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

Polythiophene films were obtained upon anodic oxidation of silylthioph ene monomers with various structures: 2,5-bis(trimethylsilyl)thiophene (1), 5,5'-bis(trimethylsilyl)bithiophene (2), 5,5''-bis(trimethylsily l)terthiophene (3), 2,4-bis(trimethylsilyl)thiophene (4) and 3-trimeth ylsilylthiophene (5). Polymerization occurred through a complete elect rodesilylation for monomers 1-3 having silyl substituents at the alpha -position of the thiophene ring. Only partial desilylation occurred up on electropolymerization of monomers 4 and 5 with silyl substituents a t the beta-position. The structural properties of the polythiophene fi lms obtained were studied by FT-IR and Raman spectroscopy. On the basi s of Raman and photoluminescence studies, the polymers obtained from 1 -3 appeared highly structured, with higher mean conjugation lengths an d lower amounts of defects, when compared to polymers obtained from th e corresponding non-silylated monomers. Therefore, in agreement with a previous report based on electrochemical studies, the presence of alp ha-silyl substituents at the thiophene ring favours the formation of h ighly structured polymers exclusively linked 2,5 throughout. Conversel y, the polymers obtained from monomers 4 and 5 revealed the presence o f some 2,4-linkages in the polymer chain and a lower mean conjugation length.