First Ln-MOF as a trifunctional luminescent probe for the efficient sensing of aspartic acid, Fe3+ and DMSO

Abstract

Five 3D network Ln³⁺ metal–organic frameworks (Ln-MOFs) formulated as [[Ln(μ₆-H₂cpboda)(μ₂-OH₂)₂]·xH₂O]_n [Ln³⁺ = La³⁺ (1), Nd³⁺ (2), Sm³⁺ (3), Eu³⁺ (4), Tb³⁺ (5), H₂cpboda = 5,5′-((5-carboxy-1,3-phenylene)bis(oxy))diisophthalic acid] were synthesized via a hydrothermal method. They were established by single-crystal X-ray and powder diffraction analyses, elemental analysis (EA) and thermogravimetric analyses (TGAs). All the compounds are isostructural with three-dimensional structures with the point symbol of (4¹³·6²)(4⁸·6⁶·8) in terms of topology, and they crystallize in the monoclinic space group P2₁/n. Interestingly, the solid-state luminescence of complexes 4 and 5 shows intense red and green emission, respectively. Besides, the Tb-MOF (5) is a good luminescent sensor, able not only to detect aspartic acid and Fe(III) ions with good stability, high efficiency and reversibility, but also to exhibit a rapid response and high selectivity to DMSO. To our knowledge, it is the first Ln-MOF that can act as a luminescent probe for the efficient sensing of DMSO, while the lone pair of electrons in the O of DMSO attacked the positive charge at the protonation carboxylic acid of H₅cpboda. Consequently, Tb-MOF (5) is a rare and versatile fluorescent probe for aspartic acid, Fe³⁺ cations and DMSO, simultaneously.