Photovoltaic-Relevant Optical and Dielectric Behavior of the Azo-Oxime Ligand and Its VO2+-, Cu2+-, and Fe3+-Based Complexes Films

Cu2+, VO22+, and Fe3+ mononuclear complexes of the oxime-based ligand, 2-hydroxy-5-(p-tolyldiazenyl)benzaldehyde oxime (H2L, 1), have been synthesized and structurally characterized by analytical, thermal, and spectral tools. They have been characterized by microanalyses (C, H, and N), 1H and 13C-NMR, FT-IR, UV-Vis, and/or ESR spectral measurements. The various analytics data indicate that the oxime-based ligand behaved as a neutral bidentate chelator binding Cu2+, VO2+, and Fe3+ cations via the nitrogen atom of the protonated oximatic group and protonated phenolic hydroxyl oxygen atom, adopting a distorted octahedral geometry. Furthermore, computational studies utilizing DFT/B3LYP/6-311(pd) include assessment of dipole moment, global reactivity descriptors, optimized geometry, LUMO-HOMO energy gaps, and molecular electrostatic potential image (MEP), which were estimated to support the geometrical structure of Cu2+, VO2+, and Fe3+ complexes. Furthermore, the optical parameters, viz. the refractive index (n) and extinction coefficient of azo-oxime ligand and its complexes, have been precisely estimated within a 300–1100 nm wavelength. The values of optical gap (Egap) for the azo-oxime ligand and its complex films diminished from 2.96 eV for H2L to 1.83 eV for the Fe3+ film; however; the n values follow an opposite behavior. The obtained n and Eg values are comparable to those reported for various semiconducting materials, suggesting the potential suitability of the investigated films for future semiconductor and optoelectronic applications. Although practical device performance remains to be evaluated, these low-cost and easily prepared materials could serve as promising candidates in these fields. Furthermore, the dielectric and nonlinear optical parameters have been thoroughly evaluated and comprehensively discussed.