Chromo/Fluorogenic Detection of Co²⁺, Hg²⁺ and Cu²⁺ by the Simple Schiff Base Sensor

Abstract

Herein, we reported the ditriazole Schiff base derivative 1 and evaluated its photophysical properties on induction of varieties of metal ions including Na⁺, Ag⁺, Ni²⁺, Mn²⁺, Pd²⁺, Co²⁺, Hg²⁺, Cu²⁺, Pb²⁺, Cd²⁺, Zn²⁺, Sn²⁺, Fe²⁺, Fe³⁺, Cr³⁺ and Al³⁺, in order to figure out its potential as ion sensor. The ligand 1 exhibited the strong colorimetric change in the reaction solution as well as absorption spectral shifting with the concomitant appearance of well-defined isosbestic points only upon Co²⁺, Hg²⁺ and Cu²⁺ addition corroborates its applicability as multichannel ion detector. The different extent of spectral shifting as well as unique chromogenic change in the probe solution upon Co²⁺, Hg²⁺ and Cu²⁺ introduction can be used as the discrimination tool for these metal ions. The ligand-metal binding stoichiometry was assessed by their optical response which was further supported by the FT-IR, NMR and mass spectrometric analysis. The association constant and the detection limits of the ligand toward Co²⁺, Hg²⁺ and Cu²⁺ ions were calculated to be 1.52 × 10⁻⁸, 3.26 × 10⁻⁹, 1.16 × 10⁻⁸ and 3.87 × 10⁻¹⁰, 5.47 × 10⁻¹¹, 8.91 × 10⁻¹¹ M, respectively, employing the Benesi-Hilderbrand equation and 3 σ slope⁻¹ methods. Furthermore, the successive addition of Co²⁺, Hg²⁺ and Cu²⁺ induce the constant decline in the fluorescence emission signal intensity of the probe. The quenching efficiency of the probe upon metallic induction was fitted to the Stern-Volmer equation which yielded the upward curvature in case of all the three metals ions (Co²⁺, Hg²⁺ and Cu²⁺) when (I_o/I-1) was plotted against the quencher concentration indicating the occurrence of both the dynamic and static quenching process in the system with the average Stern-Volmer quenching constant values of 9.25 × 10⁻⁷, 1.14 × 10⁻⁷, 1.829 × 10⁻⁷, respectively.