Synthesis and structure of color tunable and white-light emitting lanthanide metal–organic framework materials constructed from conjugated 1,1′-butadiynebenzene-3,3′,5,5′-tetracarboxylate ligand

Abstract

A series of novel lanthanide metal–organic frameworks, namely [Ln₂(BBTC)_1.5(DMF)₄]·2DMF·4H₂O [BBTC⁴⁻ = 1,1′-butadiynebenzene-3,3′,5,5′-tetracarboxylate, Ln = Sm (1), Eu (2), Gd (3), Tb (4), Dy (5), Er (6) and Yb (7)], have been prepared via solvothermal reaction. Single crystal X-ray analyses reveal that complexes 1–7 are isostructural and crystallize in the C2/c space group. They have the same three-dimensional (3D) architectures, topological analyses suggest that these frameworks possess the 3D (4,6)-connected network with Schläfli symbol of {4³·6³}₃·{4⁴·6⁷·8⁴}·{4⁸·6⁶·8}. Solid-state photoluminescent investigations at room temperature reveal that complex 2 and 4 emit the intensely red characteristic luminescence of Eu³⁺ ions and green luminescence emissions of Tb³⁺ ions, with a long lifetime up to 1.38 and 0.33 ms, respectively, during which the ligand emission of BBTC⁴⁻ was quenched by the Eu³⁺ and Tb³⁺ ions. Complexes 5, 6 and 7 also display characteristic f–f luminescence emissions in the near-infrared region, respectively. These results indicate that BBTC⁴⁻ is an ideal ligand with an “antenna effect” for Ln³⁺ ions, and an efficient energy transfer exists between them. Color tunable and white-light emitting materials were successfully achieved by carefully adjusting the doping concentration of Eu³⁺ and Tb³⁺ ions in the Gd³⁺ compound through trichromatic method.