Structure, electrical conductivity and dielectric relaxation of the 1,2-bis(methylthio)benzene-2,3-dichloro-5,6-dicyano-1,4-benzoquinone 1 : 1 charge-transfer complex

Abstract

1,2-Bis(methylthio)benzene forms a 1 : 1 charge-transfer (CT) complex with 2,3-dichloro-5,6-dicyano-1,4-benzoquinone (DDQ). X-Ray analysis shows the compound to have a columnar structure with stacks in which the equidistantly and coplanarly arranged donor and accepter molecules alternate. By the relative orientations of the successive donor and accepter molecules in the stacks an optimum overlap of the relevant HOMOs and LUMOs, which are of is-type according to MNDO calculations, is guaranteed.

The electrical conductivity of the CT complex is relatively low (as a consequence of the crystal structure), but shows a temperature dependence typical of semiconductors. The dielectric behaviour of the compound has also been studied. The results can be represented by an electrical model circuit of the ladder type, indicating that the following contributions are of similar importance: (i) hopping conduction into the bulk of the polycrystalline sample, (ii) interfacial impedance of the polycrystals, and (iii) electrode adsorption-diffusion phenomena.