Porphyrins Bearing Mono or Tripodal Benzylphosphonic Acid Tethers for Attachment to Oxide Surfaces

• Published in: Journal of organic chemistry 2004-03, Vol.69 (5), p.1453-1460
• Main Authors: Loewe, Robert S, Ambroise, Arounaguiry, Muthukumaran, Kannan, Padmaja, Kisari, Lysenko, Andrey B, Mathur, Guru, Li, Qiliang, Bocian, David F, Misra, Veena, Lindsey, Jonathan S
• Format: Article
• Language: English
• Subjects: Chemistry; Coordination compounds; Electrochemistry; Exact sciences and technology; General and physical chemistry; Inorganic chemistry and origins of life; Miscellaneous; Preparations and properties; Study of interfaces
• ISSN: 0022-3263; 1520-6904
• DOI: 10.1021/jo034946d

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 information storage devices. We describe the synthesis of a series of redox-active molecules wherein each molecule 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 prepared that is based on a tris[4-(dihydroxyphosphorylmethyl)phenyl]-derivatized methane. A zinc porphyrin is linked to the methane vertex by a 1,4-phenylene unit. The tripodal systems are designed to improve monolayer stability and ensure vertical orientation of the redox-active porphyrin on the electroactive surface. For comparison purposes, a zinc porphyrin bearing a hexylphosphonic acid tether also has been prepared. The synthetic approaches for introduction of the phosphonic acid group include derivatization of a bromoalkyl porphyrin or use of a dimethyl or diethyl phosphonate substituted 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 doped Si) 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 storage on oxide surfaces.