We report herein the synthesis, electronic structure,
experimental
and density functional theory (DFT) calculated optical properties,
and electrical conductivity of a new π-conjugated ladder polymer,
ladder poly(thienobenzothiazine) (LTBT), and its model compound, thienobis(benzothiazine)
(TBBT). The synthesis of LTBT in a mixed polyphosphoric acid/sulfolane
solvent system gave an intrinsic viscosity of 2.0 dL/g at 30 °C
in methanesulfonic acid, and the polymer could form large-area freestanding
films. Single-crystal X-ray structure of TBBT showed that it crystallizes
in an orthorhombic structure with a coplanar thienobenzothiazine ladder
backbone, which is in agreement with the DFT calculated structure.
The electrochemically derived HOMO and LUMO energy levels of −5.17
eV and −3.75 eV of LTBT thin films revealed the p-type semiconducting
nature of the conjugated ladder polymer. We thus p-doped LTBT thin
films with FeCl3, leading to an average electrical conductivity
of 0.3 S/cm. These results demonstrate the potential of the new ladder
polymer LTBT in organic electronics while providing valuable insights
into the structure–property relationships of semiconducting
ladder polymers.