Theoretical and experimental studies on structural and optical properties of two quinoxaline 1,4dioxide derivatives

The thermal vacuum evaporation technique is utilized to prepare two novel, uniform and compact thin films of quinoxaline 1,4dioxide derivatives: 6-Chloro-3-(hydrazinecarbonyl)-2-methylquinoxaline 1,4-dioxide (CHMQ) and 6-Chloro-2-methyl-3-(2-(4-nitrbenzylidene)hydrazine-1-carbonyl) quinoxaline 1,4-dioxide (CMNQ). The structures of thin films are characterized using Fourier transform infrared spectrophotometry, X-ray diffraction and atomic force microscopy techniques. The theoretical vibrational frequencies and optimized geometric parameters (bond lengths, and bond angles) and the theoretical energy gap (HOMO–LUMO optical gap) values of the CHMQ and CMNQ compounds are also calculated. Crystalline structures, lattice parameters, Miller indices, diffraction angles and interplaner spacings for both compounds, in their powder form, are computed. Crystallite size, dislocation density and microstrain values are calculated for CHMQ and CMNQ thin films. Several optical constants like refractive index and absorption index of CHMQ and CMNQ thin films are calculated from the absolute values of their transmittance and reflectance spectra measured by a spectrophotometric method. The absorption parameters such as the type of electronic transition and the optical band gap values of the thin films are estimated and showed a good agreement with the corresponding theoretical energy gap values. The dispersion parameters (oscillator energy, dispersion energy, high frequency dielectric constant, lattice dielectric constant and ratio of free charge carriers’ concentration to its effective mass) of the thin films are estimated using single oscillator model in the non-absorbing region of each spectrum. The dielectric properties and the optical conductivity of the thin films are also determined.