Star-shaped oligothiophenes for solution-processible organic field-effect transistors

We have designed and successfully synthesized star-shaped oligothiophenes, which could be used as semiconducting materials for solution-processible organic field-effect transistors (FETs). By systematically changing the chemical structure of the star-shaped oligothiophenes we obtained the structural requirements needed for making working FETs from them. UV-vis fluorescence measurements showed that a molecule of the star-shaped compound under consideration is not a fully conjugated molecule, but it has three independently conjugated oligothienyl-phenylene blocks. A possible scheme of molecular packing of the star-shaped oligothiophenes in a lamellar structure was proposed and confirmed by atomic force microscopy (AFM) and X-ray diffraction (XRD) measurements. Although the star-shaped semiconductors show a somewhat lower mobility than their linear analogs, they possess better solubility and film-forming properties, leading to improved spin-coating processing. The best FETs were made by spin-coating 1,3,5-tris(5"-decyl-2,2':5',2"-terthien-5-yl)benzene from a chloroform solution, <LF>which resulted in a mobility of 2x10(-4) cm(2)V(-1)s(-1), a 10(2) on/off ratio at gate <LF>voltages of 0 V and -20 V, and a threshold voltage close to 0 V.