Synthesis and characterization of 3-hexyl multi-substituted alpha,omega-diformyl-alpha-oligothiophenes (n=3, 6, 8)

The synthesis and characterization of a series of thienylenic a,o-diformyl-a-oligothiophenes with 3, 6 and 8 residues is reported. The chemical structure was determined by H NMR, FT-IR, mass and GPC analyses, while the electronic properties in the neutral state were studied by UV-Vis spectroscopy both in solution and in the solid state. In the UV-Us spectra of thin films, the vibronic structure is observed. The pronounced red-shift of the absorption maximum, with respect to spectra of unsubstituted a-oligothiophenes, is indicative of a contribution of carbonyl n-electrons to the overall delocalization via a mesomeric effect leading to a more planar structure. The solid state aggregation was investigated by XRD spectroscopy and optical microscopy. We observed for the longest terms a smectic arrangement typical of liquid crystalline compounds and a tendency to self-assembling onto hydrophilic substrates, forming angles ranging from 40-50" with respect to the normal to the surface.