Raman Spectroscopic Characterization of Polyselenophenes and Poly(3,4-ethylenenedioxyselenophene)s

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 pi-conjugation in PSe is presented by comparing its spectral signatures with those of a homologous series of oligoselenophenes. Our experimental data suggest that pi-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 pi-conjugational properties along the PSe backbone upon EDO substitution. The dispersity of pi-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 pi-conjugational properties of the PEDOS backbone in the non-annealed samples (with an improved pi-electron delocalization found in PEDOS-C8), but moderately affects the degree of molecular order of polymer films upon thermal annealing.