Low clearing asymmetric BTBT mesogens with perfect ambipolar charge transport

Abstract

Two new asymmetrically substituted BTBT mesogens were successfully synthesised. These mesogens were designed to achieve low melting and clearing temperatures via the decoration with swallow-tailed chains containing peripheral siloxane units. The aromatic endgroups (phenyl and phthalonitrile) have a significant impact on the bilayer smectic self-assembly. For both materials the aromatic units intercalate completely into double layers, but the phenyl derivative generates a SmC phase and the phthalonitrile derivative a SmA phase. The latter is a weak donor–acceptor system showing outstanding charge transport properties in the mesophase. It exhibits perfectly balanced ambipolar charge carrier mobility in the range of 10⁻² cm² V⁻¹ s⁻¹ resulting in a material that is extremely promising for organic electronic applications.