An amine/azine functionalized MOF as a new fluorescent probe for selective sensing of metal ions

Metal-organic frameworks are a class of attractive materials for fluorescent sensing. Here, we report the exploration of fluorescent Zn-based amine/azine-functionalized MOF, TMU-17-NH₂, ([Zn(NH₂-BDC)(4-bpdb)].2DMF; NH₂-BDC = amino-1,4-benzenedicarboxylic acid, 4-bpdb = 1,4-bis(4-pyridyl)-2,3-diaza-2,3-butadiene) for highly selective and sensitive detection of Fe³⁺ in DMF solution. TMU-17-NH₂ shows fast recognition of Fe³⁺ ion with a response time of <1 min and a detection limit of 0.7 µM (40 ppb), and the luminescence is completely quenched in 10^-3 M DMF solution of Fe³⁺. Furthermore, the static quenching constant is calculated to be upper than 41000 M^-1 by the fluorescence titration experiment in low concentration of Fe³⁺. No interferences from 250 μM As³⁺, Cd²⁺, Zn²⁺, Co³⁺, Ni²⁺, Cu²⁺, Pb²⁺, Mn²⁺ and Al³⁺ were found for the detection of Fe³⁺. The efficient fluorescent quenching effect is attributed to the photoinduced electron transfer between Fe³⁺ ions and the amino-functionalized ligand in this MOF. Moreover, the introduced azine N donors in the 4-bpdb ligand of TMU-17-NH₂ additionally donate their lone-pair electrons to the Fe³⁺ ions, leading to significantly enhanced detection ability. Furthermore, the regenerated TMU-17-NH₂ still has high selectivity for Fe³⁺ ions, which suggests that the functionalized TMU-17-NH₂ is a promising luminescent probe for selectively sensing iron ions.