A multi-responsive MOF-based fluorescent probe for detecting Fe3+, Cr2O72− and acetylacetone

Abstract

A novel Zn²⁺-based metal–organic framework (MOF) with the formula {[Zn(μ₂-η¹:η¹-BBIP)(μ₂-η¹:η¹:η¹-OBA)]·3H₂O}_n, denoted as JXUST-7, has been successfully assembled using semi-rigid N-donor 3,5-bis(benzimidazol-1-yl)pyridine (BBIP) and flexible 4,4′-oxybisbenzoate (H₂OBA). The adjacent Zn²⁺ ions are linked through an OBA²⁻ ligand with a μ₂-η¹:η¹:η¹ bridging mode to form an infinite one-dimensional (1D) Zn²⁺–OBA²⁻ chain. The neighbouring 1D chains are further connected by a BBIP ligand with a μ₂-η¹:η¹ bridging mode to gain a two-dimensional (2D) sheet layer structure. Topological analysis indicates that the whole 2D structure of JXUST-7 could be simplified as a uninodal sql topology with a point symbol of {4⁴·6²}. Furthermore, the opposite parallel 2D layers are further packed by a face-to-face π–π interaction to generate a three-dimensional supramolecular structure. Luminescence experiments reveal that JXUST-7 could be considered as a multi-responsive MOF-based fluorescent probe toward Fe³⁺, Cr₂O₇²⁻ and acetylacetone (acac) via the fluorescence quenching (turn-off) effect. The detection limits for Fe³⁺, Cr₂O₇²⁻ and acac are 0.14, 1.33 and 6.53 ppm, respectively. The fluorescence quenching mechanism was analyzed in detail by powder X-ray diffraction, fluorescence lifetime measurement, X-ray photoelectron spectra, theoretical calculation and UV-Vis absorption spectra. More importantly, JXUST-7 could be cyclically utilized at least five times for detecting Fe³⁺, Cr₂O₇²⁻ and acac.