An ampyrone based azo dye as pH-responsive and chemo-reversible colorimetric fluorescent probe for Al3+ in semi-aqueous medium: implication towards logic gate analysis

Abstract

A novel ampyrone based azo dye, 4-((6-hydroxybenzo[d][1,3]dioxol-5-yl)diazenyl)-1,5-dimethyl-2-phenyl-1H-pyrazol-3(2H)-one (1), was synthesized by coupling sesamol and 4-amino antipyrine (ampyrone) and was characterized spectroscopically. The interaction of azo dye (1) with different metal ions was studied using UV-vis and fluorescence spectra. Chemosensor 1 exhibits high selectivity and sensitivity towards Al³⁺ over other metal ions by fluorescence enhancement in methanol : water (1 : 1, v/v, at pH = 7.2), which could also be detected directly by the naked eye under visible light. The fluorescence of the 1–Al³⁺ complex was found to be reversible in the presence of EDTA. The pH-dependent absorption behavior of chemosensor 1 was also investigated. It was observed that chemosensor 1 could also be used as a selective ‘naked-eye’ colorimetric sensor for H⁺ and displayed a very strong red shift in the absorption band from 492 nm to 540 nm with a notable color change from yellow to violet-blue. Moreover, chemosensor 1 showed keto–enol tautomerization in the presence of acidic media and both forms were confirmed by ¹H and ¹³C NMR spectra. Practical applicability of sensor 1 was further explored using sensing strip analysis, which enables rapid detection of Al³⁺ and H⁺ ions. NMR and DFT optimized geometries of chemosensor 1 suggest that the compound is present in the azo form (enol form) in the ground state. In addition, an INHIBIT logic gate was constructed based on the multi-responsive properties of chemosensor 1 induced by Al³⁺ and EDTA²⁻, which contained two input signals (In1: Al³⁺, In2: EDTA) and an output signal (O1: fluorescence intensity at 613 nm). The chemosensor 1 exhibited a high association constant with a detection limit of 3.55 × 10⁻⁷ M for Al³⁺ in MeOH–water solution.