INFRARED-SPECTROSCOPY AND STEREOCHEMICAL STRUCTURE OF POLY(P-PHENYLENE VINYLENE)

Theoretical infrared (ir) spectra of trans- and cis- forms of poly(p-p henylene vinylene) (PPV) are presented, based on a single-periodic-cha in model and harmonic potential with parameters transferred from p-div inyl benzen molecule. The out-of-plane degrees of freedom and the infr ared intensities were included in the calculations. The calculations o f polarized infrared spectra of cis- and trans-PPV do not show practic ally any difference. However, as the calculations evince the absence o f the in-plane C-H bending infrared absorption band of trans-vinylene portion of experimental infrared spectrum of PPV, which is a consequen ce of a delocalized pi-electron system (similarly to the case of trans -polyacetylene but not cis-polyacetylene), it seems that stereochemica l structure of PPV is of the trans-form. Additional X-ray analysis is still necessary to support our conclusion.