DFT STUDY OF EDOT-THIOPHENE CONJUGATED SYSTEMS: ELECTRONIC STRUCTURE AND OPTOELECTRONIC PROPERTIES

Abstract

The electronic structure and optoelectronic properties of conjugated systems incorporating 3,4-ethylenedioxythiophene (EDOT) and thiophene units were investigated using density functional theory (DFT) calculations. Geometry optimizations were performed at the B3LYP/6-31G(d) level for a series of EDOT-thiophene hybrid oligomers with varying chain compositions and conjugation lengths. The study examined frontier molecular orbital energies, HOMO-LUMO band gaps, ionization potentials, electron affinities, and simulated UV-Vis absorption spectra. Results demonstrate that the incorporation of EDOT units within thiophene-based conjugated chains significantly lowers the HOMO energy level and reduces the band gap through the strong electron-donating effect of the ethylenedioxy substituent. The planar conformation adopted by EDOT-thiophene systems, stabilized by intramolecular sulfur-oxygen interactions, enhances π-conjugation and promotes effective charge delocalization. Simulated absorption spectra reveal red-shifted λmax values for EDOT-containing oligomers compared to their thiophene counterparts, consistent with experimental observations. The calculated electronic properties establish clear structure-property relationships that provide molecular-level guidance for designing EDOT-thiophene materials with tailored optoelectronic characteristics for applications in organic photovoltaics, electrochromic devices, and organic field-effect transistors.