Selective and sensitive optical probe for the recognition of Zn (II) ion through turn-on optical response in aqueous medium: Experimental and theoretical approach

Abstract

A selective and sensitive Zn(II) ion responsive optical probe (E)-N′-(2, 4-dihydroxybenzylidene)-3, 5-di-tert-butyl-2-hydroxybenzohydrazide (L) was designed, synthesized and characterized. The optical behavior of L towards different metal ions were investigated using UV–Vis and Fluorescence techniques and results indicate its higher selectivity for Zn(II) ion. The experimental results of L for Zn (II) are correlated with computational results. The probe exhibits weak fluorescence due to cis–trans isomerization and exited state intra molecular proton transfer (ESIPT) behavior in 4% aqueous acetonitrile solution. However, in the presence of Zinc (II) ion, CN isomerization and ESIPT processes are inhibited due to its coordination to metal ion by triggering CHEF (chelation-enhanced fluorescence) giving turn-on fluorescence response. The Job’s plot and B-H (Banesi- Hildebrand) experimental results indicate 1:1 stoichiometry between host-guest interaction. The association constant of L for Zn2+ ion was found to be 3.9×107 M−1 with nanomolar level of detection. The pH studies indicate that, the probe could work at physiological conditions. The reversible, highly photostable optical probe could recognizes the presence of Zn2+ ion in HeLa cells.