Series d–f Heteronuclear Metal–Organic Frameworks: Color Tunability and Luminescent Probe with Switchable Properties

Abstract

A series of five unique d-f heteronuclear luminescent metal-organic frameworks (MOFs) in an entangled polyrotaxane array and the light-harvesting block homonuclear zinc compound have been isolated successfully and characterized. The series of isostructural polymers feature 3,4-connected (4.8²)(4.8³.9²)(6.8.9)₂(6.9²)(8³) topology and high stability, exhibiting diverse void spaces. By taking advantage of the isostructural MOFs 2 and 3, the intensities of red and green emissions can be modulated by adjusting the ratios of Eu^III and Tb^III ions correspondingly, and white-light emission can be generated by a combination of different doped Tb^III and Eu^III concentrations. The Tb-Zn-based framework {[Tb₃Zn₆(bipy₂)₂(Hmimda)₇ (H₂O)₃]·5H₂O}_n (3; H₃mimda = 2-methyl-1-H-imidazole-4,5-dicarboxylic acid and bipy = 4,4'-bipyridine) can detect trace Mg^II ion with relatively high sensitivity and selectivity. Dehydrated MOF 3a shows a remarkable emission quenching effect through the introduction of I₂ solids. Further investigation indicates that it exhibits turn on/off switchable properties for small solvent molecules or heavy-metal ions. Steady/transient-state near-IR luminescence properties for MOFs 1, 4, and 5 were investigated under visible-light excitation.