Synthesis, characterization and Frequency-Dependent Dielectric Applications of New Indole–Oxindole-Based on Propanenitrile Derivati

In the current study, a new series of 3-(1H-indol-3-yl)-3-oxo-2-(2-oxoindolin-3-ylidene)propanenitrile derivatives 3a-d were prepared from condensation of 3-indolyl-3-oxopropanenitrile (1) with isatin derivatives 2a-d in the presence of piperidine as a catalyst. Compounds 3a-d was characterized using spectroscopic techniques and elemental analysis (CHNS). The dielectric properties like the permittivity (ε′), loss tangent (tan δ), and electric modulus (M′ and M″) were evaluated over a wide frequency range (0.1 Hz–10 MHz) to understand energy storage, energy loss, and relaxation processes in organic compounds 3a-d. Compounds 3a-c show higher permittivity values at low frequencies due to the contribution of dipolar and interfacial polarization. Compound 3b explores the strongest polarization and highest energy loss at low frequencies, likely influenced by its methyl group. Compound 3c exhibits moderate dielectric properties arising from the electron-withdrawing chloro group. Compound 3d shows constant ε′ and very low tan δ throughout the entire frequency range, indicating weak or absent dipolar relaxation, likely caused by its rigid benzyl substituent. Electric loss modulus (M″) analysis confirms these findings, showing clear relaxation peaks in 3a-c and no significant peak for 3d. Interestingly, the observed relative low permittivity and very loss values measured at high frequencies (10 MHz) make compounds 3b-d promising for high-speed signal transmission with minimal attenuation.