SYNTHESIS AND PROPERTIES OF METALLOPORPHYRIN MONOLAYERS AND STACKED MULTILAYERS BOUND TO AN ELECTRODE VIA SITE-SPECIFIC AXIAL LIGATION TO ASELF-ASSEMBLED MONOLAYER

A general method has been developed for the immobilization of metallop orphyrins at a gold electrode surface coated with a self-assembled mon olayer(SAM). SAMs containing imidazole-terminated adsorbates are shown to bind a series of metalloporphyrins, including bis-acetonitrile oct aethylporphyrinatoruthenium(II), Ru(OEP)(CH3CN)(2); bis-acetonitrile o ctaethyltetraazaporphyrinato ruthenium(II), Ru(OETAP)(CH3CN)(2); bis-a cetonitrile tetra-(p-chlorophenyl)porphyrinatoruthenium(II), Ru(Tp-ClP P)(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 s pectroscopy, grazing angle FT-IR spectroscopy, transmission visible sp ectroscopy, and electrochemistry. The results indicate that the metall oporphyrins an 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 micros copy images of Ru(TMP)(CO) bound to the SAM corroborate this model. Ax ial ligation of metalloporphyrins to SAMs serves as the basis for an i terative, defined approach to the preparation of stacked single compon ent and mixed metalloporphyrin multilayers on SAMs. In these materials , the bidentate ligand pyrazine serves as a bridge between successive metalloporphyrins in the stacks.