What is it about?

The length of the conjugated chain and the type and number of substituents were controlled for several types of oligothiophenes. These controls dramatically changed the optical, electrochemical, and electrical properties of the oligothiophenes. Applications to field-effect transistors and smart windows were also investigated.

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Why is it important?

Poly(3,4-ethylenedioxythiophene) (PEDOT), whose monomer unit is a thiophene ring bearing an ethylenedioxy group in the side chain (3,4-ethylenedioxythiophene, EDOT), has been widely used in organic electronic devices in recent years because of its excellent charge transport properties. However, the degree of polymerization of PEDOT obtained by oxidative polymerization is not controlled, and it is known that the degree of polymerization is in the range of 6-13mers. In this study, we synthesized several types of EDOT-containing oligothiophenes (3, 6, 7, 9, and 11mers), which are composed solely of EDOT. Oligothiophenes composed only of EDOT are chemically unstable (easily oxidized by air) and have poor solubility, but the oligothiophenes synthesized in this study partially contain EDOT, which solves these problems. The introduction of a partial EDOT unit into the oligothiophene also resulted in a significant red shift in the absorption wavelength region and a negative shift in the oxidation potential compared to the EDOT-free oligothiophene. They also found that the material can be applied as a field-effect transistor and smart window.


The molecular weight distribution of conducting polymers, such as PEDOT, is uncontrollable because they are polymers. This poses a barrier to the elucidation of the intrinsic properties of conducting polymers, not only because of the low reproducibility of synthesis, but also because of the inhomogeneity of the electronic state in conjugated compounds. In order to solve these problems, conjugated oligomers with controlled degree of polymerization and polymerization position have begun to be studied as model compounds. Recently, it has been discovered that conjugated oligomers exhibit excellent physical properties derived from the controlled structure, and the conjugated oligomers themselves have been studied as a new class of functional materials. However, due to the low chemical stability and poor solubility in common organic solvents, only a few synthetic examples of oligothiophenes consisting solely of EDOT (2-5mers) have been reported so far. In this study, we succeeded in synthesizing EDOT-containing oligothiophenes with a conjugate length comparable to that of PEDOT synthesized by oxidative polymerization. This result is expected to be used for organic electronic devices such as field-effect transistors and smart windows in the future. It is also expected to be applied to thermoelectric conversion devices, which the authors have been studying recently.

Dr Ichiro Imae
Hiroshima University

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This page is a summary of: Synthesis and electrical properties of novel oligothiophenes partially containing 3,4-ethylenedioxythiophenes, RSC Advances, January 2014, Royal Society of Chemistry, DOI: 10.1039/c3ra44129f.
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