Molecular design of benzothienobenzothiophene-cored columnar mesogens: facile synthesis, mesomorphism, and charge carrier mobility

Abstract

Benzothienobenzothiophene (BTBT) liquid-crystalline semiconductors are arousing a lot of interest due to their long-range ordered, self-organizational abilities and high-charge carrier transport properties. In this work, we report the design and the straightforward synthesis of a homologous series of compounds containing the BTBT substructure by the successive Suzuki cross-coupling and FeCl₃ oxidative Scholl cyclodehydrogenation reaction. Target π-conjugated aromatic, H-shaped sanidic mesogens self-organize into a classical hexagonal columnar mesophase over wide temperature ranges as deduced from polarized optical microscopy (POM), differential scanning calorimetry (DSC), and small-angle X-ray scattering (SAXS) investigations. UV/Vis absorption and photoluminescence spectra, measured in both solution and films, revealed strong photoluminescence with high quantum yields. The charge carrier mobility measured by the time-of-flight (TOF) technique showed a balanced ambipolar hole and electron mobility in the range of 10⁻³ cm² V⁻¹ s⁻¹ between 100 and 230 °C in the mesophase. These BTBT-based columnar liquid crystals may represent attractive candidates to be incorporated within one-dimensional organic optoelectronic devices.