In this work, a novel thieno[3,2-b]thiophene based liquid crystalline semiconductor was synthesized by Suzuki coupling reaction. According to temperature-dependent WAXS, GIWAXS, and DSC analysis, this thieno[3,2-b]thiophene derivative showed smectic phases over a wide temperature range from -40 °C to 70 °C. The extended π-conjugated mesogen drove the π-stacking which initiated the self-assembly of the molecules. Particularly, the flexible oligo-(ethylene glycol) chains were substituted to both sides of the mesogen core, acting as the ion-conductive moiety with the addition of an ionic dopant, lithium bis(trifluoromethanesulfonyl)imide (LiTFSI). The liquid crystal (LC) materials were spun cast on top of interdigitated electrode arrays, and the ionic conductivities of LCs at different Li<sup>+</sup> salt concentrations were measured by electrochemical impedance spectroscopy. The resulted ionic conductivity reached 10<sup>-3</sup> S/cm at room temperature, which was higher than previously reported liquid crystalline thieno[3,2-b]thiophene derivative. With its low crystalline to mesophase transition temperature (22 °C), more applications of the liquid crystal with a preference of room temperature can be explored.

The structural design and enhanced ionic conductivity of a fused thieno[3,2-b]thiophene based conjugated liquid crystal

ACS Fall 2021

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