Electronic and dynamical effects from the unusual features of the Raman spectra of oligo and polythiophenes

A comprehensive search for structure/property correlations in the Raman spectra of oligo and polythiophenes is carried out for many homologous series of oligothiophenes (approximately 50 compounds). The observed spectroscopic features are interpreted, with the help also of ab initio calculations, on the basis of the theories currently adopted for the understanding of the properties of polyconjugated materials. From the analysis of the vibrational spectra the behavior of π electrons as function of conjugation length (electron–phonon coupling, pinning, effective electronegativity of the heteroatoms, etc.) is discussed and frequency and intensity correlations useful in chemical diagnosis are proposed.