Synthesis, self-assembly and solution-processed field-effect transistors of a liquid crystalline bis(dithienothiophene) derivative

A new liquid crystalline dithienothiophene dimer cap-functionalized with 3,4,5-tris-n-dodecyloxyphenyl groups (1) has been synthesized. The absorption spectrum blue-shifts 7 nm, while the fluorescence spectrum redshifts 95 nm in thin film with respect to that in solution, suggesting that H-aggregate formation may occur and the molecules are cofacially aligned in the solid state. Compound 1 self-organized into highly ordered, long-range 2-dimensional nanopatterns on highly oriented pyrolytic graphite; their structures were characterized by scanning tunneling microscopy. The liquid crystalline phase was formed upon heating or cooling and was investigated using differential scanning calorimetry and polarizing optical microscopy. Thermal annealing led to a 13 nm red shift of absorption spectra of 1 in the thin film, indicating liquid crystalline enhanced ordering. Solution-processed organic field-effect transistors based on 1 exhibited a mobility of 1.7 × 10-3 cm² V^-1s^-1 and an on/off ratio of 2 × 10⁵.