E. Sánchez Martínez

Structure, electrical conductivity and dielectric relaxation of the phenothiazine-tetracyanoethene 1:1 complex

Abstract 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 σ 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 Erying equation with an activation enthalpy of ΔH ν = 0.99 eV and entropy ΔS ν ≈ 10 −3 eV K −1 . The temperature dependence was also analysed in terms of an Arrhenius equation leading to E a = 1.05 eV.

Structure and dielectric relaxation of 2,3,7,8-tetramethoxychalcogenanthrene-TCNQ complexes

Abstract 2,3,7,8-Tetramethoxychalcogenanthrenes (5,10-dichalcogena- cyclo -diveratrylenes, Vn 2 EE′) and 7,7,8,8-tetracyanoquinodimethane (TCNQ) form charge-transfer (CT) complexes of composition Vn 2 EE′·TCNQ (E = E′ = S, Se; E = S, E′ = Se, Te). The structure of the hitherto unknown compound Vn 2 STe·TCNQ is described. The dielectric relaxation of the whole series of CT complexes is determined and the results are correlated with the structural data.

Structure, electrical conductivity and dielectric relaxation of a 1,2-dimethoxybenzene-tetracyanoethene 1:1 complex

Abstract 1,2-Dimethoxybenzene (Ver) as a donor and tetracyanoethene (TCNE) as an acceptor from the dark blue charge-transfer complex Ver·TCNE. In the crystal stacks, in which the donor (D) and acceptor (A) molecules alternate according to the sequence …DAD…A…DAD…A…, centro-symmetric DAD units can be distinguished. In these units the molecules are arranged in such a way that an optimum overlap of the corresponding HOMOs and LUMOs is guaranteed, as is shown by MNDO and HAM 3 calculations. Ver·TCNE is a semiconductor with a gap energy of Eg = 0.85 eV and a pre-exponential factor of σo = 0.91 S/cm. The temperature dependence of dielectric relaxation is characterized by an Eyring equation and gives an activation enthalpy of ΔH ‡ = 0.76 eV and entropy ΔS ‡ = 0.95 × 10 −4 eV/K .

Self-stacking systems 5. Electrical and dielectric properties of 5,5-dibromo-2,3,7,8-tetramethoxyselenanthrene

Abstract The title compound is a semiconductor with a gap energy of Eg = 1.07 eV and a pre-exponential factor of σ0 = 2.5 × 10−3 S/cm. Its dielectric relaxation is of the non-Debye type (Cole-Cole circular arc with a characteristic parameter h of 0.706) showing a temperature dependence characterised by an Eyring equation with an activation enthalpy of gDH ‡ = 1.61 eV and entropy of ΔS ‡ = 2.15 × 10 −3 eV/K .

Electric and magnetic properties of charge transfer complexes with chalcogenathrene donors

Abstract Dark coloured samples of Vn 2 E 2 ·TCNQ (1,2) and Vn 2 E 2 ·DCQ (3,4) + were studied. Compounds (1) and (2) form columnar structures in which donors and acceptors alternate. Structures of (3) and (4) have not been determined until now, but scanning electron microscopy results point to their being isotypical to each other and different from (1) and (2). With polycrystalline samples dc and ac conductivities between 280 and 350 K were measured and a typical semiconducting behaviour was found. From ESR measurements spin concentration n and with σ values charge carrier mobility b were evaluated. Spin concentrations correlate with magnetic susceptibility results. At room temperature, values of spin concentration and electrical conductivity of DCQ compounds are higher than those of the corresponding TCNQ complexes.