Convergent Synthetic Routes to Orthogonally Fused Conjugated Oligomers Directed toward Molecular Scale Electronic Device Applications

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Abstract
This paper describes the synthetic organic phase of a project directed toward the construction of molecular scale electronic devices. Outlined is a convergent synthetic route to orthogonally fused conjugated organic oligomers. The final systems are to have a potentially conducting chain fused perpendicularly to a second potentially conducting chain via a σ bonded network. One of the core segments synthesized is based on a spirobithiophene moiety with a central silicon atom. It is formed by a zirconium-promoted bis(bicyclization) of a tetrapropargylsilane. The second core is a 9,9‘-spirobifluorene system. Terminal halide groups provide the linkage points for further extension of the chains via Pd-catalyzed or Pd/Cu-catalyzed cross coupling methods. All four branching arms are affixed to the core in a single operation, thus making the syntheses highly convergent. In the cases of the larger functionalized systems, alkyl substituents on the thiophenes afford soluble materials. In order to prepare the molecules with >50 Å lengths, an iterative divergent/convergent approach had to be utilized for the construction of oligo(thiophene−ethynylene) branching arms. Organopalladium-catalyzed procedures are used extensively for the syntheses of the orthogonally fused compounds.