Fabrication and DFT Calculation of Amine-Functionalized Metal-Organic Framework as a Turn-On Fluorescence Sensor for Fe 3+ and Al 3+ Ions.

Due to their important role in biological systems, it is urgent to develop a material that can rapidly and sensitively detect the concentration of Fe 3+ and Al 3+ ions. In this work, a brand-new Cd II -based metal-organic framework [Cd(BTBD) 2 (AIC)] n ( JXUST-18 , BTBD = 4,7-bis(1 H -1,2,4-triazol-1-yl)-2,1,3-benzothiadiazole and H 2 AIC = 5-aminoisophthalic acid) with a 4-connected sql topology was designed and synthesized. The symmetrical Cd II centers are linked by AIC 2- ligands with μ 3 -η 1 :η 1 :η 1 :η 1 coordination mode to form a [Cd 2 (COO) 2 ] secondary building unit (SBU). The contiguous SBUs are further connected by BTBD ligands to form a two-dimensional (2D) layer structure. JXUST-18 can remain stable in aqueous solutions with pH values of 3-12 or in boiling water. Luminescent experiments suggest that JXUST-18 displays more than eightfold fluorescence enhancement in the presence of Fe 3+ and Al 3+ ions, and the detection limits for Fe 3+ and Al 3+ ions are 0.196 and 0.184 μM, respectively. Furthermore, the change in luminescence color is uncomplicatedly distinguishable with the naked eye under ultraviolet light at 365 nm. In addition, a series of devices based on JXUST-18 including fluorescence test strips, lamp beads, and composite films were developed to detect metal ions via visual changes in luminescence color. Significantly, JXUST-18 is a rare MOF-based turn-on fluorescence sensor for the detection of Fe 3+ ions. The theoretical calculation suggests that the complexation of Fe 3+ /Al 3+ ions and the -NH 2 group contributes to fluorescence enhancement.