A Schiff Base Sensor For Relay Monitoring Of In3+ And Fe3+ Through "Off-On-Off'' Fluorescent Signals

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 x 10(-9) M and 2.59 x 10(-8) M, respectively. The structure of LB2 was characterized by H-1 NMR, C-13 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.