A Highly Sensitive and Selective Fluorescent Sensor for Zinc(II) Ions Based on a 1,2,3-Triazolyl-Functionalized 2,2’-Dipicolylamine (DPA)

The design and synthesis of a new triazolyl-DPA (TAZDPA) based Zn²⁺ fluorescent sensor is reported. The structural architect of TAZDPA contains 2,2’-dipicolylamine (DPA) and 1,2,3-triazolyl moiety as chelators, which synergistically coordinate with Zn²⁺, resulting in dramatic fluorescent emission enhancement and a notable bathochromic shift due to the inhibition of photoinduced electron transfer (PET) process. Solution state structural characterization and molecular modeling of TAZDPA suggest that N3 of 1,2,3-triazolyl moiety and DPA coordinate with Zn²⁺ to afford five-membered coordination ring. The binding behavior and stoichiometry of the TAZDPA/Zn²⁺complex was studied by Job's plot, which suggested 1 : 1 stoichiometry. The nature of binding behavior of TAZDPA with Zn²⁺ was validated by ¹H-NMR that revealed a distinct downfield shift of DPA and triazolyl protons. Under physiological condition, TAZDPA displayed high selectivity for Zn²⁺ over a wide range of competing common cations, exhibiting ultra-sensitivity with a limit of detection (LOD) of 8.3×10¹ nM. This implies that TAZDPA can detect chronic Zn²⁺ concentration for freshwater (>1.84 μM) denoted by the U.S. Environmental Protection Agency (EPA).