse electrochemical behaviour. The electrochemical activity of the oxidised porphyrin was restored by prolonged exposure of the modified gold electrode (tens of seconds) to a negative potential, whereas no response was detected after the same treatment on ITO. This novel approach provides a general and versatile strategy to bind meso-substituted porphyrins on a pre-formed monolayer without the necessity for further functionalisations.