Novel electron acceptors bearing a heteroquinonoid system, 5,5′-bis(dicyanomethylene)-5,5′-dihydro-Δ2,2′-bithiophene, its 3,3′-dichloro, 3,3′-dibromo, and 3,3′,4,4′-tetrabromo derivatives, and 5,5″-bis(dicyanomethylene)5,5″-dihydro-Δ2,2′:5′,2″-terthiophene were synthesized by the action of tetracyanoethylene oxide or by Pd(0)-catalyzed substitution reactions with sodium dicyanomethanide on the corresponding α,α′-dihalogenoheteroaromatics. They showed very small on-site Coulomb repulsion as expected, and afforded several highly conductive molecular complexes with electron donors such as hexamethylenetetratellurafulvalene.
Two conjugated homologues of thiophene-7,7,8,8-tetracyanoquinodimethane (TCNQ) have been prepared, which form highly conductive complexes with typical electron donors such as 2,2',5,5'-tetrathiafulvalene (TTF) or 5,6,11 ,I 2-tetrathiatetracene (TTT); these complexes have extensive conjugation.-t New compounds (3) and (4) were characterized by elemental and spectrocopic analyses.$ All complexes except non-stoicheiomeric (3) .TTF consist of 1 : 1 donor and acceptor components.
Three new electron donors, 5,6-dihydroacenaphtho[5,6-cd]-1,2-dithiole (1a), -diselenole (1b), and -ditellurole (1c) have been prepared with a view to developing new electron donors for low-dimensional molecular complexes. Their donor characters are markedly enhanced as compared with the corresponding dichalcogen-bridged naphthalenes. They formed charge-transfer complexes with tetracyanoquinodimethane (TCNQ). Their electrical conductivities increase in the order of polarizable chalcogen. The crystal structures of 1a–TCNQ complex and neutral 1c were determined by X-ray analyses. In the crystal, 1a and TCNQ form a unique mixed stack, that is, a pair of donors and a pair of acceptors make an alternately stacking column. Neutral 1c takes an almost planar conformation and molecules are connected to each other with strong Te–Te interactions.
ChemInform Abstract Novel heteroquinonoid compounds such as (III), (VI) and some of their brominated or oxo derivatives are prepared. They show effectively diminished on-site Coulomb repulsion owing to extensive conjugation, and most of their molecular complexes with various electron donors exhibit very high electrical conductivities up to metallic region.
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