Optical dispersion and frequency- and temperature-dependent dielectric properties of 4-ethylpiperazin-1-ium 3,5-dinitrobenzoate single crystal

Abstract

A single crystal of 4-ethylpiperazin-1-ium 3,5-dinitrobenzoate (EPDNB) was successfully grown by the slow evaporation solution growth technique at room temperature. Single-crystal X-ray diffraction analysis confirmed that EPDNB crystallizes in the monoclinic crystal system with unit cell parameters a = 19.34(3) Å, b = 8.738(19) Å, c = 19.41(2) Å, α = 90.00°, β = 96.82(5)°, γ = 90.00°, and a unit cell volume of 3257(14) Å³. Surface morphology examined by scanning electron microscopy revealed well-developed crystal facets, while XPS confirmed the presence and chemical states of carbon, nitrogen, and oxygen atoms. Optical studies demonstrated excellent transparency of 96.9% in the visible region with a lower cut-off wavelength of 437 nm. The optical band gap was estimated to be 2.92 eV, and the optical constants, including refractive index, extinction coefficient, optical conductivity, electrical conductivity, optical susceptibility, and optical polarizability, were evaluated. Dielectric studies revealed a decrease in dielectric constant and dielectric loss with increasing frequency, accompanied by an increase in AC conductivity indicating reduced space-charge polarization and enhanced charge transport. The crystalline quality, favourable optical characteristics, and stable dielectric behaviour suggest that EPDNB is a promising organic crystal for optoelectronic and electronic device applications.