Novel Electron Acceptors Bearing a Heteroquinonoid System. II. Synthesis and Conductive Complexes of 2,5-Bis(dicyanomethylene)-2,5-dihydrothieno[3,2-b]thiophene, 2,6-Bis(dicyanomethylene)-2,6-dihydrodithieno[3,2-b:2′,3′-d]thiophene, and Their Derivatives

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Abstract
Novel heteroquinonoid compounds as potential electron acceptors, 2,5-bis(dicyanomethylene)-2,5-dihydrothieno[3,2-b]thiophene (4a), 3,6-dibromo derivative, 2,6-bis(dicyanomethylene)-2,6-dihydrodithieno[3,2-b:2′,3′-d]thiophene, 3,5-dibromo derivative, and 4,4-dioxide were synthesized by the action of tetracyanoethylene oxide or by a Pd(0)-catalyzed substitution reaction with sodium dicyanomethanide on the corresponding α,α′-dihalo-substituted fused thiophenes. They show effectively diminished on-site Coulomb repulsion owing to the extensive conjugation, and most of their molecular complexes with various electron donors exhibit very high electrical conductivities up to metallic region. In addition, X-ray crystallographic analysis of the complex of 4a with bis(ethylenedithio)tetrathiafulvalene has elucidated that sulfur atoms embedded in 4a molecule are capable of inducing a significant intermolecular interaction, forming a sheet-like network structure.