A Schiff base sensor for relay monitoring of In3+ and Fe3+ through “off–on–off” fluorescent signals

Abstract

A Schiff base N′-(3-ethoxy-2-hydroxybenzylidene)-4,5-dihydronaphtho[1,2-b]thiophene-2-carbohydrazide (LB2) was designed and synthesized based on 4,5-dihydronaphtho[1,2-b]thiophene-2-carbohydrazide and 3-ethoxy-2-hydroxybenzaldehyde, and could be used as a sensor to identify In³⁺ and Fe³⁺ through fluorescence ‘off–on–off’ behavior. The probe LB2 showed high sensitivity and selectivity towards In³⁺ and Fe³⁺ in the presence of other metal ions with detection limits of 8.05 × 10⁻⁹ M and 2.59 × 10⁻⁸ M, respectively. The structure of LB2 was characterized by ¹H NMR, ¹³C NMR, FTIR and mass spectrometry. The complexation ratio of LB2 to In³⁺ and Fe³⁺ was 1 : 1 for both which was verified by mass spectrometry and the Job plot. The binding mode and sensing mechanism of LB2 with In³⁺ and Fe³⁺ were also verified.