Highly Sensitive Luminescent Probe of Aniline and Trace Water in Organic Solvents Based on Covalently Modified Lanthanide Metal–Organic Frameworks

A novel europium functionalized metal–organic framework (MOF) named Eu3+@UiO-66-NH2-IM is robustly synthesized via covalent PSM (postsynthetic modification). The ligand of matrix MOF is covalently modified via imidazole-2-carboxaldehyde after the UiO-66-NH2 is synthesized. The successful transformation of amino groups to imine groups is confirmed by Fourier transform infrared spectra (FTIR) analysis. The modified MOF named UiO-66-NH2-IM shows outstanding crystalline stability. After Eu3+ is doped into UiO-66-NH2-IM, the as-prepared fluorescent MOF displays the characteristic emission line of Eu3+. Discussion of the tunable emission color of the modified MOF is included, and white-light integration could be achieved through altering the ratio of Eu3+ doped into the MOF. In addition, the luminescent transparent film based on Eu3+@UiO-66-NH2-IM can emit white light under proper excitation wavelength, which may be helpful to some potential applications in lighting. In addition, Eu3+@UiO-66-NH2-IM shows a different emission response in water and organic solvents, and it is further developed into a sensitive probe for the detection of water content in organic solvents (ethanol, DMF) with low detection limits (0.088 and 0.054%, respectively) by utilizing its quenching behavior in water. Meanwhile, Eu3+@UiO-66-NH2-IM displays a greatly selective and sensitive response for detecting aniline with a low detection limit (0.072%) and a broad linear range (0–3.75%), and the signal of the detection is obvious, which can be seen clearly under the irradiation of UV light.