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

Three isomorphic lanthanide metal-organic frameworks (Ln-MOFs) [LnL(H2O)(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 (H3L). 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, Tbi(1-x)Eu(x)L (4) (x refers to the molar ratios of Eu3+ and Tb3+), 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 Tb3+ to Eu3+ ions by changing the doping concentration of the Eu3+ ions. In addition, 2 exhibits good stability in different solvents and excellent fluorescence sensing for small molecules, especially for CH3CN and nitrobenzene.