Theoretical study of the vibrational spectra in poly(<i>p</i>-phenylene vinylene)

Abstract

Theoretical vibrational spectra of poly(p-phenylene vinylene) (PPV) are presented, based on a single--periodic-chain model and a harmonic potential with parameters transferred from n-divinyl benzene. The out-of-plane degrees of freedom and the infrared-absorption intensities were included in the calculations. The calculations evince a missing of the in-plane C-H bending infrared-absorption band of the trans-vinylene portion of PPV, as in trans-polyacetylene, which is a consequence of delocalized \ensuremath{\pi}-electron system. However, the electron-phonon coupling in PPV is relatively weak [as in poly(p-phenylene)] as compared to trans-polyacetylene (where the frequencies of the principal Raman lines are significantly lowered). As a conequence, PPV is an example of pristine polymer with well-delocalized \ensuremath{\pi}-electron system, but without significant electron-phonon coupling.