  The emission spectra of many pi-conjugated polymers and oligomers contain
side-band replicas with apparent frequencies that do not match the Raman active
mode frequencies. Using a time dependent model we show that in such many mode
systems, the increased damping of the time dependent transition dipole moment
correlation function results in an effective elimination of the vibrational
modes from the emission spectrum; subsequently causing the appearance of a
regularly spaced progression at a new apparent frequency. We use this damping
dependent vibrational reshaping to quantitatively account for the vibronic
structure in the emission spectra of pi-conjugated systems in the form of
films, dilute solutions and single crystals. In particular, we show that by
using the experimentally measured Raman spectrum we can account in detail for
the apparent progression frequencies and their relative intensities in the
emission spectrum.
