VIBRATIONAL ANALYSIS AS A FUNCTION OF THE CHAIN-LENGTH OF WELL-BARRIER-WELL PI-CONJUGATED THIOPHENE-BASED OLIGOMERS

We have analyzed the size dependence of the infrared and Raman active modes of two neutral thiophene-based oligomers in the solid state. The compounds have a well-barrier-well structure, where the well parts ar e two bithiophene or terthiophene end-moieties and the barrier part is a non-conjugating ethylene spacer. Relevant features are correlated w ith the vibrational data previously collected on a series of medium-si ze alpha,alpha'-dimethyl end-capped oligothienyls. Experiments indicat e the existence of a rather effective conjugation in the case of 1,2-D i-[5-(2,2':5',2''-terthienyl)l-ethane, in spite of the introduction of sp(3) defects into the oligomer backbone.