Novel Unsymmetric Oligomers Based on Benzo[d, d′]Thieno[3,2-b;4,5-b′]Dithiophenes for Solution-Processed Organic Field-Effect Transistors

In this study, the synthesis of unsymmetric benzo[d,d′]thieno[3,2-b;4,5-b′]dithiophenes with extended arylacetylenes or alkyl groups is reported along with their physical, optical and electrical characterizations. Benzo[d, d ]thieno[3,2-b;4,5-b ]dithiophenes substituted with various alkyl and phenylethynyl groups were synthesized using an acid-induced intramolecular cyclization reaction of aromatic methyl sulfoxides, which was confirmed via1 H-NMR and FT-IR studies. The obtained oligomers exhibited good solubility in common organic solvents such as hexane, chloroform, and dimethyl chloride at room temperature. The UV-vis absorption, photoluminescence, atomic force microscope, and X-ray diffraction measurements demonstrated that the oligomers substituted with a phenylethynyl group had more extended intramolecular delocalization of electronic states compared to oligomers substituted with pure alkyl groups. The solution processed thin film transistors created from such oligomers substituted with the phenylethynyl group exhibited relatively high hole mobility, up to 0.1 cm² V^–1 s^–1 and I _on/I _off of 10⁶.