An oligothiophene cation radical that forms π-stacks: A model for polaron aggregation in conducting polymers
✍ Scribed by Prof. Larry L. Miller; Dr. Yuan Yu; Dr. Esmir Gunic; Dr. Robert Duan
- Book ID
- 101413506
- Publisher
- John Wiley and Sons
- Year
- 1995
- Tongue
- English
- Weight
- 252 KB
- Volume
- 7
- Category
- Article
- ISSN
- 0935-9648
No coin nor oath required. For personal study only.
✦ Synopsis
Our understanding of the structure and conductivity of polymers like polythiophene and polypyrrole is primarily based on polarons and bipolarons, cation radicals and dications that can migrate along the conjugated polymer chain."] Using model oligomers we and others have recently shown the importance of interchain cation radical n-dimers as an alternative to bipolarons in oxidized polythiophene.[' -' 1 Now, we provide evidence that a model oligothiophene cation radical forms z-stacks in solution and in the solid state. This study provides a new class of functional units for preparing charge transfer salts,[81 a connection between the usually separate fields of charge transfer salts and conducting polymers, and suggests that n-stacks may be present in some oxidized polythiophenes and similar polymers. Such stacks provide a means for interchain delocalization which would be important for electrical conductivity.
Our previous work on imide anion radicals['] and TTF cation radicals[101 demonstrated that water is the appropriate medium for the observation of z-stacks in solution. It was, therefore, necessary to prepare an oligothiophene cation radical that was soluble and stable in aqueous solution.
Compound 1 was prepared as described in Scheme 1. It was expected that the electron-donor methoxy groups would stabilize the cation radical (lo) and that the carboxylates would provide water solubility and would block polymerization.
Although chemical oxidation gave similar results, we focus attention here on the anodic oxidation of 1 in aqueous b (b~ty1)~Sn 2 + 3 c d.e -KOOC Scheme 1. a) HgO (yellow crystal), I,, benzene (97%). b) n-Butyllithium, (butyl),SnCl(XS%). c) Toluene, [(C,H,),P],Pd (44%). d) n-Butyllithium, CO, (97.5%). e) MeOH, KOH (98%).