Multifunctional Luminescent 3D Ln-MOFs with High Sensitivity for Trace Detection of Micronutrients

The synthesis of two versatile fluorescent metal-organic frameworks (MOFs), [Eu(4-NCP)(1,4-bdc)]·0.5H₂O (1) and [Eu(4-NCP)(4,4'-bpdc)]·0.75H₂O (2) (HNCP = 2-(4-carboxyphenyl)imidazo(4,5-f)-(1,10)phenanthroline, 1,4-H₂bdc = benzene-1,4-dicarboxylic acid, 4,4'-H₂bpdc = 4,4'-biphenyldicarboxylic acid), was carried out using a hydrothermal method. These MOFs were characterized through various advanced technologies to determine their structural information. The results indicate that both MOFs exhibited 3D network structures with specific topologies. Furthermore, these MOFs demonstrated exceptional thermal stabilities and adsorption capabilities. Additionally, complex 2 was utilized for studying the fluorescence sensing properties of various micronutrients including metal ions, nitro aromatic compounds, and biological small molecules. Notably, complex 2 showed promising potential as a multifunctional sensor for selectively detecting Fe³⁺, nitrobenzene, and ascorbic acid in aqueous solutions through fluorescence quenching with low limits of detection (LODs ∼ 10^-7 M) and high quenching constants (K_sv ∼ 10³ M^-1). Moreover, the detection mechanism of complex 2 was further investigated by using experimental methods and DFT calculations.