A new-AIE-ligand-based metal–organic framework “turn-on” sensor with extremely high sensitivity

Abstract

Excessive Fe³⁺ and Bi³⁺ can cause serious hazards to human-beings and microorganisms. However, it remains a great challenge to exploit more efficient methods to detect them. In this work, a two-dimensional (2-D) metal–organic framework (MOF) [Cd(3-L)(NDA)(H₂O)]_n (1) (3-L = 3,3′-((9H-fluoren-9-ylidene)-methylene)dipyridine; H₂NDA = 1,4-naphthalenedicarboxylic acid) was successfully fabricated by a new fluorenyl-containing aggregation-induced emission (AIE) functional ligand. 1 features a 2-D (4,4) network, and good water and thermal stabilities. In its stacking structure, the fluorene rings from neighboring layers overlap with each other in the opposite direction, and show very weak π–π interactions. Accordingly, 1 exhibits superior luminescence enhancement (“turn-on”) sensing of Fe³⁺ and Bi³⁺ with extremely high sensitivity in aqueous media. The detection limits of 1 for Fe³⁺ and Bi³⁺ are 4.86 × 10⁻⁴ and 1.87 × 10⁻⁵ mM, respectively, which are significantly lower than the corresponding reported works (only 23.6% and 0.8%). Interestingly, it has obviously enhanced Bi³⁺ detecting ability because of the larger ionic radius of Bi³⁺. More importantly, this is the first MOF-based “turn-on” sensor for Bi³⁺ reported to date.