Luminescent Microporous Metal-Organic Framework with Functional Lewis Basic Sites on the Pore Surface: Specific Sensing and Removal of Metal Ions

A three-dimensional luminescent metal-organic framework, {Mg(DHT)(DMF)(2)}(n) (1), based on an excited-state intramolecular proton-transfer (ESIPT) responsive linker, 2,5-dihydroxyterephthalic acid (H2DHT), has been synthesized, and its desolvated microporous framework with pendent -OH groups on the pore surface was exploited for the binding and specific sensing of metal ions via Lewis acid-base interactions. The luminescence intensity significantly quenches with Cu-II among various s- and d-block metal ions, and highly selective sensing of Cu-II ions has been realized in both solid and solution states (up to nanomolar concentration). The immobilized Cu-II metal ions can be selectively removed by chelating agents like ethylenediaminetetraacetic acid without any structural disintegration of the framework, as revealed by the luminescence and gas-adsorption studies.