Electrical anisotropy of orientedtrans-polyacetylene undoped and doped with SO3

We use extended Huckel methods of molecular orbitds and crystal orbitals (EHMO/CO) to calculate the two-dimensional band structures of highly oriented trans-polyacetylene (PA) undoped and doped with SO₃. According to the energy band theory of solids, we explain the changes of band gap (E_g) and bandwidth (BW) from undoped PA to SO_3-doped PA, and discuss the electrical anisotropy of orientedtrans-polyacetylene doped with SO₃ The calculated results show that the conductivity anisotropy ratio (σ/σ⊥,) is determined by E_g, and BW in the directions both parallel (σ) and perpendicular (σ⊥,) to the PA chains, respectively. The conductivity anisotropy ratio σ/σ⊥ decreases when PA is doped with SO₃, because the dopant plays a conjugated bridge role between the interchains of PA, and makes the dopant itself and PA chains show a strong interchain coupling. The theoretical results for undoped and doped PA are in good agreement with experimental ones.