Tunable Emission and Selective Luminescence Sensing in a Series of Lanthanide Metal–Organic Frameworks with Uncoordinated Lewis Basic Triazolyl Sites

Abstract

Four isostructural lanthanide metal–organic frameworks (Ln-MOFs) {[Ln(L)1.5(H2O)]·4H2O}n (1-Ln) (Ln = Sm, Eu, Gd, and Tb) have been successfully synthesized under solvothermal conditions with 2-(1H-1,2,4-triazol-1-yl) terephthalic acid (H2L) and Ln(NO3)3·nH2O (n = 0, 6). 1-Ln shows a binodal (3,8)-connected three-dimensional framework that possesses a one-dimensional pore channel decorated with uncoordinated Lewis basic triazolyl sites. 1-Eu and 1-Tb exhibit bright red and green emissions with absolute quantum yields of 9.1% for 1-Eu and 53.3% for 1-Tb. The luminescence explorations demonstrated that 1-Tb exhibits high quenching efficiency and low detection limit for sensing Fe3+ and nitrobenzene. Meanwhile, the fluorescence intensity of the quenched 1-Tb samples was resumed after washing with ethanol, which shows highly selective and recyclable luminescence sensing for Fe3+ and nitrobenzene. Importantly, by doping different concentrations of Eu3+ and Tb3+ ions, a series of dichromatic doped 1-EuxTb1-x MOFs were fabricated, showing an unusual fluent change of the emissions color from green, yellow, orange, orange-red, and red.