Synthesis and Optical Properties of Heteroaromatic Ring Compounds Containing EDOT

Abstract

Thiophene-based conjugated polymers and oligomers have been widely used as active materials for the fabrication of optoelectronic devices such as field-effect transistors, light-emitting devices and photovoltaic cells. The optical and electronic properties of the active material depend on the energy levels of the HOMO and LUMO. In order to control the levels, extensive studies aiming at the modification of the oligothiophene backbone have been carried out. As an electronic material, 3,4-ethylenedioxythiophene (EDOT) is an important versatile building block for the molecular engineering of functional π-conjugated systems with electronic and optical properties specifically tailored for applications in light-emitting devices, chromophores for non-linear optics, low energy gap systems or more recently organic semi-conductors. Various oligo-EDOTs have been synthesized and the analysis of their structure and electronic properties has shown that a judicious use of EDOT as building block allows a fine tunning of the electronic properties of π-conjugated systems. This increasing attention for EDOT-based systems has in turn generated a strong interest in the chemistry of the EDOT molecule itself and/or in the modification of its structure. Introduction of electron-withdrawing groups to EDOT represents the most immediate way to tune the HOMO and LUMO energy levels of a conjugated system. As shown in previous work, introduction of acceptor groups such as nitro, carboxyl or cyano at the 3-position of the thiophene unit induces a large increase in the oxidation potential. The cyclovoltammetry (CV) curve of EDOT shows oxidation at 1.3 eV and broad reduction waves, which is located between 0.30 eV and −0.60 eV. In addition, the EDOT trimer was first synthesized by Reynolds and coworkers as a precursor for electropolymerization. They demonstrated that the EDOT trimer had oxidation potential at 0.2 eV, while they did not mentioned reduction potential of EDOT trimer. Here in, we introduced the various aromatic system in EDOT unit in order to control the HOMO and LUMO levels, and the new compounds are expectant of active materials for fabrication of the various optoelectronic devices.