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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. [ABSTRACT FROM AUTHOR]

A general description of the use of the Raman spectra of polyconjugated molecules to infer their electronic and molecular properties and how these change in a number of situations is illustrated with several examples, with particular emphasis on oligothiophene molecules. The most noticeable features of the Raman spectra of these molecules and the main theoretical models developed for their understanding have been revised and explained in terms related to π-electron delocalization intimately connected with the aromatic and quinoidal characters. [ABSTRACT FROM AUTHOR]

Herein we present novel Raman spectroscopic studies carried out for polyselenophene (PSe), poly(3,4-ethylenedioxyselenophene) (PEDOS), and alkyl-substituted poly(alkyl-3,4-ethylenedioxyselenophene) (PEDOS-Cn: n = 2, 8, and 12) homologues. These spectroscopic data are combined with morphological and structural analysis techniques, such as AFM, and DFT simulations. An investigation into the extent of p-conjugation in PSe is presented by comparing its spectral signatures with those of a homologous series of oligoselenophenes. Our experimental data suggest that p-conjugation in the PSe backbone extends to more than six selenophene units. The incorporation of ethylenedioxy (EDO) groups in PEDOS results in a more complex spectrum and a downshift of the C=C/C--C stretching vibration (or effective conjugation coordinate (ECC) mode); this provides evidence for an improvement in the π-conjugational properties along the PSe backbone upon EDO substitution. The dispersity of p-conjugation lengths in different PEDOS samples obtained through different synthetic routes is evaluated as a function of different structural factors. Finally, we present experimental evidence that the insertion of alkyl chains into the EDO units slightly impacts on the pconjugational properties of the PEDOS backbone in the non-annealed samples (with an improved p-electron delocalization found in PEDOS-C8), but moderately affects the degree of molecular order of polymer films upon thermal annealing. [ABSTRACT FROM AUTHOR]

Herein we present novel Raman spectroscopic studies carried out for polyselenophene (PSe), poly(3,4-ethylenedioxyselenophene) (PEDOS), and alkyl-substituted poly(alkyl-3,4-ethylenedioxyselenophene) (PEDOS-Cn: n=2, 8, and 12) homologues. These spectroscopic data are combined with morphological and structural analysis techniques, such as AFM, and DFT simulations. An investigation into the extent of π-conjugation in PSe is presented by comparing its spectral signatures with those of a homologous series of oligoselenophenes. Our experimental data suggest that π-conjugation in the PSe backbone extends to more than six selenophene units. The incorporation of ethylenedioxy (EDO) groups in PEDOS results in a more complex spectrum and a downshift of the C[DOUBLE BOND]C/C[BOND]C stretching vibration (or effective conjugation coordinate (ECC) mode); this provides evidence for an improvement in the π-conjugational properties along the PSe backbone upon EDO substitution. The dispersity of π-conjugation lengths in different PEDOS samples obtained through different synthetic routes is evaluated as a function of different structural factors. Finally, we present experimental evidence that the insertion of alkyl chains into the EDO units slightly impacts on the π-conjugational properties of the PEDOS backbone in the non-annealed samples (with an improved π-electron delocalization found in PEDOS-C8), but moderately affects the degree of molecular order of polymer films upon thermal annealing. [ABSTRACT FROM AUTHOR]

This article investigates the excited and charged states of three branched oligothiophenes with methyl-thienyl side groups as models to promote 3D arrangements. A comparison with the properties of the parent systems, linear all-α,α-oligothiophenes, is proposed. A wide variety of spectroscopic methods (i.e., absorption, emission, triplet-triplet transient absorption, and spectroelectrochemistry) in combination with DFT calculations have been used for this purpose. Whereas the absorption spectra are slightly blueshifted upon branching, both the emission spectra and triplet-triplet absorption spectra are moderately redshifted; this indicates a larger contribution of the β-linked thienyl groups in the delocalization of the S1 and T1 states rather than into the S0 state. The delocalization through the α,β-conjugated path was found to be crucial for the stabilization of the trication species in the larger branched systems, whereas the linear sexithiophene homologue can only be stabilized up to the dication species. [ABSTRACT FROM AUTHOR]