DFT Study of Polythiophene Energy Band Gap and Substitution Effects

Polythiophene (PTh) and its derivatives are polymer-based materials with a pi-conjugation framework. PTh is a useful photoelectric material and can be used in organic semiconductor devices, such as PLED, OLED, and solar cells. Their properties are based on molecular structure; the derivatives contain different substitutes in the 3 and 5 positions, such as electron-donating or electron-withdrawing groups. All molecular geometries were optimized at B3LYP/6-31G(d,p) level of theory. The energy gap (E-gap) between the HOMO and LUMO levels is related to the pi-conjugation in the PTh polymer backbone. In this study, the DFT calculations were performed for the nonsubstituted and 3,5-substituted variants to investigate the stability geometries and electrical properties. The theoretical calculations show that the substituted forms are stable, have low E-gap, and are in good agreement with the experimental observations.