Femtosecond optical absorption in poly(3-alkyl thienylene)s

We report transient absorption measurements on poly(3-hexyl thienylene) and poly(3-dodecyl thienylene). In both materials we observe a transient absorption followed by a transient bleaching, and oscillations with a period of 120 fs. We propose that the oscillatory features are due to coupling between vibrational modes of the polymer chains and the {π}-electronic structure, and that the unusual initial absorption is due, at least in part, to electromodulation of the band edge produced by separation of electrons and holes.