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-Imma 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 (n2 = 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-ata2–, 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.