Liquid crystalline dialkyl-substituted thienylethenyl [1] benzothieno[3,2-b] benzothiophene derivatives for organic thin film transistors

New benzothieno[3,2-b]benzothiophene (BTBT)-based soluble semiconducting molecules have been synthesized through Horner-Emmons coupling reactions using 5-alkylthiophene-2-carbaldehyde and BTBT-diethylphosphonate. The only difference between the two molecules is the length of alkyl chains as a substituent. The molecules are intrinsically thermotropic liquid crystalline (LC) and exhibit good solubility in common organic solvents. The semiconducting properties of the two LC molecules were evaluated in organic thin film transistors (OTFTs). After annealing the samples at the temperature at which liquid crystallinity appears, the TFT device performance improved significantly. The two conjugated molecules 4 and 5 exhibited fairly high charge carrier mobilities of 0.020 cm2/(Vs) (Vth = −14.5 V, ION/OFF = 1.42 × 105) and 0.023 cm2/(Vs) (Vth = −2.0 V, ION/OFF = 1.20 × 106), respectively.