Synthesis and Properties of Metalloporphyrin Monolayers and Stacked
Multilayers Bound to an Electrode via Site Specific Axial Ligation to
a Self-Assembled Monolayer
posted on 1998-04-28, 00:00authored byDavid A. Offord, Sandra B. Sachs, Matthew S. Ennis, Todd A. Eberspacher, John H. Griffin, Christopher E. D. Chidsey, James P. Collman
A general method has been developed for the
immobilization of metalloporphyrins at a gold electrode
surface coated with a self-assembled monolayer (SAM). SAMs
containing imidazole-terminated adsorbates
are shown to bind a series of metalloporphyrins, including
bis-acetonitrile octaethylporphyrinatoruthenium(II),
Ru(OEP)(CH3CN)2;
bis-acetonitrile octaethyltetraazaporphyrinato ruthenium(II),
Ru(OETAP)(CH3CN)2;
bis-acetonitrile
tetra-(p-chlorophenyl)porphyrinatoruthenium(II),
Ru(Tp-ClPP)(CH3CN)2;
bis-acetonitrile octaethylporphyrinatoosmium(II),
Os(OEP)(CH3CN)2; and carbonyl
meso-tetramesitylporphyrinatoruthenium(II),
Ru(TMP)(CO). The SAM/metalloporphyrin films have been
characterized by optical ellipsometry, contact
angle goniometry, X-ray photoelectron spectroscopy, grazing angle FT-IR
spectroscopy, transmission visible
spectroscopy, and electrochemistry. The results indicate that the
metalloporphyrins are chemisorbed via axial
ligand substitution of the metal center with the porphyrin ring
parallel to the surface and the second axial
ligand position normal to the surface. Scanning tunneling
microscopy images of Ru(TMP)(CO) bound to the
SAM corroborate this model. Axial ligation of metalloporphyrins to
SAMs serves as the basis for an iterative,
defined approach to the preparation of stacked single component and
mixed metalloporphyrin multilayers on
SAMs. In these materials, the bidentate ligand pyrazine serves as
a bridge between successive metalloporphyrins
in the stacks.