The electronic and optical properties of oligo(trans‐1,2‐di(2‐thienyl)‐1,3‐butadiene): A theoretical study

Abstract

AbstractIn the present work we investigated the theoretical electronic structure of poly(trans‐1,4‐di(2‐thienyl)‐1,3‐butadiene) (PTB) and determined the optical properties of its neutral and doped oligomers. Geometrical optimizations were at the semiempirical level by using the Austin method 1 (AM1). The band structure of π electrons regarding to the neutral PTB polymer was obtained by using a tight‐binding Hamiltonian. The densities of electronic states (DOS) for neutral and doped copolymers were calculated by using the negative factor counting technique. The spatial charge distribution of the oligomeric chain was also analyzed. The energy of the electronic transitions and their associated oscillator strength values were calculated for the neutral, double, and single charged oligomers to determine the UV–vis absorption spectra. The calculations were performed using the intermediate neglect of differential overlap Hamiltonian in combination with the single configuration‐interaction technique in order to include correlation effects. The band gap obtained in the PTB was about 2.101 eV for the optics absorption and 1.73 eV for the DOS. The bipolaron states appear in the gap, about 0.57 eV and 0.48 eV below and above the conduction and valence bands, respectively. When the dopants concentration is increased the DOS showed that the energy gap tends to vanish, which may lead to semiconductor–metal transition. © 2008 Wiley Periodicals, Inc. Int J Quantum Chem, 2008