title: Quinoidal/Aromatic Transformations in π-Conjugated Oligomers: Vibrational Raman studies on the Limits of Rupture for π-Bonds.
abstract: The vibrational Raman spectra of several series of aromatic and quinoidal compounds have been analyzed considering the downshifts and upshifts of the frequencies of the relevant Raman bands as a function of the number of repeating units. Oligothiophenes, oligophenylene-vinylenes, and oligoperylenes (oligophenyls) derivatives are studied in a common context. These shifts are taken as spectroscopic fingerprints of the changes in π-conjugation. For a given family, aromatic and quinoidal oligomers have been studied together, and according to their Raman frequency shifts located in the two-well BLA-energy curve of their ground electronic state as a function of the bond-length-alternation pattern (BLA). The connection among BLA values, π-conjugation, and Raman frequencies is taken here as the basis of the study. These Raman shifts/BLA changes have been related to important electronic properties of these one-dimensional linear π-electron delocalized systems such as quinoidal (polyene) and aromatic characters.
authors.affiliation: Department of Physical Chemistry, University of Málaga, Andalucia-Tech, Campus de Teatinos s/n, 29071, Málaga, Spain.
authors.forename: Paula Mayorga
authors.initials: PM
authors.lastname: Burrezo
authors.affiliation: Department of Physical Chemistry, University of Málaga, Andalucia-Tech, Campus de Teatinos s/n, 29071, Málaga, Spain.
authors.forename: José L
authors.initials: JL
authors.lastname: Zafra
authors.affiliation: Department of Physical Chemistry, University of Málaga, Andalucia-Tech, Campus de Teatinos s/n, 29071, Málaga, Spain.
authors.forename: Juan T
authors.initials: JT
authors.lastname: López Navarrete
authors.affiliation: Department of Physical Chemistry, University of Málaga, Andalucia-Tech, Campus de Teatinos s/n, 29071, Málaga, Spain.
authors.forename: Juan
authors.initials: J
authors.lastname: Casado
keywords: aromaticity; conjugation; oligomers; radicals; raman spectroscopy