Dielectrical, conduction mechanism and thermal properties of rhodanine azodyes

In this paper, we report on the differential scanning calorimetry analysis (DSC) and thermogravimetric analysis (TGA) performed for 5-(4'-derivatives phenylazo)-2-thioxothiazolidin-4-one (HLn) (n=1, R=OCH3; n=2, R=CH3; n=3, R=H; and n=4, R=NO2) in the temperature range 46–800 °C. The values of the thermal activation energies of decomposition of HL1, HL3 and HL4 are found in the range 59.10–299.72 kJ/mol. The molecular and electronic structures of the investigated compounds (HLn) were also studied using quantum chemical calculations. The alternating current conductivity (σac) and dielectrical properties of HLn were investigated in the frequency range 0.1–100 kHz and temperature range 303–500 K. The temperature and frequency dependence of the real and the imaginary dielectrical constants are studied. The values of the thermal activation energy for derivatives under investigation were calculated at different frequencies. The values of thermal activation energies of electrical conductivity ΔE1 and ΔE2 for all ligands decrease with increasing the test frequency. The activation energies, ΔE1 and ΔE2, increase according to the following order p-(NO2>H>CH3>OCH3). This is in accordance with that expected from Hammett's substituent coefficients (σR). The conductivities are found to be dependent on the structure of the compounds. The values of σac are related to the frequency as σacα ωS where the behavior of the exponent S determines the operating conduction mechanism. The correlated barrier hopping (CBH) is the dominant conduction mechanism for HLn. The values of maximum barrier height (Wm) were calculated.