Synthesis of 3,7-Dialkylthieno[2’,3’:4,5]thieno[3,2-b]thieno[2,3-d]thiophenes (DCnFT4) and their Application in Semi-conducting Polymers

Recently much interest has been directed toward solution processable polymeric semi-conductor materials containing thiophene based moieties.[1] In particular, dialkylated tetrathienoacene (fused thiophene) copolymers have been used as high mobility semiconductors in field-effect transistors with a field-effect hole mobility exceeding 0.3 cm2/Vs.[2] Expansion of this class of materials to include new materials with either linear (DCnFT4) or branched (DbCnFT4) di-alkyl-substituted fused thiophenes has been achieved with the development of two distinct synthetic routes for ring formation and the introduction of the side-chains.DC17FT4 was prepared from tetrabromothieno[3,2-b]thiophene through a sequence of diketone formation, cyclization, hydrolysis and decarboxylation. Synthesis of the new compound di-2,4,4-trimethylpentyl-FT4 (DbC8FT4) has been accomplished in a more complex 8 step process, featuring a mono-ketone-ester as a key intermediate.DCnFT4 can be brominated in the 2- and 6-positions with NBS. The dibromide can then be used to form copolymers through cross coupling reactions. These polymers are solution processable semi-conductors. The polymers have been characterized by GPC and within organic thin-film transistor (OTFT) devices.