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 (HL_n) (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 (HL_n) were also studied using quantum chemical calculations. The alternating current conductivity (σ_ac) and dielectrical properties of HL_n 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 (σ^R). The conductivities are found to be dependent on the structure of the compounds. The values of σ_ac are related to the frequency as σ_ac α ω^S where the behavior of the exponent S determines the operating conduction mechanism. The correlated barrier hopping (CBH) is the dominant conduction mechanism for HL_n. The values of maximum barrier height (W_m) were calculated.