Self-assembled monolayers formed by 5,10,15,20-tetra(4-pyridyl)porphyrin and cobalt 5,10,15,20-tetra(4-pyridyl)-21H,23H-porphine on iodine-passivated Au(1 1 1) as observed using electrochemical scanning tunneling microscopy and cyclic voltammetry

Self-assembled monolayers (SAMs) of 5,10,15,20-tetra(4-pyridyl)porphyrin (TPyP) and cobalt 5,10,15,20-tetra(4-pyridyl)-21H,23H-porphine (CoTPyP) were formed by in situ equilibrium adsorption onto Au(1 1 1) electrodes passivated by an interposed adlayer of iodine. Adsorption of the porphyrins onto Au(1 1 1) was confirmed by cyclic voltammetry, and each of the SAMs was imaged using electrochemical scanning tunneling microscopy (EC-STM). The TPyP and CoTPyP SAMs were found to contain highly ordered domains on I–Au(1 1 1) at positive potentials where a disordered SAM would be expected for bare Au(1 1 1). Cyclic voltammetry was also used to observe in situ the assembly of binary SAMs containing TPyP and CoTPyP as they formed.

Graphical abstractFigure optionsDownload full-size imageDownload as PowerPoint slideHighlights► SAMs of water-soluble porphyrins formed on Au(1 1 1) passivated by an iodine adlayer. ► Iodine adlayer allows formation of ordered porphyrin SAMs at positive potentials. ► Free base and cobalt porphyrin SAMs contained ordered domains of similar geometry. ► CVs showed distinctive features attributed to the adsorbed porphyrin SAMs. ► CV was used to monitor the time dependent formation of binary porphyrin SAMs.