| Abstract
| - The ability to attach redox-active molecules to oxide surfaces in controlled architectures (distance,orientation, packing density) is essential for the design of a variety of molecular-based informationstorage devices. We describe the synthesis of a series of redox-active molecules wherein eachmolecule bears a benzylphosphonic acid tether. The redox-active molecules include zinc porphyrins,a cobalt porphyrin, and a ferrocene-zinc porphyrin. An analogous tripodal tether has been preparedthat is based on a tris[4-(dihydroxyphosphorylmethyl)phenyl]-derivatized methane. A zinc porphyrinis linked to the methane vertex by a 1,4-phenylene unit. The tripodal systems are designed toimprove monolayer stability and ensure vertical orientation of the redox-active porphyrin on theelectroactive surface. For comparison purposes, a zinc porphyrin bearing a hexylphosphonic acidtether also has been prepared. The synthetic approaches for introduction of the phosphonic acidgroup include derivatization of a bromoalkyl porphyrin or use of a dimethyl or diethyl phosphonatesubstituted precursor in a porphyrin-forming reaction. The latter approach makes use of dipyrromethane building blocks bearing mono or tripodal dialkyl phosphonate groups. The zinc porphyrin-tripodal compound bearing benzylphosphonic acid legs tethered to a SiO2 surface (grown on dopedSi) was electrically well-behaved and exhibited characteristic porphyrin oxidation/reduction waves.Collectively, a variety of porphyrinic molecules can now be prepared with tethers of different length,composition, and structure (mono or tripodal) for studies of molecular-based information storageon oxide surfaces.
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