Encapsulation and Sensitization of Ln3+ within Indium Metal-Organic Frameworks for Ratiometric Eu3+ Sensing and Linear Dependence of White-Light Emission

Four novel compounds {[In(FDA)(HFDA)-(H2O4] center dot 2H(2)O} (Inl.) and I [Ln(2)(FDA)(2)(H2O)(10)]center dot FDA center dot 6H(2)O} (Ln = Dy2, Eu3, Gd4) have been hydrothermally synthesized by using the ligand furan-2,5-dicarboxylic acid (H(2)FDA). Driven by hydrogen bonding and pi...pi stacking, In1 displays a supramolecular metal-organic framework (MOF) with 6-connected pcu topology. Isostructural Dy2, Eu3, and exhibit bnn topological structures with the Schlafli symbol of Gd4 possess one-dimensional "wave-like" chains and further (4(6).6(4)) via a hydrogen bonding network. The triplet state (T-1 = 22371 cm(-1)) of H(2)FAD studied by compound Gd4 indicates that the energy transition from the H(2)FDA ligand to the Eu3 ion in compound Eu3 is efficient but inefficient to the Dy3+ ion in compound Dy2. Interestingly, the uncoordinated carbonyl group of compound In1 can sensitize Ln(3+) ions to obtain Dy3+@In1 and Eu3+@In1 materials for enhancing luminescence. The possible sensitization mechanism is studied by X-ray photoelectron spectroscopy and surface photovoltage spectroscopy. When the Eu3 ion is increased from 0.0 to 1.6 mu M in aqueous solution, compound In1 exhibits a distinguishable luminescence color change from blue to red with a fast detection time (<2 min), and the ratio of luminescence intensity at 617 nm to that at 408 rim (I-617/I-408) enhances linearly with a low detection limit of 0.87 mu M. Additionally, with careful adjustment of lanthanide(III) ions, white-light emission material could be achieved with metal content of Dy0.87Eu0.13.