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. 2025 May 17.
doi: 10.1007/s10895-025-04359-y. Online ahead of print.

Imidazopyridine Based Fluorescent Turn-Off Sensor for Selective Recognition of Fe3+ Ions and its Application in Test Strips

Akanksha Manhas  1 , Sonakshi Sasan  1 , Lalita Devi  1 , Manu Sharma  2 , Avtar Changotra  3 , Pawan Kumar  2 , Kamal K Kapoor  4
Affiliations

Imidazopyridine Based Fluorescent Turn-Off Sensor for Selective Recognition of Fe3+ Ions and its Application in Test Strips

Akanksha Manhas et al. J Fluoresc. .

Abstract

A series of 2-ethoxycarbonyl imidazopyridines have been synthesised and characterised by various spectroscopic techniques (1H NMR, 13C NMR, FTIR and HRMS). Among these compounds, 3e was selected for metal sensing applications due to its favourable photophysical properties. 3e demonstrated high selectivity and sensitivity for detecting Fe3+ ions, even in the presence of other competing ions in a mixture of acetonitrile/water (1:9, v/v). It showed a turn-off fluorescence response with a fluorescence detection limit of 3.9 µM. The decrease in the fluorescence intensity of 3e is due to paramagnetic quenching resulting from its interaction with Fe3+ ions. Job's plot analysis indicated a 1:1 binding ratio between 3e and Fe3+. Density Functional Theory (DFT) calculations revealed a reduced HOMO-LUMO energy gap for the 3e-Fe3+ complex, suggesting successful complexation. The binding constant, calculated using the Benesi-Hildebrand equation, was determined to be 2.845 × 103 M-1, further confirming the strong interaction between 3e and Fe3+. Time-based studies revealed excellent photostability of 3e and its rapid response time for detecting Fe3+. Real-time detection of Fe3+ was successfully achieved using sensor-coated filter paper, demonstrating the practical utility of 3e for rapid assays in real samples.

Keywords: DFT; Fluorescence; Imidazopyridine; Iron; Job's plot; Stern–Volmer analysis.

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Conflict of interest statement

Declarations. Conflict of interest: The authors declare no competing interests.

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