Vibrational and theoretical DFT study of two regioregular methyl-disubstituted bithiophenes

We report on the vibrational infrared and Raman spectra of two beta -alkyl substituted bithiophenes with well-defined substitution patterns: the 3.3'-and the 4,4'-dimethyl-2,2'-bithiophenes. Interpretation of experimental data was aided by DFT calculations at the B3LYP/6-31G(**) level. The two bithiophenes show Raman features which are common to many other classes of oligothiophenes and that can be ascribed within the formalism of the Effective Conjugation Coordinate theory to the existence of an efficient pi -electron conjugation. (C) 2001 Elsevier Science B.V. All rights reserved.