Synthesis of Covalently Linked Oligo(phenyleneethynylene) Wires Incorporating Dithiafulvene Units ‐ Redox‐Active "H‐Cruciforms"

Controlled alignment and self-assembly of molecular wires is one of the challenges in the field of molecular electronics. Here, we take an approach by which two oligo( phenyleneethynylene) s (OPEs) are linked together through one vinylogous linker. These molecules thus incorporate a central stilbene part from which the two OPE wires propagate in a so-called "H-cruciform"- like motif. Each ring of the central stilbene unit also contains a redox-active dithiafulvene (DTF) unit and this part of the molecule can thus be considered as an extended tetrathiafulvalene (TTF). Here, we present how such H-cruciforms based on OPE3 and OPE5 molecular wires are prepared by Sonoga shira coupling reactions and how the OPEs are functionalized with thioester end-caps as potential electrode anchoring groups. The optical and redox properties of these molecules are also presented. Unsymmetrical systems are achieved by subjecting a differentially protected diethynyl-substituted derivative of terephthalaldehyde to a phosphite-mediated coupling reaction in the presence of a 1,3-dithiol-2-thione. This reaction forms the central stilbene-extended TTF with alkyne substituents and relies on an "umpolung" of the para substituents from electron-withdrawing CHO groups to electron-donating DTF groups in a conversion also promoted by the phosphite.