3-Fluoro-4-hexylthiophene as a building block for tuning the electronic properties of conjugated polythiophenes.

3-Fluoro-4-hexylthiophene has been prepared by a synthetic route involving perbromination of 3-hexylthiophene followed by protection of the 2- and 5-positions of thiophene by trimethylsilyl groups and bromine/fluorine exchange. As expected, 3-hexyl-4-fluorothiophene oxidizes at a higher potential than 3-hexylthiophene; however, all attempts to electropolymerize this new thiophenic monomer have remained unsuccessful. Three terthienyls containing 3-hexylthiophene, 3-fluoro-4-hexylthiophene, and 3-bromo-4-hexylthiophene as the median group have been synthesized and used as substrates for electropolymerization. The electronic properties of the starting terthienyls and the resulting polymers have been analyzed by cyclic voltammetry and UV-vis spectroscopy, and the effects of substitution of the median thiophene ring are discussed.