An Exceptionally Stable Porous Indium-Organic Framework with Enhanced Third-Order Nonlinear Optical Performance

Molecules featuring extended π-conjugated architectures, strong absorption characteristics, and high degrees of electronic delocalization constitute an important class of third-order nonlinear optical (NLO) materials with distinctive functional properties. In this work, we investigate an indium-based metal-organic framework (MOF) incorporating NH₂ groups and π-conjugated linkers, ({[In(DCBA)(CH₃NH₃)]_∞·Guest} (NH₂-H₄DCBA: 4″,6'-diamino-5',5″-bis(4-carboxyphenyl)-[1,1':3',1″:3″,1‴-quaterphenyl]-4,4‴-dicarboxylic acid), abbreviated as NH₂:MOF-In), which exhibits enhanced third-order NLO performance. The material crystallizes as a 6-connected framework adopting a diamond topology and displays several key structural features─namely, highly π-conjugated linkers, accessible amine functionalities, and robust framework stability─that collectively support strong NLO activity. At an excitation wavelength of 532 nm, the nonlinear optical parameters of NH₂:MOF-In were determined including the nonlinear refractive index, absorption coefficient, and third-order susceptibility. The nonlinear refractive index (n₂) falls within the range of (0.93-1.32) × 10^-7 cm²/W, while the nonlinear absorption coefficient (β) spans (1.39-3.67) × 10^-3 cm/W. In NH₂:MOF-In, the In³⁺ centers generate pronounced local electric fields that enhance polarizability and facilitate field-induced electronic redistribution. The coordination environment linking indium nodes with π-conjugated organic ligands enables efficient electron delocalization. These findings highlight NH₂:MOF-In as a promising platform for the development of advanced photonic components, including all-optical switching elements and high-speed optical data-transmission technologies.