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

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 (approximate to 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 M at pH 7.4. However, chemosensor L1 binds Zn2+ in a 1:2 ratio (receptor:metal) with an association constant of 1.85 x 10(4) (R-2 = 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 L1-2Zn(2+) complex. In addition, this turn-on fluorescence probe was effectively used to image intracellular Zn2+ ions in cultured MDA-MB-468 cells.