Long-range order induced by cobalt porphyrin adsorption on aminothiophenol-functionalized Au(111): the influence of the induced dipole

Porphyrins are useful in materials science for optical, photoelectrochemical and chemical sensor applications. Solid films of oriented porphyrins on gold can be realized through a simple procedure and without synthesizing thiol-derivatized porphyrins. In order to immobilize the porphyrin rings on the surface, we prepared a 4-aminothiophenol (4-ATP) self-assembled monolayer (SAM) on gold(111) followed by axial legation, in situ, of cobalt(II) 5,10,15,20-tetrakis(4-tert-butylphenyl)-porphyrin (CoTBPP). Ultrahigh vacuum (UHV) Scanning Tunneling Microscopy (STM) studies performed on the SAMs revealed the Au(111) herringbone structure reconstruction, probably due to adsorption/desorption processes of molecules. STM images and Scanning Tunneling Spectroscopy (STS) measurements clearly showed that the immobilization of molecules also induced an electronic perturbation on the gold surface. This effect is ascribed to the presence of oriented molecular dipole layers between the metal and the organic material.