Synthesis and investigation of linear and nonlinear optical parameters of hafnium nitrosalicylate complex

We report the synthesis and multi-technique characterization of tetrakis (5-nitrosalicylate) hafnium (IV), a previously unreported hafnium-organic complex with potential photonic applications. Optimized chelation of Hf (IV) with 5-nitrosalicylic acid yielded the target compound at 67% efficiency. Multimodal structural validation (XRD/FT-IR/EDX) confirmed an octacoordinated crystalline lattice featuring cyclic chelate motifs, exhibiting elemental homogeneity and thermal resilience. Spectroscopic ellipsometry uncovered dual-range optical functionality: In the UV-Vis region, the material exhibits strong ligand-to-metal charge-transfer (LMCT) characteristics in the UV. Conversely, across Vis-NIR wavelengths, it exhibited dielectric characteristics with positive dispersion and declining absorption, confirming high visible transparency. Nonlinear optical studies using the Z-scan technique demonstrated significant third-order susceptibility, featuring self-defocusing refraction and two-photon absorption. Calculated figures of merit confirmed its suitability for all-optical switching devices. This bifunctional optical response-dominated by strong ligand-to-metal charge-transfer (LMCT) absorption in the UV and dielectric behavior in the Vis-NIR-positions the complex as a promising material for UV-selective photodetection, UV-driven photocatalysis, and devices that exploit strong, spectrally selective absorption (e.g., optical sensors and nonlinear optical limiters). By integrating molecular chelate design with optoelectronic functionality, this work advances metal-organic frameworks for next-generation photonic technologies.