Fabrication of Ln-MOFs with color-tunable photoluminescence and sensing for small molecules

Abstract Three isomorphic lanthanide metal-organic frameworks (Ln-MOFs) [LnL(H 2 O) 2 ]·2H 2 O (Ln=Tb for 1 , Eu for 2 , Gd for 3 ) have been constructed from flexible organic ligand 4-(2-carboxyphenoxy)benzene-1,3-dioic acid (H 3 L). They exhibit two-dimensional (2D) layered structure with the rhombus windows along the b axis. This network can be described as a shubnikov plane net with Schafli symbol of (4 3 ) 2 (4 6 .6 6 .8 3 ). Solid state luminescent studies indicate that 1 and 2 show the characteristic red, and green emissions of the corresponding Ln 3+ ions, respectively, while 3 exhibits blue emission arising from the organic ligand. Then by adjusting the relative amounts of different luminescent components into the well-defined host framework, a series of new co-doped Ln-MOF, Tb 1−x Eu x L ( 4 ) (x refers to the molar ratios of Eu 3+ and Tb 3+ ), with tunable luminescence have been fabricated. The luminescent color of 4 can be tuned from green to red due to the energy transfer from the Tb 3+ to Eu 3+ ions by changing the doping concentration of the Eu 3+ ions. In addition, 2 exhibits good stability in different solvents and excellent fluorescence sensing for small molecules, especially for CH 3 CN and nitrobenzene.