Fused thiophene-split oligothiophenes with high ionization potentials for OTFTs

Fused thiophene-split oligothiophenes were synthesized by Suzuki coupling. The relationship between the structure of these fused thiophene-split oligothiophenes and DH-6T (α,ω-dihexylsexithiophene) and their performance in OTFTs was discussed. The realignment of HTTfTTTH (2,5-bis-(5′-hexyl-[2,2′]bithiophenyl-5-yl)-thieno[3,2-b] thiophene) molecule on the substrate after annealing was revealed by X-ray diffraction and atomic force microscopy. A similar but novel compound, TTfTTT (2,5-bis-[2,2′]bithiophenyl-5-yl-thieno[3,2-b]thiophene), was also prepared and evaluated as an organic transistor material. Air stabilities of these three compounds in OTFT devices were affected mainly by chemical properties, but also by the ionization potentials (Ip) of these materials. Among the three compounds, HTTfTTTH had a higher Ip because the thiophene sequence was split by fused thiophene and the best air stability, due to the end-capping of its active α-positions by hexyl substitution.