A highly sensitive and selective fluorescent sensor for Al3+ ions based on thiophene-2-carboxylic acid hydrazide Schiff base

Abstract

An efficient fluorescent receptor (E)-N-[(2-hydroxy-naphthalen-1-yl)methylene]thiophene-2-carbohydrazide (THN) for Al³⁺ ions was synthesized and characterized by physicochemical and spectroscopic tools along with single crystal X-ray crystallography. This is the first report showing the crystal structure of THN and its sensing property for Al³⁺ ions. THN selectively and sensitively detects Al³⁺ ions without any interference among various cations, Na⁺, K⁺, Ca²⁺, Cr³⁺, Mg²⁺, Mn²⁺, Fe³⁺, Co²⁺, Ni²⁺, Cu²⁺, Zn²⁺ and Hg²⁺ by a strong fluorescent change in ethanol–water medium (EtOH–H₂O, 1 : 4 v/v). The THN interacts with Al³⁺ in a tridentate mode to form a [AlCl₂(THN)(H₂O)]·H₂O complex. The binding constant was determined to be 7.06 × 10⁶ M⁻¹ and the limit of detection (LOD) was calculated to be 1.35 × 10⁻⁹ M which is the second highest reported till date in the literature. The ¹H NMR titration, ESI-MS and DFT studies have also been performed in support of the binding details of the THN–Al³⁺ complex.