Synthetic studies of extraordinarily long oligothiophenes

This paper describes synthetic approaches to extraordinarily long oligothiophenes, which correspond to mono-disperse polymers. The most successful approach is a combination of a random coupling reaction of mono- and diethynylsexithiophenes and a subsequent sodium sulfide-induced cyclization reaction of the diacetylene parts to thiophene rings, forming a series of long oligothiophenes Oct-nT up to the 48-mer. The systematic study of the Oct-nT series reveals that the effective conjugation length of conjugated polythiophenes extends to around 20 thiophene units.