Screening of biologically important Zn²⁺ by a chemosensor with fluorescent turn on-off mechanism

Reported herein the synthesis, characterization and biologically important zinc ion binding propensity of a weakly fluorescent chemosensor, 4-methyl-2,6-bis((E)-(2-(4-phenylthiazol-2-yl)hydrazono)methyl)phenol (1). ¹H NMR spectroscopic titration experiment reveals the binding knack of 1 to the essential Zn²⁺. The photo-physical studies of 1 exhibit an enhancement in the fluorescence by several folds upon binding with the zinc ions attributed to PET-off process, with a binding constant value of 5.22×10³M^-1. 1 exhibits an excellent detection range for Zn²⁺ with lower detection limit value of 2.31×10^-8M. The selectivity of 1 was studied with various mono and divalent metal cations and it was observed that most cations either quenches the fluorescence or remains unchanged except for Cd²⁺, which shows a slight enhancement in fluorescence intensity of 1. The ratiometric displacement of Cd²⁺ ions by Zn²⁺ ions shows an excellent selectivity towards in-situ detection of Zn²⁺ ions. Photo-physical studies also support the reversible binding of 1 to Zn²⁺ ions having on and off mechanism in presence of EDTA. Such recognition of the biologically important zinc ions finds potential application in live cell imaging.