Terpyridine derivatives as “turn-on” fluorescence chemosensors for the selective and sensitive detection of Zn2+ ions in solution and in live cells

Abstract

A terpyridine based compound L1 was designed and synthesized as an “off–on” chemosensor for the detection of Zn²⁺. Chemosensor L1 showed excellent selectivity and sensitivity toward Zn²⁺ by exhibiting a large fluorescence enhancement (∼51-fold) at 370 nm whereas other competitive metal ions did not show any noticeable change in the emission spectra of chemosensor L1. The chemosensor (L1) was shown to detect Zn²⁺ ions down to 9.76 μM at pH 7.4. However, chemosensor L1 binds Zn²⁺ in a 1 : 2 ratio (receptor : metal) with an association constant of 1.85 × 10⁴ (R² = 0.993) and this 1 : 2 stoichiometric fashion is established on the basis of a Job plot and mass spectroscopy. DFT/TD-DFT calculations were carried out to understand the binding nature, coordination features and electronic properties of L1 and the L1–2Zn²⁺ complex. In addition, this “turn-on” fluorescence probe was effectively used to image intracellular Zn²⁺ ions in cultured MDA-MB-468 cells.