A multi-responsive chemosensor for highly sensitive and selective detection of Fe³⁺, Cu²⁺, Cr₂O₇^2- and nitrobenzene based on a luminescent lanthanide metal-organic framework

Excessive release of some hazardous chemicals, such as Fe³⁺, Cu²⁺, Cr₂O₇^2- and nitrobenzene, may endanger public health and the environment; therefore, targeted effective sensing strategies are important. In this report, a series of lanthanide-based metal-organic frameworks (Ln-MOFs), namely {[Ln(dpc)(2H₂O)]·(Hbibp)_0.5}_n (H₄dpc = 2-(3',4'-dicarboxylphenoxy) isophthalic acid, bibp = 4,4'-bis(imidazolyl) biphenyl, for I-VI, Ln = La, Ce, Pr, Nd, Sm, and Eu) were hydrothermally synthesized and characterized. Single-crystal X-ray diffraction indicates that I-VI are isostructural and the lanthanide center is nine-coordinated with a distorted tetrakaidecahedral configuration. The as-synthesized Ln-MOFs are assembled into three-dimensional frameworks through the connections of dpc^4- ligands and hydrogen bonding interactions. Notably, Eu-MOF (VI) behaves as a multi-responsive luminescent sensor toward Fe³⁺, Cu²⁺, Cr₂O₇^2- and nitrobenzene with high sensitivity, selectivity, stability and anti-interference ability against the coexistence of other ions or molecules based on high luminescence quenching efficiency. Additionally, Eu-MOF (VI) shows excellent luminescence stability and retains its structural integrity within the pH range of 2-12 in an aqueous solution and its solid sample maintains high thermodynamic stability up to 320 °C. Furthermore, the possible luminescence sensing mechanisms have been discussed in detail, and are supported by PXRD analysis, UV-vis spectroscopy, X-ray photoelectron spectroscopy (XPS) or density functional theory (DFT).