Immobilisation of Iron Porphyrin from an Equilibrium Solution with Diazonium‐Functionalised Axial Ligand: Dependence of Film Composition on Grafting Potential

Abstract

AbstractIn dichloromethane solution, tetraphenylporphyrin iron (III) chloride (FeTPPCl) and 4‐(1H‐Imidazol‐1‐yl)aniline (Im‐Ph‐NH2) exist in equilibrium with axially‐coordinated [FeTPP(Im‐Ph‐NH2)n]+ (n=1 and 2). After in situ diazotisation of Im‐Ph‐NH2, electroreduction of the diazonium ion leads to deposition of a film incorporating [FeTPP(Im‐Ph)2]+ and uncoordinated Im‐Ph. In the 1 : 1 FeTPPCl:Im‐Ph‐NH2 grafting solution used in this work, Im‐Ph‐NH2 is mostly uncoordinated. However, the formation constant for axially coordinated Fe(II)TPP is significantly greater than for Fe(III)TPP+. Consequently, the relative amounts of coordinated and uncoordinated Im‐Ph in the films depends on whether the grafting scans traverse the potential for reduction of FeTPPCl. In addition, redox grafting can occur based on the Fe(III)/(II) couple of solution‐ and film‐based porphyrin. Electrochemistry, atomic force microscopy and X‐ray photoelectron spectroscopy reveal that the relative amount of free and coordinated Im‐Ph, and concentration of [FeTPP(Im‐Ph)2]+ in the films depend on the negative potential limit during grafting.