Ratiometric detection of I^- using a dysprosium-based metal-organic framework with a single emission center

In this study, a dysprosium-based metal-organic framework (MOF) sensor (Dy-MOF) was developed for the ratiometric detection of I^- in aqueous medium. Upon excitation at 230 nm, Dy-MOF shows two dominant emission bands at 464 nm and 574 nm assigned to (⁴F, ⁴D)_5/2 → ⁶H_9/2 + ⁶F_11/2 and ⁴F_9/2 → ⁶H_13/2 transition of Dy³⁺, respectively, which have different sensitivities toward iodide ions. The introduction of I^- slightly weakened the blue emission at 464 nm and significantly quenched the yellow emission at 574 nm. Thus, ratiometric sensing for iodide was realized using the yellow-to-blue intensity ratio of Dy³⁺. Dy-MOF exhibits superior sensing behavior towards I^- with high selectivity, sensitivity and low detection limit (24 nM). This study also provides a strategy for the construction of a ratiometric sensor with dual-emission bands originating from only one emission center.