Thieno[3,2-b]thiophene oligomers and their applications as p-type organic semiconductors

This study describes the synthesis, characterization and electronic properties of a novel series of soluble thieno[3,2-b]thiophene oligomers (1a and b and 2a and b) for thin film transistor (TFT) applications. All the compounds were synthesized in high yield using Pd-catalyzed Stille or Suzuki coupling reactions and were substituted by two dodecyl groups at the 3- or 4-position of the thiophene unit to ensure the solubility for facile device fabrication. Aryl units such as phenyl and naphthyl were used for 'end-capping' to provide stability against oxidation. The design of these materials has focused on their self-assembly and solution processability. All the compounds have been characterized by H-1, C-13 NMR, and elemental analysis. Their electronic and optical properties were investigated using UV-Vis and photoluminescence spectroscopy, cyclic voltammetry, thermal gravimetric analysis (TGA), and differential scanning calorimetry (DSC). High-resolution STM images of 1a and 2a adsorbed on HOPG revealed highly ordered self-organized domains. Two-dimensional wide-angle X-ray scattering (2D-WAXS) was used to study the solid state packing of 1a and 2a. Top-contact OTFT devices from 1a were prepared by spin coating and showed promising behaviour with mobilities up to 3.11 x 10(-2) cm(2) V-1 s(-1) and on/off ratios up to 10(4).