Template polymerization of polythiophene and organized polythiophene solids.
 
Researchers:
Ben Straw
Anna Shope
 Conjugated polymers have often been proposed as possible "molecular wires". A long-standing, unsolved challenge involves bridging isolated "wires" between electrical contacts. Our approach to this problem makes use of biopolymer templating. We are developing methods to span the gap between closely-spaced electrodes with these templates. This approach is unique because the template is grown to match the electrode gap. The design of our template polymerization of polythiophene is based upon extensive molecular mechanics modeling and utilizes monosubstituted bithiophenes to provide the proper spacing to match that of the attachment sites on the biopolymer.

We have made significant progress toward the preparation of these conjugated polymer wires. We designed and developed a new class of monomers (monosubstituted biothiophenes) that possess the correct substitution pattern necessary for templating. In addition, we prepared both regiorandom and regioregular polymers in the absence of a template to determine their properties and found that polymers derived from monosubstituted bithiophenes (owing to their reduced side chain density) offer access to a wide variety of functionalized polythiophenes and often exhibit extended conjugation compared to their fully substituted counterparts. In fact, the regioregular poly(4-octyl-2,2'-bithiophene) exhibits the highest degree of conjugation reported for an alkyl substituted polythiophene.

We are now synthesizing bithiophene-amino acid precursors to our molecular wire bundles and have prepared bithiophene-loaded polypeptide templates from them. The plan now is to use an activated form of this bithiophene-modified amino acid to grow polymer chains between the electrodes. After the connection is made, the bithiophene side chains can them be oxidatively polymerized to complete the preparation of four parallel molecular wires.

Recent publications.

Rasmussen, S. C.; Pickens, J. C.; Hutchison, J. E. "A General Synthetic Route to 4-Substituted-2,2’-Bithiophenes," J. Heterocyclic Chem. 1997, 34, 285-288.

Rasmussen, S. C.; Pickens, J. C.; Hutchison, J. E. "Highly Conjugated, Water Soluble Polymers via the Direct Oxidative Polymerization of a Monosubstituted Bithiophene," Macromolecules 1998, 31, 933-936.
Straw, B. ; Rasmussen, S. C. ; Hutchison, J. E. "Synthesis Of Regioregular Poly(4-alkyl-2,2’-bithiophene)s: Potential Precursors to Organized Conjugated Polymer Solids," Polym. Prepr., Am. Chem. Soc. Div. Polym. Chem. 1998, 39, 87-88.

Rasmussen, S. C.; Pickens, J. C.; Hutchison, J. E. "A New General Approach to Tuning the Properties of Functionalized Polythiophenes: The Oxidative Polymerization of 4-Substituted-2,2'-Bithiophenes," Chem. Mater. 1998, 1990-1999.

Straw, B. ; Rasmussen, S. C. ; Hutchison, J. E. "Tuning the Extent of Conjugation through Side Chain Placement in Substituted Polythiophenes," in Semiconducting Polymers; Hsieh, B. Ed.; ACS Symposium Series; American Chemical Society: Washington, DC, 1999; In press.
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