Synthesis and Properties of Dimethyl and Tetramethyl Anthra-bisdichalcogenoles and Their Charge-Transfer Complexes

Article abstract of DOI:10.1246/bcsj.64.2091

The dimethyl and tetramethyl derivatives of a series of anthra<1,9-cd:4,10-c'd'>bis<1,2>dithiole, diselenole, and ditellurole have been prepared as a new type of electron donor.The introduced methyl groups serve to enhance not only the donor strength, but also the solubility, enabling a ready formation of their charge-transfer complexes with various electron acceptors such as 7,7,8,8-tetracyanoquinodimethane (TCNQ), its 2,3,5,6-tetrafluoro derivative, 2,5-dimethyl derivative (DMTCNQ), 2,5-dimethoxy derivative (DMOTCNQ), 2,6-bis(dicyanomethylene)-2,6-dihydronaphthalene (TNAP), 3,3'-dichloro-5,5'-bis(dicyanomethylene)-Δ^2,2'-bi(3-thiolene) (DCBT), and 3,3'-dibromo-5,5'-bis(dicyanomethylene)-Δ^2,2'-bi(3-selenolene) (DBBS).Although the resulting complexes are mostly 1:1 stoichiometrical, the TCNQ complexes tend to favor a composition rich in acceptors; on the contrary, the DMTCNQ and DMOTCNQ complexes tend to favor a composition rich in donors.Their electrical conductivities range widely from 8 to 10^-9 S cm^-1, being apparently dependent on appropriate combinations of the donors and the acceptors.In general, the present donors have a tendency to form highly conductive complexes with TCNQ, TNAP, DCBT, and DBBS.These highly conductive complexes mostly show a broad electron absorption in the infrared region, being characteristic of a segregated stacked structure in a mixed valence state.On the other hand, the X-ray analysis of DMTCNQ complexes of 3,4-dimethyl, 8,9-dimethyl, and 3,4,8,9-tetramethylanthra<1,9-cd:4,10-c'd'>diselenoles and 3,4,8,9-tetramethylanthra<1,9-cd:4,10-c'd'>dithiole have revealed that all of the crystal structures have mixed stack columns of donor-donor-acceptor type.Of them, the 3,4-dimethyl derivative complex shows an unusually high conductivity (0.53 S cm^-1) for a mixed stacked structure, which is considered to be due to strong heteroatomic interactions of the intra- and inter-columns.