Elevating the Optical Nonlinearity: Design, Synthesis, and Properties of a Mixed-Ligand Zinc(II) Metal–Organic Framework

The molecular design of new compounds with enhanced third-order nonlinear optical (NLO) applications is an important research topic in the area of functional materials. The present study describes a new 3D metal-organic framework [Zn₃(μ₃-bta)₂(μ₄-ata)₂]_n (abbreviated as NH₂-Zn-MUM-6), generated solvothermally from a multicomponent system composed of zinc(II) ions and 2-aminoterephthalic acid (H₂ata) and 1H-benzotriazole (Hbta) as linkers. Apart from an intricate porous structure with a seh-4,6-<i>Imma</i> topology, this MOF features good thermal stability and exceptional NLO characteristics. These were investigated in detail by a Z-scan method, revealing the remarkably high values of third-order nonlinear refractive index (<i>n</i>₂ = 30.83 × 10^-8 cm²/W) and nonlinear absorption coefficient (β = 4.06 × 10^-4 cm/W). An extended π-conjugation in both aromatic ligands, μ₃-bta^- and μ₄-ata^2-, and their interaction with Zn centers contribute to the formation of a highly polarizable system, thus significantly enhancing its capacity for NLO behavior. This study broadens the family of nonlinear optical materials and provides insights into the relationship between the structure and properties of amino-functionalized mixed-linker MOFs from the viewpoint of optical applications such as all-optical switching and data transmission.