Density functional theory for investigation of optical and spectroscopic properties of zinc-quinonoid complexes as semiconductor materials

Abstract

Three Zn(II) complexes of a new organic compound [(E)-4-methyl-N1-((E)-4-methyl-6-(p-tolylimino) cyclohex-3-en-1-ylidene)-N2-(p-tolyl) benzene-1, 2-diamine] (HMBD) were prepared and characterized by various techniques, including Fourier transform infrared (FTIR), UV–visible measurements, 1H-NMR, X-ray diffraction (XRD), and scanning electron microscopy (SEM). The data revealed that the HMBD ligand has an ONS tridentate-forming structure, while the complex of HMBD with zinc metal has a distorted octahedral structure, providing sp3d2 hybridization type. The geometry, HOMO, LUMO, polarizability, and other energetic parameters were evaluated by density functional theory (DFT) on Materials Studio package. Optical band gap (Eg) was estimated by DFT theory and optical properties for [Zn(MBD)(Cl)(H2O)2].2H2O (1), [Zn(MBD)](NO3)2H2O].2H2O (2), and [Zn(MBD)(CH3COO)(H2O)].3H2O (3) thin films as well, revealing that [Zn(MBD)(CH3COO)(H2O)].3H2O (3) thin film has the smallest energy gap and can be considered a highly efficient photovoltaic material. The resulting band gap energy values from both methods were found to be close to each other. Thin films of the ligand and zinc complexes were successfully fabricated by spin coating method. The optical constants, refractive index (n), and the absorption index (k) over the spectral range of the thin films were determined.