Synthesis and optical properties of soluble sexithiophenes with one central head-to-head junction

The regioselective synthesis of three sexithiophenes characterized by the presence of one central 3,3′-dimethyl-2,2′-bithiophene subsystem is described. One of these compounds was obtained under mild conditions by microwave-mediated synthesis. All sexithiophenes were soluble in organic solvents and displayed 30–40% fluorescence quantum yields in solution. In thin films the fluorescence quantum yields dropped to 1–2%, indicating conformational changes and strong intermolecular interactions in the solid state.