Modulation of the electronic structure of polyconjugated organic molecules by geometry relaxation: A discussion based on local Raman parameters

The Raman response of some polyconjugated materials is analyzed on the basis of local Raman parameters 〈∂α/∂RCC〉 determined by Density Functional Theory calculations and discussed in the frame of the Effective Conjugation Coordinate Theory. This approach allows to explain Raman spectra even when a deviation from the common behaviour is observed, thus providing a key for the interpretation of the main spectroscopic features in terms of structural parameters. The examples reported demonstrate that any change of the 〈BLA〉 parameter, describing the average degree of CC bond alternation along a conjugated sequence, is reflected by a remarkable modulation of the Raman spectrum, which indeed shows the signature of the molecular and electronic structure resulting from different chemical substitutions, conformation changes, chain length and environment effects.