ELECTROPOLYMERIZATION OF SILYLTHIOPHENE MONOMERS - FT-IR AND RAMAN-SPECTROSCOPY CHARACTERIZATION OF POLYTHIOPHENE FILMS

Polythiophene films were obtained upon anodic oxidation of silylthiophene monomers with various structures: 2,5-bis(trimethylsilyl)thiophene (1), 5,5'-bis(trimethylsilyl)bithiophene (2), 5,5''-bis(trimethylsilyl)terthiophene (3), 2,4-bis(trimethylsilyl)thiophene (4) and 3-trimethylsilylthiophene (5). Polymerization occurred through a complete electrodesilylation for monomers 1-3 having silyl substituents at the alpha-position of the thiophene ring. Only partial desilylation occurred upon electropolymerization of monomers 4 and 5 with silyl substituents at the beta-position. The structural properties of the polythiophene films obtained were studied by FT-IR and Raman spectroscopy. On the basis of Raman and photoluminescence studies, the polymers obtained from 1-3 appeared highly structured, with higher mean conjugation lengths and lower amounts of defects, when compared to polymers obtained from the corresponding non-silylated monomers. Therefore, in agreement with a previous report based on electrochemical studies, the presence of alpha-silyl substituents at the thiophene ring favours the formation of highly structured polymers exclusively linked 2,5 throughout. Conversely, the polymers obtained from monomers 4 and 5 revealed the presence of some 2,4-linkages in the polymer chain and a lower mean conjugation length.