New molecular wires with two ferrocene hinges

Conventional molecular wires of the oligophenyleneethynylene (OPE) type are two-dimensional rigid molecules of fixed length. Possible problems concerning pi,pi stacking and device geometry associated therewith might be overcome by replacement of some of the 1,4-phenylene moieties by 1,1'-disubstituted ferrocene units. These make the wire three-dimensional thereby reducing the likelihood of intermolecular pi,pi interactions and serve in addition as hinges as a result of the almost free rotation around the Cp-Fe-Cp axis. This feature provides a limited conformational flexibility with the possibility of a length adjustment comparable to a foldable ruler. Here the syntheses and some physical properties of molecular wires containing two ferrocene hinges are described. In a number of cases the Sonogashira coupling reactions used for the coupling of the respective building blocks proceed much faster under microwave irradiation as compared to conventional heating.