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 dat a was aided by DFT calculations at the B3LYP/6-31G(**) level. The two bithi ophenes show Raman features which are common to many other classes of oligo thiophenes and that can be ascribed within the formalism of the Effective C onjugation Coordinate theory to the existence of an efficient pi -electron conjugation. (C) 2001 Elsevier Science B.V. All rights reserved.