Using the nitro group to induce π-stacking in terthiophenes
A new synthetic route to mononitrated oligothiophenes is described, as well as the preparation of halogenated derivatives (Br, I) thereof. An unusual deep red colour is observed and explained, with the aid of DFT calculations, as arising from a significant quinoidal contribution to the molecular structure. The crystal structures of two compounds, H(C4H2S)3NO2 and Br(C4H2S)3NO2, are presented. Both compounds have planar sheets held together by intermolecular short contacts (hydrogen bonds and, for the latter, NO2···Br interactions); the sheets do not directly superimpose, so the effect of the π-stacking is not maximized. Solid-state fluorescence and extended-Hückel band-structure calculations are also presented for these materials.
Re-evaluation of experimental measurements for the validation of electronic band structure calculations for LiFePO4 and FePO4