SYNTHESES AND PROPERTIES OF DIMETHYL AND TETRAMETHYL ANTHRA[1,9-CD-4,10-C'D']-BIS[1,2]DICHALCOGENOLES AND THEIR CHARGE-TRANSFER COMPLEXES

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)-DELTA-2,2'-bi(3-thiolene) (DCBT), and 3,3'-dibromo-5,5'-bis(dicyanomethylene-DELTA-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 analyses 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.