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Oligomer Porphyrins - Their Potential as Molecular Wires

Warren A. Hougha, Maxwell J. Crossley*, a, Jeffrey R. Reimersa, Noel S. Husha, Yasuo Wadab

aThe University of Sydney,
Sydney, NSW 2006 Australia

bHitachi, Ltd. Advanced Research Laboratory

This is an abstract for a presentation given at the
Eighth Foresight Conference on Molecular Nanotechnology.
There will be a link from here to the full article when it is available on the web.

 

The development of an effective "molecular wire" is the most basic requirement to the eventual construction of molecular electronic devices. The oligomer porphyrin system, based on 5,10,15,20-tetrakis(3,5-di-tert-butylphenyl)porphyrin in which the porphyrin rings are bridged by coplanar aromatic systems and the ends are capped with phenanthroline, is proposed to meet all the criteria for a molecular wire.1 This oligomer porphyrin system has a fully conjugated *-electron conduction pathway which is surrounded by a sheath of bulky insulating lipophilic alkyl groups that will act to minimise random conduction, such as electrostatic interactions and electron tunnelling, and improve solubility. These molecules should exhibit quasi one-dimensional properties where conductivity is most favoured along the porphyrin chain. These compounds are stable, rigid, safe and easy to handle. Phenanthroline caps are used as they form complexes, as typical bidentate molecules through the nitrogen atoms, with metal ions in a wide range of oxidation states.2 The strong chelating ability of the phenanthroline group provides a means of attachment to external redox centres, electrodes, devices or surfaces. The rigidity of the phenanthroline system would maintain the porphyrin's quasi one-dimensional geometry.

An outline of the synthesis of the oligomer porphyrin systems from various building blocks is presented, along with general protocols for the synthesis of oligomer porphyrin systems of varying lengths. Measurements of the conductive properties for the oligomer porphyrin systems have also been performed using a variety of methods, both experimental and theoretical, and the results are presented. Also, calculations were performed for 99 molecules, elucidating the nature of the long-distance electronic coupling and its controllability through chemical means.

References

  1. Hush, N. S., Reimers, J. R., Hall, L. E., Johnston, L. A. and Crossley, M. J., Ann. N. Y. Acad. Sci., 1998, 852, 1.
  2. Kermack, W. O.; McKail, J. E. Heterocyclic Compounds; Elderfield, R. C. Ed.; Wiley: New York, 1961; Vol. 7.

*Corresponding Address:
Maxwell J. Crossley, Professor of Chemistry
The University of Sydney
School of Chemistry, F11
Sydney, NSW 2006 Australia
Email: m.crossley@chem.usyd.edu.au
Web: http://www.chem.usyd.edu.au/~crossley



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