ELECTRONIC AND STRUCTURAL-PROPERTIES OF POLYPARAPHENYLENEVINYLENE FROM THE VIBRATIONAL-SPECTRA

The infrared and Raman spectra of oligomeric model molecules of polyparaphenylenevinylene (PPV) and of the polymer in the pristine state, and the infrared spectra of doped or photoexcited PPV are analyzed in terms of the theory of the effective conjugation coordinate (ECC). It is shown that all the spectroscopic observations (frequencies and intensities) are accounted for by ECC theory which shows that most of the observed features are due to the delocalization of pi-electrons. Measurements of the lower limit of the effective conjugation length and of the molecular chain length are made and the structural relevance of such concepts are discussed in terms of the conformation of the oligomeric or polymeric chain. Evidence is found that the charge carrier produces "quinoid" type defects, hence fully coplanar.