Syntheses, Structures, and Properties of 2,3,6,7-Tetrathiabenzo[1,3-cd:4,6-c′d′]dipentalene and Its Methyl, Ethyl, Methylthio, and Ethylthio Derivatives: Novel Fused Polynuclear Heteroarenes

The title heteroarene (TBD) isoelectronic with perylene was synthesized by way of a dimerization of thieno[2,3-b]thiophene. In addition, 1,4,5,8-tetramethyl, tetraethyl, tetrakis (methylthio), and tetrakis (ethylthio) derivatives were readily obtained from TBD. An X-ray crystallographic analysis of TBD demonstrated that the molecular structure is quite planar and symmetrical, but strained in the bond angles. The crystal structure comprises herringbone-type column stacking with intercolumnar heteroatomic interactions. TBD showed the same oxidation potential as did perylene, and like perylene, formed an iodine complex with a relatively high electrical conductivity of 0.11 S cm−1. On the other hand, all of the TBD derivatives gave poorly conductive iodine complexes. In addition, TBD and the derivatives formed charge-transfer complexes with strong electron acceptors, such as 7,7,8,8-tetracyanoquinodimethane (TCNQ), 2,3,5,6-tetrafluoro-7,7,8,8-tetracyanoquinodimethane (TCNQF4), 2,3-dichloro-5,6-dicyano-p-benzoquinone (DDQ), and 1,1,2,3,4,4-hexacyano-1,3-butadiene (HCBD). These π-complexes, however, were mostly of low conductivity. The electrolyses of TBP gave powdery conductive polymers, whereas those of tetrakis (methylthio) TBD gave crystalline radical cation salts with conductivities of the order of 10−3 S cm−1.