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

Abstract

A bottom-up approach was employed to prepare novel Self-Assembled Monolayers (SAMs) in which a naphthyl moiety acted as a “π-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.