STRUCTURE, ELECTRICAL-CONDUCTIVITY AND DIELECTRIC-RELAXATION OF THE PHENOTHIAZINE-TETRACYANOETHENE 1-1 COMPLEX

Phenothiazine (PTZ) as a donor and tetracyanoethene (TCNE) as an acceptor form the dark blue charge-transfer complex PTZ-TCNE. In the solid state stacks are found in which the donor (D) and acceptor (A) molecules alternate according to the sequence -D-A- -D-A- -D-A-. Within the stacks the donor and acceptor molecules are arranged coplanarly to each other in such a way that an optimum overlap of the corresponding HOMOs and LUMOs is guaranteed, as is shown by MNDO calculations. PTZ-TCNE is a semiconductor with a gap energy of E(g) = 1.69 eV and a pre-exponential factor of sigma(o) = 575 S cm-1. Its dielectric relaxation is of the non-Debye type (non-symmetrical Cole-Cole plot, described by a Havriliak-Negami equation) showing a temperature dependence characterized by an Eyring equation with an activation enthalpy of DELTA-H not-equal = 0.99 eV and entropy DELTA-S not-equal almost-equal-to 10(-3) eV K-1. The temperature dependence was also analysed in terms of an Arrhenius equation leading to E(a) = 1.05 eV.