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 NH 2 groups and π-conjugated linkers, ({[In(DCBA)(CH 3 NH 3 )] ∞ ·Guest} (NH 2 −H 4 DCBA: 4″,6′-diamino-5′,5″-bis(4-carboxyphenyl)-[1,1′:3′,1″:3″,1‴-quaterphenyl]-4,4‴-dicarboxylic acid), abbreviated as NH 2: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 NH 2:MOF-In were determined including the nonlinear refractive index, absorption coefficient, and third-order susceptibility. The nonlinear refractive index (n 2 ) falls within the range of (0.93−1.32) × 10 −7 cm 2 /W, while the nonlinear absorption coefficient (β) spans (1.39−3.67) × 10 −3 cm/W. In NH 2:MOF-In, the In 3+ 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 NH 2: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.