Bifunctional chemosensor based on a dye-encapsulated metal-organic framework for highly selective and sensitive detection of Cr2O72- and Fe3+ ions

A three-dimensional protonated proflavin (PF) encapsulated metal-organic framework, formulated as [Zn(NIPH)(2)(HPF)(2)] (1), has been successfully synthesized under hydrothermal conditions using the familiar and cheap ligand 5-nitroisophthalic acid (5-H2NIPH). The as-synthesized compound 1 exhibits an intense green emission in solution, whereas strong red fluorescence is observed in the crystal form. The strong green emission of 1 could be highly and selectively quenched by Fe3+ ions, even in the presence of other competing metal ions such as Ag+, Al3+, Ca2+, Cd2+, Co2+, K+, Mg2+, Mn2+, Na+ and Zn2+. In addition, 1 exhibits superior selectivity and sensitivity towards Cr2O72- ions over other anions including Br-, CH3COO-, Cl-, F-, H2PO4-, HCO3-, HPO42-, NO3-, PO43- and SO42-. The possible luminescence quenching mechanisms were investigated. This work revealed that a dye-encapsulated MOF can be used as one of the most fascinating multi-response luminescence materials for selective chemical sensing. (C) 2020 Elsevier Ltd. All rights reserved.