Structure, electrical conductivity and dielectric relaxation of charge-transfer complexes with 2,4,6,8-tetramethoxydibenzoselenophene as a donor

Abstract

2,4,6,8-Tetramethoxydibenzoselenophene (m-Se) forms 1 : 1 charge-transfer (CT) complexes with the acceptors, 7,7,8,8-tetracyanoquinodimethane (TCNQ), tetracyanoethylene (TCNE) and 2,3-dichloro-5,6-dicyano-1,4-quinone (DCQ) and is oxidized by iodine to [m-Se]I₃. X-Ray analyses of m-Se–TCNQ and m-Se–TCNE show both CT complexes to have columnar structures with stacks in which the coplanarly arranged donor and acceptor molecules alternate.

The electrical conductivities of the CT complexes with TCNQ, TCNE and DCQ and of the compound [m-Se]I₃ were relatively low (as a consequence of the crystal structures), however, and show the typical temperature dependences of semiconductors. The dielectric behaviour of the three CT complexes have also been studied, by conventional ac. measurements and by the thermostimulated depolarisation current (TSDC) technique. Relaxation peaks can be observed after a transformation of the complex permittivity ε* to the complex polarisability α*. The existence of these relaxations is confirmed by the TSDC measurements. By thermal sampling a nearly constant distribution of activation energies is obtained.