Luminescence tuning and sensing properties of stable 2D lanthanide metal–organic frameworks built with symmetrical flexible tricarboxylic acid ligands containing ether oxygen bonds

Abstract

Three isostructural lanthanide metal–organic frameworks (Ln-MOFs), {[Ln(L)(H₂O)₂]·H₂O}_n (M-Ln, Ln = Eu/Tb/Dy), were prepared with a flexible 3,5-(4-carboxybenzyloxy) benzoic acid (H₃L) ligand and lanthanide ions by a solvothermal method. M-Ln are two-dimensional (2D) grid layer-stacking frameworks. M-Eu exhibits excellent chemical stabilities against organic solvents and shows strong luminescence. The experimental results indicated that M-Eu could be used as an ideal fluorescent probe to detect nitrobenzene (NB) in different solvents with a lower detection limit. M-Eu can also be used as a pH sensor because of its superior water stability. Furthermore, M-Eu and M-Tb show unique strong luminescence properties with high absolute quantum yields. The quantum yields can even reach up to 11.8% and 60.5%, respectively. Simultaneously, various kinds of heterometallic doped M-Eu_xTb_1−x MOFs were acquired by tuning the ratios of Eu³⁺/Tb³⁺ ions, showing the unique color changes from red, orange-red, orange, orange-yellow, light yellow, yellow to green.