Synthesis of cyanoaminopyridyl enaminoates for their fluorescent “turn off” response towards Fe(iii) ions

Abstract

In the present study, a series of 2-amino-3-cyanopyridine-based enaminoates 2 were synthesized from substituted 2-amino-3-cyanopyridines 3 and ethyl cyclopentanone-2-carboxylate 4 in acetic acid. The synthesized compounds were characterized by using various techniques such as ¹H NMR, ¹³C NMR, Mass, HRMS and FTIR. The photophysical properties of all the derivatives were investigated, including their absorption maxima, emission maxima and Stokes shift. Among these, compound 2e was investigated as a fluorimetric “turn-off” sensor for the selective detection of Fe³⁺. The interaction between 2e and Fe³⁺ was confirmed through Job's plot analysis and density functional theory (DFT) studies. The fluorimetric detection limit for Fe³⁺ reached up to 9.2 μM. Photostability and response time studies were also conducted to evaluate the analytical performance of 2e. Additionally, 2e was successfully applied for analyzing Fe³⁺ in real water samples such as lake water (Sukhna Lake, Chandigarh, India), distilled water and tap water using the standard addition method. Furthermore, 2e was employed to develop fluorimetric test strips for practical applications.