Two luminescent cuprous iodides with hitherto-unknown free imidazolate sites for efficiently sensing Fe3+ and Cr2O72−

Abstract

The pursuit of an excellent dual luminescent sensor for the selective detection of Fe³⁺ and Cr₂O₇²⁻ toxic contaminants in aqueous solution is of great interest, owing to their pernicious effects on human health and the biological environment of aquatic organisms. Herein, we use 1-tetrazole-4-imidazole-benzene (HL) incorporating bifunctional imidazolate and tetrazolate groups to construct new types of one-dimensional (1-D) cuprous iodides [Cu₄I₄(HL)₂]_n (1) and [PbCu₂I₄(HL)₂]_n (2). 1 contains an infrequent non-cubane cluster [Cu₄I₄] and exhibits an orange light emission with a large Stokes shift of 241 nm. Intriguingly, each [Cu₄I₄] unit of 1, by replacing two Cu⁺ ions with one photoactive Pb²⁺ ion, leads to a unique hybrid heterometallic iodide 2, which displays a remarkable red light emission with a larger Stokes shift of 337 nm. Notably, the luminescent quantum efficiency of 2 is increased to 11.74% at room temperature, evidently higher than that of 1 (only 1.23%). To our delight, 1 and 2 exhibit a remarkable dual luminescent sensing performance toward Fe³⁺ and Cr₂O₇²⁻ in aqueous solution, owing to the existence of the hitherto never viewed free imidazolate sites. So far, a few cuprous iodides are applied for the separate sensing of Fe³⁺ and Cr₂O₇²⁻ ions, but no reports on cuprous iodides for dual sensing of Fe³⁺ and Cr₂O₇²⁻ ions have emerged to date. Therefore, 1 and 2 represent the first example of cuprous iodides as dual sensors for detecting Fe³⁺ and Cr₂O₇²⁻ ions.