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

The regioselective synthesis of three sexithiophenes characterised 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 yield in solution. In thin films the fluorescence quantum yield dropped to 1-2% indicating conformational changes and strong intermolcular interactions in the solid state.