Oligothiophene-functionalized truxene: Star-shaped compounds for organic field-effect transistors

Organic field-effect transistors (OFETs) based on oligothiophene- functionalized truxene derivatives have been fabricated for use as novel star-shaped organic semiconductors in solution-processible organic electronics. The electronic and optical properties of compounds 1-3, with increasing numbers of thiophene rings at each of the three branches, have been investigated using scanning electron microscopy (SEM), X-ray diffraction measurements, and ultraviolet-visible (UV-vis) and photoluminescence spectroscopies. The results show that with a stepwise increase of the thiophene rings at every branch, a transition from a polycrystalline to an amorphous state is observed. The characteristics of compounds 1, 2, and 3 used for OFETs exhibit a significant difference. The mobility depends greatly on the morphology in the solid state, and decreases in going from 1 to 3. Mobilities up to 1.03 × 10 ^-3 cm² V^-1 s^-1 and an on/off ratio of about 10³ for compound 1 have been achieved; these are the highest values for star-shaped organic semiconductors used for OFETs so far. All the results demonstrate that the truxene core of the oligothiophene-functionalized truxene derivatives not only extends the π-delocalized system, but also leads to high mobilities for the compounds.