Geometrical structure and optical properties of antipyrine Schiff base derivatives

Uniform thin films of 4-(4-benzalideneamine)antipyrine (L1) and 4-(4-methoxybenzalideneamine)antipyrine (L2) are prepared successfully by spin coating technique. Crystal and molecular structure of L1 and L2 are investigated by many techniques such as elemental analysis, IR spectra, H1 NMR and X-ray diffraction (XRD). The molecular structures of the investigated compounds (L1 and L2) are optimized theoretically and the quantum chemical parameters are calculated. Both of L1 and L2 powders are polycrystalline with monoclinic crystal structure. The optical properties of thin films of L1 and L2 are investigated by spectrophotometric technique in the wavelength range 200–2500 nm. The presence of methoxy group increases the value of dielectric constant at infinity, ε∞, from 3.257 to 3.328 and the value of the optical energy gap (Egopt) from 3.56 to 3.67 eV. The type of optical transition near the absorption edge is found to be indirect allowed transition for L1 and L2.